RESUMO
Smad4 is a candidate tumour-suppressor gene identified recently on chromosome 18q21.1. Both alleles are inactivated in nearly one-half of pancreatic carcinomas, but its role in the tumorigenesis of other tumours is still unknown. The aim of this study was to investigate the potential involvement of the Smad4 locus in early-stage colorectal cancers (stages I-III) in tumour samples from a randomised multicentre trial. Of a large collection of DNA samples, 73 with a loss of one allele of the Smad4 gene were analysed for the presence of point mutations in the remaining gene. Patients, from whom biopsies were isolated, were part of a previous randomised multicentre study of the Swiss Group for Clinical Cancer Research on the benefit of adjuvant chemotherapy (SAKK study 40/81). Mutation analysis was restricted to the highly conserved C-terminal domain (exons 8, 9, 10 and 11) of Smad4, using PCR and single-strand conformational variant analysis. Two of the 73 patients (3%) with loss of one allele of Smad4 had a point mutation in the remaining allele. These results indicate that whereas Smad4 point mutations are prevalent in pancreatic carcinoma, they are infrequent in early stages (I-III) of colorectal cancer.
Assuntos
Neoplasias Colorretais/genética , Proteínas de Ligação a DNA/genética , Perda de Heterozigosidade , Transativadores/genética , Ensaios Clínicos como Assunto , Dosagem de Genes , Humanos , Mutação , Estadiamento de Neoplasias , Proteína Smad4RESUMO
The gene for the transducer of transforming growth factor-beta/bone morphogenetic protein signalling SMAD4, a potential suppressor of colorectal carcinogenesis, is located at the chromosomal region 18q21. In order to evaluate the clinical relevance of SMAD4 deletion, gene copy alterations were determined by copy dosage using real-time quantitative PCR in 202 colorectal tumour biopsies from a previous randomised study of adjuvant chemotherapy. Patients with normal SMAD4 diploidy turned out to have a three-fold higher benefit of 5-fluorouracil-based adjuvant chemotherapy with a border line significance (overall survival: 3.23, P=0.056; disease-free survival: 2.89, P=0.045). These data are consistent with the previous observation that patients whose cancer had retention of the 18q21 region had a significantly higher benefit from 5-fluorouracil-based therapy. Moreover, these results may provide a refinement at the gene level of the clinical relevance of 18q21 deletion, thereby suggesting SMAD4 as a predictive marker in colorectal cancer. This data also indicate that integrity of this component of the transforming growth factor-beta/bone morphogenetic protein signalling pathway may be a critical factor for benefit of chemotherapy in patients with colorectal cancer.
Assuntos
Antimetabólitos Antineoplásicos/uso terapêutico , Cromossomos Humanos Par 18/genética , Neoplasias Colorretais/tratamento farmacológico , Neoplasias Colorretais/genética , Proteínas de Ligação a DNA/genética , Fluoruracila/uso terapêutico , Dosagem de Genes , Transativadores/genética , Biomarcadores , Quimioterapia Adjuvante , Deleção Cromossômica , Primers do DNA/química , DNA de Neoplasias/metabolismo , Feminino , Regulação Neoplásica da Expressão Gênica , Humanos , Masculino , Pessoa de Meia-Idade , Reação em Cadeia da Polimerase , Valor Preditivo dos Testes , Prognóstico , Ensaios Clínicos Controlados Aleatórios como Assunto , Transdução de Sinais/genética , Proteína Smad4 , Taxa de Sobrevida , Fator de Crescimento Transformador beta/genéticaRESUMO
Deletions of chromosome band 18q21 appear with very high frequency in a variety of carcinomas, especially in colorectal cancer. Potent tumor suppressor genes located in this region encode transforming growth factor beta (TGF-beta) signal transducers SMAD2 and SMAD4, and inactivation of either one leads to impaired TGF-beta-mediated cell growth/apoptosis. Following the assignment of SMAD7 to 18q21, we first refined the SMAD7 gene position within this region by genetically mapping SMAD7 between SMAD2 and SMAD4. Further, to compare the respective frequencies of genetic alterations of these three SMAD genes in colorectal cancer, we undertook a large-scale evaluation of the copy status of each of these genes on DNA samples from colorectal tumor biopsy material. Among a subset of 233 DNA samples for which data were available for all four genes, SMAD4, SMAD2, and the nearby gene DCC showed high deletion rates (66%, 64%, and 59%, respectively), whereas SMAD7 was deleted in only 48% of the tumors. Unexpectedly, we found some gene duplications; SMAD7 appears to be more frequently amplified (10%) than the three other genes (4-7%). Compiled data for SMAD genes in each tumor show that the most common combination (26% of all the tumors) consists of the simultaneous deletions of SMAD2 and SMAD4 associated with normal diploidy or even duplication of SMAD7. Since SMAD7 normally counteracts SMAD2 and SMAD4 in TGF-beta signaling, we hypothesize that the tumor might not benefit from simultaneous SMAD7 inactivation, thereby exerting selective pressure to retain or even to duplicate the SMAD7 gene.
Assuntos
Cromossomos Humanos Par 18/genética , Neoplasias Colorretais/genética , Proteínas de Ligação a DNA/genética , Dosagem de Genes , Transativadores/genética , Deleção Cromossômica , Mapeamento Cromossômico , Ordem dos Genes , Homologia de Genes/genética , Genes Supressores de Tumor/genética , Humanos , Transdução de Sinais/genética , Proteína Smad2 , Proteína Smad4 , Proteína Smad7 , Fator de Crescimento Transformador beta/genéticaRESUMO
We analyzed the relative expression of Hematopoietic cell phosphatase (HCP) in mononuclear cells (MNC) of peripheral blood (PB), bone marrow (BM) and spleen of patients with juvenile myelomonocytic leukemia (JMML) and normal donors. Two regions of HCP with alternative exon skipping of exon 6 or exon 12 are described. There was no difference in the expression of the amplified HCP cDNA regions in MNC of JMML patients compared to normal donors. The two forms of exon skipping were present in unstimulated MNC of JMML patients or normal donors. In contrast, phytohemagglutinin (PHA) stimulated MNC of normal donors, Epstein-Barr Virus (EBV) transformed B-cells of JMML patients, BFU-E and CFU-GM derived colonies of JMML patients, and the cell lines K562 and HEL did not or only barely express these two forms of exon skipping. These results may indicate that alternative HCP exon skipping may be associated with the proliferative state of the cell.
Assuntos
Regulação Leucêmica da Expressão Gênica , Leucemia Mielomonocítica Crônica/enzimologia , Proteínas de Neoplasias/biossíntese , Proteínas Tirosina Fosfatases/biossíntese , Células da Medula Óssea/enzimologia , Divisão Celular , Linhagem Celular Transformada , Transformação Celular Viral , Criança , Pré-Escolar , DNA Complementar/genética , Indução Enzimática , Éxons/genética , Feminino , Genes ras , Herpesvirus Humano 4 , Humanos , Lactente , Peptídeos e Proteínas de Sinalização Intracelular , Células K562/patologia , Leucemia Mielomonocítica Crônica/genética , Leucócitos Mononucleares/enzimologia , Ativação Linfocitária , Masculino , Proteínas de Neoplasias/genética , Células-Tronco Neoplásicas/enzimologia , Fito-Hemaglutininas/farmacologia , Proteína Tirosina Fosfatase não Receptora Tipo 6 , Proteínas Tirosina Fosfatases/genética , Splicing de RNA , RNA Mensageiro/genética , RNA Mensageiro/metabolismo , RNA Neoplásico/genética , RNA Neoplásico/metabolismo , Baço/enzimologia , Transcrição Gênica , Domínios de Homologia de srcRESUMO
Interferon regulatory factor 1 (IRF-1) is a transcriptional activator in the interferon system and acts as a tumor suppressor. The structurally related IRF-2 represses the effects of IRF-1 by competitive binding to the same DNA sequence elements. Changes in the relative balance between IRF-1 and IRF-2 lead to dysregulation of cell growth and may play a role in the development of neoplasias. The loss of functional IRF-1 has been observed in a number of patients with myelodysplastic syndrome (MDS) and leukemia, suggesting a potentially critical role of IRF-1 in leukemogenesis. We studied the expression of both transcription factors in peripheral blood (PB) and bone marrow (BM) cells of children with juvenile myelomonocytic leukemia (JMML) using RT-PCR and Southern blot hybridization. No significant difference between the expression levels of IRF-1 and IRF-2 could be detected in PB and BM of patients with JMML and normal donors. Although our results are preliminary they suggest that neither the tumor suppressor gene IRF-1 nor the oncogene IRF-2 is involved in the pathogenesis of JMML.
