CYTOSTATIC EFFECT OF EPSTEIN-BARR-VIRUS LATENT MEMBRANE PROTEIN-1 ANALYZED USING TETRACYCLINE-REGULATED EXPRESSION IN B-CELL LINES

Tetracycline-regulated vectors were used to obtain inducible expressio n in stable transfected B cell lines of two Epstein-Barr virus (EBV) l atent genes, LMP1 and EBNA2. The transfected genes were tightly repres sed by low, nontoxic concentrations of tetracycline (less than or equa l to 1 mu g/ml) and, following removal of tetracycline, were induced t o levels comparable to or up to 3X that of EBV-transformed normal lymp hoblastoid cell lines. In transfected DG75 cells, induced expression o f LMP1, but not of EBNA2, led to the expected upregulation of various cell surface markers, including: CD40, CD54, CD58, and HLA class I. A novel observation was that both LMP1 and EBNA2 independently caused th e downregulation of surface IgM, an effect mirrored in EBV-positive Bu rkitt lymphoma lines undergoing phenotypic drift during the transition from latency I to latency III in which both LMP1 and EBNA2 are upregu lated. Most remarkably, induced LMP1 expression almost completely inhi bited cell growth for 4 to 5 days, after which the cells recovered a l imited proliferative capacity. The cytostatic effect of LMP1 was obser ved in all three a cell lines studied: DG75, BJAB, and Akata. Further analysis showed that induction of LMP1 coincided with a reduction in t he levels of c-myc, and that the cytostatic effect was due to an accum ulation of cells at the G(2)/M phase of the cell cycle. These data sug gest a novel function for the LMP1 oncogene in controlling the prolife ration of EBV-infected cells by regulating progress through G(2)/M pha se. (C) 1996 Academic Press, Inc.