Abstract
BackgroundHuman endogenous retroviruses (HERVs) constitute 8% of the human genome and contribute substantially to the transcriptome. HERVs have been shown to generate RNAs that modulate host gene expression. However, experimental evidence for an impact of these regulatory transcripts on the cellular phenotype has been lacking.ResultsWe characterized the previously little described HERV-K(HML-10) endogenous retrovirus family on a genome-wide scale. HML-10 invaded the ancestral genome of Old World monkeys about 35 Million years ago and is enriched within introns of human genes when compared to other HERV families. We show that long terminal repeats (LTRs) of HML-10 exhibit variable promoter activity in human cancer cell lines. One identified HML-10 LTR-primed RNA was in opposite orientation to the pro-apoptotic Death-associated protein 3 (DAP3). In HeLa cells, experimental inactivation of HML-10 LTR-primed transcripts induced DAP3 expression levels, which led to apoptosis.ConclusionsIts enrichment within introns suggests that HML-10 may have been evolutionary co-opted for gene regulation more than other HERV families. We demonstrated such a regulatory activity for an HML-10 RNA that suppressed DAP3-mediated apoptosis in HeLa cells. Since HML-10 RNA appears to be upregulated in various tumor cell lines and primary tumor samples, it may contribute to evasion of apoptosis in malignant cells. However, the overall weak expression of HML-10 transcripts described here raises the question whether our result described for HeLa represent a rare event in cancer. A possible function in other cells or tissues requires further investigation.Electronic supplementary materialThe online version of this article (doi:10.1186/s13100-016-0081-9) contains supplementary material, which is available to authorized users.
Highlights
Human endogenous retroviruses (HERVs) constitute 8% of the human genome and contribute substantially to the transcriptome
HERVs are structurally similar to proviruses of present-day retroviruses where the gag, pol and env genes are flanked by two long terminal repeats (LTRs) that act as promoters [4]
The prototype member of Human Mouse mammary tumor virus (MMTV)-like (HML)-10 is an intron-located provirus in the long form of the Component 4 (C4) gene that exhibits LTR promoter activity in vitro [18, 19]
Summary
Human endogenous retroviruses (HERVs) constitute 8% of the human genome and contribute substantially to the transcriptome. HERVs have been shown to generate RNAs that modulate host gene expression. The most abundant TEs in the human genome are retroelements (REs) that amplify via a ‘copy-and-paste’ mechanism involving reverse transcription of an RNA intermediate [1, 3]. About 450,000 HERV elements constitute 8% of the human genome and are classified into about 30 families [1, 4]. HERVs are structurally similar to proviruses of present-day retroviruses where the gag, pol and env genes are flanked by two long terminal repeats (LTRs) that act as promoters [4]. HERVs and other REs have been shown to influence gene regulation by providing regulatory elements such as enhancers, promoters, splice- and polyadenylation sites, for various host genes [3]. REs of all classes often contain functional promoters and
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