Cyclosporin A stimulation of glucose-induced insulin secretion in MIN6 cells.
Effects of the immunosuppressant cyclosporin A (CsA), a specific inhibitor of Ca2+/calmodulin-dependent protein phosphatase (PP2B), were examined with regard to the induction of insulin secretion from MIN6 cells, a glucose-responsive cell line derived from mouse insulinoma. CsA had no effect on basal insulin secretion from MIN6 cells, but did increase glucose-, tolbutamide-, and KCl-induced insulin secretion. Treatment of the cells with CsA resulted in a dose-dependent increase in insulin secretion, which was maximal at 3 microM. CsA inhibited PP2B activity in a dose-dependent manner, and the increase in insulin secretion correlated with the decrease in PP2B activity. In 32P-labeled cells, treatment with CsA for 30 min increased phosphorylation of synapsin I-like protein by 50 +/- 5.7%. As revealed by one-dimensional phosphopeptide mapping of 32P-labeled synapsin I-like protein, treatment with CsA for 30 min increased phosphorylation of site II of synapsin I-like protein by 59 +/- 8%, which is phosphorylated by calmodulin kinase II. Messenger RNAs, which hybridize with complementary DNAs of calcineurin A and B subunits from rat brain, were detected in MIN6 cells. Western blot analysis showed a 61-kDa band, which interacts with rat brain calcineurin A antibody. Similar increases in secretagogue-induced insulin secretion with CsA were observed for HIT-T15 cells. These results suggest that CsA stimulates glucose-induced insulin secretion by inhibiting the activity of PP2B, an event that may be involved in mechanisms governing glucose-induced insulin secretion via dephosphorylation of synapsin I-like protein in MIN6 cells.
Ebihara
K
K
Department of Pharmacology, Kumamoto University School of Medicine, Japan.
Fukunaga
K
K
Matsumoto
K
K
Shichiri
M
M
Miyamoto
E
E
D000818:Animals; D054732:Calcium-Calmodulin-Dependent Protein Kinase Type 2; D017871:Calcium-Calmodulin-Dependent Protein Kinases / Q000378:metabolism; D002460:Cell Line; D016572:Cyclosporine / Q000494:pharmacology*; D004305:Dose-Response Relationship, Drug; D005947:Glucose / Q000494:pharmacology*; D007328:Insulin / Q000378:metabolism*; D000078790:Insulin Secretion; D007340:Insulinoma / Q000378:metabolism* / Q000473:pathology; D007515:Islets of Langerhans / Q000378:metabolism; D051379:Mice; D010190:Pancreatic Neoplasms / Q000378:metabolism* / Q000473:pathology; D010749:Phosphoprotein Phosphatases / Q000037:antagonists & inhibitors / Q000378:metabolism; D010766:Phosphorylation / Q000187:drug effects; D051381:Rats; D016704:Synapsins / Q000378:metabolism
D007328:Insulin; D016704:Synapsins; D016572:Cyclosporine; D054732:Calcium-Calmodulin-Dependent Protein Kinase Type 2; D017871:Calcium-Calmodulin-Dependent Protein Kinases; D010749:Phosphoprotein Phosphatases; D005947:Glucose