Monoclonal antibodies raised against Xenopus p53 interact with human p73

The p53 tumor suppressor gene belongs to a multigene family that includes two paralogues, p63 and p73. The structure of the p63 and p73 genes is quite similar, but both have common activities with p53, such as DNA binding and transactivation. Both p53 and p73 bind to mdm2, but only p53 is degraded through the activity of mdm2. p63 neither binds to nor is degraded by mdm2 despite important conservation in the key interacting residues. Using a panel of monoclonal antibodies raised against human and Xenopus p53, we have been able to find several antibodies that cross-react strongly with human p73. These antibodies react both with exogenous p73 expressed in mammalian cells and with endogenous p73. Interestingly, all these antibodies react with the same epitope localized in the amino-terminus of p53, but have no cross-reaction with p63. This epitope corresponds to the exact mdm2 binding site to p53. These antibodies inhibit the interaction between either p53 or p73 and mdm2, and may be useful tools for the study of these proteins. Furthermore, our studies suggest that there exist specific spatial requirements for the interaction between p53 or p73 and mdm2.     

p53基因网络的研究进展

肿瘤抑制基因p53与其上、下游功能相关基因组成了一个复杂的基因网络。p53基因位于人染色体17q13．1区带,编码的野生型p53蛋白包含N—末端的转录激活结构域、DNA结合结构域、四聚体化结构域和C—末端调节域。p73、p5l、p63等基因由于在结构上与p53基因具有同源性,因而被归为p53基因家族。p53是联系不同遗传应急和细胞应答的中间环节,离子辐射、化疗药物及异常的细胞生长信号均能刺激p53基因表达。p53表达升高后,可通过p53-mdm2、p14^ARF—mdm2环路对p53表达水平进行精确调节,p53功能的发挥还同时需要p33^MG1b基因的协同作用。磷酸化和乙酰化是细胞内调节p53活性功能的主要途径。p53可以调控下游多种基因表达,其功能主要表现在阻滞细胞周期、促进细胞凋亡、维持基因组稳定性和抑制肿瘤血管生成四个方面。认识p53基因网络的功能将有助于理解p53及其相关基因间的具体作用机制。     

Growth suppression by a p14(ARF) exon 1beta adenovirus in human tumor cell lines of varying p53 and Rb status

We have analyzed the ability of an adenoviral vector encoding the exon 1beta region of the p14(ARF) tumor suppressor (ARF) to suppress the growth and viability of an array of tumor cell lines of various origins and varying p53 and Rb status, in order to establish the clinical potential of ARF. An important activity of ARF is regulation of p53 stability and function through binding to the mdm2 protein. By sequestering mdm2, ARF may promote growth suppression through the Rb pathway as well because mdm2 can bind to Rb and attenuate its function. Whereas the high frequency of ARF gene deletion in human cancers, accounting for some 40% of cancers overall, suggests that ARF would be a strong candidate for therapeutic application, the possible dependence of ARF activity on p53 and Rb function presents a potential limitation to its application, as these functions are often impaired in cancer. We show here that a replication-defective adenovirus, Ad1beta, encoding the exon 1beta region of ARF is most effective in tumor cells expressing endogenous wild-type p53. Nevertheless, Ad1beta suppresses tumor cell growth and viability in vitro and in vivo, inducing G1 or G2 cell cycle arrest and cell death even in tumor cells lacking both functional Rb and p53 pathways, and independently of induction of the p53 downstream targets, p21, bax, and mdm2. These results point to an activity of ARF in human tumor cells that is independent of Rb or p53, and suggest that therapeutic applications based on ARF would have a broad clinical application in cancer.     

骨巨细胞瘤mdm2、p185、p21及p53免疫组化研究

[目的]探讨mdm2、p185、p21及p53在骨巨细胞瘤（GCT）的表达及与GCT病理分级和复发的关系。[方法]应用SP免疫组织化学方法检测mdm2、p185、p21及p53在52例GCT中的表达（GCT按Jaffe分级：Ⅰ级15例、Ⅱ级25例、Ⅲ级12例）。[结果]52例GCT中mdm2、p185、p21及p53的阳性表达率分别为34.6%（18/52）,21.2%(11/52),13.5%(7/52)及26.f9%(14/52)。不同病理分级阳性表达均无显著性差异。mdm2、p185、p21、p53在复发和无复发的病例中,阳性表达率分别为61.5%(8/13)、25.6%(10/39);38.5(5/13)、15.4%（6/39）;23.1%(3/13)、10.3%(4/29);46.2%(6/13)、20.5%(8/39)。GCT复发与否之间的mdm2表达有显著性差异（P=0.018),而p185、p21及p53的表达无显著性差异。[结论]mdm2、p185、p21及p53在GCT中的表达与病理分级差异无关,而mdm2的表达与其复发与否有关。     

P53和mdm2在骨巨细胞瘤中的表达

目的：探讨p53和mdm2在骨巨细胞瘤（GCT）的表达及与GCT病理分级和复发的关系。方法：应用SP免疫组织化学方法检测p53和mdm2在52例GCT（GCT按Jaffe分级：Ⅰ级15例、Ⅱ级25例、Ⅲ级12例）中的表达。结果：14例p53表达阳性,阳性率26．9％,18例mdm2表达呈阳性,阳性率达34．6％。其阳性表达与病理分级均无显著性差异（P值分别为0．699;0．871）。p53和mdm2在复发和无复发的病例中,阳性表达率分别为46．2％、20．5％和61．5％、25．6％。两者同时阳性表达有7例,p53和mdm2同时过表达与GCT复发有高度显著性差异（P＝0．008）。结论：p53和mdm2在GCT中的表达与病理分级无关而与其复发有关。