Disease-Causing Mutations in SF3B1 Alter Splicing by Disrupting Interaction with SUGP1

Area of Science:

• Molecular Biology
• Genetics
• Cancer Research

Background:

• The SF3B1 gene encodes a crucial spliceosomal protein frequently mutated in myelodysplastic syndromes (MDS) and various cancers.
• The precise molecular defect caused by SF3B1 mutations remains largely unknown, hindering therapeutic development.

Purpose of the Study:

• To investigate the functional consequences of SF3B1 mutations on RNA splicing.
• To identify the underlying molecular mechanisms responsible for splicing defects in SF3B1-mutated MDS.
• To explore potential therapeutic strategies targeting SF3B1-associated splicing errors.

Main Methods:

• Analysis of RNA sequencing data from MDS patients with SF3B1 mutations.
• Purification and biochemical analysis of spliceosomal complexes containing wild-type and mutant SF3B1.
• Experimental manipulation of SUGP1 levels through knockdown and overexpression.
• Assessment of RNA splicing fidelity and branch-site recognition.

Main Results:

• SF3B1 mutants were confirmed to utilize aberrant 3' splice sites in MDS.
• Reduced levels of the spliceosomal protein SUGP1 were observed in spliceosomes with hotspot SF3B1 mutations.
• SUGP1 knockdown phenocopied the splicing errors observed in SF3B1 mutants.
• SUGP1 overexpression partially rescued splicing defects by promoting its incorporation into mutant spliceosomes.

Conclusions:

• Loss of SUGP1 function is a common defect in spliceosomes harboring disease-causing SF3B1 mutations.
• SUGP1 plays a critical role in branch-site recognition during RNA splicing.
• The rescue of splicing defects by SUGP1 restoration offers a potential avenue for therapeutic intervention in SF3B1-mutated cancers and MDS.