RNA Polymerase III Regulates Cytosolic RNA:DNA Hybrids and Intracellular MicroRNA Expression [Gene Regulation]

January 26th, 2015 by Koo, C. X., Kobiyama, K., Shen, Y. J., LeBert, N., Ahmad, S., Khatoo, M., Aoshi, T., Gasser, S., Ishii, K. J.

RNA:DNA hybrids form in the nuclei and mitochondria of cells as transcription-induced R-loops or G-quadruplexes, but only exist in the cytosol of virus-infected cells. Little is known about the existence of RNA:DNA hybrids in the cytosol of virus-free cells, in particular cancer or transformed cells. Here, we show that cytosolic RNA:DNA hybrids are present in various human cell lines, including transformed cells. Inhibition of RNA polymerase (III), but not DNA polymerase abrogated cytosolic RNA:DNA hybrids. Cytosolic RNA:DNA hybrids bind to several components of the miRNA machinery-related proteins including AGO2 and DDX17. Furthermore, we identified miRNAs that were specifically regulated by RNA polymerase III, providing a potential link between RNA:DNA hybrids and the miRNA machinery. One of the target genes, exportin-1, was shown to regulate cytosolic RNA:DNA hybrids. Taken together, we reveal previously unknown mechanism by which the RNA polymerase III regulates the presence of cytosolic RNA:DNA hybrids and miRNA biogenesis in various human cells.