Colonic Cytokinetics and Cell Signaling: Dietary Effects

描述(申请人提供)：在饮食因素中，有令人信服的数据表明n-3多不饱和脂肪酸(PUFA)对结肠癌具有保护作用，例如二十碳五烯酸(EPA；20：5N-3)和二十二碳六烯酸(DHA，22：6N-3)。相反，富含n-6多不饱和脂肪酸的膳食脂肪，如亚油酸(18：2n-6)和花生四烯酸(20：4n-6)，促进了结肠癌的发展。这一点很重要，因为典型的西式饮食含有的n-6多出n-3多不饱和脂肪酸10到20倍。不幸的是，到目前为止，缺乏一个统一的机制假说来解释为什么n-3多不饱和脂肪酸比n-6多不饱和脂肪酸(美国饮食中多不饱和脂肪酸的主要饮食形式)选择性地抑制结肠癌。我们最近发现：(I)n-3PUFA的抗肿瘤作用部分是由于在肿瘤形成的起始阶段靶向凋亡的协同上调和肿瘤促进过程中的自发凋亡；(Ii)丁酸盐增强了这种作用；(Iii)EPA和DHA诱导线粒体膜磷脂的组成变化，从而促进细胞凋亡；以及(Iv)n-3PUFA抑制致癌的RAS激活，这是结肠中一种强大的抗凋亡信号。由于细胞凋亡的抑制现在被认为是结直肠肿瘤发生过程中不可或缺的组成部分，本研究的总体目标是了解n-3多不饱和脂肪酸如何促进结肠癌细胞的凋亡。由于n-3PUFA由于双键的数目和位置而独一无二地能够改变细胞膜的性质，我们假设n-3PUFA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允许的环境。我们建议利用一组实验模型(偶氮甲烷注射大鼠、氧化应激SOD2+/-小鼠；正常和恶性转化的小鼠和人结肠细胞系)来阐明n-3PUFA在结肠中的促凋亡信号。为了验证我们的假设，我们提出了以下具体目标：目标1将阐明n-3多不饱和脂肪酸调节内在(线粒体介导)细胞死亡信号的机制；目标2将确定n-3多不饱和脂肪酸调节外源性(非线粒体)细胞死亡信号的机制。目前，n-3多不饱和脂肪酸影响结肠癌细胞凋亡的分子基础是一个完整的黑匣子。拟议的实验是第一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.