Activation of HIF-1α/β-catenin signal pathway leads to radioresistance of prostate cancer cells

Abstract

Objective: To investigate the role of hypoxia-inducible factor-1α (HIF-1α) and β-catenin in radioresistance of prostate cancer (PCa) cells. Method: Two PCa cell lines, LNCaP and C4-2B, were grouped as: negative control (no treatment), HIF-1α overexpression group (transfected with HIF-1α plasmids), and β-catenin silencing group (transfected with HIF-1α plasmids and β-catenin-shRNA). Cell proliferation, cycle, invasion, and radiosensitivity were measured under normal or hypoxic condition. Radiosensitivity was tested in two mice PCa models (the LNCaP orthotopic BALB/c-nu mice model and the C4-2B subcutaneous SCID mice model). Results: In both LNCaP and C4-2B cells, HIF-1α transfection led to an enhanced β-catenin nuclear translocation, while β-catenin silencing inhibited the β-catenin nuclear translocation. Enhanced β-catenin nuclear translocation caused by HIF-1α overexpression resulted in enhanced cell proliferation and invasion, altered cell cycle distribution, reduced apoptosis, and improved non-homologous-end-joining (NHEJ) repair under irradiation condition. In vivo imaging of orthotopic models showed that HIF-1α overexpression LNCaP cells produced tumors with 3-fold volume (P=0.003 1) and 2-fold wet weight (P=0.039 4) than those by negative control cells at day 21, and β-catenin silencing cells aberrantly reduced both tumor volume (P=0.000 3) and wet weight (P=0.017 5) than HIF-1α overexpression cells. In addition, C4-2B subcutaneous models showed similar tumor promotion effects induced by HIF-1α overexpression (tumor volume: P=0.000 1 and wet weight: P=0.047 3) and suppressive effects by β-catenin silencing (tumor volume: P<0.000 1 and wet weight: P=0.022 1) as LNCaP orthotopic xenograft with regard to tumor volume and wet weight. Conclusions: HIF-1α overexpression enhanced β-catenin nuclear translocation, which led to the activation of the β-catenin/NHEJ signaling pathway and increased cell proliferation, invasion, and DNA repair. These results suggest that HIF-1α overexpression led to radioresistance of PCa cells.