FUNCTIONAL DIFFERENCES BETWEEN BHRF1, THE EPSTEIN-BARR-VIRUS-ENCODED BCL-2 HOMOLOG, AND BCL-2 IN HUMAN EPITHELIAL-CELLS

BHRF1 a component of the restricted early antigen complex of the Epste in-Barr virus lytic cycle, encodes a 17-kDa protein with both sequence and functional homology to the antiapoptotic Bcl-2 oncogene, Recent w ork has suggested that BHRF1 behaves like Bcl-2 in protecting cells fr om apoptosis induced by a range of stimuli. In this study, the effect of BHRF1 and Bcl-2 an the growth and differentiation of the SCC12F hum an epithelial cell line was examined. The levels of stable transfected BHRF1 expression achievable in SCC12F cells was consistently lower th an that obtained with Bcl-2. While both BHRF1 and Bcl-2 inhibited epit helial differentiation. the effect of Bcl-2 was more pronounced, resul ting in an almost complete blockade of differentiation in organotypic raft cultures. However, BHRF1-expressing SCC12F cells proliferated at a much higher rate than SCC12F cells expressing Bcl-2, and this effect was supported by cell cycle analysis which demonstrated that BHRF1. b ut not Bcl-2, promotes rapid transit through the cell cycle. These dat a highlight important differences between BHRF1 and Bcl-2 and suggest that BHRF1 may function to promote the survival and proliferation of l ytically infected cells. The proliferative properties of BHRF1 describ ed in this study, together with the demonstration that other oncogenic gamma herpesviruses encode Bcl-2 homologues, suggests that these prot eins may serve to increase the susceptibility of virus-infected cells to oncogenic transformation, thereby contributing to the development o f virus-associated tumors.