Multiple target sites of allelic imbalance on chromosome 17 in Barrett's oesophageal cancer

Abstract

Twelve Barrett's adenocarcinomas have been analysed for the occurrence of allelic imbalance (LOH) on chromosome 17 using 41 microsatellite markers. This study provides evidence for 13 minimal regions of LOH, six on 17p and seven on 17q. Four of these centre in the vicinity of the known tumour suppressor genes (TSGs) TP 53 (17p13.1), NF1 (17q11.2), BRCA1 (17q21.1), and a putative TSG (17p13.3). The tumours all displayed relatively small regions of LOH (1 ± 10 cM), and in several tumours extensive regions of LOH were detected. One tumour displayed only two very small regions of LOH; 17p11.2 and 17p13.1. The frequency of allelic imbalance has been calculated based on the LOH encompassing only one minimal region, and based on all the LOH observations. By both evaluations the highest LOH frequencies were found for regions II (p53), III (17p13.1 centromeric to p53), IV (17p12), V (17p11.2) and VII (NF1, 17q11.2). Our data supports the existence of multiple TSGs on chromosome 17 and challenges the view that p53 is the sole target of LOH on 17p in Barrett's adenocarcinoma.

Physical and transcript map of the minimally deleted region III on 17p implicated in the early development of Barrett's oesophageal adenocarcinoma

“…Our previous studies based on allelic imbalance data suggest the presence of a human Barrett's oesophageal adenocarcinoma (BOA) tumour suppressor gene (TSG) in a minimally deleted region of chromosome 17p (C17p) centromeric to the p53 TSG (Dunn et al, 1999(Dunn et al, , 2000, and multiplex PCR has confirmed that the allelic imbalance in this region is because of loss of heterozygosity (LOH) rather than amplification of the region (Dunn, unpublished). In this study, we have assembled physical and transcript maps of the deleted region (minimal region III-'MRIII') from which the candidate BOA TSG can be identified.…”

“…By using 10 pairs of normal/tumour samples for the SSCP analysis, it was assumed that any causative mutations would be identified. This is because the overall frequency of LOH at MRIII in our earlier study was 75% and, in addition, we have found LOH at MRIII in Barrett's intestinal metaplasia in 4/5 samples tested (Dunn et al, 1999(Dunn et al, , 2000. The two tumours used in the sequence analysis of x006 were selected because they were the most likely tumours to show a mutation, since they only showed LOH at MRIII (i.e.…”

“…Any exons demonstrating a polymorphism were subjected to a more rigorous SSCP analysis using a further 10 BOA DNA normal and tumour pairs. DNA was obtained as described in Dunn et al (1999).…”

“…The MRIII region is defined by four BOA tumours and is limited by the microsatellite markers D17S1852 and D17S954 in Dunn et al (1999). The overall frequency of LOH at MRIII in BOA is 75% and the defining markers both map to 11.573 Mb on chromosome 17p.…”

“…We have previously shown that chromosome 17 (C17) is the most frequent site of allelic imbalance in Barrett's oesophageal adenocarcinoma (BOA) tumours (Dolan et al, 1998), and that C17 contains 13 common minimally deleted regions in BOA tumours (Dunn et al, 1999), many of which coincide with the location of known or putative TSGs.…”