Transcriptional Repression of MMP7 by FXR in Intestinal Epithelial Cells

 描述(由申请人提供)： 结肠癌仍然是退伍军人发病率和死亡率的主要原因，因为转移性疾病的治疗效果有限。我们的长期目标是通过靶向导致结肠癌进展的关键信号转导分子来开发创新、有效和安全的治疗方法。法尼斯类X受体(FXR)是胆汁酸激活的转录因子核受体超家族成员之一，似乎就是这样一个关键分子。FXR是一种肿瘤抑制因子，其在结肠癌中的表达显著降低；在肠道肿瘤的啮齿动物模型中，FXR缺乏会增加腺瘤的大小和数量。FXR调节细胞增殖、凋亡和Wnt信号，但其肿瘤抑制作用的分子机制尚不完全清楚。我们的短期目标是填补这一知识空白。最近，我们对基质金属蛋白酶7(MMP7)是FXR靶基因进行了初步研究。MMP7是一种胶原酶，可降解细胞外基质，在大多数结肠癌中过度表达，促进细胞增殖、肿瘤侵袭和转移。我们的初步数据显示，FXR是MMP7的转录抑制因子；在正常的肠癌和结肠癌中，FXR水平的降低与MMP7表达的增加相关。此外，我们还发现，激活人结肠癌细胞中的FXR可以减少MMP7的表达，以及抑制异种移植瘤的生长和侵袭。基于这些新的发现，我们提出了范式转换的中心假设，即FXR的激活通过抑制MMP7基因的转录来抑制结肠癌的进展。为了验证这一假设，我们提出了三个具体的目标：目的1.验证FXR是MMP7的直接转录抑制因子的假设，并鉴定MMP7 FXR反应元件。目的2.验证激活肠道FXR选择性下调MMP7表达，从而抑制体内肿瘤生长的假说。目的3.在体内验证中和抗MMP7抗体延缓结肠癌进展的假说。总体影响：我们将揭示FXR作为MMP7转录抑制因子的新作用，并确定FXR抑制结肠癌细胞增殖和疾病进展的新机制。此外，我们将展示使用肠道选择性FXR激动剂非那拉明的临床潜力，用于化疗预防和晚期疾病的抗MMP7抗体。

 DESCRIPTION (provided by applicant): Colon cancer remains a leading cause of morbidity and mortality in Veterans because therapy for metastatic disease has limited efficacy. Our long-term goal is to develop innovative, effective, and safe therapies by targeting pivotal signal transduction molecules underlying colon cancer progression. The Farnesoid X Receptor (FXR), a member of the nuclear receptor superfamily of bile acid-activated transcription factors, appears to be such a pivotal molecule. FXR is a tumor suppressor whose expression is strikingly reduced in colon cancer; in rodent models of intestinal neoplasia FXR deficiency increases adenoma size and number. FXR regulates cell proliferation, apoptosis, and Wnt signaling but the molecular mechanisms underlying its tumor-suppressive actions are incompletely understood. Our short-term goal is to fill this gap in knowledge. Recently, we made the seminal observation that matrix metalloproteinase 7 (MMP7) is an FXR target gene. MMP7, a collagenase that degrades extracellular matrix, is over-expressed in most colon tumors and enhances cell proliferation, tumor invasion, and metastasis. Our preliminary data show that FXR is a transcriptional repressor for MMP7; decreased FXR levels correlate with increased MMP7 expression in normal intestine and colon cancer. Also, we found that activating FXR in human colon cancer cells attenuates MMP7 expression, as well as xenograft growth and invasion. Based on these novel findings we propose the paradigm-shifting central hypothesis that FXR activation inhibits colon cancer progression by repressing MMP7 gene transcription. To test this hypothesis we propose three Specific Aims: Aim 1. Test the hypothesis that FXR is a direct transcriptional repressor of MMP7 and identify the MMP7 FXR responsive element. Aim 2. Test the hypothesis that activating intestinal FXR selectively down-regulates MMP7 expression, thereby inhibiting tumor growth in vivo. Aim 3. Test the hypothesis that neutralizing anti-MMP7 antibody attenuates colon cancer progression in vivo. Overall impact: We will reveal a novel role for FXR as a transcriptional repressor of MMP7 and identify a new mechanism whereby FXR suppresses colon cancer cell proliferation and disease progression. Moreover, we will demonstrate the clinical potential of using fexaramine, an intestine-selective FXR agonist, for chemo- prevention and anti-MMP7 antibody for advanced disease.