De NovoRNA Synthesis by RNA-Dependent RNA Polymerase Activity of Telomerase Reverse Transcriptase
RNA-dependent RNA polymerase (RdRP) plays key roles in RNA silencing to generate double-stranded RNAs. In model organisms, such asCaenorhabditis elegansandNeurospora crassa, two types of small interfering RNAs (siRNAs), primary siRNAs and secondary siRNAs, are expressed; RdRP produces secondary siRNAsde novo, without using either Dicer or primers, while primary siRNAs are processed by Dicer. We reported that human telomerase reverse transcriptase (TERT) has RdRP activity and produces endogenous siRNAs in a Dicer-dependent manner. However,de novosynthesis of siRNAs by human TERT has not been elucidated. Here we show that the TERT RdRP generates short RNAs that are complementary to template RNAs and have 5′-triphosphorylated ends, which indicatesde novosynthesis of the RNAs. In addition, we confirmed short RNA synthesis by TERT in several human carcinoma cell lines and found that TERT protein levels are positively correlated with RdRP activity.