Nuclear Hormone Receptors in Intestinal Biology

描述(申请人提供)：结肠癌和直肠癌是美国癌症相关死亡的第二大原因，因此是一个主要的公共卫生问题。这种疾病的发生是由于失去了控制从未分化的干细胞向成熟的结肠上皮细胞过渡的正常调控途径。核激素受体(NHR)超家族转录因子是包括细胞分化在内的许多生物学途径的重要调节因子。过氧化物酶体增殖物激活受体(PPAR)是NHR的一个家族，由脂肪酸和某些脂肪酸代谢物激活，在代谢动态平衡中发挥重要作用。例如，PPAR亚型是脂肪细胞分化的中央调节因子，该受体的合成激动剂增强胰岛素敏感性，并被广泛用于II型糖尿病的治疗。我们和其他人发现PPAR在有丝分裂后分化的结肠上皮细胞中强烈表达，并证明在广泛的结直肠癌细胞系中PPAR的激活导致与细胞周期01期延迟相关的生长抑制。该受体的激活还导致肠上皮细胞分化的几个标志物增加。与PPAR在结肠中的抗肿瘤、促进分化作用一致，在大肠肿瘤和细胞系的一部分中发现了该受体功能突变的缺失。总之，这些发现提高了PPAR激动剂作为结直肠癌分化治疗的一种形式的临床价值的可能性。然而，尽管有这些进展，我们对结肠中PPAR信号的理解仍然很肤浅。这一建议的主要焦点是确定PPAR激活在结直肠癌细胞中诱导生物学表型的机制基础。具体地说，我们假设配体与apo-PPAR的结合会导致受体的构象变化，导致一组特定的协同调节分子的招募，然后导致对靶基因的调节，这些靶基因是结肠上皮细胞生长和分化的重要修饰物。我们的实验方法将集中在1)确定PPAR亚型特有的结构域，使配体结合的受体能够诱导结直肠癌细胞分化；2)确定对PPAR介导的分化至关重要的协同调节因子，特别是在结肠；以及3)确定PPAR靶基因转化生长因子刺激的克隆-22(TSC-22)在肠上皮细胞功能中的作用。这些实验的结果不仅有可能导致设计出具有增强抗肿瘤效果的PPAR激活剂，而且还有助于阐明肠上皮细胞分化的分子基础。

DESCRIPTION (provided by applicant): Carcinoma of the colon and rectum is the second-leading cause of cancer related deaths in the United States and thus represents a major public health concern. The disease develops due to a loss of the normal regulatory pathways that govern the transition from undifferentiated stem cell to mature colon epithelial cell. The nuclear hormone receptor (NHR) super family of transcription factors are important regulators of many biological pathways including cellular differentiation. One family of NHRs, the peroxisome proliferator-activated receptors (PPARs), is activated by fatty acids and certain fatty acid metabolites and plays important role in metabolic homeostasis. For example, the PPAR subtype is a central regulator of adipocyte differentiation and synthetic agonists of the receptor enhance insulin sensitivity and are being widely used in the treatment of type ll diabetes mellitus. We and others have found PPAR to be strongly expressed in post-mitotic, differentiated colon epithelial cells and have demonstrated that activation of PPAR in a broad spectrum of colorectal cancer cell lines induces growth inhibition associated with a delay in the 01 phase of the cell cycle. Activation of the receptor also leads to an increase in several markers of intestinal epithelial cell differentiation. Consistent with an anti-oncogenic, pro-differentiation role for PPAR in the colon, loss of function mutations in the receptor have been identified in a subset of colorectal tumors and cell lines. Collectively, these findings raise the possibility that PPAR agonists may have clinical value as a form of differentiation therapy for colorectal cancer. However, despite these advances our understanding of PPAR signaling in the colon remains superficial. The major focus of this proposal is to define the mechanistic basis for the biological phenotype induced by PPAR activation in colorectal cancer cells. Specifically, we hypothesize that binding of ligand to apo-PPAR causes conformational changes in the receptor leading to the recruitment of a specific set of co-regulatory molecules that then leads to the regulation of target genes that are important modifiers of colon epithelial cell growth and differentiation. Our experimental approach will focus on 1) identifying the structural domains unique to the PPAR subtype that allows the ligand-bound receptor to induce colorectal cancer cell differentiation; 2) identify the co-regulators critical for PPAR-mediated differentiation specifically in the colon; and 3) define the role of the PPAR target gene transforming growth factor-stimulated clone-22 (TSC-22) in intestinal epithelial cell function. Results from these experiments have the potential not only to lead to the design of PPAR activators with enhanced anti-tumor efficacy, but also help clarify the molecular basis of intestinal epithelial cell differentiation.