Department of Neurosurgery, Shanghai Changzheng Hospital, Second Military Medical University, Shanghai 200003, China, Department of Neurosurgery, the 105th Hospital of PLA, Hefei 230000, Anhui Province, China.
Department of Neurosurgery, Shanghai Changzheng Hospital, Second Military Medical University, Shanghai 200003, China.
Carcinogenesis. 2014 Jul;35(7):1500-9. doi: 10.1093/carcin/bgu015. Epub 2014 Jan 20.
The mouse double minute 4 (MDM4) oncoprotein may inhibit tumorigenesis by regulating the apoptotic mediator p53. Ubiquitin-specific protease 2a (USP2a) is a deubiquitinating enzyme that protects MDM4 against degradation, so USP2-MDM4 interaction may be a key determinant of the malignant potential of human cancers. MDM4 and USP2a, as well as the MDM4-USP2a complex, were more highly expressed in glioblastoma multiforme tissue samples from patients with good prognosis compared with patients with poor prognosis. Analysis of the prognostic parameters indicated that MDM4 expression was positively correlated with an increased likelihood for survival. Compared with the poor prognosis patients, mitochondria from good prognosis glioma patients contained higher levels of both MDM4 and the proapoptotic protein p53Ser46(P). In U87MG glioma cell line, the overexpression of MDM4 enhanced ultraviolet (UV)-induced cytochrome c release and apoptosis. In contrast, MDM4 knockdown decreased mitochondrial p53Ser46(P) levels and rescued cells from UV-induced apoptosis. The expression of MDM4 and USP2a were positively correlated with each other. MDM4-USP2a complexes were found only in the cytoplasmic fraction, whereas the mitochondrial fraction contained MDM4-p53Ser46(P) and MDM4-Bcl-2 complexes. Overexpression of USP2a increased p53 and p53Ser46(P) levels in the mitochondria, whereas simultaneous MDM4 knockdown completely reversed this effect. UV-induced apoptosis was reduced by USP2a knockdown but restored by the simultaneous overexpression of MDM4. This apoptotic response was reduced by knockdown of p53 but not p21. Our results suggest that USP2a binds to and stabilizes MDM4; thus in turn, it enhances the mitochondrial localization of p53 and promotes apoptosis in glioma cells.
鼠双微体基因 4（MDM4）癌蛋白可能通过调节凋亡介质 p53 来抑制肿瘤发生。泛素特异性蛋白酶 2a（USP2a）是一种去泛素化酶，可保护 MDM4 免受降解，因此 USP2-MDM4 相互作用可能是人类癌症恶性潜能的关键决定因素。与预后不良的患者相比，预后良好的胶质母细胞瘤患者的组织样本中 MDM4 和 USP2a 以及 MDM4-USP2a 复合物的表达水平更高。对预后参数的分析表明，MDM4 的表达与存活可能性的增加呈正相关。与预后不良的患者相比，来自预后良好的神经胶质瘤患者的线粒体中 MDM4 和促凋亡蛋白 p53Ser46（P）的水平更高。在 U87MG 神经胶质瘤细胞系中，MDM4 的过表达增强了紫外线（UV）诱导的细胞色素 c 释放和细胞凋亡。相比之下，MDM4 的敲低降低了线粒体 p53Ser46（P）水平，并挽救了细胞免受 UV 诱导的凋亡。MDM4 和 USP2a 的表达呈正相关。MDM4-USP2a 复合物仅存在于细胞质部分，而线粒体部分含有 MDM4-p53Ser46（P）和 MDM4-Bcl-2 复合物。USP2a 的过表达增加了线粒体中 p53 和 p53Ser46（P）的水平，而同时敲低 MDM4 则完全逆转了这一作用。USP2a 的敲低减少了 UV 诱导的细胞凋亡，但同时过表达 MDM4 则恢复了这种作用。这种凋亡反应被 p53 的敲低所减弱，但不是被 p21 的敲低所减弱。我们的研究结果表明，USP2a 与 MDM4 结合并稳定其结构；从而反过来增强了 p53 的线粒体定位并促进了神经胶质瘤细胞的凋亡。
