p53 and neoplastic progression in Barrett's esophagus

Sammanfattning: p53 and Neoplastic Progression in Barrett's Esophagus Stig Ramel Department of Surgery, Ersta Hospital, S-l16 91 Stockholm, and Department of Surgery, Huddinge Hospital, S-141 86 Stockholm, Sweden Barrett's esophagus is a condition in which the normal squamous epithelium is replacedby columnar epithelium as a response to acid reflux. It develops as a complication in 10-20%of patients with gastroesophageal reflux disease. The presence of specialized columnarepithelium is necessary for the development of adenocarcinoma of the esophagus and gastriccardia, the most rapidly increasing malignancies in many western countries. A DNAcontent/p53 protein multiparameter flow cytometry technique was developed for the analysisof p53 abnormalities in endoscopic biopsies from patients in surveillance for the detection ofneoplastic progression in Barrett's esophagus. p53 abnormalities as assessed by p53 protein overexpression and p53 allele deletion (17pallelic loss) were evaluated in patients with esophageal adenocarcinomas. 92% of patients had17p allelic loss and 67% had p53 protein overexpression indicating a high frequency of p53abnormalities in Barrett's adenocarcinomas. During neoplastic progression in premalignant Barrett's epithelium p53 proteinoverexpression was detected both in diploid and aneuploid premalignant tissue at increasingfrequency in advancing stages of histologic progression to malignancy. Proliferative abnormalities with increased S phase fractions and DNA contentabnormalities with the development of aneuploidy are frequently detected in Barrett'sesophagus during neoplastic progression. The relationship with p53 inactivation was studied inSV 40 transgenic mice and in p53 deficient mice in vitro and in vivo. Aneuploid and tetraploidcell populations occur after the development of p53 inactivation, indicating a function of p53 inmaintaining the diploid state. In mouse embryo fibroblasts in vitro a p53 dependent checkpointfiunction in mitosis is present, preventing new cell cycle rounds without completion ofchromosome segregation in previous mitosis. The relationship between p53 inactivation, aneuploidy, and increased S phase fractionswas studied in premalignant Barrett's epithelium in wvo; the results indicating that p53inactivation may be sufficient for the frequently detected development of aneuploid cellpopulations, but that p53 inactivation alone is not sufficient to cause the increased S phasefractions, also frequently detected during neoplastic progression in Barrett's esophagus. p53 overexpression, 17p allelic loss, and mutations of the remaining p53 allele wereinvestigated in 12 esophagectomy specimens, all of which were found to have 17p allelic lossand mutations of the remaining 17p allele. p53 overexpression was detected in all but 4patients. In all cases without p53 overexpression the mutations caused stop codons,presumably with truncated proteins, not detectable by flow cytometry. p53 protein overexpression can be detected in endoscopic biopsies from patients withBarrett's esophagus by multiparameter flow cytometry. The assay may prove useful indetecting patients at high risk of neoplastic progression, but has to be interpreted with cautionbecause some p53 mutations do not cause protein overexpression.Key words: Barrett's esophagus, neoplastic progression, flow cytometry, p53 gene, p53protein, 17p allelic loss, p53 mutations, S phase fractions, aneuploidy, SV 40 large T antigen,elastase-SV 40 T antigen transgenic mice. ISBN 91-628-1790-6