Human herpesvirus 6 (HHV-6) U94/REP protein inhibits betaherpesvirus replication.

Human herpesvirus 6 (HHV-6) is the only human herpesvirus encoding U94/rep, homologue to the parvovirus non-structural gene rep68/78. Results to date suggest that HHV-6 U94/rep might regulate viral gene expression and have a role in viral latency. To determine the effect of U94/REP upon viral replication, the protein was produced. The purified U94/REP retained the characteristic immunological features. It was internalized and localized in the nucleus of human cells, showing marked inhibitory activity on the replication of HHV-6 (both variants A and B). The effect of U94/REP was dose-dependent and sensitive to treatment with single-stranded but not double-stranded DNA. U94/REP inhibited the replication of other betaherpesviruses, HHV-7 and human cytomegalovirus, but had no effect on herpes simplex virus. These results confirm the action of U94/rep latency gene in the regulation of HHV-6 replication with implications for co-reactivations and latency of human betaherpesviruses.

Detection of antibodies directed against human herpesvirus 6 U94/REP in sera of patients affected by multiple sclerosis.

The association between human herpesvirus 6 (HHV-6) and multiple sclerosis (MS) is controversial. In fact, it is difficult to establish a causative role of HHV-6, due to the high prevalence of latently infected individuals in the healthy population. Therefore, the presence of virus sequences in tissue biopsy does not support a viral role, and serological assays do not show significant differences between MS patients and control populations. The only viral gene expressed during latency is U94/rep. Therefore, we have developed a serological assay for the detection of antibodies specifically directed against U94/REP protein. Different populations were analyzed by enzyme-linked immunosorbent assay, including healthy controls, MS patients, and subjects with diseases unrelated to HHV-6 infection, including other neurological diseases. The results show statistically significant differences (P > 0.01) between MS patients and control groups, both in antibody prevalence (87 and 43.9%, respectively) and in geometric mean titer (1:515 and 1:190, respectively). The detection of antibodies specific for HHV-6 U94/REP shows that the immune system is exposed to this antigen during natural infection. The higher prevalence and higher titers of antibodies to U94/REP suggest that MS patients and control groups might experience different exposures to HHV-6.

Human herpesvirus-8 (Kaposi's sarcoma-associated herpesvirus) ORF50 interacts synergistically with the tat gene product in transactivating the human immunodeficiency virus type 1 LTR.

Human herpesvirus-8 (HHV-8) is a lymphotropic virus associated with several AIDS-related neoplasms. Two ORFs play a critical role in the regulation of virus replication: ORF50, encoding an immediate-early transcriptional activator, and ORF57, encoding a post-transcriptional regulator. We analysed their effects on the activation of the human immunodeficiency virus type 1 (HIV-1) LTR. ORF50 interacted synergically with tat, inducing a 10-fold enhancement of HIV-1 LTR transactivation. This effect occurred both in BCBL-1 cells, latently infected with HHV-8, and in HL3T1 cells, an epithelial cell line non-permissive to HHV-8 infection. Also, ORF57 enhanced tat-induced transactivation of HIV-1 LTR, but only in BCBL-1 cells, suggesting that its action was likely mediated by the induction of other viral functions. Finally, when both ORFs were expressed, the enhancement of transactivation induced by ORF50 was partially inhibited. The findings suggest that ORF57 can modulate ORF50 activity and that ORF50 may render biologically active small amounts of tat.