ARF MDM2 P53 TUMOR SUPPRESSION PATHWAY

p53和Rb介导两种主要的肿瘤抑制途径，它们被认为在大多数（如果不是全部的话）人类癌症中是功能失活的。 了解这两种途径是如何调节的已成为当代癌细胞生物学的主要目标。 沿着于p53，ARF-INK 4a基因座是人类癌症中两个最常改变的基因座之一。 在功能上，p16 INK 4a抑制细胞周期蛋白D依赖性激酶（CDK 4和CDK 6）的活性，从而维持视网膜母细胞瘤蛋白（Rb）的生长抑制状态。 另一方面，ARF通过结合并拮抗MDM 2的核输出介导癌基因激活的过度增殖检查点途径，从而防止p53的胞质降解。 通过关注ARF和p53之间的联系，我试图帮助我们理解这两个主要途径，从而了解癌症的发展。我以前发现ARF通过结合并拮抗MDM 2（p53的负调节因子）的活性来稳定p53，从而揭示了ARF-MDM 2-p53肿瘤抑制途径。 随后，我进一步阐明了ARF p53稳定化的机制：ARF与MDM 2和p53在核质中形成核体，从而阻断p53的核输出并阻止其胞质降解。 我还证明了在人类ARF蛋白中频繁发生的肿瘤源性突变损害了其阻断p53核输出的功能。 最近，我获得了新的证据，表明：（a）MDM 2与核糖体蛋白L5的结合是MDM 2核输出所必需的，这种调节被MDM 2中频繁的癌症衍生突变所破坏。(b)核糖体蛋白L5结合缺陷MDM 2未能促进p53降解，但保留其抑制p53的反式激活活性的能力。(c)ARF参与多肽复合物，和（d）MDM 2通过蛋白水解有效降解。 本论文的主要研究内容如下：（1）阐明核糖体蛋白L5和/或ARF调控p53和MDM 2核质穿梭的机制。(b)通过纯化ARF复合物来确定ARF-MDM 2-p53核体的功能，以及（c）作为长期目标来确定MDM 2泛素化和降解的机制和调节。 总之，这些实验应该促进对ARF-MDM 2-p53通路的调节及其在人类癌症中改变的功能后果的理解。

p53 and Rb mediate two major tumor suppression pathways that are believed to be functionally inactivated inmost, if not all, human cancers. Understanding how these two pathways are regulated has become a major goal of contemporary cancer cell biology. Along withp53, the ARF-INK4a locus is one of the two most frequently altered loci in human cancer. Functionally, p16INK4a inhibits the activity of cyclin D-dependent kinases (CDK4 and CDK6), thereby maintaining the retinoblastoma protein (Rb) in its growth suppressive state. ARF, on the other hand, mediates an oncogene- activated hyperproliferative checkpoint pathway through binding to and antagonizing the nuclear export of MDM2, thereby preventing cytoplasmic degradation of p53. With a focus on the connection between ARF and p53, I have tried to contribute to our understanding of these two major pathways and thereby cancer development. I had previously discovered that ARF stabilizes p53 through binding to and antagonizing the activity of MDM2-a negative regulator of p53, and thus revealed an ARF-MDM2-p53 tumor suppression pathway. Subsequently, I further elucidated the mechanism of ARFs p53 stabilization: ARF forms nuclear bodies in the nucleoplasm with MDM2 and p53, thereby blocking nuclear export of p53 and preventing its cytoplasmic degradation. I also demonstrated that frequently occurring tumor-derived mutations in the human ARF protein impair its function in blocking p53 nuclear export. More recently, I obtained new evidence showing that: (a) Association of MDM2 with ribosomal protein L5 is necessary for MDM2 nuclear export and this regulation is disrupted by frequent cancer-derived mutations in MDM2. (b) Ribosomal protein L5- binding deficient MDM2 failed to promote p53 degradation but retains its ability to suppress p53's transactivation activity. (c) ARF participates in a multipeptide complex, and (d) MDM2 is efficiently degraded by proteolysis. My current and future studies are aimed at several issues concerning the regulation of ARF-MDM2-p53 pathway: (a) Elucidate the mechanism of p53 and MDM2 nucleo-cytoplasmic shuttling controlled by ribosomal protein L5 and/or ARF. (b) Define the function of ARF-MDM2-p53 nuclear bodies by purifying the ARF complex, and (c) as a long-term goal to identify the mechanism and regulation of MDM2 ubiquitination and degradation. Together these experiments should advance understanding of the regulation of the ARF-MDM2-p53 pathway and the functional consequences of its alterations in human cancer.