Adenosine 3', 5'-Cyclic Monophosphate-Dependent Protein Kinase (A Kinase) Regulation of Insulin Receptor Function

Phosphorylation of Insulin Receptor with A Kinase Decreases the Insulin Binding Activity

Abstract

The effect of phosphorylation of insulin receptor with adenosine 3', 5'-cyclic monophosphate-dependent protein kinase (A kinase) on its insulin binding activity was investigated by using insulin receptors prepared from rat liver in vitro. A 95 KDa protein was phosphorylated by stimulation of insulin receptor kinase. This protein was also phosphorylated by A kinase. Analysis of phosphoamino acid showed that tyrosine residue (s) was phosphorylated by activation of insulin receptor kinase, whereas phosphoserine and phosphothreonine were dominantly generated by activation of A kinase.[¹²⁵I] Iodoinsulin binding activity was decreased by prior phosphorylation of the receptor with A kinase. Scatchard analysis showed that the affinity for insulin was decreased by the phosphorylation with A kinase. Although the maximal activity of insulin receptor kinase was not affected by phosphorylation with A kinase, the insulin concentration which induced half maximal activity (ED₅₀) of the receptor kinase was increased by the phosphorylation with A kinase.
These results suggested that counter regulatory hormones whose actions are mediated by the generation of adenosine 3', 5'-cyclic monophosphate regulate the insulin binding to the a subunit through phosphorylation of the β subunit of insulin receptor.