Target genes of the largest human SWI/SNF complex subunit control cell growth

Abstract

The largest subunit of the mammalian SWI/SNF-A or BAF (BRG1-associated factor) chromatin-remodelling complex is encoded by two related cDNAs hOsa1/BAF250a and hOsa2/BAF250b that are unique to the BAF complex and absent in the related PBAF (Polybromo BAF). hOsa/BAF250 has been shown to interact with transcriptional activators and bind to DNA suggesting that it acts to target the remodelling complex to chromatin. To better understand the functions of hOsa2, we established inducible stable HeLa cell lines over-expressing FLAG-hOsa2 or a derivative lacking the ARID (AT-rich interactive domain) DNA-binding domain. Immunopurification of complexes containing hOsa2 that was followed by mass spectrometry and immunoblotting demonstrated the presence of BRG1 and known BAFs, but not hOsa1 or hBRM. Deletion of the ARID did not compromise the integrity of the complex. Induction of hOsa2 expression caused impaired cell growth and accumulation of cells in the G0/G1 cell cycle phase. Elevated levels of the p53 and p21 proteins were detected in these cells while c-Myc mRNA and protein levels were found to decrease. Chromatin immunoprecipitation and reporter assays suggested that hOsa2 had a direct effect on c-myc and p21 promoter activity. Thus hOsa2 plays an important role in controlling genes regulating the cell cycle.

ARID1A, a Factor That Promotes Formation of SWI/SNF-Mediated Chromatin Remodeling, Is a Tumor Suppressor in Gynecologic Cancers

“…It remains unclear, however, whether they act globally to facilitate transcriptional activity in transcriptionally active domains, or if they locally target a set of selected genes that work in concert for specific cellular functions. The data presented in this study, together with a recent report (40), favor the latter view, as evidenced by downregulation of specific genes upon ARID1A silencing. Analysis of ARID1A downstream genes reveals that the tumor suppressor role of ARID1A mainly involves negative regulation of cell cycle progression and identifies two p53-regulated genes, CDKN1A and SMAD3, which may serve as the major target genes to mediate its tumor suppressor functions.…”

The genomic landscape of Waldenström macroglobulinemia is characterized by highly recurring MYD88 and WHIM-like CXCR4 mutations, and small somatic deletions associated with B-cell lymphomagenesis

“…34,35 Both ARID1A and ARID1B are members of the switch/sucrose nonfermentable family of proteins that are known to be mutated in other neoplastic malignancies, wherein they are thought to exert their effects via p53 and CDKN1A regulation. [36][37][38] TP53 itself was mutated in 2 of 30 (7%) of the sequenced genomes, including 1 case of biallelic mutation. Both PRDM2 and TOP1 participated in TP53-related signaling and were deleted in 8 of 10 (80%; 28 of 30 in validation) and 6 of 10 (60%) patients, respectively.…”

ARID1a-DNA Interactions Are Required for Promoter Occupancy by SWI/SNF

“…Mutant protein is stably expressed, and it incorporates into a SWI/SNF complex with core catalytic function. ARID domains do not appear to be required for complex integrity, nor do they appear to be required for the core catalytic properties of the complex (52,53). However, point mutations like V1068G could influence protein stability and/or conformation, leading to loss of multiple interaction surfaces.…”