Conrad Ryan J, Fozouni Parinaz, Thomas Sean, Sy Hendrik, Zhang Qiang, Zhou Ming-Ming, Ott Melanie
Gladstone Institutes, University of California, San Francisco, San Francisco, CA 94158, USA; Graduate Program in Pharmaceutical Sciences and Pharmacogenomics, University of California, San Francisco, San Francisco, CA 94158, USA; Department of Medicine, University of California, San Francisco, San Francisco, CA 94158, USA.
Gladstone Institutes, University of California, San Francisco, San Francisco, CA 94158, USA; Department of Medicine, University of California, San Francisco, San Francisco, CA 94158, USA.
Mol Cell. 2017 Sep 21;67(6):1001-1012.e6. doi: 10.1016/j.molcel.2017.07.025. Epub 2017 Aug 24.
BET proteins commonly activate cellular gene expression, yet inhibiting their recruitment paradoxically reactivates latent HIV-1 transcription. Here we identify the short isoform of BET family member BRD4 (BRD4S) as a corepressor of HIV-1 transcription. We found that BRD4S was enriched in chromatin fractions of latently infected T cells, and it was more rapidly displaced from chromatin upon BET inhibition than the long isoform. BET inhibition induced marked nucleosome remodeling at the latent HIV-1 promoter, which was dependent on the activity of BRG1-associated factors (BAF), an SWI/SNF chromatin-remodeling complex with known repressive functions in HIV-1 transcription. BRD4S directly bound BRG1, a catalytic subunit of BAF, via its bromodomain and extraterminal (ET) domain, and this isoform was necessary for BRG1 recruitment to latent HIV-1 chromatin. Using chromatin immunoprecipitation sequencing (ChIP-seq) combined with assay for transposase-accessible chromatin coupled to high-throughput sequencing (ATAC-seq) data, we found that the latent HIV-1 promoter phenotypically resembles endogenous long terminal repeat (LTR) sequences, pointing to a select role of BRD4S-BRG1 complexes in genomic silencing of invasive retroelements.
BET蛋白通常会激活细胞基因表达，但抑制它们的募集却反常地重新激活了潜伏的HIV-1转录。在此，我们鉴定出BET家族成员BRD4的短异构体（BRD4S）是HIV-1转录的共抑制因子。我们发现BRD4S在潜伏感染的T细胞的染色质组分中富集，并且在BET抑制后，它比长异构体更快地从染色质上被置换下来。BET抑制在潜伏的HIV-1启动子处诱导了显著的核小体重塑，这依赖于BRG1相关因子（BAF）的活性，BAF是一种在HIV-1转录中具有已知抑制功能的SWI/SNF染色质重塑复合体。BRD4S通过其溴结构域和末端外（ET）结构域直接结合BAF的催化亚基BRG1，并且这种异构体对于BRG1募集到潜伏的HIV-1染色质是必需的。使用染色质免疫沉淀测序（ChIP-seq）结合转座酶可及染色质分析与高通量测序（ATAC-seq）数据，我们发现潜伏的HIV-1启动子在表型上类似于内源性长末端重复序列（LTR），这表明BRD4S-BRG1复合体在侵袭性逆转录元件的基因组沉默中具有特定作用。
