Kim Paul J, Plescia Janet, Clevers Hans, Fearon Eric R, Altieri Dario C
Department of Cancer Biology and the Cancer Center, University of Massachusetts, Medical School, Worcester, MA, USA.
Lancet. 2003 Jul 19;362(9379):205-9. doi: 10.1016/S0140-6736(03)13910-4.
Colorectal cancer is thought to originate in the expansion of colonic crypt cells as a result of aberrant gene expression caused by transcription factors of the T-cell factor (TCF)/beta-catenin family. Survivin is a bifunctional regulator of cell death and cell proliferation expressed during embryonic development but undetectable in healthy adult tissues and re-expressed in many cancers, including colorectal cancer.
We investigated gene expression by promoter analysis, mutagenesis, and electrophoretic mobility shift assay in colorectal cancer cells. Survivin expression in human and mouse embryonic intestine was determined by in-situ hybridisation and immunohistochemistry. Changes in apoptosis were monitored in cell lines engineered to express stabilising mutations in beta catenin.
TCF/beta catenin stimulated a six-fold to 12-fold increased expression of the survivin gene in colorectal cancer cells. Three TCF-binding elements (TBE) in the survivin promoter were occupied by nuclear factors in colorectal cancer cells, and mutagenesis of the two proximal TBE sites abolished survivin gene expression by 75-79%. Strongly expressed at the bottom of human and mouse embryonic intestinal crypts, expression of survivin was lost in TCF-4 knockout animals, and a TCF-4 dominant negative mutant blocked survivin gene transcription in colorectal cancer cells. Expression of non-destructible beta catenin mutants increased survivin expression and protected against ultraviolet-B-induced apoptosis.
Stimulation of survivin expression by TCF/beta catenin might impose a stem cell-like phenotype to colonic crypt epithelium coupling enhanced cell proliferation with resistance to apoptosis, and contribute to the molecular pathogenesis of colorectal cancer.
结直肠癌被认为起源于结肠隐窝细胞的扩增，这是由T细胞因子（TCF）/β-连环蛋白家族的转录因子引起的异常基因表达所致。存活素是一种细胞死亡和细胞增殖的双功能调节因子，在胚胎发育过程中表达，但在健康成人组织中无法检测到，而在包括结直肠癌在内的许多癌症中重新表达。
我们通过启动子分析、诱变和电泳迁移率变动分析研究了结直肠癌细胞中的基因表达。通过原位杂交和免疫组织化学确定人及小鼠胚胎肠道中存活素的表达。在工程改造以表达β-连环蛋白稳定突变的细胞系中监测细胞凋亡的变化。
TCF/β-连环蛋白刺激结直肠癌细胞中存活素基因的表达增加6至12倍。存活素启动子中的三个TCF结合元件（TBE）被结直肠癌细胞中的核因子占据，两个近端TBE位点的诱变使存活素基因表达减少75-79%。存活素在人及小鼠胚胎肠道隐窝底部强烈表达，在TCF-4基因敲除动物中存活素表达缺失，TCF-4显性负性突变体阻断结直肠癌细胞中存活素基因的转录。不可破坏的β-连环蛋白突变体的表达增加了存活素的表达，并保护细胞免受紫外线B诱导的凋亡。
TCF/β-连环蛋白对存活素表达的刺激可能使结肠隐窝上皮具有干细胞样表型，将增强的细胞增殖与抗凋亡能力相结合，并有助于结直肠癌的分子发病机制。
