Expression of programmed cell death regulatory p53 and bcl-2 proteins in oral lesions

With the ultimate goal of characterizing the molecular pathogenesis of oral cancer, the most predominant malignancy in India, immunocytochemical evaluation of p53 and bcl-2 proteins was carried out in hypeplastic oral mucosa, dysplastic oral mucosa and invasive oral cancer. All subjects gave a similar and almost uniform history of prolonged use of betal quid and tobacco. Expression of p53 was insignificant while bcl-2 was absent in hyperplastic leukoplakia lesions. Both proteins were however expressed in leukoplakia with apparent dysplasia. Almost all invasive cancer lesions showed high levels of both p53 and bcl-2. Good correlation was therefore evident between expression of these two proteins and increasing histologic abnormality. Moreover relative risk evaluation revealed that lesions expressing p53 and bcl-2 had a high probability of having a histology of dysplasia or worse. Since it has been previously shown that wild type p53 regulates the expression of bcl-2, it may be presumed that the protein detected in the dysplastic and malignant oral tissue is of the mutant type. It is also known that p53 is a positive regulator of programmed cell death or apoptosis while bcl-2 is an anti-apoptotic protein. This suggests the possibility that alterations in p53 followed by over-expression of bcl-2 occur early in oral carcinogenesis resulting in defective apoptosis and subsequent tumor progression.