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INDUCIBLE HEAT SHOCK PROTEIN (HSP70-1) PROTECTS MCF-7 CELLS FROM THE CYTOTOXIC AND GENOTOXIC EFFECTS OF ARSENITE
Citation:
Barnes, J, D J. Dix, J B. Garges, B W. Collins, AND J W. Allen. INDUCIBLE HEAT SHOCK PROTEIN (HSP70-1) PROTECTS MCF-7 CELLS FROM THE CYTOTOXIC AND GENOTOXIC EFFECTS OF ARSENITE. Presented at GEMS, October 25, 1999.
Description:
Heat shock proteins (HSPs) belong to the highly conserved family of stress proteins and are induced following exposure to arsenic. Elevated HSPs protect against cellular damage from heat but it is unclear wether HSP induction alters the damaging effects of environmental chemical contaminants. Therefore, this study was designed to investigate the effects of sodium arsenite (As) in MCF-7 cells that overexpress inducible HSP70 (HSP70-1). A tetracycline-controlled expression system was developed to regulate HSP70-1 levels. Clone 14 (C 14) cells exhibited the highest induction of HSP70-1 in the absence of doxycycline ("ON") and HSP70-1 could be down-regulated to control levels in the presence of doxycycline ("OFF"). In order to examine the cytotoxic and genotoxic effects of sodium arsenite, C140N and C140FF cells were exposed to either 0 (control), 5 uM or 10 uM As. For cytotoxicity studies, cells were exposed for 24 hours and assayed for viability and apoptosis using acridine orange and ethidium bromide staining. Both C14ON and C14OFF cells showed a dose-dependent decrease in cell viability and increase in apoptosis in response to arsenite. However, cells expressing elevated HSP70-1 were significantly less affected than cells that did not overexpress HSP70-1. The genotoxicity of arsenite was evaluated using a cytokinesis-block micronucleus (MN) assay. MN were induced in both C140N and C140FF cells in response to As. However, induction levels of MN were significantly lower in HSP70-1 overexpressing cells as compared to cells that expressed control levels of HSP70-1 (p< 0.05). Kinetochore immunostaining of MN revealed that both kinetochore positive (K+) and kinetochore negative (K-) MN were elevated in response to As. Interestingly, K+ MN were more elevated over control levels than were K- MN. Collectively, these data demonstrate a protective effect of HSP70-1 expression on the cytotoxic and genotoxic effects of arsenite in MCF-7 cells.