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Longsen Chang - One of the best experts on this subject based on the ideXlab platform.
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Inhibition of EGFR pathway promotes the cytotoxicity of ABT-263 in human leukemia K562 cells by blocking MCL1 upregulation
Biochemical pharmacology, 2020Co-Authors: Yuan-chin Lee, Chiahui Huang, Liang-jun Wang, Jing-ting Chiou, Yi-jun Shi, Longsen ChangAbstract:Abstract ABT-263 induces MCL1 upregulation in cancer cells, which confers resistance to the drug. An increased understanding of the mechanism underlying ABT-263-induced MCL1 expression may provide a strategy to improve its tumor-suppression activity. The present study revealed that ABT-263 reduced the turnover of MCL1 mRNA, thereby upregulating MCL1 expression in human K562 leukemia cells. Furthermore, ABT-263-induced EGFR activation promoted AGO2 phosphorylation at Y393 and reduced miR-125b maturation. Treatment with EGFR inhibitors mitigated MCL1 upregulation induced by ABT-263. Additionally, lithium chloride (LiCl) alleviated ABT-263-induced MCL1 upregulation through EGFR-AGO2 axis-modulated miR-125b suppression. Ectopic expression of dominant negative AGO2(Y393F) or transfection with miR-125b abolished ABT-263-induced upregulation of MCL1 mRNA and protein levels. Co-treatment with either EGFR inhibitors or LiCl collaboratively enhanced ABT-263 cytotoxicity, while MCL1 overexpression eliminated this synergistic effect. Collectively, our data reveal that ABT-263 increases EGFR-mediated AGO2 phosphorylation, which in turn suppresses miR-125b-mediated MCL1 mRNA degradation in K562 cells. The suppression of this signaling pathway results in the synergistic cytotoxic effect of EGFR inhibitors or LiCl and ABT-263.
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Autophagic HuR mRNA degradation induces survivin and MCL1 downregulation in YM155-treated human leukemia cells
Toxicology and applied pharmacology, 2019Co-Authors: Jing-ting Chiou, Chiahui Huang, Yuan-chin Lee, Liang-jun Wang, Yi-jun Shi, Longsen ChangAbstract:The aim of this study was to investigate the mechanism of YM155 cytotoxicity in human chronic myeloid leukemia (CML) cells. YM155-induced apoptosis of human CML K562 cells was characterized by ROS-mediated p38 MAPK activation, mitochondrial depolarization, and survivin and MCL1 downregulation. Moreover, YM155-induced autophagy caused degradation of HuR mRNA and downregulation of HuR protein expression, which resulted in destabilized survivin and MCL1 mRNA. Interestingly, survivin and MCL1 suppression contributed to autophagy-mediated HuR mRNA destabilization in YM155-treated cells. Pretreatment with inhibitors of p38 MAPK or autophagy alleviated YM155-induced autophagy and apoptosis in K562 cells, as well as YM155-induced downregulation of HuR, survivin, and MCL1. Ectopic overexpression of HuR, survivin, or MCL1 attenuated the cytotoxic effect of YM155 on K562 cells. Conversely, YM155 sensitized K562 cells to ABT-199 (a BCL2 inhibitor), and circumvented K562 cell resistance to ABT-199 because of its inhibitory effect on survivin and MCL1 expression. Overall, our data indicate that YM155-induced apoptosis is mediated by inducing autophagic HuR mRNA degradation, and reveal the pathway responsible for YM155-induced downregulation of survivin and MCL1 in K562 cells. Our findings also indicate a similar pathway underlying YM155-induced death in human CML MEG-01 cells.
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amsacrine induced apoptosis of human leukemia u937 cells is mediated by the inhibition of akt and erk induced stabilization of MCL1
Apoptosis, 2017Co-Authors: Yingjung Chen, Chiahui Huang, Longsen ChangAbstract:Previous studies have attributed the anticancer activity of amsacrine to its inhibitory effect on topoisomerase II. However, 9-aminoacridine derivatives, which have the same structural scaffold as amsacrine, induce cancer cell apoptosis by altering the expression of BCL2 family proteins. Therefore, in the present study, we assessed whether BCL2 family proteins mediated the cytotoxic effects of amsacrine on human leukemia U937 cells. Amsacrine-induced apoptosis of U937 cells was characterized by caspase-9 and caspase-3 activation, increased intracellular Ca2+ concentration, mitochondrial depolarization, and MCL1 down-regulation. Amsacrine induced MCL1 down-regulation by decreasing its stability. Further, amsacrine-treated U937 cells showed AKT degradation and Ca2+-mediated ERK inactivation. Blockade of ERK-mediated phosphorylation of MCL1 inhibited the effect of Pin1 on the stabilization of MCL1, and AKT degradation promoted GSK3β-mediated degradation of MCL1. Restoration of ERK phosphorylation and AKT expression abrogated amsacrine-induced MCL1 down-regulation. Moreover, MCL1 over-expression inhibited amsacrine-induced depolarization of mitochondria membrane and increased the viability of amsacrine-treated cells. Taken together, our data indicate that amsacrine abolishes ERK- and Pin1-mediated stabilization of MCL1 and promotes GSK3β-mediated degradation of MCL1, leading to activate mitochondria-mediated apoptosis pathway in U937 cells.
Seiji Arai - One of the best experts on this subject based on the ideXlab platform.
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MARCH5 mediates NOXA-dependent MCL1 degradation driven by kinase inhibitors and integrated stress response activation.
eLife, 2020Co-Authors: Seiji Arai, Andreas Varkaris, Mannan Nouri, Sheng Chen, Lisha Xie, Steven P. BalkAbstract:MCL1 has critical antiapoptotic functions and its levels are tightly regulated by ubiquitylation and degradation, but mechanisms that drive this degradation, particularly in solid tumors, remain to be established. We show here in prostate cancer cells that increased NOXA, mediated by kinase inhibitor activation of an integrated stress response, drives the degradation of MCL1, and identify the mitochondria-associated ubiquitin ligase MARCH5 as the primary mediator of this NOXA-dependent MCL1 degradation. Therapies that enhance MARCH5-mediated MCL1 degradation markedly enhance apoptosis in response to a BH3 mimetic agent targeting BCLXL, which may provide for a broadly effective therapy in solid tumors. Conversely, increased MCL1 in response to MARCH5 loss does not strongly sensitize to BH3 mimetic drugs targeting MCL1, but instead also sensitizes to BCLXL inhibition, revealing a codependence between MARCH5 and MCL1 that may also be exploited in tumors with MARCH5 genomic loss.
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Ubiquitin Ligase MARCH5 Regulates Apoptosis through Mediation of Stress-Induced and NOXA-Dependent MCL1 Degradation
2020Co-Authors: Seiji Arai, Lisha Xie, Sen Chen, Steve BalkAbstract:MCL1 has critical antiapoptotic functions and its levels are tightly regulated by ubiquitylation and degradation, but mechanisms that drive this degradation, particularly in solid tumors, remain to be established. We show here in prostate cancer cells that increased NOXA, mediated by activation of an integrated stress response, drives the degradation of MCL1, and identify the mitochondria-associated ubiquitin ligase MARCH5 as the primary mediator of this NOXA dependent MCL1 degradation. Therapies that enhance MARCH5-mediated MCL1 degradation markedly enhance apoptosis in response to a BH3 mimetic agent targeting BCLXL, which may provide for a broadly effective therapy in solid tumors. Conversely, increased MCL1 in response to MARCH5 loss does not sensitize to BH3 mimetic drugs targeting MCL1, but instead also sensitizes to BCLXL inhibition, revealing a codependence between MARCH5 and MCL1 that may also be exploited in tumors with MARCH5 genomic loss.
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tyrosine kinase inhibitors increase MCL1 degradation and in combination with bclxl bcl2 inhibitors drive prostate cancer apoptosis
Clinical Cancer Research, 2018Co-Authors: Seiji Arai, Steven P. Balk, Oliver Jonas, Matthew Whitman, Eva Corey, Sheng ChenAbstract:Purpose: Clinically available BH3 mimetic drugs targeting BCLXL and/or BCL2 (navitoclax and venetoclax, respectively) are effective in some hematological malignancies, but have limited efficacy in solid tumors. This study aimed to identify combination therapies that exploit clinical BH3 mimetics for prostate cancer (PCa). Experimental Design: PCa cells or xenografts were treated with BH3 mimetics as single agents or in combination with other agents, and effects on MCL1 and apoptosis were assessed. MCL1 was also targeted directly using RNAi, CRISPR, or an MCL1 specific BH3 mimetic, S63845. Results: We initially found that MCL1 depletion or inhibition markedly sensitized PCa cells to apoptosis mediated by navitoclax, but not venetoclax, in vitro and in vivo, indicating that they are primed to undergo apoptosis and protected by MCL1 and BCLXL. Small molecule EGFR kinase inhibitors (erlotinib, lapatinib) also dramatically sensitized to navitoclax-mediated apoptosis, and this was associated with markedly increased proteasome-dependent degradation of MCL1. This increased MCL1 degradation appeared to be through a novel mechanism as it was not dependent upon GSK3b-mediated phosphorylation and subsequent ubiquitylation by the ubiquitin ligases bTRCP and FBW7, or through other previously identified MCL1 ubiquitin ligases or deubiquitinases. Inhibitors targeting additional kinases (cabozantinib and sorafenib) similarly caused GSK3b-independent MCL1 degradation, and in combination with navitoclax drove apoptosis in vitro and in vivo. Conclusions: These results show that PCa cells are primed to undergo apoptosis, and that co-targeting BCLXL and MCL1, directly or indirectly through agents that increase MCL1 degradation, can induce dramatic apoptotic responses.
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Tyrosine Kinase Inhibitors Increase MCL1 Degradation and in Combination with BCLXL/BCL2 Inhibitors Drive Prostate Cancer Apoptosis.
Clinical cancer research : an official journal of the American Association for Cancer Research, 2018Co-Authors: Seiji Arai, Steven P. Balk, Oliver Jonas, Matthew Whitman, Eva Corey, Sen ChenAbstract:Purpose: Clinically available BH3 mimetic drugs targeting BCLXL and/or BCL2 (navitoclax and venetoclax, respectively) are effective in some hematological malignancies, but have limited efficacy in solid tumors. This study aimed to identify combination therapies that exploit clinical BH3 mimetics for prostate cancer (PCa). Experimental Design: PCa cells or xenografts were treated with BH3 mimetics as single agents or in combination with other agents, and effects on MCL1 and apoptosis were assessed. MCL1 was also targeted directly using RNAi, CRISPR, or an MCL1 specific BH3 mimetic, S63845. Results: We initially found that MCL1 depletion or inhibition markedly sensitized PCa cells to apoptosis mediated by navitoclax, but not venetoclax, in vitro and in vivo, indicating that they are primed to undergo apoptosis and protected by MCL1 and BCLXL. Small molecule EGFR kinase inhibitors (erlotinib, lapatinib) also dramatically sensitized to navitoclax-mediated apoptosis, and this was associated with markedly increased proteasome-dependent degradation of MCL1. This increased MCL1 degradation appeared to be through a novel mechanism as it was not dependent upon GSK3b-mediated phosphorylation and subsequent ubiquitylation by the ubiquitin ligases bTRCP and FBW7, or through other previously identified MCL1 ubiquitin ligases or deubiquitinases. Inhibitors targeting additional kinases (cabozantinib and sorafenib) similarly caused GSK3b-independent MCL1 degradation, and in combination with navitoclax drove apoptosis in vitro and in vivo. Conclusions: These results show that PCa cells are primed to undergo apoptosis, and that co-targeting BCLXL and MCL1, directly or indirectly through agents that increase MCL1 degradation, can induce dramatic apoptotic responses.
Jeffrey Easthamanderson - One of the best experts on this subject based on the ideXlab platform.
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deubiquitinase usp9x stabilizes MCL1 and promotes tumour cell survival
Nature, 2010Co-Authors: Martin Schwickart, Xiaodong Huang, Jennie R Lill, Jinfeng Liu, Ronald E Ferrando, Dorothy French, Heather Maecker, Karen Orourke, Fernando Bazan, Jeffrey EasthamandersonAbstract:MCL1 is essential for the survival of stem and progenitor cells of multiple lineages, and is unique among pro-survival BCL2 family members in that it is rapidly turned over through the action of ubiquitin ligases. B- and mantle-cell lymphomas, chronic myeloid leukaemia, and multiple myeloma, however, express abnormally high levels of MCL1, contributing to chemoresistance and disease relapse. The mechanism of MCL1 overexpression in cancer is not well understood. Here we show that the deubiquitinase USP9X stabilizes MCL1 and thereby promotes cell survival. USP9X binds MCL1 and removes the Lys 48-linked polyubiquitin chains that normally mark MCL1 for proteasomal degradation. Increased USP9X expression correlates with increased MCL1 protein in human follicular lymphomas and diffuse large B-cell lymphomas. Moreover, patients with multiple myeloma overexpressing USP9X have a poor prognosis. Knockdown of USP9X increases MCL1 polyubiquitination, which enhances MCL1 turnover and cell killing by the BH3 mimetic ABT-737. These results identify USP9X as a prognostic and therapeutic target, and they show that deubiquitinases may stabilize labile oncoproteins in human malignancies.
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deubiquitinase usp9x stabilizes MCL1 and promotes tumour cell survival
Nature, 2010Co-Authors: Martin Schwickart, Xiaodong Huang, Jennie R Lill, Ronald E Ferrando, Dorothy French, Heather Maecker, Karen Orourke, Fernando Bazan, Jeffrey Easthamanderson, David DornanAbstract:The induced myeloid leukaemia cell-differentiation protein MCL1 is often overexpressed in tumours, where it promotes cancer cell survival. Schwickart et al. now show that the deubiquitinase USP9X stabilizes MCLl and is itself often overexpressed in cancer. In multiple myelomas, higher levels of USP9X are associated with poorer prognosis. RNAi knockdown of USP9X in human embryonic kidney 293 cells promotes MCLl degradation and sensitizes cells to anticancer compounds that induce apoptosis, suggesting that targeting USP9X may represent a novel therapeutic strategy for tumours with MCLl overexpression. MCL1 — essential for the survival of stem and progenitor cells of multiple lineages — is unique among pro-survival BCL2 family members in that it is rapidly turned over through the action of ubiquitin ligases. Abnormally high levels of MCL1 are expressed in some cancers, but the mechanism of MCL1 overexpression is not well understood. The deubiquitinase USP9X is now shown to stabilize MCL1 and thereby promote cell survival; this makes it a potential therapeutic target. MCL1 is essential for the survival of stem and progenitor cells of multiple lineages1,2, and is unique among pro-survival BCL2 family members in that it is rapidly turned over through the action of ubiquitin ligases3,4,5,6. B- and mantle-cell lymphomas, chronic myeloid leukaemia, and multiple myeloma7,8,9, however, express abnormally high levels of MCL1, contributing to chemoresistance and disease relapse. The mechanism of MCL1 overexpression in cancer is not well understood. Here we show that the deubiquitinase USP9X stabilizes MCL1 and thereby promotes cell survival. USP9X binds MCL1 and removes the Lys 48-linked polyubiquitin chains that normally mark MCL1 for proteasomal degradation. Increased USP9X expression correlates with increased MCL1 protein in human follicular lymphomas and diffuse large B-cell lymphomas. Moreover, patients with multiple myeloma overexpressing USP9X have a poor prognosis. Knockdown of USP9X increases MCL1 polyubiquitination, which enhances MCL1 turnover and cell killing by the BH3 mimetic ABT-737. These results identify USP9X as a prognostic and therapeutic target, and they show that deubiquitinases may stabilize labile oncoproteins in human malignancies.
Courtney L. Andersen - One of the best experts on this subject based on the ideXlab platform.
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Targeting melanoma's MCL1 bias unleashes the apoptotic potential of BRAF and ERK1/2 pathway inhibitors.
Nature communications, 2019Co-Authors: Matthew J. Sale, Courtney L. Andersen, Emma Minihane, Noel R. Monks, Rebecca Gilley, Frances M. Richards, Kevin Schifferli, Emma J Davies, Mario Aladren Vicente, Eiko OzonoAbstract:BRAF and MEK1/2 inhibitors are effective in melanoma but resistance inevitably develops. Despite increasing the abundance of pro-apoptotic BIM and BMF, ERK1/2 pathway inhibition is predominantly cytostatic, reflecting residual pro-survival BCL2 family activity. Here, we show that uniquely low BCL-XL expression in melanoma biases the pro-survival pool towards MCL1. Consequently, BRAF or MEK1/2 inhibitors are synthetic lethal with the MCL1 inhibitor AZD5991, driving profound tumour cell death that requires BAK/BAX, BIM and BMF, and inhibiting tumour growth in vivo. Combination of ERK1/2 pathway inhibitors with BCL2/BCL-w/BCL-XL inhibitors is stronger in CRC, correlating with a low MCL1:BCL-XL ratio; indeed the MCL1:BCL-XL ratio is predictive of ERK1/2 pathway inhibitor synergy with MCL1 or BCL2/BCL-w/BCL-XL inhibitors. Finally, AZD5991 delays acquired BRAFi/MEKi resistance and enhances the efficacy of an ERK1/2 inhibitor in a model of acquired BRAFi + MEKi resistance. Thus combining ERK1/2 pathway inhibitors with MCL1 antagonists in melanoma could improve therapeutic index and patient outcomes. BRAF or MEK1/2 inhibitors are cytostatic in melanoma and the surviving cells develop drug resistance. This study shows that the pro-survival pool is biased towards MCL1 in melanoma so that BRAF or MEK1/2 inhibitors are synthetic lethal with the MCL1 inhibitor AZD5991, improving tumour growth inhibition.
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targeting melanoma s MCL1 bias unleashes the apoptotic potential of braf and erk1 2 pathway inhibitors
Nature Communications, 2019Co-Authors: Matthew J. Sale, Courtney L. Andersen, Emma Minihane, Noel R. Monks, Rebecca Gilley, Frances M. Richards, Kevin Schifferli, Emma J Davies, Mario Aladren Vicente, Eiko OzonoAbstract:BRAF and MEK1/2 inhibitors are effective in melanoma but resistance inevitably develops. Despite increasing the abundance of pro-apoptotic BIM and BMF, ERK1/2 pathway inhibition is predominantly cytostatic, reflecting residual pro-survival BCL2 family activity. Here, we show that uniquely low BCL-XL expression in melanoma biases the pro-survival pool towards MCL1. Consequently, BRAF or MEK1/2 inhibitors are synthetic lethal with the MCL1 inhibitor AZD5991, driving profound tumour cell death that requires BAK/BAX, BIM and BMF, and inhibiting tumour growth in vivo. Combination of ERK1/2 pathway inhibitors with BCL2/BCL-w/BCL-XL inhibitors is stronger in CRC, correlating with a low MCL1:BCL-XL ratio; indeed the MCL1:BCL-XL ratio is predictive of ERK1/2 pathway inhibitor synergy with MCL1 or BCL2/BCL-w/BCL-XL inhibitors. Finally, AZD5991 delays acquired BRAFi/MEKi resistance and enhances the efficacy of an ERK1/2 inhibitor in a model of acquired BRAFi + MEKi resistance. Thus combining ERK1/2 pathway inhibitors with MCL1 antagonists in melanoma could improve therapeutic index and patient outcomes. BRAF or MEK1/2 inhibitors are cytostatic in melanoma and the surviving cells develop drug resistance. This study shows that the pro-survival pool is biased towards MCL1 in melanoma so that BRAF or MEK1/2 inhibitors are synthetic lethal with the MCL1 inhibitor AZD5991, improving tumour growth inhibition.
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The CUL5 ubiquitin ligase complex mediates resistance to CDK9 and MCL1 inhibitors in lung cancer cells
eLife, 2019Co-Authors: Shaheen Kabir, Justin Cidado, Courtney L. Andersen, Cortni Dick, Pei-chun Lin, Therese Mitros, Seung Hyun Baik, Matthew A. Belmonte, Lisa DrewAbstract:Overexpression of anti-apoptotic proteins MCL1 and Bcl-xL are frequently observed in many cancers. Inhibitors targeting MCL1 are in clinical development, however numerous cancer models are intrinsically resistant to this approach. To discover mechanisms underlying resistance to MCL1 inhibition, we performed multiple flow-cytometry based genome-wide CRISPR screens interrogating two drugs that directly (MCL1i) or indirectly (CDK9i) target MCL1. Remarkably, both screens identified three components (CUL5, RNF7 and UBE2F) of a cullin-RING ubiquitin ligase complex (CRL5) that resensitized cells to MCL1 inhibition. We find that levels of the BH3-only pro-apoptotic proteins Bim and Noxa are proteasomally regulated by the CRL5 complex. Accumulation of Noxa caused by depletion of CRL5 components was responsible for re-sensitization to CDK9 inhibitor, but not MCL1 inhibitor. Discovery of a novel role of CRL5 in apoptosis and resistance to multiple types of anticancer agents suggests the potential to improve combination treatments.
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The CUL5 ubiquitin ligase complex mediates resistance to CDK9 and MCL1 inhibitors in lung cancer cells
2019Co-Authors: Jacob E. Corn, Shaheen Kabir, Justin Cidado, Courtney L. Andersen, Cortni Dick, Pei-chun Lin, Therese Mitros, Seung Hyun Baik, Matthew A. BelmonteAbstract:Overexpression of anti-apoptotic proteins MCL1 and Bcl-xL is a frequent event in blood and solid cancers. Inhibitors targeting MCL1 are in clinical development, however many cancer models are intrinsically resistant to this approach. To discover mechanisms underlying resistance to MCL1 inhibition, we performed multiple flow-cytometry based genome-wide CRISPR screens that interrogate two drugs directly or indirectly targeting MCL1. Remarkably, both screens identified three components (CUL5, RNF7 and UBE2F) of a cullin-RING ubiquitin ligase complex (CRL5) that resensitized cells to MCL1 inhibition. We find that levels of the BH3-only pro-apoptotic proteins Bim and Noxa are proteasomally regulated by the CRL5 complex. Accumulation of Noxa caused by depletion of CRL5 components particularly skewed the balance in favor of apoptosis when cells were challenged with an MCL1 inhibitor. Discovery of a novel role of CRL5 in apoptosis and resistance to MCL1 inhibitors exposes new drug targets and the potential to improve combination treatments.
Toru Okamoto - One of the best experts on this subject based on the ideXlab platform.
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MARCH5 requires MTCH2 to coordinate proteasomal turnover of the MCL1:NOXA complex.
Cell death and differentiation, 2020Co-Authors: Tirta Mario Djajawi, Toru Okamoto, Lei Liu, Jia-nan Gong, Allan Shuai Huang, Ming-jie Luo, Melissa J. Call, David C. S. Huang, Mark F. Van DelftAbstract:MCL1, a BCL2 relative, is critical for the survival of many cells. Its turnover is often tightly controlled through both ubiquitin-dependent and -independent mechanisms of proteasomal degradation. Several cell stress signals, including DNA damage and cell cycle arrest, are known to elicit distinct E3 ligases to ubiquitinate and degrade MCL1. Another trigger that drives MCL1 degradation is engagement by NOXA, one of its BH3-only protein ligands, but the mechanism responsible has remained unclear. From an unbiased genome-wide CRISPR-Cas9 screen, we discovered that the ubiquitin E3 ligase MARCH5, the ubiquitin E2 conjugating enzyme UBE2K, and the mitochondrial outer membrane protein MTCH2 co-operate to mark MCL1 for degradation by the proteasome-specifically when MCL1 is engaged by NOXA. This mechanism of degradation also required the MCL1 transmembrane domain and distinct MCL1 lysine residues to proceed, suggesting that the components likely act on the MCL1:NOXA complex by associating with it in a specific orientation within the mitochondrial outer membrane. MTCH2 has not previously been reported to regulate protein stability, but is known to influence the mitochondrial localization of certain key apoptosis regulators and to impact metabolism. We have now pinpointed an essential but previously unappreciated role for MTCH2 in turnover of the MCL1:NOXA complex by MARCH5, further strengthening its links to BCL2-regulated apoptosis.
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enhanced stability of MCL1 a prosurvival bcl2 relative blunts stress induced apoptosis causes male sterility and promotes tumorigenesis
Proceedings of the National Academy of Sciences of the United States of America, 2014Co-Authors: Toru Okamoto, Leigh Coultas, Donald Metcalf, Mark F Van Delft, Stefan P GlaserAbstract:The B-cell CLL/lymphoma 2 (Bcl2) relative Myeloid cell leukemia sequence 1 (MCL1) is essential for cell survival during development and for tissue homeostasis throughout life. Unlike Bcl2, MCL1 turns over rapidly, but the physiological significance of its turnover has been unclear. We have gained insight into the roles of MCL1 turnover in vivo by analyzing mice harboring a modified allele of MCL1 that serendipitously proved to encode an abnormally stabilized form of MCL1 due to a 13-aa N-terminal extension. Although the mice developed normally and appeared unremarkable, the homozygous males unexpectedly proved infertile due to defective spermatogenesis, which was evoked by enhanced MCL1 prosurvival activity. Under unstressed conditions, the modified MCL1 is present at levels comparable to the native protein, but it is markedly stabilized in cells subjected to stresses, such as protein synthesis inhibition or UV irradiation. Strikingly, the modified MCL1 allele could genetically complement the loss of Bcl2, because introduction of even a single allele significantly ameliorated the severe polycystic kidney disease and consequent runting caused by Bcl2 loss. Significantly, the development of c-MYC–induced acute myeloid leukemia was also accelerated in mice harboring that MCL1 allele. Our collective findings reveal that, under certain circumstances, the N terminus of MCL1 regulates its degradation; that some cell types require degradation of MCL1 to induce apoptosis; and, most importantly, that rapid turnover of MCL1 can serve as a tumor-suppressive mechanism.
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Sensitivity to antitubulin chemotherapeutics is regulated by MCL1 and FBW7
Nature, 2011Co-Authors: Ingrid E. Wertz, Toru Okamoto, Saritha Kusam, Cynthia Lam, Wendy Sandoval, Daniel J. Anderson, Elizabeth Helgason, James A. Ernst, Mike Eby, Jinfeng LiuAbstract:Microtubules have pivotal roles in fundamental cellular processes and are targets of antitubulin chemotherapeutics. Microtubule-targeted agents such as Taxol and vincristine are prescribed widely for various malignancies, including ovarian and breast adenocarcinomas, non-small-cell lung cancer, leukaemias and lymphomas. These agents arrest cells in mitosis and subsequently induce cell death through poorly defined mechanisms. The strategies that resistant tumour cells use to evade death induced by antitubulin agents are also unclear. Here we show that the pro-survival protein MCL1 (ref. 3) is a crucial regulator of apoptosis triggered by antitubulin chemotherapeutics. During mitotic arrest, MCL1 protein levels decline markedly, through a post-translational mechanism, potentiating cell death. Phosphorylation of MCL1 directs its interaction with the tumour-suppressor protein FBW7, which is the substrate-binding component of a ubiquitin ligase complex. The polyubiquitylation of MCL1 then targets it for proteasomal degradation. The degradation of MCL1 was blocked in patient-derived tumour cells that lacked FBW7 or had loss-of-function mutations in FBW7, conferring resistance to antitubulin agents and promoting chemotherapeutic-induced polyploidy. Additionally, primary tumour samples were enriched for FBW7 inactivation and elevated MCL1 levels, underscoring the prominent roles of these proteins in oncogenesis. Our findings suggest that profiling the FBW7 and MCL1 status of tumours, in terms of protein levels, messenger RNA levels and genetic status, could be useful to predict the response of patients to antitubulin chemotherapeutics.