The role of HIF2alpha in colon carcinogenesis

描述（由申请人提供）：结肠癌是男性和女性的第三大常见癌症，也是美国癌症死亡的第二大原因。由于目前的化疗和手术治疗策略对晚期结肠癌无效，因此需要新的方法来预防和治疗这种疾病。炎症是结肠癌的主要危险因素，识别炎症和癌症的相关通路将为结肠癌的治疗提供新的治疗靶点。低氧诱导因子（HIFs）是由α亚基（HIF1a或HIF2a）和β亚基（芳烃核转运子（ARNT））组成的异二聚体转录因子。HIF2a在结肠上皮细胞中表达，尽管对这些细胞中HIF2a的功能知之甚少。我们最近的数据表明，HIF2a的激活增强了肠道炎症和结肠癌。拟议研究的长期目标是阐明HIF2a如何影响这些过程，从而推动可用于治疗结肠癌的治疗方案的发展。该提议的具体假设是，慢性激活hif2a信号诱导促炎介质，导致结肠癌发生增加。这一假设是基于我们最近的数据证明：1)肠道特异性激活HIF2a导致慢性结肠炎症。2)结肠中HIF2a的破坏可以防止急性肠道炎症。3)促炎介质巨噬细胞迁移抑制因子（MIF）和前列腺素E2 （PGE2）是hif2a诱导的结肠炎症的早期启动因子。4) HIF2a促进结肠癌细胞生长和癌变。基于这些观察结果，本提案的实验重点是通过以下3个相互关联的特定目的来研究HIF2a在结肠炎症和癌症发病机制中的调节作用：目的1：确定MIF和环氧化酶-2 （COX2）衍生的PGE2在HIF2a促进结肠癌细胞生长中的作用。这将在肠道特异性过表达HIF2a的小鼠和过表达HIF2a的结肠来源细胞系中进行检验。目的2：确定结肠炎相关结肠癌（CAC）对HIF2a的需求。这将在一个特征良好的CAC模型中进行检验，该模型使用偶氮氧甲烷（AOM）和葡聚糖硫酸钠（DSS）在HIF2a被破坏的小鼠或在结肠中特异性过表达HIF2a的小鼠中进行。目的3：评估HIF2a调节促炎介质表达的分子基础。这将通过启动子和基因表达分析来检验，重点关注与结肠炎症发展相关的HIF2a靶基因。该Aim还将利用从Aim 2分离的结肠组织的全基因组基因表达分析和启动子结合研究，确定新的HIF2a促炎靶点。总之，拟议的体内和体外研究将为HIF2a在结肠中功能的基本方面提供新的见解。最终，这些研究将确定HIF2a是否是结肠炎症的潜在治疗靶点，并可能为预防和治疗结肠癌提供另一种策略。

DESCRIPTION (provided by applicant): Colon cancer is the third most common cancer in both men and women, and is the second leading cause of cancer death in the United States. There is a need for new approaches to prevent and treat this disease as the current strategies of chemotherapy and surgical treatments are not effective for late stage colon cancer. Inflammation is a major risk factor for colon cancer, and identifying pathways involved in both inflammation and cancer will provide new therapeutic targets for the treatment of colon cancer. Hypoxia-inducible factors (HIFs) are heterodimeric transcription factors consisting of an alpha subunit (HIF1a or HIF2a) and beta subunit (aryl hydrocarbon nuclear translocator (ARNT)). HIF2a is expressed in colon epithelial cells, although little is known about HIF2a function in these cells. Our recent data demonstrates that the activation of HIF2a potentiates intestinal inflammation and colon cancer. The long-term objectives of the proposed studies are to elucidate how HIF2a impact these processes as an impetus to the development of therapeutic regimens that can be used to treat colon cancer. The specific hypothesis of this proposal is that chronic activation of HIF2 a signaling induces proinflammatory mediators leading to an increase in colon carcinogenesis. This hypothesis is based on our recent data demonstrating: 1) Intestine-specific activation of HIF2a leads to chronic colon inflammation. 2) Disruption of HIF2a in the colon protects from acute intestinal inflammation. 3) The proinflammatory mediators, macrophage migration inhibitory factor (MIF) and prostaglandin E2 (PGE2) are early initiating factors in HIF2a-induced colon inflammation. 4) HIF2a increases colon cancer cell growth and carcinogenesis. Based on these observations, the experimental focus of this proposal is on the regulatory role of HIF2a in the pathogenesis of colon inflammation and cancer through the following 3 interconnected specific aims: Aim 1: determine the role of MIF and cyclooxygenase-2 (COX2)-derived PGE2 in HIF2a- promoted colon cancer cell growth. This will be examined in the intestine-specific HIF2a overexpressing mice and in colon-derived cell lines that overexpress HIF2a. Aim 2: determine the requirement for HIF2a in colitis- associated colon carcinogenesis (CAC). This will be examined in a well-characterized CAC model using azoxymethane (AOM) and dextran sulfate sodium (DSS) in mice that are disrupted for HIF2a or mice that overexpress HIF2a specifically in the colon. Aim 3: assess the molecular basis by which HIF2a regulates the expression of proinflammatory mediators. This will be examined by promoter and gene expression analysis with a focus on HIF2a target genes relevant to the development of colon inflammation. This Aim will also identify novel proinflammatory targets of HIF2a using genome-wide gene expression analysis and promoter binding studies in colon tissues isolated from Aim 2. Taken together, the proposed in vivo and in vitro studies will provide novel insights into the fundamental aspects of HIF2a function in the colon. Ultimately these studies will determine if HIF2a is a potential therapeutic target in colon inflammation and may provide an alternative strategy for preventing and treating colon cancer. PUBLIC HEALTH RELEVANCE: Colon cancer is the third most common cancer in both men and women, and is the second leading cause of cancer death in the United States. Inflammation is a major risk factor for colon cancer. This proposal examines the role of HIF in the regulation of inflammation and colon cancer. The goal of this work is to determine if HIF represents a new target for the prevention and treatment of colon cancer. The proposal has relevance for patients with ulcerative colitis, Crohn's disease and colon cancer.