Aberrant genes expression, genomic instability and increased cell proliferation of mouse testicular Leydig cells by sodium arsenite: a possible mechanism for arsenic-induced carcinogenesis

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Arsenic is an established environmental carcinogen, however, the mechanism for arsenic-induced cancer is not well understood. Genotoxicity of arsenic has been a topic of controversy. We have recently reported arsenic-induced cell proliferation and genetic (mutations) and epigenetic changes (methylation) in mouse testicular Leydig cells. The purpose of this study was to elucidate the mechanism for arsenic-induced genomic instability and increased cell proliferation by identifying the genes with aberrant expression in long- term arsenic treated TM3 cells, a mouse testicular Leydig cells. Cells were plated onto a 100-mm Petri dish and were grown in the medium containing various concentrations of sodium arsenite (1ng/ml, 100ng/ml, and 1μg/ml). After every 5 days, the cells grown to near confluence were sub-cultured, replated at the same cell density, and treated with arsenite at the same concentrations. Using this approach the cells were grown in sodium arsenite containing medium for 15 passages. RNA was isolated from cells collected at final passage (passage # 15). Real-time quantitative RT-PCR was performed to measure the expression of genes for the maintenance of genomic stability, transcription factors, and cell cycles. Global gene expression profiling by differential display method was also performed with the objective to identify additional gene(s) whose altered expression might be associated with arsenic-induced carcinogenesis. The result of this study revealed reduced expression of DNA repair genes and increased expression of DNA methyl Transferase I (DNMT-I), as well as cell proliferation marker genes. Additionally, the data of differential display revealed dose dependently either increase or decrease of several genes transcripts in arsenic treated cells. Further characterizations of these target gene transcripts are underway. Thus the present finding of aberrant expression of known genes (DNA repair, DNA methyl transferase I, and cell cycle genes) and its consequences resulting in the genomic instability as reported previously by us provides a mechanistic basis for the arsenic-induced carcinogenesis.

Acknowledgements: This work was supported by NIH grant # RR03045.