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

Area of Science:

• Molecular Biology
• Genetics
• Oncology

Background:

• Hotspot mutations in the spliceosome gene SF3B1 occur in approximately 20% of uveal melanomas.
• SF3B1 plays a critical role in recognizing 3'-splice sites (3'ss) during RNA splicing.
• The precise molecular mechanisms by which SF3B1 mutations lead to cancer remain largely unknown.

Purpose of the Study:

• To elucidate the molecular mechanisms by which SF3B1 mutations induce splicing alterations in uveal melanoma.
• To investigate the functional consequences of SF3B1 mutations on RNA splicing patterns.
• To identify the role of alternative branchpoint usage in SF3B1-mutated cancers.

Main Methods:

• RNA sequencing (RNA-Seq) analysis of uveal melanoma samples.
• Modeling of differential splicing patterns in SF3B1 wild-type (WT) and mutant cell lines.
• Mutagenesis of predicted branchpoints to assess their role in splicing alterations.

Main Results:

• SF3B1(R625/K666) mutations lead to deregulated splicing, primarily through the utilization of alternative 3'ss.
• The observed splicing alterations are dependent on SF3B1 status and the 3'ss sequence context.
• SF3B1(R625/K666) mutations function as change-of-function mutants, as knockdown or overexpression of SF3B1(WT) did not replicate the observed splicing patterns.
• Alternative branchpoint usage is directly responsible for the splicing patterns promoted by SF3B1(R625/K666) mutations.

Conclusions:

• This study enhances the understanding of splicing alterations caused by mutant SF3B1 in cancer.
• The findings reveal a significant role for alternative branchpoints in the pathogenesis of SF3B1-mutated cancers, particularly uveal melanoma.
• The research provides mechanistic insights into how spliceosome mutations contribute to cancer development.