A Novel Repressive E2F6 Complex Containing the Polycomb Group Protein, EPC1, That Interacts with EZH2 in a Proliferation-specific Manner

Abstract

The transcriptional repressor E2F6 has been identified as a component of two distinct polycomb group protein (PcG)-containing complexes, suggesting a mechanism for the recruitment of repressive complexes to target sequences in DNA. Whereas one complex is involved in the repression of classic E2F target genes in G 0 , a role for E2F6 within the cell cycle has yet to be defined. We searched for novel E2F6-binding proteins using a yeast two-hybrid screen and identified the PcG protein, EPC1. We showed that, both in vitro and in vivo, E2F6, DP1, and EPC1 form a stable core complex with repressive activity. Furthermore, we identified the proliferation-specific PcG, EZH2, as an EPC1-interacting protein. Using affinity purification, we showed that E2F6, DP1, EPC1, EZH2, and Sin3B co-elute, suggesting the identification of a novel E2F6 complex that exists in vivo in both normal and transformed human cell lines. EZH2 is required for cellular proliferation and consistent with this, EZH2 elutes with the E2F6-EPC1 complex only in proliferating cells. Thus we have identified a novel E2F6-PcG complex (E2F6-EPC1) that interacts with EZH2 and may regulate genes required for cell cycle progression.

Retinoblastoma family genes

“…Consistent with these structural features, this subgroup of E2Fs functions mainly as repressors of E2F target gene expression, and they translocate into the nucleus when in complex with the Rb family of proteins during the G0/G1 phases of the cell cycle (Muller et al, 1997;Verona et al, 1997). E2Fs 6-8, representing the remaining two subgroups, also function as transcriptional repressors (Trimarchi et al, 1998(Trimarchi et al, , 2001de Bruin et al, 2003a;Di Stefano et al, 2003;Attwooll et al, 2004b;Maiti et al, 2005). However, in contrast to E2Fs 1-5, these E2F proteins do not have the Rb-binding sequence at the C-terminus, and therefore their function and regulation are independent of the Rb family of proteins.…”

Recent lessons in gene expression, cell cycle control, and cell biology from adenovirus

“…CtBPs inhibit transcription in part by binding to several distinct histone deacetylases (HDACs) (Chinnadurai, 2002). However, repression at some promoters occurs by HDAC-independent mechanisms since it is not affected by the general HDAC inhibitor trichostatin A. HDAC-independent mechanisms include recruitment of histone methylating Polycomb complex proteins (Meloni et al, 1999;Sewalt et al, 1999;Dahiya et al, 2001;Nielsen et al, 2001;Trimarchi et al, 2001;Vandel et al, 2001;Ogawa et al, 2002;Attwooll et al, 2005) and the subsequent binding of HP1 and other heterochromatin-associated proteins that probably repress transcription by inhibiting promoter access to general transcription factors (Cao and Zhang, 2004;Levine et al, 2004;Lund and van Lohuizen, 2004;Ringrose and Paro, 2004).…”

A comprehensive ChIP–chip analysis of E2F1, E2F4, and E2F6 in normal and tumor cells reveals interchangeable roles of E2F family members

“…For example, E2F6 has been purified in a complex containing EZH2 (Attwooll et al 2005), which is involved in trimethylation of histone H3 at lysine 27, a modification associated with gene repression (Levine et al 2004). Others have purified E2F6 in a complex with a histone methyltransferase that modifies lysine 9 of histone H3 (Ogawa et al 2002), another mark associated with gene silencing.…”