Wnt signaling in obesity-associated colorectal cancer

项目摘要 肥胖影响42%的美国人口，是结直肠癌发展的主要风险因素。 肥胖的结直肠癌患者与正常体重相比，死亡风险增加5倍 同行然而，肥胖增加结直肠癌进展的机制， 转移知之甚少，这限制了有效预防和治疗的发展 肥胖者的结直肠癌治疗策略绝大多数结直肠癌是由丢失引起的。 肿瘤抑制基因Apc在结肠干细胞中的表达，以及随后Wnt信号的激活 通路Wnt信号传导也是维持晚期结直肠癌和转移所必需的。 我们小组的研究表明，饮食诱导的肥胖显著上调Wnt信号， 通过促进过氧化物酶体增殖物激活受体δ（PPAR-d） 转录程序，这反过来又会增加癌症的发展。这些发现表明， Wnt信号转导是治疗肥胖相关结直肠癌的一个非常有吸引力的策略。我们和其他人 已经证明结肠肿瘤由Lgr 5+癌症干细胞和单细胞RNA维持， 我们实验室的测序数据显示，这些细胞是Wnt活性的，而非癌症干细胞是Wnt低的。 然而，开发Wnt抑制剂来治疗APC缺陷型癌症或靶向癌症干细胞， 被证明难以捉摸Rac 1-GTP是GTP酶Rho家族的成员，是一种细胞内转导物， 通过介导β-连环蛋白的核转位促进Wnt信号传导。Prex 1是Rac特异性Rho 通过促进GTP交换成GTP来激活Rac 1的GTP鸟嘌呤核苷酸交换因子。 我们发现Prex 1和活性Rac 1-GTP在治疗小鼠的肠和结肠癌中高度富集 高脂饮食或PPAR-d激动剂。Rac 1信号转导的缺失显著降低了肠道肿瘤的发生 通过抑制Wnt激活。我们的长期目标是了解结直肠癌中Wnt激活的机制， 癌症，并为这种疾病开发新的治疗策略。在这里，我们假设Prex 1依赖性 Rac 1-GTP活性通过诱导Lgr 5+癌干细胞中的Wnt信号传导介导肥胖诱导的肿瘤发生 细胞在目标1中，我们将确定Prex 1信号在高脂饮食和PPAR-d介导的肠道炎症中的作用。 干细胞再生和肿瘤起始。在目标2中，我们将确定Prex 1/Rac 1-GTP的功能 高脂饮食和PPAR-d依赖性结直肠癌干细胞功能中的信号传导轴。在目标3中，我们 确定PPAR-d转录靶点在饮食环境中结肠直肠癌干细胞功能中的作用- 诱发性肥胖这项提案的目的是确定肥胖诱导的Wnt信号传导的机制， 促进结肠直肠癌的进展。我们的研究将为临床试验提供临床前依据， Rac 1-GTP抑制剂通过抑制Wnt而用于治疗结肠直肠癌，特别是肥胖个体的结肠直肠癌 发信号。

Project Summary Obesity affects 42% of the U.S. population and is a major risk factor for the development of colorectal cancer. Obese colorectal cancer patients have a five-fold increased risk of death compared to normal weight counterparts. However, the mechanisms by which obesity increases colorectal cancer progression and metastasis are poorly understood, which limits the development of effective prevention and treatment strategies for colorectal cancer in obese individuals. The vast majority of colorectal cancers are initiated by loss of the tumor suppressor gene Apc in colonic stem cells, and subsequent activation of the Wnt signaling pathway. Wnt signaling is also required for maintenance of advanced colorectal cancers and metastases. Research from our group demonstrates that diet-induced obesity markedly upregulates Wnt signaling in intestinal and colonic stem cells by promoting a peroxisome proliferator-activated receptor delta (PPAR-d) transcriptional program, which in turn increases cancer development. These findings suggest that inhibition of Wnt signaling is a highly attractive therapeutic strategy for obesity-associated colorectal cancer. We and others have demonstrated that colon tumors are maintained by Lgr5+ cancer stem cells, and single cell RNA sequencing data from our lab shows that these cells are Wnt-active, while non-cancer stem cells are Wnt-low. However, development of Wnt inhibitors to treat Apc-deficient cancers or to target cancer stem cells has proven elusive. Rac1-GTP, a member of the Rho family of GTPases, is an intracellular transducer that promotes Wnt signaling by mediating nuclear translocation of beta-catenin. Prex1 is a Rac-specific Rho GTPase guanine nucleotide exchange factor that activates Rac1 by facilitating the exchange of GTP to GTP. We found that Prex1 and active Rac1-GTP are highly enriched in intestines and colon cancers of mice treated with high fat diet or an agonist of PPAR-d. Loss of Rac1 signaling markedly reduces intestinal tumor initiation by inhibiting Wnt activation. Our long-term goal is to understand mechanisms of Wnt activation in colorectal cancer and to develop new treatment strategies for this disease. Here, we hypothesize that Prex1-dependent Rac1-GTP activity mediates obesity-induced tumorigenesis by inducing Wnt signaling in Lgr5+ cancer stem cells. In Aim 1, we will determine the role of Prex1 signaling in high fat diet and PPAR-d-mediated intestinal stem cell regeneration and tumor initiation. In Aim 2, we will determine the function of the Prex1 / Rac1-GTP signaling axis in high fat diet and PPAR-d-dependent colorectal cancer stem cell function. In Aim 3, we will identify the role of PPAR-d transcriptional targets in colorectal cancer stem cell function in the setting of diet- induced obesity. The goal of this proposal is to identify mechanisms by which obesity-induced Wnt signaling promotes colorectal cancer progression. Our studies will provide preclinical rationale for clinical trials to test Rac1-GTP inhibitors for the treatment of colorectal cancer, particularly in obese individuals, by inhibiting Wnt signaling.