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

Area of Science:

• Molecular Biology
• Genetics
• Cancer Biology

Background:

• The SWItch/Sucrose Non-Fermentable (SWI/SNF) complex is crucial for gene expression via nucleosome remodeling.
• The SMARCB1 subunit is essential for SWI/SNF complex function and is frequently inactivated in pediatric cancers.
• The impact of SMARCB1 missense mutations on function is not well understood, and diagnostics often overlook mutation status.

Purpose of the Study:

• To comprehensively assess the functional impact of SMARCB1 alterations using deep mutational scanning.
• To investigate how missense mutations affect SMARCB1's role in chromatin remodeling and cancer.

Main Methods:

• Deep mutational scanning of 8418 SMARCB1 alterations.
• Functional assays to assess anti-proliferation activity, SWI/SNF complex stability, and chromatin remodeling.
• Comparison of missense mutations to nonsense mutations.

Main Results:

• Missense mutations in SMARCB1 impair its anti-proliferation function, comparable to nonsense mutations.
• These mutations destabilize the SWI/SNF complex, affecting chromatin remodeling and transcriptional regulation.
• Functional defects persist despite detectable SMARCB1 protein expression, challenging immunohistochemistry-based diagnostics.

Conclusions:

• SMARCB1 missense mutations have significant functional consequences in pediatric malignancies.
• Current diagnostic reliance on immunohistochemistry for SMARCB1 may be insufficient due to retained protein expression with functional defects.
• A deeper understanding of SMARCB1 mutation status is critical for accurate cancer diagnosis and classification.