Cd 2+-induced c- myc mRNA accumulation in NRK-49F cells is blocked by the protein kinase inhibitor H7 but not by HA1004, indicating that protein kinase C is a mediator of the response

Abstract

Cd 2+ is a toxic cation that, at sublethal and marginally lethal levels, modifies cell growth and metabolism. Cd 2+ exposure of NRK-49F cells results in inhibition of early EGF-induced DNA synthesis, but induction of delayed DNA synthesis; in stimulation of anchorage independent growth; in accumulation of specific oncogene mRNAs; and in an hypertrophic response. Determining whether specific signal transduction pathways (STPs) are involved in specific gene deregulation by cadmium in NRK-49F cells is important to defining possible mechanisms by which Cd 2+ elicits these physiological responses. In this study it is shown that Cd 2+ induces delayed myc (8–10 h) and jun (12 h) mRNA accumulation, as well as both early (0.5–1 h) and late (12 h) fos but not TGFβ mRNA accumulation. The times of appearance of Cd 2+-induced c- fos, c- myc and c- jun expression are dose dependent. The Cd 2+ induced accumulation of these specific mRNAs is insensitive to cycloheximide and therefore not due to preinduction of TGFβ or other gene-activating growth factors, but rather to direct induction of oncogene expression and/or mRNA stabilization. Accumulation of c- myc mRNA is shown further to be inhibited by the protein kinase inhibitor H7 but not HA1004, indicating a role for one or more protein kinases C in the STPs by which Cd 2+ induces oncogene expression. Thapsigargin, a compound which stimulates increased cytosolic [Ca 2+], induces c- myc expression also by an H7 sensitive, HA1004 insensitive pathway. These results suggest that Cd 2+ acts through one or more defined signal transduction pathways involving specific protein kinases C to induce the accumulation of c- fos, c- myc and c- jun messenger RNAs.