XRCC5 and carcinoma: Moreover, 50% reduction in the expression of Ku80 either by small interfering RNA (siRNA) or by functional inactivation of one allele in two telomerase-positive carcinoma cell lines, HeLa and HCT116, is sufficient to alter telomere homeostasis, as demonstrated by rapid telomere shortening and, at least in one of the studies, stronger telomere overhang signal [16, 18].