The human PAF complex coordinates transcription with events downstream of RNA synthesis

HRPT2 ͉ hyperparathyroidism ͉ parathyroid cancer ͉ PAF1 complex T he tumor suppressor gene HRPT2 was recently identified by positional candidate cloning (1). Germline mutation of HRPT2 confers susceptibility to the hyperparathyroidism-jaw tumor syndrome (HPT-JT), an autosomal dominant syndrome with high but incomplete penetrance (2). The major features are primary hyperparathyroidism (including 15% of all affected by HPT-JT with parathyroid cancer), jaw tumors, bilateral renal cysts, and, less commonly, solid renal tumors (2, 3). Germline inactivating HRPT2 mutation has also been reported in a minority of kindreds with familial isolated hyperparathyroidism (FIHP) (1, 4) and in up to 30% of patients with apparently sporadic parathyroid cancer (5, 6).HRPT2 encodes parafibromin, a 531 amino acid, putative tumor suppressor protein. Parafibromin demonstrates weak homology to Cdc73p, a budding yeast protein component of the RNA polymerase II-associated Paf1 complex. Recent evidence suggests that in humans, parafibromin interacts with RNA polymerase II via a human PAF1 complex whose other protein components include human Paf1, CTR9, Leo1 (7-9), and the WD40-repeat protein Ski8 (9). The molecular targets of parafibromin and the mechanism by which its inactivation can lead to neoplastic transformation are poorly understood. We show here that parafibromin, in the context of the PAF1 complex, mediates repression of the c-myc protooncogene through both transcriptional and posttranscriptional mechanisms. This finding provides a previously uncharacterized mechanism for the anti-proliferative action of parafibromin and a plausible mechanism by which its loss of function promotes neoplasia.

Section: Resultsmentioning

confidence: 93%

mentioning

confidence: 99%

The parafibromin tumor suppressor protein inhibits cell proliferation by repression of the c-myc proto-oncogene

Zhang²,

Panicker³

et al. 2008

“…To establish the functional role of PAF1c in CARM1-regulated transcription, we attempted to knockdown PAF1c components and measure the effects on mRNA levels of CARM1-regulated ER targets. Knocking down Ctr9 was previously reported to affect expression of other PAF1c subunits in yeast and human cells (17,18), and Ctr9 and Paf1 were shown as scaffold proteins for the formation of PAF1c (19). Therefore, we generated a Dox-inducible Ctr9 knockdown cell line, MCF7-tet-on-shCtr9, which allows transient knockdown of Ctr9 to minimize cellular toxicity associated with the loss of functional PAF1c.…”

Section: Paf1c and Carm1 Coordinately Regulate A Common Set Of Erαmentioning

confidence: 99%

Histone H3R17me2a mark recruits human RNA Polymerase-Associated Factor 1 Complex to activate transcription

2012

The histone coactivator-associated arginine methyltransferase 1 (CARM1) is a coactivator for a number of transcription factors, including nuclear receptors. Although CARM1 and its asymmetrically deposited dimethylation at histone H3 arginine 17 (H3R17me2a) are associated with transcription activation, the mechanism by which CARM1 activates transcription remains unclear. Using an unbiased biochemical approach, we discovered that the transcription elongation-associated PAF1 complex (PAF1c) directly interacts with H3R17me2a. PAF1c binds to histone H3 tails harboring dimethylation at R17 in CARM1-methylated histone octamers. Knockdown of either PAF1c subunits or CARM1 affected transcription of CARM1-regulated, estrogen-responsive genes. Furthermore, either CARM1 knockdown or CARM1 enzyme-deficient mutant knockin resulted in decreased H3R17me2a accompanied by the reduction of PAF1c occupancy at the proximal promoter estrogen-responsive elements. In contrast, PAF1c knockdown elicited no effects on H3R17me2a but reduced the H3K4me3 level at estrogen-responsive elements. These observations suggest that, apart from PAF1c's established roles in directing histone modifications, PAF1c acts as an arginine methyl histone effector that is recruited to promoters and activates a subset of genes, including targets of estrogen signaling.estrogen receptor-α | histone arginine methylation | PRMT

“…Paf1C associates with RNA pol II from the 5′ end of a gene to the poly(A) site (22, 23); interacts functionally and physically with the transcription elongation factors Spt4-Spt5/DSIF, Spt16-Pob3/FACT, and TFIIS (8,(24)(25)(26)(27); regulates the phosphorylation state of RNA pol II (28, 29); and is required for proper 3′ end formation of certain transcripts (30-32). Important to this study, deletion of RTF1 from yeast cells causes dramatic reductions in H2B K123 ubiquitylation and H3 K4 and K79 methylation (33-36), and this role in histone modification, like other Paf1C functions, is conserved in higher eukaryotes (37)(38)(39)(40).The mechanisms by which Paf1C promotes histone modifications have yet to be elucidated. Deletion of RTF1, CTR9, or PAF1 reduces the occupancies of Rad6 and Set1/COMPASS on coding regions (33,35,41), and purified Paf1C interacts with Bre1 in vitro (42,43), suggesting that Paf1C serves as a platform for recruiting histone-modifying enzymes to RNA pol II during elongation.…”

mentioning

confidence: 99%

Small region of Rtf1 protein can substitute for complete Paf1 complex in facilitating global histone H2B ubiquitylation in yeast

Piro

Mayekar

Warner

et al. 2012

Histone modifications regulate transcription by RNA polymerase II and maintain a balance between active and repressed chromatin states. The conserved Paf1 complex (Paf1C) promotes specific histone modifications during transcription elongation, but the mechanisms by which it facilitates these marks are undefined. We previously identified a 90-amino acid region within the Rtf1 subunit of Paf1C that is necessary for Paf1C-dependent histone modifications in Saccharomyces cerevisiae. Here we show that this histone modification domain (HMD), when expressed as the only source of Rtf1, can promote H3 K4 and K79 methylation and H2B K123 ubiquitylation in yeast. The HMD can restore histone modifications in rtf1Δ cells whether or not it is directed to DNA by a fusion to a DNA binding domain. The HMD can facilitate histone modifications independently of other Paf1C subunits and does not bypass the requirement for Rad6-Bre1. The isolated HMD localizes to chromatin, and this interaction requires residues important for histone modification. When expressed outside the context of fulllength Rtf1, the HMD associates with and causes Paf1C-dependent histone modifications to appear at transcriptionally inactive loci, suggesting that its function has become deregulated. Finally, the Rtf1 HMDs from other species can function in yeast. Our findings suggest a direct and conserved role for Paf1C in coupling histone modifications to transcription elongation.transcription-coupled histone modifications | nucleosome I n eukaryotes, transcription occurs within the context of a restrictive, yet dynamic, chromatin environment. The posttranslational modification of histones represents a major mechanism by which cells control the structure of chromatin. Some modifications of histones include acetylation, methylation, and ubiquitylation. These modifications can alter the structural properties of nucleosomes and serve as specific effectors for the recruitment of proteins that further modify the chromatin template and regulate transcription (1).Monoubiquitylation of histone H2B on lysine (K) 123 in Saccharomyces cerevisiae is a conserved modification that is enriched on active genes but plays roles in both transcriptional repression and activation (2-4). Consistent with a repressive role, H2B monoubiquitylation stabilizes nucleosomes at yeast promoters (5), inhibits the association of the RNA polymerase (pol) II kinase Ctk1 with genes in yeast (6), and interferes with the recruitment of the elongation factor TFIIS to genes in human cells (7). In other studies, H2B monoubiquitylation has been shown to stimulate transcription of chromatin templates (8), promote nucleosome reassembly during transcription elongation (9), and inhibit chromatin compaction (10). H2B monoubiquitylation is also a prerequisite for other histone modifications that mark active genes. Ubiquitylation of H2B K123 by the Rad6-Bre1 ubiquitin conjugase-ligase proteins in yeast (11-13) is required for dimethylation and trimethylation of H3 K4 and K79 by the Set1/COMPASS and Dot1 methy...