PI3K has been shown to play a role in the regulation of cell growth and function by a variety of growth factors, oncogenes, and other factors that act via tyrosine kinases. It has also been implicated in the mechanism of insulin action. Thus, three years ago, the applicant showed that insulin stimulates PI3K to produce the reaction products PIP2 and PIP3 in CHO cells transfected with normal human insulin receptors. During the preceding grant period, this work was extended to cells with mutant insulin receptors and to mammalian tissues. Of particular note were studies in isolated rat adipocytes, in which it was found that insulin stimulates the appearance of PI3K activity in both plasma and low density membranes, where it is associated with IRS-1, a recently identified substrate of the insulin receptor tyrosine kinase. The applicant has also found that PI3K in unstimulated adipocytes is located principally in the cytosol and that its activation by insulin is inhibited by norepinephrine. Based on these findings, studies are proposed with the following aims: 1) to determine whether the stimulatory effect of insulin on P13K in the two membranes occurs in parallel or in sequence, and how it is correlated to the tyrosyl phosphorylation of IRS-1; 2) to characterize the membrane vesicles in which PI3K activity is expressed in response to insulin with respect to the presence of proteins such as the glucose transporter and insulin receptor; 3) to define the time course of synthesis and metabolism of PIP3 and PIP2 in vivo. It will be determined whether these lipids are produced in parallel or in sequence, and at what subcellular sites they are generated and metabolized; and 4) to explore the physiological role of P13K in the adipocyte, and the mechanism by which its activation by insulin is antagonized by norepinephrine.

Agency
National Institute of Health (NIH)
Institute
National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK)
Type
Research Project (R01)
Project #
5R01DK042621-07
Application #
2142430
Study Section
Endocrinology Study Section (END)
Project Start
1990-04-01
Project End
1999-03-31
Budget Start
1996-04-01
Budget End
1999-03-31
Support Year
7
Fiscal Year
1996
Total Cost
Indirect Cost
Name
Boston Medical Center
Department
Type
DUNS #
005492160
City
Boston
State
MA
Country
United States
Zip Code
02118