GO:0090535 WICH complex: Components and Methods

The WICH complex (GO:0090535) is an ISWI-family chromatin-remodelling complex that contains an ATPase subunit of the ISWI family, specifically SNF2H in mammals, together with the Williams Syndrome Transcription Factor (WSTF, also known as BAZ1B). Chromatin-remodelling complexes use ATP hydrolysis to slide, eject or restructure nucleosomes, thereby controlling access of the transcriptional machinery to DNA. The WICH complex is best understood through its close relative B-WICH, which shares the WSTF/BAZ1B subunit and regulates RNA polymerase I and III transcription. For researchers, GO:0090535 provides a precise annotation for experiments that interrogate how ISWI-type remodellers and WSTF/BAZ1B cooperate at ribosomal and small-RNA gene loci. The complex has been linked to RNA polymerase III transcription through Max-dependent c-Myc recruitment, to rRNA gene activation via histone acetyltransferase recruitment, and to glucose-responsive ribosomal transcription together with NuRD. These findings place the WICH/B-WICH axis at the intersection of chromatin remodelling, ribosome biogenesis and metabolic signalling. Because WSTF/BAZ1B is deleted in Williams-Beuren syndrome, the WICH complex also offers a mechanistic entry point into a well-characterized neurodevelopmental disorder. Understanding its composition, regulation and downstream targets is therefore relevant to both basic chromatin biology and disease-oriented research.

According to the Gene Ontology, GO:0090535 (WICH complex) is a cellular component defined as an ISWI complex that contains an ATPase subunit of the ISWI family (specifically SNF2H in mammals, which contain two ISWI homologs) and WSTF (Williams Syndrome Transcription Factor). The WICH complex plays roles in regulation of RNA polymerase I and III transcription and in DNA replication and repair. In practice, this means the term annotates a multi-subunit chromatin-remodelling machine whose identity depends on the presence of both an ISWI-type ATPase and the WSTF/BAZ1B accessory protein.

The WICH complex matters because it connects ATP-dependent chromatin remodelling to the transcription of ribosomal and small-RNA genes, two of the most heavily transcribed loci in proliferating cells. Through its WSTF/BAZ1B subunit, the complex has been shown to regulate RNA polymerase III transcription by promoting Max-dependent c-Myc binding, to alter chromatin structure and recruit histone acetyltransferases to active rRNA genes, and to cooperate with NuRD in glucose-responsive ribosomal transcription. Because WSTF/BAZ1B is the gene deleted in Williams-Beuren syndrome, the complex also provides a direct molecular link between chromatin remodelling and a human neurodevelopmental disorder. Studying GO:0090535 therefore helps researchers understand how cells coordinate ribosome production, metabolic state and gene expression, and how disruption of these processes may contribute to disease.

The following genes and proteins are the principal components and functional partners of the WICH complex and its related B-WICH complex.

The WICH/B-WICH axis is regulated at multiple levels. Its activity at ribosomal genes is responsive to glucose availability, where B-WICH and NuRD cooperate to adjust ribosomal transcription according to metabolic state. At RNA polymerase III targets, B-WICH promotes Max-dependent c-Myc binding, linking the complex to growth-factor and oncogenic signalling pathways that control c-Myc abundance. Chromatin-level regulation involves recruitment of histone acetyltransferases to active rRNA genes, which reinforces the open chromatin state required for transcription. In addition, WSTF/BAZ1B participates in DNA repair-related processes through interaction with ATAD5 and modulation of PCNA ubiquitination, indicating that its regulation extends beyond transcription.

WSTF/BAZ1B is the Williams Syndrome Transcription Factor and is encoded by a gene deleted in Williams-Beuren syndrome, a neurodevelopmental disorder characterized by cardiovascular, cognitive and craniofacial features. Because BAZ1B is the defining accessory subunit of the WICH and B-WICH complexes, loss of one copy of this gene is expected to affect chromatin remodelling at ribosomal and small-RNA gene loci. Research on BAZ1B as a protean protein has highlighted its multiple roles in development and disease.

The B-WICH complex regulates RNA polymerase III transcription by promoting Max-dependent c-Myc binding. c-Myc is a well-known oncogenic transcription factor, and its ability to drive RNA polymerase III output is relevant to cancer cell growth. By influencing c-Myc recruitment at RNA polymerase III targets, the WICH/B-WICH axis may contribute to the elevated small-RNA synthesis observed in proliferating tumour cells.

B-WICH and NuRD regulate ribosomal transcription in response to glucose, connecting the complex to metabolic sensing. Dysregulation of ribosome biogenesis is increasingly recognized in metabolic and proliferative disorders. Because the complex adjusts rRNA synthesis according to nutrient availability, its dysfunction could perturb the balance between energy status and protein synthesis capacity.

The GO definition of GO:0090535 includes roles in DNA replication and repair. Studies of BAZ1B have linked it to DNA repair processes through interaction with ATAD5 and modulation of PCNA ubiquitination. These findings suggest that WSTF/BAZ1B-containing complexes contribute to genome stability, and their impairment could sensitize cells to DNA damage.

ChIP-seq against WSTF/BAZ1B or tagged SNF2H can map the genomic binding sites of the WICH/B-WICH complex. This approach has been used to study how B-WICH associates with active rRNA genes and how it recruits histone acetyltransferases. Combining ChIP-seq with histone modification profiling provides a readout of the chromatin changes induced by the complex.

Because the WICH/B-WICH complex regulates RNA polymerase I and III transcription, quantitative PCR, Northern blotting and metabolic labelling can measure rRNA and small RNA outputs. These assays are used to test how loss or overexpression of BAZ1B affects ribosomal and tRNA synthesis, and how glucose availability modulates these outputs.

Affinity purification coupled to mass spectrometry can identify the subunit composition of the WICH complex and its interaction partners. Studies of BAZ1B have revealed interactions with proteins involved in DNA repair, including ATAD5, and with chromatin-modifying enzymes. Proteomic mapping helps define which complexes contain WSTF/BAZ1B under different conditions.

CRISPR knockout, point-mutation knock-in and overexpression models allow causal testing of WICH complex subunits. Knockout of BAZ1B or SMARCA5 can reveal which transcriptional programmes depend on the complex, while tagged knock-in enables localization and interaction studies. CRISPR library screening combined with bioinformatics can identify genetic dependencies and modifiers of the WICH/B-WICH pathway.

Researchers studying WICH complex-related genes often need to determine whether a candidate gene is causally involved in chromatin remodelling, ribosomal transcription or genome maintenance. Rigorous causal testing requires well-controlled genetic models in which the gene of interest is deleted, mutated, tagged or overexpressed in a defined cellular background. EDITGENE provides these models together with the screening and bioinformatics support needed to interpret the resulting data.

The WICH complex (GO:0090535) is a defined ISWI-family chromatin-remodelling complex built around SNF2H and WSTF/BAZ1B. Its best-characterized functions include regulation of RNA polymerase I and III transcription, chromatin modification at active rRNA genes, glucose-responsive ribosomal transcription and contributions to DNA replication and repair. Because WSTF/BAZ1B is linked to Williams-Beuren syndrome and c-Myc-driven transcription, the complex sits at the interface of chromatin biology, metabolism and disease. CRISPR-based knockout, point-mutation, knock-in and overexpression models, combined with screening and bioinformatics, provide a rigorous path to dissect its mechanisms and therapeutic relevance.