IGF Signalling, Apoptosis and Adenoma Risk

描述（由申请人提供）：确定有利于结肠癌早期阶段（如腺瘤的形成）的介质和机制，是改善结肠癌监测和预防的组成部分。我们最近的研究表明，正常肠黏膜细胞凋亡的减少与人类癌前腺瘤病变的风险之间存在很强的相关性。初步和已发表的证据表明，血浆胰岛素升高、循环或局部表达的胰岛素样生长因子（IGF-I或IGF-II）水平或生物利用度升高是减少结肠细胞凋亡和腺瘤的重要危险因素。胰岛素和IGF作用于细胞凋亡或腺瘤生长的常见介质可能是腺瘤风险的特别强大的生物标志物。胰岛素受体底物1 （IRS-I）是IGF-I、IGF-II和胰岛素抗凋亡作用的常见介质。小鼠模型的初步数据表明，体内正常肠道中IGF-I的抗凋亡作用需要IRS-1，在肠息肉病APC/Min-+模型中，IRS-1基因拷贝的丢失会增加细胞凋亡并减少腺瘤的形成。最近的研究将人类IRS-1基因的多态性与结肠癌风险联系起来。总之，这些数据支持了我们的中心假设，即正常人结肠粘膜中IRS-1的表达水平通过介导胰岛素和IGFs的抗凋亡作用来预测细胞凋亡水平和腺瘤风险。我们的研究将使用来自结直肠腺瘤的大型病例对照研究的现有样本来验证我们的假设。在同一研究人群中已经收集了关于细胞凋亡、血浆胰岛素、IGFs和血浆或结肠胰岛素样生长因子结合蛋白（igfbp）水平的数据。目的1：将验证正常结肠黏膜中IRS-1基因Gly972Arg多态性和/或IRS-1 mRNA表达水平预测腺瘤风险和细胞凋亡水平的假设。基因分型将通过基于等位基因辨别的PCR进行，IRS-1 mRNA将通过实时PCR进行检测。初步分析将测试IRS-1基因型或表达水平与腺瘤或细胞凋亡之间的关系。二级分析，我们将测试IRS-1基因型或IRS-1表达与胰岛素/IGFs或igfbp在预测细胞凋亡和腺瘤风险方面是否存在相互作用。目的2将验证IGF-II基因印迹缺失（LOI）增加结肠局部IGF-II表达并增加腺瘤或低凋亡风险的假设。将鉴定IGF-II基因820G/A和266C/T多态性杂合的受试者。IGF-II的等位基因和总表达水平将通过实时PCR评估。将测试IGF-II和IGF-II表达的LOI与腺瘤或细胞凋亡的关系，以及与IRS-1基因型或表达水平的相互作用，以预测腺瘤风险或细胞凋亡。

DESCRIPTION (provided by applicant): Defining mediators and mechanisms which favor the early stages of the colon cancer such as formation of adenoma, is integral to improved surveillance and prevention of colon cancer. Our recent studies demonstrate strong correlations between reduced apoptosis in the normal intestinal mucosa and risk of precancerous adenomatous lesions in humans. Preliminary and published evidence indicates elevated plasma insulin and increased levels or bioavailability of circulating or locally expressed insulin-like growth factors (IGF-I or IGF-II) as significant risk factors for reduced apoptosis and adenoma in the colon. Common mediators of insulin and IGF action on apoptosis or adenoma growth may represent particularly powerful biomarkers of adenoma risk. Insulin receptor substrate 1 (IRS-I) is a common mediator of the anti-apoptotic actions of IGF-I, IGF-II and insulin. Preliminary data in mouse models demonstrate that IRS-1 is required for anti-apoptotic actions of IGF-I in the normal intestine in vivo and that loss of just 1 copy of the IRS-1 gene increases apoptosis and reduces adenoma formation in the APC/Min-+model of intestinal polyposis. Recent studies link polymorphisms in the human IRS-1 gene to colon cancer risk. Together, this data supports our central hypothesis that levels of expressed IRS-1 in normal human colonic mucosa predict the levels of apoptosis and adenoma risk by mediating the anti-apoptotic actions of insulin and the IGFs. Our studies will use existing samples from a large case-control study of colorectal adenomas to test our hypothesis. Data on apoptosis, plasma insulin, IGFs and plasma or colonic levels of insulin-like growth factor binding proteins (IGFBPs) have already been collected in this same study population. Aim 1: will test the hypothesis that a Gly972Arg polymorphisms in the IRS-I gene, and/or levels of expressed IRS-1 mRNA in the normal colonic mucosa predict adenoma risk and levels of apoptosis. Genotyping will be performed by PCR based allelic discrimination and IRS-1 mRNA will be measured by real time PCR. Primary analyses will test for associations between IRS-1 genotype or expression levels and adenoma or apoptosis. Secondary analysis, we will test if there are interactions between IRS-1 genotype or IRS-1 expression with insulin/IGFs or IGFBPs in predicting apoptosis and adenoma risk. Aim 2 will test the hypothesis that loss of imprinting (LOI) for the IGF-II gene increases local IGF-II expression in colon and increases risk of adenoma or low apoptosis. Subjects heterozygous for 820G/A and 266C/T polymorphisms in the IGF-II gene will be identified. Allelic and total expression levels for IGF-II will be assessed by real time PCR. LOI for IGF-II and IGF-II expression will be tested for associations with adenoma or apoptosis and for interactions with IRS-1 genotype or expression levels in predicting adenoma risk or apoptosis.