Insulin stimulates the kinase activity of RAC‐PK, a pleckstrin homology domain containing ser/thr kinase

• Published in: The EMBO journal Vol. 14; no. 17; pp. 4288 - 4295
• Main Authors: Kohn, A. D., Kovacina, K. S., Roth, R. A.
• Format: Journal Article
• Language: English
• Published: England 01-09-1995
• Subjects: Animals; Base Sequence; Blood Proteins - chemistry; CHO Cells; Cloning, Molecular; Cricetinae; DNA Primers; Enzyme Activation; Epitopes - analysis; HeLa Cells; Hemagglutinins; Humans; Insulin - pharmacology; Kinetics; Molecular Sequence Data; Phosphatidylinositol 3-Kinases; Phosphoproteins; Phosphotransferases (Alcohol Group Acceptor) - metabolism; Polymerase Chain Reaction; Protein Serine-Threonine Kinases - biosynthesis; Protein Serine-Threonine Kinases - chemistry; Protein Serine-Threonine Kinases - metabolism; Proto-Oncogene Proteins c-akt; Recombinant Proteins - chemistry; Recombinant Proteins - metabolism; Sequence Homology, Amino Acid; Signal Transduction; Transfection
• ISSN: 0261-4189; 1460-2075
• DOI: 10.1002/j.1460-2075.1995.tb00103.x

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.