The role of Klf5 in GI epithelial homeostasis

描述（由申请人提供）：Klf5 （IKLF; BTEB2）是kruppel样因子（KLF）家族的成员，在体外具有转化特性的细胞增殖的正调节因子。在胃肠道上皮中，Klf5在细胞增殖活跃的区域表达，包括食管基底层、小肠隐窝和结肠隐窝的下三分之一。在体外，KLF5介导致癌H-Ras的转化活性，负调控Klf4 （GKLF）。我们之前通过基因靶向实验研究了Klf4在体内的作用，并证明了Klf4在几种胃肠道上皮中作为细胞增殖的负调节因子和正常分化的促进因子具有重要作用。尽管如此，Klf5也被认为是人类乳腺、前列腺和肠道中可能的肿瘤抑制基因，这导致了K/f5在正常上皮稳态和肿瘤发生中的作用的相互矛盾的假设。因此，我们将通过验证以下假设来研究Klf5在胃肠道增殖和分化中的作用：(1)胃肠道上皮中Klf5表达增加导致上皮过度增殖和分化改变；(2)胃肠道上皮中Klf5表达缺失导致上皮细胞增殖减少。具体目的如下：(1)利用上游调控元件ED-L2和villin分别在小鼠食管上皮和肠上皮中直接过表达Klf5，分析其在体内胃肠道增殖和分化中的功能；(2)通过在原代食管上皮细胞中过表达Klf5来检测Klf5在胃肠道上皮中表达增加的影响；(3)通过对原代食管上皮细胞功能丧失的研究，探讨Klf5在胃肠道上皮稳态中的作用。这项工作将为胃肠道上皮细胞增殖和分化的调控提供重要的新见解，并为理解粘膜损伤和恶性转化的分子事件提供一个框架。

DESCRIPTION (provided by applicant): Klf5 (IKLF; BTEB2) is a member of the Kruppel-like factor (KLF) family implicated as a positive regulator of cell proliferation with transforming properties in vitro. In gastrointestinal epithelia, Klf5 is expressed in regions of active cell proliferation, including the basal layer of the esophagus, the small intestinal crypts, and the lower third of colonic crypts. In vitro, KLF5 mediates the transforming activity of oncogenic H-Ras and negatively regulates Klf4 (GKLF). We have previously investigated the role of Klf4 in vivo through gene targeting experiments and demonstrated a vital role for Klf4 as a negative regulator of cell proliferation and promoter of normal differentiation in several gastrointestinal epithelia. Nonetheless, Klf5 has also been suggested to be a possible tumor suppressor gene in human breast, prostate, and intestine, leading to conflicting hypotheses of the role of K/f5 in normal epithelial homeostasis and tumorigenesis. Thus, we will investigate the role of Klf5 in gastrointestinal proliferation and differentiation by testing the following hypotheses: (1) increased expression of Klf5 in gastrointestinal epithelia leads to epithelial hyperproliferation and altered differentiation; (2) loss of Klf5 expression in gastrointestinal epithelia results in decreased epithelial proliferation. The following Specific Aims will be pursued: (1) to analyze the function of Klf5 in gastrointestinal proliferation and differentiation in vivo by direct overexpression of Klf5 in murine esophageal and intestinal epithelia using the upstream regulatory elements of ED-L2 and villin respectively; (2) to examine the effects of increased Klf5 expression in gastrointestinal epithelia by overexpressing Klf5 in primary esophageal epithelial cells; (3) to investigate the role of Klf5 in gastrointestinal epithelial homeostasis through loss-of-function studies in primary esophageal epithelial cells. This work will provide important new insights into the regulation of gastrointestinal epithelial proliferation and differentiation and provide a framework to understand the molecular events underlying mucosal injury and malignant transformation.