An insulin-stimulated (ribosomal S6) protein kinase from soluble extracts of H4 hepatoma cells.
Insulin stimulates the phosphorylation of the 40 S ribosomal subunit protein, S6, in intact 32P-labeled H4IIE-C3 cells, a rat hepatoma line. Cell-free cytosolic extracts from H4 cells exhibit a 5- to 10-fold increase in S6 protein kinase activity (measured by transfer of 32P to exogenous 40 S rat liver ribosomal subunits) when prepared from cells exposed to insulin prior to homogenization. Stimulation of S6 phosphorylation in intact cells and activation of S6 protein kinase in cell-free extracts are both detectable within 2 min after insulin, and are maximally stimulated by 10 min. Half-maximal stimulation is observed at 10(-11) M insulin. The stimulated S6 kinase activity requires ethylene glycol bis(beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid to be present during the kinase assay for full expression. Despite the presence of a 5- to 10-fold increase in S6 protein kinase activity, the extracts from insulin-treated cells exhibit no stimulated kinase activity toward casein, histone, or ATP-citrate lyase assayed under the conditions employed for S6. Thus, insulin mediates the rapid activation of protein kinase specific for ribosomal protein S6 by an as yet unidentified mechanism.
D000818:Animals; D002460:Cell Line; D004591:Electrophoresis, Polyacrylamide Gel; D004789:Enzyme Activation / Q000187:drug effects; D007328:Insulin / Q000494:pharmacology*; D008114:Liver Neoplasms, Experimental / Q000201:enzymology; D008297:Male; D010766:Phosphorylation; D011494:Protein Kinases / Q000378:metabolism*; D051381:Rats; D011919:Rats, Inbred Strains; D038601:Ribosomal Protein S6; D012269:Ribosomal Proteins / Q000378:metabolism*; D012995:Solubility
D007328:Insulin; D038601:Ribosomal Protein S6; D012269:Ribosomal Proteins; D011494:Protein Kinases