Journal of Biological Chemistry
Volume 284, Issue 15, 10 April 2009, Pages 10067-10075
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Transcription, Chromatin, and Epigenetics
Antagonistic Roles for BRM and BRG1 SWI/SNF Complexes in Differentiation*

https://doi.org/10.1074/jbc.M808782200Get rights and content
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The mammalian SWI/SNF chromatin-remodeling complex is essential for the multiple changes in gene expression that occur during differentiation. However, the basis within the complex for specificity in effecting positive versus negative changes in gene expression has only begun to be elucidated. The catalytic core of the complex can be either of two closely related ATPases, BRM or BRG1, with the potential that the choice of alternative subunits is a key determinant of specificity. Short hairpin RNA-mediated depletion of the ATPases was used to explore their respective roles in the well characterized multistage process of osteoblast differentiation. The results reveal an unexpected role for BRM-specific complexes. Instead of impeding differentiation as was seen with BRG1 depletion, depletion of BRM caused accelerated progression to the differentiation phenotype. Multiple tissue-specific differentiation markers, including the tightly regulated late stage marker osteocalcin, become constitutively up-regulated in BRM-depleted cells. Chromatin immunoprecipitation analysis of the osteocalcin promoter as a model for the behavior of the complexes indicates that the promoter is a direct target of both BRM- and BRG1-containing complexes. BRG1 complexes, which are required for activation, are associated with the promoter well before induction, but the concurrent presence of BRM-specific complexes overrides their activation function. BRM-specific complexes are present only on the repressed promoter and are required for association of the co-repressor HDAC1. These findings reveal an unanticipated degree of specialization of function linked with the choice of ATPase and suggest a new paradigm for the roles of the alternative subunits during differentiation.

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The abbreviations used are: BRM, Brahma; BRG1, Brahma-related gene 1; shRNA, short hairpin RNA; ChIP, chromatin immunoprecipitation; HDAC, histone deacetylase; PBS, phosphate-buffered saline; NBT, nitro blue tetrazolium; BCIP, 5-bromo-4-chloro-3-indolyl phosphate; QPCR, quantitative real-time reverse transcription-PCR.

*

This work was supported, in whole or in part, by National Institutes of Health Grant GM073257 from the USPSH (to E. M.). The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked “advertisement” in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.

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Present address: Interquest Medical and Scientific Communications, Mountain Lakes, NJ 07046.