Involvement of Erks activation in cadmium‐induced AP‐1 transactivation in vitro and in vivo

Cadmium is a potent and effective carcinogen in rodents and has recently been accepted by IARC (International Agency for Research on Cancer) as a category 1 carcinogen. Cadmium-induced up‐regulation of intracellular signaling pathways leading to increased mitogenesis is thought to be a major mechanism for the carcinogenic activity following chronic cadmium exposure. In the present study, we found that exposure of cells to cadmium induced significant activation of AP‐1 and all three members of the MAP kinase family in mouse epidermal JB6 cells. The induction of AP‐1 activity by cadmium appears to involve activation of Erks, since the induction of AP‐1 activity by cadmium was blocked by pretreatment of cells with PD98058. Interestingly, the induction of AP‐1 by cadmium was greatly enhanced by the chemical tumor promoter, TPA and the growth factor EGF, but not by ultraviolet C radiation. In vivo studies demonstrated that cadmium could also induce transactivation of AP‐1 in AP‐1‐luciferase report transgenic mice. Considering the role of AP‐1 activation in tumor promotion, the results presented in this study provide a possible molecular mechanism for cadmium‐induced carcinogenesis.