Novel gamma-2-herpesvirus of the Rhadinovirus 2 lineage in gibbons

Kaposi sarcoma herpesvirus pathogenesis

Kaposi sarcoma herpesvirus (KSHV), taxonomical name human gammaherpesvirus 8, is a phylogenetically old human virus that co-evolved with human populations, but is now only common (seroprevalence greater than 10%) in sub-Saharan Africa, around the Mediterranean Sea, parts of South America and in a few ethnic communities. KSHV causes three human malignancies, Kaposi sarcoma, primary effusion lymphoma, and many cases of the plasmablastic form of multicentric Castleman's disease (MCD) as well as occasional cases of plasmablastic lymphoma arising from MCD; it has also been linked to rare cases of bone marrow failure and hepatitis. As it has colonized humans physiologically for many thousand years, cofactors are needed to allow it to unfold its pathogenic potential. In most cases, these include immune defects of genetic, iatrogenic or infectious origin, and inflammation appears to play an important role in disease development. Our much improved understanding of its life cycle and its role in pathogenesis should now allow us to develop new therapeutic strategies directed against key viral proteins or intracellular pathways that are crucial for virus replication or persistence. Likewise, its limited (for a herpesvirus) distribution and transmission should offer an opportunity for the development and use of a vaccine to prevent transmission.

This article is part of the themed issue ‘Human oncogenic viruses’.

African great apes are naturally infected with roseoloviruses closely related to human herpesvirus 7

Primates are naturally infected with herpesviruses. During the last 15 years, the search for homologues of human herpesviruses in nonhuman primates allowed the identification of numerous viruses belonging to the different herpesvirus subfamilies and genera. No simian homologue of human herpesvirus 7 (HHV7) has been reported to date. To investigate the putative existence of HHV7-like viruses in African great apes, we applied the consensus-degenerate hybrid oligonucleotide primers (CODEHOP) program-mediated PCR strategy to blood DNA samples from the four common chimpanzee subspecies (Pan troglodytes verus, P. t. ellioti, P. t. troglodytes, and P. t. schweinfurthii), pygmy chimpanzees (Pan paniscus), as well as lowland gorillas (Gorilla gorilla gorilla). This study led to the discovery of a novel roseolovirus close to HHV7 in each of these nonhuman primate species and subspecies. Generation of the partial glycoprotein B (1,111-bp) and full-length DNA polymerase (3,036/3,042-bp) gene sequences allowed the deciphering of their evolutionary relationships. Phylogenetic analyses revealed that HHV7 and its African great ape homologues formed well-supported monophyletic lineages whose topological resemblance to the host phylogeny is suggestive of virus-host codivergence. Notably, the evolutionary branching points that separate HHV7 from African great ape herpesvirus 7 are remarkably congruent with the dates of divergence of their hosts. Our study shows that African great apes are hosts of human herpesvirus homologues, including HHV7 homologues, and that the latter, like other DNA viruses that establish persistent infections, have cospeciated with their hosts.

IMPORTANCE

Human herpesviruses are known to possess simian homologues. However, surprisingly, none has been identified to date for human herpesvirus 7 (HHV7). This study is the first to describe simian homologues of HHV7. The extensive search performed on almost all African great ape species and subspecies, i.e., common chimpanzees of the four subspecies, bonobos, and lowland gorillas, has allowed characterization of a specific virus in each. Genetic characterization of the partial glycoprotein B and full-length DNA polymerase gene sequences, followed by their phylogenetic analysis and estimation of divergence times, has shed light on the evolutionary relationships of these viruses. In this respect, we conclusively demonstrate the cospeciation between these new viruses and their hosts and report cases of cross-species transmission between two common chimpanzee subspecies in both directions.

Next-generation sequence analysis of the genome of RFHVMn, the macaque homolog of Kaposi's sarcoma (KS)-associated herpesvirus, from a KS-like tumor of a pig-tailed macaque

The complete sequence of retroperitoneal fibromatosis-associated herpesvirus Macaca nemestrina (RFHVMn), the pig-tailed macaque homolog of Kaposi's sarcoma-associated herpesvirus (KSHV), was determined by next-generation sequence analysis of a Kaposi's sarcoma (KS)-like macaque tumor. Colinearity of genes was observed with the KSHV genome, and the core herpesvirus genes had strong sequence homology to the corresponding KSHV genes. RFHVMn lacked homologs of open reading frame 11 (ORF11) and KSHV ORFs K5 and K6, which appear to have been generated by duplication of ORFs K3 and K4 after the divergence of KSHV and RFHV. RFHVMn contained positional homologs of all other unique KSHV genes, although some showed limited sequence similarity. RFHVMn contained a number of candidate microRNA genes. Although there was little sequence similarity with KSHV microRNAs, one candidate contained the same seed sequence as the positional homolog, kshv-miR-K12-10a, suggesting functional overlap. RNA transcript splicing was highly conserved between RFHVMn and KSHV, and strong sequence conservation was noted in specific promoters and putative origins of replication, predicting important functional similarities. Sequence comparisons indicated that RFHVMn and KSHV developed in long-term synchrony with the evolution of their hosts, and both viruses phylogenetically group within the RV1 lineage of Old World primate rhadinoviruses. RFHVMn is the closest homolog of KSHV to be completely sequenced and the first sequenced RV1 rhadinovirus homolog of KSHV from a nonhuman Old World primate. The strong genetic and sequence similarity between RFHVMn and KSHV, coupled with similarities in biology and pathology, demonstrate that RFHVMn infection in macaques offers an important and relevant model for the study of KSHV in humans.

The ORF59 DNA polymerase processivity factor homologs of Old World primate RV2 rhadinoviruses are highly conserved nuclear antigens expressed in differentiated epithelium in infected macaques

Background

ORF59 DNA polymerase processivity factor of the human rhadinovirus, Kaposi's sarcoma-associated herpesvirus (KSHV), is required for efficient copying of the genome during virus replication. KSHV ORF59 is antigenic in the infected host and is used as a marker for virus activation and replication.

Results

We cloned, sequenced and expressed the genes encoding related ORF59 proteins from the RV1 rhadinovirus homologs of KSHV from chimpanzee (PtrRV1) and three species of macaques (RFHVMm, RFHVMn and RFHVMf), and have compared them with ORF59 proteins obtained from members of the more distantly-related RV2 rhadinovirus lineage infecting the same non-human primate species (PtrRV2, RRV, MneRV2, and MfaRV2, respectively). We found that ORF59 homologs of the RV1 and RV2 Old World primate rhadinoviruses are highly conserved with distinct phylogenetic clustering of the two rhadinovirus lineages. RV1 and RV2 ORF59 C-terminal domains exhibit a strong lineage-specific conservation. Rabbit antiserum was developed against a C-terminal polypeptide that is highly conserved between the macaque RV2 ORF59 sequences. This anti-serum showed strong reactivity towards ORF59 encoded by the macaque RV2 rhadinoviruses, RRV (rhesus) and MneRV2 (pig-tail), with no cross reaction to human or macaque RV1 ORF59 proteins. Using this antiserum and RT-qPCR, we determined that RRV ORF59 is expressed early after permissive infection of both rhesus primary fetal fibroblasts and African green monkey kidney epithelial cells (Vero) in vitro. RRV- and MneRV2-infected foci showed strong nuclear expression of ORF59 that correlated with production of infectious progeny virus. Immunohistochemical studies of an MneRV2-infected macaque revealed strong nuclear expression of ORF59 in infected cells within the differentiating layer of epidermis corroborating previous observations that differentiated epithelial cells are permissive for replication of KSHV-like rhadinoviruses.

Conclusion

The ORF59 DNA polymerase processivity factor homologs of the Old World primate RV1 and RV2 rhadinovirus lineages are phylogenetically distinct yet demonstrate similar expression and localization characteristics that correlate with their use as lineage-specific markers for permissive infection and virus replication. These studies will aid in the characterization of virus activation from latency to the replicative state, an important step for understanding the biology and transmission of rhadinoviruses, such as KSHV.

Genetic diversity and molecular evolution of human and non-human primate Gammaherpesvirinae

The Gammaherpesvirinae sub-family is divided into two genera: Lymphocryptovirus and Rhadinovirus. Until the middle of the 1990s, the Rhadinovirus genus was only represented by Herpesvirus saimiri and Herpesvirus ateles, which infect New World monkey species. Until the year 2000, Epstein-Barr virus (EBV), the human prototype of the Lymphocryptovirus, and simian homologues had only been detected in humans and Old World non-human primates. It was thought, therefore, that the separation of the continents had resulted in drastic changes in Gammaherpesvirinae evolution. The discovery of Kaposi's sarcoma-associated herpesvirus in humans, belonging to the Rhadinovirus, followed by the identification of CalHV3 (Callitrichine herpesvirus 3), a lymphocryptovirus of the marmoset, challenged this paradigm. The description of numerous viruses belonging to this sub-family from various Old and New World primate species enabled a cospeciation hypothesis for these viruses and their hosts to be developed. This review focuses on the current knowledge of primate Gammaherpesvirinae genetic diversity and molecular evolution. We discuss the various theories based on current genetic data regarding evolutionary relationships between lymphocryptoviruses of Old World primates, the use of these data as a tool to study evolutionary relationships between New World monkey species, and the possible existence of a ninth human herpesvirus belonging to the Rhadinovirus genus.

Prevalence and molecular characterization of the polymerase gene of gibbon lymphocryptovirus

BACKGROUND

Lymphocryptovirus (LCV) is found in various non-human primates. As a herpesvirus naturally infecting gibbons it is closely related to human Epstein-Barr virus (EBV) with which it shares considerable genetic, biological and epidemiologic features.

METHODS

We collected blood samples from 70 gibbons (51 Hylobates lar, 18 Hylobates pileatus and 1 Hylobates agilis) for further separation into serum and peripheral blood mononuclear cells (PBMC).

RESULTS

Only 13 of 70 (18.6%) sera were serologically positive for human EBV IgG but 64 of 70 (91.4%) PBMCs yielded the partial LCV DNA polymerase gene by semi-nested PCR, which we subjected to direct sequencing. All sequences showed 84% nucleic acid and 91% amino acid identity to human EBV. Phylogenetic tree analysis demonstrated gibbon LCVs clustered separately from other gammaherpesvirinae but closely related to LCV of other species.

CONCLUSIONS

Based on LCV DNA detection, we discovered a high prevalence of LCV infection among gibbons. Further characterization of non-human primate LCV might thus provide new insight into both evolution and pathogenicity of gammaherpesvirinae.