Identification of a transactivating function mapping to the putative immediate-early locus of human herpesvirus 6

Abstract

Sequencing studies have indicated that the unique component of the human herpesvirus 6 (HHV-6) genome and the unique long segment of the human cytomegalovirus genome are genetically colinear. Of particular interest is the identification of a region of local CpG dinucleotide suppression in the genome of HHV-6, a feature conserved in the genomes of human cytomegalovirus, murine cytomegalovirus, and simian cytomegalovirus, and a characteristic of the major immediate-early loci of these viruses. Adjacent to this region in HHV-6 are approximately 30 copies of a 103- to 108-bp sequence element, which contains consensus binding sites for the transcription factors AP2 and NF kappa B, in addition to a single KpnI recognition site. Together, these KpnI repeat units may compose an immediate-early enhancer, analogous to those found in the cytomegaloviruses. We present the sequence of this region of HHV-6 and demonstrate that a transactivating function is encoded by this region. We have used polymerase chain reaction to synthesize fragments containing open reading frames and 5' sequences with or without the upstream KpnI repeat units. Effector plasmids containing these HHV-6 coding and 5' sequences were able to effect activation of heterologous promoter-chloramphenicol acetyltransferase (CAT) constructs, including adenovirus E3-CAT and E4-CAT, human T-cell lymphotropic virus type I long terminal repeat (LTR)-CAT, and human immunodeficiency virus LTR-CAT, in cotransfection experiments in Vero cells and peripheral blood lymphocytes. Furthermore, we have identified the major open reading frame (RF4; 2.3 kb) as being essential for activation, and we have shown that the NF kappa B, SP1, and TATA box motifs in the human immunodeficiency virus LTR are all required for full induction of the promoter by the HHV-6-encoded transactivator.

Human herpesvirus‐6 and ‐7 in transplantation

“…The HHV-6 genome contains consensus binding sites for the transcription factors AP2 and NF-kB and contains KpnI repeat units believed to function as an immediate-early enhancer analogous to that of CMV [27]. This immediate-early enhancer performs a transactivating function for b-herpesviruses but is also capable of inducing the activation of the adenovirus, HTLV-1 and HIV gene enhancer promoter region.…”

Enhancement of TAT-induced transactivation of the HIV-1 LTR by two genomic fragments of HHV-6

“…Several reports have demonstrated that the HIV-1 LTR is transactivated by HHV-6 infection, as well as by HHV-6 genomic fragments [Lusso et al, 1989;Ensoli et al, 1989;Horvat et al, 1989;Geng et al, 1992;Martin et al, 1991;Wang et al, 1994;Horvat et al, 19911. Both major HHV-6 subgroups A and B exert this effect [Horvat et al, 1991;Garzino-Demo, unpublished results]. The present study demonstrates an enhanced transactivation of the HIV-1 LTR by TAT in combination with two HHV-6 genomic clones, suggesting that once initiated HIV-1 replication can be amplified in cells coinfected by HHV-6 and HIV-1.…”

“…A series of clinical and experimental observations indicates that HHV-6 may be a cofactor in the progression of HIV infection toward full-blown AIDS [Lusso et al, 19941. Like other herpesviruses HHV-6 was shown to transactivate the expression of the HIV-regulatory elements contained in the viral long terminal repeat (LTR) [Lusso et al, 7989;Ensoli et al, 1989;Horvat et al, 1989;Geng et al, 1992;Martin et al, 1991;Wang et al, 19941. By using HIV-LTR deletion mutants, the region of the LTR responsive to HHV-6 transactivation was mapped to the NFKB sites in the enhancer element of HIV-1 [Ensoli et al, 19891. In the case of HHV-6, however, such transactivating ability may be biologically significant because this virus can coinfect CD4+ T cells with HIV [Lusso et al, 19891 and, thereby, has the possibility to directly trigger or enhance the replication of HIV in vivo.…”

Human herpesvirus 6 variant a infects human term syncytiotrophoblasts in vitro and induces replication of human immunodeficiency virus type 1 in dually infected cells

“…Sequences encoding the above ORFs were cloned into pUC19. The expression plasmid pBC-ORF contains the entire U89 ORF from the IE-A region of HHV-6A cloned into pBC/CMV [Martin et al, 1991]. The construction of the pHV6U86 plasmid containing the ORF U86 from the IE-A region of HHV-6A in pBluescriptSK vector has been described by Flamand et al [1998].…”

“…It has been shown that HHV-6 reactivates to active infections early in the course of HIV infection, and that lymph node infections at those early timepoints are predominantly due to HHV-6A [Knox and Carrigan, 1996]. The ®ndings that HHV-6 infections Di Luca et al, 1991] and cotransfections of subgenomic fragments of HHV-6 [Martin et al, 1991;Geng et al, 1992;Kashanchi et al, 1994;Nicholas and Martin, 1994;Thomson et al, 1994;Wang et al, 1994;Zhou et al, 1994] can activate transcription directed by the HIV-1 long terminal repeat (LTR) indicate the potential for HHV-6 to activate HIV-1 from latency and enhance its replication. In addition, the ability of HHV-6 to activate CD4 gene has been demonstrated in CD8 T lymphocytes [Lusso et al, 1991], natural killer cells [Lusso et al, 1993], and hematopoietic progenitor cells [Furlini et al, 1996].…”