Decreased induction of an hepatic mRNA by phorbol esters after insulin desensitization

Insulin and phorbol esters rapidly induce the transcription and cytoplasmic accumulation of a specific mRNA (p33) in rat hepatoma cells. We have studied the effects of insulin desensitization on the regulation of p33 gene expression by insulin and phorbol esters. Insulin desensitization is associated with down-regulation of the insulin receptor and post-receptor defects. When cells were treated with insulin (5 x 10(-7) M) for 24 h, a greater than 50% reduction in insulin binding was observed and insulin's stimulation of p33 transcription and cytoplasmic mRNA levels was prevented. The induction of p33 gene transcription and mRNA levels by phorbol esters was also decreased. Beta-tubulin gene expression was unaffected by insulin or phorbol esters and the stimulatory effect of dexamethasone on p33 gene expression was not impaired. Since insulin desensitization impaired phorbol esters' induction of p33 gene expression, one intracellular defect in insulin-desensitized cells may include an alteration in protein kinase C-dependent events.