De Novo RNA 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 as Caenorhabditis elegans and Neurospora crassa, two types of small interfering RNAs (siRNAs), primary siRNAs and secondary siRNAs, are expressed; RdRP produces secondary siRNAs de 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 novo synthesis 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 indicates de novo synthesis 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.