Rajakrishnan Veluthakal - Academia.edu (original) (raw)
Papers by Rajakrishnan Veluthakal
The FASEB Journal, Apr 1, 2019
Frontiers in Endocrinology, Feb 11, 2022
Skeletal muscle accounts for~80% of insulin-stimulated glucose uptake. The Group I p21-activated ... more Skeletal muscle accounts for~80% of insulin-stimulated glucose uptake. The Group I p21-activated kinase 1 (PAK1) is required for the non-canonical insulin-stimulated GLUT4 vesicle translocation in skeletal muscle cells. We found that the abundances of PAK1 protein and its downstream effector in muscle, ARPC1B, are significantly reduced in the skeletal muscle of humans with type 2 diabetes, compared to the non-diabetic controls, making skeletal muscle PAK1 a candidate regulator of glucose homeostasis. Although whole-body PAK1 knockout mice exhibit glucose intolerance and are insulin resistant, the contribution of skeletal muscle PAK1 in particular was unknown. As such, we developed inducible skeletal muscle-specific PAK1 knockout (skmPAK1-iKO) and overexpression (skmPAK1-iOE) mouse models to evaluate the role of PAK1 in skeletal muscle insulin sensitivity and glucose homeostasis. Using intraperitoneal glucose tolerance and insulin tolerance testing, we found that skeletal muscle PAK1 is required for maintaining whole body glucose homeostasis. Moreover, PAK1 enrichment in GLUT4-myc-L6 myoblasts preserves normal insulin-stimulated GLUT4 translocation under insulin resistance conditions. Unexpectedly, skmPAK1-iKO also showed aberrant plasma insulin levels following a glucose challenge. By applying conditioned media from PAK1-enriched myotubes or myoblasts to b-cells in culture, we established that a muscle-derived circulating factor(s) could enhance b-cell function. Taken together, these data suggest that PAK1 levels in the skeletal muscle can regulate not only skeletal muscle insulin sensitivity, but can also engage in tissue crosstalk with pancreatic b-cells, unveiling a new molecular mechanism by which PAK1 regulates whole-body glucose homeostasis.
Cell Reports, May 1, 2023
The Journal of Nutritional Biochemistry, 2000
The present study was undertaken to evaluate the potential role of curcumin, the antioxidant prin... more The present study was undertaken to evaluate the potential role of curcumin, the antioxidant principal from Curcuma longa Linn., and the sulphur-containing amino acid N-acetylcysteine against ethanol-induced changes in the levels of prostanoids. Biochemical assessment of liver damage was done by measuring the activities of serum enzymes (i.e., aspartate transaminase and alkaline phosphatase), which were significantly increased in rats fed ethanol, whereas the elevated levels of these enzymes were decreased after curcumin and N-acetylcysteine treatment to rats fed ethanol. We observed a significant increase in the levels of prostaglandins E(1), E(2), F(2alpha), and D(2) in liver, kidney, and brain. Administration of curcumin and N-acetylcysteine was shown to decrease the level of these prostanoids in the tissue studied.
Hepatology Research, 1998
Chronic administration of carbon tetrachloride caused liver fibrosis in rats. Carbon tetrachlorid... more Chronic administration of carbon tetrachloride caused liver fibrosis in rats. Carbon tetrachloride-induced fibrosis was found to significantly elevate the marker enzymes, serum transaminases and alkaline phosphatase as well as lipid peroxidation end product, malondialdehyde or thiobarbituric acid reactive substance in the liver. Fibrosis also caused increase in the serum and tissue cholesterol and decreased tissue phospholipids and free fatty acids. Histopathological examinations also confirm the severe hepatological damage occurred as a consequence of carbon tetrachloride-induced fibrosis. Treatment of curcumin to the fibrotic rats showed a significant improvement after hepatic damage as well as restoration of lipid profile, marker enzymes and thiobarbituric acid reactive substances towards normal.
Objective: Post-translational prenylation [eg, farnesylation] of small G-proteins is felt to be r... more Objective: Post-translational prenylation [eg, farnesylation] of small G-proteins is felt to be requisite for cytoskeletal remodeling and fusion of secretory vesicles with the plasma membrane. Herein, we investigated roles of protein farnesylation in the signaling steps ...
Investigative Ophthalmology & Visual Science, 2014
Diabetes Metabolism, 2002
AJP Cell Physiology
ABSTRACT
Diabetes & metabolism, 2002
Recently, we have demonstrated regulatory roles for G-proteins (e.g., H-Ras) in IL-1beta induced ... more Recently, we have demonstrated regulatory roles for G-proteins (e.g., H-Ras) in IL-1beta induced NO release from HIT-T15 cells. Herein, we report a similar regulatory mechanism for IL-1beta induced NO release from RIN5F and INS-1 cells. Our data indicate that functional inactivation of Ras, either by Clostridial toxins or by specific inhibitors of Ras function, results in a significant inhibition in IL-1beta induced NO release, suggesting that activation of specific G-proteins is essential for IL-1beta induced NO release. In the present study, we report possible loci where IL-1beta treatment might result in functional activation of these G-proteins. For example, IL-1beta treatment resulted in significant reduction in (high-and low-affinity) GTPase activities in lysates derived from normal rat islets; such a scenario might lead to retention of candidate G-proteins in GTP-bound, active conformation. Further, IL-1beta treatment increased the G-protein carboxyl methyl transferase activi...
Apoptosis : an international journal on programmed cell death, 2002
It is well established that long-term exposure of isolated beta cells to cytokines [e.g., IL-1bet... more It is well established that long-term exposure of isolated beta cells to cytokines [e.g., IL-1beta] results in increased expression of inducible nitric oxide synthase and subsequent release of nitric oxide, which in turn, has been shown to mediate a wide array of effects, including alterations in cellular high-energy metabolism. In this context, several extant studies have demonstrated significant reduction in adenine and guanine nucleotide triphosphate levels in beta cells exposed to IL-1beta. Herein, we examined the functional status of glyceraldehyde-3-phosphate dehydrogenase [GAPDH] in insulin-secreting cells exposed to IL-1beta, since it represents the first enzyme in the glycolytic pathway that is involved in the generation of ATP. GAPDH was assayed spectrophotometrically in the cytosolic fraction derived from control and IL-1beta -treated [300 pM for 24 hrs] insulin-secreting cell lines [HIT-T15 and RINm5F]. IL-treatment resulted in marked attenuation of GAPDH activity in HIT...
Endocrine, 2005
We previously identified and characterized a glutamateand magnesium-sensitive PP2A-like phosphata... more We previously identified and characterized a glutamateand magnesium-sensitive PP2A-like phosphatase (GAPP), which dephosphorylated and activated acetyl-CoA carboxylase (ACC) in the islet b b b b b cell. Herein, we studied potential regulatory mechanisms by which GAPP is activated by glutamate and magnesium, and also quantitated the degree of activation, by glutamate-and magnesium, of ACC in normal rat islets and islets derived from the diabetic Goto-Kakizaki (GK) rat, a model for type 2 diabetes in humans. Our findings indicate that magnesium, but not glutamate, specifically activates the post-translational carboxylmethylation (CML) of the 36 kDa catalytic subunit of GAPP. Okadaic acid (OKA), which inhibits GAPP-mediated activation of ACC, also reduced the magnesium-stimulated CML of the catalytic subunit of GAPP in all the b b b b b cell preparations studied. These data suggest that the CML step may be necessary for magnesium-and glutamate-mediated activation of ACC. We also observed a marked attenuation in magnesium-and glutamate-facilitated activation of ACC activity in islets derived from the GK rat. Together, our findings raise an interesting possibility that inhibition of GAPP-catalyzed inactivation of ACC (and subsequent reduction in the generation of long-chain fatty acids) could contribute toward the abnormalities in insulin secretion demonstrable in this animal model for type 2 diabetes.
![Research paper thumbnail of Phagocyte-Like NADPH Oxidase [Nox2] Promotes Activation of P38MAPK in Pancreatic Beta-Cells under Glucotoxic Conditions: Evidence for a Novel Role of Rac1](https://attachments.academia-assets.com/100241052/thumbnails/1.jpg)
](Free Radical Biology and Medicine, 2014
Biochemical Pharmacology, 2003
We recently demonstrated that functional inactivation of H-Ras results in significant reduction i... more We recently demonstrated that functional inactivation of H-Ras results in significant reduction in interleukin 1b (IL-1b)-mediated effects on isolated b cells. Since palmitoylation of Ras has been implicated in its membrane targeting, we examined the contributory roles of palmitoylation of Ras in IL-1b-induced nitric oxide (NO) release and subsequent activation of caspases. Preincubation of HIT-T15 or INS-1 cells with cerulenin (CER, 134 mM; 3 hr), an inhibitor of protein palmitoylation, significantly reduced (À95%) IL-1b-induced NO release from these cells. 2-Bromopalmitate, a structurally distinct inhibitor of protein palmitoylation, but not 2-hydroxymyristic acid, an inhibitor of protein myristoylation, also reduced (À67%) IL-1b-induced NO release from HIT cells. IL-induced inducible nitric oxide synthase gene expression was markedly attenuated by CER. Further, CER markedly reduced incorporation of [ 3 H]palmitate into H-Ras and caused significant accumulation of Ras in the cytosolic fraction. CER-treatment also prevented IL-1b-induced activation of caspase 3 in these cells. Moreover, N-monomethyl-L-arginine, a known inhibitor of inducible nitric oxide synthase, markedly inhibited IL-induced activation of caspase 3, thus establishing a link between IL-induced NO release and caspase 3 activation. Depletion of membrane-bound cholesterol using methyl-b-cyclodextrin, which also disrupts caveolar organization within the plasma membrane, abolished IL-1binduced NO release suggesting that IL-1b-mediated Ras-dependent signaling in these cells involves the intermediacy of caveolae and their key constituents (e.g. caveolin-1) in isolated b cells. Confocal light microscopic evidence indicated significant colocalization of Ras with caveolin-1. Taken together, our data provide the first evidence to indicate that palmitoylation of Ras is essential for IL-1b-induced cytotoxic effects on the islet b cell.
Apoptosis, 2014
Nuclear lamins form the lamina on the interior surface of the nuclear envelope, and regulate nucl... more Nuclear lamins form the lamina on the interior surface of the nuclear envelope, and regulate nuclear metabolic events, including DNA replication and organization of chromatin. The current study is aimed at understanding the role of executioner caspase 6 on lamin A integrity in islet βcells under duress of glucotoxic (20 mM glucose; 24 hrs) and diabetic conditions. Under glucotoxic conditions, glucose-stimulated insulin secretion (GSIS) and metabolic cell viability were significantly attenuated in INS-1 832/13 cells. Further, exposure of normal human islets, rat islets and INS-1 832/13 cells to glucotoxic conditions leads to caspase 6 activation and lamin A degradation, which is also observed in islets from the Zucker diabetic fatty rat, a model for type 2 diabetes (T2D), and in islets from a human donor with T2D. Z-Val-Glu-Ile-Aspfluoromethylketone, a specific inhibitor of caspase 6, markedly attenuated high glucose-induced caspase 6 activation and lamin A degradation, confirming that caspase 6 mediates lamin A degradation under high glucose exposure conditions. Moreover, Z-Asp-Glu-Val-Aspfluoromethylketone, a known caspase 3 inhibitor, significantly inhibited high glucose-induced caspase 6 activation and lamin A degradation, suggesting that activation of caspase 3 might be upstream to caspase 6 activation in the islet β-cell under glucotoxic conditions. Lastly, we report expression of ZMPSTE24, a zinc metallopeptidase involved in the processing of prelamin A to mature lamin A, in INS-1 832/13 cells and human islets; was unaffected by high glucose. We conclude that caspases 3 and 6 could contribute to alterations in the integrity of nuclear lamins leading to metabolic dysregulation and failure of the islet β-cell.
Endocrine, 2007
Among various phosphatases, the protein phosphatase 2A (PP2A) is relatively well studied in the i... more Among various phosphatases, the protein phosphatase 2A (PP2A) is relatively well studied in the islet. Previously, we have demonstrated that the catalytic subunit of PP2A (PP2Ac) undergoes okadaic acid (OKA)-sensitive, reversible carboxylmethylation (CML), which appears to be requisite for glucose-stimulated insulin secretion (GSIS). Using the siRNA approach, we examined, herein, the contributory roles of PP2Ac in GSIS from insulin-secreting pancreatic beta-(INS-1 832/13) cells. Immunologically, PP2Ac was detectable in all the subcellular fractions studied in rank order of: cytosol > microsomes > secretory granules = nucleus > mitochondria. Transfection of PP2Ac-specific, but not scrambled-siRNA, markedly attenuated PP2A activity and GSIS in these cells. Together, our findings provide a direct evidence for a positive modulatory role for PP2Ac in signaling steps leading to GSIS.
Apoptosis, 2002
Aims/hypothesis: It is well established that long-term exposure of isolated ß cells to cytokines ... more Aims/hypothesis: It is well established that long-term exposure of isolated ß cells to cytokines [e.g., IL-1ß] results in increased expression of inducible nitric oxide synthase and subsequent release of nitric oxide, which in turn, has been shown to mediate a wide array of effects, including alterations in cellular high-energy metabolism. In this context, several extant studies have demonstrated significant reduction in adenine and guanine nucleotide triphosphate levels in ß cells exposed to IL-1ß. Herein, we examined the functional status of glyceraldehyde-3-phosphate dehydrogenase [GAPDH] in insulin-secreting cells exposed to IL-1ß, since it represents the first enzyme in the glycolytic pathway that is involved in the generation of ATP.
The FASEB Journal, Apr 1, 2019
Frontiers in Endocrinology, Feb 11, 2022
Skeletal muscle accounts for~80% of insulin-stimulated glucose uptake. The Group I p21-activated ... more Skeletal muscle accounts for~80% of insulin-stimulated glucose uptake. The Group I p21-activated kinase 1 (PAK1) is required for the non-canonical insulin-stimulated GLUT4 vesicle translocation in skeletal muscle cells. We found that the abundances of PAK1 protein and its downstream effector in muscle, ARPC1B, are significantly reduced in the skeletal muscle of humans with type 2 diabetes, compared to the non-diabetic controls, making skeletal muscle PAK1 a candidate regulator of glucose homeostasis. Although whole-body PAK1 knockout mice exhibit glucose intolerance and are insulin resistant, the contribution of skeletal muscle PAK1 in particular was unknown. As such, we developed inducible skeletal muscle-specific PAK1 knockout (skmPAK1-iKO) and overexpression (skmPAK1-iOE) mouse models to evaluate the role of PAK1 in skeletal muscle insulin sensitivity and glucose homeostasis. Using intraperitoneal glucose tolerance and insulin tolerance testing, we found that skeletal muscle PAK1 is required for maintaining whole body glucose homeostasis. Moreover, PAK1 enrichment in GLUT4-myc-L6 myoblasts preserves normal insulin-stimulated GLUT4 translocation under insulin resistance conditions. Unexpectedly, skmPAK1-iKO also showed aberrant plasma insulin levels following a glucose challenge. By applying conditioned media from PAK1-enriched myotubes or myoblasts to b-cells in culture, we established that a muscle-derived circulating factor(s) could enhance b-cell function. Taken together, these data suggest that PAK1 levels in the skeletal muscle can regulate not only skeletal muscle insulin sensitivity, but can also engage in tissue crosstalk with pancreatic b-cells, unveiling a new molecular mechanism by which PAK1 regulates whole-body glucose homeostasis.
Cell Reports, May 1, 2023
The Journal of Nutritional Biochemistry, 2000
The present study was undertaken to evaluate the potential role of curcumin, the antioxidant prin... more The present study was undertaken to evaluate the potential role of curcumin, the antioxidant principal from Curcuma longa Linn., and the sulphur-containing amino acid N-acetylcysteine against ethanol-induced changes in the levels of prostanoids. Biochemical assessment of liver damage was done by measuring the activities of serum enzymes (i.e., aspartate transaminase and alkaline phosphatase), which were significantly increased in rats fed ethanol, whereas the elevated levels of these enzymes were decreased after curcumin and N-acetylcysteine treatment to rats fed ethanol. We observed a significant increase in the levels of prostaglandins E(1), E(2), F(2alpha), and D(2) in liver, kidney, and brain. Administration of curcumin and N-acetylcysteine was shown to decrease the level of these prostanoids in the tissue studied.
Hepatology Research, 1998
Chronic administration of carbon tetrachloride caused liver fibrosis in rats. Carbon tetrachlorid... more Chronic administration of carbon tetrachloride caused liver fibrosis in rats. Carbon tetrachloride-induced fibrosis was found to significantly elevate the marker enzymes, serum transaminases and alkaline phosphatase as well as lipid peroxidation end product, malondialdehyde or thiobarbituric acid reactive substance in the liver. Fibrosis also caused increase in the serum and tissue cholesterol and decreased tissue phospholipids and free fatty acids. Histopathological examinations also confirm the severe hepatological damage occurred as a consequence of carbon tetrachloride-induced fibrosis. Treatment of curcumin to the fibrotic rats showed a significant improvement after hepatic damage as well as restoration of lipid profile, marker enzymes and thiobarbituric acid reactive substances towards normal.
Objective: Post-translational prenylation [eg, farnesylation] of small G-proteins is felt to be r... more Objective: Post-translational prenylation [eg, farnesylation] of small G-proteins is felt to be requisite for cytoskeletal remodeling and fusion of secretory vesicles with the plasma membrane. Herein, we investigated roles of protein farnesylation in the signaling steps ...
Investigative Ophthalmology & Visual Science, 2014
Diabetes Metabolism, 2002
AJP Cell Physiology
ABSTRACT
Diabetes & metabolism, 2002
Recently, we have demonstrated regulatory roles for G-proteins (e.g., H-Ras) in IL-1beta induced ... more Recently, we have demonstrated regulatory roles for G-proteins (e.g., H-Ras) in IL-1beta induced NO release from HIT-T15 cells. Herein, we report a similar regulatory mechanism for IL-1beta induced NO release from RIN5F and INS-1 cells. Our data indicate that functional inactivation of Ras, either by Clostridial toxins or by specific inhibitors of Ras function, results in a significant inhibition in IL-1beta induced NO release, suggesting that activation of specific G-proteins is essential for IL-1beta induced NO release. In the present study, we report possible loci where IL-1beta treatment might result in functional activation of these G-proteins. For example, IL-1beta treatment resulted in significant reduction in (high-and low-affinity) GTPase activities in lysates derived from normal rat islets; such a scenario might lead to retention of candidate G-proteins in GTP-bound, active conformation. Further, IL-1beta treatment increased the G-protein carboxyl methyl transferase activi...
Apoptosis : an international journal on programmed cell death, 2002
It is well established that long-term exposure of isolated beta cells to cytokines [e.g., IL-1bet... more It is well established that long-term exposure of isolated beta cells to cytokines [e.g., IL-1beta] results in increased expression of inducible nitric oxide synthase and subsequent release of nitric oxide, which in turn, has been shown to mediate a wide array of effects, including alterations in cellular high-energy metabolism. In this context, several extant studies have demonstrated significant reduction in adenine and guanine nucleotide triphosphate levels in beta cells exposed to IL-1beta. Herein, we examined the functional status of glyceraldehyde-3-phosphate dehydrogenase [GAPDH] in insulin-secreting cells exposed to IL-1beta, since it represents the first enzyme in the glycolytic pathway that is involved in the generation of ATP. GAPDH was assayed spectrophotometrically in the cytosolic fraction derived from control and IL-1beta -treated [300 pM for 24 hrs] insulin-secreting cell lines [HIT-T15 and RINm5F]. IL-treatment resulted in marked attenuation of GAPDH activity in HIT...
Endocrine, 2005
We previously identified and characterized a glutamateand magnesium-sensitive PP2A-like phosphata... more We previously identified and characterized a glutamateand magnesium-sensitive PP2A-like phosphatase (GAPP), which dephosphorylated and activated acetyl-CoA carboxylase (ACC) in the islet b b b b b cell. Herein, we studied potential regulatory mechanisms by which GAPP is activated by glutamate and magnesium, and also quantitated the degree of activation, by glutamate-and magnesium, of ACC in normal rat islets and islets derived from the diabetic Goto-Kakizaki (GK) rat, a model for type 2 diabetes in humans. Our findings indicate that magnesium, but not glutamate, specifically activates the post-translational carboxylmethylation (CML) of the 36 kDa catalytic subunit of GAPP. Okadaic acid (OKA), which inhibits GAPP-mediated activation of ACC, also reduced the magnesium-stimulated CML of the catalytic subunit of GAPP in all the b b b b b cell preparations studied. These data suggest that the CML step may be necessary for magnesium-and glutamate-mediated activation of ACC. We also observed a marked attenuation in magnesium-and glutamate-facilitated activation of ACC activity in islets derived from the GK rat. Together, our findings raise an interesting possibility that inhibition of GAPP-catalyzed inactivation of ACC (and subsequent reduction in the generation of long-chain fatty acids) could contribute toward the abnormalities in insulin secretion demonstrable in this animal model for type 2 diabetes.
Free Radical Biology and Medicine, 2014
Biochemical Pharmacology, 2003
We recently demonstrated that functional inactivation of H-Ras results in significant reduction i... more We recently demonstrated that functional inactivation of H-Ras results in significant reduction in interleukin 1b (IL-1b)-mediated effects on isolated b cells. Since palmitoylation of Ras has been implicated in its membrane targeting, we examined the contributory roles of palmitoylation of Ras in IL-1b-induced nitric oxide (NO) release and subsequent activation of caspases. Preincubation of HIT-T15 or INS-1 cells with cerulenin (CER, 134 mM; 3 hr), an inhibitor of protein palmitoylation, significantly reduced (À95%) IL-1b-induced NO release from these cells. 2-Bromopalmitate, a structurally distinct inhibitor of protein palmitoylation, but not 2-hydroxymyristic acid, an inhibitor of protein myristoylation, also reduced (À67%) IL-1b-induced NO release from HIT cells. IL-induced inducible nitric oxide synthase gene expression was markedly attenuated by CER. Further, CER markedly reduced incorporation of [ 3 H]palmitate into H-Ras and caused significant accumulation of Ras in the cytosolic fraction. CER-treatment also prevented IL-1b-induced activation of caspase 3 in these cells. Moreover, N-monomethyl-L-arginine, a known inhibitor of inducible nitric oxide synthase, markedly inhibited IL-induced activation of caspase 3, thus establishing a link between IL-induced NO release and caspase 3 activation. Depletion of membrane-bound cholesterol using methyl-b-cyclodextrin, which also disrupts caveolar organization within the plasma membrane, abolished IL-1binduced NO release suggesting that IL-1b-mediated Ras-dependent signaling in these cells involves the intermediacy of caveolae and their key constituents (e.g. caveolin-1) in isolated b cells. Confocal light microscopic evidence indicated significant colocalization of Ras with caveolin-1. Taken together, our data provide the first evidence to indicate that palmitoylation of Ras is essential for IL-1b-induced cytotoxic effects on the islet b cell.
Apoptosis, 2014
Nuclear lamins form the lamina on the interior surface of the nuclear envelope, and regulate nucl... more Nuclear lamins form the lamina on the interior surface of the nuclear envelope, and regulate nuclear metabolic events, including DNA replication and organization of chromatin. The current study is aimed at understanding the role of executioner caspase 6 on lamin A integrity in islet βcells under duress of glucotoxic (20 mM glucose; 24 hrs) and diabetic conditions. Under glucotoxic conditions, glucose-stimulated insulin secretion (GSIS) and metabolic cell viability were significantly attenuated in INS-1 832/13 cells. Further, exposure of normal human islets, rat islets and INS-1 832/13 cells to glucotoxic conditions leads to caspase 6 activation and lamin A degradation, which is also observed in islets from the Zucker diabetic fatty rat, a model for type 2 diabetes (T2D), and in islets from a human donor with T2D. Z-Val-Glu-Ile-Aspfluoromethylketone, a specific inhibitor of caspase 6, markedly attenuated high glucose-induced caspase 6 activation and lamin A degradation, confirming that caspase 6 mediates lamin A degradation under high glucose exposure conditions. Moreover, Z-Asp-Glu-Val-Aspfluoromethylketone, a known caspase 3 inhibitor, significantly inhibited high glucose-induced caspase 6 activation and lamin A degradation, suggesting that activation of caspase 3 might be upstream to caspase 6 activation in the islet β-cell under glucotoxic conditions. Lastly, we report expression of ZMPSTE24, a zinc metallopeptidase involved in the processing of prelamin A to mature lamin A, in INS-1 832/13 cells and human islets; was unaffected by high glucose. We conclude that caspases 3 and 6 could contribute to alterations in the integrity of nuclear lamins leading to metabolic dysregulation and failure of the islet β-cell.
Endocrine, 2007
Among various phosphatases, the protein phosphatase 2A (PP2A) is relatively well studied in the i... more Among various phosphatases, the protein phosphatase 2A (PP2A) is relatively well studied in the islet. Previously, we have demonstrated that the catalytic subunit of PP2A (PP2Ac) undergoes okadaic acid (OKA)-sensitive, reversible carboxylmethylation (CML), which appears to be requisite for glucose-stimulated insulin secretion (GSIS). Using the siRNA approach, we examined, herein, the contributory roles of PP2Ac in GSIS from insulin-secreting pancreatic beta-(INS-1 832/13) cells. Immunologically, PP2Ac was detectable in all the subcellular fractions studied in rank order of: cytosol > microsomes > secretory granules = nucleus > mitochondria. Transfection of PP2Ac-specific, but not scrambled-siRNA, markedly attenuated PP2A activity and GSIS in these cells. Together, our findings provide a direct evidence for a positive modulatory role for PP2Ac in signaling steps leading to GSIS.
Apoptosis, 2002
Aims/hypothesis: It is well established that long-term exposure of isolated ß cells to cytokines ... more Aims/hypothesis: It is well established that long-term exposure of isolated ß cells to cytokines [e.g., IL-1ß] results in increased expression of inducible nitric oxide synthase and subsequent release of nitric oxide, which in turn, has been shown to mediate a wide array of effects, including alterations in cellular high-energy metabolism. In this context, several extant studies have demonstrated significant reduction in adenine and guanine nucleotide triphosphate levels in ß cells exposed to IL-1ß. Herein, we examined the functional status of glyceraldehyde-3-phosphate dehydrogenase [GAPDH] in insulin-secreting cells exposed to IL-1ß, since it represents the first enzyme in the glycolytic pathway that is involved in the generation of ATP.