Insulin stimulates the kinase activity of RAC-PK, a pleckstrin homology domain containing ser/thr kinase.
In the present study, insulin is shown to rapidly stimulate by 8- to 12-fold the enzymatic activity of RAC-PK alpha, a pleckstrin homology domain containing ser/thr kinase. In contrast, activation of protein kinase C by phorbol esters had almost no effect on the enzymatic activity of RAC-PK alpha. Insulin activation was accompanied by a shift in molecular weight of the RAC-PK alpha protein, and the activated kinase was deactivated by treatment with a phosphatase, indicating that insulin activated the enzyme by stimulating its phosphorylation. This insulin-induced shift in RAC-PK was also observed in primary rat epididymal adipocytes, as well as in a muscle cell line called C2C12 cells. The insulin-stimulated increase in RAC-PK alpha activity was inhibited by wortmannin (an inhibitor of phosphatidylinositol 3-kinase) in a dose-dependent manner with a half-maximal inhibition of 10 nM, but not by 20 ng/ml of rapamycin. Activation of RAC-PK alpha activity was also observed in a variant RAC lacking the pleckstrin homology domain. These results indicate that RAC-PK alpha activity can be regulated by the insulin receptor. RAC-PK alpha may therefore play a general role in intracellular signaling mediated by receptor tyrosine kinases.
Kohn
A D
AD
Department of Molecular Pharmacology, Stanford University School of Medicine, CA 94305, USA.
Kovacina
K S
KS
Roth
R A
RA
D000818:Animals; D001483:Base Sequence; D001798:Blood Proteins / Q000737:chemistry*; D016466:CHO Cells; D003001:Cloning, Molecular; D006224:Cricetinae; D017931:DNA Primers; D004789:Enzyme Activation; D000939:Epitopes / Q000032:analysis; D006367:HeLa Cells; D006388:Hemagglutinins; D006801:Humans; D007328:Insulin / Q000494:pharmacology*; D007700:Kinetics; D008969:Molecular Sequence Data; D019869:Phosphatidylinositol 3-Kinases; D010750:Phosphoproteins; D017853:Phosphotransferases (Alcohol Group Acceptor) / Q000378:metabolism; D016133:Polymerase Chain Reaction; D017346:Protein Serine-Threonine Kinases / Q000096:biosynthesis / Q000737:chemistry* / Q000378:metabolism*; D051057:Proto-Oncogene Proteins c-akt; D011994:Recombinant Proteins / Q000737:chemistry / Q000378:metabolism; D017386:Sequence Homology, Amino Acid; D015398:Signal Transduction; D014162:Transfection
D001798:Blood Proteins; D017931:DNA Primers; D000939:Epitopes; D006388:Hemagglutinins; D007328:Insulin; D019869:Phosphatidylinositol 3-Kinases; D010750:Phosphoproteins; D017853:Phosphotransferases (Alcohol Group Acceptor); D017346:Protein Serine-Threonine Kinases; D051057:Proto-Oncogene Proteins c-akt; D011994:Recombinant Proteins; C039077:platelet protein P47