Colonic Cytokinetics and Cell Signaling: Dietary Effects

描述（由申请人提供）：在膳食因素中，有令人信服的数据表明n-3多不饱和脂肪酸（PUFA），如二十碳五烯酸（EPA; 20:5n-3）和二十二碳六烯酸（DHA, 22:6n-3）对结肠癌有保护作用。相反，富含n-6 PUFA的膳食脂质，如亚油酸（18:2n-6）和花生四烯酸（20:4n-6），促进结肠肿瘤的发展。这一点很重要，因为典型的西方饮食中n-6 PUFA的含量是n-3 PUFA的10到20倍。不幸的是，迄今为止，还没有一个统一的机制假设来解释为什么n-3 PUFA比n-6 PUFA（美国饮食中主要的PUFA形式）有选择性地抑制结肠癌。我们最近表明(i) n-3 PUFA的抗肿瘤作用部分是由于肿瘤发生起始阶段靶向细胞凋亡和肿瘤促进过程中自发细胞凋亡的协调上调；（ii）丁酸盐增强了效果；（iii） EPA和DHA诱导线粒体膜磷脂组成改变，促进细胞凋亡；（iv） n-3 PUFA抑制致癌Ras激活，这是结肠中一个强大的抗凋亡信号。由于细胞凋亡的抑制现在被认为是结直肠肿瘤发生的一个组成部分，本提案的总体目标是了解n-3 PUFA如何促进结肠细胞凋亡。由于n-3 PUFA由于双键的数量和位置而具有改变细胞膜性质的独特能力，我们假设n-3 PUFA改变了结肠细胞线粒体和质膜的组成和功能，从而为细胞凋亡创造了一个有利的环境。为了阐明n-3 PUFA在结肠中的凋亡信号通路，我们拟采用多种实验模型（注射偶氮氧甲烷大鼠、氧化应激SOD2+/-小鼠、正常和恶性转化小鼠和人类结肠细胞系）。为了验证我们的假设，提出了以下具体目标：目标1将阐明n-3 PUFA调节内在（线粒体介导的）细胞死亡信号的机制；Aim #2将确定n-3 PUFA调节外源性（非线粒体）细胞死亡信号的机制。目前，n-3 PUFA对结肠细胞凋亡作用的分子基础完全是一个黑匣子。提出的实验是首次尝试在分子水平上解释EPA和DHA的作用。

DESCRIPTION (provided by applicant): Among dietary factors, there are cogent data indicating a protective effect of n-3 polyunsaturated fatty acids (PUFA) e.g., eicosapentaenoic acid (EPA; 20:5n-3) and docosahexaenoic acid (DHA, 22:6n-3), on colon cancer. In contrast, dietary lipids rich in n-6 PUFA, e.g., linoleic acid (18:2n-6) and arachidonic acid (20:4n-6), enhance the development of colon tumors. This is significant because the typical Western diet contains 10 to 20 times more n-6 than n-3 PUFA. Unfortunately, to date, a unifying mechanistic hypothesis addressing why n-3 PUFA selectively suppress colon cancer compared to n-6 PUFA (the major dietary form of PUFA in the U.S. diet) is lacking. We have recently shown that (i) the antitumorigenic effects of n-3 PUFA are in part the result of the coordinated upregulation of targeted apoptosis dudng the initiation phase of tumorigenesis and spontaneous apoptosis during tumor promotion; (ii) the effect is enhanced by butyrate; (iii) EPA and DHA induce compositional changes in mitochonddal membrane phospholipids which facilitate apoptosis; and (iv) n-3 PUFA suppress oncogenic Ras activation, a powerful antiapoptotic signal in the colon. Since the inhibition of apoptosis is now thought to be an integral component in the genesis of colorectal tumors, the overall goal of this proposal is to understand how n-3 PUFA promote apoptosis in colonocytes. Since n-3 PUFA are uniquely capable of altering cell membrane properties due to both the number and position of double bonds, we have hypothesized that n-3 PUFA alter colonocyte mitochondrial and plasma membrane composition and function, thereby creating a permissive environment for apoptosis. We propose to utilize a combination of experimental models (azoxymethane-injected rat, oxidatively stressed SOD2+/- mouse; normal and malignant transformed mouse and human colonocyte cell lines) in order to elucidate n-3 PUFA apoptogenic signaling in the colon. To test our hypothesis the following specific aims are proposed: Aim #1 will elucidate the mechanisms by which n-3 PUFA modulate intrinsic (mitochondria-mediated) cell death signaling; and Aim #2 will determine the mechanisms by which n-3 PUFA modulate extrinsic (non-mitochondrial) cell death signaling. At present, the molecular basis of the n-3 PUFA effects on colonocyte apoptosis is a complete black box. The proposed experiments represent the first attempt to provide an explanation of EPA and DHA action at the molecular level.