Prolonged proliferation of primary chicken embryo fibroblasts transfected with cDNAs from the BamHI-H gene family of Marek's disease virus

Oncogenic virus-specific 1.69 kb and 1.5 kb cDNAs, derived from the tumorigenicity-associated BamHI-H gene family of Marek's disease virus (MDV), were cloned into the eukaryotic expression vector (PRC/CMV) and designated as PRC/CMV-1.69 and PRC/CMV-1.5, respectively. Chicken embryo fibroblasts (CEFs) transfected with PRC/CMV-1.69 or PRC/CMV-1.5 plasmid DNA showed reduced serum-dependence for growth compared with PRC/CMV vector-transfected CEFs. Also, PRC/CMV-1.69 or PRC/CMV-1.5 DNA transfected CEFs proliferated for a longer period of time (20-22 passages) compared with the CEFs transfected with PRC/CMV plasmid DNA (10 passages). Reduced serum-dependence for growth and prolonged proliferation of CEFs after in vitro transfection with PRC/CMV- 1.69 or PRC/CMV-1.5 indicated that these two cDNAs stimulate cell growth. These data indicated that one of the functions of the BamHI-H gene family of MDV is cell-growth control, which may play an important role in the establishment and maintenance of uncontrolled growth of tumor cells induced by MDV.