Human herpesvirus 8 LANA interacts with proteins of the mSin3 corepressor complex and negatively regulates Epstein-Barr virus gene expression in dually infected PEL cells

The human herpesvirus 8 (HHV-8) latency-associated nuclear antigen (LANA) is expressed in all latently HHV-8 infected cells and in HHV-8-associated tumors, including primary effusion lymphoma (PEL). To better understand the contribution of LANA to tumorigenesis and to the PEL phenotype, we performed a yeast two-hybrid screen which identified the corepressor protein SAP30 as a LANA binding protein. SAP30 is a constituent of a large multicomponent complex that brings histone deacetylases to the promoter. Glutathione S-transferase affinity assays confirmed interaction between LANA and SAP30 and also demonstrated interactions between LANA and two other members of the corepressor complex, mSin3A and CIR. The corepressors bound to the amino-terminal 340-amino-acid domain of LANA. In transient expression assays, this same domain of LANA mediated repression when targeted to a 5xGal4tk-CAT reporter as a GAL4-LANA fusion. PEL cells have the unusual feature that they are frequently dually infected with both HHV-8 and Epstein-Barr virus (EBV). We found that EBV EBNA-1 expression is downregulated in PEL cells at both the RNA and protein levels. In transient expression assays, LANA repressed activated expression from the EBV Qp and Cp latency promoters. Reduction of endogenous Qp activity could also be demonstrated in EBV-infected Rael cells transfected with a LANA expression plasmid. In contrast to the effect of LANA on EBV latency promoters, LANA activated expression from its own promoter. The data indicate that LANA can mediate transcriptional repression through recruitment of an mSin3 corepressor complex and further that LANA-mediated repression is likely to contribute to the low level of EBV latency gene expression seen in dually infected PEL cells.