Klf4 in tumor initiation and maintenance of squamous cell carcinoma

描述（由申请人提供）：KLF4转录因子在上皮细胞的细胞命运和分化中很重要。KLF4在小鼠中迅速启动皮肤鳞状细胞癌（SCC），并在人类皮肤肿瘤进展的早期阶段被解除调控。使用条件KLF4- er融合蛋白，我们确定了细胞命运决定因子Notch 1是KLF4的转录靶点。在培养细胞、转基因小鼠和人类肿瘤中，KLF4的表达与Notch1、Notch1配体和Notch1效应物如Cyclin D1的表达相关。RK3E上皮细胞的转化需要Notch1。这些研究发现了一个KLF4-Notch1通路，在正常上皮细胞和肿瘤细胞的细胞命运规范中似乎很重要。KLF4的诱变鉴定出阻断KLF4体外转化的显性阴性（DN）等位基因。KLF4- dns鉴定了KLF4在体外特定人类细胞类型生长中的作用，以及通过特定转化癌基因（如ErbB2和c-MYC）的转化。

DESCRIPTION (provided by applicant): The KLF4 transcription factor is important in cell fate and differentiation of epithelial cells. KLF4 rapidly initiates cutaneous squamous cell carcinoma (SCC) in mice, and is deregulated at an early step in human skin tumor progression. Using a conditional KLF4-ER fusion protein, we identified the cell fate determinant Notch 1 as a transcriptional target of KLF4. In cultured cells, in transgenic mice and in human tumors, KLF4 expression is associated with expression of Notch1, Notch1 ligands, and Notch1 effectors such as Cyclin D1. Transformation of RK3E epithelial cells requires Notch1. These studies identify a KLF4-Notch1 pathway that appears important in cell fate specification of normal epithelial cells and tumor cells. Mutagenesis of KLF4 identified dominant negative (DN) alleles that block transformation in vitro by KLF4. KLF4-DNs identify a role of KLF4 in growth of specific human cell types in vitro, and in transformation by specific transforming oncogenes such as ErbB2 and c-MYC. To study the role of Klf4 in cutaneous SCC we developed a novel highly penetrant model of SCC by administering carcinogens to genetically-engineered mice. Tumors were histologically similar to human SCC, and expressed SCC markers such as p53, keratin 14, and Notch1. SCCs that developed in this model included KLF4-positive tumors and some tumors that were KLF4-negative. To understand the mechanisms that normally regulate KLF4, we will study the role of posttranslational modifications in the DN activity of mutant KLF4 proteins (Aim 1). The role of endogenous Klf4 in tumor initiation and maintenance will be studied in the new SCC mouse model using conditional, Cre-mediated deletion of Klf4/LoxP alleles, and by tetracycline-inducible expression of siRNA or KLF4-DN in transgenic mice (Aim 2). Using similar loss- and gain-of-function strategies, the role of Klf4 in mammary epithelial development and in transformation by ErbB2 will be determined (Aim 3). In Aim 4, a posttranslational control that appears responsible for upregulation of Klf4 transcripts in mouse and human SCC will be analyzed by identifying RNA destabilizing elements in the KLF4 cDNA. These studies may provide support of a role for KLF4 and Notch1 in pathogenesis of common human cancers such as SCC and breast cancer. Thus, completion of the studies would identify this pathway as a target for prevention and treatment, and provide new animal models in which to assess such therapies.