REQUIREMENT FOR PHOSPHATIDYLINOSITOL 3-KINASE IN EPIDERMAL GROWTH FACTOR-INDUCED AP-1 TRANSACTIVATION AND TRANSFORMATION IN JB6 P+ CELLS

Phosphatidylinositol 3-kinase (PI 3-kinase) plays a role in a variety of biological processes, including regulation of gene expression, cell growth, and differentiation, However, little is known about its role in the cytoplasmic events involved in epidermal growth factor (EGF)-in duced transduction of signals to the transcriptional machinery of the nucleus and in EGF-induced cell transformation, In this study, we exam ined whether PI 3-kinase is a mediator for the activation of AP-1 and neoplastic transformation by EGF in the murine epidermal cell line JB6 , The results showed the following, (i) EGF not only induced a high le vel of PI 3-kinase activity by itself but also enhanced insulin-induce d PI 3-kinase activity in JB6 P+ cells, the EGF-induced PI-3 kinase ac tivity could be blocked by constitutive overexpression of a dominant n egative P85 subunit of PI 3-kinase (Delta P85), and insulin could mark edly promote EGF-induced AP-I activity in a dose-dependent manner in J B6 P+ cells as well as promote EGF-induced JB6 P+ cell transformation, (ii) Inhibition of PI-3 kinase with wortmannin or LY294002 markedly d ecreased the AP-1 activity induced by insulin, EGF, or EGF and insulin in a dose-dependent manner, while wortmannin did not block UVB-induce d AP-1 activity, (iii) AP-1 activation by insulin, EGF, or EGF and ins ulin could be completely inhibited by overexpression of Delta P85 in a ll the dose and time courses studied, (iv) Inhibitors of PI 3-kinase ( wortmannin and LY294002) and stable overexpression of Delta P85 inhibi ted EGF-induced transformation but had no significant inhibitory effec t on cell proliferation induced by EGF or EGF and insulin, These resul ts demonstrate for the first time that PI 3-kinase appears to be requi red for EGF- or insulin-induced AP-1 transactivation and cell transfor mation but not cell proliferation in JB6 cells.