Protease-activated kinase II as the potential mediator of insulin-stimulated phosphorylation of ribosomal protein S6.
One of the earliest responses to insulin in target cells is stimulation of the phosphorylation of ribosomal protein S6. When exponentially growing 3T3-L1 cells are serum-starved, little phosphorylation of S6 is observed; however, following addition of insulin (10(-7) M), up to 5 phosphoryl groups are incorporated into S6. An enzyme mediating the insulin-stimulated phosphorylation of S6 has been identified as protease-activated kinase II. Two-dimensional peptide maps of tryptic digests of S6 from insulin-treated 3T3-L1 cells contain 5 phosphopeptides; the same 5 phosphopeptides are observed with tryptic digests of 40 S ribosomal subunits phosphorylated in vitro by protease-activated kinase II from rabbit reticulocytes. Protease-activated kinase II has also been identified and partially purified from the postribosomal supernatant of serum-starved and insulin-treated 3T3-L1 cells. The enzyme is present in the inactive proenzyme form in serum-starved cells; following insulin treatment, approximately 50% of the enzyme is in an activated form. Identical tryptic phosphopeptide maps are observed with these enzymes.
D000818:Animals; D002460:Cell Line; D004591:Electrophoresis, Polyacrylamide Gel; D004789:Enzyme Activation; D007328:Insulin / Q000494:pharmacology*; D051379:Mice; D010447:Peptide Hydrolases / Q000378:metabolism*; D010748:Phosphopeptides / Q000032:analysis; D010766:Phosphorylation; D011494:Protein Kinases / Q000378:metabolism*; D038601:Ribosomal Protein S6; D012269:Ribosomal Proteins / Q000378:metabolism*
D007328:Insulin; D010748:Phosphopeptides; D038601:Ribosomal Protein S6; D012269:Ribosomal Proteins; D011494:Protein Kinases; D010447:Peptide Hydrolases