Chromium(VI) induces p53-dependent apoptosis in diploid human lung and mouse dermal fibroblasts

Some forms of hexavalent chromium [Cr(VI)] are known to cause damage to res piratory-tract tissue and DNA and are thought to be human lung carcinogens. In general, Cr(VI) is mutagenic and carcinogenic at doses that also evoke some cell death, and we previously showed that the predominant mode of deat h is apoptosis. Because p53 has been shown to initiate apoptosis after geno toxic insults, the objective of these experiments was to determine whether p53 is activated in and necessary for apoptosis of normal diploid human lun g fibroblasts (HLF cells) after chromium exposure. By using annexin(V) stai ning and fluorescent microscopy, we found that Cr(Vt) caused up to 14% of H LF cells to undergo apoptosis within 24 h after exposure. In addition, by u sing western blotting, we found that p53 protein levers increased fourfold to sixfold after exposure to sodium chromate. Because the major function of p53 is as a transcription factor, it must be translocated from the cytopla sm to the nucleus after chromate exposure to be active. Immunofluorescence studies using an antibody against p53 showed that, after chromate exposure, p53 was located in the nucleus of the treated HLF cells. The necessity of p53 for chromium-induced apoptosis was examined in two ways. One approach u sed dermal fibroblasts from p53 wild-type, heterozygous, and null mice, and the other approach used HLF cells that were transiently transfected with t he human papilloma virus E6 gene, which targets p53 for degradation and cre ates a functional p53-null cell. These studies showed that chromium-induced apoptosis was p53 dependent. Moi. Carcinog. 28:111-118, 2000. (C) 2000 Wil ey-Liss, Inc.