Regulation and Role of Ornithine Decarboxylase in Cell Proliferation and Cancer

描述（由申请人提供）：Myc家族的致癌转录因子在约70%的人类癌症中被激活，它们调节基因组的大部分（10-15%）的转录，以协调代谢、细胞生长和分裂、分化和发育。此外，Myc位于在人类癌症中频繁突变的活化Ras癌蛋白的下游，其中Ras信号传导损害Myc蛋白的周转并增强其转录活性。在过去的资助周期中，我们证明了Myc的增殖反应是肿瘤发展的速率限制。值得注意的是，这一途径严格依赖于一个单一的Myc转录靶，鸟氨酸脱羧酶（Odc），多胺生物合成的限速酶。在这里，我们证明了用Odc自杀抑制剂DFMO治疗，或简单地将Odc水平减半（在Odc+/-小鼠中），使易患肿瘤的Myc转基因小鼠的寿命延长三倍，并且它还损害了表皮癌发生，这与Ras中的激活突变有关。总的来说，这些研究结果表明，靶向Odc将在癌症预防中具有广泛的益处，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验证。此外，我们确定靶向Odc通过选择性地影响Myc引起细胞周期蛋白依赖性激酶抑制剂p27 Kip 1（一种抑制进入S期和通过S期进展的肿瘤抑制剂）降解的能力来使Myc的增殖反应失效。在这里，我们首先证明了Myc通过激活Cks 1的转录来触发p27 Kip 1降解，Cks 1是SCFSkp 2 E3泛素连接酶复合物的一个组分，其指导p27 Kip 1的破坏。令人惊讶的是，我们现在已经表明，Odc是Myc诱导Cks 1转录所必需的。总的来说，这些发现表明Myc>Odc> Cks 1-to-p27 Kip 1通路驱动Myc诱导的增殖和肿瘤发生。使用经验证的Myc驱动的B细胞淋巴瘤和乳腺癌小鼠模型，以及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中的作用，恶性状态的维持及其与肿瘤抑制途径的相互作用。这些研究包括评估潜在治疗指数的研究，其中将确定Odc损失对预先存在的肿瘤细胞的内在影响与其在正常细胞中的影响。我们还将严格评估p27 Kip 1和Cks 1作为Odc下游靶点在癌症发展和肿瘤维持中的作用，并将确定Odc调节Cks 1和p27 Kip 1表达的机制。考虑到Myc和Ras相关恶性肿瘤在人类癌症中的普遍性和侵袭性，特别是在本文所述的三种恶性肿瘤中，以及建立靶向Odc在人类癌症化学预防中的功效的临床试验，所提出的研究显然与NCI的使命高度相关。公共卫生相关性：这项修订后的竞争性更新申请（R 01 CA 100603 A1）支持的研究与三种难治性、毁灭性人类恶性肿瘤（淋巴瘤、乳腺癌和肺腺癌）的化学预防和可能的治疗直接、临床相关。我们的研究集中在临床验证的目标鸟氨酸脱羧酶（Odc）上，这是一种代谢酶，其表达直接由Myc癌蛋白和突变的Ras癌基因诱导，它们在>75%的人类肿瘤中被激活。重要的是，我们已经表明，靶向Odc损害Myc的增殖反应，并使易患肿瘤的Myc转基因小鼠的寿命延长三倍，并且这也损害了具有Ras癌基因参与的皮肤肿瘤的发展。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中的作用，并将解决Odc如何调节癌基因引起的增殖反应，期望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.