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) i s expressed in all latently HHV-8 infected cells and in HHV-8-associated tu mors, including primary effusion lymphoma (PEL). To better understand the c ontribution of LANA to tumorigenesis and to the PEL phenotype, we performed a yeast two-hybrid screen which identified the corepressor protein SAP30 a s a LANA binding protein. SAP30 is a constituent of a large multicomponent complex that brings histone deacetylases to the promoter. Glutathione S-tra nsferase affinity assays confirmed interaction between LANA and SAP30 and a lso demonstrated interactions between LANA and two other members of the cor epressor complex, mSin3A and CIR The corepressors bound to the amino-termin al 340-amino-acid domain of LANA. In transient expression assays, this same domain of LANA mediated repression when targeted to a 5xGal4tk-CAT reporte r as a GAL4-LANA fusion. PEL cells have the unusual feature that they are f requently 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 acti vated expression from the EBV Qp and Cp latency promoters. Reduction of end ogenous Qp activity could also be demonstrated in EBV-infected Rael cells t ransfected with a LANA expression plasmid. In contrast to the effect of LAN A on EBV latency promoters, LANA activated expression from its own promoter . The data indicate that LANA can mediate transcriptional repression throug h recruitment of an mSin3 corepressor complex and further that LANA-mediate d repression is likely to contribute to the low level of EBV latency gene e xpression seen in dually infected PEL cells.