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Human Endogenous Retrovirus K (HERV-K) can drive gene expression as a promoter in Caenorhabditis elegans.

ABSTRACT: Endogenous retroviruses (ERVs) are retrotransposons present in various metazoan genomes and have been implicated in metazoan evolution as well as in nematodes and humans. The long terminal repeat (LTR) retrotransposons contain several regulatory sequences including promoters and enhancers that regulate endogenous gene expression and thereby control organismal development and response to environmental change. ERVs including the LTR retrotransposons constitute 8% of the human genome and less than 0.6% of the Caenorhabditis elegans (C. elegans) genome, a nematode genetic model system. To investigate the evolutionarily conserved mechanism behind the transcriptional activity of retrotransposons, we generated a transgenic worm model driving green fluorescent protein (GFP) expression using Human endogenous retroviruses (HERV)-K LTR as a promoter. The promoter activity of HERV-K LTR was robust and fluorescence was observed in various tissues throughout the developmental process. Interestingly, persistent GFP expression was specifically detected in the adult vulva muscle. Using deletion constructs, we found that the region from positions 675 to 868 containing the TATA box was necessary for promoter activity driving gene expression in the vulva. Interestingly, we found that the promoter activity of the LTR was dependent on che-1 transcription factor, a sensory neuron driver, and lin-15b, a negative regulator of RNAi and germline gene expression. These results suggest evolutionary conservation of the LTR retrotransposon activity in transcriptional regulation as well as the possibility of che-1 function in non-neuronal tissues. [BMB Reports 2020; 53(10): 521-526].

SUBMITTER: Durnaoglu S

PROVIDER: S-EPMC7607151 | biostudies-literature | 2020 Nov

REPOSITORIES: biostudies-literature

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Human Endogenous Retrovirus K (HERV-K) can drive gene expression as a promoter in Caenorhabditis elegans.

Durnaoglu Serpen S Kim Heui-Soo HS Ahnn Joohong J Lee Sun-Kyung SK

BMB reports 20201101 10

Endogenous retroviruses (ERVs) are retrotransposons present in various metazoan genomes and have been implicated in metazoan evolution as well as in nematodes and humans. The long terminal repeat (LTR) retrotransposons contain several regulatory sequences including promoters and enhancers that regulate endogenous gene expression and thereby control organismal development and response to environmental change. ERVs including the LTR retrotransposons constitute 8% of the human genome and less than ...[more]

PMID: 32867919

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Project description:UnlabelledHuman endogenous retroviruses (HERV) make up 8% of the human genome. While the youngest of these retroviruses, HERV-K(HML-2), termed HK2, is able to code for all viral proteins and produce virus-like particles, it is not known if these virus particles package and transmit HK2-related sequences. Here, we analyzed the capacity of HK2 for packaging and transmitting HK2 sequences. We created an HK2 probe, termed Bogota, which can be packaged into HK2 viruses, and transfected it into cells that make HK2 particles. Supernatants of the transfected cells, which contained HK2 viral particles, then were added to target cells, and the transmissibility of the HK2 Bogota reporter was tracked by G418 resistance. Our studies revealed that contemporary HK2 virions produced by some teratocarcinoma and breast cancer cell lines, as well as by peripheral blood lymphocytes from lymphoma patients, can package HK2 Bogota probes, and these viruses transmitted these probes to other cells. After transmission, HK2 Bogota transcripts undergo reverse transcription, a step impaired by antiretroviral agents or by introduction of mutations into the probe sequences required for reverse transcription. HK2 viruses were more efficiently transmitted in the presence of HK2 Rec or HIV-1 Tat and Vif. Transmitted Bogota probes formed episomes but did not integrate into the cellular genome. Resistance to integration might explain the relatively low number of HK2 insertions that were acquired during the last 25 million years of evolution. Whether transient transmission of modern HK2 sequences, which encode two putative oncoproteins, can lead to disease remains to be studied.ImportanceRetroviruses invaded the genome of human ancestors over the course of millions of years, yet these viruses generally have been inactivated during evolution, with only remnants of these infectious sequences remaining in the human genome. One of these viruses, termed HK2, still is capable of producing virus particles, although these particles have been regarded as being noninfectious. Using a genetic probe derived from HK2, we have discovered that HK2 viruses produced in modern humans can package HK2 sequences and transmit them to various other cells. Furthermore, the genetic sequences packaged in HK2 undergo reverse transcription. The transmitted probe circularized in the cell and failed to integrate into the cellular genome. These findings suggest that modern HK2 viruses can package viral RNA and transmit it to other cells. Contrary to previous views, we provide evidence of an extracellular viral phase of modern HK2 viruses. We have no evidence of sustained, spreading infection.

Project description:Endogenous retroviruses are the remnants of past retroviral infections that are scattered within mammalian genomes. In humans, most of these elements are old degenerate sequences that have lost their coding properties. The HERV-K(HML2) family is an exception: it recently amplified in the human genome and corresponds to the most active proviruses, with some intact open reading frames and the potential to encode viral particles. Here, using a reconstructed consensus element, we show that HERV-K(HML2) proviruses are able to inhibit Tetherin, a cellular restriction factor that is active against most enveloped viruses and acts by keeping the viral particles attached to the cell surface. More precisely, we identify the Envelope protein (Env) as the viral effector active against Tetherin. Through immunoprecipitation experiments, we show that the recognition of Tetherin is mediated by the surface subunit of Env. Similar to Ebola glycoprotein, HERV-K(HML2) Env does not mediate Tetherin degradation or cell surface removal; therefore, it uses a yet-undescribed mechanism to inactivate Tetherin. We also assessed all natural complete alleles of endogenous HERV-K(HML2) Env described to date for their ability to inhibit Tetherin and found that two of them (out of six) can block Tetherin restriction. However, due to their recent amplification, HERV-K(HML2) elements are extremely polymorphic in the human population, and it is likely that individuals will not all possess the same anti-Tetherin potential. Because of Tetherin's role as a restriction factor capable of inducing innate immune responses, this could have functional consequences for individual responses to infection.Tetherin, a cellular protein initially characterized for its role against HIV-1, has been proven to counteract numerous enveloped viruses. It blocks the release of viral particles from producer cells, keeping them tethered to the cell surface. Several viruses have developed strategies to inhibit Tetherin activity, allowing them to efficiently infect and replicate in their host. Here, we show that human HERV-K(HML2) elements, the remnants of an ancient retroviral infection, possess an anti-Tetherin activity which is mediated by the envelope protein. It is likely that this activity was an important factor that contributed to the recent, human-specific amplification of this family of elements. Also, due to their recent amplification, HERV-K(HML2) elements are highly polymorphic in the human population. Since Tetherin is a mediator of innate immunity, interindividual variations among HERV-K(HML2) Env genes may result in differences in immune responses to infection.

Dataset Information

Human Endogenous Retrovirus K (HERV-K) can drive gene expression as a promoter in Caenorhabditis elegans.

Publications

Human Endogenous Retrovirus K (HERV-K) can drive gene expression as a promoter in Caenorhabditis elegans.

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