Association of p53 genomic instability with the glutathione S- transferase null genotype in gastric cancer in the Portuguese population

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Abstract
AIMS: p53 gene mutations are the most common genetic changes known to occur in human cancer. In previous studies, the presence of alterations to the p53 gene has been linked to the null phenotype of the glutathione S-transferase mu gene (GSTM1). GSTM1 appears to be part of a protective mechanism against the development of cancers in which environmental chemical carcinogens are involved. To screen for such an association in stomach cancer, p53 allelic loss and genomic instability and GSTM1 genotypes were investigated in gastric tumour DNA samples from 113 patients. METHODS: The polymerase chain (PCR) reaction was used to amplify a (CA) repeat array in the p53 locus; electrophoresis, genotyping, and allele quantification were performed using an automated DNA sequencer and Genescan software. The presence of the GSTM1 gene was determined by means of a differential PCR in which multiple genes were co-amplified in the same reaction tube. RESULTS: Loss of heterozygosity (LOH) of the p53 gene was found in 36 of 87 informative cases and genomic instability was present in eight of 113 cases. Further analysis into histological subtypes and sites of tumours did not show any positive association with p53 loss. An association between the presence of LOH and the GSTM1 null genotype was not seen; however, all the samples with genomic instability of the p53 gene (eight of 113) also showed a GSTM1 null genotype. CONCLUSION: This study does not support the hypothesis of an association between LOH in the p53 gene and the GSTM1 null genotype, but suggests that the GSTM1 null genotype might influence p53 genomic instability.