The superantigen-homologous viral immediate-early gene ie14/vsag in herpesvirus saimiri-transformed human T cells

Abstract

Herpesvirus saimiri C488 transforms human T lymphocytes to stable growth in culture. The growth-transformed human T cells harbor the viral genome in a nonintegrated episomal form without production of virus particles. In these cells, virus gene expression was previously found to be confined to the transforming genes stpC and tip. In order to analyze virus gene expression in more detail, we applied a subtractive hybridization technique and compared stimulated virus-transformed cells with uninfected parental T cells of the same donor. A number of known T-cell activation genes were isolated. Viral stpC/tip cDNAs were enriched after subtraction. In addition, the viral immediate-early, superantigen-homologous gene ie14/vsag was represented by numerous cDNA clones that comprised the entire spliced transcript. Whereas a weak basal expression of ie14/vsag was detected by reverse transcription-PCR only, the phorbol ester-induced transcripts were readily shown by Northern blotting. ie14/vsag, which before had been classified as a major immediate-early gene of herpesvirus saimiri, is localized within a highly conserved region with extensive homologies to the cellular genome. Mutant viruses without the ie14/vsag gene are replication competent and fully capable of transforming human and marmoset T cells. Since ie14/vsag is transiently expressed after stimulation, it may increase T-cell proliferation in an activation-dependent and superantigen-like but apparently V␤-independent way.

Herpesvirus Saimiri Transforms Human T-Cell Clones to Stable Growth without Inducing Resistance to Apoptosis

“…We found that the expression of both HVS-flip and HVS-bcl-2 was restricted to cultures with viral replication. Activation with PMA does not induce lytic replication of HVS in human transformed T cells but enhances the expression of some viral genes (17,30). HVS-flip and HVS-bcl-2 transcripts were not detected by Northern blot hybridization in human transformed T cells, neither constitutively nor after activation with PMA ( Fig.…”

“…Therefore, we cloned and sequenced the gene coding for HVS-flip of strain C488 that transforms human T cells and found that the amino acid sequence identity of the FLIPs of strains A11 and C488 was 94%. Likewise, the sequence identity of the HVS-Bcl-2 of strains A11 and C488 is 92.5% (30). This suggests that strain-specific sequence differences of the two HVS antiapoptotic genes do not contribute to the different transforming capacities.…”

Downregulation of Major Histocompatibility Complex Class I Molecules by Kaposi's Sarcoma-Associated Herpesvirus K3 and K5 Proteins

“…. HVS viral superantigen is expressed in the immediate-early lytic phase and powerfully induces the proliferation of CD4-positive cells (6,14,36). At a position equivalent to that of the HVS viral superantigen, KSHV contains unique membrane proteins called K3, K4.2, and K5 (25).…”

The URNA Genes of Herpesvirus Saimiri (Strain C488) Are Dispensable for Transformation of Human T Cells In Vitro

“…The expression of viral genes in herpesvirus saimiri-transformed human cells is highly restricted. The bicistronic mRNA carrying the StpC and Tip genes which are essential for viral transformation and the mRNA needed for a putative viral superantigen have been detected in strain C488-transformed human T cells (10,15). In contrast, transcription of various viral genes is detectable from transformed marmoset or rabbit cell lines, where limited viral replication occurs.…”