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The protein encoded by this gene is a member of the SWI/SNF family of proteins and is similar to the brahma protein of Drosophila. Members of this family have helicase and ATPase activities and are thought to regulate transcription of certain genes by altering the chromatin structure around those genes. The encoded protein is part of the large ATP-dependent chromatin remodeling complex SWI/SNF, which is required for transcriptional activation of genes normally repressed by chromatin. In addition, this protein can bind BRCA1, as well as regulate the expression of the tumorigenic protein CD44.[2]
BRG1 works to activate or repress transcription. Having functional BRG1 is important for development past the pre-implantation stage. Without having a functional BRG1, exhibited with knockout research, the embryo will not hatch out of the zona pellucida, which will inhibit implantation from occurring on the endometrium (uterine wall). BRG1 is also crucial to the development of sperm. During the first stages of meiosis in spermatogenesis there are high levels of BRG1. When BRG1 is genetically damaged, meiosis is stopped in prophase 1, hindering the development of sperm and would result in infertility. More knockout research has concluded BRG1’s aid in the development of smooth muscle. In a BRG1 knockout, smooth muscle in the gastrointestinal tract lacks contractility, and intestines are incomplete in some cases. Another defect occurring in knocking out BRG1 in smooth muscle development is heart complications such as an open ductus arteriosus after birth.[3][4]
Clinical significance
BRG1 (or SMARCA4) is the most frequently mutated chromatin remodeling ATPase in cancer.[5] Mutations in this gene were first recognized in human cancer cell lines derived from adrenal gland[6] and lung.[7] Later it was recognized that mutations exist in a significant frequency of medulloblastoma and pancreatic cancers, and in many other tumor subtypes.[8][9][10]
In cancer, mutations in BRG1 show an unusually high preference for missense mutations that are frequently heterozygous and target the ATPase domain.[11][5] Mutations are enriched at highly conserved ATPase sequences[12], which lie on important functional surfaces such as the ATP pocket or DNA-binding surface.[11] These mutations act in a genetically dominant manner to alter chromatin regulatory function at enhancers[11] and promoters.[12]
Mutations of BRG1 are associated with context-dependent expression changes at MYC-genes, which indicates that the BRG1 and MYC proteins are functionally related.[11][7][13] Another study demonstrated a causal role of BRG1 in the control of retinoic acid and glucocorticoid-induced cell differentiation in lung cancer and in other tumor types. This enables the cancer cell to sustain undifferentiated gene expression programs that affect the control of key cellular processes. Furthermore, it explains why lung cancer and other solid tumors are completely refractory to treatments based on these compounds that are effective therapies for some types of leukemia.[14]
The role of BRG1 in sensitivity or resistance to anti-cancer drugs had been recently highlighted by the elucidation of the mechanisms of action of darinaparsin, an arsenic-based anti-cancer drugs. Darinaparsin has been shown to induce phosphorylation of BRG1, which leads to its exclusion from chromatin. When excluded from the chromatin, BRG1 can no longer act as a transcriptional co-regulator. This leads to the inability of cells to express HO-1, a cytoprotective enzyme.[15]
↑Dunaief JL, Strober BE, Guha S, Khavari PA, Alin K, Luban J, Begemann M, Crabtree GR, Goff SP (October 1994). "The retinoblastoma protein and BRG1 form a complex and cooperate to induce cell cycle arrest". Cell. 79 (1): 119–30. PMID7923370.
↑ 7.07.1Medina PP, Romero OA, Kohno T, Montuenga LM, Pio R, Yokota J, Sanchez-Cespedes M (May 2008). "Frequent BRG1/SMARCA4-inactivating mutations in human lung cancer cell lines". Human Mutation. 29 (5): 617–22. doi:10.1002/humu.20730. PMID18386774.
↑Romero OA, Sanchez-Cespedes M (May 2014). "The SWI/SNF genetic blockade: effects in cell differentiation, cancer and developmental diseases". Oncogene. 33 (21): 2681–9. doi:10.1038/onc.2013.227. PMID23752187.
↑ 17.017.117.217.317.417.517.6Zhao K, Wang W, Rando OJ, Xue Y, Swiderek K, Kuo A, Crabtree GR (November 1998). "Rapid and phosphoinositol-dependent binding of the SWI/SNF-like BAF complex to chromatin after T lymphocyte receptor signaling". Cell. 95 (5): 625–36. doi:10.1016/S0092-8674(00)81633-5. PMID9845365.
↑Inoue H, Furukawa T, Giannakopoulos S, Zhou S, King DS, Tanese N (November 2002). "Largest subunits of the human SWI/SNF chromatin-remodeling complex promote transcriptional activation by steroid hormone receptors". The Journal of Biological Chemistry. 277 (44): 41674–85. doi:10.1074/jbc.M205961200. PMID12200431.
↑Hill DA, de la Serna IL, Veal TM, Imbalzano AN (April 2004). "BRCA1 interacts with dominant negative SWI/SNF enzymes without affecting homologous recombination or radiation-induced gene activation of p21 or Mdm2". Journal of Cellular Biochemistry. 91 (5): 987–98. doi:10.1002/jcb.20003. PMID15034933.
↑Bochar DA, Wang L, Beniya H, Kinev A, Xue Y, Lane WS, Wang W, Kashanchi F, Shiekhattar R (July 2000). "BRCA1 is associated with a human SWI/SNF-related complex: linking chromatin remodeling to breast cancer". Cell. 102 (2): 257–65. doi:10.1016/S0092-8674(00)00030-1. PMID10943845.
↑Wong AK, Shanahan F, Chen Y, Lian L, Ha P, Hendricks K, Ghaffari S, Iliev D, Penn B, Woodland AM, Smith R, Salada G, Carillo A, Laity K, Gupte J, Swedlund B, Tavtigian SV, Teng DH, Lees E (November 2000). "BRG1, a component of the SWI-SNF complex, is mutated in multiple human tumor cell lines". Cancer Research. 60 (21): 6171–7. PMID11085541.
↑Ichinose H, Garnier JM, Chambon P, Losson R (March 1997). "Ligand-dependent interaction between the estrogen receptor and the human homologues of SWI2/SNF2". Gene. 188 (1): 95–100. doi:10.1016/S0378-1119(96)00785-8. PMID9099865.
↑ 29.029.129.229.329.4Otsuki T, Furukawa Y, Ikeda K, Endo H, Yamashita T, Shinohara A, Iwamatsu A, Ozawa K, Liu JM (November 2001). "Fanconi anemia protein, FANCA, associates with BRG1, a component of the human SWI/SNF complex". Human Molecular Genetics. 10 (23): 2651–60. doi:10.1093/hmg/10.23.2651. PMID11726552.
↑Reuter TY, Medhurst AL, Waisfisz Q, Zhi Y, Herterich S, Hoehn H, Gross HJ, Joenje H, Hoatlin ME, Mathew CG, Huber PA (October 2003). "Yeast two-hybrid screens imply involvement of Fanconi anemia proteins in transcription regulation, cell signaling, oxidative metabolism, and cellular transport". Experimental Cell Research. 289 (2): 211–21. doi:10.1016/S0014-4827(03)00261-1. PMID14499622.
↑Ewing RM, Chu P, Elisma F, Li H, Taylor P, Climie S, McBroom-Cerajewski L, Robinson MD, O'Connor L, Li M, Taylor R, Dharsee M, Ho Y, Heilbut A, Moore L, Zhang S, Ornatsky O, Bukhman YV, Ethier M, Sheng Y, Vasilescu J, Abu-Farha M, Lambert JP, Duewel HS, Stewart II, Kuehl B, Hogue K, Colwill K, Gladwish K, Muskat B, Kinach R, Adams SL, Moran MF, Morin GB, Topaloglou T, Figeys D (2007). "Large-scale mapping of human protein-protein interactions by mass spectrometry". Molecular Systems Biology. 3 (1): 89. doi:10.1038/msb4100134. PMC1847948. PMID17353931.
↑Lee D, Kim JW, Seo T, Hwang SG, Choi EJ, Choe J (June 2002). "SWI/SNF complex interacts with tumor suppressor p53 and is necessary for the activation of p53-mediated transcription". The Journal of Biological Chemistry. 277 (25): 22330–7. doi:10.1074/jbc.M111987200. PMID11950834.
↑Huang M, Qian F, Hu Y, Ang C, Li Z, Wen Z (October 2002). "Chromatin-remodelling factor BRG1 selectively activates a subset of interferon-alpha-inducible genes". Nature Cell Biology. 4 (10): 774–81. doi:10.1038/ncb855. PMID12244326.
↑Marignani PA, Kanai F, Carpenter CL (August 2001). "LKB1 associates with Brg1 and is necessary for Brg1-induced growth arrest". The Journal of Biological Chemistry. 276 (35): 32415–8. doi:10.1074/jbc.C100207200. PMID11445556.
Further reading
Medina PP, Sanchez-Cespedes M, Cespedes MS (2008). "Involvement of the chromatin-remodeling factor BRG1/SMARCA4 in human cancer". Epigenetics. 3 (2): 64–8. doi:10.4161/epi.3.2.6153. PMID18437052.