Acetylation of UBF changes during the cell cycle and regulates the interaction of UBF with RNA polymerase I

Abstract

The upstream binding factor UBF, an activator of RNA polymerase I transcription, is posttranslationally modified by phosphorylation and acetylation. We found that in NIH3T3 cells, UBF is acetylated in S-phase but not in G1-phase. To assess the role of acetylation in regulation of UBF activity, we have established an NIH3T3 cell line that inducibly overexpresses HDAC1. Both in vivo and in vitro, HDAC1 efficiently hypoacetylates UBF. Immunoprecipitation with antibodies against the Pol I-associated factor PAF53 co-precipitated UBF in mock cells but not in cells overexpressing HDAC1. Pull-down experiments showed that acetylation of UBF augments the interaction with Pol I. Consistent with acetylation of UBF being important for association of PAF53 and recruitment of Pol I, the level of Pol I associated with rDNA and pre-rRNA synthesis were reduced in cells overexpressing HDAC1. The results suggest that acetylation and deacetylation of UBF regulate rRNA synthesis during cell cycle progression.

A Runx2-HDAC1 co-repressor complex regulates rRNA gene expression by modulating UBF acetylation

“…4A, bar graphs). These results are consistent with the known role of HDAC1 in suppressing rRNA genes in fibroblasts and kidney cells (Meraner et al, 2006;Meraner et al, 2008). Interestingly, introduction of exogenous RUNX2 into osseous cells in which endogenous HDAC1 had been depleted failed to suppress prerRNA expression (Fig.…”

“…However, how the RUNX2 association with UBF regulates rRNA gene expression is not well understood. Here, we show that HDAC1, a co-regulator of RUNX2 and known repressor of RNA Pol I transcription (Meraner et al, 2006;Pelletier et al, 2000;Zhou et al, 2002) is recruited to rDNA loci to modulate UBF and histone acetylation in a RUNX2-dependent manner. Our key finding is that RUNX2 and HDAC1 participate in fine-tuning rRNA gene expression to respond to cellular requirements for protein synthesis and growth.…”

“…1A, lower-right panel). The nucleolar periphery was identified by staining for UBF, a key nucleolar regulatory factor (Kuhn and Grummt, 1992;Meraner et al, 2006) and this staining also showed signal overlap with HDAC1 (Fig. 1A, upper panels).…”

“…HDAC1 is a known regulator of rRNA gene expression (Meraner et al, 2006;Young et al, 2007a;Zhou et al, 2002) and interacts with RUNX2 ). Here, we tested the hypothesis that HDAC1 interacts with RUNX2 at the rDNA locus in osseous cells and contributes to RUNX2-mediated downregulation of rRNA gene transcription.…”

Dynamic epigenetic states of ribosomal RNA promoters during the cell cycle

“…11,12 Recently it was found that UBF undergoes cell cycle-dependent acetylation which affects its binding to and ability to activate transcription from the rRNA promoter. 13 We therefore reasoned that epigenetic marks are also involved in cell cycle dependent regulation of rRNA gene expression. We tested here whether the epigenetic marks of the rRNA promoter are dynamic and respond to cellular physiological dynamics or whether they are a fixed property of the cell that was delineated by its developmental history.…”