1. ¹Department of Pathology, Josephine Nefkens Institute, Erasmus University Medical Center, Rotterdam, The Netherlands
2. ²Department of Surgery, Erasmus University Medical Center, Rotterdam, The Netherlands
3. ³Hubrecht Laboratory, Center for Biomedical Genetics, Utrecht, The Netherlands
4. ⁴Department of Clinical Genetics, Erasmus University Medical Center, Rotterdam, The Netherlands

Correspondence: Dr WNM Dinjens, Department of Pathology, Erasmus MC, Josephine Nefkens Institute, room BE 312a, PO Box 1738, 3000 DR Rotterdam, The Netherlands. E-mail: w.dinjens@erasmusmc.nl

⁵These authors contributed equally to the work. LB Koppert is sponsored by the Dutch Cancer Society/KWF

Received 28 August 2003; Accepted 23 November 2003.

Abstract

Up to 60% of gastro-oesophageal junction (GEJ) adenocarcinomas show nuclear -catenin expression, pointing to activated T-cell factor (TCF)/-catenin-driven gene transcription. We demonstrate in five human GEJ adenocarcinoma cell lines that nuclear -catenin expression indeed correlates with enhanced TCF-mediated transcription of a reporter gene. In several tumour types, TCF/-catenin activation is caused by mutations in either adenomatous polyposis coli (APC), -catenin exon 3, AXIN1, AXIN2 or -transducin repeat-containing protein (-TrCP). In GEJ adenocarcinomas, very few APC and -catenin mutations have been found. Therefore, the mechanism of Wnt pathway activation remains unclear. In the present study, we did not find AXIN1 gene mutations in 17 GEJ tumours with nuclear -catenin expression (without -catenin exon 3 mutations). Six intragenic single nucleotide polymorphisms (SNPs) were identified. One of these, the AXIN1 gene T1942C SNP, has a frequency of 21% but is only very recently described despite numerous AXIN1 gene mutational studies. We provide evidence why this SNP was missed in single strand conformation polymorphism analyses. The AXIN1 gene G2063A variation was previously described as a gene mutation but we demonstrate that this is a polymorphism. With these six SNPs loss of heterozygosity (LOH) was found in 11 of 15 (73%) informative tumours. To investigate a possible AXIN1 gene dosage effect in GEJ tumours expressing nuclear -catenin, AXIN1 locus LOH was determined in 20 tumours expressing membranous and no nuclear -catenin. LOH was found in 10 of 13 (77%) informative cases. AXIN1 protein immunohistochemistry revealed cytoplasmic expression in all tumours irrespective of the presence of AXIN1 locus LOH. These data indicate that nuclear -catenin expression is indicative for activated Wnt signalling and that neither AXIN1 gene mutations nor AXIN1 locus LOH are involved in Wnt pathway activation in GEJ adenocarcinomas.