THE 222-KILODALTON TO 234-KILODALTON LATENT NUCLEAR-PROTEIN (LNA) OF KAPOSIS-SARCOMA-ASSOCIATED HERPESVIRUS (HUMAN-HERPESVIRUS-8) IS ENCODED BY ORF73 AND IS A COMPONENT OF THE LATENCY-ASSOCIATED NUCLEAR ANTIGEN

Kaposi's sarcoma (KS)-associated herpesvirus or human herpesvirus 8 (K SHV/HHV8) is the likely cause of KS and primary effusion lymphomas or body cavity-based lymphomas (BCBLs). A latency-associated nuclear immu nofluorescence antigen (LANA) (D. H. Kedes, E. Operskalski, M. Busch, R. Kohn, J. Flood, and D. Ganem, Nat. Med. 2:918-924, 1996; S. J. Gao, L. Kingsley, M. Li, W. Zheng, C. Parravicini, J. Ziegler, R. Newton, C. R. Rinaldo, A. Saah, J. Phair, R. Detels, Y. Chang, and P. S. Moore , Nat. Med. 2:925-928, 1996) and a 222- to 234-kDa nuclear protein (LN A) (S. J. Gao, L. Kingsley, D. R. Hoover, T. J. Spira, C. R. Rinaldo, A. Saah, J. Phair, R. Detels, P. Parry, Y. Chang, and P. S. Moore, N. Engl. J. Med. 335:233-241, 1996) have previously been described in BCB L cell lines by immunofluorescence and Western blotting techniques, re spectively. To identify the viral gene(s) encoding this antigen(s) we screened a cDNA library from HBL-6 cells, a B-cell lymphoma cell line persistently infected with KSHV/HHV8, with KS patient sera. One set of positive clones contained the 3' end of orf73, as well as the complet e orf72 and orfK13, and another set contained the 5' end of orf73. Com parison of cDNA sequences with the KSHV/HHV8 genomic sequence revealed a splice event, occurring upstream of orf73. Immunoaffinity purified antibodies to a recombinant carboxy-terminal fragment of the orf73-enc oded protein shelved the characteristic speckled nuclear immunofluores cence pattern of LANA and reacted with the 222- to ZM-kDa LNA on Weste rn blots. Expression of full-length orf73 in bacteria and COS7 cells r eproduced the LNA banding pattern. Immunohistochemistry on cases of no dular KS revealed that orf73/LNA is expressed in the nucleus of KS spi ndle cells. These findings demonstrate that orf73 encodes the 222- to 234-kDa LNA, is a component of LANA, and is expressed in KS tumor cell s.