The role of glutaminase 2, a novel p53 target gene in metabolism, in liver cancer

描述(申请人提供)：肝细胞癌是美国增长最快、死亡率最高的癌症类型。抑癌基因P53通过调控细胞周期停滞、细胞凋亡和衰老，在包括肝细胞癌在内的肿瘤预防中发挥重要作用。最近的研究表明，P53在肿瘤抑制中有一个新的功能，即P53调节能量代谢。作为肿瘤细胞的标志，代谢改变(如Warburg效应)最近被认为是肿瘤发生的关键因素，也是肿瘤治疗的潜在靶点。我们发现了一个新的P53靶基因，线粒体谷氨酰胺酶2(GLS2)，这是一个编码参与线粒体呼吸的酶的基因，为P53和代谢提供了直接的联系。引人注目的是，我们从有限数量的样本中获得的数据显示，与邻近的正常或肝硬变肝组织相比，我们分析的几乎所有肝癌组织中GLS2的表达都缺失或显著降低(超过20倍)。我们的初步数据进一步表明，GLS2可能抑制肿瘤的发生并调节能量代谢。根据我们的结果，我们假设GLS2可能通过调节代谢在肿瘤抑制中发挥关键作用。在这项拟议的研究中，我们计划：1)测定另外100例肝癌标本中GLS2的表达，以确定GLS2缺失是肝癌的常见和特异事件，可能成为潜在的肿瘤生物标志物。2)验证GLS2表达缺失促进裸鼠成瘤，而GLS2表达恢复抑制裸鼠肝脏成瘤的假说。3)明确GLS2抑制肿瘤的机制。特别是，我们将确定GLS2的S在能量代谢、应激反应和抗氧化方面的调节作用。4)确定肝细胞癌中GLS2表达缺失的机制。针对RFA(PA-08-243)题为《肝细胞癌的病因、预防和治疗》，这项研究将极大地提高我们对肝肿瘤发生机制的理解，并扩大我们对p53在肿瘤抑制中的机制，特别是代谢变化在肿瘤发生中的作用以及逆转代谢变化在肿瘤治疗中的作用的理解。我们期待GLS2作为一种新的肿瘤生物标志物和治疗靶点应用于肿瘤治疗，特别是对肝癌的治疗，具有直接的潜力。 公共卫生相关性：在这项拟议的研究中，我们将研究GLS2基因在肿瘤抑制中的作用和机制。这项研究将极大地加深我们对肿瘤发生的分子机制，特别是代谢变化在肿瘤发生发展中的作用的理解。本研究将为GLS2作为一种新的肿瘤生物标志物用于肿瘤诊断和肿瘤治疗特别是肝癌的治疗靶点提供直接的可能性。

DESCRIPTION (provided by applicant): Hepatocellular carcinoma (HCC) is the most rapidly increasing type of cancer with high mortality in the United States. Tumor suppressor p53 plays a crucial role in tumor prevention, including HCC, through its regulation of cell cycle arrest, apoptosis and senescence. Recent studies suggested a novel function for p53 in tumor suppression, i.e. p53 regulates energy metabolism. As a hallmark of tumor cells, metabolic changes (e.g. Warburg effect) were recently suggested to be a key contributor to tumorigenesis and a potential target for tumor therapy. We identified a novel p53 target gene, the mitochondrial glutaminase 2 (GLS2), a gene encoding an enzyme involved in mitochondrial respiration, which provides a direct link for p53 and metabolism. Strikingly, our data from a limited number of samples show that GLS2 expression is absent or significantly decreased (by over 20-fold) in almost all of the HCC specimens we analyzed as compared with the adjacent normal or cirrhotic liver tissues. Our preliminary data further suggest that GLS2 may suppress tumorigenesis and regulates energy metabolism. Based on our results, we hypothesize that GLS2 may play a critical role in tumor suppression through its regulation of metabolism. In this proposed study we plan to: 1) determine the GLS2 expression in additional 100 HCC specimens to establish the loss of GLS2 as a common and specific event for HCC which could be a potential tumor biomarker. 2) Test the hypothesis that loss of GLS2 epxression promotes tumorigenesis while restoration of GLS2 expression inhibits liver tumorigenesis in nude mice. 3) Identify mechanisms for GLS2 in tumor suppression. In particular, we will determine GLS2's role in regulation of energy metabolism, stress responses and antioxidantion. 4) Identify mechanisms underlying the loss of the GLS2 expression in HCC. In response to RFA (PA-08-243) entitled "Etiology, Prevention, and Treatment of Hepatocellular Carcinoma", this proposed study will greatly increase our understanding of the mechanisms for liver tumorigenesis and expand our understanding of mechanisms of p53 in tumor suppression, especially the role of metabolic changes in tumorigenesis and the role of reversing metabolic changes in tumor therapy. It is our anticipation that this study will have direct potential to provide GLS2 as a novel tumor biomarker and therapeutic target for tumor therapy, especially for HCC. PUBLIC HEALTH RELEVANCE: In this proposed study we will study the role and mechanisms of GLS2 gene in tumor suppression. This study will greatly increase our understanding of the molecular mechanisms for tumorigenesis, especially the role of metabolic changes in tumor initiation and progression. This study will have direct potential to provide GLS2 as a novel tumor biomarker for tumor diagnosis and therapeutic target for tumor therapy, especially for liver cancer.