The role of nicotinamide phosphoribosyltransferase (NAMPT) for oncogenic MYC functions and tumor-stroma crosstalk

原癌基因c-MYC及其产物MYC蛋白的失调与大多数癌症的发生有关。我们最近发现了一个正反馈环，其中MYC激活烟酰胺磷酸核糖基转移酶（NAMPT），增强SIRT 1功能，从而增加MYC活性。NAMPT是NAD+补救途径的限速酶，并调节NAD+依赖性脱乙酰酶SIRT 1的活性，从而促进细胞存活。该提案的总体目标是使用功能性体外测定和MYC驱动的淋巴瘤小鼠模型建立MYC，NAMPT和SIRT 1之间连接的肿瘤生物学相关性。此外，我们将确定eNAMPT是否在肿瘤微环境中具有旁分泌功能。为了实现这些目标，将使用四种方法：1。将在结直肠癌样本中分析MYC介导的NAMPT和SIRT 1上调，以建立与临床参数（如进展、生存和转移）的相关性。2.将使用人类和小鼠成纤维细胞中的条件性MYC等位基因研究NAMPT对MYC功能的作用，例如诱导细胞周期进展、永生化、转化、糖酵解和基因调控。3.在Eµ-Myc模型中，使用CD 19-Cre介导的B细胞特异性缺失一个NAMPT等位基因，分析NAMPT对MYC诱导的淋巴瘤的作用。我们还将评估NAMPT的药理学抑制对预防和治疗Eµ-Myc淋巴瘤的作用。4.分泌的细胞外NAMPT（eNAMPT）以类精氨酸的方式起作用，传递抗凋亡和生长信号。癌症患者血清水平升高和癌细胞系分泌表明癌细胞可能是eNAMPT的可能来源。在这里，我们将确定肿瘤释放的eNAMPT在结直肠癌细胞系中的功能，并测量Eµ-Myc小鼠血清中的eNAMPT。我们将讨论eNAMPT分泌是否受MYC调节，（e）NAMPT是否具有体外诱导迁移和侵袭的能力，以及在异种移植试验中影响结直肠癌细胞系的转移。总之，这些研究将有助于了解内和细胞外NAMPT功能的生理和病理生理设置，作为致癌激活MYC。这些研究可能建立eNAMPT作为癌症中代谢串扰的新介质，并评估eNAMPT作为诊断标志物的潜力。此外，关于MYC，NAMPT和SIRT 1在肿瘤进展中的调控联系的详细知识可能会在未来开发创新的肿瘤治疗方法。

Deregulation of the proto-oncogene c-MYC and its product, the MYC protein, has been implicated in the genesis of the majority of cancers. We recently identified a positive feedback loop, in which MYC activates nicotinamide phosphoribosyltransferase (NAMPT) which enhances SIRT1 function and thereby increases MYC activity. NAMPT is the rate limiting enzyme of NAD+ salvage pathway and regulates the activity of the NAD+-dependent deacetylase SIRT1, thereby promoting cellular survival. The overall goal of this proposal is to establish the tumor biological relevance of the connection between MYC, NAMPT and SIRT1 using functional in vitro assays and a MYC-driven lymphoma mouse model. Furthermore, we will determine whether eNAMPT has a paracrine function in the tumor microenvironment. To achieve these goals, four approaches will be used: 1. The MYC-mediated up-regulation of NAMPT and SIRT1 will be analyzed in colorectal cancer samples to establish correlations with clinical parameters, such as progression, survival and metastasis. 2. The role of NAMPT for MYC functions such as induction of cell cycle progression, immortalization, transformation, glycolysis and gene regulation will be studied using conditional MYC alleles in human and mouse fibroblasts. 3. The role of NAMPT for MYC-induced lymphomas will be analyzed using a CD19-Cre-mediated B cell-specific deletion of one NAMPT allele in the Eµ-Myc model. We will also evaluate the effect of pharmacological inhibition of NAMPT for prevention and therapy of Eµ-Myc lymphomas. 4. Secreted, extracellular NAMPT (eNAMPT) acts in a cytokine-like fashion, conveying anti-apoptotic and growth signals. Elevated serum levels in cancer patients and secretion by cancer cell lines suggest that cancer cells may represent a possible source for eNAMPT. Here we will determine the function of tumor-released eNAMPT in colorectal cancer cell lines, and measure eNAMPT in serum of Eµ-Myc mice. We will address whether eNAMPT secretion is regulated by MYC, whether (e)NAMPT has the capacity to induce migration and invasion in vitro, and affects metastasis of colorectal cancer cell lines in xenografts assays. In summary, these studies will contribute to the understanding of intra- and extracellular NAMPT function in physiological and patho-physiological settings, as oncogenic activation of MYC. These studies may establish eNAMPT as a novel mediator of a metabolic crosstalk in cancer, and evaluate the potential of eNAMPT as a diagnostic marker. Furthermore, the detailed knowledge about the regulatory connections between MYC, NAMPT and SIRT1 in tumor progression may allow the development of innovative tumor therapeutic approaches in the future.