The latency-associated nuclear antigen encoded by kaposi's sarcoma-associated herpesvirus activates two major essential Epstein-Barr virus latent promoters

The latency-associated nuclear antigen (LANA) encoded by the Kaposi's sarco ma-associated herpesvirus (KSHV) is expressed in the majority of KSHV-infec ted cells and in cells coinfected with Epstein-Barr virus (EBV). In coinfec ted body cavity-based lymphomas (BCBLs), EBV latent membrane protein 1 (LMP 1), which is essential for B-lymphocyte transformation, is expressed. EBNA2 upregulates the expression of LMP1 and other cellular genes through specif ic interactions with cellular transcription factors tethering EBNA2 to its responsive promoters. In coinfected BCBL cells, EBNA2 is not detected but L ANA, which is constitutively expressed, contains motifs suggestive of poten tial transcriptional activity. Additionally, recent studies have shown that LANA is capable of activating cellular promoters. Therefore, we investigat ed whether LANA can affect transcription from two major EBV latent promoter s. In this study, we demonstrated that LANA can efficiently transactivate b oth the LMP1 and C promoters in the human B-cell line BJAB as well as in th e human embryonic kidney 293 cell line. Moreover, we demonstrated that spec ific domains of LANA containing the putative leucine zipper and the glutami c acid-rich region are highly effective in upregulating these viral promote rs, while the amino-terminal region (435 amino acids) exhibited little or n o transactivation activity in our assays. We also specifically tested trunc ations of the LMP1 promoter element and showed that the -204 to +40 region had increased levels of activation compared with a larger region, -512 to 40, which contains two recombination signal-binding protein JK binding site s. The smaller, -204 to +40 promoter region contains specific binding sites for the Ets family transcription factor PU.1, transcription activating fac tor/cyclic AMP response element, and Spl, all of which are known to functio n as activators of transcription. Our data therefore suggest a potential ro le for LANA in regulation of the major EBV latent promoters in KSHV- and EB V-coinfected cells. Furthermore, LANA may be able to activate transcription of viral and cellular promoters in the absence of EBNA2, potentially throu gh association with transcription factors bound to their cognate sequences within the -204 to +40 region. This regulation of viral gene expression is critical for persistence of these DNA tumor viruses and most likely involve d in mediating the oncogenic process in these coinfected cells.