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Insulin-stimulated phosphorylation of recombinant pp120/HA4, an endogenous substrate of the insulin receptor tyrosine kinase.

Authors: Najjar, SM  Philippe, N  Suzuki, Y  Ignacio, GA  Formisano, P  Accili, D  Taylor, SI 
Citation: Najjar SM, etal., Biochemistry. 1995 Jul 25;34(29):9341-9.
Pubmed: (View Article at PubMed) PMID:7626603

Insulin binding to the alpha-subunit of its receptor stimulates the receptor tyrosine kinase to phosphorylate the beta-subunit and several endogenous protein substrates, including pp120/HA4, a liver-specific plasma membrane glycoprotein of M(r) 20,000. Analysis of the deduced amino acid sequence of rat liver pp120/HA4 revealed two potential sites for tyrosine phosphorylation in the cytoplasmic domain (Tyr488 and Tyr513), as well as a potential cAMP-dependent protein kinase phosphorylation site (Ser503). To determine which of these sites is phosphorylated in response to insulin, each of these amino acid residues was altered by site-directed mutagenesis. Mutant cDNAs were then expressed by stable transfection in NIH 3T3 cells. Two mutations (Phe488 and Ala503) impaired insulin-induced phosphorylation of pp120/HA4, suggesting that pp120/HA4 undergoes multisite phosphorylation. It seems likely that Tyr488 is phosphorylated by the insulin receptor kinase, and phosphorylation of Ser513 may contribute to the regulation of tyrosine phosphorylation. Since pp120/HA4 is believed to be associated with a Ca2+/Mg(2+)-dependent ecto-ATPase activity, we determined the effects of insulin-induced phosphorylation on this enzymatic activity. In NIH 3T3 cells co-expressing the insulin receptor and pp120/HA4, insulin caused a 2-fold increase in ecto-ATPase activity. Moreover, elimination of the phosphorylation sites of pp120/HA4 impaired the ability of insulin to stimulate the ecto-ATPase activity. These data suggest that tyrosine phosphorylation of pp120/HA4 may regulate Ca2+/Mg(2+)-dependent ecto-ATPase activity.


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CRRD Object Information
CRRD ID: 11059572
Created: 2016-04-16
Species: All species
Last Modified: 2016-04-16
Status: ACTIVE


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