Research Department of Cancer Biology, Cancer Institute, University College London, London, United Kingdom.
Centre for Genomic Regulation (CRG), Barcelona Institute of Science and Technology, Barcelona, Spain.
Elife. 2023 Apr 3;12:e79386. doi: 10.7554/eLife.79386.
Most studies of cohesin function consider the Stromalin Antigen (STAG/SA) proteins as core complex members given their ubiquitous interaction with the cohesin ring. Here, we provide functional data to support the notion that the SA subunit is not a mere passenger in this structure, but instead plays a key role in the localization of cohesin to diverse biological processes and promotes loading of the complex at these sites. We show that in cells acutely depleted for RAD21, SA proteins remain bound to chromatin, cluster in 3D and interact with CTCF, as well as with a wide range of RNA binding proteins involved in multiple RNA processing mechanisms. Accordingly, SA proteins interact with RNA, and R-loops, even in the absence of cohesin. Our results place SA1 on chromatin upstream of the cohesin ring and reveal a role for SA1 in cohesin loading which is independent of NIPBL, the canonical cohesin loader. We propose that SA1 takes advantage of structural R-loop platforms to link cohesin loading and chromatin structure with diverse functions. Since SA proteins are pan-cancer targets, and R-loops play an increasingly prevalent role in cancer biology, our results have important implications for the mechanistic understanding of SA proteins in cancer and disease.
大多数研究黏连蛋白功能的学者认为，Stromalins Antigen (STAG/SA) 蛋白是核心复合物的成员，因为它们与黏连蛋白环普遍相互作用。在这里，我们提供了功能数据来支持这样一种观点，即 SA 亚基在这个结构中不仅仅是一个乘客，而是在将黏连蛋白定位到各种生物过程中发挥关键作用，并促进该复合物在这些部位的加载。我们发现，在急性 RAD21 耗尽的细胞中，SA 蛋白仍然与染色质结合，在 3D 中聚集，并与 CTCF 以及涉及多种 RNA 处理机制的广泛的 RNA 结合蛋白相互作用。因此，SA 蛋白与 RNA 以及 R-环相互作用，即使在没有黏连蛋白的情况下也是如此。我们的结果将 SA1 置于黏连蛋白环的上游染色质上，并揭示了 SA1 在黏连蛋白加载中的作用独立于 NIPBL，后者是经典的黏连蛋白加载器。我们提出，SA1 利用结构 R-环平台将黏连蛋白加载和染色质结构与各种功能联系起来。由于 SA 蛋白是泛癌靶点，并且 R-环在癌症生物学中发挥着越来越重要的作用，因此我们的结果对癌症和疾病中 SA 蛋白的机制理解具有重要意义。
