Silencing of human RNA polymerase I subunit A34 influences multiple cellular processes including rDNA transcription...

Human RNA polymerase I (Pol I) is responsible for the synthesis of 18S, 28S, and 5.8S rRNA in cells. These rRNAs are essential to ribosome assembly and play a critical role in protein synthesis. However, the roles of Pol I specific subunits in many cellular processes remain unknown. Here, we found that human Pol I specific subunit A34/G (hRPA34/POLRG) participates in the regulation of multiple molecular and cellular processes, including rDNA transcription, cell migration, and others. We show that hRPA34 depletion inhibited rRNA synthesis, protein synthesis, and cell growth, but it promoted cell migration. In contrast, up-regulating hRPA34 expression exhibited an adverse effect on these processes. The inhibition of rRNA synthesis caused by hRPA34 depletion induces nucleolar stress and cell apoptosis. We show that hRPA34 silencing reduced the occupancies of components of the Pol I transcription machinery at the rDNA promoter and down-regulated hRPA49 expression. It indicates that hRPA34 silencing can affect rDNA transcription by changing RPA49 expression and the recruitment of the Pol I transcription machinery factors at the rDNA promoter. We demonstrate that hRPA34 depletion increased cell migration by up-regulating the expression of c-Jun and Integrin-β1 proteins. hRPA34 silencing caused cell growth arrest by activating p21 expression and increasing Caspase-3 and cleaved Caspase-3 levels. Collectively, these findings indicate that hRPA34 is required for the regulation of multiple molecular and cellular processes, extending the understanding of hRPA34 functions in human cells.