A tightly associated serine/threonine protein kinase regulates phosphoinositide 3-kinase activity.
We identified a serine/threonine protein kinase that is associated with and phosphorylates phosphoinositide 3-kinase (PtdIns 3-kinase). The serine kinase phosphorylates both the 85- and 110-kDa subunits of PtdIns 3-kinase and purifies with it from rat liver and immunoprecipitates with antibodies raised to the 85-kDa subunit. Tryptic phosphopeptide maps indicate that p85 from polyomavirus middle T-transformed cells is phosphorylated in vivo at three sites phosphorylated in vitro by the associated serine kinase. The 85-kDa subunit of PtdIns 3-kinase is phosphorylated in vitro on serine at a stoichiometry of approximately 1 mol of phosphate per mol of p85. This phosphorylation results in a three- to sevenfold decrease in PtdIns 3-kinase activity. Dephosphorylation with protein phosphatase 2A reverses the inhibition. This suggests that the association of protein phosphatase 2A with middle T antigen may function to activate PtdIns 3-kinase.
Hematology-Oncology Division, Beth Israel Hospital, Boston, Massachusetts.
C L
CL
Carpenter
K R
KR
Auger
B C
BC
Duckworth
W M
WM
Hou
B
B
Schaffhausen
L C
LC
Cantley
D000818:Animals; D000952:Antigens, Polyomavirus Transforming; D002472:Cell Transformation, Viral; D015971:Gene Expression Regulation, Enzymologic; D008099:Liver / Q000201:enzymology; D046911:Macromolecular Substances; D008297:Male; D008345:Manganese / Q000494:pharmacology; D010449:Peptide Mapping; D019869:Phosphatidylinositol 3-Kinases; D010748:Phosphopeptides / Q000032:analysis; D010749:Phosphoprotein Phosphatases / Q000378:metabolism; D010766:Phosphorylation; D010770:Phosphotransferases / Q000187:drug effects / Q000378:metabolism*; D011233:Precipitin Tests; D054648:Protein Phosphatase 2; D017346:Protein Serine-Threonine Kinases / Q000302:isolation & purification / Q000378:metabolism*; D051381:Rats; D017207:Rats, Sprague-Dawley; D012694:Serine / Q000378:metabolism; D013379:Substrate Specificity
D000952:Antigens, Polyomavirus Transforming; D046911:Macromolecular Substances; D008345:Manganese; D019869:Phosphatidylinositol 3-Kinases; D010748:Phosphopeptides; D010749:Phosphoprotein Phosphatases; D010770:Phosphotransferases; D054648:Protein Phosphatase 2; D017346:Protein Serine-Threonine Kinases; D012694:Serine