SMARCB1 missense mutants disrupt SWI/SNF complex stability and remodeling activity

Area of Science:

• Molecular Biology
• Cancer Genomics
• Epigenetics

Background:

• The SWI/SNCH complex is crucial for gene regulation via chromatin remodeling.
• SMARCB1 is an essential core subunit of the SWI/SNF complex.
• Biallelic SMARCB1 inactivation drives aggressive pediatric cancers, but missense mutation effects are unclear.

Purpose of the Study:

• To comprehensively assess the functional impact of SMARCB1 missense mutations using deep mutational scanning.
• To understand the molecular mechanisms by which SMARCB1 mutations affect tumor suppressor function.
• To evaluate the limitations of current diagnostic methods based on protein expression.

Main Methods:

• Performed deep mutational scanning (DMS) on 8,418 SMARCB1 amino acid substitutions.
• Assessed the functional impact of mutations on chromatin remodeling and transcriptional regulation.
• Analyzed mutation effects on SWI/SNF complex stability and winged-helix domain flexibility.

Main Results:

• Identified missense mutations in the RPT2 domain that destabilize the SWI/SNF complex.
• Demonstrated that some missense mutations impair chromatin remodeling and gene regulation as severely as nonsense mutations.
• Showed these functionally disruptive mutations can maintain detectable SMARCB1 protein expression.

Conclusions:

• SMARCB1 missense mutations, particularly in the RPT2 domain, can inactivate tumor suppressor functions.
• Current diagnostic reliance on immunohistochemistry (IHC) for SMARCB1 may miss functionally significant mutations.
• This study provides a functional framework for understanding the SMARCB1 mutational landscape in cancer.