Transactivation of elements in the human endogenous retrovirus W family by viral infection - PubMed (original) (raw)
Transactivation of elements in the human endogenous retrovirus W family by viral infection
Christoffer Nellåker et al. Retrovirology. 2006.
Abstract
Background: Aberrant expression of human endogenous retrovirus (HERV) elements in the W family has previously been associated with schizophrenia, multiple sclerosis and preeclampsia. Little is know regarding the basal expression, transcriptional regulation and functional significance of individual HERV-elements. Since viral infections have previously been reported to transactivate retroviral long terminal repeat regions we examined the basal expression of HERV-W elements and following infections by influenza A/WSN/33 and Herpes simplex 1 viruses in human cell-lines.
Methods: Relative levels of transcripts encoding HERV-W elements and cellular genes were analyzed by qPCR methods. An analysis of amplicon melting temperatures was used to detect variations in the frequencies of amplicons in discrete ranges of such melting temperatures. These frequency-distributions were taken as proxy markers for the repertoires of transcribed HERV-W elements in the cells.
Results: We report cell-specific expression patterns of HERV-W elements during base-line conditions. Expressed elements include those with intact regulatory long terminal repeat regions (LTRs) as well as elements flanked by truncated LTRs. Subsets of HERV-W elements were transactivated by viral infection in the different cell-lines. Transcriptional activation of these elements, including that encoding syncytin, was dependent on viral replication and was not induced by antiviral responses. Serum deprivation of cells induced similar changes in the expression of HERV-W elements suggesting that the observed phenomena are, in part, an effect of cellular stress.
Conclusion: We found that HERV-W elements, including elements lacking regulatory LTRs, are expressed in cell-specific patterns which can be modulated by environmental influences. This brings into light that mechanisms behind the regulation of expression of HERV-W elements are more complex than previously assumed and suggests biological functions of these transcripts.
Figures
Figure 1
Gene expression in infected SK-N-MC cells. Relative levels of transcripts from HERV-W env, HERV-W gag and IFNB1 in SK-N-MC cells infected with increasing doses of herpes simplex type 1 (A) or influenza A/WSN/33 (B) as compared to uninfected control cell-cultures. Relative levels of transcripts from the US6 gene of herpes simplex type 1 (A) and segment 8 of the influenza A/WSN/33 virus strain (B) were determined in infected cultures. Relative levels of viral transcripts were normalized to those observed in cells infected with the lowest dose of each virus (n controls = 4, n virus = 5).
Figure 2
Expression of HERV-W elements in human cell-lines following influenza A/WSN/33 virus infection (A) or serum deprivation (B). CCF-STTG1, 293F and U937 cells infected with influenza A/WSN/33 virus (n = 7-9) were analyzed for HERV-W related transcripts relative to uninfected control cells (n = 7-12). Cells deprived of serum (n = 5-7) were analyzed for HERV-W related transcripts relative to control cells in serum enriched culture media (n = 5-8). Error bars indicate the standard error of the difference between the means of infected or serum deprived cells and corresponding control cells. Statistical significance is indicated by * = p < 0.05, ** = p < 0.01, *** = p < 0.001.
Figure 3
Influence of influenza A/WSN/33 virus infection and serum deprivation on the detectable frequency distribution of transcribed HERV-W related sequences in CCF-STTG1, 293F and U937 cells. (A) Distribution of detected HERV-W gag amplicons into four melting temperature ranges observed in control cells (n = 38-44), influenza A/WSN/33 infected cells (n = 24-39) and serum deprived cells (n = 11-18). (B) Distribution of detected HERV-W env amplicons into three melting temperature ranges observed. Statistical significance is indicated by * = p < 0.05, ** = p < 0.01, *** = p < 0.001.
Figure 4
Expression of specific HERV-W elements following influenza A/WSN/33 infection. Levels of transcripts from the HERV-W gag on chromosomes 5p13, 11q13, 3q26 and the HERV-W env ORF encoding syncytin on 7q21 in CCF-STTG1, 293F and U937 cells infected with influenza A/WSN/33 (n = 3-7) relative to uninfected control cells (n = 3-9). Transcripts from 5p13 were not detectable in CCF-STTG1 or 293F cells in either control or infected cells, indicated by nd (not detectable). Syncytin transcripts were not detected in 293F control cells but were readily detectable (ct 34–35 using 500 ng input total RNA) in influenza A/WSN/33 infected cells, resulting in an infinite relative expression as indicated by ∞. Statistical significance is indicated by * = p < 0.05, ** = p < 0.01, *** = p < 0.001.
References
- Seifarth W, Frank O, Zeilfelder U, Spiess B, Greenwood AD, Hehlmann R, Leib-Mosch C. Comprehensive analysis of human endogenous retrovirus transcriptional activity in human tissues with a retrovirus-specific microarray. J Virol. 2005;79:341–352. doi: 10.1128/JVI.79.1.341-352.2005. - DOI - PMC - PubMed
Publication types
MeSH terms
Substances
LinkOut - more resources
Full Text Sources
Other Literature Sources