Transcriptional upregulation of HSP70-2 by HIF-1 in cancer cells in response to hypoxia

Abstract

Heat shock protein 70-2 (HSP70-2) can be expressed by cancer cells and act as an important regulator of cancer cell growth and survival. Here, we show the molecular mechanisms by which hypoxia regulate HSP70-2 expression in cancer cells. When cells were subjected to hypoxia (1% O2), the expression of HSP70-2 had a significant increase in cancer cells. Such increase was due to the direct binding of hypoxia-inducible factor to hypoxia-responsive elements (HREs) in the HSP70-2 promoter. By luciferase assays, we demonstrated that the HRE1 at position -446 was essential for transcriptional activation of HSP70-2 promoter under hypoxic conditions. We also demonstrated that HIF-1alpha binds to the HSP70-2 promoter and the binding is specific, as revealed by HIF binding/competition and chromatin immunoprecipitation assays. Consequently, the upregulation of HSP70-2 enhanced the resistance of tumor cells to hypoxia-induced apoptosis. These findings provide a new insight into how tumor cells overcome hypoxic stress and survive, and also disclose a new regulatory mechanism of HSP70-2 expression in tumor cells.