The bromodomain and extra-terminal motif (BET) protein BRD4 binds to acetylated histones at enhancers and promoters via its bromodomains (BDs) to regulate transcriptional elongation. In human colorectal cancer cells, we found that BRD4 was recruited to enhancers that were co-occupied by mutant p53 and supported the synthesis of enhancer-directed transcripts (eRNAs) in response to chronic immune signaling. BRD4 selectively associated with eRNAs that were produced from BRD4-bound enhancers. Using biochemical and biophysical methods, we found that BRD4 BDs function cooperatively as docking sites for eRNAs and that the BDs of BRD2, BRD3, BRDT, BRG1, and BRD7 directly interact with eRNAs. BRD4-eRNA interactions increased BRD4 binding to acetylated histones in vitro and augmented BRD4 enhancer recruitment and transcriptional cofactor activities. Our results suggest a mechanism by which eRNAs are directly involved in gene regulation by modulating enhancer interactions and transcriptional functions of BRD4.

The maintenance of eukaryotic telomeres requires telomerase, which is minimally composed of a telomerase reverse transcriptase (TERT) and an associated RNA component. Telomerase activity is tightly regulated by expression of human (h) TERT at both the transcriptional and post-translational levels. The Hsp90 and p23 molecular chaperones have been shown to associate with hTERT for the assembly of active telomerase. Here, we show that CHIP (C terminus of Hsc70-interacting protein) physically associates with hTERT in the cytoplasm and regulates the cellular abundance of hTERT through a ubiquitin-mediated degradation. Overexpression of CHIP prevents nuclear translocation of hTERT and promotes hTERT degradation in the cytoplasm, thereby inhibiting telomerase activity. In contrast, knockdown of endogenous CHIP results in the stabilization of cytoplasmic hTERT. However, it does not affect the level of nuclear hTERT and has no effect on telomerase activity and telomere length. We further show that the binding of CHIP and Hsp70 to hTERT inhibits nuclear translocation of hTERT by dissociating p23. However, Hsp90 binding to hTERT was not affected by CHIP overexpression. These results suggest that CHIP can remodel the hTERTchaperone complexes. Finally, the amount of hTERT associated with CHIP peaks in G 2 /M phases but decreases during S phase, suggesting a cell cycle-dependent regulation of hTERT. Our data suggest that CHIP represents a new pathway for modulating telomerase activity in cancer.Telomeres, the specialized nucleoprotein complexes at the ends of eukaryotic chromosomes, are essential for the maintenance of chromosome integrity (1, 2). In most organisms, telomere DNA consists of long tracts of duplex telomere repeats (TTAGGG in vertebrates) with 3Ј single-stranded G overhangs (3) and is tightly associated with the six-protein complex, shelterin, which protects chromosome termini from being recognized as sites of DNA damage (4, 5). Loss of telomere function results in chromosome end fusions, degradation, and other inappropriate reactions, leading to cell senescence, apoptosis, or abnormal cell proliferation (6, 7). In the absence of a telomere maintenance pathway, dividing somatic cells show a progressive loss of telomeric DNA during successive rounds of cell division because of a DNA end replication problem (8, 9). Thus, telomere shortening functions as a control mechanism that regulates the proliferative capacity of cells. Although recombination-mediated telomere elongation has been demonstrated for replenishing telomere DNA (10, 11), the major mechanism to offset telomere erosion is based on telomerase (12, 13). In humans, telomerase is strongly repressed in normal somatic tissues but is expressed in most cancer cells, suggesting that the activation of telomerase is a critical step in human oncogenesis (14,15).Although the enzymatic activity of telomerase is regulated by hTERT 2 at the transcriptional level (16, 17), several lines of evidence have suggested a post-translational regulation of telomerase activity....

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SUMMARY The function of enhancer RNAs (eRNAs) in transcriptional regulation remains obscure. By analyzing the genome-wide nascent transcript profiles in breast cancer cells, we identify a special group of eRNAs that are essential for estrogen-induced transcriptional repression. Using eRNAs of TM4SF1 and EFEMP1 as the paradigms, we find that these RNA molecules not only stabilize promoter-enhancer interactions but also recruit liganded estrogen receptor α (ERα) to particular enhancer regions, facilitate the formation of a functional transcriptional complex, and cause gene silencing. Interestingly, ERα is shown to directly bind with eRNAs by its DNA-binding domain. These eRNAs help with the formation of a specific ERα-centered transcriptional complex and promote the association of the histone demethylase KDM2A, which dismisses RNA polymerase II from designated enhancers and suppresses the transcription of target genes. Our work demonstrates a complete mechanism underlying the action of eRNAs in modulating and refining the locus-specific transcriptional program.