Expression of Bcl-2 and Bcl-x Genes in Lymphocytes and Tumor Cell Lines Derived from MDV-infected Chickens

To characterize the molecular events involved in both apoptosis and transformation process induced by Marek's disease virus (MDV), the expressions of the bcl-2 and bcl-x genes, ones of the dominant apoptosis-regulating genes, in Marek's disease (MD) tumor cell lines and cells prepared from MDV-infected chickens were analyzed. The expression of bcl-2 was down-regulated in both CD4+ and CD8+ T cells prepared from MDV-infected chickens at 3 weeks p.i. No bcl-2 transcript was detected in MD tumor-derived MSB1 and MTB1 cell lines, which had been established from primary MD tumors. On the other hand, the bcl-xL transcript whose product can also inhibit apoptosis was expressed in cell lines derived from MD. By the treatment with phorbol 12-myristate 13-acetate (PMA) and ionomycin, normal CD4+ T cells were induced to express bcl-xS which can promote apoptosis, while bcl-xL was constitutively expressed in MD cell lines. Our results suggest that bcl-xL rather than bcl-2 might play an important role in the transformation process by MDV.