ARID1A regulates histone octamer transfer activity of human canonical BAF complex

Area of Science:

• Molecular Biology
• Cancer Biology
• Chromatin Remodeling

Background:

• Mammalian SWI/SNF (mSWI/SNF or BAF) complexes are crucial for chromatin remodeling.
• Mutations in BAF subunits, particularly ARID1A, are prevalent in over 20% of human cancers.
• ARID1A loss-of-function mutations are common, but its precise biochemical role remains unclear.

Purpose of the Study:

• To biochemically characterize the in vitro activities of different BAF complexes (cBAF, PBAF, ncBAF).
• To define the specific roles of subunits within the cBAF complex, including ARID1A.
• To investigate the functional significance of ARID1A in BAF-mediated chromatin remodeling.

Main Methods:

• In vitro reconstitution of cBAF, PBAF, and ncBAF complexes.
• Reconstitution of various cBAF subcomplexes to dissect subunit functions.
• Biochemical assays measuring nucleosome binding, nucleosome sliding, ATPase activity, and histone octamer transfer.

Main Results:

• ARID1A is dispensable for nucleosome binding, sliding, and ATPase activity in cBAF.
• ARID1A is essential for the cBAF complex's ability to transfer histone octamers between DNA templates.
• Specific subunits were identified as critical for high-affinity nucleosome binding and sliding.

Conclusions:

• ARID1A's primary role in cBAF is histone octamer transfer, not core remodeling activities.
• Histone octamer transfer mediated by BAF complexes, involving ARID1A, is a critical mechanism for cancer prevention.
• This study provides a biochemical basis for ARID1A's tumor suppressor function.