Showing papers by "Chuanshu Huang published in 1996"

Requirement for phosphatidylinositol 3-kinase in epidermal growth factor-induced AP-1 transactivation and transformation in JB6 P+ cells.

Abstract: 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)-induced transduction of signals to the transcriptional machinery of the nucleus and in EGF-induced cell transformation. In this study, we examined 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 level of PI 3-kinase activity by itself but also enhanced insulin-induced PI 3-kinase activity in JB6 P+ cells, the EGF-induced PI-3 kinase activity could be blocked by constitutive overexpression of a dominant negative P85 subunit of PI 3-kinase (deltaP85), and insulin could markedly promote EGF-induced AP-1 activity in a dose-dependent manner in JB6 P+ cells as well as promote EGF-induced JB6 P+ cell transformation. (ii) Inhibition of PI-3 kinase with wortmannin or LY294002 markedly decreased the AP-1 activity induced by insulin, EGF, or EGF and insulin in a dose-dependent manner, while wortmannin did not block UVB-induced AP-1 activity. (iii) AP-1 activation by insulin, EGF, or EGF and insulin could be completely inhibited by overexpression of deltaP85 in all the dose and time courses studied. (iv) Inhibitors of PI 3-kinase (wortmannin and LY294002) and stable overexpression of deltaP85 inhibited EGF-induced transformation but had no significant inhibitory effect on cell proliferation induced by EGF or EGF and insulin. These results demonstrate for the first time that PI 3-kinase appears to be required for EGF- or insulin-induced AP-1 transactivation and cell transformation but not cell proliferation in JB6 cells.

Inhibitory effects of ascorbic acid on AP-1 activity and transformation of JB6 cells.

Abstract: Ascorbic acid (vitamin C) has been reported as an anti-cancer agent. Previous in vitro studies using either primary cell cultures from cancer patients or tumor cell lines have indicated that different kinds of tumor cells may have different sensitivities to ascorbic acid for the inhibition of tumorigeneity or growth. Because the JB6 mouse epidermal cell system has been used extensively as an in vitro model for the study of tumor promotion and progression, we assessed the effects of ascorbic acid on transformation in JB6 cell variants. The results show that ascorbic acid could inhibit 5.5% to 97.1% of transformation of JB6 P+ cell Cl 41-19 induced by TPA, EGF or EGF + insulin, but has no effect on anchorage-independent growth of JB6 transformed cell A33. Since our previous results indicated that induced AP-1 activity is required for tumor promoter induced-transformation, we tested whether inhibition of tumor promoter-induced transformation by ascorbic acid is through an AP-1 inhibition mechanism. Our results indicated that ascorbic acid inhibited AP-I activity at the same dose range for inhibition of transformation. These results demonstrated that ascorbic acid has inhibitory effects on JB6 cell tumor promoter-induced transformation, but no influence on tumor cell phenotype expression and provided the basic knowledge for understanding of vitamin C action on tumor prevention.