BHRF1 Is Highly Conserved in Primate Virus Analogues of Epstein-Barr Virus

Abstract

The Epstein-Barr virus (EBV) protein BHRF1 (BamHI rightward reading frame 1) was the first viral member of the Bcl-2 family of apoptosis-regulating proteins described. In vitro studies imply that BHRF1 is dispensable for virus-induced cellular transformation and virus replication. However, in contrast to several essential viral genes that show divergence outwith their functional domains, sequence data from a wide range of EBV isolates show there is striking conservation of the BHRF1 gene. Contrary to the in vitro studies, the high degree of conservation hints at a more important role for BHRF1. Analogous viruses are endemic in each of the higher primate species. Whilst their genome organisation is colinear, limited sequence analysis indicates that the viruses have diverged significantly and that only important functional domains of proteins are likely to be conserved. We have isolated the BHRF1 equivalents from the viruses which infect chimpanzees (Herpesvirus pan) and baboons (Herpesvirus papio) and find that they are highly homologous in both species, strengthening the hypothesis that BHRF1 plays a significant, evolutionarily conserved function in vivo and that changes to the protein are not well tolerated.

Evolutionary Conservation of Primate Lymphocryptovirus MicroRNA Targets

“…Given these similarities, it is not surprising that rLCV ϩ rLCLs also exhibit cellular miRNA expression patterns comparable to those of EBV ϩ LCLs shown here (i.e., high levels of miR-155 and miR-21 and moderate levels of miR-17 family members), which suggests that LCVs employ similar mechanisms to modulate the cellular miRNA environment and have encountered a similar set of conserved host miRNAs throughout evolution. Most Old World LCVs are known to encode LMP1 and BHRF1 homologs (44,45,50,66), which we predict to be subject to the same viral and cellular miRNA regulation as that observed for EBV and rLCV homologs. In an attempt to determine the extent to which the miR-17 family binding sites are conserved in other LCVs, we sequenced the LMP1 3=UTR region for herpesvirus papio and analyzed published BHRF1 sequences for herpesvirus papio and herpesvirus pan.…”

“…This prompted us to ask if the miR-17 binding site is conserved in additional primate lymphocryptoviruses. Homologous to EBV and rLCV, an miR-17 binding site is present in the BHFR1 3=UTRs of herpesvirus papio and herpesvirus pan (45) and sits adjacent to the BHRF1 stop codon (Fig. 4F), providing further evidence of a connection between the miR-17 family and the BHRF1 mRNA(s) that has been conserved during lymphocryptovirus evolution.…”

Epstein-Barr Virus BALF1 Is a BCL-2-Like Antagonist of the Herpesvirus Antiapoptotic BCL-2 Proteins

“…In addition, the gammaherpesviruses all encode a functional BCL-2 homologue (5,32,54,62). BHRF1 of EBV is an early lytic cycle gene product that inhibits apoptosis induced by a variety of stimuli and may prevent cell death during viral lytic replication, although other possibilities remain (25,27,32,37,40,71,75). Interestingly, B-cell-associated mutant viruses lacking BHRF1 are still able to replicate in cell culture (43,51), raising the possibility of redundant lytic cycle antideath genes in the EBV genome.…”

“…We show here that BALF1 is conserved in other gamma-1 viruses and that the BALF1 map position in these genomes is analogous to that of the antiapoptotic BCL-2 homologues present in gamma-2 herpesviruses like herpesvirus saimiri and Kaposi's sarcoma-associated herpesvirus (also known as human herpesvirus 8) genomes. However, BALF1 proteins are more distantly related to the antiapoptotic herpesvirus BCL-2 proteins than to BALF1 proteins from other viruses, forming a subgroup of BALF1-like proteins (75).…”

Solution Structure of the BHRF1 Protein From Epstein-Barr Virus, a Homolog of Human Bcl-2

“…27 The BHRF1 sequence is highly conserved in primate virus analogs of EBV, suggesting an evolutionarily conserved function in vivo. 28 Studies on both the adenovirus and the g-herpes virus ghV68 Bcl-2 homologs, indicate an important in vivo role for these proteins in chronic and latent infection. 5,7 However, the exact role of BHRF1 in the virus lifecycle or in pathogenesis is not known.…”