ACTIVATION OF CJUN NH2-TERMINAL KINASE STRESS-ACTIVATED PROTEIN-KINASE BY INSULIN/

One of insulin's many biological effects is the increased transcriptio n of AP-1-regulated genes, cJun is the principal component of the AP-1 transcription complex, which is regulated by the newly discovered mem bers of the MAPK superfamily referred to as cJun NH2-terminal kinases (JNKs) or stress-activated protein kinases (SAPKs). We show that insul in stimulates a dose- and time-dependent increase in JNK activity in R at 1 fibroblasts overexpressing human insulin receptors (Rat 1 HIR cel ls). Using two different polyclonal anti-JNK antibodies, JNK activity was measured after immunoprecipitation from whole cell extracts by pho sphorylation of GSTcJun(1-79). Peak activation occurred 15 min after i nsulin addition, resulting in a 2.5-fold increase in GSTcJun(1-79) pho sphorylation over unstimulated controls. Maximal JNK activation correl ated with the onset of AP-1 DNA binding activity. Both insulin-stimula ted JNK activity and insulin-induced AP-1 transcriptional activity wer e found to be Ras-dependent. These data suggest that in Rat 1 cells, J NK activation may play a role in insulin-regulated AP-1 transcriptiona l activity leading to a mitogenic response.