Comparative analysis of p270 /ARID1A and ARID1B: Alternate members that convey functional specificity to mammalian SWI /SNF complexes.

摘要

Mammalian SWI/SNF complexes are ATPase-powered nucleosome remodeling assemblies crucial for proper cell cycle regulation and control of tissue-specific gene expression. These large, multisubunit complexes are composed of one of two alternate catalytic, core ATPases, BRG1 or BRM. While BRG1 or BRM power the enzymatic activity of the complexes, additional noncatalytic subunits direct the activity of the catalytic core. Two such subunits are p270 and its alternate, mutually exclusive homologue ARID1B. These independent gene products are both members of the ARID family of DNA-binding proteins. p270 expression is sharply reduced in several forms of human cancer, suggesting that p270 contributes to the tumor suppressor function associated with SWI/SNF complexes.;The scope of this thesis was to determine the functions of both p270 and ARID1B, and determine the contribution these proteins bring to SWI/SNF complexes in which they are found. The body of work presented here shows that p270- and ARID1B-containing SWI/SNF complexes have very divergent functions with respect to regulation of genes that control cell proliferation. An osteoblast differentiation model system shows that loss of p270 causes severe defects in cell cycle arrest, including failed repression of factors that promote cell cycle progression (such as E2F-target genes), and lack of induction of cell cycle inhibitory molecules (like p21WAF1/CIP1). Conversely, ARID1B-depleted cells show defects in cell cycle reentry, and show delayed induction of factors that promote proliferation. Direct promoter targets of p270- and ARID1B-containing complexes have been identified (including E2F-targets and c-myc), suggesting that these complexes are able to repress or activate specific targets, respectively. Anti-proliferative p270-containing complexes associate with factors that negatively regulate cell cycle progression such as repressive E2F factors and histone deacetylases (HDACs). Conversely, ARID1B-containing complexes associate directly with pro-proliferative factors such as activator E2Fs and histone acetylases (HATs). This work further defines the functions of specific subsets of p270-SWI/SNF complexes in transcriptional repression, identifying new gene targets and complex associations. Additionally, experiments shown here provide some of the first elucidation of the pro-proliferative functions of specific ARID1B-SWI/SNF complexes.