Cancer-associated SF3B1 mutations affect alternative splicing by promoting alternative branchpoint usage

Abstract

Abstract Hotspot mutations in the spliceosome gene SF3B1 are reported in ∼20% of uveal melanomas. SF3B1 is involved in 3′-splice site (3′ss) recognition during RNA splicing; however, the molecular mechanisms of its mutation have remained unclear. Here we show, using RNA-Seq analyses of uveal melanoma, that the SF3B1 R625/K666 mutation results in deregulated splicing at a subset of junctions, mostly by the use of alternative 3′ss. Modelling the differential junctions in SF3B1 WT and SF3B1 R625/K666 cell lines demonstrates that the deregulated splice pattern strictly depends on SF3B1 status and on the 3’ss-sequence context. SF3B1 WT knockdown or overexpression do not reproduce the SF3B1 R625/K666 splice pattern, qualifying SF3B1 R625/K666 as change-of-function mutants. Mutagenesis of predicted branchpoints reveals that the SF3B1 R625/K666 -promoted splice pattern is a direct result of alternative branchpoint usage. Altogether, this study provides a better understanding of the mechanisms underlying splicing alterations induced by mutant SF3B1 in cancer, and reveals a role for alternative branchpoints in disease.

Keywords

Affiliated Institutions

• Laboratoire de Biologie du Développement FR
• Institut de Génétique Humaine FR
• Institut Curie FR
• Génétique et biologie du développement
• Intégrité du génome, ARN et cancer FR

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