Androgens stimulate hypoxia-inducible factor 1 activation via autocrine loop of tyrosine kinase receptor/phosphatidylinositol 3'-kinase/protein kinase B in prostate cancer cells.

Abstract

Androgen deprivation is implicated in reducing neoangiogenesis in prostate cancer (PCA). Androgens regulate the expression of the vascular endothelial growth factor (VEGF); hypoxia stimulates VEGF expression through the activation of the transcriptional factor, hypoxia-inducible factor 1 (HIF-1). We tested the hypothesis that an effect of androgens on VEGF expression is regulated directly by HIF-1 and HIF-2, and antiandrogens block HIF function. Androgen and antiandrogen effects were evaluated on HIF-1alpha protein and HIF-1 transcriptional activation in human PCA cells. Dihydrotestosterone (DHT) activates HIF-1alpha nuclear protein expression in LNCaP cells but not in androgen receptor-negative PC-3 cells. HIF-1alpha expression is correlated with the transactivation of a hypoxia-responsive element-driven reporter gene and with the production of VEGF protein. The effect of DHT on HIF-1 was blocked by nonsteroidal antiandrogens, flutamide and bicalutamide. DHT does not affect HIF-1alpha mRNA levels but regulates HIF-1alpha protein expression through a translation-dependent pathway. PC-3 cells when incubated with increasing amounts of conditioned medium from LNCaP cells treated with DHT experienced a dose-dependent increase in HIF-1alpha. This induction was not seen either when LNCaP cells were treated with flutamide or conditioned medium were pretreated with antibody to the epidermal growth factor (EGF). HIF-1 activation by DHT was blocked by LY294002, a potent inhibitor of the phosphatidylinositol 3'-kinase signaling pathway, whereas HIF-1 activation by EGF, as ligand, was not inhibited by flutamide. In contrast, HIF-2alpha protein was not affected by androgens or antiandrogens. Androgens activate HIF-1, driving VEGF expression in androgen-sensitive LNCaP cells. This regulation is mediated through an autocrine loop involving EGF/phosphatidylinositol 3'-kinase/protein kinase B, which in turn activate HIF-1alpha and HIF-1-regulated gene expression. Therapeutic actions of antiandrogens in PCA include inhibition of HIF-1 function.