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GENE EXPRESSION PROFILES IN ARSENIC-TREATED MCF-7 BREAST CANCER CELLS EXPRESSING DIFFERENT LEVELS OF HSP70
Citation:
Allen, J W., G M. Nelson, E. Winkfield, S D. Hester, AND J A. Barnes. GENE EXPRESSION PROFILES IN ARSENIC-TREATED MCF-7 BREAST CANCER CELLS EXPRESSING DIFFERENT LEVELS OF HSP70. Presented at AACR 95th Annual Meeting, Orlando, Florida, 3/27-31/04.
Description:
Gene expression profiles in arsenic-treated MCF-7 breast cancer cells expressing different levels of HSP70
Gail Nelson, Susan Hester, Ernest Winkfield, Jill Barnes, James Allen
Environmental Carcinogenesis Division, NHEERL, ORD, US Environmental Protection Agency, Research Triangle Park, NC and College of Veterinary Medicine, North Carolina State University, Raleigh, NC
Arsenic is a naturally-occurring element that has carcinogenic potential. Widespread human exposure to arsenic can occur through consumption of contaminated drinking water. Stress responses to arsenic are known to involve increased levels of the cytoprotective protein, HSP70, a molecular chaperone which functions in DNA repair and apoptosis pathways. We have previously developed an MCF-7 breast cancer cell line with doxycycline regulation of HSP70 expression and demonstrated that HSP70 over-expression is associated with faster cell cycling, and with protection from arsenic-induced clastogenic and aneugenic effects. In the present studies, arsenic effects on gene expression were evaluated in MCF-7 cells under both HSP70 overexpressing and non-overexpressing conditions. Total RNA was isolated from 5 M sodium arsenite-treated (24 hrs. exposure) and untreated cells. Differential gene expression was determined for duplicate samples using custom spotted 20K oligo microarrays and 2-dye (Cy3/Cy5) flourescent labeling. Of the 63 genes identified as differentially expressed (> 2.5-fold up- or down-regulated by arsenic in both replicates), 33 were up-regulated in at least one of the HSP70 expression conditions, and 31 were down-regulated. Genes with altered expression fell primarily into the signal transduction and cell growth functional categories. Of the differentially expressed genes, 12 were up-regulated in both HSP70 expression conditions, including heme oxygenase, serine threonine kinase, and metallothionein genes, all of which are reported in the literature to be arsenic-induced. While these results help confirm the reliability of our data, of greater interest to this study is identifying genes for which the arsenic-induced expression differs between the two alternative HSP70 expression conditions. Heme oxygenase and serine threonine kinase 39 expression, although up-regulated in both conditions, are approximately 5-fold and 8-fold higher, respectively, in the HSP70 overexpressing cells than in the non-overexpressing cells. Both of these genes are involved in cell cycle regulation. Expression of other genes, such as Ca++ transporting ATPase, insulinoma-associated 1, and growth arrest specific, are 7-fold or more lower in the HSP70 overexpressing cells as compared to the non-overexpressing cells. Growth differentiation factor 3 is down-regulated approximately 4-fold more in the HSP70 non-overexpressing cells than in the overexpressing cells. The gene expression profiles reported here, suggesting altered cell regulation and growth, are consistent with the observed phenotype of rapid cycling in HSP70 overexpressing cells. Further gene expression research to clarify the protective role of HSP70 and associated cell cycle patterns in relation to arsenic genotoxicity is underway. [This abstract does not necessarily reflect EPA policy].