The role of butyrate-producing bacteria in CIMP colorectal cancer tumorigenesis

项目摘要 结直肠癌（CRC）的锯齿状途径占所有CRC的35%。出现的病变子集 沿着这一途径的特征是参与基因启动子中CPG岛的甲基化， 肿瘤抑制和错配修复导致其表观遗传沉默。因此，这组肿瘤 CpG岛甲基化表型（CpG island methylator phenotype，CIMP）流行病学研究表明， 导致CIMP CRC的锯齿状病变可能更容易被结肠镜检查遗漏，这可能是由于其 在近端结肠、形态学或快速生长速率中占优势。CIMP肿瘤也被 与CRC相关死亡风险增加相关。尽管公共卫生的重要性， 这些异常表观遗传变化的原因仍然未知。识别导致异常的因素 CIMP的甲基化可能导致风险评估和预防治疗的新策略 干预措施。我们最近进行了一项初步研究，以检查微生物组在CIMP中的作用。 CRC。我们的研究表明，主要的丁酸盐产生细菌（BPB）种群和丁酸盐 与非CIMP CRCs相比，它们产生的CIMP缺乏。我们假设结肠癌的缺乏 丁酸是纤维发酵的细菌代谢产物，具有已知的抗肿瘤和表观遗传作用， CIMP CRC中异常CpG岛甲基化的主要原因。为了验证这一假设，我们将描述 CIMP和非CIMP肿瘤患者的活检，并在转基因肿瘤中进行机制研究。 小鼠模型在目标1中，我们将使用细菌16S rRNA基因的高通量测序，以评估 CIMP和非CIMP肿瘤患者之间微生物群的组特异性差异，并研究 CIMP和非CIMP组织之间的功能差异，包括丁酸和其他 短链脂肪酸，如丙酸和乙酸。在目标2中，我们将量化和比较 CIMP患者肿瘤和正常组织中丁酸盐和其他脂肪酸的浓度 非CIMP肿瘤在目标3中，我们将询问锯齿状的转基因HBUS小鼠模型， 研究膳食纤维缺乏和BPB缺乏的功能后果 人群和丁酸盐对肿瘤进展和CIMP的影响。在这些研究结束时，我们将有 扩大了我们对微生物群在CRC不同分子表型中的作用的认识， 支持或反对BPB和丁酸盐缺乏在异常CpG岛甲基化中的因果作用的证据发现， 在CIMP肿瘤中。

PROJECT SUMMARY The serrated pathway to colorectal carcinoma (CRC) accounts for 35% of all CRC. A subset of lesions arising along this pathway are characterized by methylation of CPG islands in the promoters of genes involved in tumor suppression and mismatch repair leading to their epigenetic silencing. Accordingly, this group of tumors is known by the acronym CIMP (CpG island methylator phenotype). Epidemiological studies suggest that serrated lesions leading to CIMP CRCs may be more likely to be missed with colonoscopy perhaps due to their predominance in the proximal colon, morphology, or rapid growth rate. CIMP tumors have also been associated with an increased risk of CRC-related death. Despite the public health importance, the underlying cause of these aberrant epigenetic changes remains unknown. Identification of factors contributing to aberrant methylation in CIMP could lead to new strategies for risk assessment and preventative therapeutic interventions. We recently conducted a preliminary study to examine the role of the microbiome in CIMP CRCs. Our research suggests that prominent butyrate-producing bacterial (BPB) populations and the butyrate they produce are deficient in CIMP compared to Non-CIMP CRCs. We hypothesize that deficiency in colonic butyrate, a bacterial metabolite of fiber fermentation with known anti-neoplastic and epigenetic effects, is the primary cause of abnormal CpG island methylation in CIMP CRCs. To test this hypothesis, we will characterize biopsies from patients with CIMP and Non-CIMP tumors and pursue mechanistic studies in a transgenic mouse model. In Aim 1, we will use high-throughput sequencing of the bacterial 16S rRNA gene, to evaluate group-specific differences in the microbiota between patients with CIMP and Non-CIMP tumors and investigate functional differences between the CIMP and Non-CIMP tissues, including synthesis of butyrate and other short-chain fatty acids, such as propionate and acetate. In Aim 2, we will quantitate and compare concentrations of butyrate and other fatty acids directly in tumors and normal tissue from patients with CIMP and Non-CIMP tumors. In Aim 3, we will interrogate the transgenic HBUS mouse model of serrated tumorigenesis to investigate the functional consequences of dietary fiber deficiency and deficient BPB populations and butyrate on tumor progression and CIMP. At the conclusion of these studies, we will have expanded our knowledge of the role of the microbiota in different molecular phenotypes of CRC and provided evidence for or against a causal role for BPB and butyrate deficiency in aberrant CpG island methylation found in CIMP tumors.