Controlled overexpression of selected domains of the P85 subunit of phosphatidylinositol 3-kinase reverts v-Ha-Ras transformation

Abstract Selected domains of the regulatory p85 subunit of phosphatidylinositol 3-kinase have been expressed under the control of the tetracycline transactivator in NIH 3T3 fibroblasts transformed by the v-Ha-Ras oncogene. The domains expressed were the SH3 domain, the BCR homology domain, the region between the two SH2 domains which contains the p110 binding site (the inter SH2 (IS) domain), and the C-terminal (CT) domain (containing both SH2 domains and the IS domain). The levels of IS or SH3 domain expressed in the presence of tetracycline were sufficient to reverse the transforming effects of v-Ha-Ras, and no further inhibition of proliferation was observed when expression was increased 7-fold by removal of tetracycline. In contrast inhibition of proliferation by the CT domain was observed only when the level of expression was increased 5-fold by removal of tetracycline. Overexpression of the BCR domain of p85 had no effect on v-Ha-Ras transformation. Expression of the IS domain disrupted the interaction of the p85 regulatory subunit with the p110 catalytic subunit. These results indicate that the association of the p85 subunit of PI 3-kinase with the p110 subunit is necessary for v-Ha-Ras-induced transformation in NIH 3T3 cells.