Arsenite stabilizes HIF-1α protein through p85α-mediated up-regulation of inducible Hsp70 protein expression

Hypoxia-inducible factor-1α (HIF-1α) has been reported to regulate over 100 gene expressions in response to hypoxia and other stress conditions. In the present study, we found that arsenite could induce HIF-1α protein accumulation in both mouse epidermal Cl41 cells and mouse embryonic fibroblasts (MEFs). Knockout of p85α, a regulatory subunit of PI-3K, in MEFs (p85α(-/-)) dramatically decreased the arsenite-induced HIF-1α accumulation, indicating that p85α is crucial for arsenite effects on the stabilization of HIF-1α protein. Our further studies suggest that arsenite could induce inducible Hsp70 expression, and transfection of inducible Hsp70 into p85α(-/-) MEFs could restore HIF-1α protein accumulation. Moreover, the results using EMSA and Supershift assays indicate that p85α is crucial for arsenite-induced activation of the heat-shock transcription factor 1 (HSF-1), which is responsible for transcription of inducible Hsp70. Taken together, p85α-mediated HIF-1α stabilization upon arsenite exposure is specifically through HSF-1 activation and subsequent up-regulation of the inducible Hsp70 expression.