Abstract
The bromodomain-containing protein BRD4 has been thought to transmit epigenetic information across cell divisions by binding to both mitotic chromosomes and interphase chromatin. UV-released BRD4 mediates the recruitment of active P-TEFb to the promoter, which enhances transcriptional elongation. However, the dynamic associations between BRD4 and P-TEFb and BRD4-mediated gene regulation after UV stress are largely unknown. In this study, we found that BRD4 dissociates from chromatin within 30 min after UV treatment and thereafter recruits chromatin. However, P-TEFb binds tightly to chromatin right after UV treatment, suggesting that no interactions occur between BRD4 and P-TEFb within 30 min after UV stress. BRD4 knockdown changes the distribution of P-TEFb among nuclear soluble and chromatin and downregulates the elongation activity of RNA polymerase II. Inhibition of JNK kinase but not other MAP kinases impedes the interactions between BRD4 and P-TEFb. RNA-seq and ChIP assays indicate that BRD4 both positively and negatively regulates gene transcription in cells treated with UV stress. These results reveal previously unrecognized dynamics of BRD4 and P-TEFb after UV stress and regulation of gene transcription by BRD4 acting as either activator or repressor in a context-dependent manner.
Highlights
During mitosis, most transcription factors are dissociated from chromosomes; BRD4 persistently associates with chromatin in interphase and chromosomes during mitosis to transmit epigenetic memory across cell divisions (Dey et al, 2003), indicating that BRD4 is involved in epigenetic memory
Two separable P-TEFb complexes exist in the cell, one bound to BRD4 and the other bound to the inhibitory subunit composed of 7SK small nuclear RNA (7SK snRNA) and HEXIM1 (Jang et al, 2005; Yang et al, 2005)
We used 0.15 M salt to investigate the dynamic associations of BRD4 and P-TEFb with chromatin in the nucleus of cells treated with UV at different time points
Summary
Most transcription factors are dissociated from chromosomes; BRD4 persistently associates with chromatin in interphase and chromosomes during mitosis to transmit epigenetic memory across cell divisions (Dey et al, 2003), indicating that BRD4 is involved in epigenetic memory. BRD4 binds to acetylated histones, resulting in dramatic decondensation. UV Regulates BRD4-Mediated Gene Transcription of nearby chromatin. BRD4 stimulates G1 gene transcription by binding to multiple G1 gene promoters, allowing cells to progress toward S phase (Yang et al, 2008; Dey et al, 2009). The treatment of cells with anti-mitotic drugs, including nocodazole, results in BRD4 release from mitotic chromosomes (Nishiyama et al, 2012). BRD4 plays important roles in maintaining epigenetic regulation and chromatin structure in cells. BRD4 plays important roles in regulating gene expression through phase separation, and it forms nuclear puncta with MED1 at super-enhancers that exhibit properties of liquid-like condensates (Sabari et al, 2018)
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