RESUMO
DNA was analyzed from 57 sporadic gastrointestinal tumors (34 pancreatic cancers, 23 colon tumors) and cognate normal tissues to verify whether mutations at coding sequences were associated with microsatellite instability (MSI). Genomic instability was present in 41% (14/34) of pancreatic samples and in 26% (6/23) of colon cancers previously tested by six microsatellite markers. The tumors included 37 cases showing no MSI; 15 cases with MSI at only 1 locus and 5 cases with MSI at 2 or more loci. All the samples were screened for mutations in genes containing repeated tracts in their coding sequences (TGFbetaRII, IGFRII and bax) and in codon 12 of the K-ras oncogene. Furthermore, loss of heterozygosity (LOH) at NM23.H1 locus was tested, 17/34 (50%) pancreatic tumors and 6/23 (26%) colon cancers showed mutations in codon 12 of K-ras; allelic loss of NM23. H1 locus was found in 6/18 (33%) informative colon tumors and in no pancreatic cancers. The TGFbetaRII, IGFRII and bax genes were altered in 3 (13%), 1 (4%) and 3 (13%) out of 23 colon tumors respectively, but no mutation was detected in pancreatic cancers. Mutations in the repeated nucleotide stretches within the coding sequences of TGFbetaRII, IGFRII and bax genes were found only in colon tumors with a high unstable phenotype (more than 3 microsatellite loci altered).
Assuntos
Neoplasias do Colo/genética , Genes ras/genética , Núcleosídeo-Difosfato Quinase , Neoplasias Pancreáticas/genética , Proteínas Proto-Oncogênicas c-bcl-2 , Proteínas Proto-Oncogênicas/genética , Receptor IGF Tipo 2/genética , Receptores de Fatores de Crescimento Transformadores beta/genética , Adulto , Idoso , Idoso de 80 Anos ou mais , Pareamento Incorreto de Bases , Transformação Celular Neoplásica/genética , Códon , Neoplasias do Colo/patologia , Reparo do DNA , Feminino , Mutação da Fase de Leitura , Humanos , Perda de Heterozigosidade , Masculino , Repetições de Microssatélites/genética , Pessoa de Meia-Idade , Proteínas Monoméricas de Ligação ao GTP/genética , Nucleosídeo NM23 Difosfato Quinases , Neoplasias Pancreáticas/patologia , Mutação Puntual , Biossíntese de Proteínas , Proteínas Serina-Treonina Quinases , Receptor do Fator de Crescimento Transformador beta Tipo II , Fatores de Transcrição/genética , Proteína X Associada a bcl-2RESUMO
Genomic instability has been proposed as a new mechanism of carcinogenesis involved in hereditary non-polyposis colorectal cancer (HNPCC) and in a large number of sporadic cancers like pancreatic and colon tumours. Mutations in human mismatch repair genes have been found in HNPCC patients, but their involvement in sporadic cancer has not been clarified yet. In this study we screened 21 pancreatic and 23 colorectal sporadic cancers for microsatellite instability by ten and six different microsatellite markers respectively. Microsatellite alterations were observed at one or more loci in 66.6% (14/21) of pancreatic cancers and in 26% (6/23) colon tumours, but all the pancreatic and half of the colon samples showed a low rate of microsatellite instability. All the unstable samples were further analysed for mutations in the hMLH1 and hMSH2 genes and for hypermethylation of the hMLH1 promoter region. Alterations in the hMLH1 gene were found only in colorectal tumours with a large presence of microsatellite instability. None of the pancreatic tumours showed any alteration in the two genes analysed. Our results demonstrate that microsatellite instability is unlikely to play a role in the tumorigenesis of sporadic pancreatic cancers and confirm the presence of mismatch repair gene alterations only in sporadic colon tumours with a highly unstable phenotype.