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Ad A. C. M. Peijnenburg - One of the best experts on this subject based on the ideXlab platform.
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pi3k akt jnk and erk pathways are not crucial for the induction of cholesterol biosynthesis gene transcription in intestinal epithelial cells following treatment with the potato glycoalkaloid alpha chaconine
Journal of Agricultural and Food Chemistry, 2008Co-Authors: Tafadzwa Mandimika, Hakan Baykus, Jenneke Poortman, Cutberto Garza, H Kuiper, Ad A. C. M. PeijnenburgAbstract:We previously reported that exposure of the intestinal epithelial Caco-2 cell line to noncytotoxic concentrations of potato glycoalkaloids resulted in increased expression of cholesterol biosynthesis genes. Genes involved in mitogen-activated protein kinase (MAPK) and phosphatidylinositol 3-kinase (PI3K)/v-akt murine thymoma viral oncogene homologue (AKT) pathways and their downstream effectors such as Jun, c-Myc, and Fos also were induced. MAPK and PI3K/AKT pathways have been described to regulate the activity of sterol regulatory element binding transcription factors (SREBPs) and consequently the expression of cholesterol biosynthesis genes. In this study, to understand the mechanism of induction of cholesterol biosynthesis upon ?-chaconine treatment, its effect on SREBP-2 protein levels was investigated. We also examined whether MAPK and PI3K/AKT pathways are required for the observed induction of these genes following exposure of cells to ?-chaconine. Differentiated Caco-2 cells were pretreated with LY294002 (PI3K inhibitor), PD98059 (MEK1 inhibitor), or SP600125 (JNK inhibitor) or a combination of all inhibitors for 24 h prior to coincubation with 10 ?M ?-chaconine for 6 h. Significant increases in precursor and mature protein levels of SREBP-2 were observed after ?-chaconine exposure. We also observed that ?-chaconine treatment resulted in significant phosphorylation of AKT, extracellular signal related protein kinase (ERK), and c-jun N terminal protein kinase (JNK) but not that of p38. In general, the kinase inhibitor experiments revealed that phosphorylation of kinases of PI3K/AKT, ERK, and JNK pathways was not crucial for the induction of expression of cholesterol biosynthesis genes, with the exception of SC5DL. The transcription of this later gene was reduced when all three pathways were inhibited. On the basis of these results, it can be postulated that other mechanisms, which may be independent of the MAPK and PI3K/AKT pathways, including possibly post-translational activation of SREBP-2, may be more pivotal for the induction of cholesterol biosynthesis genes following exposure of intestinal cells to ?-chaconine.
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PI3K/AKT, JNK, and ERK pathways are not crucial for the induction of cholesterol biosynthesis gene transcription in intestinal epithelial cells following treatment with the potato glycoalkaloid Alpha-Chaconine.
Journal of agricultural and food chemistry, 2008Co-Authors: Tafadzwa Mandimika, Hakan Baykus, Jenneke Poortman, Cutberto Garza, Harry A Kuiper, Ad A. C. M. PeijnenburgAbstract:We previously reported that exposure of the intestinal epithelial Caco-2 cell line to noncytotoxic concentrations of potato glycoalkaloids resulted in increased expression of cholesterol biosynthesis genes. Genes involved in mitogen-activated protein kinase (MAPK) and phosphatidylinositol 3-kinase (PI3K)/v-akt murine thymoma viral oncogene homologue (AKT) pathways and their downstream effectors such as Jun, c-Myc, and Fos also were induced. MAPK and PI3K/AKT pathways have been described to regulate the activity of sterol regulatory element binding transcription factors (SREBPs) and consequently the expression of cholesterol biosynthesis genes. In this study, to understand the mechanism of induction of cholesterol biosynthesis upon Alpha-Chaconine treatment, its effect on SREBP-2 protein levels was investigated. We also examined whether MAPK and PI3K/AKT pathways are required for the observed induction of these genes following exposure of cells to Alpha-Chaconine. Differentiated Caco-2 cells were pretreated with LY294002 (PI3K inhibitor), PD98059 (MEK1 inhibitor), or SP600125 (JNK inhibitor) or a combination of all inhibitors for 24 h prior to coincubation with 10 microM Alpha-Chaconine for 6 h. Significant increases in precursor and mature protein levels of SREBP-2 were observed after Alpha-Chaconine exposure. We also observed that Alpha-Chaconine treatment resulted in significant phosphorylation of AKT, extracellular signal related protein kinase (ERK), and c-jun N terminal protein kinase (JNK) but not that of p38. In general, the kinase inhibitor experiments revealed that phosphorylation of kinases of PI3K/AKT, ERK, and JNK pathways was not crucial for the induction of expression of cholesterol biosynthesis genes, with the exception of SC5DL. The transcription of this later gene was reduced when all three pathways were inhibited. On the basis of these results, it can be postulated that other mechanisms, which may be independent of the MAPK and PI3K/AKT pathways, including possibly post-translational activation of SREBP-2, may be more pivotal for the induction of cholesterol biosynthesis genes following exposure of intestinal cells to Alpha-Chaconine.
Mendel Friedman - One of the best experts on this subject based on the ideXlab platform.
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distribution of glycoalkaloids in potato tubers of 59 accessions of two wild and five cultivated solanum species
Journal of Agricultural and Food Chemistry, 2008Co-Authors: Nobuyuki Kozukue, Kyungsoon Yoon, Gwangin Byun, Shuji Misoo, Carol Levin, Mendel FriedmanAbstract:Steroidal glycoalkaloids are naturally occurring, secondary plant metabolites that are found in foods, including potatoes and tomatoes. Their content in plants is controlled by both genetic and environmental factors. Glycoalkaloid profiles can be passed to progenies during breeding and hybridization of wild and cultivated potatoes designed to develop improved potatoes. The most common potato, Solanum tuberosum, contains primarily the glycoalkaloids, alpha-solanine and Alpha-Chaconine. However, wild-type potatoes being used for breeding new varieties contain other, less common glycoalkaloids. Because glycoalkaloid composition is a major criterion for the release of new potato cultivars, we used HPLC, TLC, GC, and GC/MS to determine their nature and content in several Solanum species widely used in potato breeding and hybridization programs. Solanum tuberosum, as well as S. andigena and S. stenotomum, contained alpha-solanine and Alpha-Chaconine. S. canasense was found to contain only dehydrocommersonine. S. acaule contained alpha-tomatine and demissine. S. juzepczukii and S. curtilobum contained demissine and two previously unidentified glycoalkaloids. We characterized them as demissidine-glucose/rhamnose (1/1 ratio) and demissidine-galactose/glucose/rhamnose (1/1/1 ratio), tentatively named dihydro-beta(1)-chaconine and dihydrosolanine, respectively. We found extensive variability in the glycoalkaloid profiles in the tested potato varieties. The possible significance of these findings for plant breeding and food safety is discussed.
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analysis of biologically active compounds in potatoes solanum tuberosum tomatoes lycopersicon esculentum and jimson weed datura stramonium seeds
Journal of Chromatography A, 2004Co-Authors: Mendel FriedmanAbstract:Potatoes and tomatoes, members of the Solanaceae plant family, serve as major, inexpensive low-fat food sources providing for energy, high-quality protein, fiber, vitamins, pigments, as well as other nutrients. These crops also produce biologically active secondary metabolites, which may have both adverse and beneficial effects in the diet. This limited overview, based largely on our studies with the aid of HPLC, TLC, ELISA, GC-MS, and UV spectroscopy, covers analytical aspects of two major potato trisaccharide glycoalkaloids, Alpha-Chaconine and alpha-solanine, and their hydrolysis products (metabolites) with two, one, and zero carbohydrate groups; the potato water-soluble nortropane alkaloids calystegine A3 and B2; the principal potato polyphenolic compound chlorogenic acid; potato inhibitors of digestive enzymes; the tomato tetrasaccharide glycoalkaloids dehydrotomatine and alpha-tomatine and hydrolysis products; the tomato pigments beta-carotene, lycopene, and chlorophyll; and the anticholinergic alkaloids atropine and scopolamine present in Datura stramonium (jimson weed) seeds that contaminate grain and animal feed. Related studies by other investigators are also mentioned. Accurate analytical methods for these food ingredients help assure the consumer of eating a good-quality and safe diet.
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glycoalkaloids and metabolites inhibit the growth of human colon ht29 and liver hepg2 cancer cells
Journal of Agricultural and Food Chemistry, 2004Co-Authors: Kaprang Lee, Nobuyuki Kozukue, Jaesook Han, Joonhong Park, Eunyoung Chang, Eunjung Baek, Jongsun Chang, Mendel FriedmanAbstract:As part of an effort to improve plant-derived foods such as potatoes, eggplants, and tomatoes, the antiproliferative activities against human colon (HT29) and liver (HepG2) cancer cells of a series of structurally related individual compounds were examined using a microculture tetrazolium (MTT) assay. The objective was to assess the roles of the carbohydrate side chain and aglycon part of Solanum glycosides in influencing inhibitory activities of these compounds. Evaluations were carried out with four concentrations each (0.1, 1, 10, and 100 microg/mL) of the the potato trisaccharide glycoalkaloids Alpha-Chaconine and alpha-solanine; the disaccharides beta(1)-chaconine, beta(2)-chaconine, and beta(2)-solanine; the monosaccharide gamma-chaconine and their common aglycon solanidine; the tetrasaccharide potato glycoalkaloid dehydrocommersonine; the potato aglycon demissidine; the tetrasaccharide tomato glycoalkaloid alpha-tomatine, the trisaccharide beta(1)-tomatine, the disaccharide gamma-tomatine, the monosaccharide delta-tomatine, and their common aglycon tomatidine; the eggplant glycoalkaloids solamargine and solasonine and their common aglycon solasodine; and the nonsteroidal alkaloid jervine. All compounds were active in the assay, with the glycoalkaloids being the most active and the hydrolysis products less so. The effectiveness against the liver cells was greater than against the colon cells. Potencies of alpha-tomatine and Alpha-Chaconine at a concentration of 1 microg/mL against the liver carcinoma cells were higher than those observed with the anticancer drugs doxorubicin and camptothecin. Because Alpha-Chaconine, alpha-solanine, and alpha-tomatine also inhibited normal human liver HeLa (Chang) cells, safety considerations should guide the use of these compounds as preventative or therapeutic treatments against carcinomas.
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Feeding of potato, tomato and eggplant alkaloids, affects food consumption and body and liver weights in mice
The Journal of nutrition, 1996Co-Authors: Mendel Friedman, Philip R. Henika, Bruce E. MackeyAbstract:Reduced liver weight was used to evaluate the potential toxicity in mice of four naturally occurring steroidal glycoalkaloids: Alpha-Chaconine and alpha-solanine, alpha-tomatine and solasonine. Increased liver weights was used to evaluate the three corresponding steroidal aglycones: solanidine, tomatidine, and solasodine and the non-alkaloid adrenal steroid dehydroepiandrosterone (DHEA). Adult female Swiss-Webster mice were fed diets containing test compound concentrations of 0 (control), 1.2, 2.4 or 4.8 mmol/kg diet for 7, 14 or 28 d. Absolute liver weights (LW) and relative liver weights (liver weight/body weight x 100, %LW/BW) were determined at autopsy. The %LW/BW was lower than that of controls in mice fed the potato glycoalkaloid Alpha-Chaconine (-10%, P < or = 0.05) for 7 d with the 2.4 mmol/kg diet dose. Under these same conditions, %LW/BW was greater than that of controls in mice fed two aglycones: solanidine (27%, P < or = 0.001) and solasodine (8%, P < or = 0.01). Relative liver weight increases induced by the aglycones were determined under time and dose conditions in which differences in body weight and food consumption were not significant (2.4 mmol/kg diet for 28 d). Under these conditions, the observed %LW/BW increases relative to the controls were as follows: solanidine (32%, P < or = 0.001), solasodine (22%, P < or = 0.001) and DHEA (16%, P < or = 0.001). Solanidine, solasodine and DHEA were equally potent and were more potent than tomatidine. We also observed that the greater %LW/BW in mice fed 2.4 mmol/kg diet solasodine or solanidine for 14 d declined to near control values if they were fed control diets for another 14 d. The increase in relative liver weight induced by solanidine and solasodine is a reversible adaptive response. These findings and the apparent effects of structure on biological activity should serve as a guide for the removal of the most toxic ++compounds from plant foods. The implications of the results for food safety and health are discussed.
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acid catalyzed partial hydrolysis of carbohydrate groups of the potato glycoalkaloid alpha chaconine in alcoholic solutions
Journal of Agricultural and Food Chemistry, 1995Co-Authors: Mendel Friedman, Gary M. McdonaldAbstract:As part of an effort to improve the safety of plant-derived foods, the role of the carbohydrate side chain has been explored in biological effects of potato glycoalkaloids such as α-chaconine. This steroid glycoalkaloid has a trisaccharide attached to the 3-hydroxy position of the steroidal aglycon solanidine. This study attempts to define the effect of structurally different alcohols on the partial hydrolysis of α-chaconine to β 1 -chaconine, β 2 -chaconine, γ-chaconine, and solanidine. Partial hydrolyses were carried out in 97.5% alcohol-0.25 N HCl at 60 °C. HPLC was used to measure the distribution of hydrolysis products as a function of time. The rate of hydrolysis of α-chaconine in the straight-chain alcohol solutions was as follows : methanol > ethanol = 1-butanol > propanol > pentanol » water. The longer the chain, the slower the rate of hydrolysis except for the anomalous result that the extent of hydrolysis in 1-butanol was equal to that in ethanol. However, hydrolysis in 2-butanol was slower than in 1-butanol. Surprisingly, hydrolysis in tert-butyl alcohol was slowest, proceeding more slowly than even in 1-pentanol. The formation of γ-chaconine was also greatly reduced in tert-butyl alcohol. Mechanistic rationalizations are offered to explain the observed trends in terms of the hydrophobic-hydrophilic nature of the glycoalkaloids and the solvation properties of the alcohols. The results should be generally useful for optimizing or minimizing the formation of specific hydrolysis products.
Tafadzwa Mandimika - One of the best experts on this subject based on the ideXlab platform.
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pi3k akt jnk and erk pathways are not crucial for the induction of cholesterol biosynthesis gene transcription in intestinal epithelial cells following treatment with the potato glycoalkaloid alpha chaconine
Journal of Agricultural and Food Chemistry, 2008Co-Authors: Tafadzwa Mandimika, Hakan Baykus, Jenneke Poortman, Cutberto Garza, H Kuiper, Ad A. C. M. PeijnenburgAbstract:We previously reported that exposure of the intestinal epithelial Caco-2 cell line to noncytotoxic concentrations of potato glycoalkaloids resulted in increased expression of cholesterol biosynthesis genes. Genes involved in mitogen-activated protein kinase (MAPK) and phosphatidylinositol 3-kinase (PI3K)/v-akt murine thymoma viral oncogene homologue (AKT) pathways and their downstream effectors such as Jun, c-Myc, and Fos also were induced. MAPK and PI3K/AKT pathways have been described to regulate the activity of sterol regulatory element binding transcription factors (SREBPs) and consequently the expression of cholesterol biosynthesis genes. In this study, to understand the mechanism of induction of cholesterol biosynthesis upon ?-chaconine treatment, its effect on SREBP-2 protein levels was investigated. We also examined whether MAPK and PI3K/AKT pathways are required for the observed induction of these genes following exposure of cells to ?-chaconine. Differentiated Caco-2 cells were pretreated with LY294002 (PI3K inhibitor), PD98059 (MEK1 inhibitor), or SP600125 (JNK inhibitor) or a combination of all inhibitors for 24 h prior to coincubation with 10 ?M ?-chaconine for 6 h. Significant increases in precursor and mature protein levels of SREBP-2 were observed after ?-chaconine exposure. We also observed that ?-chaconine treatment resulted in significant phosphorylation of AKT, extracellular signal related protein kinase (ERK), and c-jun N terminal protein kinase (JNK) but not that of p38. In general, the kinase inhibitor experiments revealed that phosphorylation of kinases of PI3K/AKT, ERK, and JNK pathways was not crucial for the induction of expression of cholesterol biosynthesis genes, with the exception of SC5DL. The transcription of this later gene was reduced when all three pathways were inhibited. On the basis of these results, it can be postulated that other mechanisms, which may be independent of the MAPK and PI3K/AKT pathways, including possibly post-translational activation of SREBP-2, may be more pivotal for the induction of cholesterol biosynthesis genes following exposure of intestinal cells to ?-chaconine.
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PI3K/AKT, JNK, and ERK pathways are not crucial for the induction of cholesterol biosynthesis gene transcription in intestinal epithelial cells following treatment with the potato glycoalkaloid Alpha-Chaconine.
Journal of agricultural and food chemistry, 2008Co-Authors: Tafadzwa Mandimika, Hakan Baykus, Jenneke Poortman, Cutberto Garza, Harry A Kuiper, Ad A. C. M. PeijnenburgAbstract:We previously reported that exposure of the intestinal epithelial Caco-2 cell line to noncytotoxic concentrations of potato glycoalkaloids resulted in increased expression of cholesterol biosynthesis genes. Genes involved in mitogen-activated protein kinase (MAPK) and phosphatidylinositol 3-kinase (PI3K)/v-akt murine thymoma viral oncogene homologue (AKT) pathways and their downstream effectors such as Jun, c-Myc, and Fos also were induced. MAPK and PI3K/AKT pathways have been described to regulate the activity of sterol regulatory element binding transcription factors (SREBPs) and consequently the expression of cholesterol biosynthesis genes. In this study, to understand the mechanism of induction of cholesterol biosynthesis upon Alpha-Chaconine treatment, its effect on SREBP-2 protein levels was investigated. We also examined whether MAPK and PI3K/AKT pathways are required for the observed induction of these genes following exposure of cells to Alpha-Chaconine. Differentiated Caco-2 cells were pretreated with LY294002 (PI3K inhibitor), PD98059 (MEK1 inhibitor), or SP600125 (JNK inhibitor) or a combination of all inhibitors for 24 h prior to coincubation with 10 microM Alpha-Chaconine for 6 h. Significant increases in precursor and mature protein levels of SREBP-2 were observed after Alpha-Chaconine exposure. We also observed that Alpha-Chaconine treatment resulted in significant phosphorylation of AKT, extracellular signal related protein kinase (ERK), and c-jun N terminal protein kinase (JNK) but not that of p38. In general, the kinase inhibitor experiments revealed that phosphorylation of kinases of PI3K/AKT, ERK, and JNK pathways was not crucial for the induction of expression of cholesterol biosynthesis genes, with the exception of SC5DL. The transcription of this later gene was reduced when all three pathways were inhibited. On the basis of these results, it can be postulated that other mechanisms, which may be independent of the MAPK and PI3K/AKT pathways, including possibly post-translational activation of SREBP-2, may be more pivotal for the induction of cholesterol biosynthesis genes following exposure of intestinal cells to Alpha-Chaconine.
Cutberto Garza - One of the best experts on this subject based on the ideXlab platform.
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pi3k akt jnk and erk pathways are not crucial for the induction of cholesterol biosynthesis gene transcription in intestinal epithelial cells following treatment with the potato glycoalkaloid alpha chaconine
Journal of Agricultural and Food Chemistry, 2008Co-Authors: Tafadzwa Mandimika, Hakan Baykus, Jenneke Poortman, Cutberto Garza, H Kuiper, Ad A. C. M. PeijnenburgAbstract:We previously reported that exposure of the intestinal epithelial Caco-2 cell line to noncytotoxic concentrations of potato glycoalkaloids resulted in increased expression of cholesterol biosynthesis genes. Genes involved in mitogen-activated protein kinase (MAPK) and phosphatidylinositol 3-kinase (PI3K)/v-akt murine thymoma viral oncogene homologue (AKT) pathways and their downstream effectors such as Jun, c-Myc, and Fos also were induced. MAPK and PI3K/AKT pathways have been described to regulate the activity of sterol regulatory element binding transcription factors (SREBPs) and consequently the expression of cholesterol biosynthesis genes. In this study, to understand the mechanism of induction of cholesterol biosynthesis upon ?-chaconine treatment, its effect on SREBP-2 protein levels was investigated. We also examined whether MAPK and PI3K/AKT pathways are required for the observed induction of these genes following exposure of cells to ?-chaconine. Differentiated Caco-2 cells were pretreated with LY294002 (PI3K inhibitor), PD98059 (MEK1 inhibitor), or SP600125 (JNK inhibitor) or a combination of all inhibitors for 24 h prior to coincubation with 10 ?M ?-chaconine for 6 h. Significant increases in precursor and mature protein levels of SREBP-2 were observed after ?-chaconine exposure. We also observed that ?-chaconine treatment resulted in significant phosphorylation of AKT, extracellular signal related protein kinase (ERK), and c-jun N terminal protein kinase (JNK) but not that of p38. In general, the kinase inhibitor experiments revealed that phosphorylation of kinases of PI3K/AKT, ERK, and JNK pathways was not crucial for the induction of expression of cholesterol biosynthesis genes, with the exception of SC5DL. The transcription of this later gene was reduced when all three pathways were inhibited. On the basis of these results, it can be postulated that other mechanisms, which may be independent of the MAPK and PI3K/AKT pathways, including possibly post-translational activation of SREBP-2, may be more pivotal for the induction of cholesterol biosynthesis genes following exposure of intestinal cells to ?-chaconine.
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PI3K/AKT, JNK, and ERK pathways are not crucial for the induction of cholesterol biosynthesis gene transcription in intestinal epithelial cells following treatment with the potato glycoalkaloid Alpha-Chaconine.
Journal of agricultural and food chemistry, 2008Co-Authors: Tafadzwa Mandimika, Hakan Baykus, Jenneke Poortman, Cutberto Garza, Harry A Kuiper, Ad A. C. M. PeijnenburgAbstract:We previously reported that exposure of the intestinal epithelial Caco-2 cell line to noncytotoxic concentrations of potato glycoalkaloids resulted in increased expression of cholesterol biosynthesis genes. Genes involved in mitogen-activated protein kinase (MAPK) and phosphatidylinositol 3-kinase (PI3K)/v-akt murine thymoma viral oncogene homologue (AKT) pathways and their downstream effectors such as Jun, c-Myc, and Fos also were induced. MAPK and PI3K/AKT pathways have been described to regulate the activity of sterol regulatory element binding transcription factors (SREBPs) and consequently the expression of cholesterol biosynthesis genes. In this study, to understand the mechanism of induction of cholesterol biosynthesis upon Alpha-Chaconine treatment, its effect on SREBP-2 protein levels was investigated. We also examined whether MAPK and PI3K/AKT pathways are required for the observed induction of these genes following exposure of cells to Alpha-Chaconine. Differentiated Caco-2 cells were pretreated with LY294002 (PI3K inhibitor), PD98059 (MEK1 inhibitor), or SP600125 (JNK inhibitor) or a combination of all inhibitors for 24 h prior to coincubation with 10 microM Alpha-Chaconine for 6 h. Significant increases in precursor and mature protein levels of SREBP-2 were observed after Alpha-Chaconine exposure. We also observed that Alpha-Chaconine treatment resulted in significant phosphorylation of AKT, extracellular signal related protein kinase (ERK), and c-jun N terminal protein kinase (JNK) but not that of p38. In general, the kinase inhibitor experiments revealed that phosphorylation of kinases of PI3K/AKT, ERK, and JNK pathways was not crucial for the induction of expression of cholesterol biosynthesis genes, with the exception of SC5DL. The transcription of this later gene was reduced when all three pathways were inhibited. On the basis of these results, it can be postulated that other mechanisms, which may be independent of the MAPK and PI3K/AKT pathways, including possibly post-translational activation of SREBP-2, may be more pivotal for the induction of cholesterol biosynthesis genes following exposure of intestinal cells to Alpha-Chaconine.
Hakan Baykus - One of the best experts on this subject based on the ideXlab platform.
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pi3k akt jnk and erk pathways are not crucial for the induction of cholesterol biosynthesis gene transcription in intestinal epithelial cells following treatment with the potato glycoalkaloid alpha chaconine
Journal of Agricultural and Food Chemistry, 2008Co-Authors: Tafadzwa Mandimika, Hakan Baykus, Jenneke Poortman, Cutberto Garza, H Kuiper, Ad A. C. M. PeijnenburgAbstract:We previously reported that exposure of the intestinal epithelial Caco-2 cell line to noncytotoxic concentrations of potato glycoalkaloids resulted in increased expression of cholesterol biosynthesis genes. Genes involved in mitogen-activated protein kinase (MAPK) and phosphatidylinositol 3-kinase (PI3K)/v-akt murine thymoma viral oncogene homologue (AKT) pathways and their downstream effectors such as Jun, c-Myc, and Fos also were induced. MAPK and PI3K/AKT pathways have been described to regulate the activity of sterol regulatory element binding transcription factors (SREBPs) and consequently the expression of cholesterol biosynthesis genes. In this study, to understand the mechanism of induction of cholesterol biosynthesis upon ?-chaconine treatment, its effect on SREBP-2 protein levels was investigated. We also examined whether MAPK and PI3K/AKT pathways are required for the observed induction of these genes following exposure of cells to ?-chaconine. Differentiated Caco-2 cells were pretreated with LY294002 (PI3K inhibitor), PD98059 (MEK1 inhibitor), or SP600125 (JNK inhibitor) or a combination of all inhibitors for 24 h prior to coincubation with 10 ?M ?-chaconine for 6 h. Significant increases in precursor and mature protein levels of SREBP-2 were observed after ?-chaconine exposure. We also observed that ?-chaconine treatment resulted in significant phosphorylation of AKT, extracellular signal related protein kinase (ERK), and c-jun N terminal protein kinase (JNK) but not that of p38. In general, the kinase inhibitor experiments revealed that phosphorylation of kinases of PI3K/AKT, ERK, and JNK pathways was not crucial for the induction of expression of cholesterol biosynthesis genes, with the exception of SC5DL. The transcription of this later gene was reduced when all three pathways were inhibited. On the basis of these results, it can be postulated that other mechanisms, which may be independent of the MAPK and PI3K/AKT pathways, including possibly post-translational activation of SREBP-2, may be more pivotal for the induction of cholesterol biosynthesis genes following exposure of intestinal cells to ?-chaconine.
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PI3K/AKT, JNK, and ERK pathways are not crucial for the induction of cholesterol biosynthesis gene transcription in intestinal epithelial cells following treatment with the potato glycoalkaloid Alpha-Chaconine.
Journal of agricultural and food chemistry, 2008Co-Authors: Tafadzwa Mandimika, Hakan Baykus, Jenneke Poortman, Cutberto Garza, Harry A Kuiper, Ad A. C. M. PeijnenburgAbstract:We previously reported that exposure of the intestinal epithelial Caco-2 cell line to noncytotoxic concentrations of potato glycoalkaloids resulted in increased expression of cholesterol biosynthesis genes. Genes involved in mitogen-activated protein kinase (MAPK) and phosphatidylinositol 3-kinase (PI3K)/v-akt murine thymoma viral oncogene homologue (AKT) pathways and their downstream effectors such as Jun, c-Myc, and Fos also were induced. MAPK and PI3K/AKT pathways have been described to regulate the activity of sterol regulatory element binding transcription factors (SREBPs) and consequently the expression of cholesterol biosynthesis genes. In this study, to understand the mechanism of induction of cholesterol biosynthesis upon Alpha-Chaconine treatment, its effect on SREBP-2 protein levels was investigated. We also examined whether MAPK and PI3K/AKT pathways are required for the observed induction of these genes following exposure of cells to Alpha-Chaconine. Differentiated Caco-2 cells were pretreated with LY294002 (PI3K inhibitor), PD98059 (MEK1 inhibitor), or SP600125 (JNK inhibitor) or a combination of all inhibitors for 24 h prior to coincubation with 10 microM Alpha-Chaconine for 6 h. Significant increases in precursor and mature protein levels of SREBP-2 were observed after Alpha-Chaconine exposure. We also observed that Alpha-Chaconine treatment resulted in significant phosphorylation of AKT, extracellular signal related protein kinase (ERK), and c-jun N terminal protein kinase (JNK) but not that of p38. In general, the kinase inhibitor experiments revealed that phosphorylation of kinases of PI3K/AKT, ERK, and JNK pathways was not crucial for the induction of expression of cholesterol biosynthesis genes, with the exception of SC5DL. The transcription of this later gene was reduced when all three pathways were inhibited. On the basis of these results, it can be postulated that other mechanisms, which may be independent of the MAPK and PI3K/AKT pathways, including possibly post-translational activation of SREBP-2, may be more pivotal for the induction of cholesterol biosynthesis genes following exposure of intestinal cells to Alpha-Chaconine.