Background: To understand the mechanism of frequent and early lymph node metastasis in high-risk human papillomavirus (HPV)-associated oropharyngeal squamous cell carcinoma (OPSCC), this study investigated whether β-catenin is regulated by the HPV oncoprotein and contributes to OPSCC metastasis.
Methods: Expression levels of p16, β-catenin, and epidermal growth factor receptor (EGFR) were examined in OPSCC samples (n = 208) by immunohistochemistry. The expression and subcellular localization of β-catenin and EGFR activation were also studied in HPV-positive and HPV-negative head and neck squamous cell carcinoma cell lines with western blot analysis. HPV16 E6 small interfering RNA was used to elucidate the effect of the HPV oncoprotein on β-catenin translocation. The involvement of EGFR in β-catenin translocation was confirmed by treatment with erlotinib. Moreover, the invasive capacity was evaluated after HPV16 E6/E7 repression.
Results: The results showed that the membrane weighted index of β-catenin was inversely correlated with p16 positivity (P < .001) and lymph node metastasis (P = .026), whereas nuclear staining of β-catenin was associated with p16-positive OPSCC (P < .001). A low level of membrane β-catenin expression was significantly associated with disease-free and overall survival (P < .0001 in both cases). Furthermore, the membrane weighted index of EGFR was inversely correlated with p16 positivity (P < .001) and positively correlated with membrane β-catenin (P < .001). The in vitro study showed that HPV16 E6 repression led to reductions of phospho-EGFR and nuclear β-catenin, which were also observed after erlotinib treatment, and inhibition of invasion.
Conclusions: The findings suggest that HPV16 E6 mediates the translocation of β-catenin to the nucleus, which may be regulated by activated EGFR.
Keywords: epidermal growth factor receptor (EGFR); human papillomavirus 16 (HPV); lymph node metastasis; oropharyngeal squamous cell carcinoma; β-catenin.
© 2014 American Cancer Society.