Cell phenotype-dependent control of Epstein-Barr virus latent membrane protein 1 gene regulatory sequences.

Growth transformation-associated Epstein-Barr virus-encoded genes are differentially regulated depending on the host cell phenotype. We have previously identified an LMP1 regulatory region (LRS) 5' of the LMP1 gene (+40 to -634) and analyzed its role in transcription initiation in the EBV-negative Burkitt's lymphoma line DG 75 (Fåhraeus et al., 1990a). In order to investigate the cell phenotype dependence of LMP1 gene regulation we have now compared the activity of positive and negative cis-acting LRS elements in cell lines of B lymphoid and epithelial cell origin in the presence and absence of the virus-encoded nuclear antigen EBNA2. Our results show that reporter plasmids that contain only the -54/+40 region of LRS are active in all tested cell lines. Furthermore, the previously identified negative cis-elements in the -144/-54 region were found to suppress promoter activity independent of the cell phenotype. EBNA2 was able to override the effect of the negative elements in all lines of B-cell origin, whereas it had no effect in epithelial lines. The positive effect of EBNA2 was mediated by cis-acting elements in the -214/-144-bp region. In all six tested cell lines of epithelial origin, reporter plasmids that carried the full-length LRS were active, independent of EBNA2. The LMP1 promoter in these constructs was activated by the concerted action of EBNA2-independent, positive elements in the -214/-144 and -324/-214 positions that counteracted the effect of the negative LRS elements.