摘要：

The effect of 8-bromo-CAMP and forskolin on the phosphorylation state and protein kinase activity of the insulin receptor was evaluated in cultured IM-9 lymphoblasts. 8-Bromo-CAMP (1 mM) or forskolin (10 PM) enhanced the phosphorylation of the insulin recep- tor purified from 32P-labeled cells by affinity chromatography on wheat germ agglutinin-agarose and im- munoprecipitation with monoclonal antibody. In the absence of insulin, phosphorylation of the fi subunit of the receptor was increased approximately 2-fold by raising intracellular CAMP. Phosphoamino acid analysis of the fi subunit following treatment of cells with forskolin revealed an increase in phosphoserine and phosphothreonine residues. In contrast, the insulin- stimulated phosphorylation of the receptor occurred on serine, threonine, and tyrosine residues and was di- minished by prior exposure of cells to forskolin. Pulse-chase experiments indicated that forskolin did not en- hance the turnover of phosphate on the receptor of cells previously exposed to insulin. Furthermore, ex- tracts from forskolin-treated cells did not differ from control extracts in their capacity to dephosphorylate 32P-labeled receptor isolated from cells treated with insulin. The insulin-dependent tyrosine protein kinase activity of each thin on voltage

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