RESUMO
Many molecular investigations of colorectal cancer (CRC) have suggested that the accumulation of specific mutations in proto-oncogenes and tumor suppressor genes regulating cell growth via signal transduction trigger the stagewise progression to malignancy. In this study, the frequency, location, and type of mutations of the K-ras proto-oncogene exon I and p53 tumor suppressor gene exons 5-8 were analyzed in colorectal carcinomas of 65 patients from Central Europe, using polymerase chain reaction (PCR)-cold single-strand conformation polymorphism (SSCP) screening and direct sequencing. The incidence of K-ras activating mutations in these Central European samples was lower (25%) compared to that obtained in American and western European populations (40-50% at least), while the incidence of p53 inactivating mutations was similar (58%). These results suggest that some other genetically linked mechanisms may play a role in CRC development and progression, and hence K-ras and p53 mutations cannot be considered to be universal genetic markers for CRC.
Assuntos
Neoplasias Colorretais/genética , Genes ras/genética , Proteína Supressora de Tumor p53/genética , Neoplasias Colorretais/metabolismo , Primers do DNA , DNA de Neoplasias/genética , DNA de Neoplasias/isolamento & purificação , Europa (Continente) , Éxons/genética , Humanos , Íntrons/genética , Polimorfismo Conformacional de Fita Simples , Proto-Oncogene Mas , Reação em Cadeia da Polimerase Via Transcriptase Reversa , Análise de Sequência de DNARESUMO
We have studied the frequency of p53 mutations in genomic DNA extracted from peripheral blood or the spleen of 61 patients with hairy cell leukemia using PCR-SSCP and automated cycle sequencing. We identified exon 5-8 mutations in 17 cases, corresponding to a frequency of 28%. In four cases, mutations were localized in exon 5; one patient with atypical HCL had a mutation in exon 6 at the 3' boundary; five cases showed mutations in exon 7, while exon 8 was found to be mutated in seven cases. The mutations found could be divided into three major categories: structural (n=9), inactivating (n= 6), and neutral (n= 2) mutations. None of the three transitions found occurred at CpG dinucleotides. The rate of p53 mutations found in this large cohort of HCL patients is unexpectedly high as in other non-Hodgkin lymphomas p53 mutations predict for poor treatment outcome. The character of the mutations we have found is entirely different from that described in other hematologic malignancies.
Assuntos
Genes p53 , Leucemia de Células Pilosas/genética , Mutação , Adulto , Idoso , Substituição de Aminoácidos , Ciclo Celular , Códon , Estudos de Coortes , Ilhas de CpG , Análise Mutacional de DNA , DNA de Neoplasias/sangue , DNA de Neoplasias/genética , Feminino , Humanos , Leucemia de Células Pilosas/mortalidade , Leucemia de Células Pilosas/patologia , Linfoma não Hodgkin/genética , Linfoma não Hodgkin/mortalidade , Masculino , Pessoa de Meia-Idade , Mutação Puntual , Reação em Cadeia da Polimerase , Polimorfismo Conformacional de Fita Simples , Prognóstico , Deleção de Sequência , Baço/químicaRESUMO
Mutations of the p53 gene may alter the specific regulatory domains of the protein. We examined the conserved domains III, IV and V by SSCP using PCR primers covering exons 5, 6, 7 and 8 from hairy cell leukemia (HCL), polyps, colorectal and gastric carcinomas. A low rate of p53 mutations was detected in HCL and polyps. These mutations may predict the risk of malignant development. However, multiple mutations were a frequent occurrence in tumors. Sequence analysis of our samples did not demonstrate the high frequency of transition mutations (C-->T) that would be predicted if the major course of p53 mutations is deamination of 5-methylcytosine (5mC). Rather, most mutations were found to be single base insertions or deletions.
