Department of Biological Sciences, Columbia University, New York, NY 10027, USA.
Irving Cancer Research Center, Columbia University, New York, NY 10032, USA.
Mol Cell. 2019 Oct 3;76(1):82-95.e7. doi: 10.1016/j.molcel.2019.07.017. Epub 2019 Aug 29.
SF3B1, which encodes an essential spliceosomal protein, is frequently mutated in myelodysplastic syndromes (MDS) and many cancers. However, the defect of mutant SF3B1 is unknown. Here, we analyzed RNA sequencing data from MDS patients and confirmed that SF3B1 mutants use aberrant 3' splice sites. To elucidate the underlying mechanism, we purified complexes containing either wild-type or the hotspot K700E mutant SF3B1 and found that levels of a poorly studied spliceosomal protein, SUGP1, were reduced in mutant spliceosomes. Strikingly, SUGP1 knockdown completely recapitulated the splicing errors, whereas SUGP1 overexpression drove the protein, which our data suggest plays an important role in branchsite recognition, into the mutant spliceosome and partially rescued splicing. Other hotspot SF3B1 mutants showed similar altered splicing and diminished interaction with SUGP1. Our study demonstrates that SUGP1 loss is a common defect of spliceosomes with disease-causing SF3B1 mutations and, because this defect can be rescued, suggests possibilities for therapeutic intervention.
SF3B1 编码一种必需的剪接体蛋白，在骨髓增生异常综合征（MDS）和许多癌症中经常发生突变。然而，突变型 SF3B1 的缺陷尚不清楚。在这里，我们分析了 MDS 患者的 RNA 测序数据，并证实 SF3B1 突变体使用异常的 3'剪接位点。为了阐明潜在的机制，我们纯化了含有野生型或热点 K700E 突变 SF3B1 的复合物，并发现突变剪接体中一种研究甚少的剪接体蛋白 SUGP1 的水平降低。引人注目的是，SUGP1 的敲低完全再现了剪接错误，而 SUGP1 的过表达将该蛋白（我们的数据表明该蛋白在分支位点识别中发挥重要作用）驱动到突变剪接体中，并部分挽救了剪接。其他热点 SF3B1 突变体也表现出类似的改变剪接和与 SUGP1 相互作用减弱。我们的研究表明，SUGP1 的缺失是导致疾病的 SF3B1 突变的剪接体的常见缺陷，并且由于这种缺陷可以得到挽救，因此提示了治疗干预的可能性。
