E2F mediates cell cycle-dependent transcriptional repression in vivo by recruitment of an HDAC1/mSin3B corepressor complex

Abstract

Despite biochemical and genetic data suggesting that E2F and pRB (pocket protein) families regulate transcription via chromatin-modifying factors, the precise mechanisms underlying gene regulation by these protein families have not yet been defined in a physiological setting. In this study, we have investigated promoter occupancy in wild-type and pocket protein-deficient primary cells. We show that corepressor complexes consisting of histone deacetylase (HDAC1) and mSin3B were specifically recruited to endogenous E2F-regulated promoters in quiescent cells. These complexes dissociated from promoters once cells reached late G 1 , coincident with gene activation. Interestingly, recruitment of HDAC1 complexes to promoters depended absolutely on p107 and p130, and required an intact E2F-binding site. In contrast, mSin3B recruitment to certain promoters did not require p107 or p130, suggesting that recruitment of this corepressor can occur via E2F-dependent and -independent mechanisms. Remarkably, loss of pRB had no effect on HDAC1 or mSin3B recruitment. p107/p130 deficiency triggered a dramatic loss of E2F4 nuclear localization as well as transcriptional derepression, which is suggested by nucleosome mapping studies to be the result of localized hyperacetylation of nucleosomes proximal to E2F-binding sites. Taken together, these findings show that p130 escorts E2F4 into the nucleus and, together with corepressor complexes that contain mSin3B and/or HDAC1, directly represses transcription from target genes as cells withdraw from the cell cycle.

E2F4 regulates a stable G2 arrest response to genotoxic stress in prostate carcinoma

“…Previous ChIP studies indicated that E2F members occupied gene promoters in a cell cycle-specific manner, suggesting their specific roles during the cell cycle through coordinated targeting and regulation of specific genes (Takahashi et al, 2000;Wells et al, 2000;Rayman et al, 2002). Together with other reports indicating multiple promoter occupancies that lead to both positive and negative transcriptional activation thresholds , we suggest a physiological role for E2F4 in the radiation-dependent stable G 2 arrest, just as exogenous E2F 1-3a can promote cell cycle progression.…”

Retinoblastoma gene family expression in lymphoid tissues

“…They are believed to accomplish this by recruiting a variety of chromatin-modifying activities to E2F-responsive promoters (Frolov and Dyson, 2004). Pocket proteins recruit type I histone deacetylases (HDACs), resulting in removal of acetyl groups from histones H3 and H4, and in a compacted chromatin structure that is refractory to transcription initiation (Takahashi et al, 2000;Rayman et al, 2002). The recruitment of HDACs is indirect (Lai et al, 2001) and accompanied by recruitment of other co-repressors, chromatin remodelling factors and histone methyltransferases (Frolov and Dyson, 2004).…”

“…E2F4 and E2F5 then relocate to the cytoplasm, and the promoters generally bind to E2F1-3. For many promoters, the binding of E2F1-3 correlates with recruitment of histone acetyltransferases, increased histone acetylation and transcriptional activation (Takahashi et al, 2000;Rayman et al, 2002;Taubert et al, 2004). A model for pRb2/p130 and p107 control during cell proliferation has been proposed based on experimental data.…”

Targeting an E2F site in the mouse genome prevents promoter silencing in quiescent and post-mitotic cells

“…The pocket proteins bind a number of chromatin modifying factors that may account for transcriptional repression by E2F complexes (reviewed by Cobrinik (2005)). For example, pocket protein/E2F complexes recruit histone deacetylases (HDACs) to remove acetyl groups from histones H3 and H4 (Rayman et al, 2002), resulting in a more compact chromatin structure that inhibits transcription initiation.…”

“…Moreover, studies of endogenous promoters in mouse cells lacking E2F and/or pocket proteins, and in human cells expressing viral oncoproteins such as E1A, are complicated by the fact that these cells suffer profound phenotypic changes affecting cell cycle regulatory processes. Previously, we generated stable NIH 3T3 cell lines carrying low copy numbers of an integrated B-myb promoter-regulated reporter and showed that the E2F site is required for recruitment of p130 and HDAC-1 to repress this gene following serum starvation (Rayman et al, 2002). To allow investigation of promoter regulation in its natural chromatin context, we have now introduced an E2F site mutation into the endogenous B-myb promoter in mouse embryonal stem (ES) cells and have generated mice carrying this mutant allele.…”