Androgen receptor and HIF-1α interaction in prostate cancer.

Abstract

197 Background: Prostate cancer is the most common noncutaneous cancer among men in the United States, and its progression is largely controlled by the androgen receptor (AR). Androgen deprivation therapy (ADT) is an initially effective treatment for prostate cancer, but most tumors eventually become castrate resistant. Tumor hypoxia also appears to be associated with a poor prognosis in prostate cancer. HIF-1a regulates the transcription of genes that allow tumor survival and growth in low oxygen conditions. Our laboratory has data showing that in response to castration and anti-androgen therapy in mice, there was a strong transcriptional relationship between HIF-1a and AR, as measured by quantitative RT-PCR, suggesting an interaction between the two proteins. Thus, the purpose of this study was to determine if there is a molecular interaction between HIF-1a and AR in prostate cancer cells. Methods: We used Western blot analysis to examine the expression levels of HIF-1a and AR in LNCaP prostate cancer cells to determine if they are upregulated together at the protein level. Four experimental conditions were tested: control (no treatment), DHT for induction of AR expression, CoCl2 for induction of HIF-1a, and a combination treatment of DHT and CoCl2. Immunoprecipitation experiments were carried out to determine if there is an association between HIF-1a and AR. In addition, cells were fractionated into nuclear and cellular cells extracts, followed by Western blot analysis to determine where in the cells this interaction occurs. Results: Western blot analysis of cell lysates showed synergistic upregulation of both HIF-1a and AR expression only under combined CoCl2 and DHT treatment conditions. In addition, immunoprecipitation experiments showed that HIF-1a and AR exist in a complex with one another, and fractionation experiments indicated this complex occurs in the nucleus. Conclusions: Our results demonstrate that HIF-1a and AR associate with one another in cells. Binding assays are in progress to determine the nature of this interaction. In addition, we are examining the cellular consequences of this protein interaction, as it is possible that upregulation of HIF-1a in response to low androgen contributes to the development of tumor resistance to ADT.