Post-Transcriptional Regulation in Colorectal Cancer

描述(申请人提供)：结直肠癌是成人癌症死亡的主要原因。在结肠癌细胞和肿瘤中常见的是许多与生长和炎症相关的即刻早期反应基因的过度表达。控制这些因子在正常肠上皮中的表达的一个临界点是通过转录后机制来调节mRNA的衰退。与转录后调控相关的两个主要的RNA结合蛋白是mRNA稳定因子Hu抗原R(Hur)和mRNA衰退因子Tristetraprolin(TTP)。这两个因子都结合了大多数癌症相关的即刻-早期反应基因转录本中存在的富含AU的信使核糖核酸元件(Are)，并针对稳定或快速衰退的信使核糖核酸。然而，在结肠癌细胞和肿瘤中观察到的一个特征是稳定因子HUR的过度表达和衰退因子TTP的缺失。这些组合缺陷允许癌症相关生长因子的稳定和过度表达。基于这些观察，我们假设转录后调控的丧失通过选择性地稳定富含AU元素的转录本来促进肠上皮细胞肿瘤的发生。为了检验这一假设，我们提出了以下具体目标。特异性目的1：确定mRNA稳定因子HUR和mRNA衰变因子TTP的表达改变是否能促进肠道细胞转化和肿瘤发生。在目标1中，我们将确定Hur过表达和TTP缺失是否通过有缺陷的快速mRNA衰退和癌症相关基因过度表达的机制在促进上皮细胞转化和肿瘤发生中起因果作用。具体目的2：确定HUR的低分子抑制剂和病毒介导的TTP对结肠癌细胞生长和基因表达的影响。这一目的的重点是研究靶向Hur介导的mRNA稳定的治疗潜力。具体目标3：确定Hur在小鼠胃肠道中的过度表达和TTP缺失是否促进了体内癌症相关基因的表达和肿瘤的发生。在这个特定的目标中，我们将确定Hur过表达和TTP缺失在促进肠道肿瘤发生中的体内意义。具体目标4：确定在结肠癌细胞和肿瘤中促进HUR过表达和TTP表达沉默的分子事件。在这一目标下，我们将确定在结肠癌中促进Hur表达和TTP基因沉默的机制。这项研究将增进我们对结直肠癌生物学的理解，并导致新的分子靶点的确定，这将改善目前的治疗和预防策略。

DESCRIPTION (provided by applicant): Colorectal cancer is a leading cause of cancer mortality among adults. Commonly observed in colon cancer cells and tumors is overexpression of many growth- and inflammation-associated immediate-early response genes. A critical point in controlling the expression of these factors in normal intestinal epithelium occurs through post-transcriptional mechanisms that regulate mRNA decay. The two primary RNA-binding proteins associated with post-transcriptional regulation are the mRNA stability factor Hu antigen R (HuR) and the mRNA decay factor tristetraprolin (TTP). Both of these factors bind AU-rich mRNA elements (ARE) present in a majority of cancer-associated immediate-early response gene transcripts and target the mRNA for stabilization or rapid decay. However, a characteristic feature observed in colon cancer cells and tumors is overexpression of the stability factor HuR and loss of expression of the decay factor TTP. These combined defects allow for stabilization and overexpression of cancer-associated growth factors. Based on these observations we hypothesize that loss of post-transcriptional regulation promotes intestinal epithelial cell tumorigenesis by selectively stabilizing AU-rich element containing-mRNA transcripts. The following specific aims are proposed to test this hypothesis. Specific Aim 1: Determine whether altered expression of the mRNA stability factor HuR and the mRNA decay factor TTP can promote intestinal cell transformation and tumorigenesis. Under Aim 1 we will determine whether HuR overexpression and TTP loss play a causal role in promoting epithelial cell transformation and tumorigenesis through a mechanism of defective rapid mRNA decay and cancer-associated gene overexpression. Specific Aim 2: Determine the ability of low-molecular- weight inhibitors of HuR and viral-mediated delivery of TTP to impact colon cancer cell growth and gene expression. The emphasis of this aim is to investigate the therapeutic potential of targeting HuR-mediated mRNA stabilization. Specific Aim 3: Determine if HuR overexpression and TTP loss in the murine gastrointestinal tract promotes cancer-associated gene expression and tumorigenesis in vivo. In this Specific Aim we will determine the in vivo significance of HuR overexpression and TTP loss in promoting intestinal tumorigenesis. Specific Aim 4: Determine the molecular events in colon cancer cells and tumors that promote HuR overexpression and silencing of TTP expression. Under this aim, we will determine the mechanisms promoting HuR expression and TTP gene silencing in colon cancer. This study will enhance our understanding of colorectal cancer biology and lead to the identification of novel molecular targets, which will improve current treatment and prevention strategies.