LEF/TCF Expression in Colon Cancer

描述（由申请人提供）：结肠癌的分子遗传学分析已经确定Wnt信号通路参与早期肿瘤发展，特别是结肠癌。 将信号转化为靶基因表达变化的转录因子是类淋巴细胞增强因子/T细胞因子（LEF/TCF）家族的成员。 该家族的两个成员TCF 1和LEF 1的基因产生截短的显性负性形式，其限制Wnt信号，并且可能起生长抑制剂的作用。 我们发现LEF 1基因在结肠癌中被异位诱导，但只有全长激活形式表达-显性阴性形式不表达。 LEF 1和TCF 1在结肠癌进展过程中的表达模式尚不清楚。 TCF 1通常在人类结肠中表达，但在正常结肠和癌症中全长和显性阴性形式的相对量也是未知的。 基于我们的初步研究结果，我们提出LEF/TCF的全长亚型在结肠癌中占主导地位。 此外，我们提出Wnt通路本身在促进全长亚型的表达中起作用。 为了验证这些假设，我们将确定LEF 1和TCF 1亚型在正常、息肉和结肠癌中的表达（具体目标1）。 为了探索LEF 1异常表达的机制，将在结肠癌细胞系中评估LEF 1基因的遗传完整性及其对染色质结构表观遗传变化的敏感性（特异性目标2）。 TCF 1/a-连环蛋白和TCF 4/a-连环蛋白复合物可以在瞬时转染测定中激活LEF 1启动子，而其他LEF/TCF不能。 我们提出LEF 1是癌症中特异性TCF 1/4/α-连环蛋白复合物的靶标。 提出实验来探索这种调节并测试其与结肠癌细胞中内源性LEF 1基因的相关性（具体目标3）。 基于TCFI/4对LEF 1启动子的选择性作用，我们假设每个LEF/TCF家族成员携带独特的靶基因特异性，并且它们在癌症中的表达赋予不同的作用。 为了验证这一假设，将使用两种策略来破坏结肠癌细胞中的LEF/TCF功能。 将通过总体基因表达谱和细胞生长和活力试验（特定目标4）评估效应。

DESCRIPTION (provided by applicant): Molecular genetic analysis of colon cancers has established that the Wnt signaling pathway is involved in early tumor development, particularly in colon cancer. The transcription factors that commute the signal into changes in target gene expression are members of the Lymphoid Enhancer Factor/T Cell Factor (LEF/TCF) family. The genes for two members of this family, TCF1 and LEF1, produce truncated dominant negative forms that limit Wnt signals and may function as growth suppressors. We have found that the LEF1 gene is ectopically induced in colon cancer, but only the full-length activating form is expressed - the dominant negative form is not. The patterns of LEF1 and TCF1 expression during colon cancer progression are not known. TCF1 is normally expressed in human colon, but the relative amounts of full-length and dominant negative forms in normal colon and cancer are also not known. Based on results from our preliminary studies, we propose that full-length isoforms of LEF/TCFs predominate in colon cancer. Furthermore, we propose that the Wnt pathway itself plays a role in promoting expression of full-length isoforms. To test these hypotheses we will determine the expression of LEF1 and TCF1 isoforms in normal, polyp and colon carcinoma (Specific Aim 1). To probe the mechanism of aberrant LEF1 expression, the genetic integrity of the LEF1 gene and its sensitivity to epigenetic changes in chromatin structure will be assessed in colon cancer cell lines (Specific Aim 2). TCFl/a-catenin and TCF4/ a-catenin complexes can activate the LEF1 promoter in transient transfection assays, other LEF/TCFs cannot. We propose that LEF1 is a target of specific TCFl/4/ a-catenin complexes in cancer. Experiments are proposed to explore this regulation and test for its relevance to the endogenous LEF1 gene in colon cancer cells (Specific Aim 3). Based on the selective effect of TCFI/4 on the LEF1 promoter, we hypothesize that each LEF/TCF family member carries unique target gene specificities and that their expression in cancer imparts distinct effects. To test this hypothesis, two strategies will be used to disrupt LEF/TCF function in colon cancer cells. Effects will be assessed by global gene expression profiles and cell growth and viability assays (Specific Aim 4).