Chromatin remodeling complexes interact dynamically with a glucocorticoid receptor-regulated promoter

Area of Science:

• Molecular Biology
• Epigenetics
• Gene Regulation

Background:

• SWI/SNF complexes, containing Brahma (BRM) and Brahma-related gene 1 (BRG1) subunits, are crucial for chromatin remodeling.
• These complexes play vital roles in cell cycle, differentiation, and cancer.
• Steroid hormone signaling pathways frequently intersect with chromatin regulation.

Purpose of the Study:

• To investigate the hormone-dependent recruitment and function of BRG1 and BRM in chromatin remodeling at the MMTV promoter.
• To elucidate the kinetic properties and mechanistic role of SWI/SNF complexes in steroid hormone-inducible gene expression.

Main Methods:

• Utilized imaging approaches with MMTV-LTR tandem repeats in a cell line.
• Employed restriction enzyme accessibility assays and DNA fluorescence in situ hybridization (FISH).
• Performed in vivo photobleaching experiments and expressed ATPase-deficient mutants (BRG1-K-R, BRM-K-R).

Main Results:

• BRG1 and BRM were recruited to the MMTV promoter in a hormone-dependent manner.
• Recruitment led to chromatin decondensation, increased restriction enzyme accessibility, and larger FISH signals.
• Chromatin remodeling correlated with increased RNA polymerase II occupancy and transcriptional activation.
• ATPase-deficient mutants inhibited chromatin remodeling and attenuated transcription.
• In vivo photobleaching revealed distinct dynamic association/dissociation kinetics for BRG1 and BRM complexes.

Conclusions:

• BRG1 and BRM SWI/SNF complexes are recruited to the MMTV promoter in a hormone-dependent manner.
• This recruitment facilitates chromatin remodeling and transcriptional activation.
• The ATPase activity and dynamic properties of these complexes are essential for regulating gene expression at steroid hormone-inducible promoters.