Bcl-2 proto-oncogene expression in Epstein-Barr-virus-associated nasopharyngeal carcinoma

The bcl-2 proto-oncogene product inhibits apoptosis. Increased levels of bcl-2 protein are associated with prolonged B-cell survival and have been demonstrated in a high proportion of follicular B-cell lymphoma. Recent studies have shown that bcl-2 protein expression in B cells immortalized by Epstein-Barr virus (EBV) in vitro is up-regulated by the EBV-latency-associated antigen, latent membrane protein (LMP) 1. The epithelial malignancy, undifferentiated nasopharyngeal carcinoma (UNPC), has a well-established association with EBV and the tumour cells characteristically display a restricted latent viral phenotype including LMP 1. This study has investigated the relationship between the presence of EBV DNA, EBV phenotypic profiles and bcl-2 protein expression in conventionally processed and cryopreserved samples of NPC using in situ hybridization, immunocytochemical and immunoblotting techniques. bcl-2 was detected in most (80%) samples of UNPC as well as in 1/3 samples of keratinizing NPC and 2/2 samples of nasopharyngeal adenocarcinoma. However, no close correlation was found between the presence of EBV DNA, and profiles for LMP 1 and bcl-2 protein expression in 45 UNPC. In addition, bcl-2 protein was shown to be selectively expressed in the basal compartment of normal nasopharyngeal epithelia. bcl-2 protein expression has not been reported previously in malignant tumours of epithelial origin. The findings in this study implicate a role for bcl-2 both in normal keratinocyte differentiation and in the pathogenesis of epithelial malignancy.