Role of Wnt/β-catenin signaling pathway in epithelial-mesenchymal transition of human prostate cancer induced by hypoxia-inducible factor-1α

Objectives: Epithelial-mesenchymal transition (EMT) is an important process in tumor development, and several studies suggest that the Wnt/beta-catenin signal pathway may play an important role in EMT. However, there is no direct evidence showing that the Wnt/beta-catenin pathway actually determines the EMT induced by an exogenous signal. Our previous research has successfully proved that overexpression of hypoxia-inducible factor-1 alpha (HIF-1 alpha) could induce EMT in LNCaP cells, but not in PC-3. The present study aims to determine whether the signal of HIF-1 alpha for inducing prostate cancer cells to undergo EMT might possibly pass through the Wnt/beta-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/beta-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-1 alpha are EMT negative cell lines, whereas LNCaP/HIF-1 alpha and IA8 have undergone the EMT process. EMT positive cells (LNCaP/HIF-1 alpha 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-1 alpha 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 3 beta (GSK-3 beta) and phospho-GSK-3 beta in LNCaP/HIF-1 alpha, IA8 and PC-3/HIF-1 alpha cells significantly decreased; however, the relative ratios of p-GSK3 beta/t-GSK3 beta in LNCaP/HIF-1 alpha, IA8 and PC-3/HIF-1 alpha cells were significantly higher than PC-3 and LNCaP. Consistently, beta-catenin protein expression increased in LNCaP/HIF-1 alpha and IA8 cells, but not in PC-3/HIF-1 alpha; RT-PCR confirmed these results, except for the enhanced transcription activity of beta-catenin mRNA in PC-3/HIF-1 alpha. Conclusion:Our data suggests that activation of the Wnt/beta-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-1 alpha in prostate cancer cells.