biostudies-literatureXing PChinese Academy of SciencesNIH National Institute of General Medical SciencesNational Natural Science Foundation of ChinaNational Institutes of HealthNIGMS NIH HHSBeijing Natural Science Foundation116075https://www.ebi.ac.uk/biostudies/studies/S-EPMC12434867biostudies-literatureUnknown44(8)SF3B1 is the most frequently mutated splicing factor in cancer. Such mutations cause missplicing by promoting aberrant 3' splice site usage; however, how this occurs mechanistically remains controversial. To address this issue, we employed a computational screen of 600 splicing-related proteins to identify those whose reduced expression recapitulates mutant SF3B1-induced splicing dysregulation. Strikingly, our analysis reveals only two proteins whose knockdown or knockout reproduces this effect. Extending our previous findings, loss of the G-patch protein SUGP1 recapitulates almost all splicing defects induced by SF3B1 hotspot mutations. Unexpectedly, loss of the RNA helicase Aquarius (AQR) reproduces ∼40% of these defects. However, we find that AQR knockdown causes significant SUGP1 missplicing and reduced SUGP1 levels, suggesting that AQR loss reproduces mutant SF3B1 splicing defects only indirectly. This study advances our understanding of missplicing caused by oncogenic SF3B1 mutations and highlights the fundamental role of SUGP1 in this process.Cell reportsSUGP1 loss drives SF3B1 hotspot mutant missplicing in cancer.PMC12434867Z22001232170565R35 GM118136Liu ZZhang JXie JBak-Gordon PManley JLXing PfalseSUGP1 loss drives SF3B1 hotspot mutant missplicing in cancer.SF3B1 is the most frequently mutated splicing factor in cancer. Such mutations cause missplicing by promoting aberrant 3' splice site usage; however, how this occurs mechanistically remains controversial. To address this issue, we employed a computational screen of 600 splicing-related proteins to identify those whose reduced expression recapitulates mutant SF3B1-induced splicing dysregulation. Strikingly, our analysis reveals only two proteins whose knockdown or knockout reproduces this effect. Extending our previous findings, loss of the G-patch protein SUGP1 recapitulates almost all splicing defects induced by SF3B1 hotspot mutations. Unexpectedly, loss of the RNA helicase Aquarius (AQR) reproduces ∼40% of these defects. However, we find that AQR knockdown causes significant SUGP1 missplicing and reduced SUGP1 levels, suggesting that AQR loss reproduces mutant SF3B1 splicing defects only indirectly. This study advances our understanding of missplicing caused by oncogenic SF3B1 mutations and highlights the fundamental role of SUGP1 in this process.2025-01-01T00:00:00Z2025 Aug2026-06-01T14:03:05.214Z2026-04-08T13:16:11.355ZS-EPMC124348674071463510.1016/j.celrep.2025.116075