Regulation and Role of Ornithine Decarboxylase in Cell Proliferation and Cancer

描述(申请人提供)：Myc致癌转录因子家族在~70%的人类癌症中被激活，它们调节基因组的大CAST(10%-15%)的转录，以协调新陈代谢、细胞生长和分裂、分化和发育。此外，Myc位于激活的Ras癌蛋白的下游，Ras信号在人类癌症中频繁突变，从而削弱Myc蛋白的周转并增强其转录活性。在过去的资金周期中，我们证明了Myc的增殖反应对肿瘤的发展是限速的。值得注意的是，这一途径严格依赖于单一的Myc转录靶标-鸟氨酸脱羧酶(ODC)，它是多胺生物合成的限速酶。在这里，我们证明了ODC自杀抑制剂DFMO的治疗，或简单地将ODC水平减半(在ODC+/-小鼠中)，使易患肿瘤的Myc转基因小鼠的寿命增加两倍，而且它还削弱了与RAS激活突变相关的表皮癌变。总而言之，这些发现表明，靶向ODC将在癌症预防中具有广泛的好处，这一事实现已在正在进行的人类癌症化学预防试验中得到证实。此外，我们还发现，靶向ODC通过选择性地影响Myc启动细胞周期蛋白依赖的激酶抑制物p27Kip1的降解能力来抑制Myc的增殖反应，p27Kip1是一种肿瘤抑制物，可以通过S期抑制细胞的进入和进展。在这里，我们首先证明了Myc通过激活Cks1的转录来触发p27Kip1的降解，Cks1是SCFSkp2 E3泛素连接酶复合体的一个组成部分，指导p27Kip1的破坏。令人惊讶的是，我们现在已经证明了ODC是Myc诱导Cks1转录所必需的。总而言之，这些发现表明，Myc诱导的增殖和肿瘤形成是由Myc&>ODC&gt；Cks1-to-p27Kip1途径驱动的。利用经验证的Myc驱动的B细胞淋巴瘤、乳腺癌和K-RAS导向的肺腺癌模型，我们将测试ODC在癌基因驱动的增殖和肿瘤发展、维持恶性状态以及它与肿瘤抑制通路的相互作用中的作用。这些研究包括那些评估潜在治疗指数的研究，其中将确定ODC丢失对先前存在的肿瘤细胞的内在影响与其对正常细胞的影响。我们还将严格评估p27Kip1和Cks1作为ODC下游靶点在癌症发生和肿瘤维持中的作用，并将确定ODC调节Cks1和p27Kip1表达的机制。鉴于Myc和RAS相关恶性肿瘤在人类癌症中的普遍和侵袭性，特别是在本文询问的三种恶性肿瘤中，以及确定靶向ODC在人类癌症化学预防中的有效性的临床试验，拟议的研究显然与NCI的使命高度相关。公共卫生相关性：这项由修订后的竞争性更新申请(R01 CA100603A1)支持的研究与化学预防直接相关，在临床上可能与三种难治性、破坏性的人类恶性肿瘤--淋巴瘤、乳腺癌和肺腺癌的治疗相关。我们的研究集中在临床验证的靶鸟氨酸脱羧酶(ODC)，这是一种代谢酶，其表达直接由Myc癌蛋白诱导，也由突变的RAS癌基因引起，这两种基因一起在75%的人类肿瘤中被激活。重要的是，我们已经证明，靶向ODC会损害Myc的增殖反应，并使易患肿瘤的Myc转基因小鼠的寿命增加两倍，这也损害了涉及RAS癌基因的皮肤肿瘤的发展。拟议的研究将确定ODC在调节淋巴瘤、肺癌和乳腺癌的发展和维持方面的作用，并将解决ODC如何调节由癌基因引起的增殖反应，以期这些研究将揭示癌症预防和治疗的新靶点。

DESCRIPTION (provided by applicant): The Myc family of oncogenic transcription factors is activated in ~70% of human cancers and they regulate the transcription of a large cast (10-15%) of the genome to coordinate metabolism, cell growth and division, differentiation, and development. Further, Myc lies downstream of activated Ras oncoproteins that are frequently mutated in human cancers, where Ras signaling impairs turnover of Myc protein and augments its transcriptional activity. Over the past funding cycle we demonstrated that Myc's proliferative response is rate limiting for tumor development. Remarkably, this pathway strictly relies on a single Myc transcription target, ornithine decarboxylase (Odc), the rate limiting enzyme of polyamine biosynthesis. Here we demonstrated that treatment with the Odc suicide inhibitor DFMO, or simply halving the levels of Odc (in Odc+/- mice), triples the lifespan of tumor-prone, Myc transgenic mice and that it also impairs epidermal carcinogenesis, which is associated with activating mutations in Ras. Collectively, these findings suggest that targeting Odc will have widespread benefit in cancer prevention, a fact now validated in ongoing human cancer chemoprevention trials. Further, we established that targeting Odc disables Myc's proliferative response by selectively affecting Myc's ability to provoke the degradation of the cyclin- dependent kinase inhibitor p27Kip1, a tumor suppressor that inhibits entry and progression through S-phase. Here we first demonstrated that Myc triggers p27Kip1 degradation by activating the transcription of Cks1, a component of the SCFSkp2 E3 ubiquitin ligase complex that directs p27Kip1 destruction. Surprisingly, we have now shown that Odc is required for Myc to induce Cks1 transcription. Collectively, these findings suggest a Myc>Odc>Cks1-to-p27Kip1 pathway drives Myc-induced proliferation and tumorigenesis. Using validated Myc-driven mouse models of B cell lymphoma and mammary adenocarcinoma, and of K-Ras-directed lung adenocarcinoma, we will test the roles of Odc in oncogene-driven proliferation and tumor development, the maintenance of the malignant state, and its interplay with tumor suppressor pathways. These studies include those that evaluate potential therapeutic index, where the intrinsic effects of Odc loss on pre- existing tumor cells versus its effects in normal cells will be determined. We will also critically assess the roles of p27Kip1 and Cks1 as downstream targets of Odc in cancer development and tumor maintenance, and will define the mechanism by which Odc regulates Cks1 and p27Kip1 expression. Given the pervasive and aggressive nature of Myc- and Ras-associated malignancies in human cancer, especially in the three malignancies interrogated herein, and clinical trials establishing the efficacy of targeting Odc in human cancer chemoprevention, the proposed studies are clearly highly relevant to the mission of the NCI. PUBLIC HEALTH RELEVANCE: The research supported by this revised, competitive renewal application (R01 CA100603A1) is directly, clinically relevant to chemoprevention and perhaps therapy for three refractory, devastating human malignancies, lymphoma, breast cancer, and lung adenocarcinoma. Our studies have focused on the clinically validated target ornithine decarboxylase (Odc), a metabolic enzyme whose expression is directly induced by Myc oncoproteins, and also by mutated Ras oncogenes, which together are activated in >75% of human tumors. Importantly, we have shown that targeting Odc impairs Myc's proliferative response and triples the lifespan of tumor-prone, Myc transgenic mice, and that this also compromises the development of skin tumors having Ras oncogene involvement. The proposed studies will define the roles of Odc in regulating the development and maintenance of lymphoma and lung and breast cancer, and will resolve how Odc regulates the proliferative response provoked by oncogenes, with the expectation that these studies will reveal new targets for cancer prevention and treatment.