P53 IS FREQUENTLY MUTATED IN BARRETTS METAPLASIA OF THE INTESTINAL-TYPE

Barrett's Esophagus (BE) is a complication of gastroesophageal reflux in which the normal squamous epithelium of the lower esophagus is repl aced by metaplastic tissue. The clinical significance of this conditio n is the associated predisposition to adenocarcinomas (ADCs). Three ty pes of BE have been characterized: the gastric fundic (F) type, the ga stric cardial (C) type, and the intestinal (I) type. The latter is the most closely associated with the development of ADCs; the causes of t his bias remain unknown. To determine whether p53 and/or K-ms gene alt erations (a) are present in preneoplastic lesions and (b) are associat ed with a specific histotype, we performed PCR-based denaturing gradie nt gel electrophoresis (DGGE) analysis of exon 1 (codons 12-13) of K-m s gene and of exons 5-8 of the p53 gene in biopsies obtained from 30 p atients with BE of the I type (9 patients), combined I type (I + C +/- F; 10 patients) and non-I type (C, F, or C + F; 11 patients). None of the cases under study revealed K-ras mutations, whereas biopsies from 12 patients showed at least one p53 DGGE variant. Four patients showe d the exact same variants in leukocytes also (polymorphisms), whereas eight cases revealed specific DGGE variants only in biopsies. The mole cular characterization of these variants revealed that four of them sh owed a single base pair substitution, and four showed multiple mutatio ns. Of 17 somatic mutations, all but 1 were base pair substitutions lo cated mainly in exons 7 and 8. The majority of these mutations were GC targeted (13 of 16; 81%), 54% (7 of 13) of which were transitions occ urring at CpG sites. All somatic mutations were found in BE with at le ast one I component. The association with the histotype was statistica lly significant (P < 0.03; pure I type versus non-I type; P < 0.04, co mbined I type versus non-I type; Fisher's exact test). Loss of heteroz ygosity in the vicinity of the p53 locus was evaluated by PCR using a highly polymorphic variable number of tandem repeats marker on 25 out of 30 cases. Ninety-two % of the cases analyzed were informative, and none of them showed LOH. In conclusion, we showed that p53 mutations a re frequently observed in specimens from BE patients of the I-type, wh ereas no involvement of K-ras (exon 1) mutational activation was obser ved. In light of the key roles that the p53 protein plays in controlli ng cell cycle and cell diploidy, this result may suggest why this type of metaplasia is the most closely associated to the development of AD Cs.