Abstract
Human endogenous retroviruses (HERV) and related elements account for more than 8% of the human genome and significantly contribute to the human transcriptome by long terminal repeat (LTR) promoter activity. In this context, HERVs are thought to intervene in the expression of adjacent genes by providing regulatory sequences (cis-effect) or via noncoding RNA including natural antisense transcripts. To address the potential impact of HERV activity in urothelial carcinoma, we comparatively analyzed the HERV transcription profiles in paired samples of non-malignant urothelium and urothelial carcinoma derived from 13 patients with bladder cancer by means of a retrovirus-specific microarray (RetroArray). We established a characteristic HERV signature consisting of six ubiquitously active HERV subgroups (E4-1, HERV-Rb, ERV9, HERV-K-T47D, NMWV3, HERV-KC4). The transcription pattern is largely identical in human urothelial carcinoma, non-malignant urothelial tissue, four tumor-derived cell lines and in a non-malignant urothelial cell line (UROtsa). Quantitative reverse transcriptase PCR (qRT-PCR) of HERV-E4-1, HERV-K(HML-6) and HERV-T(S71-TK1) revealed a bias to lower HERV activity in carcinoma samples compared to non-malignant tissue. Determination of active HERV-E4-1 loci by cloning and sequencing revealed six HERV-E4-1 proviral loci that are differentially regulated in urothelial carcinoma cells and normal tissue. Two full-length HERV-E4-1 proviruses, HERV-Ec1 and HERV-Ec6, are located in antisense orientation in introns of the genes PLA2G4A and RNGTT, respectively. PLA2G4A encodes a cytosolic phospholipase A2 (cPLA2) that is dysregulated in many human tumors. PLA2G4A and HERV-Ec1 displayed reciprocal transcript levels in 7 of 11 urothelial carcinoma patients. Moreover, reciprocal shifts were observed after treatment of UROtsa cells with HERV-Ec1 and PLA2G4A-directed siRNAs or 5-aza-2′-deoxycytidine (aza-dC) pointing to an antagonistic regulation of PLA2G4A and HERV-Ec1 transcription in human urothelial cells. We suggest that transcription of HERV-Ec1 contributes to fine tuning of cPLA2 expression, thereby facilitating tumorigenesis.
Highlights
Constituting at least 40% of the human genome it is becoming increasingly evident that genetic mobile elements are an integral part of the transcriptional regulatory machinery of the cell and can influence gene expression at transcription and protein levels [1,2,3,4,5,6]
To investigate Human endogenous retroviruses (HERV) transcriptional activity, we performed RetroArray analysis on 13 pairs of non-malignant (N) and urothelial carcinoma (T) tissue samples, each pair derived from the same patient (Table 1)
In some cases cancer-related RNA quality was at large better leading to brighter HERV signatures compared to RNA derived from corresponding non-malignant samples
Summary
Constituting at least 40% of the human genome it is becoming increasingly evident that genetic mobile elements are an integral part of the transcriptional regulatory machinery of the cell and can influence gene expression at transcription and protein levels [1,2,3,4,5,6]. Human TEs have been considered to contribute tens of thousands of natural antisense transcripts to human genes [13]. Their role in regulatory mechanisms such as RNA interference (RNAi) and epigenetics needs to be investigated in both healthy and malignant cells. Whereas some LTR elements such as mammalian apparent LTR retrotransposons (MaLR) represent ancient retrotransposons, class I, II and III HERVs are considered to be remnants of germ line infections by exogenous retroviruses that were endogenized and genetically fixed in the human population [17,18,19] (reviewed in [14]). In the course of evolution endogenous retroviruses have been amplified several times and spread throughout the genome by repeated events of retrotransposition and/or reinfection [20]
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
