Expression data by telomere elongation in xenograft.

Telomere erosion causes cell mortality, suggesting that longer telomeres allow greater number of cell division. In telomerase-positive human cancer cells, however, telomeres are often kept shorter than the surrounding normal tissues. Recently, we have shown that telomere elongation in cancer cells represses innate immune genes and promotes their differentiation in vivo. This implies that short telomeres contribute to cancer malignancy, but it is unclear how such genetic repression is caused by long telomeres. Here we report that telomeric repeat-containing RNA (TERRA) induces genome-wide alteration of gene expression in telomere-elongated cancer cells in vivo. Using three different cell lines, we found that telomere elongation upregulates TERRA and downregulates innate immune genes in vivo xenograft tumors. Most of the suppressed genes belonged to innate immune system categories and were upregulated in various cancers. We propose that TERRA G4 counteracts cancer malignancy through suppression of innate immune genes. Four samples are telomere-elongated cells (PC3/LhTERTL, PC3/LhTERTL/cre, HBC4/hTERT and MKN74/hTERT), and the other four samples are control cell lines.