Immunohistochemical inactivation of p14ARF concomitant with MDM2 overexpression inversely correlates with p53 overexpression in oral squamous cell carcinoma

The CDKN2 gene encodes two structurally different proteins: a cyclin-depend ent kinase inhibitor called p16, which regulates retinoblastoma protein (pR b)-dependent G1 arrest, and a cell cycle inhibitor designated p14ARF, which arrests cell growth in G1-S and also in G2-M. Whereas inactivation of p16 has been described as a frequent event in various cancers, including oral c ancer, the current function of p14ARF is still poorly understood. A physica l association between p14ARF and MDM2 blocks MDM2-induced p53 degradation, resulting in increased levels of p53, which in turn leads to cell cycle arr est. The present study immunohistochemically examined the expression of p16 and p14ARF together with pRb, MDM2 and p53 status in a series of oral canc ers. The results showed that p14ARF was frequently absent in the oral cance rs (15/37, 41%) as was p16 immunostaining. Concomitant immunopositivity for p14ARF and MDM2 overexpression was frequently observed in a subset of the cancers, whereas an inverse correlation between p14ARF and MDM2 expression and the diffuse staining of p53 was clearly detected. Moreover, the results showed that in most cases of oral cancer (35/37, 95%) at least one protein was altered, and lymph node metastasis was more frequent in the tumors wit h alterations in both the p16/pRb and p14ARF/p53 pathway (8/16, 50%) than i n the tumors with one or no alteration of these two major pathways.