RELATIONSHIP OF P53 OVEREXPRESSION TO OTHER CELL-CYCLE REGULATORY PROTEINS IN ORAL SQUAMOUS-CELL CARCINOMA

Aberrations of the p53 gene and the overexpression of its protein are described in a variety of neoplasms, including oral and other head and neck cancers. Here we report the association of p53 (over)expression with a downstream cell cycle inhibitor p21/waf1 in oral squamous cell carcinoma (SCC). The loss of expression of p16 and p27, two other cycl in-dependent kinase (cdk) inhibitors, was also examined. In this panel of tumours, 10/24 carcinomas were p53-immunopositive. Heterogeneous e xpression of p21 and p27 was seen in 10/24 SCC and 9/16 SCC, respectiv ely, and this was not correlated to p53 status. The expression of p21 and p27 in these SCCs suggests the existence of mechanisms by which so me growing tumour cells may tolerate these cell cycle inhibitors; eigh t SCCs lacked expression of both inhibitors but only two of these canc ers overexpressed p53, suggesting that accumulation of p21/p27 can be independent of the functional status of the p53 gene. Data do not supp ort a clear example of a phenotype that shows an overexpression of p53 with downregulation of p21 or p27 leading to cell cycle alterations. Furthermore, only three SCCs were p16-negative and p53-positive. This suggests that these two tumour suppressors may act in separate pathway s.