Landscape of somatic retrotransposition in human cancers
http://science.sciencemag.org/content/337/6097/967.long 194 insertions in 43 WGS, mostly L1s w. ~50% near genes
Landscape of Somatic Retrotransposition in Human Cancers
Lovelace J. Luquette III1,
Jens G. Lohr4,5,
Christopher C. Harris6,
Richard K. Wilson6,
David A. Wheeler7,
Richard A. Gibbs7,
Peter V. Kharchenko1,9,*,
Peter J. Park1,2,9,*,
The Cancer Genome Atlas Research Network
Science 24 Aug 2012:
Vol. 337, Issue 6097, pp. 967-971
The paper describes the analysis of transposable elements (TE) insertions at single nucleotide resolution in 43 high coverage whole genome datasets from five cancer types. The authors developed a computational method that uses as input paired-end whole genome sequence data from tumor and normal sample aligned against a reference genome and a custom repeat assembly of TE sequences to detect the position and mechanism of TE insertion. The method identified 194 TE insertions (183 L1s, 10 Alus and 1 ERV). The diversity in the frequency of TE insertions in the same cancer type (ranging from 45-60 to 106 events per tumour) suggests the presence of tumour subtypes with respect to TE activity.
By intersecting the 194 TE with genome annotation, the authors found that 64 TE are in known genes (in UTRs and introns), most of which are implicated in tumour suppressor functions. Also, the TE events targeted genes that are frequently/recurrently mutated, suggesting that TE insertions can potentially contribute to cancer development. Gene expression analysis showed that TE insertion results in significantly decreasing the expression levels for the host gene. TE orientation also has an impact on the expression level, with antisense insertion being less disruptive.
Comparing the germline and somatic insertion sites shows notable differences. Germline L1s are significantly more depleted from genes compared to somatic L1s. Somatic L1s are significantly overrepresented within regions of DNA hypomethylation suggesting the DNA
hypomethylation promoted L1 integration.