SWI/SNF related, matrix associated, actin dependent regulator of chromatin, subfamily b, member 1
The SMARCB1 gene provides instructions for making a protein that forms one piece (subunit) of several different SWI/SNF protein complexes. SWI/SNF complexes regulate gene activity (expression) by a process known as chromatin remodeling. Chromatin is the network of DNA and protein that packages DNA into chromosomes. The structure of chromatin can be changed (remodeled) to alter how tightly DNA is packaged. Chromatin remodeling is one way gene expression is regulated during development; when DNA is tightly packed, gene expression is lower than when DNA is loosely packed.
Through their ability to regulate gene activity, SWI/SNF complexes are involved in many processes, including repairing damaged DNA; copying (replicating) DNA; and controlling the growth, division, and maturation (differentiation) of cells. The SMARCB1 protein and other SWI/SNF subunits are thought to act as tumor suppressors, which keep cells from growing and dividing too rapidly or in an uncontrolled way.
The role of the SMARCB1 protein within the SWI/SNF complex is not completely understood.
At least two mutations in the SMARCB1 gene can cause Coffin-Siris syndrome. This condition is characterized by delayed development, abnormalities of the fifth (pinky) fingers or toes, and characteristic facial features that are described as coarse. These SMARCB1 gene mutations change or remove single protein building blocks (amino acids) in the SMARCB1 protein. Although it is unclear how these changes affect SWI/SNF complexes, researchers suggest that SMARCB1 gene mutations result in abnormal chromatin remodeling. Disturbance of this process alters the activity of many genes and disrupts several cellular processes, which could explain the diverse signs and symptoms of Coffin-Siris syndrome. People with Coffin-Siris syndrome do not appear to have an increased risk of cancer (see below).
Mutations in the SMARCB1 gene cause rhabdoid tumor predisposition syndrome (RTPS). Individuals with this condition have an increased risk of developing aggressive cancerous growths called rhabdoid tumors, which form in the brain (often called atypical teratoid/rhabdoid tumors) and in the kidney (often called malignant rhabdoid tumors). These tumors usually occur in infants and young children. Some children with RTPS also develop schwannomas, which are noncancerous (benign) tumors of the nerve cells. RTPS is caused by a single inherited mutation in the SMARCB1 gene that is present in cells throughout the body. An additional mutation that deletes the normal copy of the gene is needed for tumors to develop. This second mutation, called a somatic mutation, is acquired during a person's lifetime and is present only in tumor cells. In combination, the inherited and somatic mutations lead to the absence of SMARCB1 protein.
Somatic mutations in the SMARCB1 gene that result in the absence of SMARCB1 protein cause noninherited (sporadic) rhabdoid tumors in children. The mechanism by which inherited or somatic SMARCB1 gene mutations lead to rhabdoid tumors is unknown.
Inherited SMARCB1 gene mutations can also cause schwannomatosis, which is characterized by the development of multiple schwannomas. In contrast to gene mutations that cause rhabdoid tumors, these mutations are thought to lead to production of an altered SMARCB1 protein that likely has some function. However, it is unclear how the altered protein leads to development of schwannomas. It is likely that other genetic changes in addition to SMARCB1 gene mutations are necessary for schwannoma development.
- BRG1-associated factor 47
- integrase interactor 1 protein
- SNF5 homolog
- sucrose nonfermenting, yeast, homolog-like 1
- SWI/SNF-related matrix-associated actin-dependent regulator of chromatin subfamily B member 1
- Johns Hopkins Medicine: Schwannomatosis
- Molecular Biology of the Cell (fourth edition, 2002): ATP-Driven Chromatin Remodeling Machines Change Nucleosome Structure
- Molecular Biology of the Cell (fourth edition, 2002): Chromosomal DNA and Its Packaging in the Chromatin Fiber
- The Children's Hospital of Philadelphia: Rhabdoid Tumor Predisposition Syndrome (RTPS)