Glucose-stimulated protein phosphorylation in the pancreatic islet

Colca, Jerry R.; Kotagal, Nirmala; Lacy, Paul E.; Brooks, Charles L.; Norling, Laura L.; Landt, Michael; McDaniel, Michael L.

doi:10.1042/bj2200529

Cited by 13 publications

(10 citation statements)

References 43 publications

(26 reference statements)

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“…We propose, further, that such an inhibition in PP2A activity results in retention of putative exocytotic proteins in their phosphorylated state, which may be necessary for insulin secretion. It is important to point out that several earlier studies from us and others (9,16,17,20,25,30,37,47) have indicated glucose-mediated increases in phosphorylation of several signaling proteins in the islet ␤-cell. Together, our current findings and extant observations in this area indicate rather dual effects by nutrient secretagogues, such as glucose, on the phosphorylation of candidate proteins, namely, stimulation of kinases as well as inhibition of respective phosphoprotein phosphatases.…”

Section: Discussionmentioning

confidence: 99%

Regulation by glucose and calcium of the carboxylmethylation of the catalytic subunit of protein phosphatase 2A in insulin-secreting INS-1 cells

Palanivel¹,

Veluthakal²,

Kowluru³

2004

American Journal of Physiology-Endocrinology and Metabolism

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Palanivel, Rengasamy, Rajakrishnan Veluthakal, and Anjaneyulu Kowluru. Regulation by glucose and calcium of the carboxylmethylation of the catalytic subunit of protein phosphatase 2A in insulin-secreting INS-1 cells. Am J Physiol Endocrinol Metab 286: E1032-E1041, 2004. First published February 17, 2004 10.1152/ajpendo.00587.2003.-Previously, we reported that the catalytic subunit of protein phosphatase 2A (PP2Ac) undergoes carboxylmethylation (CML) at its COOH-terminal leucine, and that inhibitors of such a posttranslational modification markedly attenuate nutrientinduced insulin secretion from isolated ␤-cells. More recent studies have suggested direct inhibitory effects of glucose metabolites on PP2A activity in isolated ␤-cells, implying that inhibition of PP2A leads to stimulation of insulin secretion. Because the CML of PP2Ac has been shown to facilitate the holoenzyme assembly and subsequent functional activation of PP2A, we investigated putative regulation by glucose of the CML of PP2Ac in insulin-secreting (INS)-1 cells. Our data indicated a marked inhibition by specific intermediates of glucose metabolism (e.g., citrate and phosphoenolpyruvate) of the CML of PP2Ac in INS-1 cell lysates. Such inhibitory effects were also demonstrable in intact cells by glucose. Mannoheptulose, an inhibitor of glucose metabolism, completely prevented inhibitory effects of glucose on the CML of PP2Ac. Moreover, glucose-mediated inhibition of the CML of PP2Ac was resistant to diazoxide, suggesting that glucose metabolism and the generation of glucose metabolites might control inhibition of the CML of PP2Ac. A membrane-depolarizing concentration of KCl also induced inhibition of the CML of PP2Ac in intact INS cells. On the basis of these data, we propose that glucose metabolism and increase in intracellular calcium facilitate inhibition of the CML of PP2Ac, resulting in functional inactivation of PP2A. This, in turn, might retain the key signaling proteins of the insulin exocytotic cascade in their phosphorylated state, leading to stimulated insulin secretion. glucose metabolism; insulin-secreting cells THE PHOSPHORYLATION STATUS of proteins is regulated by the balance of activities of protein kinases and phosphatases, which induce the addition and removal of phosphoprotein phosphate, respectively (8, 42). Although several previous studies were focused on the identification and characterization of protein kinases in islets (4, 11, 16), little information is available on the localization and regulation of phosphoprotein phosphatases in the pancreatic ␤-cell. With use of relatively specific inhibitors of protein phosphatase function, recent studies (1,2,23,31,36,40) have suggested important roles for various phosphoprotein phosphatases, such as protein phosphatase 2A (PP2A), in the pancreatic ␤-cell function. For example, okadaic acid (OKA), a selective inhibitor of protein phosphatases, stimulates basal and cAMP-stimulated insulin secretion from electrically permeabilized islets (31). There is also evidence to indicate inhi...

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Section: Discussionmentioning

confidence: 99%

Regulation by glucose and calcium of the carboxylmethylation of the catalytic subunit of protein phosphatase 2A in insulin-secreting INS-1 cells

Palanivel¹,

Veluthakal²,

Kowluru³

2004

American Journal of Physiology-Endocrinology and Metabolism

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“…The mechanism of action of alloxan has not been firmly established. It has been shown that alloxan inhibits a Ca2+-calmodulindependent protein kinase in extracts of rat islets (Colca et al, 1983). This finding is ofconsiderable interest in view of the growing evidence, reviewed by Harrison et al (1984), implicating protein phosphorylation as a major control mechanism in the regulation of insulin release.…”

Section: Introductionmentioning

confidence: 99%

Effects of dehydrouramil on protein phosphorylation and insulin secretion in rat islets of Langerhans

Harrison¹,

Poje²,

Ročić³

et al. 1986

Biochemical Journal

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Dehydrouramil hydrate hydrochloride (DHU), a stable analogue of alloxan, inhibited the phosphorylation of an endogenous protein of Mr 53,000 catalysed by a Ca2+-calmodulin-dependent protein kinase in extracts of islets of Langerhans. The concentration of DHU required for 50% inhibition was 0.09 mM. DHU did not inhibit islet cyclic AMP-dependent protein kinase and caused only slight inhibition of Ca2+-phospholipid-dependent protein kinase. Inhibition of Ca2+-calmodulin-dependent protein kinase was neither prevented nor reversed by dithiothreitol. DHU did not affect the ability of calmodulin to activate cyclic AMP phosphodiesterase. In intact islets, pre-exposure to DHU impaired the insulin-secretory response to glucose and blocked the potentiatory effect on insulin secretion of forskolin, an activator of adenylate cyclase, and of tetradecanoylphorbol acetate (TPA), an activator of Ca2+-phospholipid-dependent protein kinase. The increase in islet cyclic AMP elicited by forskolin was not affected by DHU. The data are consistent with the hypothesis that protein phosphorylation catalysed by a Ca2+-calmodulin-dependent protein kinase may play a central role in the regulation of insulin secretion.

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“…This B-cell selectivity may result from the capacity of the cells to rapidly incorporate both drugs with a short half-life (38)(39)(40) and from the exquisite sensitivity of the cells to the cytotoxic action of these drugs. The alloxan toxicity has been attributed to its direct interactions with islet protein kinase (41) and to its well-known ability to generate highly reactive oxygen radicals (42,43). It is not yet clear whether the destructive effects of streptozotocin are also elicited by free radicals or whether they develop after alkylation of DNA bases (44)(45)(46)(47)(48)(49).…”

Section: Four Different Conditions Leading To B-cell Death In Vitromentioning

confidence: 99%

Pancreatic B cells possess defense mechanisms against cell-specific toxicity.

Pipeleers¹,

Winkel²

1986

Proc. Natl. Acad. Sci. U.S.A.

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Insulin-dependent diabetes develops when more than 90% of the insulin containing B cells are destroyed. The present study investigates whether the target B cells can counteract the damaging effects of cytotoxic substances. Purified islet cells were first exposed for 3-10 min to tbutylhydroperoxide, alloxan, streptozotocin, or B-cell surface antibodies plus complement, then cultured for 20 hr before the percent of dead cells was counted. t-Butylhydroperoxide destroyed all islet cell types whereas the three other agents exerted a dose-dependent toxicity upon islet B cells only. The survival of drug-and complement-treated cells varied with the culture conditions present between the initial cellular attack and the moment of cell death.

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Glucose-stimulated protein phosphorylation in the pancreatic islet

Cited by 13 publications

References 43 publications

Regulation by glucose and calcium of the carboxylmethylation of the catalytic subunit of protein phosphatase 2A in insulin-secreting INS-1 cells

Regulation by glucose and calcium of the carboxylmethylation of the catalytic subunit of protein phosphatase 2A in insulin-secreting INS-1 cells

Effects of dehydrouramil on protein phosphorylation and insulin secretion in rat islets of Langerhans

Pancreatic B cells possess defense mechanisms against cell-specific toxicity.

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