Proto-Oncogene Amplification and Overexpression in Cadmium-Induced Cell Transformation

Abstract

Cadmium (Cd) is an essential material used in the battery, metal-coating, and alloy industries. In addition to these industrial uses, it is also a component of cigarette smoke. Therefore, exposure to cadmium is widespread and presents a considerable health concern. Cadmium is known to be a carcinogen; however, the possible mechanism of carcinogenesis with regards to the activation and inactivation of cancer-related genes has not yet been fully elucidated. In this study, amplification, expression, and point mutation of cancer-related genes associated with Cd-induced cell transformation in BALB/c-3T3 cells were studied. Six proto-oncogenes (K-ras, c-myc, c-fos, c-jun, c-sis, and erbB), as well as the p53 tumor suppressor, were investigated for gene amplification using differential polymerase chain reaction (PCR), while the expression of the proteins produced by these genes was evaluated by Western blot analysis. Point mutations in K-ras and p53 were studied by PCR restriction fragment length polymorphism analysis and DNA sequencing. There were no point mutations observed in codons 12, 13, and 61 of K-ras or in exons 4-10 of p53 and no observed differences in the levels of any of the proteins studied. Among 10 Cd-induced transformed cell lines, significant gene amplification was found for c-myc and c-jun in 50% and 80% of the cell lines, respectively. Chromosome painting was performed to confirm that this amplification was not simply due to additional copies of the chromosomes carrying these oncogenes. In addition, reverse-transcription PCR (RT-PCR) was performed to confirm increased expression of c-myc and c-jun. These results suggest that cell transformation induced by Cd may be attributed, at least in part, to gene amplification of c-myc and c-jun and that some of the Cd-transformed cells may possess neoplastic potential resulting from genomic instability.

Mitigative action of monoisoamyl-2,3-dimercaptosuccinate (MiADMS) against cadmium-induced damage in cultured rat normal liver cells

“…Hence, cadmium's effect on cell cycle depends on the type of cells, cadmium concentration and duration of the treatment. Inhibition of cells treated with CdCl 2 in S phase may be as a result of its interference with genes associated with cell growth as reported in earlier studies (Joseph et al, 2001; Spruill et al, 2002). The shifting of the arrest to G0/G1 from S phase by MiADMS may be as a result of MiADMS inhibiting the signal-regulated kinase (ERK) activation responsible for cell proliferation as seen in study with NAC (Kim et al, 2005).…”

Effects of long-term low-dose cadmium exposure on genomic DNA methylation in human embryo lung fibroblast cells

“…Studies showed that cadmium can activate oncogenes or genes associated with cell proliferation, such as c-myc, c-jun or c-fos, both in vivo and in vitro (Joseph et al, 2001;Spruill et al, 2002). This activation may well enhance proliferation in cell population.…”

Cadmium-induced Apoptosis in Murine Macrophages is Antagonized by Antioxidants and Caspase Inhibitors

“…Metallothionein induced by cadmium plays an important role not only as a cadmium carrier by which cadmium accumulates in the nucleus, but also as an inhibitor of zinc finger proteins, which comprise transcriptional factors related to apoptosis (Abshire et al, 1996;Hamada et al, 1997). Cadmiuminduced c-myc, p53, and c-jun expression was suggested as a prelude to apoptosis in human prostate epithelial RWPE-1 and BALB/c 3T3 cells Spruill et al, 2002). Stimulation of p38 mitogen-activated protein kinase (MAPK) was responsible for the cadmium-induced apoptosis in U-937 human promonocytic cells (Galan et al, 2000).…”