Koppert L B, van der Velden A W, van de Wetering M, Abbou M, van den Ouweland A M W, Tilanus H W, Wijnhoven B P L, Dinjens W N M
Department of Pathology, Josephine Nefkens Institute, Erasmus University Medical Center, Rotterdam, The Netherlands.
Br J Cancer. 2004 Feb 23;90(4):892-9. doi: 10.1038/sj.bjc.6601589.
Up to 60% of gastro-oesophageal junction (GEJ) adenocarcinomas show nuclear beta-catenin expression, pointing to activated T-cell factor (TCF)/beta-catenin-driven gene transcription. We demonstrate in five human GEJ adenocarcinoma cell lines that nuclear beta-catenin expression indeed correlates with enhanced TCF-mediated transcription of a reporter gene. In several tumour types, TCF/beta-catenin activation is caused by mutations in either adenomatous polyposis coli (APC), beta-catenin exon 3, AXIN1, AXIN2 or beta-transducin repeat-containing protein (beta-TrCP). In GEJ adenocarcinomas, very few APC and beta-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 beta-catenin expression (without beta-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 beta-catenin, AXIN1 locus LOH was determined in 20 tumours expressing membranous and no nuclear beta-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 beta-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.
高达60%的胃食管交界（GEJ）腺癌显示核β-连环蛋白表达，提示激活的T细胞因子（TCF）/β-连环蛋白驱动的基因转录。我们在五个人类GEJ腺癌细胞系中证明，核β-连环蛋白表达确实与报告基因的TCF介导的转录增强相关。在几种肿瘤类型中，TCF/β-连环蛋白激活是由腺瘤性息肉病（APC）、β-连环蛋白外显子3、AXIN1、AXIN2或含β-转导蛋白重复序列的蛋白（β-TrCP）中的突变引起的。在GEJ腺癌中，很少发现APC和β-连环蛋白突变。因此，Wnt通路激活的机制仍不清楚。在本研究中，我们在17例有核β-连环蛋白表达（无β-连环蛋白外显子3突变）的GEJ肿瘤中未发现AXIN1基因突变。鉴定出六个基因内单核苷酸多态性（SNP）。其中一个，AXIN1基因T1942C SNP，频率为21%，尽管对AXIN1基因进行了大量突变研究，但直到最近才被描述。我们提供了证据说明为什么这个SNP在单链构象多态性分析中被遗漏。AXIN1基因G2063A变异先前被描述为基因突变，但我们证明这是一个多态性。在15例信息充分的肿瘤中的11例（73%）中发现了这六个SNP的杂合性缺失（LOH）。为了研究在表达核β-连环蛋白的GEJ肿瘤中可能的AXIN1基因剂量效应，在20例表达膜性而非核β-连环蛋白的肿瘤中测定了AXIN1基因座LOH。在13例信息充分的病例中的10例（77%）中发现了LOH。AXIN1蛋白免疫组织化学显示所有肿瘤中均有细胞质表达，与AXIN1基因座LOH的存在无关。这些数据表明核β-连环蛋白表达指示Wnt信号激活，并且AXIN1基因突变和AXIN1基因座LOH均不参与GEJ腺癌中的Wnt通路激活。
