RNF12 Regulates RNA Polymerase ?-dependent Transcription Via Catalyzing BRF1 Ubiquitination

As the largest of the eukaryotic DNA-dependent RNA polymerases,RNA polymerase ?(Pol ?)is responsible for the transcription of small non-coding RNAs,including tRNAs,5S rRNA,and U6 snRNA.These Pol ? transcripts control several fundamental metabolic processes such as protein translation and RNA processing,thereby dictating the growth rate of a cell.The accurate initiation of Pol?-dependent transcription requires at least two general transcription factors TF?B and TF?C.TF?C recognizes and binds to specific sequence elements in target gene promoters,thereafter allowing the recruitment of TF?B.The binding of TFIIIB to the promoter in turn precisely positions Pol ? at the transcription start site.It has been shown that the post-translational modification of TF?B and TF?C,such as phosphorylation,is involved in the regulation of Pol ?-dependent transcription.However,it remains unknown whether Pol ?-dependent transcription is also regulated by protein ubiquitination.Intriguingly,it has long been recognized that compared to normal cells,both transformed and tumor cells exhibit elevated Pol ?-dependent transcription.In addition,enhanced Pol ?-dependent transcription is required for oncogenic transformation of normal cells,indicating that enhanced Pol ?-dependent transcription not only allows cancer cells to meet their high demands for protein synthesis,but it is also actively involved in tumorigenesis.However,the molecular mechanisms underlying the dysregulation of RNA polymerase ? in cancer cells remain largely unclear.In this study,we show that RNF12,a RING domain-containing ubiquitin E3 ligase,physically interacts with BRF1.The results from domain mapping experiments suggest that RNF12(206-409)directly interacts with BRF1(1-260).Via direct interaction,RNF12 catalyzes Lys27-and Lys33-linked polyubiquitination of BRF1.Furthermore,RNF12 is able to negatively regulate Pol ?-dependent transcription and cell proliferation via BRF1.These findings uncover a novel mechanism for the regulation of BRF1 and reveal RNF12-mediated BRF1 ubiquitination plays an important role in the regulation of Pol ?-dependent transcription.