Overexpression of p16 and p14ARF is associated with human papillomavirus infection in cervical squamous cell carcinoma and dysplasia

The CDKN2 gene encodes two structurally different proteins: a cyclin-dependent kinase inhibitor, p16, which regulates retinoblastoma protein (pRb)-dependent G1 arrest, and a cell cycle inhibitor, p14ARF, which blocks MDM2-induced p53 degradation resulting in an increase in p53 levels that leads to cell cycle arrest. Recent studies have revealed that expression of p16 and p14ARF is influenced markedly by the status of pRb and p53, and p16 overexpression has been demonstrated in cervical neoplasia because of functional inactivation of pRb by the human papillomavirus (HPV) E7 protein. To clarify the p14ARF status and the relationship between p16/p14ARF and other cell cycle molecules in cervical carcinogenesis, immunohistochemical analysis of p16, p14ARF, p53 and MDM2 was performed on 65 samples of cervical and genital condylomatous and neoplastic lesions, including nine HPV-negative tumors. In most cervical cancers and preneoplastic lesions with HPV infection of high and intermediate risk, a marked overexpression of p14ARF as well as the p16 protein (i.e. dotted nuclear immunostaining) was observed. All condyloma acuminata except one and low-grade dysplasia with HPV infection of low risk, such as HPV 6, immunohistochemically showed completely negative staining for p14ARF, also seen in non-neoplastic and mesenchymal cells. Our results clearly show that the mode of p14ARF overexpression in cervical neoplastic cells with HPV association differs from that in cancers of other organs without HPV association, and the p14ARF overexpression may be attributable to a negative feedback result in the functional inactivation of the pRb and p53 proteins by HPV oncoproteins.