EGFR-VDR signals in diet-promoted inflammation and cancer

描述(申请人提供)：饮食被认为在散发性结肠癌的发展中起主要作用。实验性结肠癌的偶氮甲烷(AOM)模型模拟了人类结肠癌的许多特征，包括西式高脂肪饮食促进肿瘤的发生。炎症被认为是饮食促进的肿瘤形成的原因。我们最近发现，饮食脂肪诱导的肿瘤促进需要表皮生长因子受体(EGFR)信号，并涉及促炎环氧合酶-2(COX-2)的增加。相反，我们证明了补充维生素D类似物F6-D3可以抑制炎症和肿瘤的发生。维生素D的作用是由维生素D受体(VDR)介导的。我们发现VDR可以拮抗包括NFkB和b-catenin在内的关键炎症和致癌转录因子的信号。在最近的初步研究中，我们证明了在肿瘤发生中上调的EGFR信号抑制了VDR的表达。此外，VDR缺失的小鼠似乎更容易发生肿瘤。在目标1中，使用AOM模型，我们将描述饮食与EGFR信号和VDR下调之间的关系，并识别抑制饮食促进的炎症和肿瘤发生的VDR途径。我们将利用AOM处理的VDR野生型和VDR缺失突变小鼠来剖析VDR通路。我们将调整饮食脂肪，以评估饮食对炎症和肿瘤形成的影响。我们还将包括单独补充F6-D3或F6-D3加EGFR抑制剂吉非替尼的饮食，以剖析饮食促进的炎症和肿瘤发生中的VDR和EGFR信号。我们推测，膳食脂肪会增加EGFR信号，减少VDR的表达，而F6-D3会增加VDR水平，减少炎症和致癌信号，并抑制肿瘤的发生。在目标2中，我们将剖析结肠癌细胞和结肠成纤维细胞中下调VDR的EGFR通路，并揭示VDR对抗EGFR和促炎细胞因子信号的机制。Caco-2结肠癌细胞和结肠成纤维细胞表达功能性的EGFR和VDR。在初步研究中，EGF下调这些细胞中的VDR，而EGFR抑制或活性维生素D上调VDR。因此，这些转化的和未转化的结肠细胞中的EGFR激活在体外模拟了在体内结肠肿瘤发生中EGFR信号对VDR表达的影响。我们将揭示通过EGFR调节VDR下调的转录和转录后机制。可能的机制包括抑制启动子的激活，减少转录本或蛋白质的半衰期。我们还将使用可诱导的显性负性EGFR表达载体来控制EGFR，以及siRNA和cDNA策略来调节VDR的水平，我们还将剖析控制炎症和肿瘤发生的EGFR和VDR途径。使用特定途径的蛋白质组和基因组学方法，我们还将寻找在体外控制炎症的新的EGFR和VDR调节的细胞因子和生长因子信号，并在我们的体内模型中测试它们的相关性。这些研究将确定潜在的新靶点，以开发化学预防策略。 公共卫生相关性：结肠癌是美国癌症相关死亡的第三大原因。这些恶性肿瘤中有一半以上被认为是可以通过改变饮食来预防的。我们已经证明，西式高脂饮食促进肿瘤需要表皮生长因子受体(EGFR)信号来抑制抗炎维生素D信号。我们将发现EGFR和维生素D细胞通路相互作用，调节饮食炎症和结肠肿瘤风险。

DESCRIPTION (provided by applicant): Diet is believed to play a major role in the development of sporadic colon cancer. The azoxymethane (AOM) model of experimental colon cancer mimics many features of human colon cancer, including tumor promotion by Western style high fat diets. Inflammation is thought to contribute to diet-enhanced tumorigenesis. We recently showed that tumor promotion induced by dietary fat required epidermal growth factor receptor (EGFR) signals and involved increased pro-inflammatory cyclooxygenase-2 (Cox-2). In contrast, we demonstrated that dietary supplementation with a vitamin D analogue F6-D3 inhibited inflammation and tumorigenesis. Vitamin D effects are mediated by the vitamin D receptor (VDR). We showed that the VDR could antagonize signals from key inflammatory and oncogenic transcription factors, including NFkB and b-catenin. In recent preliminary studies, we demonstrated that EGFR signals, which are up-regulated in tumorigenesis, suppressed VDR expression. Furthermore, VDR null mice appear to be more susceptible to tumorigenesis. In Aim 1 using the AOM model we will characterize the relationships between diet and EGFR signals and VDR down- regulation and identify VDR pathways that inhibit diet-promoted inflammation and tumorigenesis. We will utilize AOM-treated VDR wild type and VDR null mutant mice to dissect VDR pathways. We will modulate dietary fat to assess the effects of diet on inflammation and tumorigenesis. We will also include a diet supplemented with F6-D3 alone, or F6-D3 plus EGFR inhibitor Gefitinib to dissect VDR and EGFR signals in diet-promoted inflammation and tumorigenesis. We postulate that dietary fat will increase EGFR signals and decrease VDR expression, whereas F6-D3 will increase VDR levels and reduce inflammatory and oncogenic signals and inhibit tumorigenesis. In Aim 2 we will dissect EGFR pathways in colon cancer cells and colonic fibroblasts that down-regulate VDR and uncover VDR mechanisms that oppose EGFR and pro- inflammatory cytokine signals. Caco-2 colon cancer cells and colonic fibroblasts express functional EGFR and VDR. In preliminary studies, EGF down-regulated the VDR in these cells, whereas EGFR inhibition or active vitamin D up-regulated VDR. Thus, EGFR activation in these transformed and non-transformed colonic cells mimics in vitro the effects of EGFR signals on VDR expression in colonic tumorigenesis in vivo. We will uncover the transcriptional and post-transcriptional mechanisms that mediate this VDR down-regulation by EGFR. Potential mechanisms include inhibited promoter activation, and reduced transcript or protein half-life. Using inducible dominant negative EGFR expressing transfectants to control EGFR, and siRNA and cDNA strategies to modulate VDR levels, we will also dissect EGFR and VDR pathways that control inflammation and oncogenesis. Using pathway-specific proteomic and genomic approaches, we will also search for new EGFR and VDR-regulated cytokine and growth factor signals that control inflammation in vitro and test their relevance in our in vivo models. These studies will identify potential new targets to exploit for chemopreventive strategies. PUBLIC HEALTH RELEVANCE: Colon cancer is the 3rd leading cause of cancer-related deaths in the US. More than half of these malignancies are believed to be preventable by dietary modifications. We have shown that tumor promotion by Western style high fat diets requires epidermal growth factor receptor (EGFR) signals that inhibit anti-inflammatory vitamin D signals. We will uncover EGFR and vitamin D cellular pathways that interact to modulate dietary inflammation and colonic tumor risk.