Abstract:Endogenous retroviruses (ERVs) are remnants of ancestral retroviral infections of germ cells. Retroviral endogenization is an adaptation process for the host genome, and ERVs are gradually attenuated or inactivated by mutation. However, some ERVs that have been "domesticated" by their hosts eventually gain physiological functions, such as placentation or viral resistance. We previously reported the discovery of Refrex-1, a soluble antiretroviral factor in domestic cats that specifically inhibits infection by f… Show more
“…Inspection of the hsaHTenv and orthologous env sequences in gorillas and orangutans revealed mutations at the site where proteolytic cleavage by furin-like proteases generates surface (SU) and transmembrane (TM) subunits (Hallenberger et al, 1992) (Figure 4E). Insertion of these cleavage site mutations into ancHTenv abolished cleavage and pseudotype infection, while reversion of mutations in hsaHTenv did not correct the cleavage defect and did not yield infectious MLV particles (Figure 4—figure supplement 1), Thus, loss of HERV-T envelope function by hsaHTenv was a multi-step process, including loss of furin cleavability, similar to findings with feline endogenous retroviral Env proteins (Ito et al, 2016). 10.7554/eLife.22519.012Figure 4.The human genome encodes a HERV-T Env ORF that does not function as a retroviral envelope.( A ) Infectiousness of MLV particles pseudotyped with untagged or C-terminally HA-tagged ancHTenv or hsaHTenv (Mean ± SD, n = 3 replicates, one of two experiments).…”
Endogenous retroviral sequences provide a molecular fossil record of ancient infections whose analysis might illuminate mechanisms of viral extinction. A close relative of gammaretroviruses, HERV-T, circulated in primates for ~25 million years (MY) before apparent extinction within the past ~8 MY. Construction of a near-complete catalog of HERV-T fossils in primate genomes allowed us to estimate a ~32 MY old ancestral sequence and reconstruct a functional envelope protein (ancHTenv) that could support infection of a pseudotyped modern gammaretrovirus. Using ancHTenv, we identify monocarboxylate transporter-1 (MCT-1) as a receptor used by HERV-T for attachment and infection. A single HERV-T provirus in hominid genomes includes an env gene (hsaHTenv) that has been uniquely preserved. This apparently exapted HERV-T env could not support virion infection but could block ancHTenv mediated infection, by causing MCT-1 depletion from cell surfaces. Thus, hsaHTenv may have contributed to HERV-T extinction, and could also potentially regulate cellular metabolism.DOI:
http://dx.doi.org/10.7554/eLife.22519.001
“…Inspection of the hsaHTenv and orthologous env sequences in gorillas and orangutans revealed mutations at the site where proteolytic cleavage by furin-like proteases generates surface (SU) and transmembrane (TM) subunits (Hallenberger et al, 1992) (Figure 4E). Insertion of these cleavage site mutations into ancHTenv abolished cleavage and pseudotype infection, while reversion of mutations in hsaHTenv did not correct the cleavage defect and did not yield infectious MLV particles (Figure 4—figure supplement 1), Thus, loss of HERV-T envelope function by hsaHTenv was a multi-step process, including loss of furin cleavability, similar to findings with feline endogenous retroviral Env proteins (Ito et al, 2016). 10.7554/eLife.22519.012Figure 4.The human genome encodes a HERV-T Env ORF that does not function as a retroviral envelope.( A ) Infectiousness of MLV particles pseudotyped with untagged or C-terminally HA-tagged ancHTenv or hsaHTenv (Mean ± SD, n = 3 replicates, one of two experiments).…”
Endogenous retroviral sequences provide a molecular fossil record of ancient infections whose analysis might illuminate mechanisms of viral extinction. A close relative of gammaretroviruses, HERV-T, circulated in primates for ~25 million years (MY) before apparent extinction within the past ~8 MY. Construction of a near-complete catalog of HERV-T fossils in primate genomes allowed us to estimate a ~32 MY old ancestral sequence and reconstruct a functional envelope protein (ancHTenv) that could support infection of a pseudotyped modern gammaretrovirus. Using ancHTenv, we identify monocarboxylate transporter-1 (MCT-1) as a receptor used by HERV-T for attachment and infection. A single HERV-T provirus in hominid genomes includes an env gene (hsaHTenv) that has been uniquely preserved. This apparently exapted HERV-T env could not support virion infection but could block ancHTenv mediated infection, by causing MCT-1 depletion from cell surfaces. Thus, hsaHTenv may have contributed to HERV-T extinction, and could also potentially regulate cellular metabolism.DOI:
http://dx.doi.org/10.7554/eLife.22519.001
“…ERV-DC10 and ERV-DC18 are the first feline ERVs that were identified as replication-competent proviruses residing within the host genome (32,60,61). In this study, we newly identified ERV-DC14 as another replication-competent ERV and characterized this virus in detail.…”
Section: Discussionmentioning
confidence: 98%
“…Our previous study demonstrated that ERV-DC14 did not interfere with ERV-DC10, indicating that these viruses use different viral receptors (29,32). In this study, we compared the host ranges of ERV-DC14 and ERV-DC10 in detail by using the ERV-DC14TA mutant so that it would be easier to monitor viral infection.…”
Endogenous retroviruses (ERVs) are the remnants of ancient retroviral infections of germ cells. Previous work identified one of the youngest feline ERV groups, ERV-DC, and reported that two ERV-DC loci, ERV-DC10 and ERV-DC18 (ERV-DC10/DC18), can replicate in cultured cells. Here, we identified another replication-competent provirus, ERV-DC14, on chromosome C1q32. ERV-DC14 differs from ERV-DC10/DC18 in its phylogeny, receptor usage, and, most notably, transcriptional activities; although ERV-DC14 can replicate in cultured cells, it cannot establish a persistent infection owing to its low transcriptional activity. Furthermore, we examined ERV-DC transcription and its regulation in feline tissues. Quantitative reverse transcription-PCR (RT-PCR) detected extremely low ERV-DC10 expression levels in feline tissues, and bisulfite sequencing showed that 5= long terminal repeats (LTRs) of ERV-DC10/DC18 are significantly hypermethylated in feline blood cells. Reporter assays found that the 5=-LTR promoter activities of ERV-DC10/DC18 are high, whereas that of ERV-DC14 is low. This difference in promoter activity is due to a single substitution from A to T in the LTR, and reverse mutation at this nucleotide in ERV-DC14 enhanced its replication and enabled it to persistently infect cultured cells. Therefore, ERV-DC LTRs can be divided into two types based on this nucleotide, the A type or T type, which have strong or attenuated promoter activity, respectively. Notably, ERV-DCs with T-type LTRs, such as ERV-DC14, have expanded in the cat genome significantly more than A-type ERV-DCs, despite their low promoter activities. Our results provide insights into how the host controls potentially infectious ERVs and, conversely, how ERVs adapt to and invade the host genome.
IMPORTANCEThe domestic cat genome contains many endogenous retroviruses, including ERV-DCs. These ERV-DCs have been acquired through germ cell infections with exogenous retroviruses. Some of these ERV-DCs are still capable of producing infectious virions. Hosts must tightly control these ERVs because replication-competent viruses in the genome pose a risk to the host. Here, we investigated how ERV-DCs are adapted by their hosts. Replication-competent viruses with strong promoter activity, such as ERV-DC10 and ERV-DC18, were suppressed by promoter methylation in LTRs. On the other hand, replication-competent viruses with weak promoter activity, such as ERV-DC14, seemed to escape strict control via promoter methylation by the host. Interestingly, ERV-DCs with weak promoter activity, such as ERV-DC14, have expanded in the cat genome significantly more than ERV-DCs with strong promoter activity. Our results improve the understanding of the host-virus conflict and how ERVs adapt in their hosts over time.
Endogenous retroviruses (ERVs) are resident DNA copies that abound in host chromosomal DNA and compromise ϳ8 to 10% of human and mouse genomes (1, 2). They have been found in all vertebrates, including mammals, fish, birds, reptiles, and amphibians (3). ERVs we...
“…Because it was unclear how ERV-DC7 and ERV-DC16 evolved into Refrex-1, we investigated the process of Refrex-1 evolution using the reconstructed full-length env genes of ERV-DC7 and ERV-DC16 (ERV-DC7fl and ERV-DC16fl, respectively) [ 50 ]. An infectivity analysis of ERV-DC7fl and ERV-DC16fl revealed that they are unable to produce viruses because the cleavage between SU and TM is disrupted.…”
Section: Refrex-1 Is Under Robust Control By Accumulated Inactivatmentioning
An endogenous retrovirus (ERV) is a remnant of an ancient retroviral infection in the host genome. Although most ERVs have lost their viral productivity, a few ERVs retain their replication capacity. In addition, partially inactivated ERVs can present a potential risk to the host via their encoded virulence factors or the generation of novel viruses by viral recombination. ERVs can also eventually acquire a biological function, and this ability has been a driving force of host evolution. Therefore, the presence of an ERV can be harmful or beneficial to the host. Various reports about paleovirology have revealed each event in ERV evolution, but the continuous processes of ERV evolution over millions of years are mainly unknown. A unique ERV family, ERV-DC, is present in the domestic cat (Felis silvestris
catus) genome. ERV-DC proviruses are phylogenetically classified into three genotypes, and the specific characteristics of each genotype have been clarified: their capacity to produce infectious viruses; their recombination with other retroviruses, such as feline leukemia virus or RD-114; and their biological functions as host antiviral factors. In this review, we describe ERV-DC-related phenomena and discuss the continuous changes in the evolution of this ERV in the domestic cat.
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