Bacteria-derived xenobiotics in colon cancer prevention: Link to GPR109A and colonic ketogenesis

项目概述：饮食中的化学致癌物和外源性物质在结肠癌（CC）中起着重要作用 阵包括结肠在内的肠道通常是暴露于这些致癌物质的第一个部位， 异生物质CC是男性和女性中常见的恶性肿瘤，并且p53突变（p53 D）或失活是 在约60%的CC和约90%的所有人类癌症中观察到。因此，治疗策略的发展 这将使野生型（WT）p53功能或靶向p53 D恢复活力，这将对人类的免疫系统产生深远的影响。 CC的预防和治疗。类似地，观察到高频率（40-60%）的KRAS突变（KRASD 在暴露于环境化学污染物的生物体中，约40-45%的CC与KRASD有关。 我们发现GPR 109 A表达与KRASD CC之间存在相互关联。GPR 109 A是Gai耦合的 细菌发酵产物丁酸盐（BTR）的受体，酮体b-羟基丁酸盐（bHB），和 维生素烟酸（NA）。约85%的CC显示GPR 109 A的表达降低。GPR 109 A激动剂NA是 NAD+和p53的前体是NAD+依赖性分子，NA缺乏损害p53功能。 因此，GPR 109 A可能是KRAsD的分子靶点，在KRAsD介导的细胞凋亡中起重要作用。 p53信号的调节。NA的药理剂量，一种维生素，也是FDA批准的药物， 血脂异常，被数百万美国人服用。虽然NA在降低LDL和升高HDL中的作用是 众所周知，对其抗肿瘤潜力知之甚少。同样，肠道细菌和 CC预防是众所周知的，但这种联系的机制还没有很好地理解。BTR， 结肠中主要的细菌代谢物，是结肠上皮中GPR 109 A的内源性激动剂。BHB 是固有层中存在的免疫细胞中GPR 109 A的天然激动剂， 在结肠上皮中使用细菌代谢物BTR通过生酮作用。这突出了生物学意义 结肠作为生酮器官。此外，肠道细菌控制GPR 109 A的表达和酮生成。 在结肠中通过它们的异生代谢物（丁酸盐、吲哚衍生物、1，3-二氨基丙烷和罗伊素）。 这为肠道细菌和CC预防之间提供了一种新的分子联系。我们的核心假设是 在结肠上皮和免疫细胞中GPR 109 A的激活导致p53和抗- 肿瘤免疫我们将用三个具体目标来检验这一假设：（目标1）确定GPR 109 A的作用， p53轴在KRASD、化学品和饮食致癌物诱导的CC中的作用;（目的2）阐明KRASD、化学品和饮食致癌物诱导的CC的分子机制。 GPR 109 A激动剂诱导的p53活化的机制，并测试GPR 109 A激动剂是否可用作新的 靶向p53 D CC的治疗药物;和（目的3）证明肠道细菌代谢物维持 WTP 53通过GPR 109 A发挥功能并防止免疫系统在结肠中过度激活， 参与结肠生酮。这些研究将涉及使用转基因小鼠品系， 不仅Gpr 109 a和p53的结肠特异性缺失，而且生酮中的限速酶Hmgcs 2也是结肠特异性缺失。

Project Summary: Chemical carcinogens and xenobiotics in the diet play a significant role in colon cancer (CC) formation. The intestinal tract, including the colon, is often the first site that is exposed to these carcinogens and xenobiotics. CC is a common malignancy in men and women, and p53 mutation (p53D) or inactivation is observed in ~60% of CC and ~90% of all human cancers. As such, the development of therapeutic strategies that will rejuvenate wild-type (WT) p53 function or target p53D should have profound implications in the prevention and treatment of CC. Similarly, a high frequency (40-60%) of KRAS mutation (KRASD) is observed in organisms exposed to environmental chemical contaminants, and ~40-45% of CC is associated with KRASD. We found a reciprocal association between GPR109A expression and KRASD CC. GPR109A is a Gai-coupled receptor for the bacterial fermentation product butyrate (BTR), the ketone body b-hydroxybutyrate (bHB), and the vitamin Niacin (NA). About 85% of CC shows a reduced expression of GPR109A. GPR109A agonists NA is the precursor of NAD+ and p53 is an NAD+-dependent molecule and NA deficiency impairs p53 function. Therefore, GPR109A could be the molecular target of KRAsD and it plays an important role in the regulation of p53 signaling. Pharmacologic doses of NA, a vitamin and also an FDA-approved drug for dyslipidemia, is taken by millions of Americans. Though the role of NA in decreasing LDL and increasing HDL is well recognized, little is known about its anti-tumor potential. Similarly, the link between commensal bacteria and CC prevention is known for a long time, but the mechanisms underlying this link are not well understood. BTR, the prominent bacterial metabolite in the colon, is the endogenous agonist for GPR109A in colonic epithelia. bHB is the natural agonist for GPR109A in immune cells present in the lamina propria and this agonist is synthesized in colonic epithelia using the bacterial metabolite BTR via ketogenesis. This highlights the biological significance of the colon as a ketogenic organ. In addition, commensal bacteria control GPR109A expression and ketogenesis in the colon via their xenobiotic metabolites (butyrate, indole derivatives, 1,3-diaminopropane, and reuterin). This offers a novel molecular link between commensal bacteria and CC prevention. Our central hypothesis is that activation of GPR109A in colonic epithelia and immune cells lead to sustained activation of p53 and anti- tumor immunity. We will test this hypothesis with three specific aims: (Aim 1) Determine the role of the GPR109A- p53 axis in KRASD, chemical, and dietary carcinogen-induced CC; (Aim 2) Elucidate the molecular mechanism(s) of GPR109A agonists-induced p53 activation and test if GPR109A agonists can be used as novel therapeutic drugs to target p53D CC; and (Aim 3) Demonstrate that commensal bacterial metabolites maintain WTp53 function and prevent the immune system from undue activation in colon via GPR109A with an obligatory involvement of colonic ketogenesis. These studies will involve the use of genetically modified mouse lines with colon-specific deletion of not only Gpr109a and p53, but also the rate-limiting enzyme in ketogenesis, Hmgcs2.