Fig. 1

Global DNA hypomethylation leads to TE reactivation in cancer cells. In somatic cells, TEs are mostly silenced by epigenetic modifications, such as DNA methylation. However, a detectable portion of transcripts expressed from normal somatic cells (blue cells in the left panel) are still characterized as TE-containing transcripts with potential physiological functions. In cancer cells (right panel), global hypomethylation is observed, including removal of the repressive marks on TEs. Consequently, increased levels of long/small RNA products from TE-containing regions are observed. Excessive sense or antisense TE transcripts might cause the targeted degradation of TE-containing mRNAs based on reverse complementarity. In addition, TE transcripts may cause alternative splicing, gene mutation and genomic instability, including DNA DSBs and chromosomal rearrangement via somatic retrotransposition. Modified from [9]