THE EPSTEIN-BARR-VIRUS LMP1 CYTOPLASMIC CARBOXY-TERMINUS IS ESSENTIALFOR B-LYMPHOCYTE TRANSFORMATION - FIBROBLAST COCULTIVATION COMPLEMENTS A CRITICAL FUNCTION WITHIN THE TERMINAL-155 RESIDUES

Recombinant Epstein-Barr viruses (EBVs) were made with mutated latent membrane protein 1 (LMP1) genes that express only the LMP1 amino-termi nal cytoplasmic and sis transmembrane domains (MS187) or these domains and the first 44 amino acids of the 200-residue LMP1 carboxy-terminal domain (MS231). After infection of primary B lymphocytes with virus s tocks having small numbers of recombinant virus and large numbers of P 3HR-1 EBV which is transformation defective but wild type (WT) for for LMP1, all lymphoblastoid cell lines (LCLs) that had MS187 or MS231 LM P1 also had WT LMP1 provided by the coinfecting P3HR-1 EBV. Lytic viru s infection was induced in these coinfected LCLs, and primary B lympho cytes were infected. In over 200 second-generation LCLs, MS187 LMP1 wa s never present without WT LMP1. Screening of over 600 LCLs infected w ith virus from MS231 recombinant virus-infected LCLs identified two LC Ls which were infected with an MS231 recombinant without WT LMP1. The MS231 recombinant virus could growth transform primary B lymphocytes w hen cells were grown on fibroblast feeders. Even after 6 months on fib roblast feeder layers, cells transformed by the MS231 recombinant viru s died when transferred to medium without fibroblast feeder cells. The se data indicate that the LMP1 carboxy terminus is essential for WT gr owth transforming activity. The first 44 amino acids of the carboxy-te rminal cytoplasmic domain probably include an essential effector of ce ll growth transformation, while a deletion of the rest of LMP1 can be complemented by growth on fibroblast feeder lavers. LMP1 residues 232 to 386 therefore provide a growth factor-like effect for the transform ation of B lymphocytes. This effect may be indicative of the broader r ole of LMP1 in cell growth transformation.