Roles of insulin receptor substrate-1, phosphatidylinositol 3-kinase, and release of intracellular Ca2+ stores in insulin-stimulated insulin secretion in beta -cells.
The signaling pathway by which insulin stimulates insulin secretion and increases in intracellular free Ca(2+) concentration ([Ca(2+)](i)) in isolated mouse pancreatic beta-cells and clonal beta-cells was investigated. Application of insulin to single beta-cells resulted in increases in [Ca(2+)](i) that were of lower magnitude, slower onset, and longer lifetime than that observed with stimulation with tolbutamide. Furthermore, the increases in [Ca(2+)](i) originated from interior regions of the cell rather than from the plasma membrane as with depolarizing stimuli. The insulin-induced [Ca(2+)](i) changes and insulin secretion at single beta-cells were abolished by treatment with 100 nm wortmannin or 1 micrometer thapsigargin; however, they were unaffected by 10 micrometer U73122, 20 micrometer nifedipine, or removal of Ca(2+) from the medium. Insulin-stimulated insulin secretion was also abolished by treatment with 2 micrometer bisindolylmaleimide I, but [Ca(2+)](i) changes were unaffected. In an insulin receptor substrate-1 gene disrupted beta-cell tumor line, insulin did not evoke either [Ca(2+)](i) changes or insulin secretion. The data suggest that autocrine-activated increases in [Ca(2+)](i) are due to release of intracellular Ca(2+) stores, especially the endoplasmic reticulum, mediated by insulin receptor substrate-1 and phosphatidylinositol 3-kinase. Autocrine activation of insulin secretion is mediated by the increase in [Ca(2+)](i) and activation of protein kinase C.
Aspinwall
C A
CA
Department of Chemistry, University of Florida, Gainesville, Florida 32611-7200, USA.
Qian
W J
WJ
Roper
M G
MG
Kulkarni
R N
RN
Kahn
C R
CR
Kennedy
R T
RT
D000818:Animals; D019898:Autocrine Communication; D002118:Calcium / Q000378:metabolism*; D002478:Cells, Cultured; D007004:Hypoglycemic Agents / Q000494:pharmacology; D007328:Insulin / Q000378:metabolism* / Q000494:pharmacology; D055504:Insulin Receptor Substrate Proteins; D000078790:Insulin Secretion; D007515:Islets of Langerhans / Q000378:metabolism*; D051379:Mice; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism*; D010750:Phosphoproteins / Q000378:metabolism*; D015398:Signal Transduction
D007004:Hypoglycemic Agents; D007328:Insulin; D055504:Insulin Receptor Substrate Proteins; C526295:Irs1 protein, mouse; D010750:Phosphoproteins; D019869:Phosphatidylinositol 3-Kinases; D002118:Calcium