Insulin action inhibits insulin-like growth factor-II (IGF-II) receptor phosphorylation in H-35 hepatoma cells. IGF-II receptors isolated from insulin-treated cells exhibit enhanced in vitro phosphorylation by casein kinase II.

摘要: Abstract Insulin caused a rapid, dose-dependent increase in the binding of 125I-insulin-like growth factor-II (IGF-II) to surface cultured H-35 hepatoma cells. The [32P]phosphate content IGF-II receptors, immunoprecipitated from extracts cell monolayers previously incubated with for 24 h, was decreased after brief exposure cells insulin. Analysis tryptic digests labeled receptors by bidimensional peptide mapping revealed that decrease occurred varying degrees on three phosphopeptides. Thin layer electrophoresis an acid hydrolysate isolated presence [32P] phosphoserine and [32P]phosphothreonine. treatment phosphothreonine receptors. ability number highly purified protein kinases (cAMP-dependent kinase, kinase C, phosphorylase casein II) catalyze phosphorylation examined. Casein II only capable catalyzing receptor serine threonine residues under conditions our assay. Bidimensional catalyzed phosphopeptide which comigrated main found obtained vivo [32P]phosphate. immunoadsorption insulin-treated were phosphorylated vitro greater extent than control Similarly, plasma membranes adipocytes adipocyte membranes. Thus, insulin-regulated sites appear serve as substrates or enzyme similar substrate specificity.