CHARACTERIZATION OF INSULIN-STIMULATED SERYL THREONYL PROTEIN-KINASESIN RAT SKELETAL-MUSCLE

Postinsulin receptor signal transduction is mediated by a cascade of s eryl/threonyl protein kinases which includes a family of mitogen-activ ated protein (MAP) kinases, ribosomal protein S6 kinases, and casein k inase-2. Previous studies have characterized these kinases primarily i n cultured or isolated cells. We have demonstrated that intravenous in jection of insulin into fasted rats significantly stimulated the activ ities of MAP kinases and S6 kinases in skeletal muscle, independently of the blood glucose levels in these animals. Anion exchange chromatog raphy on Mono Q afforded the resolution of at least five peaks of insu lin-stimulated myelin basic protein kinase activity. By immunological criteria, these myelin basic protein kinases included the p42mapk and p44erk1 as well as other potentially novel 44-kDa MAP kinases. Insulin -activated ribosomal S6 kinases were resolved into two major peaks by Mono Q chromatography, the latter of which contained a 100-kDa isoform of p90rsk as revealed by immunoblotting with an anti-rsk-peptide anti body. A 32-kDa S6 kinase in the earlier peak may represent a novel pro tein kinase in this tissue. Skeletal muscle casein kinase-2 was not si gnificantly stimulated following insulin injection into rats under our experimental conditions. These results indicate that the intact rat c an serve as a useful model system to investigate the mechanisms of ins ulin signal transduction.