ARID1B

ARID1B Full Name

AT rich interactive domain 1B (SWI1-like)

ARID1B Introduction

ARID1B (AT-rich interaction domain-containing protein 1B) is a core component of the SWI/SNF chromatin remodeling complex (also known as the BAF complex), which uses ATP to remodel nucleosome positioning and regulate gene expression. The gene is located on chromosome 6q25.3 and encodes a large protein of 2,252 amino acids with a molecular weight of approximately 250 kDa. ARID1B is ubiquitously expressed in human tissues, with particularly high expression in the brain during development. As a subunit of the BAF complex, ARID1B functions as a DNA-binding subunit that targets the complex to specific genomic loci, particularly AT-rich sequences. The BAF complex plays essential roles in cell differentiation, proliferation, development, and the maintenance of stem cell pluripotency. ARID1B is one of two mutually exclusive DNA-binding subunits of the BAF complex (the other being ARID1A), and the inclusion of ARID1B versus ARID1A defines distinct BAF complex subtypes with different biological functions. Haploinsufficiency of ARID1B causes Coffin-Siris syndrome (CSS), a rare neurodevelopmental disorder characterized by intellectual disability, coarse facial features, hypoplastic or absent fifth fingernails/toenails, and developmental delay. ARID1B is also frequently mutated in various human cancers, where it functions as a tumor suppressor, particularly in neuroblastoma, hepatocellular carcinoma, and other malignancies.

Figure 1. Schematic structure of ARID1B.

Structural Characteristics and Molecular Binding Mechanism of ARID1B
ARID1B possesses a multi-domain modular structure typical of the ARID family, which underpins its DNA-binding capacity, complex assembly and epigenetic regulatory functions. The signature N-terminal ARID domain enables specific recognition and stable binding to AT-rich DNA sequences across promoters and enhancers, mediating sequence-specific chromatin targeting independent of conventional transcription factor motifs. Multiple conserved internal interaction domains facilitate tight binding with core components of the SWI/SNF complex, including ATPase subunits BRG1/BRM and auxiliary scaffold proteins, maintaining the overall structural integrity and catalytic activity of chromatin remodeling complexes. ARID1B also contains numerous post-translational modification sites for phosphorylation, ubiquitination and acetylation, which dynamically regulate protein stability, nuclear retention and cofactor recruitment. Unlike ARID1A-containing complexes, ARID1B-assembled SWI/SNF complexes exhibit distinct target gene selectivity and tissue-specific activity. Pathogenic mutations, protein truncation or domain deletion disrupt DNA binding and complex formation, leading to abnormal chromatin accessibility and widespread dysregulation of downstream gene networks.

Functions in Chromatin Remodeling and Gene Expression
ARID1B is a core component of the BAF complex (mammalian SWI/SNF complex), an ATP-dependent chromatin remodeling complex that regulates gene expression by altering nucleosome positioning and accessibility. The BAF complex is composed of approximately 15 subunits, including the ATPase subunits BRG1 or BRM, the core subunits SMARCC1/BAF155 and SMARCC2/BAF170, the actin-related proteins ACTL6A/BAF53A or ACTL6B/BAF53B, and the DNA-binding subunits ARID1A, ARID1B, or ARID2. ARID1B and ARID1A are mutually exclusive DNA-binding subunits; complexes containing ARID1B (BAF complex) are distinct from those containing ARID1A, and they regulate different sets of target genes. The BAF complex is recruited to specific genomic loci by transcription factors and by the DNA-binding specificity of its ARID subunit. Once recruited, the ATPase subunit BRG1 or BRM uses ATP hydrolysis to slide or evict nucleosomes, exposing regulatory elements such as promoters, enhancers, and silencers to transcription factors and RNA polymerase II. Through this mechanism, the BAF complex regulates gene expression programs involved in cell differentiation, proliferation, development, and the maintenance of stem cell pluripotency. ARID1B is particularly important for neural development; it regulates the expression of genes involved in neurogenesis, neuronal migration, dendrite morphogenesis, and synapse formation. In the developing brain, ARID1B is essential for the proper formation of the cerebral cortex, hippocampus, and cerebellum. ARID1B also plays roles in other tissues including the heart, limbs, and craniofacial structures, reflecting the multiple developmental abnormalities observed in Coffin-Siris syndrome.

Alternate Names for ARID1B

ARID1B; AT rich interactive domain 1B (SWI1-like); OSA2; 6A3-5; DAN15; MRD12; P250R; BRIGHT; BAF250B; ELD/OSA1; AT-rich interactive domain-containing protein 1B; ELD (eyelid)/OSA protein; BRG1-associated factor 250b; BRG1-binding protein ELD/OSA1; ARID domain-containing protein 1B;