Germline Nonsense Mutation and Somatic Inactivation of SMARCA4/BRG1 in a Family with Rhabdoid Tumor Predisposition Syndrome

Department of Pediatric Hematology and Oncology, University Medical Center Hamburg-Eppendorf, Martinistrasse 52, Hamburg, Germany.
The American Journal of Human Genetics (Impact Factor: 10.93). 02/2010; 86(2):279-84. DOI: 10.1016/j.ajhg.2010.01.013
Source: PubMed


Rhabdoid tumors of early infancy are highly aggressive with consequent poor prognosis. Most cases show inactivation of the SMARCB1 (also known as INI1 and hSNF5) tumor suppressor, a core member of the ATP-dependent SWI/SNF chromatin-remodeling complex. Familial cases, described as rhabdoid tumor predisposition syndrome (RTPS), have been linked to heterozygous SMARCB1 germline mutations. We identified inactivation of another member of the SWI/SNF chromatin-remodeling complex, its ATPase subunit SMARCA4 (also known as BRG1), due to a SMARCA4/BRG1 germline mutation and loss of heterozygosity by uniparental disomy in the tumor cells of two sisters with rhabdoid tumors lacking SMARCB1 mutations. SMARCA4 is thus a second member of the SWI/SNF complex involved in cancer predisposition. Its general involvement in other tumor entities remains to be established.

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Available from: Markus Kreuz, Aug 14, 2014
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    • "Patients with rhabdoid tumor (RT) predisposition syndrome, in which RTs occur on a familial basis, harbor a heterozygous germline BRG1 mutation that truncates the encoded protein, and their RTs are homozygous for this mutation [64]. Mutations in SNF5, which are present in the germline of most cases of RT predisposition syndrome, were not detected in the patients analyzed in that study. "
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    ABSTRACT: Chromatin-regulating proteins represent a large class of novel targets for cancer therapy. In the context of radiotherapy, acetylation and deacetylation of histones by histone acetyltransferases (HATs) and histone deacetylases (HDACs) play important roles in the repair of DNA double-strand breaks generated by ionizing irradiation, and are therefore attractive targets for radiosensitization. Small-molecule inhibitors of HATs (garcinol, anacardic acid and curcumin) and HDACs (vorinostat, sodium butyrate and valproic acid) have been shown to sensitize cancer cells to ionizing irradiation in preclinical models, and some of these molecules are being tested in clinical trials, either alone or in combination with radiotherapy. Meanwhile, recent large-scale genome analyses have identified frequent mutations in genes encoding chromatin-regulating proteins, especially in those encoding subunits of the SWI/SNF chromatin-remodeling complex, in various human cancers. These observations have driven researchers toward development of targeted therapies against cancers carrying these mutations. DOT1L inhibition in MLL-rearranged leukemia, EZH2 inhibition in EZH2-mutant or MLL-rearranged hematologic malignancies and SNF5-deficient tumors, BRD4 inhibition in various hematologic malignancies, and BRM inhibition in BRG1-deficient tumors have demonstrated promising anti-tumor effects in preclinical models, and these strategies are currently awaiting clinical application. Overall, the data collected so far suggest that targeting chromatin-regulating proteins is a promising strategy for tomorrow's cancer therapy, including radiotherapy and molecularly targeted chemotherapy.
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    • "Haploinsufficiency of SMARCA4 causes an increased susceptibility to rhabdoid tumors (Rhabdoid Tumor Predisposition Syndrome) [Schneppenheim et al., 2010]. Haploinsufficiency of SMARCA2 has not been linked to human disease. "
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    • "The critical function of SNF5 in rhabdoid tumor development is supported by knock-out mouse models of SNF5 showing development of lymphomas and MRTs with 100% penetrance and a median onset of only 11 weeks [30]. Besides genomic alterations leading to SNF5 loss of function, truncating deletions of BRG1 are present in a small subset of MRTs [34], further indicating that alterations in SWI/SNF function are causative for the development of this tumor type. However, other concomitant genomic aberrations are rarely found in MRTs. "
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