title: Insulin-induced Ca(2+) entry in hepatocytes is important for PI 3-kinase activation, but not for insulin receptor and IRS-1 tyrosine phosphorylation.
abstract: Insulin produces an influx of Ca(2+) into isolated rat hepatocyte couplets that is important to couple its tyrosine kinase receptor to MAPK activity (Benzeroual et al., Am. J. Physiol. 272, (1997) G1425-G1432. In the present study, we have examined the implication of Ca(2+) in the phosphorylation state of the insulin receptor (IR) beta-subunit and of insulin receptor substrate-1 (IRS-1), as well as in the stimulation of PI 3-kinase activity in cultured hepatocytes. External Ca(2+) chelation (EGTA 4 mM) or administration of Ca(2+) channel inhibitors gadolinium 50 microM or nickel 500 microM inhibited insulin-induced PI 3-kinase activation by 85, 50 and 50%, respectively, whereas 200 microM verapamil was without effect. In contrast, the insulin-induced tyrosine phosphorylation of IR beta-subunit and of IRS-1 was not affected by any of the experimental conditions. Our data demonstrate that the stimulation of PI 3-kinase activity by the activated insulin receptor, but not the phosphorylation of IR beta-subunit and IRS-1, requires an influx of Ca(2+). Ca(2+) thus appears to play an important role as a second messenger in insulin signaling in liver cells.
authors.affiliation: Groupe de Recherche en Transport Membranaire, Université de Montréal, Montreal, Canada.
authors.forename: K
authors.initials: K
authors.lastname: Benzeroual
authors.forename: S K
authors.initials: SK
authors.lastname: Pandey
authors.forename: A K
authors.initials: AK
authors.lastname: Srivastava
authors.forename: G
authors.initials: G
authors.lastname: van de Werve
authors.forename: P S
authors.initials: PS
authors.lastname: Haddad
mesh_terms: D000818:Animals; D002118:Calcium / Q000494:pharmacology; D002121:Calcium Channel Blockers / Q000494:pharmacology; D004789:Enzyme Activation / Q000187:drug effects; D007328:Insulin / Q000494:pharmacology*; D055504:Insulin Receptor Substrate Proteins; D008099:Liver / Q000187:drug effects*; D008297:Male; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism*; D010750:Phosphoproteins / Q000737:chemistry / Q000378:metabolism; D010766:Phosphorylation / Q000187:drug effects; D051381:Rats; D017207:Rats, Sprague-Dawley; D011972:Receptor, Insulin / Q000737:chemistry / Q000187:drug effects; D015398:Signal Transduction / Q000187:drug effects; D013997:Time Factors
chemical_list: D002121:Calcium Channel Blockers; D007328:Insulin; D055504:Insulin Receptor Substrate Proteins; C526296:Irs1 protein, rat; D010750:Phosphoproteins; D019869:Phosphatidylinositol 3-Kinases; D011972:Receptor, Insulin; D002118:Calcium