Tumor suppressive functions of the urea cycle in renal cell carcinoma

 描述（由申请方提供）：透明细胞肾细胞癌（ccRCC）是最常见的肾脏恶性肿瘤。它对化疗和放疗都有抗性，目前对这种疾病的治疗选择有限，特别是因为每4名患者中就有1名最初诊断为播散性、转移性疾病状态。这些临床特征的基础是分子水平上的许多变化，其中最明显的是促进恶性肿瘤的代谢改变。其中一个改变是尿素循环，这是ccRCC中第二个最低表达的代谢途径。尿素循环发生在肾脏中，并参与游离氨的解毒。该循环中的两种关键酶是精氨酸酶II（ARG 2）和精氨酸琥珀酸合酶1（ASS 1）; ARG 2包含在染色体14 q上，该区域的缺失与ccRCC中的高恶性度和较差的预后相关。来自癌症基因组图谱（TCGA）数据集中近500个原发性ccRCC肿瘤的数据表明，与正常肾组织相比，ARG 2在40%的ccRCC中表现出拷贝数丢失，并且在mRNA水平上表达不足，而ASS 1在ccRCC中显著表达不足，但未缺失。在初步实验中，我们已经证明在ccRCC细胞系中重新表达这些酶在异种移植肿瘤生长期间抑制体外和体内增殖。此外，ARG 2和ASS 1的再表达降低了糖酵解通量并降低了mTOR活性。该提议的中心假设是ARG 2和ASS 1通过调节尿素循环和糖酵解代谢以及通过抑制mTORC 1依赖性生长途径而作为肿瘤抑制因子。具体目标1：确定ARG 2和ASS 1在ccRCC中介导mTORC 1驱动的增殖中的作用。具体目标2：确定ARG 2和ASS 1重新表达引起的代谢改变如何影响ccRCC的发病机制。完成这些研究将需要结合体外和体内方法，包括生物化学、细胞生物学、免疫组织化学和代谢通量分析。该项目的目的是确定ARG 2和ASS 1丢失改变细胞代谢以促进ccRCC肿瘤生长的分子机制。阐明这些机制将为该病的靶向治疗提供新的途径。

 DESCRIPTION (provided by applicant): Clear cell renal cell carcinoma (ccRCC) is the most common form of kidney malignancy. It is both chemotherapy and radiation resistant and current treatment options for this disease are limited, particularly because 1 out of 4 patients are initialy diagnosed at a disseminated, metastatic disease state. Underlying these clinical characteristics are a number of changes at the molecular level, the most pronounced of which are metabolic alterations that promote malignancy. One of these modifications is to the urea cycle, which is the second most underexpressed metabolic pathway in ccRCC. The urea cycle occurs in the kidney and is involved in detoxification of free ammonia species. Two key enzymes in this cycle are arginase II (ARG2) and argininosuccinate synthase 1 (ASS1); ARG2 is included on chromosome 14q and loss of this region correlates with high malignancy grade and a poorer prognosis in ccRCC. Data from nearly 500 primary ccRCC tumors in The Cancer Genome Atlas (TCGA) dataset demonstrates that ARG2 exhibits copy number loss in 40% of ccRCC and is underexpressed at the mRNA level, whereas ASS1 is significantly underexpressed, but not deleted, in ccRCC compared to normal kidney tissue. In preliminary experiments, we have demonstrated that re-expressing these enzymes in ccRCC cell lines suppresses proliferation in vitro and in vivo during xenograft tumor growth. Furthermore, re-expression of ARG2 and ASS1 reduces glycolytic flux and decreases mTOR activity. The central hypothesis of this proposal is that ARG2 and ASS1 act as tumor suppressors by modulating urea cycle and glycolytic metabolism and by repressing mTORC1 dependent growth pathways. Based on this hypothesis, the following specific aims will be pursued: Specific Aim 1: To determine the role ARG2 and ASS1 play in mediating mTORC1 driven proliferation in ccRCC. Specific Aim 2: To determine how metabolic alterations caused by ARG2 and ASS1 re-expression influence the pathogenesis of ccRCC. Completion of these studies will require a combination of in vitro and in vivo methods that include biochemistry, cell biology, immunohistochemistry, and metabolic flux analysis. The objective of this project is to determine the molecular mechanisms by which ARG2 and ASS1 loss alters cellular metabolism to promote ccRCC tumor growth. Delineating these mechanisms will provide new therapeutic avenues to target in this disease.