Decreased expression of bcl-2 in moderate and severe oral epithelia dysplasias.

The bcl-2 gene family plays an important role in regulation of apoptosis. We previously reported loss of bcl-2 in peripheries of well and moderately differentiated oral squamous cell carcinoma tumour islands. We aimed to determine bcl-2 and bax gene expression in oral epithelial dysplasias (OED) in relation to apoptosis and proliferation. Samples of normal oral epithelium (OE, n=7), focal epithelial hyperplasia (n=9), mild (n=9), moderate (n=8) and severe (n=18) OED were evaluated by immunohistochemistry, the TUNEL method and in situ hybridisation for bcl-2 and bax mRNA. bcl-2 mRNA and protein were markedly decreased in the basal parts of moderate and severe OED compared with the basal layer of OE (P<0.001) and correlated with a 3-4 fold increase in apoptosis and increased proliferation. bax mRNA and protein were not significantly altered in normal, hyperplastic and dysplastic epithelia. From OE to severe OED, there was an inverse relationship between the bcl-2/bax ratio and apoptosis. Our results indicate that suppression of bcl-2 may have a role in oral tumourigenesis.