Brabletz T, Jung A, Dag S, Reu S, Kirchner T
Pathologisches Institut, Universität Erlangen-Nürnberg, Germany.
Verh Dtsch Ges Pathol. 2000;84:175-81.
beta-catenin was shown to be a major oncoprotein in colon cancer development. Its oncogenic function as a transcriptional activator is upregulated by mutations in the APC tumor suppressor gene, leading to a constitutive activation of the proliferation-associated genes c-myc and cyclin D. The aim of this study was to demonstrate a role of APC-mutations and dysregulated beta-catenin also for the progression of colorectal cancer, by identifying new target genes of beta-catenin associated with tumor invasion and metastasis. Potential invasion genes regulated by beta-catenin and its DNA binding partner TCF4 were identified by a computer search for the consensus DNA binding sequence in relevant promoter regions. Specific DNA binding was confirmed by gel shift assays. Functional importance of beta-catenin for the activation of identified genes was determined by luciferase reporter assays. The significance was demonstrated by coexpression of nuclear beta-catenin and the identified target genes by immunohistochemistry. Among other invasion genes, we identified the matrix metallo proteinases MMP-7 and MMP-1 activated by beta-catenin in the tumor cells. MMP-7 is an important factor for invasion and metastasis and overexpressed in 75% of colon carcinomas. The significance for human colon cancer development was demonstrated by a correlated overexpression of beta-catenin and the MMPs, beginning in large, severely dysplastic adenomas. Our results explain the high percentage of MMP-7 overexpression in colorectal tumors and the resulting activation of invasive growth. Moreover by identifying dysregulated beta-catenin as a transcriptional activator of MMPs and other invasion factors, we demonstrated an important role of mutated APC not only for early steps but also for the progression of colorectal carcinogenesis.
β-连环蛋白被证明是结肠癌发生过程中的一种主要癌蛋白。其作为转录激活因子的致癌功能通过APC肿瘤抑制基因的突变而上调，导致增殖相关基因c-myc和细胞周期蛋白D的组成性激活。本研究的目的是通过鉴定与肿瘤侵袭和转移相关的β-连环蛋白的新靶基因，来证明APC突变和失调的β-连环蛋白在结直肠癌进展中的作用。通过计算机搜索相关启动子区域中的共有DNA结合序列，鉴定了受β-连环蛋白及其DNA结合伴侣TCF4调控的潜在侵袭基因。通过凝胶迁移试验证实了特异性DNA结合。通过荧光素酶报告试验确定了β-连环蛋白对已鉴定基因激活的功能重要性。通过免疫组织化学检测核β-连环蛋白和已鉴定的靶基因的共表达，证明了其意义。在其他侵袭基因中，我们在肿瘤细胞中鉴定出了由β-连环蛋白激活的基质金属蛋白酶MMP-7和MMP-1。MMP-7是侵袭和转移的重要因素，在75%的结肠癌中过表达。从大的、严重发育异常的腺瘤开始，β-连环蛋白和MMPs的相关过表达证明了其对人类结肠癌发生的意义。我们的结果解释了MMP-7在结直肠癌中高比例过表达以及由此导致的侵袭性生长激活的原因。此外，通过鉴定失调的β-连环蛋白作为MMPs和其他侵袭因子的转录激活因子，我们证明了突变的APC不仅在结直肠癌发生的早期阶段，而且在其进展过程中都起着重要作用。
