1A6/DRIM, a Novel t-UTP, Activates RNA Polymerase I Transcription and Promotes Cell Proliferation

Abstract

BackgroundRibosome biogenesis is required for protein synthesis and cell proliferation. Ribosome subunits are assembled in the nucleolus following transcription of a 47S ribosome RNA precursor by RNA polymerase I and rRNA processing to produce mature 18S, 28S and 5.8S rRNAs. The 18S rRNA is incorporated into the ribosomal small subunit, whereas the 28S and 5.8S rRNAs are incorporated into the ribosomal large subunit. Pol I transcription and rRNA processing are coordinated processes and this coordination has been demonstrated to be mediated by a subset of U3 proteins known as t-UTPs. Up to date, five t-UTPs have been identified in humans but the mechanism(s) that function in the t-UTP(s) activation of Pol I remain unknown. In this study we have identified 1A6/DRIM, which was identified as UTP20 in our previous study, as a t-UTP. In the present study, we investigated the function and mechanism of 1A6/DRIM in Pol I transcription.Methodology/Principal FindingsKnockdown of 1A6/DRIM by siRNA resulted in a decreased 47S pre-rRNA level as determined by Northern blotting. Ectopic expression of 1A6/DRIM activated and knockdown of 1A6/DRIM inhibited the human rDNA promoter as evaluated with luciferase reporter. Chromatin immunoprecipitation (ChIP) experiments showed that 1A6/DRIM bound UBF and the rDNA promoter. Re-ChIP assay showed that 1A6/DRIM interacts with UBF at the rDNA promoter. Immunoprecipitation confirmed the interaction between 1A6/DRIM and the nucleolar acetyl-transferase hALP. It is of note that knockdown of 1A6/DRIM dramatically inhibited UBF acetylation. A finding of significance was that 1A6/DRIM depletion, as a kind of nucleolar stress, caused an increase in p53 level and inhibited cell proliferation by arresting cells at G1.ConclusionsWe identify 1A6/DRIM as a novel t-UTP. Our results suggest that 1A6/DRIM activates Pol I transcription most likely by associating with both hALP and UBF and thereby affecting the acetylation of UBF.

HIV-1 Infection Causes a Down-Regulation of Genes Involved in Ribosome Biogenesis

“…The nine annotated genes we found associated to the nucleolus and deregulated ( DDX21 , DHX33 , HEATR1 , RRS1 , WDR43 , GRWD1 , NOM1 , POLR1B and UTP20 ) encode for proteins involved or supposed to be involved in the regulation of the ribosome biogenesis, from pre-rRNA transcription and processing to ribosomal RNP assembly and export. In particular, POL1RB , HEATR1 , WDR43 , UTP20 and DHX33 gene products play a role in rRNA transcription [11] , [12] , [13] . POL1RB gene product is one of the subunit of the RNA polymerase I, HEATR1 and WDR43 are t-UTP proteins (UTP10 and UTP5 respectively), with a proven involvement in both transcription and U3 snoRNA-dependent pre-rRNA processing [11] .…”

“…POL1RB gene product is one of the subunit of the RNA polymerase I, HEATR1 and WDR43 are t-UTP proteins (UTP10 and UTP5 respectively), with a proven involvement in both transcription and U3 snoRNA-dependent pre-rRNA processing [11] . UTP20 encodes for a protein that may affect the acetylation of UBF thus activating RNA Pol I transcription [12] , and DHX33 protein participates in rRNA transcription by increasing the association of Pol I with rDNA loci [13] . The rss1 gene product in yeast is required for maturation of the 25S rRNA and has an essential function in the assembly of the 60S ribosomal subunit [14] .…”

The nucleolus, an ally, and an enemy of cancer cells

“…3 ). On the other hand, disturbed functioning of these factors reducing ribosome production can activate pathways leading to the halt of cell divisions (Ghalei et al 2015 ; Peng et al 2010 ; Yuan et al 2018 ). Ribosome formation involves coordinated action of three main RNA polymerases, I, II, and III, so that adequate amounts of rRNA transcripts, RPs, and factors necessary for this process could be synthesized.…”

“…Then, ribosomal stress leads to activation of p53 pathway and to cell cycle arrest. On the other hand, 1A6/DRIM upregulation, promoting cell proliferation, occurs in certain cancer types (Peng et al 2010 ).…”

Chromatin Remodelling and RNA Processing

“…It was proposed that a slower elongation rate produces improper recruitment of processing proteins and snoRNA. It has long been unclear how t-UTPs affect transcription, but recently a t-UTP, 1A6/DRIM (t-UTP20), was found to associate with a histone acetyltransferase-like protein, hALP, in human cells (Peng et al, 2010, Kong et al, 2011. The hALP is involved in acetylating UBF, and by being recruited to 1A6/DRIM, the processome promotes transcriptional initiation and, possibly, elongation.…”