Insulin-stimulated phosphorylation of recombinant pp120/HA4, an endogenous substrate of the insulin receptor tyrosine kinase
SM Najjar, N Philippe, Y Suzuki, GA Ignacio… - Biochemistry, 1995 - ACS Publications
Biochemistry, 1995•ACS Publications
Insulin binding to the a-subunit of its receptor stimulates the receptor tyrosine kinase to
phosphorylate the/3-subunit and several endogenous protein substrates, including
ppl20/HA4, a liver-specific plasma membrane glycoprotein of Mr 120 000. Analysis of the
deduced amino acid sequence of rat liver ppl20/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 …
phosphorylate the/3-subunit and several endogenous protein substrates, including
ppl20/HA4, a liver-specific plasma membrane glycoprotein of Mr 120 000. Analysis of the
deduced amino acid sequence of rat liver ppl20/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 …
Abstract
Insulin binding to the a-subunit of its receptor stimulates the receptor tyrosine kinase to phosphorylate the/3-subunit and several endogenous protein substrates, including ppl20/HA4, a liver-specific plasma membrane glycoprotein of Mr 120 000. Analysis of the deduced amino acid sequence of rat liver ppl20/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. MutantcDNAs were then expressed by stable transfection in NIH 3T3 cells. Two mutations (Phe488 and Ala503) impaired insulin-induced phosphorylation of ppl20/HA4, suggesting that ppl20/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
ACS Publications