RESUMEN
Numerous cytogenetic and molecular studies of breast cancer have identified frequent loss of heterozygosity (LOH) of the long arm of human chromosome 16. On the basis of these data, the likely locations of breast cancer tumor suppressor genes are bands 16q22.1 and 16q24.3. We have mapped the CBFA2T3 (MTG16) gene, previously cloned as a fusion partner of the AML1 protein from a rare (16;21) leukemia translocation, to the 16q24.3 breast cancer LOH region. The expression of CBFA2T3 was significantly reduced in a number of breast cancer cell lines and in primary breast tumors, including early ductal carcinomas in situ, when compared with nontransformed breast epithelial cell lines and normal breast tissue. Reintroduction of CBFA2T3 into different breast tumor derived cell lines with decreased expression of this gene reduced colony growth on plastic and in soft agar. CBFA2T3 was shown to function as a transcriptional repressor when tethered to the GAL4 DNA-binding domain in a reporter gene assay and, therefore, has the potential to be a transcriptional repressor in normal breast epithelial cells. Taken together, these findings suggest that CBFA2T3 is a likely candidate for the breast cancer tumor suppressor gene that is the target for the frequent 16q24 LOH in breast neoplasms.
Asunto(s)
Neoplasias de la Mama/genética , Cromosomas Humanos Par 16/genética , Genes Supresores de Tumor , Pérdida de Heterocigocidad , Fosfoproteínas , Proteínas/genética , Proteínas Supresoras de Tumor , División Celular/genética , Regulación Neoplásica de la Expresión Génica , Humanos , Biosíntesis de Proteínas , Proteínas/fisiología , ARN Mensajero/genética , ARN Mensajero/metabolismo , ARN Neoplásico/biosíntesis , ARN Neoplásico/genética , Proteínas Represoras , Células Tumorales CultivadasRESUMEN
BACKGROUND: The CBFA2T3 locus located on the human chromosome region 16q24.3 is frequently deleted in breast tumors. CBFA2T3 gene expression levels are aberrant in breast tumor cell lines and the CBFA2T3B isoform is a potential tumor suppressor gene. In the absence of identified mutations to further support a role for this gene in tumorigenesis, we explored whether the CBFA2T3B promoter region is aberrantly methylated and whether this correlates with expression. RESULTS: Aberrant hypo and hypermethylation of the CBFA2T3B promoter was detected in breast tumor cell lines and primary breast tumor samples relative to methylation index interquartile ranges in normal breast counterpart and normal whole blood samples. A statistically significant inverse correlation between aberrant CBFA2T3B promoter methylation and gene expression was established. CONCLUSION: CBFA2T3B is a potential breast tumor suppressor gene affected by aberrant promoter methylation and gene expression. The methylation levels were quantitated using a second-round real-time methylation-specific PCR assay. The detection of both hypo and hypermethylation is a technicality regarding the methylation methodology.
Asunto(s)
Neoplasias de la Mama/genética , Fosfoproteínas/genética , Fosfoproteínas/metabolismo , Regiones Promotoras Genéticas/genética , Proteínas Represoras/genética , Proteínas Represoras/metabolismo , Proteínas Supresoras de Tumor/genética , Proteínas Supresoras de Tumor/metabolismo , Neoplasias de la Mama/patología , Línea Celular Tumoral , ADN de Neoplasias/química , ADN de Neoplasias/genética , Regulación de la Expresión Génica/genética , Regulación Neoplásica de la Expresión Génica/genética , Humanos , Metilación , Fosfoproteínas/química , Subunidades de Proteína/genética , Proteínas Represoras/química , Análisis de Secuencia de ADN/métodos , Sulfitos/metabolismo , Proteínas Supresoras de Tumor/químicaRESUMEN
The 16p13.3 breakpoints of two de novo translocations of chromosome 16, t(1;16) and t(14;16), were shown by initial mapping studies to have physically adjacent breakpoints. The translocations were ascertained in patients with abnormal phenotypes characterized by predominant epilepsy in one patient and mental retardation in the other. Distamycin/DAPI banding showed that the chromosome 1 breakpoint of the t(1;16) was in the pericentric heterochromatin therefore restricting potential gene disruption to the 16p13.3 breakpoint. The breakpoints of the two translocations were localized to a region of 3.5 and 115 kb respectively and were approximately 900 kb apart. The mapping was confirmed by fluorescence in situ hybridization (FISH) of clones that spanned the breakpoints to metaphase spreads derived from the patients. The mapping data showed both translocations disrupted the ataxin-2-binding protein 1 ( A2BP1) gene that encompasses a large genomic region of 1.7 Mb. A2BP1 encodes a protein that is known to interact with the spinocerebellar ataxia type 2 ( SCA2) protein. It is proposed that disruption of the A2BP1 gene is a cause of the abnormal phenotype of the two patients. Ninety-six patients with sporadic epilepsy and 96 female patients with mental retardation were screened by SSCP for potential mutations of A2BP1. No mutations were found, suggesting that disruption of the A2BP1 gene is not a common cause of sporadic epilepsy or mental retardation.
Asunto(s)
Cromosomas Humanos Par 16 , Epilepsia/genética , Discapacidad Intelectual/genética , Proteínas de Unión al ARN/genética , Translocación Genética , Adolescente , Ataxinas , Preescolar , Mapeo Cromosómico , Exones , Femenino , Humanos , Hibridación Fluorescente in Situ , Intrones , Masculino , Modelos Genéticos , Mutación , Proteínas del Tejido Nervioso , Fenotipo , Mapeo Físico de Cromosoma , Polimorfismo Conformacional Retorcido-Simple , Proteínas/genética , Factores de Empalme de ARNRESUMEN
Rett syndrome (RTT) is a severe neurodevelopmental disorder caused, in most classic cases, by mutations in the X-linked methyl-CpG-binding protein 2 gene (MECP2). A large degree of phenotypic variation has been observed in patients with RTT, both those with and without MECP2 mutations. We describe a family consisting of a proband with a phenotype that showed considerable overlap with that of RTT, her identical twin sister with autistic disorder and mild-to-moderate intellectual disability, and a brother with profound intellectual disability and seizures. No pathogenic MECP2 mutations were found in this family, and the Xq28 region that contains the MECP2 gene was not shared by the affected siblings. Three other candidate regions were identified by microsatellite mapping, including 10.3 Mb at Xp22.31-pter between Xpter and DXS1135, 19.7 Mb at Xp22.12-p22.11 between DXS1135 and DXS1214, and 16.4 Mb at Xq21.33 between DXS1196 and DXS1191. The ARX and CDKL5 genes, both of which are located within the Xp22 region, were sequenced in the affected family members, and a deletion of nucleotide 183 of the coding sequence (c.183delT) was identified in CDKL5 in the affected family members. In a screen of 44 RTT cases, a single splice-site mutation, IVS13-1G-->A, was identified in a girl with a severe phenotype overlapping RTT. In the mouse brain, Cdkl5 expression overlaps--but is not identical to--that of Mecp2, and its expression is unaffected by the loss of Mecp2. These findings confirm CDKL5 as another locus associated with epilepsy and X-linked mental retardation. These results also suggest that mutations in CDKL5 can lead to a clinical phenotype that overlaps RTT. However, it remains to be determined whether CDKL5 mutations are more prevalent in specific clinical subgroups of RTT or in other clinical presentations.