Evaluation of HPV16 E7 expression in head and neck carcinoma cell lines and clinical specimens

Human papillomavirus (HPV) 16 infection in the oropharynx is one of the major risk factors for oropharyngeal carcinoma. Although the HPV E6 and E7 proteins are known to have a role in head and neck carcinogenesis, whether their expression is maintained once the tumour has developed still remains unclear. We evaluated the expression of these proteins in HPV16-positive cancer cell lines and clinical oropharyngeal specimens. Two out of the four commercially available antibodies directed against the E7 protein could detect the E7 protein overexpressed in the 293FT cells, human embryonic kidney cells, although none of the four commercially available anti-E6 antibodies could detect the overexpressed E6 protein. Whereas HPV16-positive head and neck or cervical carcinoma cell lines expressed the E7 mRNA, the antibodies with an ability to detect the E7 protein could not detect it in western blotting in these HPV16-positive cell lines. In clinical specimens, E7 protein was partially detected in p16-positive area in p16-positive and HPV16 DNA-positive samples, but not in p16-negative and HPV DNA-negative or p16-positive and HPV DNA-negative samples. Consistent with these findings, the E7 protein was poorly translated from the endogenous structure of the E7 mRNA, although significant E7 mRNA expression was detected in these samples. Our findings indicate that E7 protein is partially expressed in p16-positive area in p16-positive and HPV16 DNA-positive clinical specimens.