Background Up-regulation of the most abundant H family human endogenous retrovirus (HERV-H), especially env-related transcripts, correlates with colon cancer. However, expression pattern of spliced non-coding transcripts of HERV-H is not clear. Methodology/Principal Findings In this study, expression of HERV-H spliced transcripts in colon cancer was investigated by a RT-PCR strategy using primers targeting the tRNAHis primer-binding site and the R region in the 3′ long terminal repeat (LTR), followed by cloning and sequencing of the amplicons. Sequences were then assigned to individual HERV-H loci by employing private nucleotide differences between loci. Different expression patterns of HERV-H spliced transcripts from distinct active elements were found in colon cancer cell lines HT29, LS 174T, RKO, SW480 and SW620. Furthermore, the expression patterns in SW480 and RKO were significantly changed by demethylation treatment. Interestingly, more HERV-H elements were found to be transcriptionally active in colon tumor tissues than in adjacent normal tissues (14 vs. 7). Conclusions/Significance This is the first research to study the character of expression of non-coding spliced transcripts of HERV-H elements in colon cancer. Expression patterns of HERV-H spliced transcripts differed among colon cancer cell lines and could be affected by genomic DNA methylation levels. More importantly, besides the commonly accepted view of up-regulation of HERV-H expression in colon tumor tissues, we found more active HERV-H loci in colon tumor as compared with adjacent normal tissues.
References
[1]
Lander ES, Linton LM, Birren B, Nusbaum C, Zody MC, et al. (2001) Initial sequencing and analysis of the human genome. Nature 409: 860–921.
[2]
Lower R, Lower J, Kurth R (1996) The viruses in all of us: characteristics and biological significance of human endogenous retrovirus sequences. Proc Natl Acad Sci U S A 93: 5177–5184.
[3]
Hirose Y, Takamatsu M, Harada F (1993) Presence of env genes in members of the RTVL-H family of human endogenous retrovirus-like elements. Virology 192: 52–61.
[4]
Wilkinson DA, Goodchild NL, Saxton TM, Wood S, Mager DL (1993) Evidence for a functional subclass of the RTVL-H family of human endogenous retrovirus-like sequences. J Virol 67: 2981–2989.
[5]
Jern P, Sperber GO, Ahlsen G, Blomberg J (2005) Sequence variability, gene structure, and expression of full-length human endogenous retrovirus H. J Virol 79: 6325–6337.
[6]
de Parseval N, Casella J, Gressin L, Heidmann T (2001) Characterization of the three HERV-H proviruses with an open envelope reading frame encompassing the immunosuppressive domain and evolutionary history in primates. Virology 279: 558–569.
[7]
Jern P, Sperber GO, Blomberg J (2004) Definition and variation of human endogenous retrovirus H. Virology 327: 93–110.
[8]
Sch？n U, Seifarth W, Baust C, Hohenadl C, Erfle V, et al. (2001) Cell type-specific expression and promoter activity of human endogenous retroviral long terminal repeats. Virology 279: 280–291.
[9]
Schon U, Diem O, Leitner L, Gunzburg WH, Mager DL, et al. (2009) Human endogenous retroviral long terminal repeat sequences as cell type-specific promoters in retroviral vectors. J Virol 83: 12643–12650.
[10]
Mangeney M, de Parseval N, Thomas G, Heidmann T (2001) The full-length envelope of an HERV-H human endogenous retrovirus has immunosuppressive properties. J Gen Virol 82: 2515–2518.
[11]
Wentzensen N, Wilz B, Findeisen P, Wagner R, Dippold W, et al. (2004) Identification of differentially expressed genes in colorectal adenoma compared to normal tissue by suppression subtractive hybridization. Int J Oncol 24: 987–994.
[12]
Pichon JP, Bonnaud B, Cleuziat P, Mallet F (2006) Multiplex degenerate PCR coupled with an oligo sorbent array for human endogenous retrovirus expression profiling. Nucleic Acids Res 34: e46.
[13]
Liang Q, Ding J, Zheng S (2009) Identification and detection of a novel human endogenous retrovirus-related gene, and structural characterization of its related elements. Genet Mol Biol.
[14]
Liang Q, Ding J, Xu R, Xu Z, Zheng S (2009) Identification of a novel human endogenous retrovirus and promoter activity of its 5′ U3. Biochem Biophys Res Commun 382: 470–474.
[15]
Liang Q, Ding J, Xu R, Xu Z, Zheng S (2010) The novel human endogenous retrovirus-related gene, psiTPTE22-HERV, is silenced by DNA methylation in cancers. Int J Cancer 127: 1833–1843.
[16]
Sjottem E, Anderssen S, Johansen T (1996) The promoter activity of long terminal repeats of the HERV-H family of human retrovirus-like elements is critically dependent on Sp1 family proteins interacting with a GC/GT box located immediately 3′ to the TATA box. J Virol 70: 188–198.
[17]
Lettini AA, Guidoboni M, Fonsatti E, Anzalone L, Cortini E, et al. (2007) Epigenetic remodelling of DNA in cancer. Histol Histopathol 22: 1413–1424.
[18]
Okahara G, Matsubara S, Oda T, Sugimoto J, Jinno Y, et al. (2004) Expression analyses of human endogenous retroviruses (HERVs): tissue-specific and developmental stage-dependent expression of HERVs. Genomics 84: 982–990.
[19]
Forsman A, Yun Z, Hu L, Uzhameckis D, Jern P, et al. (2005) Development of broadly targeted human endogenous gammaretroviral pol-based real time PCRs Quantitation of RNA expression in human tissues. J Virol Methods 129: 16–30.
[20]
Cameron EE, Bachman KE, My？h？nen S, Herman JG, Baylin SB (1999) Synergy of demethylation and histone deacetylase inhibition in the re-expression of genes silenced in cancer. Nat Genet 21: 103–107.
