Lim S K, Gopalan G
Laboratory of Gene Structure and Expression, Division of Molecular and Cellular Research, National Cancer Centre, Singapore, Singapore.
Oncogene. 2007 Oct 11;26(46):6593-603. doi: 10.1038/sj.onc.1210482. Epub 2007 Apr 23.
Overexpression of Aurora-A oncogene has been shown to induce genomic instability and tumorigenesis. Cellular levels of Aurora-A are regulated by multiple mechanisms including the proteasome-dependent degradation of Aurora-A protein. Cell-cycle-dependent turnover of Aurora-A protein is mediated by cdh1 through ubiquitin (Ub)- and proteasome-dependent pathway. However, Aurora-A kinase interacting protein 1 (AURKAIP1), a negative regulator of Aurora-A, also promotes proteasome-dependent Aurora-A degradation through an Ub-independent mechanism. In an attempt to understand how AURKAIP1 promotes Aurora-A degradation through Ub-independent pathway, we demonstrate here that antizyme1 (Az1), a well-studied mediator of Ub-independent protein degradation pathway, regulates Aurora-A protein stability. We show that ectopic or polyamine-induced expression of Az1 can lower the steady-state levels of Aurora-A. The effect of Az1 on Aurora-A turnover was shown to be proteasome-dependent, but Ub-independent. Az1 interacts with Aurora-A in vivo and the interaction between Aurora-A and Az1 is essential for the Az1-mediated Aurora-A degradation. Furthermore, we observed that AURKAIP1 could not promote degradation of Aurora-A mutant, which is defective in Az1 interaction. Coexpression of the Az inhibitor (AzI), which downregulates Az1 functions, also abrogated AURKAIP1-mediated degradation of Aurora-A. We further demonstrated that AURKAIP1, Az1 and Aurora-A could exist as a ternary complex and AURKAIP1 enhances the interaction between Az1 and Aurora-A. We propose that AURKAIP1 might function upstream of the Az1 by enhancing the binding affinity of Az1 to Aurora-A to promote recognition, targeting to proteasome and subsequent degradation.
已有研究表明，极光激酶A（Aurora-A）癌基因的过表达会诱导基因组不稳定和肿瘤发生。Aurora-A的细胞水平受多种机制调控，包括Aurora-A蛋白的蛋白酶体依赖性降解。Aurora-A蛋白的细胞周期依赖性周转由cdh1通过泛素（Ub）和蛋白酶体依赖性途径介导。然而，Aurora-A激酶相互作用蛋白1（AURKAIP1）作为Aurora-A的负调节因子，也通过一种不依赖Ub的机制促进蛋白酶体依赖性的Aurora-A降解。为了理解AURKAIP1如何通过不依赖Ub的途径促进Aurora-A降解，我们在此证明抗酶1（Az1）作为一种研究充分的不依赖Ub的蛋白质降解途径的介质，可调节Aurora-A蛋白的稳定性。我们发现异位表达或多胺诱导表达的Az1可降低Aurora-A的稳态水平。Az1对Aurora-A周转的影响显示为蛋白酶体依赖性，但不依赖Ub。Az1在体内与Aurora-A相互作用，且Aurora-A与Az1之间的相互作用对于Az1介导的Aurora-A降解至关重要。此外，我们观察到AURKAIP1无法促进与Az1相互作用存在缺陷的Aurora-A突变体的降解。下调Az1功能的Az抑制剂（AzI）的共表达也消除了AURKAIP1介导的Aurora-A降解。我们进一步证明AURKAIP1、Az1和Aurora-A可形成三元复合物，且AURKAIP1增强了Az1与Aurora-A之间的相互作用。我们提出，AURKAIP1可能通过增强Az1与Aurora-A的结合亲和力，在Az1的上游发挥作用，以促进识别、靶向蛋白酶体及随后的降解。
