title: Insulin receptor substrate 1-induced inhibition of endoplasmic reticulum Ca2+ uptake in beta-cells. Autocrine regulation of intracellular ca2+ homeostasis and insulin secretion.
abstract: To understand the role of the insulin receptor pathway in beta-cell function, we have generated stable beta-cells (betaIRS1-A) that overexpress by 2-fold the insulin receptor substrate-1 (IRS-1) and compared them to vector-expressing controls. IRS-1 overexpression dramatically increased basal cytosolic Ca2+ levels from 81 to 278 nM, but it did not affect Ca2+ response to glucose. Overexpression of the insulin receptor also caused an increase in cytosolic Ca2+. Increased cytosolic Ca2+ was due to inhibition of Ca2+ uptake by the endoplasmic reticulum, because endoplasmic reticulum Ca2+ uptake and content were reduced in betaIRS1-A cells. Fractional insulin secretion was significantly increased 2-fold, and there was a decrease in betaIRS1-A insulin content and insulin biosynthesis. Steady-state insulin mRNA levels and glucose-stimulated ATP were unchanged. High IRS-1 levels also reduced beta-cell proliferation. These data demonstrate a direct link between the insulin receptor signaling pathway and the Ca2+-dependent pathways regulating insulin secretion of beta-cells. We postulate that during regulated insulin secretion, released insulin binds the beta-cell insulin receptor and activates IRS-1, thus further increasing cytosolic Ca2+ by reducing Ca2+ uptake. We suggest the existence of a novel pathway of autocrine regulation of intracellular Ca2+ homeostasis and insulin secretion in the beta-cell of the endocrine pancreas.
authors.affiliation: Department of Pathology and Laboratory Medicine, University of Pennsylvania School of Medicine, Philadelphia, Pennsylvania 19104, USA.
authors.forename: G G
authors.initials: GG
authors.lastname: Xu
authors.forename: Z Y
authors.initials: ZY
authors.lastname: Gao
authors.forename: P D
authors.initials: PD
authors.lastname: Borge
authors.forename: B A
authors.initials: BA
authors.lastname: Wolf
mesh_terms: D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D002118:Calcium / Q000037:antagonists & inhibitors / Q000378:metabolism*; D002455:Cell Division; D004721:Endoplasmic Reticulum / Q000378:metabolism*; D005786:Gene Expression Regulation; D005947:Glucose / Q000494:pharmacology; D007328:Insulin / Q000235:genetics / Q000378:metabolism; D055504:Insulin Receptor Substrate Proteins; D007515:Islets of Langerhans / Q000378:metabolism*; D051379:Mice; D010750:Phosphoproteins / Q000235:genetics / Q000378:metabolism*; D010766:Phosphorylation; D012333:RNA, Messenger / Q000378:metabolism; D011972:Receptor, Insulin / Q000378:metabolism; D015398:Signal Transduction; D014162:Transfection
chemical_list: D007328:Insulin; D055504:Insulin Receptor Substrate Proteins; C526295:Irs1 protein, mouse; D010750:Phosphoproteins; D012333:RNA, Messenger; D000255:Adenosine Triphosphate; D011972:Receptor, Insulin; D005947:Glucose; D002118:Calcium