PI-3 kinase mediates EGF-induced ap-1 transactivation and neoplastic transformation in JB6 cells

Little is known about the role of PI-3 kinase in the cytoplasmic events involved in signal transduction to the transcriptional machinery in the nucleus and its role in cell transformation. In this study, we examined whether PI-3 kinase is a mediator for the activation of AP-1 and neoplastic transformation in the murine epidermal cell line JB6. The results showed that: (a) insulin was able to induce AP-1 activation by itself and could markedly promote EGF-induced AP-1 activity in a dose-dependent manner in JB6 P+ (promoter-sensitive) cells as well as EGF-induced JB6 P+ cell transformation; (b) EOF not only induced a high level of PI-3 kinase activity by itself, but also promoted insulin-induced PI-3 kinase activity in JB6 P cells; this enhancement could be blocked by wortmannin; (c) inhibition of PI-3 kinase with wortmannin or LY294002 decreased the AP-1 activity induced by insulin, EGF or EGF+insulin in a dose-dependent manner and inhibited JB6 P cell transformation induced by EGF; (d) AP-1 activation by insulin or EGF could be blocked by expression of constitutively dominant negative P85 subunit of PI-3 kinase (AP85); and (e) wortmannin and LY294002 also inhibited normal EGF-induced transformation at a dose of 50-200 nM. These results demonstrate for the first time that PI-3 kinase may play an important role during AP-1 transactivation and cell transformation.