Phosphatidylinositol 3-Kinase Signals Activation of p70 S6 Kinase in situ through Site-Specific p70 Phosphorylation

• Published in: Proceedings of the National Academy of Sciences - PNAS 1995-06, Vol.92 (12), p.5744-5748
• Main Authors: Weng, Qing-Ping, Andrabi, Khurshid, Klippel, Anke, Kozlowski, Mark T., Williams, Lewis T., Avruch, Joseph
• Format: Article
• Language: English
• Subjects: Amino Acid Sequence; Amino acids; Androstadienes - pharmacology; Animals; Antibodies; Biochemistry; Complementary DNA; COS cells; Enzyme Activation; Enzymes; Immunoprecipitation; Memory interference; Mitogens; Molecular Sequence Data; Phosphatidylinositol 3-Kinases; Phosphorylation; Phosphotransferases (Alcohol Group Acceptor) - antagonists & inhibitors; Phosphotransferases (Alcohol Group Acceptor) - metabolism; Physiological regulation; Protein-Serine-Threonine Kinases - metabolism; Rats; Ribosomal Protein S6 Kinases; Signal Transduction; Transfection; Wortmannin
• ISSN: 0027-8424; 1091-6490
• DOI: 10.1073/pnas.92.12.5744

The p70 S6 kinase is activated by insulin and mitogens through multisite phosphorylation of the enzyme. One set of activating phosphorylations occurs in a putative autoinhibitory domain in the noncatalytic carboxyl-terminal tail. Deletion of this tail yields a variant (p70ΔCT104) that nevertheless continues to be mitogen regulated. Coexpression with a recombinant constitutively active phosphatidylinositol (PI) 3-kinase (EC 2.7.1.137) gives substantial activation of both full-length p70 and p70ΔCT104 but not Rsk. Activation of p70ΔCT104 by PI 3-kinase and inhibition by wortmannin are each accompanied by parallel and selective changes in the phosphorylation of p70 Thr-252. A Thr or Ser at this site, in subdomain VIII of the catalytic domain just amino-terminal to the APE motif, is necessary for p70 40S kinase activity. The inactive ATP-binding site mutant K123M p70ΔCT104 undergoes phosphorylation of Thr-252 in situ but does not undergo direct phosphorylation by the active PI 3-kinase in vitro. PI 3-kinase provides a signal necessary for the mitogen activation of the p70 S6 kinase, which directs the site-specific phosphorylation of Thr-252 in the p70 catalytic domain, through a distinctive signal transduction pathway.