Identification of a Spliced Gene from Kaposi’s Sarcoma-Associated Herpesvirus Encoding a Protein with Similarities to Latent Membrane Proteins 1 and 2A of Epstein-Barr Virus

Abstract

Kaposi’s sarcoma-associated herpesvirus (KSHV) or human herpesvirus 8 (HHV-8) is a novel herpesvirus implicated as the causative agent of Kaposi’s sarcoma (KS), primary effusion lymphoma, and some cases of multicentric Castleman’s disease. KSHV persists in the majority of KS spindle (endothelial tumor) cells and lymphoid cells in a latent form, with only a limited set of viral genes expressed in a tissue-specific manner. Here, we report the identification of a family of alternatively-spliced transcripts of approximately 7.5 kb expressed in latently infected body cavity-based lymphoma (BCBL) cell lines which are predicted to encode membrane proteins with similarities to the LMP2A and LMP1 proteins of Epstein-Barr virus. In two highly divergent sequence variants of the right end of the KSHV genome, alternative splicing of eight exons located between KSHV ORF 75 and the terminal repeats yields transcripts appropriate for proteins with up to 12 transmembrane domains, followed by a hydrophilic C-terminal, presumably cytoplasmic, domain. This C-terminal domain contains several YxxI/L motifs reminiscent of LMP2A and a putative TRAF binding site as in LMP1. In latently (persistently) infected BCBL cells the predominant transcript utilizes all eight exons, whereas in phorbol-ester-induced cells, a shorter transcript, lacking exons 4 and 5, is also abundant. We also found evidence for an alternative use of exon 1. Transfection of an epitope-tagged cDNA construct containing all exons indicates that the encoded protein is localized on cell surface and intracellular membranes, and glutathione S-transferase pull-down experiments indicate that its cytoplasmic domain, like that of LMP1, interacts with TRAF1, -2, and -3. Two of 20 KS patients had antibodies to the hydrophilic C-terminal domain, suggesting that the protein is expressed in vivo.

Human Herpesvirus 8 K1-Associated Nuclear Factor-kappa B-Dependent Promoter Activity: Role in Kaposi's Sarcoma Inflammation?

“…ITAM-containing receptors include subunits of the B-cell receptor, T-cell receptor, and Fc receptor, which contain one or more copies of ITAMs within their cytoplasmic tails (56). Specifically, these ITAM-bearing proteins include human proteins TCR-, CD3␦, and FcRI and viral proteins, such as HHV8 LMP2A-like protein, Hantavirus glycoprotein G1, bovine leukemia virus gp30, Epstein-Barr virus LMP2A, and rhesus monkey rhadinovirus R1 (32,45,53,(57)(58)(59)(60)(61).…”

Molecular epidemiology of Kaposi's sarcoma‐associated herpesvirus/human herpesvirus 8 strains from Russian patients with classic, posttransplant, and AIDS‐associated Kaposi's sarcoma

“…The extreme right-hand side (RHS) genomic region comprises K14.1 and K15 genes. The latter encodes for an integral membrane protein related to the LMP2 latency protein of Epstein-Barr virus (EBV) [Glenn et al, 1999;Choi et al, 2000]. Recent data indicate the existence of several highly divergent subtypes in this genomic region, including at least two major subtypes labeled P (predominant) and M (minor) [Poole et al, 1999;Zong et al, 2002].…”

Complex Alternative Cytoplasmic Protein Isoforms of the Kaposi's Sarcoma-Associated Herpesvirus Latency-Associated Nuclear Antigen 1 Generated through Noncanonical Translation Initiation

“…The BC1 strain LANA1 is predicted to be an ϳ135-kDa protein (theoretical pI/molecular weight, 3.83/135,213. 27 [ExPASY]) (22), but it migrates aberrantly as a doublet at 226 to 234 kDa on SDS-PAGE (15,23,24). The doublet pattern results from a weak C-terminal noncanonical polyadenylation site that truncates approxi-mately half of the LANA1 proteins, which are unable to bind the viral genome (25).…”