Objectives: Epithelial-mesenchymal transition (EMT) is an important process in tumor development, and several studies suggest that the Wnt/b-catenin signal pathway may play an important role in EMT. However, there is no direct evidence showing that the Wnt/b-catenin pathway actually determines the EMT induced by an exogenous signal. Our previous research has successfully proved that overexpression of hypoxiainducible factor-1a (HIF-1a) could induce EMT in LNCaP cells, but not in PC-3. The present study aims to determine whether the signal of HIF-1a for inducing prostate cancer cells to undergo EMT might possibly pass through the Wnt/b-catenin pathway. Methods: Epithelial-mesenchymal transition associated proteins were detected in several human prostate carcinoma cell lines by Western blot, and then we distinguished the EMT positive cell lines from the EMT negative cell lines. Furthermore, we evaluated the possible correlation between potency of invasiveness and proliferation among these cell lines with different characteristics of EMT using Matrigel transwell and thiazolyl blue tetrazolium bromide (MTT) assays. Finally, the different expression of some critical proteins and genes in Wnt/b-catenin signaling pathway were analyzed by Western blot and reverse transcription-polymerase chain reaction (RT-PCR) in these cells with different characteristics of EMT. Results: Among several prostate cancer cell lines, PC-3, LNCaP and PC-3/HIF-1a are EMT negative cell lines, whereas LNCaP/HIF-1a and IA8 have undergone the EMT process. EMT positive cells (LNCaP/HIF-1a and IA8) exhibit much stronger potency of invasiveness and proliferation than those of PC-3 and LNCaP, which belong to EMT negative cells. Interestingly, although PC-3/HIF-1a had not completed the EMT process, it still displayed stronger potency of invasion and proliferation, resembling EMT positive cells. The protein expression level of total glycogensynthase kinase 3b (GSK-3b) and phospho-GSK-3b in LNCaP/HIF-1a, IA8 and PC-3/HIF-1a cells significantly decreased; however, the relative ratios of p-GSK3b/t-GSK3b in LNCaP/HIF-1a, IA8 and PC-3/HIF-1a cells were significantly higher than PC-3 and LNCaP. Consistently, b-catenin protein expression increased in LNCaP/HIF-1a and IA8 cells, but not in PC-3/HIF-1a; RT-PCR confirmed these results, except for the enhanced transcription activity of b-catenin mRNA in PC-3/HIF-1a. Conclusion: Our data suggests that activation of the Wnt/b-catenin signaling pathway correlates with the characteristic of EMT and potency of invasiveness and proliferation. This may be the critical factor that directly controls the process of EMT induced by HIF-1a in prostate cancer cells.

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Hypoxia-inducible factor-1α (HIF-1α) is known to play crucial roles in tumor radioresistance; however, the molecular mechanisms responsible for the promotion of tumor radioresistance by HIF-1α remain unclear. β-catenin is known to be involved in the metastatic potential of prostate cancer (PCa). In this study, to investigate the role of HIF-1α and β-catenin in the radioresistance of PCa, two PCa cell lines, LNCaP and C4-2B, were grouped as follows: Negative control (no treatment), HIF-1α overexpression group (transfected with HIF-1α overexpression plasmid) and β-catenin silenced group (transfected with HIF-1α plasmids and β-catenin-shRNA). Cell proliferation, cell cycle, cell invasion and radiosensitivity were examined under normal or hypoxic conditions. In addition, radiosensitivity was examined in two mouse PCa models (the LNCaP orthotopic BALB/c-nu mice model and the C4-2B subcutaneous SCID mice model). Our results revealed that in both the LNCaP and C4-2B cells, transfection with HIF-1α overexpression plasmid led to an enhanced β-catenin nuclear translocation, while β-catenin silencing inhibited β-catenin nuclear translocation. The enhanced β-catenin nuclear translocation induced by HIF-1α overexpression resulted in an enhanced cell proliferation and cell invasion, an altered cell cycle distribution, decreased apoptosis, and improved non-homologous end joining (NHEJ) repair under normal and irradiation conditions. Similar results were observed in the animal models. HIF-1α overexpression enhanced β-catenin nuclear translocation, which led to the activation of the β-catenin/NHEJ signaling pathway and increased cell proliferation, cell invasion and DNA repair. These results thus suggest that HIF-1α overexpression promotes the radioresistance of PCa cells.