Phosphatidylinositol 3-kinase signals activation of p70 S6 kinase in situ through site-specific p70 phosphorylation.
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 (p70 delta CT104) 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 p70 delta CT104 but not Rsk. Activation of p70 delta CT104 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 p70 delta CT104 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.
Weng
Q P
QP
Diabetes Unit and Medical Service, Massachusetts General Hospital, Harvard Medical School, Charlestown 02129-2060, USA.
Andrabi
K
K
Klippel
A
A
Kozlowski
M T
MT
Williams
L T
LT
Avruch
J
J
D000595:Amino Acid Sequence; D000730:Androstadienes / Q000494:pharmacology; D000818:Animals; D004789:Enzyme Activation; D008969:Molecular Sequence Data; D019869:Phosphatidylinositol 3-Kinases; D010766:Phosphorylation; D017853:Phosphotransferases (Alcohol Group Acceptor) / Q000037:antagonists & inhibitors / Q000378:metabolism*; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism*; D051381:Rats; D019893:Ribosomal Protein S6 Kinases; D015398:Signal Transduction; D000077191:Wortmannin
D000730:Androstadienes; D019869:Phosphatidylinositol 3-Kinases; D017853:Phosphotransferases (Alcohol Group Acceptor); D017346:Protein Serine-Threonine Kinases; D019893:Ribosomal Protein S6 Kinases; D000077191:Wortmannin