Genome-wide Analysis of Transcription Factor E2F1 Mutant Proteins Reveals That N- and C-terminal Protein Interaction Domains Do Not Participate in Targeting E2F1 to the Human Genome

Genome Center, University of California, Davis, California 95616, USA.
Journal of Biological Chemistry (Impact Factor: 4.57). 02/2011; 286(14):11985-96. DOI: 10.1074/jbc.M110.217158
Source: PubMed

ABSTRACT Previous studies of E2F family members have suggested that protein-protein interactions may be the mechanism by which E2F proteins are recruited to specific genomic regions. We have addressed this hypothesis on a genome-wide scale using ChIP-seq analysis of MCF7 cell lines that express tagged wild type and mutant E2F1 proteins. First, we performed ChIP-seq for tagged WT E2F1. Then, we analyzed E2F1 proteins that lacked the N-terminal SP1 and cyclin A binding domains, the C-terminal transactivation and pocket protein binding domains, and the internal marked box domain. Surprisingly, we found that the ChIP-seq patterns of the mutant proteins were identical to that of WT E2F1. However, mutation of the DNA binding domain abrogated all E2F1 binding to the genome. These results suggested that the interaction between the E2F1 DNA binding domain and a consensus motif may be the primary determinant of E2F1 recruitment. To address this possibility, we analyzed the in vivo binding sites for the in vitro-derived consensus E2F1 motif (TTTSSCGC) and also performed de novo motif analysis. We found that only 12% of the ChIP-seq peaks contained the TTTSSCGC motif. De novo motif analysis indicated that most of the in vivo sites lacked the 5' half of the in vitro-derived consensus, having instead the in vivo consensus of CGCGC. In summary, our findings do not provide support for the model that protein-protein interactions are involved in recruiting E2F1 to the genome, but rather suggest that recognition of a motif found at most human promoters is the critical determinant.

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Available from: Peggy J Farnham, Jan 07, 2015
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    • "Since EAPP interacts with the activating E2F proteins [12] it was conceivable that E2F proteins are involved in the activation of MDR1. Even though there are no canonical E2F binding sites within the MDR1 promoter it is not implausible that E2F plays a role in its regulation, considering the huge number of promoters where E2F is present even without an E2F binding site [19] [20]. Reporter gene assays with both, the wt and the MDR1 promoter with a mutated Y-Box [18] were carried out. "
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    ABSTRACT: Multidrug resistance (MDR), one of the main reasons for diminishing efficacy of prolonged chemotherapy, is frequently caused by the elevated expression of the ABCB1/MDR1 gene encoding PGP (P-glycoprotein). EAPP (E2F-Associated-PhosphoProtein) is a frequently overexpressed protein in human tumor cells. It inhibits apoptosis in a p21-dependent manner. We show here that EAPP stimulates the MDR1 promoter resulting in higher PGP levels. Independently of EAPP, E2F1 also increases the activity of the MDR1 promoter. Co-expression of pRb inhibits E2F1-, but not EAPP-dependent promoter activation. The upregulation of PGP might contribute to the survival of tumor cells during chemotherapy and worsen the prognosis for the patient.
    FEBS letters 03/2013; 587(10). DOI:10.1016/j.febslet.2013.03.026 · 3.17 Impact Factor
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    • "DNA binding of the E2F6-8 proteins has been associated with transcriptional repression [57]. All members of the E2F family share a conserved DNA-binding domain [59,60] and have been reported to bind the same TTT(C/G)(C/G)CGC motif in vitro [54]. "
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    ABSTRACT: Background The binding of transcription factors to specific locations in the genome is integral to the orchestration of transcriptional regulation in cells. To characterize transcription factor binding site function on a large scale, we predicted and mutagenized 455 binding sites in human promoters. We carried out functional tests on these sites in four different immortalized human cell lines using transient transfections with a luciferase reporter assay, primarily for the transcription factors CTCF, GABP, GATA2, E2F, STAT, and YY1. Results In each cell line, between 36% and 49% of binding sites made a functional contribution to the promoter activity; the overall rate for observing function in any of the cell lines was 70%. Transcription factor binding resulted in transcriptional repression in more than a third of functional sites. When compared with predicted binding sites whose function was not experimentally verified, the functional binding sites had higher conservation and were located closer to transcriptional start sites (TSSs). Among functional sites, repressive sites tended to be located further from TSSs than were activating sites. Our data provide significant insight into the functional characteristics of YY1 binding sites, most notably the detection of distinct activating and repressing classes of YY1 binding sites. Repressing sites were located closer to, and often overlapped with, translational start sites and presented a distinctive variation on the canonical YY1 binding motif. Conclusions The genomic properties that we found to associate with functional TF binding sites on promoters -- conservation, TSS proximity, motifs and their variations -- point the way to improved accuracy in future TFBS predictions.
    Genome biology 09/2012; 13(9):R50. DOI:10.1186/gb-2012-13-9-r50 · 10.81 Impact Factor
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    • "To further support the regulation of the 3'-end processing machinery by E2F, we searched for publicly available datasets that profiled E2F-chromatin interactions on a genomic scale. ChIP-Seq analyses were recently applied to the E2F1 [26] and E2F4 [27] members of this family. While E2F4 mainly acts as transcriptional repressor, to a large extent it shares its binding signature and target genes with E2F1-3, which are transcriptional activators [25]. "
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    ABSTRACT: Background The majority of mammalian genes contain multiple poly(A) sites in their 3' UTRs. Alternative cleavage and polyadenylation are emerging as an important layer of gene regulation as they generate transcript isoforms that differ in their 3' UTRs, thereby modulating genes' response to 3' UTR-mediated regulation. Enhanced cleavage at 3' UTR proximal poly(A) sites resulting in global 3' UTR shortening was recently linked to proliferation and cancer. However, mechanisms that regulate this enhanced alternative polyadenylation are unknown. Results Here, we explored, on a transcriptome-wide scale, alternative polyadenylation events associated with cellular proliferation and neoplastic transformation. We applied a deep-sequencing technique for identification and quantification of poly(A) sites to two human cellular models, each examined under proliferative, arrested and transformed states. In both cell systems we observed global 3' UTR shortening associated with proliferation, a link that was markedly stronger than the association with transformation. Furthermore, we found that proliferation is also associated with enhanced cleavage at intronic poly(A) sites. Last, we found that the expression level of the set of genes that encode for 3'-end processing proteins is globally elevated in proliferation, and that E2F transcription factors contribute to this regulation. Conclusions Our results comprehensively identify alternative polyadenylation events associated with cellular proliferation and transformation, and demonstrate that the enhanced alternative polyadenylation in proliferative conditions results not only in global 3' UTR shortening but also in enhanced premature cleavage in introns. Our results also indicate that E2F-mediated co-transcriptional regulation of 3'-end processing genes is one of the mechanisms that links enhanced alternative polyadenylation to proliferation.
    Genome biology 07/2012; 13(7):R59. DOI:10.1186/gb-2012-13-7-r59 · 10.81 Impact Factor
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