Stoehr Robert, Krieg Rene C, Knuechel Ruth, Hofstaedter Ferdinand, Pilarsky Christian, Zaak Dirk, Schmitt Ruediger, Hartmann Arndt
Institute of Pathology, University of Regensburg, 93042 Regensburg, Germany.
Int J Oncol. 2002 May;20(5):905-11.
The wnt pathway plays an important role in embryonal patterning and cell fate determination, involving stabilization of nuclear and cytoplasmic beta-catenin (CTNNB1) mediated by APC, axin, and other proteins. Uncomplexed beta-catenin binds to TCF/LEF transcription factors and activates the expression of growth regulatory target genes such as c-myc or cyclin D1. In colorectal and other cancers, constitutive wnt signaling results frequently from mutations in one or more pathway components, e.g. APC and beta-catenin, resulting in nuclear and/or cytoplasmic accumulation of beta-catenin. In the present study, the most frequent alterations in the CTNNB1 and APC genes were investigated in primary urothelial bladder tumors and cell lines. Snap-frozen bladder tumors (n=99) of different stages and grades and 4 cell lines (RT4, RT112, J82, UROtsa) were investigated for APC allelic deletions by loss of heterozygosity (LOH) analysis. The most frequent mutated regions of CTNNB1 (degradation box in the third exon) and APC (mutation cluster region) were directly sequenced. Beta-catenin expression was analyzed by immunofluorescence in the cell lines. LOH at the APC gene locus on chromosome 5q21 was found in 7 of 72 (10%) of the informative cases. No mutations were found in either CTNNB1 or APC. A previously described polymorphism at codon 1493 of the APC gene was detected in 8 tumors and 3 cell lines. All cell lines showed normal membranous beta-catenin staining without evidence for nuclear or cytoplasmic accumulation. Alteration of APC and beta-catenin, which are the most frequent wnt pathway alterations in many tumor types, are rare events in urothelial carcinomas. Other wnt pathway members, such as axin, may play an important role in urothelial carcinogenesis.
Wnt信号通路在胚胎模式形成和细胞命运决定中发挥重要作用，涉及由APC、轴蛋白和其他蛋白质介导的核和细胞质β-连环蛋白（CTNNB1）的稳定。未结合的β-连环蛋白与TCF/LEF转录因子结合并激活生长调节靶基因如c-myc或细胞周期蛋白D1的表达。在结直肠癌和其他癌症中，组成性Wnt信号传导常常源于一个或多个通路成分（如APC和β-连环蛋白）的突变，导致β-连环蛋白在核内和/或细胞质中积累。在本研究中，对原发性膀胱尿路上皮肿瘤和细胞系中CTNNB1和APC基因最常见的改变进行了研究。通过杂合性缺失（LOH）分析，对不同分期和分级的99例速冻膀胱肿瘤以及4种细胞系（RT4、RT112、J82、UROtsa）进行了APC等位基因缺失检测。对CTNNB1最常见的突变区域（第三外显子中的降解框）和APC（突变簇区域）进行直接测序。通过免疫荧光分析细胞系中的β-连环蛋白表达。在72例信息性病例中的7例（10%）中发现了5号染色体q21位点上APC基因座的LOH。在CTNNB1或APC中均未发现突变。在8例肿瘤和3种细胞系中检测到APC基因第1493密码子处先前描述的多态性。所有细胞系均显示β-连环蛋白膜染色正常，无核内或细胞质积累的证据。APC和β-连环蛋白的改变是许多肿瘤类型中最常见的Wnt信号通路改变，但在膀胱尿路上皮癌中是罕见事件。其他Wnt信号通路成员，如轴蛋白，可能在膀胱尿路上皮癌发生中起重要作用。
