Citrulline-urea cycle in KSHV cellular transformation

卡波西肉瘤相关疱疹病毒(KSHV)是卡波西肉瘤(KS)和其他几种恶性肿瘤的病原体。我们已经发现，不像大多数其他类型的癌细胞那样，KSHV转化的细胞对葡萄糖和有氧糖酵解上瘾，不依赖葡萄糖，有氧糖酵解水平降低。相反，KSHV转化的细胞对谷氨酰胺上瘾。更令人惊讶的是，谷氨酰胺主要用于核苷酸和氨基酸的合成。为了维持代谢流并清除有毒产物，KSHV通过上调关键限速代谢酶精氨酸琥珀酸合成酶1(ASS1)来阻断瓜氨酸-尿素循环。值得注意的是，ASS1对于KSHV转化细胞的增殖和生存是必不可少的，瓜氨酸-尿素循环的上调进一步通过诱导一氧化氮提供了必要的STAT3致癌信号。我们的假设是，KSHV编码特定的基因(S)来劫持瓜氨酸-尿素循环，以支持KSHV转化的细胞的增殖和存活，因此靶向这一途径对于KSHV诱导的肿瘤的治疗是有效的。我们开发了KSHV诱导的细胞转化和肿瘤发生的有效模型，KSHV转化细胞的三维(3D)培养模型，以及先进的代谢谱和示踪技术，所有这些都对检验这一新假说特别有用。我们将研究ASS1和瓜氨酸-尿素循环在维持代谢流、清除有毒产物和激活STAT3途径以支持KSHV诱导的细胞转化中的重要作用(目标1)；确定ASS1和激活的瓜氨酸-尿素循环激活STAT3途径支持KSHV诱导的细胞转化的机制(目标2)；确定KSHV上调ASS1和劫持瓜氨酸-尿素循环的机制(目标3)；以及确定靶向瓜氨酸-尿素循环中的关键酶治疗KSHV诱导的肿瘤发生的可能性(目标4)。这项拟议的项目意义重大，因为它将使用多学科创新方法和模型系统测试KSHV操纵关键细胞代谢途径的新假说。我们期望该项目的完成将有助于识别新的癌症驱动因素和KSHV诱发癌症的脆弱性，从而为开发新的治疗方法提供科学依据。

Kaposi’s sarcoma-associated herpesvirus (KSHV) is the causal agent of Kaposi’s sarcoma (KS) and several other malignancies. We have discovered that, unlike most other types of cancer cells that are addicted to glucose and aerobic glycolysis, KSHV-transformed cells do not depend on glucose and have a reduced level of aerobic glycolysis. Instead, KSHV-transformed cells are addicted to glutamine. More surprisingly, glutamine is primarily shunted to the syntheses of nucleotides and amino acids. To maintain the metabolic flow and clear the toxic products, KSHV hijacks the citrulline-urea cycle by upregulating the key rate-limiting metabolic enzyme argininosuccinate synthase 1 (ASS1). Significantly, ASS1 is essential for the proliferation and survival of KSHV- transformed cells and upregulation of the citrulline-urea cycle further provides an essential STAT3 oncogenic signal by inducing nitric oxide. Our hypothesis is that KSHV encodes specific gene(s) to hijack the citrulline-urea cycle to support the proliferation and survival of KSHV-transformed cells, and hence targeting this pathway is effective for treating KSHV-induced tumors. We have developed an efficient model of KSHV-induced cellular transformation and tumorigenesis, three-dimensional (3D) culture models KSHV- transformed cells, and advanced metabolic profiling and tracing technologies, all of which are particularly useful for testing this novel hypothesis. We will examine the essential roles of ASS1 and citrulline-urea cycle for maintaining metabolic flow, clearing toxic products and activating STAT3 pathway to support KSHV-induced cellular transformation (Aim 1); determine the mechanism by which ASS1 and active citrulline-urea cycle activate the STAT3 pathway to support KSHV-induced cellular transformation (Aim 2); determine the mechanism by which KSHV upregulates ASS1 and hijacks the citrulline-urea cycle (Aim 3); and determine the therapeutic potential of targeting key enzymes in the citrulline-urea cycle for treating KSHV-induced tumorigenesis (Aim 4). The proposed project is highly significant as it will test a novel hypothesis of KSHV manipulation of a key cellular metabolic pathway using multidisciplinary innovative approaches and model systems. It is our expectations that accomplishment of this project will lead to the identification of novel cancer drivers and vulnerabilities of KSHV-induced cancers, which could provide a scientific basis for developing novel therapies.