Effects of the Protein Phosphatase Inhibitors Okadaic Acid and Calyculin A on Insulin Release from Rat Pancreatic Islets.

Tamagawa, Tatsuo; Iguchi, Akihisa; Uemura, Kazunori; Miura, Hisayuki; Nonogaki, Katsunori; Ishiguro, Toshiaki; Sakamoto, Nobuo

doi:10.1507/endocrj1954.39.325

Cited by 13 publications

(14 citation statements)

References 12 publications

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“…The data from the present study suggest further that inhibition of glucose-induced insulin release from isolated islets by OA, as observed by Tamagawa et al (1992) and Ratcliff and Jones (1993) is, at least partly, due to prevention of the elevation of [ -Ca2 +]i following Ca 2+ influx across the plasma membrane.…”

Section: Oa and [Ca2+]isupporting

confidence: 80%

“…Recently, it has been observed that insulin secretion in response to glucose, glyceraldehyde and KC1 is inhibited by okadaic acid (OA), a potent inhibitor of protein phosphatase-1 (PP-1) and -2A (PP-2A), in rat pancreatic islets (Tamagawa et al 1992;Ratcliff and Jones 1993). On the other hand, when the adenylate cyclase activator forskolin is introduced OA even acts synergistically in mouse pancreatic fi cells (~mm~ilfi et al 1994) and RINm5F cells (Mayer et al 1994) whereas OA decreased forskolin-or 4/%phorbolmyristate acetate (PMA)-potentiated insulin release in rat islets (Tamagawa et al 1992 andRatcliff andJones 1993). Taking these different actions of OA in consideration, it seems possible that phosphorylations of proteins related to insulin release are located at different steps in the secretory machinery -in the initiation or in the modulation site -and it is also possible that phosphorylation of such proteins may produce variable actions in insulin secretion.…”

Section: Introductionmentioning

confidence: 99%

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The phosphatase inhibitor okadaic acid blocks KCl-depolarization-induced rise of cytosolic calcium of rat insulinoma cells (RINm5F)

Ammon

Heurich

Kolb

et al. 1996

Naunyn-Schmiedeberg's Arch Pharmacol

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It has been shown that okadaic acid (OA) diminishes insulin secretion of rat pancreatic islets in response to glucose, glyceraldehyde and KCl. Glucose, glyceraldehyde and KCl cause release of insulin by depolarization and subsequent opening of L-type calcium channels. Calcium entry into cells is thought to be related to protein phosphorylation. To evaluate whether or not OA mediated inhibition of insulin secretion in response to depolarization might be due to an interference with calcium uptake, we studied its effect on KCl (30 mM)-induced increases of cytosolic calcium and discharge of insulin in the insulin secreting clonal tumor cell line RINm5F. OA inhibited KCl-stimulated insulin release in concentrations > or = 1 microM. In intact RINm5F cells similar concentrations of OA decreased the activity of protein phosphates PP-1/PP-2A and inhibited the depolarization-induced rise of cytosolic calcium ([Ca2+]i). The latter action could also be achieved with the protein phosphatase inhibitor calyculin A, whereas the OA analogue 1-nor-okadaone, which is without effect on phosphatases, did not affect [Ca2+]i or insulin release. It is concluded that depression of depolarization-induced insulin secretion by OA is due to inhibition of calcium entry along voltage dependent calcium channels. The data also suggest that in RINm5F cells protein phosphatases PP-1/PP-2A are related to the function of voltage-dependent calcium channels.

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Section: Oa and [Ca2+]isupporting

confidence: 80%

Section: Introductionmentioning

confidence: 99%

The phosphatase inhibitor okadaic acid blocks KCl-depolarization-induced rise of cytosolic calcium of rat insulinoma cells (RINm5F)

Ammon

Heurich

Kolb

et al. 1996

Naunyn-Schmiedeberg's Arch Pharmacol

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“…First, using isotope-labeling methods and vapor-phase equilibration assay, we have demonstrated that post-translational CML of PP2Ac is necessary for insulin secretion [5,8]. Second, several earlier studies have utilized specific inhibitors of PP2A, such as OKA to examine its role in insulin-secretion [24][25][26][27][28][29], and indeed, we have also demonstrated that OKA specifically inhibits the CML of PP2Ac [5,8]. Together, these findings implicate a principal role for PP2Ac in islet function.…”

Section: Discussionsupporting

confidence: 57%

Depletion of the catalytic subunit of protein phosphatase-2A (PP2Ac) markedly attenuates glucose-stimulated insulin secretion in pancreatic β-cells

Jangati

Veluthakal

Susick

et al. 2007

Endocr

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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.

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“…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 inhibition by OKA of glucose, glyceraldehyde, and KCl-stimulated insulin secretion from the ␤-cell (2,40). These findings thus implicate protein (de)phosphorylation in insulin secretion.…”

mentioning

confidence: 99%

“…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).…”

mentioning

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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Effects of the Protein Phosphatase Inhibitors Okadaic Acid and Calyculin A on Insulin Release from Rat Pancreatic Islets.

Cited by 13 publications

References 12 publications

The phosphatase inhibitor okadaic acid blocks KCl-depolarization-induced rise of cytosolic calcium of rat insulinoma cells (RINm5F)

The phosphatase inhibitor okadaic acid blocks KCl-depolarization-induced rise of cytosolic calcium of rat insulinoma cells (RINm5F)

Depletion of the catalytic subunit of protein phosphatase-2A (PP2Ac) markedly attenuates glucose-stimulated insulin secretion in pancreatic β-cells

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

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