PI3K/Akt/HIF-1α signaling pathway mediates HPV-16 oncoprotein-induced expression of EMT-related transcription factors in non-small cell lung cancer cells

Our previous studies have demonstrated that human papillomaviruse (HPV)-16 oncoproteins promoted epithelial-mesenchymal transition (EMT), leading to non-small cell lung cancer (NSCLC) progression, but the underlying molecular mechanisms still remain unclear. PI3K/Akt/HIF-1 signaling pathway has been reported to mediate hypoxia-induced EMT. In this study, we further explored the role of PI3K/Akt/HIF-1 signaling pathway in HPV-16 oncoprotein-induced EMT in NSCLC cells. Methods: A549 and NCI-H460 NSCLC cells were transiently transfected with pEGFP-HPV-16 E6 or E7 constructs. Western blotting and RT-qPCR were respectively performed to determine the protein and mRNA expression of EMT-related transcription factors. HPV-16 E6 or E7-transfected NSCLC cells were co-transfected with specific HIF-1-siRNA or pretreated with different concentrations of LY294002, a specific PI3K inhibitor, followed by the analysis of expression of EMT-related transcription factors. The correlation between HIF-1 and EMT-related transcription factors in NSCLC tissues was analyzed by immunohistochemical staining and Spearman rank correlation coefficient. Results: HPV-16 E6 and E7 oncoproteins upregulated the expression of Slug and Twist1, the EMT-related transcription factors, at both protein and mRNA levels in A549 and NCI-H460 cells. The co-transfection with specific HIF-1-siRNA, but not the non-specific (NS)-siRNA, significantly abrogated HPV-16 oncoprotein-induced upregulation of ZEB1, Snail1, Slug, and Twist1 at both protein and mRNA levels. Additionally, pretreatment with LY294002 obviously blocked HPV-16 E6-and E7-induced Snail1, Slug, and Twist1 protein expression in A549 and NCI-H460 cells. Further analysis of clinical specimens showed that HIF-1 protein was strongly expressed in NSCLC tissues, which was positively correlated with ZEB1, Snail1, Slug, and Twist1 protein expression.