SLC5A8

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Vadivel Ganapathy - One of the best experts on this subject based on the ideXlab platform.

  • deficiency of dietary fiber in SLC5A8 null mice promotes bacterial dysbiosis and alters colonic epithelial transcriptome towards proinflammatory milieu
    Canadian Journal of Gastroenterology & Hepatology, 2019
    Co-Authors: Sathish Sivaprakasam, Sabarish Ramachandran, Pramodh K Ganapathy, Mohd Omar Faruk Sikder, Moamen M Elmassry, Kameswara Rao Kottapalli, Vadivel Ganapathy
    Abstract:

    Inflammatory bowel disease (IBD) is characterized by chronic inflammation in the intestinal tract due to disruption of the symbiotic relationship between the host immune system and microbiota. Various factors alter the gut microbiota which lead to dysbiosis; in particular, diet and dietary fibers constitute important determinants. Dietary fiber protects against IBD; bacteria ferment these dietary fibers in colon and generate short-chain fatty acids (SCFAs), which mediate the anti-inflammatory actions of dietary fibers. SLC5A8 is a high-affinity transporter in the apical membrane of colonic epithelium which mediates the entry of SCFAs from the lumen into cells in Na+-coupled manner. Due to the unique transport kinetics, the function of the transporter becomes important only under conditions of low dietary fiber intake. Here, we have examined the impact of dietary fiber deficiency on luminal microbial composition and transcriptomic profile in colonic epithelium in wild-type (WT) and SLC5A8-null (KO) mice. We fed WT and KO mice with fiber-containing diet (FC-diet) or fiber-free diet (FF-diet) and analyzed the luminal bacterial composition by sequencing 16S rRNA gene in feces. Interestingly, results showed significant differences in the microbial community depending on dietary fiber content and on the presence or absence of SLC5A8. There were also marked differences in the transcriptomic profile of the colonic epithelium depending on the dietary fiber content and on the presence or absence of SLC5A8. We conclude that absence of fiber in diet in KO mice causes bacterial dysbiosis and alters gene expression in the colon that is conducive for inflammation.

  • abstract 2037 the butyrate transporter SLC5A8 is a tumor suppressor in colon linked to dietary fiber content
    Cancer Research, 2015
    Co-Authors: Vadivel Ganapathy, Ashish Gurav, Nagendra Singh
    Abstract:

    Dietary fiber has long been known to protect against colonic inflammation and colon cancer. Short-chain fatty acids (SCFA) such as butyrate generated in colonic lumen by bacterial fermentation of dietary fiber mediate most of these protective effects, but the underlying molecular mechanisms are poorly understood. We examined the role of the plasma membrane transporter SLC5A8 in the beneficial effects of these bacterial metabolites against colitis and colon cancer. SLC5A8 is expressed on the luminal membrane of colonic epithelial cells and also in mucosal immune cells including the antigen-presenting dendritic cells. The transporter mediates the entry of SCFAs into colonic epithelium from the lumen and also into dendritic cells in the lamina propria. We interrogated the role of the transporter in colon by comparing the function of dendritic cells and progression of experimentally induced colitis and colon cancer between wild type mice and SLC5A8-null mice. Since the amount of SCFAs generated in colonic lumen depends on the fiber content in the diet, we used two different diets, one with optimal fiber content (FC diet) and the other with no fiber (FF diet). These studies have shown that SLC5A8 is obligatory for butyrate-dependent inhibition of histone deacetylases in colonic epithelium and dendritic cells and also for the maintenance of the intestinal barrier function; but this obligatory need for the transporter is evident only when the mice are fed FF diet. The transporter is dispensable with FC diet. Compared to wild type mice, SLC5A8-null mice exhibit increased susceptibility to dextran sulfate sodium-induced colitis and azoxymethane/dextran sulfate sodium-induced colon cancer, again only with FF diet and not with FC diet. Butyrate induces the immunosuppressive enzymes indoleamine dioxygenase 1 (IDO1) and aldehyde dehydrogenase 1A2 (Aldh1A2) in dendritic cells in an SLC5A8-dependent manner. This is corroborated by the decreased expression of these two enzymes in the colon of germ-free mice compared to conventional mice. IDO1 and Aldh1A2 play a critical role in dendritic cells to maintain an immunosuppressive phenotype. Butyrate, which induces the expression of both enzymes, promotes the ability of dendritic cells to convert naive T cells into FoxP3-positive immunosuppressive Tregs and also their ability to suppress interferon-gamma-secreting pro-inflammatory T cells. As such, SLC5A8-null mice have decreased Tregs and increased IFN-gamma-positive T cells in colon. We conclude that SLC5A8 may be dispensable in colon under dietary conditions associated with high fiber content when the luminal concentrations of SCFAs are high, but the transporter is indispensable for protection against colonic inflammation and colon cancer with a diet containing suboptimal fiber which results in decreased concentrations of SCFAs in the lumen. Thus, SLC5A8 is a conditional tumor suppressor in colon linked to dietary fiber content. Citation Format: Vadivel Ganapathy, Ashish Gurav, Nagendra Singh. The butyrate transporter SLC5A8 is a tumor suppressor in colon linked to dietary fiber content. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 2037. doi:10.1158/1538-7445.AM2015-2037

  • SLC5A8 a na coupled high affinity transporter for short chain fatty acids is a conditional tumour suppressor in colon that protects against colitis and colon cancer under low fibre dietary conditions
    Biochemical Journal, 2015
    Co-Authors: Ashish Gurav, Thomas Boettger, Nagendra Singh, Yangzom D Bhutia, Sathish Sivaprakasam, Vadivel Ganapathy
    Abstract:

    Mammalian colon harbours trillions of bacteria under physiological conditions; this symbiosis is made possible because of a tolerized response from the mucosal immune system. The mechanisms underlying this tolerogenic phenomenon remain poorly understood. In the present study we show that SLC5A8 (solute carrier gene family 5a, member 8), a Na + -coupled high-affinity transporter in colon for the bacterial fermentation product butyrate, plays a critical role in this process. Among various immune cells in colon, dendritic cells (DCs) are unique not only in their accessibility to luminal contents but also in their ability to induce tolerogenic phenotype in T-cells. We found that DCs exposed to butyrate express the immunosuppressive enzymes indoleamine 2,3-dioxygenase 1 (IDO1) and aldehyde dehydrogenase 1A2 (Aldh1A2), promote conversion of naive T-cells into immunosuppressive forkhead box P3 + (FoxP3 + ) Tregs (regulatory T-cells) and suppress conversion of naive T-cells into pro-inflammatory interferon (IFN)-γ-producing cells. SLC5A8 -null DCs do not induce IDO1 and Aldh1A2 and do not generate Tregs or suppress IFN-γ-producing T-cells in response to butyrate. We also provide in vivo evidence for an obligatory role for SLC5A8 in suppression of IFN-γ-producing T-cells. Furthermore, SLC5A8 protects against colitis and colon cancer under conditions of low-fibre intake but not when dietary fibre intake is optimal. This agrees with the high-affinity nature of the transporter to mediate butyrate entry into cells. We conclude that SLC5A8 is an obligatory link between dietary fibre and mucosal immune system via the bacterial metabolite butyrate and that this transporter is a conditional tumour suppressor in colon linked to dietary fibre content.

  • abstract 2461 SLC5A8 a strategic target for advanced metastatic breast cancer
    Cancer Research, 2014
    Co-Authors: Sabarish Ramachandran, Puttur D Prasad, Vadivel Ganapathy, Selvakumar Elangovan, Rajneesh Pathania, Ravi Padia, Veena Coothankandaswamy, Muthusamy Thangaraju
    Abstract:

    Despite intense efforts and great advances in cancer research, breast cancer remains the leading cause of death among women worldwide. Most breast cancer-related deaths are not due to cancer at the primary site, but rather due to metastasis, a process in which cancer cells spread from the primary site to distant secondary sites like lung, bones and brain. However, the molecular mechanism by which tumor cells invade from primary tumor site to distant metastasis has not been identified. Recently, we identified a tumor suppressor SLC5A8, which is not only prevent the mammary tumor incidence but also blocks tumor-metastasis by inactivating several metastasis-deriving molecules. SLC5A8, a transporter for small-chain fatty acids (SCFA) and monocarboxylates, is silenced in more than 10 different types of cancers including breast cancer. In breast cancer, irrespective of estrogen-receptor status SLC5A8 is inactivated in more than 90% of breast tumor tissues and in breast cancer cell lines. Ectopic expression of SLC5A8 in human breast cancer cells leads to translocation of the anti-apoptotic protein survivin to the plasma membrane through protein-protein interaction, thereby depleting nuclear survivin level. Further, tetracycline-inducible SLC5A8 expression in human breast cancer cells significantly reduced mammary tumor growth. In addition, functional inactivation of SLC5A8 in human immortalized normal mammary epithelial cells by lentivirus expressing shRNA showed differential regulation of genes that are involved in cellular transformation, oncogenesis, epithelial-mesenchymal-transition (EMT) and tumor metastasis. This is a totally unexpected finding and represents first of its kind for a plasma membrane transporter where mere expression itself, independent of its substrates, leads to tumor suppression. Reinforcing our findings further, deletion of SLC5A8 in mice is associated with increased stem/progenitor cells and mammary gland hyperplasia. By crossing the SLC5A8-null mice with spontaneous mouse mammary tumor mice, we observed increased cancer-initiating stem cells, early onset of mammary tumor formation and increased incidence of lung metastasis. More fascinatingly, mammary gland-specific overexpression of SLC5A8 or induction of endogenous SLC5A8 expression efficiently protects mice from breast cancer and associated lung metastasis resulting in extended life-span. Overall, our study provide a strong mechanism based evidence that SLC5A8 is a novel tumor suppressor in the mammary epithelium and it could be used as a potential new therapeutic target for treatment of breast cancer. Citation Format: Sabarish Ramachandran, Rajneesh Pathania, Ravi N. Padia, Selvakumar Elangovan, Veena Coothankandaswamy, Puttur D. Prasad, Vadivel Ganapathy, Muthusamy Thangaraju. SLC5A8: A strategic target for advanced metastatic breast cancer. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 2461. doi:10.1158/1538-7445.AM2014-2461

  • a critical role for SLC5A8 in the suppression of colonic inflammation by commensal bacteria derived metabolites muc9p 821
    Journal of Immunology, 2014
    Co-Authors: Ashish Gurav, Nagendra Singh, Vadivel Ganapathy
    Abstract:

    Presence of trillions of bacteria in healthy colon presents an immunological challenge. Colonic bacteria ferment dietary fibers into short-chain fatty acids (butyrate, propionate, and acetate; SCFAs); among which, butyrate and propionate are inhibitors of histone deacetylases (HDACs). Depletion of SCFAs correlates with increased incidence of intestinal inflammation. SLC5A8 is a high-affinity transporter for SCFAs, which is essential for intracellular actions of SCFAs such as HDAC inhibition. Among various immune cells in colon, dendritic cells (DCs) are unique in having access to colonic lumen, thus getting exposed to bacterial antigens. It is known that colonic DCs exhibit tolerogenic properties with ability to suppress conversion and proliferation of naive T cells into pro-inflammatory T cells. However, the mechanisms involved in the generation of tolerogenic DCs in colon are poorly understood. We hypothesized that SLC5A8-mediated transport of SCFAs into DCs and consequent inhibition of HDACs induces tolerogenic phenotype in these cells. In support of our hypothesis, we found that butyrate and propionate induce the immune-suppressive enzyme Indoleamine 2,3-dioxygenase (IDO) in DCs in an SLC5A8-dependent manner. Further, these DCs are able suppress conversion of naive T cells into interferon-γ (IFNγ) producing Th1 cells. Together, our data identify the SCFA transporter SLC5A8 as a key determinant of SCFA-mediated protection against intestinal inflammation.

Puttur D Prasad - One of the best experts on this subject based on the ideXlab platform.

  • abstract 2461 SLC5A8 a strategic target for advanced metastatic breast cancer
    Cancer Research, 2014
    Co-Authors: Sabarish Ramachandran, Puttur D Prasad, Vadivel Ganapathy, Selvakumar Elangovan, Rajneesh Pathania, Ravi Padia, Veena Coothankandaswamy, Muthusamy Thangaraju
    Abstract:

    Despite intense efforts and great advances in cancer research, breast cancer remains the leading cause of death among women worldwide. Most breast cancer-related deaths are not due to cancer at the primary site, but rather due to metastasis, a process in which cancer cells spread from the primary site to distant secondary sites like lung, bones and brain. However, the molecular mechanism by which tumor cells invade from primary tumor site to distant metastasis has not been identified. Recently, we identified a tumor suppressor SLC5A8, which is not only prevent the mammary tumor incidence but also blocks tumor-metastasis by inactivating several metastasis-deriving molecules. SLC5A8, a transporter for small-chain fatty acids (SCFA) and monocarboxylates, is silenced in more than 10 different types of cancers including breast cancer. In breast cancer, irrespective of estrogen-receptor status SLC5A8 is inactivated in more than 90% of breast tumor tissues and in breast cancer cell lines. Ectopic expression of SLC5A8 in human breast cancer cells leads to translocation of the anti-apoptotic protein survivin to the plasma membrane through protein-protein interaction, thereby depleting nuclear survivin level. Further, tetracycline-inducible SLC5A8 expression in human breast cancer cells significantly reduced mammary tumor growth. In addition, functional inactivation of SLC5A8 in human immortalized normal mammary epithelial cells by lentivirus expressing shRNA showed differential regulation of genes that are involved in cellular transformation, oncogenesis, epithelial-mesenchymal-transition (EMT) and tumor metastasis. This is a totally unexpected finding and represents first of its kind for a plasma membrane transporter where mere expression itself, independent of its substrates, leads to tumor suppression. Reinforcing our findings further, deletion of SLC5A8 in mice is associated with increased stem/progenitor cells and mammary gland hyperplasia. By crossing the SLC5A8-null mice with spontaneous mouse mammary tumor mice, we observed increased cancer-initiating stem cells, early onset of mammary tumor formation and increased incidence of lung metastasis. More fascinatingly, mammary gland-specific overexpression of SLC5A8 or induction of endogenous SLC5A8 expression efficiently protects mice from breast cancer and associated lung metastasis resulting in extended life-span. Overall, our study provide a strong mechanism based evidence that SLC5A8 is a novel tumor suppressor in the mammary epithelium and it could be used as a potential new therapeutic target for treatment of breast cancer. Citation Format: Sabarish Ramachandran, Rajneesh Pathania, Ravi N. Padia, Selvakumar Elangovan, Veena Coothankandaswamy, Puttur D. Prasad, Vadivel Ganapathy, Muthusamy Thangaraju. SLC5A8: A strategic target for advanced metastatic breast cancer. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 2461. doi:10.1158/1538-7445.AM2014-2461

  • the plasma membrane transporter SLC5A8 suppresses tumour progression through depletion of survivin without involving its transport function
    Biochemical Journal, 2013
    Co-Authors: Veena Coothankandaswamy, Muthusamy Thangaraju, Puttur D Prasad, Selvakumar Elangovan, Nagendra Singh, Vadivel Ganapathy
    Abstract:

    SLC5A8 is a sodium-coupled transporter for monocarboxylates. Among its substrates are the HDAC inhibitors butyrate, propionate, and pyruvate. Expression of SLC5A8 is silenced in cancers via DNA methylation, and ectopic expression of SLC5A8 in cancer cells induces apoptosis in the presence of its substrates that are HDAC inhibitors. Here we show that ectopic expression of SLC5A8 in cancer cells translocates the anti-apoptotic protein survivin to plasma membrane through protein-protein interaction resulting in depletion of nuclear survivin and also decreases cellular levels of survivin through inhibition of transcription. These SLC5A8-induced changes in the location and levels of survivin result in cell cycle arrest, disruption of the chromosome passenger complex involved in mitosis, induction of apoptosis, and enhancement in chemosensitivity. These effects are seen independent of the transport function of SLC5A8 and histone acetylation status of the cell; in the presence of pyruvate, a SLC5A8 substrate and also an HDAC inhibitor, these effects are amplified. Ectopic expression of SLC5A8 in the breast cancer cell line MB231 inhibits the ability of the cell to form colonies in vitro and to form tumors in mouse xenografts in vivo. The suppression of survivin transcription occurs independent of HDAC inhibition, and the underlying mechanism is associated with decreased phosphorylation of STAT3. The observed effects are specific for survivin with no apparent changes in expression of other inhibitor-of-apoptosis proteins. These studies unravel a novel, hitherto unrecognized, mechanism for the tumor-suppressive role of a plasma membrane transporter independent of its transport function.

  • abstract 18 SLC5A8 inactivation is associated with mammary gland involution delay early onset of mammary tumorigenesis and accelerated lung metastasis
    Cancer Research, 2012
    Co-Authors: Sabarish Ramachandran, Puttur D Prasad, Vadivel Ganapathy, Selvakumar Elangovan, Rajneesh Pathania, Muthusamy Thangaraju
    Abstract:

    Accumulation of milk during mammary gland involution induces apoptosis in mammary epithelium, but the underlying molecular mechanism is not known. SLC5A8, a plasma membrane transporter and a candidate tumor suppressor, is silenced in many human cancers, including breast and colon cancers. The tumor-suppressive function of SLC5A8 is believed to be due to its ability to mediate the entry of butyrate and pyruvate into cells in a Na+-coupled manner. Butyrate and pyruvate are inhibitors of histone deacetylases (HDACs), and SLC5A8-mediated concentrative entry of these compounds into cells causes HDAC inhibition. Normal cells possess low HDAC activity, and inhibition of HDACs does not induce apoptosis. In contrast, tumor cells possess high HDAC activity, and these cells are propelled into apoptosis by HDAC inhibition. This probably explains why tumor cells silence this transporter. Breast milk contains significant amounts of butyrate. We postulated that SLC5A8 might play an important role not only in normal mammary gland but also in breast cancer by transporting butyrate into mammary epithelial cells and consequently causing HDAC inhibition. Here we have shown that milk stasis-associated mechanical stretching, which occurs in early onset of mammary gland involution, dramatically induced SLC5A8 expression in luminal epithelium. Deletion of SLC5A8 in mouse is associated with mammary gland hyperplasia, stem cell and progenitor cell proliferation, and delayed mammary gland involution. We hypothesize that the mammary gland hyperplasia and involution delay in SLC5A8-null mice are due to lack of butyrate-induced HDAC inhibition because the absence of the transporter prevents the entry of butyrate into mammary epithelial cells. In wild type mice, mammary gland involution was associated with decreased expression of HDAC1/3, and exogenous administration of butyrate accelerated the involution process. Further, deletion of SLC5A8 predisposed mice to early onset of mammary tumorigenesis in two different mammary tumor models (MMTV-Neu and MMTV-HRas), accelerated lung metastasis, and reduced disease-free survival. Mammary gland-specific overexpression of SLC5A8 (SLC5A8-MMTV-Tg mouse) induced early onset mammary gland involution, reduced mammary tumor incidence, delayed mammary tumor formation, and reduced lung metastasis. Induction of SLC5A8 with a DNA methyltransferase inhibitor (5-azacytidine), coupled with exogenous administration of butyrate, dramatically reduced mammary tumor incidence, delayed mammary tumorigenesis, and increased disease-free survival. We conclude that SLC5A8 functions as a tumor suppressor in mammary gland and that induction of SLC5A8 with DNA methyltransferase inhibitors coupled with butyrate administration might represent a novel approach to breast cancer treatment. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 18. doi:1538-7445.AM2012-18

  • abstract 17 tumor suppressive function of SLC5A8 in renal cancer cells
    Cancer Research, 2012
    Co-Authors: Veena Coothankandaswamy, Muthusamy Thangaraju, Vadivel Ganapathy, Selvakumar Elangovan, Elangovan Gopal, Joo Hee Kim, Keith D Robertson, Puttur D Prasad
    Abstract:

    SLC5A8, a Na+-coupled high-affinity transporter for monocarboxylates, and the closely related SLC5A12, a Na+-coupled low-affinity transporter for monocarboxylates, are both highly expressed in kidney, where they mediate the reuptake of lactate and pyruvate from the glomerular filtrate. Recent studies have shown that SLC5A8 is a tumor-suppressor that is silenced in many cancers by promoter hypermethylation. We investigated if SLC5A8 serves as a tumor suppressor in renal cancer cells (RCC). Comparison of the expression of SLC5A8 at the mRNA and protein levels in two RCC (A498 & 786-0) and two normal kidney cell lines (HK-2 & HEK-293) revealed that the expression of SLC5A8 was significantly lower in RCC. Analysis of methylation status of the CpG island in the regulatory region of SLC5A8 showed that the extent of methylation was significantly higher in the two RCC compared to the two normal cells. Culturing A498 cells in the presence of 5-aza-deoxycytidine resulted in re-expression of SLC5A8, confirming that the silencing of the gene is due to DNA methylation. Ectopic expression of SLC5A8 in A498 cells caused apoptosis when cultured in the presence of HDAC inhibitors butyrate and pyruvate. These data show that SLC5A8-mediated concentrative entry of HDAC inhibitors causes cell death in RCC. Interestingly, normal proximal tubular cells, which express SLC5A8 robustly and are exposed to pyruvate, do not undergo apoptosis; HDAC inhibitor-mediated apoptosis is specific to cancer cells. To investigate if HDAC isoforms play a role in this differential sensitivity of normal and RCC to pyruvate, we compared the expression of various HDAC isoforms in HK-2 and A498 cells by RT-PCR. The results indicated that the expression of HDAC1 and HDAC3 was higher in RCC compared to normal cells. The total HDAC enzyme activity was ∼2-3-fold higher in RCC compared to normal cells. If intracellular pyruvate is detrimental to the survival of tumor cells and the tumor cells silence SLC5A8 to prevent entry of extracellular pyruvate into cells, the levels of pyruvate inside tumor cells should be lower in RCC compared to normal cells. To confirm this, we measured pyruvate and lactate levels in normal cells and RCC and found that pyruvate levels were ∼4-fold lower while lactate was ∼2-fold higher in RCC cells compared to normal cells. Finally, to conclusively demonstrate the tumor-suppressive role for SLC5A8 in RCC, we performed mouse xenograft studies using control A498 & 786-0 cells, which do not express SLC5A8 constitutively, and A498 & 786-0 cells, which were made to express SLC5A8 by lentiviral mediated transfection of SLC5A8 cDNA. The growth of the tumor was significantly slower with SLC5A8-expressing cells than with SLC5A8-negative parent cells. These studies demonstrate that SLC5A8 is indeed a tumor suppressor in kidney, suggesting that pharmacological induction of the transporter expression in renal cancer might be a novel strategy for treatment of renal cancer. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 17. doi:1538-7445.AM2012-17

  • abstract 2194 SLC5A8 a novel transporter with tumor suppressor function mediates its effect through survivin depletion
    Cancer Research, 2011
    Co-Authors: Veena Coothankandaswamy, Muthusamy Thangaraju, Puttur D Prasad, Selvakumar Elangovan, Vadivel Ganapathy
    Abstract:

    Proceedings: AACR 102nd Annual Meeting 2011‐‐ Apr 2‐6, 2011; Orlando, FL Introduction: SLC5A8 is a Na+-coupled transporter for lactate, pyruvate, nicotinate and ketone bodies and is down-regulated in a wide variety of cancers. It is expressed in normal cells whereas tumor cells suppress its expression by methylation of CpG islands in its promoter. Studies from our laboratory have shown that (i) pyruvate (but not lactate) is a tumor suppressor through its ability to inhibit HDAC1/3, and that ectopic expression of SLC5A8 in breast cancer cells suppresses expression of the anti-apoptotic protein survivin. Apart from its role in protecting tumor cells from apoptosis, survivin also serves as an important determinant of chemoresistance. Based on these findings, we hypothesized that forced expression of SLC5A8 in breast cancer cells will deplete survivin and consequently enhance chemosensitivity. Methods: The estrogen receptor-positive human breast cancer cell line MCF7 does not express SLC5A8. These cells were engineered to express SLC5A8 by a doxycycline-inducible promoter. The expression of the transporter was monitored by Na+-coupled nicotinate uptake and by immunocytochemistry. The interaction between SLC5A8 and survivin was investigated by immunocytochemical analysis for co-localization. The chemosensitivity was studied by monitoring the cytotoxic effects of docetaxel in SLC5A8-negative control cells and SLC5A8-expressing cells. Results: MCF7 cells transfected with vector alone did not show Na+-coupled nicotinate uptake, indicating the absence of functional expression of SLC5A8. In contrast, MCF7 cells transfected with the SLC5A8 construct under a doxycycline-inducible promoter exhibited marked activity for Na+-coupled nicotinate uptake but only when exposed to doxycycline. This was complemented with immunocytochemical evidence of SLC5A8 protein expression in the plasma membrane. In SLC5A8-expressing control MCF7 cells, survivin was expressed robustly and the expression was restricted predominantly to the nucleus. In contrast, in SLC5A8-expressing MCF7 cells, the cellular levels of survivin were depleted. Furthermore, the location of survivin was shifted from the nucleus to the plasma membrane. Co-localization studies revealed merging of immuno-positive signals for SLC5A8 and survivin at the plasma membrane. Chemosensitivity studies showed that SLC5A8-expressing MCF7 cells were more susceptible to docetaxel than SLC5A8-negative control MCF7 cells. Conclusions: MCF7 cells are SLC5A8-negative, but express survivin with its localization found predominantly in the nucleus. Ectopic expression of SLC5A8 in these cells depletes survivin as well as changes the localization of survivin from the nucleus to the plasma membrane through interaction with SLC5A8. This is accompanied with a marked increase in chemosensitivity. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 2194. doi:10.1158/1538-7445.AM2011-2194

Muthusamy Thangaraju - One of the best experts on this subject based on the ideXlab platform.

  • abstract 2461 SLC5A8 a strategic target for advanced metastatic breast cancer
    Cancer Research, 2014
    Co-Authors: Sabarish Ramachandran, Puttur D Prasad, Vadivel Ganapathy, Selvakumar Elangovan, Rajneesh Pathania, Ravi Padia, Veena Coothankandaswamy, Muthusamy Thangaraju
    Abstract:

    Despite intense efforts and great advances in cancer research, breast cancer remains the leading cause of death among women worldwide. Most breast cancer-related deaths are not due to cancer at the primary site, but rather due to metastasis, a process in which cancer cells spread from the primary site to distant secondary sites like lung, bones and brain. However, the molecular mechanism by which tumor cells invade from primary tumor site to distant metastasis has not been identified. Recently, we identified a tumor suppressor SLC5A8, which is not only prevent the mammary tumor incidence but also blocks tumor-metastasis by inactivating several metastasis-deriving molecules. SLC5A8, a transporter for small-chain fatty acids (SCFA) and monocarboxylates, is silenced in more than 10 different types of cancers including breast cancer. In breast cancer, irrespective of estrogen-receptor status SLC5A8 is inactivated in more than 90% of breast tumor tissues and in breast cancer cell lines. Ectopic expression of SLC5A8 in human breast cancer cells leads to translocation of the anti-apoptotic protein survivin to the plasma membrane through protein-protein interaction, thereby depleting nuclear survivin level. Further, tetracycline-inducible SLC5A8 expression in human breast cancer cells significantly reduced mammary tumor growth. In addition, functional inactivation of SLC5A8 in human immortalized normal mammary epithelial cells by lentivirus expressing shRNA showed differential regulation of genes that are involved in cellular transformation, oncogenesis, epithelial-mesenchymal-transition (EMT) and tumor metastasis. This is a totally unexpected finding and represents first of its kind for a plasma membrane transporter where mere expression itself, independent of its substrates, leads to tumor suppression. Reinforcing our findings further, deletion of SLC5A8 in mice is associated with increased stem/progenitor cells and mammary gland hyperplasia. By crossing the SLC5A8-null mice with spontaneous mouse mammary tumor mice, we observed increased cancer-initiating stem cells, early onset of mammary tumor formation and increased incidence of lung metastasis. More fascinatingly, mammary gland-specific overexpression of SLC5A8 or induction of endogenous SLC5A8 expression efficiently protects mice from breast cancer and associated lung metastasis resulting in extended life-span. Overall, our study provide a strong mechanism based evidence that SLC5A8 is a novel tumor suppressor in the mammary epithelium and it could be used as a potential new therapeutic target for treatment of breast cancer. Citation Format: Sabarish Ramachandran, Rajneesh Pathania, Ravi N. Padia, Selvakumar Elangovan, Veena Coothankandaswamy, Puttur D. Prasad, Vadivel Ganapathy, Muthusamy Thangaraju. SLC5A8: A strategic target for advanced metastatic breast cancer. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 2461. doi:10.1158/1538-7445.AM2014-2461

  • the plasma membrane transporter SLC5A8 suppresses tumour progression through depletion of survivin without involving its transport function
    Biochemical Journal, 2013
    Co-Authors: Veena Coothankandaswamy, Muthusamy Thangaraju, Puttur D Prasad, Selvakumar Elangovan, Nagendra Singh, Vadivel Ganapathy
    Abstract:

    SLC5A8 is a sodium-coupled transporter for monocarboxylates. Among its substrates are the HDAC inhibitors butyrate, propionate, and pyruvate. Expression of SLC5A8 is silenced in cancers via DNA methylation, and ectopic expression of SLC5A8 in cancer cells induces apoptosis in the presence of its substrates that are HDAC inhibitors. Here we show that ectopic expression of SLC5A8 in cancer cells translocates the anti-apoptotic protein survivin to plasma membrane through protein-protein interaction resulting in depletion of nuclear survivin and also decreases cellular levels of survivin through inhibition of transcription. These SLC5A8-induced changes in the location and levels of survivin result in cell cycle arrest, disruption of the chromosome passenger complex involved in mitosis, induction of apoptosis, and enhancement in chemosensitivity. These effects are seen independent of the transport function of SLC5A8 and histone acetylation status of the cell; in the presence of pyruvate, a SLC5A8 substrate and also an HDAC inhibitor, these effects are amplified. Ectopic expression of SLC5A8 in the breast cancer cell line MB231 inhibits the ability of the cell to form colonies in vitro and to form tumors in mouse xenografts in vivo. The suppression of survivin transcription occurs independent of HDAC inhibition, and the underlying mechanism is associated with decreased phosphorylation of STAT3. The observed effects are specific for survivin with no apparent changes in expression of other inhibitor-of-apoptosis proteins. These studies unravel a novel, hitherto unrecognized, mechanism for the tumor-suppressive role of a plasma membrane transporter independent of its transport function.

  • abstract 18 SLC5A8 inactivation is associated with mammary gland involution delay early onset of mammary tumorigenesis and accelerated lung metastasis
    Cancer Research, 2012
    Co-Authors: Sabarish Ramachandran, Puttur D Prasad, Vadivel Ganapathy, Selvakumar Elangovan, Rajneesh Pathania, Muthusamy Thangaraju
    Abstract:

    Accumulation of milk during mammary gland involution induces apoptosis in mammary epithelium, but the underlying molecular mechanism is not known. SLC5A8, a plasma membrane transporter and a candidate tumor suppressor, is silenced in many human cancers, including breast and colon cancers. The tumor-suppressive function of SLC5A8 is believed to be due to its ability to mediate the entry of butyrate and pyruvate into cells in a Na+-coupled manner. Butyrate and pyruvate are inhibitors of histone deacetylases (HDACs), and SLC5A8-mediated concentrative entry of these compounds into cells causes HDAC inhibition. Normal cells possess low HDAC activity, and inhibition of HDACs does not induce apoptosis. In contrast, tumor cells possess high HDAC activity, and these cells are propelled into apoptosis by HDAC inhibition. This probably explains why tumor cells silence this transporter. Breast milk contains significant amounts of butyrate. We postulated that SLC5A8 might play an important role not only in normal mammary gland but also in breast cancer by transporting butyrate into mammary epithelial cells and consequently causing HDAC inhibition. Here we have shown that milk stasis-associated mechanical stretching, which occurs in early onset of mammary gland involution, dramatically induced SLC5A8 expression in luminal epithelium. Deletion of SLC5A8 in mouse is associated with mammary gland hyperplasia, stem cell and progenitor cell proliferation, and delayed mammary gland involution. We hypothesize that the mammary gland hyperplasia and involution delay in SLC5A8-null mice are due to lack of butyrate-induced HDAC inhibition because the absence of the transporter prevents the entry of butyrate into mammary epithelial cells. In wild type mice, mammary gland involution was associated with decreased expression of HDAC1/3, and exogenous administration of butyrate accelerated the involution process. Further, deletion of SLC5A8 predisposed mice to early onset of mammary tumorigenesis in two different mammary tumor models (MMTV-Neu and MMTV-HRas), accelerated lung metastasis, and reduced disease-free survival. Mammary gland-specific overexpression of SLC5A8 (SLC5A8-MMTV-Tg mouse) induced early onset mammary gland involution, reduced mammary tumor incidence, delayed mammary tumor formation, and reduced lung metastasis. Induction of SLC5A8 with a DNA methyltransferase inhibitor (5-azacytidine), coupled with exogenous administration of butyrate, dramatically reduced mammary tumor incidence, delayed mammary tumorigenesis, and increased disease-free survival. We conclude that SLC5A8 functions as a tumor suppressor in mammary gland and that induction of SLC5A8 with DNA methyltransferase inhibitors coupled with butyrate administration might represent a novel approach to breast cancer treatment. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 18. doi:1538-7445.AM2012-18

  • abstract 17 tumor suppressive function of SLC5A8 in renal cancer cells
    Cancer Research, 2012
    Co-Authors: Veena Coothankandaswamy, Muthusamy Thangaraju, Vadivel Ganapathy, Selvakumar Elangovan, Elangovan Gopal, Joo Hee Kim, Keith D Robertson, Puttur D Prasad
    Abstract:

    SLC5A8, a Na+-coupled high-affinity transporter for monocarboxylates, and the closely related SLC5A12, a Na+-coupled low-affinity transporter for monocarboxylates, are both highly expressed in kidney, where they mediate the reuptake of lactate and pyruvate from the glomerular filtrate. Recent studies have shown that SLC5A8 is a tumor-suppressor that is silenced in many cancers by promoter hypermethylation. We investigated if SLC5A8 serves as a tumor suppressor in renal cancer cells (RCC). Comparison of the expression of SLC5A8 at the mRNA and protein levels in two RCC (A498 & 786-0) and two normal kidney cell lines (HK-2 & HEK-293) revealed that the expression of SLC5A8 was significantly lower in RCC. Analysis of methylation status of the CpG island in the regulatory region of SLC5A8 showed that the extent of methylation was significantly higher in the two RCC compared to the two normal cells. Culturing A498 cells in the presence of 5-aza-deoxycytidine resulted in re-expression of SLC5A8, confirming that the silencing of the gene is due to DNA methylation. Ectopic expression of SLC5A8 in A498 cells caused apoptosis when cultured in the presence of HDAC inhibitors butyrate and pyruvate. These data show that SLC5A8-mediated concentrative entry of HDAC inhibitors causes cell death in RCC. Interestingly, normal proximal tubular cells, which express SLC5A8 robustly and are exposed to pyruvate, do not undergo apoptosis; HDAC inhibitor-mediated apoptosis is specific to cancer cells. To investigate if HDAC isoforms play a role in this differential sensitivity of normal and RCC to pyruvate, we compared the expression of various HDAC isoforms in HK-2 and A498 cells by RT-PCR. The results indicated that the expression of HDAC1 and HDAC3 was higher in RCC compared to normal cells. The total HDAC enzyme activity was ∼2-3-fold higher in RCC compared to normal cells. If intracellular pyruvate is detrimental to the survival of tumor cells and the tumor cells silence SLC5A8 to prevent entry of extracellular pyruvate into cells, the levels of pyruvate inside tumor cells should be lower in RCC compared to normal cells. To confirm this, we measured pyruvate and lactate levels in normal cells and RCC and found that pyruvate levels were ∼4-fold lower while lactate was ∼2-fold higher in RCC cells compared to normal cells. Finally, to conclusively demonstrate the tumor-suppressive role for SLC5A8 in RCC, we performed mouse xenograft studies using control A498 & 786-0 cells, which do not express SLC5A8 constitutively, and A498 & 786-0 cells, which were made to express SLC5A8 by lentiviral mediated transfection of SLC5A8 cDNA. The growth of the tumor was significantly slower with SLC5A8-expressing cells than with SLC5A8-negative parent cells. These studies demonstrate that SLC5A8 is indeed a tumor suppressor in kidney, suggesting that pharmacological induction of the transporter expression in renal cancer might be a novel strategy for treatment of renal cancer. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 17. doi:1538-7445.AM2012-17

  • abstract 1310 SLC5A8 functions as a tumor suppressor through redistribution and depletion of survivin
    Cancer Research, 2012
    Co-Authors: Veena Coothankandaswamy, Muthusamy Thangaraju, Selvakumar Elangovan, Vadivel Ganapathy
    Abstract:

    SLC5A8 is a Na+-coupled transporter for lactate, pyruvate, and nicotinate. Its expression is silenced in a wide variety of cancers including breast, colon, brain, thyroid, prostate, and pancreas, by methylation of CpG islands of its promoter. Increasing SLC5A8 expression through inhibition of DNA methylation in cancer cells leads to apoptosis. The silencing of SLC5A8 is essential for tumor cell survival because of the ability of this transporter to increase cellular levels of pyruvate by actively transporting circulating pyruvate into cells. Pyruvate is considered as an efficient fuel source for tumor cells, but our studies have shown that this metabolite is actually a tumor suppressor through its ability to inhibit HDAC1 and HDAC3. Our recent studies have shown that HDAC inhibition alone is not responsible for the tumor suppressive function of SLC5A8. Survivin, an anti-apoptotic protein and also a chromosomal passenger complex protein, is sequestered to the plasma membrane by SLC5A8 through protein-protein interaction and is also downregulated by transcriptional inhibition. This phenomenon is seen in two different human breast cancer cell lines, MCF7 and MB231. These cell lines do not express SLC5A8, and survivin is localized predominantly in the nucleus in these cells. However, upon lentiviral-mediated expression of SLC5A8 in these cells, survivin gets depleted in the nucleus but gets concentrated in the plasma membrane, colocalizing with the transporter. In the absence of SLC5A8, survivin localizes at the centromere during metaphase, and is essential for recruitment of the other component of the chromosomal passenger complex, Aurora B, to the centromere. But SLC5A8-induced translocation of survivin out of the nucleus disrupts the chromosomal passenger complex and consequently interferes with cell division. Additionally, apoptosis is induced in these cells upon forced expression of the transporter. Redistribution of survivin from the nucleus to the plasma membrane is not the only change observed in breast cancer cells upon SLC5A8 expression. The total cellular pool of survivin is also decreased, resulting from decreased transcription of the survivin gene. This process is associated with decreased phosphorylation of STAT3. The redistribution and depletion of survivin in these breast cancer cells upon SLC5A8 expression increases their sensitivity to chemotherapeutic agents. All these effects are independent of HDAC inhibition because these effects are seen in the absence of pyruvate in the culture medium. The growth of MB231 cells in mouse xenografts is drastically reduced when SLC5A8 is expressed. We conclude that SLC5A8 functions as a tumor suppressor by two different mechanisms, one involving HDAC inhibition in the presence of pyruvate and the other involving survivin redistribution and depletion. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 1310. doi:1538-7445.AM2012-1310

Nagendra Singh - One of the best experts on this subject based on the ideXlab platform.

  • abstract 2037 the butyrate transporter SLC5A8 is a tumor suppressor in colon linked to dietary fiber content
    Cancer Research, 2015
    Co-Authors: Vadivel Ganapathy, Ashish Gurav, Nagendra Singh
    Abstract:

    Dietary fiber has long been known to protect against colonic inflammation and colon cancer. Short-chain fatty acids (SCFA) such as butyrate generated in colonic lumen by bacterial fermentation of dietary fiber mediate most of these protective effects, but the underlying molecular mechanisms are poorly understood. We examined the role of the plasma membrane transporter SLC5A8 in the beneficial effects of these bacterial metabolites against colitis and colon cancer. SLC5A8 is expressed on the luminal membrane of colonic epithelial cells and also in mucosal immune cells including the antigen-presenting dendritic cells. The transporter mediates the entry of SCFAs into colonic epithelium from the lumen and also into dendritic cells in the lamina propria. We interrogated the role of the transporter in colon by comparing the function of dendritic cells and progression of experimentally induced colitis and colon cancer between wild type mice and SLC5A8-null mice. Since the amount of SCFAs generated in colonic lumen depends on the fiber content in the diet, we used two different diets, one with optimal fiber content (FC diet) and the other with no fiber (FF diet). These studies have shown that SLC5A8 is obligatory for butyrate-dependent inhibition of histone deacetylases in colonic epithelium and dendritic cells and also for the maintenance of the intestinal barrier function; but this obligatory need for the transporter is evident only when the mice are fed FF diet. The transporter is dispensable with FC diet. Compared to wild type mice, SLC5A8-null mice exhibit increased susceptibility to dextran sulfate sodium-induced colitis and azoxymethane/dextran sulfate sodium-induced colon cancer, again only with FF diet and not with FC diet. Butyrate induces the immunosuppressive enzymes indoleamine dioxygenase 1 (IDO1) and aldehyde dehydrogenase 1A2 (Aldh1A2) in dendritic cells in an SLC5A8-dependent manner. This is corroborated by the decreased expression of these two enzymes in the colon of germ-free mice compared to conventional mice. IDO1 and Aldh1A2 play a critical role in dendritic cells to maintain an immunosuppressive phenotype. Butyrate, which induces the expression of both enzymes, promotes the ability of dendritic cells to convert naive T cells into FoxP3-positive immunosuppressive Tregs and also their ability to suppress interferon-gamma-secreting pro-inflammatory T cells. As such, SLC5A8-null mice have decreased Tregs and increased IFN-gamma-positive T cells in colon. We conclude that SLC5A8 may be dispensable in colon under dietary conditions associated with high fiber content when the luminal concentrations of SCFAs are high, but the transporter is indispensable for protection against colonic inflammation and colon cancer with a diet containing suboptimal fiber which results in decreased concentrations of SCFAs in the lumen. Thus, SLC5A8 is a conditional tumor suppressor in colon linked to dietary fiber content. Citation Format: Vadivel Ganapathy, Ashish Gurav, Nagendra Singh. The butyrate transporter SLC5A8 is a tumor suppressor in colon linked to dietary fiber content. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 2037. doi:10.1158/1538-7445.AM2015-2037

  • SLC5A8 a na coupled high affinity transporter for short chain fatty acids is a conditional tumour suppressor in colon that protects against colitis and colon cancer under low fibre dietary conditions
    Biochemical Journal, 2015
    Co-Authors: Ashish Gurav, Thomas Boettger, Nagendra Singh, Yangzom D Bhutia, Sathish Sivaprakasam, Vadivel Ganapathy
    Abstract:

    Mammalian colon harbours trillions of bacteria under physiological conditions; this symbiosis is made possible because of a tolerized response from the mucosal immune system. The mechanisms underlying this tolerogenic phenomenon remain poorly understood. In the present study we show that SLC5A8 (solute carrier gene family 5a, member 8), a Na + -coupled high-affinity transporter in colon for the bacterial fermentation product butyrate, plays a critical role in this process. Among various immune cells in colon, dendritic cells (DCs) are unique not only in their accessibility to luminal contents but also in their ability to induce tolerogenic phenotype in T-cells. We found that DCs exposed to butyrate express the immunosuppressive enzymes indoleamine 2,3-dioxygenase 1 (IDO1) and aldehyde dehydrogenase 1A2 (Aldh1A2), promote conversion of naive T-cells into immunosuppressive forkhead box P3 + (FoxP3 + ) Tregs (regulatory T-cells) and suppress conversion of naive T-cells into pro-inflammatory interferon (IFN)-γ-producing cells. SLC5A8 -null DCs do not induce IDO1 and Aldh1A2 and do not generate Tregs or suppress IFN-γ-producing T-cells in response to butyrate. We also provide in vivo evidence for an obligatory role for SLC5A8 in suppression of IFN-γ-producing T-cells. Furthermore, SLC5A8 protects against colitis and colon cancer under conditions of low-fibre intake but not when dietary fibre intake is optimal. This agrees with the high-affinity nature of the transporter to mediate butyrate entry into cells. We conclude that SLC5A8 is an obligatory link between dietary fibre and mucosal immune system via the bacterial metabolite butyrate and that this transporter is a conditional tumour suppressor in colon linked to dietary fibre content.

  • a critical role for SLC5A8 in the suppression of colonic inflammation by commensal bacteria derived metabolites muc9p 821
    Journal of Immunology, 2014
    Co-Authors: Ashish Gurav, Nagendra Singh, Vadivel Ganapathy
    Abstract:

    Presence of trillions of bacteria in healthy colon presents an immunological challenge. Colonic bacteria ferment dietary fibers into short-chain fatty acids (butyrate, propionate, and acetate; SCFAs); among which, butyrate and propionate are inhibitors of histone deacetylases (HDACs). Depletion of SCFAs correlates with increased incidence of intestinal inflammation. SLC5A8 is a high-affinity transporter for SCFAs, which is essential for intracellular actions of SCFAs such as HDAC inhibition. Among various immune cells in colon, dendritic cells (DCs) are unique in having access to colonic lumen, thus getting exposed to bacterial antigens. It is known that colonic DCs exhibit tolerogenic properties with ability to suppress conversion and proliferation of naive T cells into pro-inflammatory T cells. However, the mechanisms involved in the generation of tolerogenic DCs in colon are poorly understood. We hypothesized that SLC5A8-mediated transport of SCFAs into DCs and consequent inhibition of HDACs induces tolerogenic phenotype in these cells. In support of our hypothesis, we found that butyrate and propionate induce the immune-suppressive enzyme Indoleamine 2,3-dioxygenase (IDO) in DCs in an SLC5A8-dependent manner. Further, these DCs are able suppress conversion of naive T cells into interferon-γ (IFNγ) producing Th1 cells. Together, our data identify the SCFA transporter SLC5A8 as a key determinant of SCFA-mediated protection against intestinal inflammation.

  • the plasma membrane transporter SLC5A8 suppresses tumour progression through depletion of survivin without involving its transport function
    Biochemical Journal, 2013
    Co-Authors: Veena Coothankandaswamy, Muthusamy Thangaraju, Puttur D Prasad, Selvakumar Elangovan, Nagendra Singh, Vadivel Ganapathy
    Abstract:

    SLC5A8 is a sodium-coupled transporter for monocarboxylates. Among its substrates are the HDAC inhibitors butyrate, propionate, and pyruvate. Expression of SLC5A8 is silenced in cancers via DNA methylation, and ectopic expression of SLC5A8 in cancer cells induces apoptosis in the presence of its substrates that are HDAC inhibitors. Here we show that ectopic expression of SLC5A8 in cancer cells translocates the anti-apoptotic protein survivin to plasma membrane through protein-protein interaction resulting in depletion of nuclear survivin and also decreases cellular levels of survivin through inhibition of transcription. These SLC5A8-induced changes in the location and levels of survivin result in cell cycle arrest, disruption of the chromosome passenger complex involved in mitosis, induction of apoptosis, and enhancement in chemosensitivity. These effects are seen independent of the transport function of SLC5A8 and histone acetylation status of the cell; in the presence of pyruvate, a SLC5A8 substrate and also an HDAC inhibitor, these effects are amplified. Ectopic expression of SLC5A8 in the breast cancer cell line MB231 inhibits the ability of the cell to form colonies in vitro and to form tumors in mouse xenografts in vivo. The suppression of survivin transcription occurs independent of HDAC inhibition, and the underlying mechanism is associated with decreased phosphorylation of STAT3. The observed effects are specific for survivin with no apparent changes in expression of other inhibitor-of-apoptosis proteins. These studies unravel a novel, hitherto unrecognized, mechanism for the tumor-suppressive role of a plasma membrane transporter independent of its transport function.

  • abstract 26 deletion of SLC5A8 in mice promotes metabolic syndrome colonic inflammation and colon cancer a phenomenon dependent on dietary fiber content
    Cancer Research, 2012
    Co-Authors: Yangzom D Bhutia, Nagendra Singh, Vadivel Ganapathy
    Abstract:

    SLC5A8 is a candidate tumor suppressor that is silenced in colon cancer. It is a transporter that mediates concentrative entry of short-chain fatty acids (SCFAs: acetate, propionate, and butyrate) into colon cells. SCFAs are produced at high concentrations in colon by bacterial fermentation of dietary fiber (acetate, ∼60 mM; propionate, ∼20 mM; butyrate, ∼10 mM). Among SCFAs, propionate and butyrate are inhibitors of histone deacetylases (HDACs). These HDAC inhibitors induce differentiation in normal colon cells but cause apoptosis in colon cancer cells. They also suppress colonic inflammation. We postulate that the transporter is silenced in colon cancer to prevent the entry of these HDAC inhibitors into tumor cells. We have demonstrated the tumor-suppressive function of SLC5A8 in vitro in colon cancer cells and hence hypothesized that deletion of SLC5A8 in mice would promote inflammation and cancer in colon. Surprisingly however, there was no difference between wild type (WT) mice and SLC5A8-null (KO) mice in progression of colonic inflammation and colon cancer in experimental model systems when mice were fed optimal dietary fiber. SLC5A8 transports butyrate and propionate with a Michaelis constant of ∼0.05 mM; under in vivo conditions where butyrate and propionate are present at >10 mM in colon, the transporter plays only a minor role in the entry of these compounds into colon cells. At high concentrations, they diffuse into cells bypassing the transporter. As such we postulated that SLC5A8-null mice would have enhanced colonic inflammation and colon cancer only under low-fiber dietary conditions where butyrate/propionate concentrations in colon are low enough that the transporter is obligatory for their entry into colon cells. To test this hypothesis, we maintained WT and KO mice with a low-fiber diet starting at 4-weeks of age. We found that, under these conditions, the KO mice gained more weight than WT mice, became obese with increased abdominal fat, and exhibited hyperglycemia. When dextran sulfate sodium was administered in drinking water (2% for 1 week), KO mice died from severe colonic inflammation whereas WT mice were able to withstand the treatment and did not die. We then examined the incidence of colon cancer in these mice by crossing them with ApcMin/+ mouse. Under optimal dietary fiber conditions, there was no difference between SLC5A8+/+/ApcMin/+ mice and SLC5A8-/-/ApcMin/+ mice in the incidence of colon cancer. But, under low-fiber dietary conditions, the incidence of colon cancer was much higher in SLC5A8-/-/ApcMin/+ mice than in SLC5A8+/+/ApcMin/+ mice. These studies show that SLC5A8 indeed functions as a tumor suppressor in colon in vivo, but only if dietary fiber content is low. In addition, under these dietary conditions, SLC5A8 also protects against metabolic syndrome and colonic inflammation. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 26. doi:1538-7445.AM2012-26

Elangovan Gopal - One of the best experts on this subject based on the ideXlab platform.

  • abstract 17 tumor suppressive function of SLC5A8 in renal cancer cells
    Cancer Research, 2012
    Co-Authors: Veena Coothankandaswamy, Muthusamy Thangaraju, Vadivel Ganapathy, Selvakumar Elangovan, Elangovan Gopal, Joo Hee Kim, Keith D Robertson, Puttur D Prasad
    Abstract:

    SLC5A8, a Na+-coupled high-affinity transporter for monocarboxylates, and the closely related SLC5A12, a Na+-coupled low-affinity transporter for monocarboxylates, are both highly expressed in kidney, where they mediate the reuptake of lactate and pyruvate from the glomerular filtrate. Recent studies have shown that SLC5A8 is a tumor-suppressor that is silenced in many cancers by promoter hypermethylation. We investigated if SLC5A8 serves as a tumor suppressor in renal cancer cells (RCC). Comparison of the expression of SLC5A8 at the mRNA and protein levels in two RCC (A498 & 786-0) and two normal kidney cell lines (HK-2 & HEK-293) revealed that the expression of SLC5A8 was significantly lower in RCC. Analysis of methylation status of the CpG island in the regulatory region of SLC5A8 showed that the extent of methylation was significantly higher in the two RCC compared to the two normal cells. Culturing A498 cells in the presence of 5-aza-deoxycytidine resulted in re-expression of SLC5A8, confirming that the silencing of the gene is due to DNA methylation. Ectopic expression of SLC5A8 in A498 cells caused apoptosis when cultured in the presence of HDAC inhibitors butyrate and pyruvate. These data show that SLC5A8-mediated concentrative entry of HDAC inhibitors causes cell death in RCC. Interestingly, normal proximal tubular cells, which express SLC5A8 robustly and are exposed to pyruvate, do not undergo apoptosis; HDAC inhibitor-mediated apoptosis is specific to cancer cells. To investigate if HDAC isoforms play a role in this differential sensitivity of normal and RCC to pyruvate, we compared the expression of various HDAC isoforms in HK-2 and A498 cells by RT-PCR. The results indicated that the expression of HDAC1 and HDAC3 was higher in RCC compared to normal cells. The total HDAC enzyme activity was ∼2-3-fold higher in RCC compared to normal cells. If intracellular pyruvate is detrimental to the survival of tumor cells and the tumor cells silence SLC5A8 to prevent entry of extracellular pyruvate into cells, the levels of pyruvate inside tumor cells should be lower in RCC compared to normal cells. To confirm this, we measured pyruvate and lactate levels in normal cells and RCC and found that pyruvate levels were ∼4-fold lower while lactate was ∼2-fold higher in RCC cells compared to normal cells. Finally, to conclusively demonstrate the tumor-suppressive role for SLC5A8 in RCC, we performed mouse xenograft studies using control A498 & 786-0 cells, which do not express SLC5A8 constitutively, and A498 & 786-0 cells, which were made to express SLC5A8 by lentiviral mediated transfection of SLC5A8 cDNA. The growth of the tumor was significantly slower with SLC5A8-expressing cells than with SLC5A8-negative parent cells. These studies demonstrate that SLC5A8 is indeed a tumor suppressor in kidney, suggesting that pharmacological induction of the transporter expression in renal cancer might be a novel strategy for treatment of renal cancer. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 17. doi:1538-7445.AM2012-17

  • sodium coupled electrogenic transport of pyroglutamate 5 oxoproline via SLC5A8 a monocarboxylate transporter
    Biochimica et Biophysica Acta, 2010
    Co-Authors: Seiji Miyauchi, Vadivel Ganapathy, Yoshiyuki Kubo, Sonne R Srinivas, Ellappan Babu, Elangovan Gopal, Nagavedi S Umapathy, Santosh V Thakkar, Puttur D Prasad
    Abstract:

    Abstract Pyroglutamate, also known as 5-oxoproline, is a structural analog of proline. This amino acid derivative is a byproduct of glutathione metabolism, and is reabsorbed efficiently in kidney by Na+-coupled transport mechanisms. Previous studies have focused on potential participation of amino acid transport systems in renal reabsorption of this compound. Here we show that it is not the amino acid transport systems but instead the Na+-coupled monocarboxylate transporter SLC5A8 that plays a predominant role in this reabsorptive process. Expression of cloned human and mouse SLC5A8 in mammalian cells induces Na+-dependent transport of pyroglutamate that is inhibitable by various SLC5A8 substrates. SLC5A8-mediated transport of pyroglutamate is saturable with a Michaelis constant of 0.36 ± 0.04 mM. Na+-activation of the transport process exhibits sigmoidal kinetics with a Hill coefficient of 1.8 ± 0.4, indicating involvement of more than one Na+ in the activation process. Expression of SLC5A8 in Xenopuslaevis oocytes induces Na+-dependent inward currents in the presence of pyroglutamate under voltage-clamp conditions. The concentration of pyroglutamate necessary for induction of half-maximal current is 0.19 ± 0.01 mM. The Na+-activation kinetics is sigmoidal with a Hill coefficient of 2.3 ± 0.2. Ibuprofen, a blocker of SLC5A8, suppressed pyroglutamate-induced currents in SLC5A8-expressing oocytes; the concentration of the blocker necessary for causing half-maximal inhibition is 14 ± 1 μM. The involvement of SLC5A8 can be demonstrated in rabbit renal brush border membrane vesicles by showing that the Na+-dependent uptake of pyroglutamate in these vesicles is inhibitable by known substrates of SLC5A8. The Na+ gradient-driven pyroglutamate uptake was stimulated by an inside-negative K+ diffusion potential induced by valinomycin, showing that the uptake process is electrogenic.

  • transport by SLC5A8 with subsequent inhibition of histone deacetylase 1 hdac1 and hdac3 underlies the antitumor activity of 3 bromopyruvate
    Cancer, 2009
    Co-Authors: Muthusamy Thangaraju, Shiro Itagaki, Puttur D Prasad, Selvakumar Elangovan, Elangovan Gopal, Senthil Karunakaran, Vadivel Ganapathy
    Abstract:

    BACKGROUND: 3-Bromopyruvate is an alkylating agent with antitumor activity. It is currently believed that blockade of adenosine triphosphate production from glycolysis and mitochondria is the primary mechanism responsible for this antitumor effect. The current studies uncovered a new and novel mechanism for the antitumor activity of 3-bromopyruvate. METHODS: The transport of 3-bromopyruvate by sodium-coupled monocarboxylate transporter SMCT1 (SLC5A8), a tumor suppressor and a sodium (Na+)-coupled, electrogenic transporter for short-chain monocarboxylates, was studied using a mammalian cell expression and the Xenopus laevis oocyte expression systems. The effect of 3-bromopyruvate on histone deacetylases (HDACs) was monitored using the lysate of the human breast cancer cell line MCF7 and human recombinant HDAC isoforms as the enzyme sources. Cell viability was monitored by fluorescence-activated cell-sorting analysis and colony-formation assay. The acetylation status of histone H4 was evaluated by Western blot analysis. RESULTS: 3-Bromopyruvate is a transportable substrate for SLC5A8, and that transport process is Na+-coupled and electrogenic. MCF7 cells did not express SLC5A8 and were not affected by 3-bromopyruvate. However, when transfected with SLC5A8 or treated with inhibitors of DNA methylation, these cells underwent apoptosis in the presence of 3-bromopyruvate. This cell death was associated with the inhibition of HDAC1/HDAC3. Studies with different isoforms of human recombinant HDACs identified HDAC1 and HDAC3 as the targets for 3-bromopyruvate. CONCLUSIONS: 3-Bromopyruvate was transported into cells actively through the tumor suppressor SLC5A8, and the process was energized by an electrochemical Na+ gradient. Ectopic expression of the transporter in MCF7 cells led to apoptosis, and the mechanism involved the inhibition of HDAC1/HDAC3. Cancer 2009. © 2009 American Cancer Society.

  • SLC5A8 triggers tumor cell apoptosis through pyruvate dependent inhibition of histone deacetylases
    Cancer Research, 2006
    Co-Authors: Muthusamy Thangaraju, Puttur D Prasad, Sudha Ananth, Elangovan Gopal, Pamela M Martin, Sylvia B Smith, Esta Sterneck, Vadivel Ganapathy
    Abstract:

    Tumor cells up-regulate glycolysis but convert pyruvate into lactate instead of oxidizing it. Here, we show that pyruvate, but not lactate, is an inhibitor of histone deacetylases (HDAC) and an inducer of apoptosis in tumor cells and that SLC5A8, a Na+/monocarboxylate cotransporter, is obligatory for this process. We found that SLC5A8 is expressed in nontransformed breast epithelial cell lines but silenced by DNA methylation in tumor cell lines. The down-regulation of the gene is also evident in primary breast tumors. When MCF7 breast tumor cells are transfected with SLC5A8 cDNA, the cells undergo pyruvate-dependent apoptosis. Butyrate and propionate also induce apoptosis in SLC5A8-expressing cells, whereas lactate does not. The differential ability of these monocarboxylates to cause apoptosis in SLC5A8-expressing MCF7 cells correlates with their ability to inhibit HDACs. Apoptosis induced by SLC5A8/pyruvate in MCF7 cells is associated with up-regulation of p53, Bax, tumor necrosis factor–related apoptosis-inducing ligand (TRAIL), TRAIL receptor (TRAILR) 1, and TRAILR2 and down-regulation of Bcl2 and survivin. Lactate dehydrogenase isozymes are differentially expressed in nontransformed cells and tumor cells such that the latter convert pyruvate into lactate. Silencing of SLC5A8 coupled with conversion of pyruvate into lactate in tumor cells correlates with increased HDAC activity in these cells compared with nontransformed cells. Our studies thus identify pyruvate as a HDAC inhibitor and indicate that the Na+-coupled pyruvate transport underlies the tumor-suppressive role of SLC5A8. We propose that tumor cells silence SLC5A8 and convert pyruvate into lactate as complementary mechanisms to avoid pyruvate-induced cell death. (Cancer Res 2006; 66(24): 11560-4)

  • biological functions of SLC5A8 a candidate tumour suppressor
    Biochemical Society Transactions, 2005
    Co-Authors: Vadivel Ganapathy, Elangovan Gopal, Seiji Miyauchi, Puttur D Prasad
    Abstract:

    SLC5A8 is a candidate tumour suppressor gene that is silenced in colon cancer, gastric cancer and possibly other cancers in humans. This gene codes for a transporter belonging to the Na+/glucose co-transporter gene family ( SLC5 ). The cancer-associated silencing of the gene involves hypermethylation of CpG islands present in exon 1 of the gene. SLC5A8 is expressed in colon, ileum, kidney and thyroid gland. The protein coded by the gene mediates the Na+-coupled and electrogenic transport of a variety of monocarboxylates, including short-chain fatty acids, lactate and nicotinate. It may also transport iodide. The normal physiological function of this transporter in the intestinal tract and kidney is likely to facilitate the active absorption of short-chain fatty acids, lactate and nicotinate. One of the short-chain fatty acids that serves as a substrate for SLC5A8 is butyrate. This fatty acid is an inhibitor of histone deacetylases and is known to induce apoptosis in a variety of tumours including colonic tumour. Since butyrate is produced in the colonic lumen at high concentrations by bacterial fermentation of dietary fibre, we speculate that the ability of SLC5A8 to mediate the entry of this short-chain fatty acid into colonic epithelial cells underlies the potential tumour suppressor function of this transporter. Abbreviations: AIT, apical iodide transporter; MCT, monocarboxylate transporter; NIS, Na/I symporter; SMCT, sodium-coupled monocarboxylate transporter

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