Src-dependent association of Cas and p85 phosphatidylinositol 3'-kinase in v-crk-transformed cells.

Cellular changes associated with oncogenic transformation are generally caused by deregulation of signal transduction pathways. We show that, in cells transformed by the v-crk oncogene, the adapter protein Cas forms a stable complex with the p85 regulatory subunit of phosphatidylinositol 3'-kinase (PI3K) coincident with the appearance of Cas-associated PI3K activity. The interaction between Cas and p85 PI3K appears to be driven primarily by Src-dependent tyrosine phosphorylation of Cas, and mapping studies indicate that the carboxyl terminus of Cas is necessary and sufficient for binding to p85 PI3K. One of the cellular effects of v-Crk expression is to promote DNA synthesis in the presence of low serum. This effect is potentiated in Cas-null fibroblasts when wild-type Cas is expressed, but not when a Cas variant is expressed that lacks the carboxyl-terminal p85 PI3K binding region. This suggests that the association of Cas with p85 PI3K may play a role in uncoupling growth regulatory pathways through v-Crk.