The role of acetylation in rDNA transcription

Abstract

Treatment of NIH 3T3 cells with trichostatin A (TSA), an inhibitor of histone deacetylase (HDAC), resulted in a dose-dependent increase in transcription from a rDNA reporter and from endogenous rRNA genes. Chromatin immunoprecipitation using anti-acetyl-histone H4 antibodies demonstrated a direct effect of TSA on the acetylation state of the ribosomal chromatin. TSA did not reverse inhibition of transcription from the rDNA reporter by retinoblastoma (Rb) protein, suggesting that the main mechanism by which Rb blocks rDNA transcription may not involve recruitment of deacetylases to rDNA chromatin. Overexpression of histone transacetylases p300, CBP and PCAF stimulated transcription in transfected NIH 3T3 cells. Recombinant p300, but not PCAF, stimulated rDNA transcription in vitro in the absence of nucleosomes, suggesting that the stimulation of rDNA transcription by TSA might have a chromatin-independent component. We found that the rDNA transcription factor UBF was acetylated in vivo. Finally, we also demonstrated the nucleolar localization of CBP. Our results suggest that the organization of ribosomal chromatin of higher eukaryotes is not static and that acetylation may be involved in affecting these dynamic changes directly through histone acetylation and/or through acetylation of UBF or one of the other components of rDNA transcription.

Different Functional Modes of p300 in Activation of RNA Polymerase III Transcription from Chromatin Templates

“…The HAT function of p300/CBP was shown to be required for transcription activation in vivo (29,39) and in vitro (1,2,19,31,33). While p300/CBP has also been implicated in the stimulation of Pol I activity (20), no function in Pol III transcription has been reported to date.…”

Dynamic epigenetic states of ribosomal RNA promoters during the cell cycle

“…In addition, several groups as well as our own have previously shown multiple levels of epigenetic regulation of rRNA gene expression: rRNA gene expression is inhibited by DNA methylation; 38 MBD3 marks active copies of rRNA genes for demethylation and maintains their demethylated states; 9 histone H4 acetylation at the rRNA promoter marks active alleles of rRNA genes. 10 We have shown that the state of methylation of rRNA genes is critical for their expression and that modulation of MBD3 levels results in changes in methylation of rRNA genes and their expression. 9 The remaining question was whether these epigenetic marks fluctuate during the cell cycle.…”

“…Similar to genes transcribed by RNA polymerase II (Pol II), rRNA transcription is induced by the addition of trichostatin A (TSA), a histone deacetylase inhibitor, which leads to increased histone 4 acetylation. 10 We therefore delineated the state of H4 acetylation at the rRNA promoters at different points in the cell cycle. Using chromatin immunoprecipitation (ChIP) assays with antibodies directed against acetylated histone 4 (AcH4) we found that the levels of AcH4 peaks at t = 0, decreases at t = 6, but increases again at t = 10 ( Fig.…”

“…9 Active promoters are associated with acetylated histone 4, and addition of the histone deacetylase inhibitor trichostatin A (TSA) has been shown to induce acetylation of histone 4 and increase rRNA transcription. 10 On the other hand, epigenetic silencing of rRNA promoters occurs through binding of the nucleosomal remodeling complex, NoRC, recruitment of transcriptional repressors including histone deacetylases and DNA methyltransferases. 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.…”

DNA Binding by the Ribosomal DNA Transcription Factor Rrn3 Is Essential for Ribosomal DNA Transcription

“…The binding of UBF (14 -16) and possibly a second molecule of SL1 to the upstream promoter element is required for template commitment and efficient transcription in vitro. Both SL1 and UBF are subject to regulation via phosphorylation and acetylation (17)(18)(19)(20)(21)(22). In addition, Rb, the protein product of the retinoblastoma susceptibility gene, interacts with UBF and prevents UBF-dependent activation of rDNA * This work was supported, in whole or in part, by National Institutes of Health Grants GM069841 and HL077814 (to L. I. R.) and GM084946 (to D. A. S.).…”