Laboratory of Metabolism, Center for Cancer Research, National Cancer Institute, National Institutes of Health, Bethesda, Maryland.
Department of Pathology, Huashan Hospital, Fudan University, Shanghai, China.
Gastroenterology. 2019 Sep;157(3):744-759.e4. doi: 10.1053/j.gastro.2019.05.057. Epub 2019 May 30.
BACKGROUND & AIMS: Many genetic and environmental factors, including family history, dietary fat, and inflammation, increase risk for colon cancer development. Peroxisome proliferator-activated receptor alpha (PPARα) is a nuclear receptor that regulates systemic lipid homeostasis. We explored the role of intestinal PPARα in colon carcinogenesis.
Colon cancer was induced in mice with intestine-specific disruption of Ppara (Ppara), Ppara (control), and mice with disruption of Ppara that express human PPARA (human PPARA transgenic mice), by administration of azoxymethane with or without dextran sulfate sodium (DSS). Colons were collected from mice and analyzed by immunoblots, quantitative polymerase chain reaction, and histopathology. Liquid chromatography coupled with mass spectrometry-based metabolomic analyses were performed on urine and colons. We used molecular biology and biochemical approaches to study mechanisms in mouse colons, primary intestinal epithelial cells, and colon cancer cell lines. Gene expression data and clinical features of patients with colorectal tumors were obtained from Oncomine, and human colorectal-tumor specimens and adjacent normal tissues were collected and analyzed by immunohistochemistry.
Levels of Ppara messenger RNA were reduced in colon tumors from mice. Ppara mice developed more and larger colon tumors than control mice following administration of azoxymethane, with or without DSS. Metabolomic analyses revealed increases in methylation-related metabolites in urine and colons from Ppara mice, compared with control mice, following administration of azoxymethane, with or without DSS. Levels of DNA methyltransferase 1 (DNMT1) and protein arginine methyltransferase 6 (PRMT6) were increased in colon tumors from Ppara mice, compared with colon tumors from control mice. Depletion of PPARα reduced the expression of retinoblastoma protein, resulting in increased expression of DNMT1 and PRMT6. DNMT1 and PRMT6 decreased expression of the tumor suppressor genes Cdkn1a (P21) and Cdkn1b (p27) via DNA methylation and histone H3R2 dimethylation-mediated repression of transcription, respectively. Fenofibrate protected human PPARA transgenic mice from azoxymethane and DSS-induced colon cancer. Human colon adenocarcinoma specimens had lower levels of PPARA and retinoblastoma protein and higher levels of DNMT1 and PRMT6 than normal colon tissues.
Loss of PPARα from the intestine promotes colon carcinogenesis by increasing DNMT1-mediated methylation of P21 and PRMT6-mediated methylation of p27 in mice. Human colorectal tumors have lower levels of PPARA messenger RNA and protein than nontumor tissues. Agents that activate PPARα might be developed for chemoprevention or treatment of colon cancer.
许多遗传和环境因素，包括家族史、饮食中的脂肪和炎症，都会增加结肠癌发展的风险。过氧化物酶体增殖物激活受体α（PPARα）是一种核受体，可调节全身脂质稳态。我们探讨了肠道 PPARα 在结肠癌发生中的作用。
通过给予氧化偶氮甲烷加或不加葡聚糖硫酸钠（DSS），在肠道特异性敲除 Ppara（Ppara）、Ppara（对照）和表达人 PPARA 的 Ppara 敲除（人 PPARA 转基因小鼠）的小鼠中诱导结肠癌。收集小鼠的结肠进行免疫印迹、定量聚合酶链反应和组织病理学分析。采用基于液相色谱与质谱联用的代谢组学方法分析尿液和结肠中的代谢物。我们使用分子生物学和生化方法研究了小鼠结肠、原代肠上皮细胞和结肠癌细胞系中的机制。从 Oncomine 获得结直肠肿瘤患者的基因表达数据和临床特征，收集和分析人结直肠肿瘤标本和相邻正常组织的免疫组织化学。
小鼠结肠癌组织中 Ppara 信使 RNA 水平降低。与对照组小鼠相比，给予氧化偶氮甲烷后，Ppara 小鼠形成了更多和更大的结肠肿瘤，无论是否给予 DSS。代谢组学分析显示，与对照组小鼠相比，给予氧化偶氮甲烷后，Ppara 小鼠的尿液和结肠中的甲基化相关代谢物增加。与对照组相比，Ppara 小鼠的结肠肿瘤中 DNA 甲基转移酶 1（DNMT1）和蛋白精氨酸甲基转移酶 6（PRMT6）的水平升高。PPARα 耗竭降低了视网膜母细胞瘤蛋白的表达，导致 DNMT1 和 PRMT6 的表达增加。DNMT1 和 PRMT6 通过 DNA 甲基化和组蛋白 H3R2 二甲基化介导的转录抑制分别降低肿瘤抑制基因 Cdkn1a（P21）和 Cdkn1b（p27）的表达。非诺贝特可保护人 PPARA 转基因小鼠免受氧化偶氮甲烷和 DSS 诱导的结肠癌。人结肠腺癌标本中 PPARA 和视网膜母细胞瘤蛋白的水平低于正常结肠组织，而 DNMT1 和 PRMT6 的水平高于正常结肠组织。
肠道中 PPARα 的缺失通过增加小鼠中 DNMT1 介导的 P21 甲基化和 PRMT6 介导的 p27 甲基化促进结肠癌的发生。人结直肠肿瘤中的 PPARA 信使 RNA 和蛋白水平低于非肿瘤组织。激活 PPARα 的药物可能被开发用于结肠癌的化学预防或治疗。
