HERV-K(HML-2) rec and np9 transcripts not restricted to disease but present in many normal human tissues.
BACKGROUND
Human endogenous retroviruses of the HERV-K(HML-2) group have been associated with the development of tumor diseases. Various HERV-K(HML-2) loci encode retrovirus-like proteins, and expression of such proteins is upregulated in certain tumor types. HERV-K(HML-2)-encoded Rec and Np9 proteins interact with functionally important cellular proteins and may contribute to tumor development. Though, the biological role of HERV-K(HML-2) transcription and encoded proteins in health and disease is less understood. We therefore investigated transcription specifically of HERV-K(HML-2) rec and np9 mRNAs in a panel of normal human tissues.


RESULTS
We obtained evidence for rec and np9 mRNA being present in all examined 16 normal tissue types. A total of 18 different HERV-K(HML-2) loci were identified as generating rec or np9 mRNA, among them loci not present in the human reference genome and several of the loci harboring open reading frames for Rec or Np9 proteins. Our analysis identified additional alternative splicing events of HERV-K(HML-2) transcripts, some of them encoding variant Rec/Np9 proteins. We also identified a second HERV-K(HML-2) locus formed by L1-mediated retrotransposition that is likewise transcribed in various human tissues.


CONCLUSIONS
HERV-K(HML-2) rec and np9 transcripts from different HERV-K(HML-2) loci appear to be present in various normal human tissues. It is conceivable that Rec and Np9 proteins and variants of those proteins are part of the proteome of normal human tissues and thus various cell types. Transcription of HERV-K(HML-2) may thus also have functional relevance in normal human cell physiology.
Institute of Human Genetics, Center of Human and Molecular Biology, Medical Faculty, University of Saarland, 66424 Homburg/Saar, Germany ; Sanofi-Aventis Deutschland GmbH, Industriepark Hoechst, K703, Elisabeth Kuhn Street, Frankfurt/Main, 65926 Germany.
Katja
K
Schmitt
José Carreras Research Center, Medical Faculty, University of Saarland, 66424 Homburg/Saar, Germany.
Kristina
K
Heyne
José Carreras Research Center, Medical Faculty, University of Saarland, 66424 Homburg/Saar, Germany.
Klaus
K
Roemer
Institute of Human Genetics, Center of Human and Molecular Biology, Medical Faculty, University of Saarland, 66424 Homburg/Saar, Germany.
Eckart
E
Meese
Institute of Human Genetics, Center of Human and Molecular Biology, Medical Faculty, University of Saarland, 66424 Homburg/Saar, Germany ; Center of Human and Molecular Biology, University of Saarland, 66424 Homburg/Saar, Germany.
Jens
J
Mayer
HERV-K Rec protein; HERV-K Np9 protein; Human endogenous retrovirus; L1 element; Provirus; Retrotransposition; Splicing; Transcription