Identification of a major latent nuclear antigen, LNA-1, in the human herpesvirus 8 genome

Human herpesvirus 8 (HHV-8) is strongly associated with all forms of Kaposi's sarcoma (KS) and with primary effusion lymphomas (PEL). KS patients' sera are immunoreactive against discrete nuclear localizing antigens in PEL cell lines. This study sought to identify and characterize these nuclear localizing proteins.

KS patients' sera were used to screen a cDNA expression library derived from a PEL cell line (BCP-1) latently infected with HHV-8.

An HHV-8-specific cDNA clone was isolated. It encoded one partial and two complete open reading frames (ORFs): ORF 73, ORF 72 (v-cyclin), and K13, respectively. The immunodominant epitope was mapped to the C-terminal domain of ORF 73. Analysis with the KS patients' sera of HEK 293 cells transfected with a clone encompassing the complete coding region of ORF 73, ORF 72, and K13 gave a nuclear immunofluorescence pattern similar to that observed in BCP-1 cells. Western blot analysis with KS patients' sera of transfected HEK 293 cells revealed an immunoreactive protein of 220 to 230 kD that was similar to that observed previously in PEL cell lines. After induction of lytic replication of HHV-8 in BCP-1 cells with n-butyrate, we observed a major reduction in the expression of an ORF 73-specific 6.6-kb mRNA, indicating that this region is under latent control.

These data identify a region of HHV-8 encoding for a major immunoreactive latent nuclear antigen (LNA-1), analogous to the Epstein-Barr virus latent nuclear antigens.