title: Human endogenous retrovirus HERV-K(HML-2) activity in prostate cancer is dominated by a few loci.
abstract: BACKGROUND
  Increased expression of human endogenous retroviruses, especially HERV-K(HML-2) proviruses, has recently been associated with prostate carcinoma progression. In particular, a HML-2 locus in chromosome 22q11.23 (H22q) is upregulated in many cases. We therefore aimed at delineating the extent and repertoire of HML-2 transcription in prostate cancer tissues and cell lines and to define the transcription pattern and biological effects of H22q.
  
  
  METHODS
  Sanger and high throughput amplicon sequencing was used to define the repertoire of expressed HML-2 in a selected set of samples. qRT-PCR was used to quantify expression of selected proviruses in an extended set of prostate cancer tissues. Transcription factor binding sites (TFBS) were compared bioinformatically using the Transfac database. Expression of H22q was further characterized by siRNA-mediated knockdown, 5' RACE mapping of transcriptional start sites (TSS) and identification of splice sites. Functional effects of H22q knockdown were investigated by viability and apoptosis assays.
  
  
  RESULTS
  In addition to H22q, a limited number of other proviruses were found expressed by sequencing. Of these, provirus ERVK-5 and to a lesser degree ERVK-15 were frequently upregulated in prostate cancer. In contrast, expression of ERVK-24, predominant in germ cell tumors, was not detectable in prostatic tissues. While HML-2 LTRs contain binding sites for the androgen receptor and cofactors, no consistent differences in transcription factor binding sites were found between expressed and non-expressed proviruses. The H22q locus contains two 5'-LTRs of which the upstream LTR is predominantly used in prostatic cells, with an imprecise TSS. Splicing of H22q transcripts is complex, generating, among others, a transcript with an Np9-like ORF. Knockdown of H22q did not significantly affect proliferation or apoptosis of prostate cancer cells.
  
  
  CONCLUSIONS
  Our findings further underline that HML-2 expression is commonly highly tissue-specific. In prostate cancer, a limited number of loci become activated, especially H22q and ERVK-5. As expressed and non-expressed proviruses do not differ significantly in TFBS, tissue- and tumor-specific expression may be governed primarily by chromatin context. Overexpression of HML-2 H22q is more likely consequence than cause of prostate cancer progression.
authors.affiliation: Department of Urology, Medical Faculty, Heinrich Heine University Düsseldorf, Düsseldorf, Germany.
authors.forename: Wolfgang
authors.initials: W
authors.lastname: Goering
authors.affiliation: Institute of Human Genetics, Center of Human and Molecular Biology, Medical Faculty, Saarland University, Homburg, Germany.
authors.forename: Katja
authors.initials: K
authors.lastname: Schmitt
authors.affiliation: Department of Urology, Medical Faculty, Heinrich Heine University Düsseldorf, Düsseldorf, Germany.
authors.forename: Melanie
authors.initials: M
authors.lastname: Dostert
authors.affiliation: Institute of Virology, Medical Faculty, Heinrich Heine University Düsseldorf, Düsseldorf, Germany.
authors.forename: Heiner
authors.initials: H
authors.lastname: Schaal
authors.affiliation: GTL, Biomedical Research Center, Heinrich Heine University Düsseldorf, Düsseldorf, Germany.
authors.forename: René
authors.initials: R
authors.lastname: Deenen
authors.affiliation: Institute of Human Genetics, Center of Human and Molecular Biology, Medical Faculty, Saarland University, Homburg, Germany.
authors.forename: Jens
authors.initials: J
authors.lastname: Mayer
authors.affiliation: Department of Urology, Medical Faculty, Heinrich Heine University Düsseldorf, Düsseldorf, Germany.
authors.forename: Wolfgang A
authors.initials: WA
authors.lastname: Schulz
mesh_terms: D000230:Adenocarcinoma / Q000235:genetics / Q000378:metabolism* / Q000473:pathology; D017209:Apoptosis; D002470:Cell Survival; D018450:Disease Progression; D006801:Humans; D008297:Male; D011471:Prostatic Neoplasms / Q000235:genetics / Q000378:metabolism* / Q000473:pathology; D014764:Viral Proteins / Q000378:metabolism*
chemical_list: C406149:HERV-K cORF protein, Human endogenous retrovirus K; D014764:Viral Proteins
keywords: alternative splicing; androgen receptor; human endogenous retrovirus; next generation sequencing; prostate cancer; transcription factor binding sites