BMI1-UBR5 axis regulates transcriptional repression at damaged chromatin
BMI1-UBR5 axis regulates transcriptional repression at damaged chromatin
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DOI：
10.1073/pnas.1610735113
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发表时间：
2016-10-04
影响因子：
11.1
通讯作者：
Kee, Younghoon
中科院分区：
文献类型：
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作者：
Sanchez, Anthony;De Vivo, Angelo;Kee, Younghoon
BMI1是Polycomb suppression Complex 1 （PRC1）的一个组成部分，在发育过程中维持表观遗传沉默发挥关键作用。BMI1也参与DNA损伤应答过程中的基因沉默，但BMI1在基因沉默中的确切下游功能尚不清楚。在这里，我们确定了UBR5 E3连接酶是BMI1的下游因子。我们发现UBR5以依赖于PRC1组分BMI1、RNF1 （RING1a）和RNF2 （RING1b）的方式形成损伤诱导的核灶。尽管在紫外线诱导的染色质损伤处转录受到抑制，但PRC1成员的缺失或UBR5单独抑制了这些位点的转录延伸，这表明UBR5与PRC1在诱导损伤处基因沉默的线性途径中起作用。质谱（MS）分析显示UBR5与BMI1以及FACT成分SPT16和SSRP1相关。我们发现UBR5与SPT16一起定位于紫外线诱导的病变。我们发现UBR5泛素化SPT16，并且UBR5或BMI1的缺失导致紫外线病变处SPT16病灶大小的增大，这表明UBR5和BMI1抑制了受损部位SPT16的富集。一致地，FACT成分的缺失有效地逆转了UBR5和BMI1 KO细胞中发生的转录抑制。最后，UBR5和BMI1 KO细胞对紫外线极度敏感，这支持了在受损部位有缺陷的RNA合成对细胞适应性有害的观点。总之，这些结果表明，BMI1和UBR5通过负向调节事实依赖的Pol II延伸，抑制聚合酶II （Pol II）介导的受损位点的转录。
BMI1 is a component of the Polycomb Repressive Complex 1 (PRC1), which plays a key role in maintaining epigenetic silencing during development. BMI1 also participates in gene silencing during DNA damage response, but the precise downstream function of BMI1 in gene silencing is unclear. Here we identified the UBR5 E3 ligase as a downstream factor of BMI1. We found that UBR5 forms damage-inducible nuclear foci in a manner dependent on the PRC1 components BMI1, RNF1 (RING1a), and RNF2 (RING1b). Whereas transcription is repressed at UV-induced lesions on chromatin, depletion of the PRC1 members or UBR5 alone derepressed transcription elongation at these sites, suggesting that UBR5 functions in a linear pathway with PRC1 in inducing gene silencing at lesions. Mass spectrometry (MS) analysis revealed that UBR5 associates with BMI1 as well as FACT components SPT16 and SSRP1. We found that UBR5 localizes to the UV-induced lesions along with SPT16. We show that UBR5 ubiquitinates SPT16, and depletion of UBR5 or BMI1 leads to an enlargement of SPT16 foci size at UV lesions, suggesting that UBR5 and BMI1 repress SPT16 enrichment at the damaged sites. Consistently, depletion of the FACT components effectively reversed the transcriptional derepression incurred in the UBR5 and BMI1 KO cells. Finally, UBR5 and BMI1 KO cells are hypersensitive to UV, which supports the notion that faulty RNA synthesis at damaged sites is harmful to the cell fitness. Altogether, these results suggest that BMI1 and UBR5 repress the polymerase II (Pol II)-mediated transcription at damaged sites, by negatively regulating the FACT-dependent Pol II elongation.