Cloning and characterization of the human RNA polymerase I subunit hRPA40

A prognostic signature based on three-genes expression in triple-negative breast tumours with residual disease

Residual disease after neoadjuvant chemotherapy (NAC) in triple-negative breast cancer (TNBC) is related with poor prognosis; however, the risk of recurrence after 3 years from surgery, becomes similar to other breast cancer subtypes indicating that TNBC is composed of tumours of different prognosis. To evaluate genes related to TNBC aggressiveness in the outcome of TNBC resistant to NAC, we profiled 82 samples of residual tumours whose expression for 449 genes was quantified with NanoString. The validation set (GSE25066) consisted of 113 TNBC cases with residual disease. The stepwise multivariate survival analysis performed by the Cox proportional hazards mode selected CCL5, DDIT4 and POLR1C as independent prognostic factors for distant recurrence-free survival (DRFS). We developed a three-genes signature using the regression coefficients for each gene (−0.393×CCL5+0.443×DDIT4+0.490×POLR1C). The median score in the discovery set (0.1494) identified two subgroups with different DRFS (P<0.001). The median score in the validation set was 0.0024 and was able to discriminate patients with different DRFS (P=0.002). In addition, the three-genes signature was a prognostic factor in TNBC patients regardless their response to NAC (data set GSE58812; P=0.001) and in patients with oestrogen-receptor-negative tumours (data set GSE16446; P=0.041). Here we describe a prognostic signature based on expression levels of CCL5, DDIT4 and POLR1C. The knowledge about the involvement of these genes in chemotherapy resistance could improve the therapeutic strategies in TNBC.

Characterization of human RNA polymerase III identifies orthologues for Saccharomyces cerevisiae RNA polymerase III subunits

Unlike Saccharomyces cerevisiae RNA polymerase III, human RNA polymerase III has not been entirely characterized. Orthologues of the yeast RNA polymerase III subunits C128 and C37 remain unidentified, and for many of the other subunits, the available information is limited to database sequences with various degrees of similarity to the yeast subunits. We have purified an RNA polymerase III complex and identified its components. We found that two RNA polymerase III subunits, referred to as RPC8 and RPC9, displayed sequence similarity to the RNA polymerase II RPB7 and RPB4 subunits, respectively. RPC8 and RPC9 associated with each other, paralleling the association of the RNA polymerase II subunits, and were thus paralogues of RPB7 and RPB4. Furthermore, the complex contained a prominent 80-kDa polypeptide, which we called RPC5 and which corresponded to the human orthologue of the yeast C37 subunit despite limited sequence similarity. RPC5 associated with RPC53, the human orthologue of S. cerevisiae C53, paralleling the association of the S. cerevisiae C37 and C53 subunits, and was required for transcription from the type 2 VAI and type 3 human U6 promoters. Our results provide a characterization of human RNA polymerase III and show that the RPC5 subunit is essential for transcription.

WRN helicase accelerates the transcription of ribosomal RNA as a component of an RNA polymerase I-associated complex

Werner syndrome (WS) is a rare autosomal recessive genetic disorder causing premature aging. The gene (WRN) responsible for WS encodes a protein homologous to the RecQ-type helicase. WRN has a nucleolar localization signal and shows intranuclear trafficking between the nucleolus and the nucleoplasm. WRN is recruited into the nucleolus when rRNA transcription is reactivated in quiescent cells. Inhibition of mRNA transcription with alpha-amanitin has no effect on nucleolar localization of WRN whereas inhibition of rRNA transcription with actinomycin D releases WRN from nucleoli, suggesting that nucleolar WRN is closely related to rRNA transcription by RNA polymerase I (RPI). A possible function of WRN on rRNA transcription through interaction with RPI is supported by the results described here showing that WRN is co-immunoprecipitated with an RPI subunit, RPA40. Here we show that WS fibroblasts are characterized by a decreased level of rRNA transcription compared with wild-type cells, and that the decreased level of rRNA transcription in WS fibroblasts recovers when wild-type WRN is exogenously expressed. By contrast, exogenously expressed mutant-type WRN lacking an ability to migrate into the nucleolus fails to stimulate rRNA transcription. These results suggest that WRN promotes rRNA transcription as a component of an RPI-associated complex in the nucleolus.

Reconstitution of transcription from the human U6 small nuclear RNA promoter with eight recombinant polypeptides and a partially purified RNA polymerase III complex

The human U6 small nuclear (sn) RNA core promoter consists of a proximal sequence element, which recruits the multisubunit factor SNAP(c), and a TATA box, which recruits the TATA box-binding protein, TBP. In addition to SNAP(c) and TBP, transcription from the human U6 promoter requires two well defined factors. The first is hB", a human homologue of the B" subunit of yeast TFIIIB generally required for transcription of RNA polymerase III genes, and the second is hBRFU, one of two human homologues of the yeast TFIIIB subunit BRF specifically required for transcription of U6-type RNA polymerase III promoters. Here, we have partially purified and characterized a RNA polymerase III complex that can direct transcription from the human U6 promoter when combined with recombinant SNAP(c), recombinant TBP, recombinant hB", and recombinant hBRFU. These results open the way to reconstitution of U6 transcription from entirely defined components.