Insulin-stimulated MAP-2 kinase phosphorylates and activates ribosomal protein S6 kinase II.
Ribosomal protein S6 is a component of the eukaryotic 40S ribosomal subunit that becomes phosphorylated on multiple serine residues in response to a variety of mitogens, including insulin, growth factors, and transforming proteins of many oncogenic viruses. Recently, an activated S6 kinase (S6 K II) has been purified to homogeneity from Xenopus eggs, and characterized immunologically and at the molecular level. Purified S6 K II can be deactivated in vitro by incubation with either protein phosphatase 1 or protein phosphatase 2A. Reactivation and phosphorylation of S6 K II occurs in vitro with an insulin-stimulated microtubule-associated protein-2 (MAP-2) protein kinase which is itself a phosphoprotein that can be deactivated by protein phosphatase 2A. These studies suggest that a step in insulin signalling involves sequential activation by phosphorylation of at least two serine/threonine protein kinases.
Sturgill
T W
TW
Department of Internal Medicine, University of Virginia School of Medicine, Charlottesville 22903.
Ray
L B
LB
Erikson
E
E
Maller
J L
JL
D000818:Animals; D017871:Calcium-Calmodulin-Dependent Protein Kinases; D002460:Cell Line; D004789:Enzyme Activation / Q000187:drug effects; D005260:Female; D007328:Insulin / Q000494:pharmacology*; D009865:Oocytes / Q000201:enzymology; D010749:Phosphoprotein Phosphatases / Q000378:metabolism; D010766:Phosphorylation; D011494:Protein Kinases / Q000378:metabolism*; D054645:Protein Phosphatase 1; D054648:Protein Phosphatase 2; D019893:Ribosomal Protein S6 Kinases; D014981:Xenopus
D007328:Insulin; D011494:Protein Kinases; D019893:Ribosomal Protein S6 Kinases; D017871:Calcium-Calmodulin-Dependent Protein Kinases; D010749:Phosphoprotein Phosphatases; D054645:Protein Phosphatase 1; D054648:Protein Phosphatase 2