Hsu Hsin-Ling, Choy Chik On, Kasiappan Ravi, Shih Hung-Ju, Sawyer Jeffrey R, Shu Chung-Li, Chu Kang-Lin, Chen Yi-Rong, Hsu Hsin-Fen, Gartenhaus Ronald B
National Health Research Institutes, No. 35, Keyan Road, Zhunan Town, Miaoli County 350, Taiwan, ROC.
DNA Repair (Amst). 2007 Sep 1;6(9):1319-32. doi: 10.1016/j.dnarep.2007.02.028. Epub 2007 Apr 6.
Tumor suppressor p53 protein mediates checkpoint controls and the apoptotic program that are critical for maintaining genomic integrity and preventing tumorigenesis. Forced-induction of MCT-1 decreased p53 expression before and after genomic insults. While inhibiting protein synthesis, the levels of ubiquinated-p53 and the phospho-MDMA2 were significantly increased in ectopic MCT-1 cells. Abrogation of the proteosome degradation process attenuated p53 destabilization and p21 down-regulation by MCT-1. Concomitantly, MCT-1 overexpression enhanced the phosphorylation status of MAPK (ERK1/ERK2). While MCT-1 gene knockdown or MEK/ERK pathway inhibition dramatically reduced MAPK phosphorylation, the genotoxin-induced p53 and p21 production were noticeably elevated. Upon Etoposide treatment, ectopic MCT-1 cells relaxed S-phase and G2/M checkpoints followed by G1 phase progressing. Moreover, cells inducing with MCT-1 abridged accumulations of G2/M populations in the response to gamma-irradiation. The polyploidy (DNA content>4N) populations were increased in association with p53 loss in MCT-1 oncogenic cells. Alkaline comet assay validated that ectopic MCT-1 cells were less susceptibility to the genotoxicity. Furthermore, the allocation of nuclear MCT-1 induced by the genotoxic stress was moderately coincided with gamma-H2AX appearances. Throughout damage-repairing process, ectopic MCT-1 cells displayed many larger chromosomes and multiple chromosomal fusions compared to the controls that showed increase in chromosomal breaks/gaps and minute chromosomal fragments. Spectral karyotyping analysis precisely identified the acquisition of a single extra copy of chromosome 14 together with a complex genome organizations in ectopic MCT-1 cells, including extra copies of chromosome segments that had been translocated to derivative chromosomes 6 [der(6)] and 9 [der(9)]. In conclusion, MCT-1 deregulates p53-p21 network and impairs the damage checkpoints those are robustly connected to oncogenic chromosomal abnormalities.
肿瘤抑制蛋白p53介导着对维持基因组完整性和预防肿瘤发生至关重要的检查点控制和凋亡程序。在基因组损伤前后，MCT-1的强制诱导均降低了p53的表达。在抑制蛋白质合成的情况下，异位表达MCT-1的细胞中泛素化p53和磷酸化MDMA2的水平显著增加。蛋白酶体降解过程的废除减弱了MCT-1对p53稳定性的破坏和p21的下调。同时，MCT-1的过表达增强了MAPK（ERK1/ERK2）的磷酸化状态。虽然MCT-1基因敲低或MEK/ERK途径抑制显著降低了MAPK磷酸化，但基因毒素诱导的p53和p21产生明显升高。在用依托泊苷处理后，异位表达MCT-1的细胞放松了S期和G2/M检查点，随后G1期进展。此外，用MCT-1诱导的细胞在对γ射线照射的反应中缩短了G2/M群体的积累。在MCT-1致癌细胞中，多倍体（DNA含量>4N）群体随着p53的缺失而增加。碱性彗星试验证实异位表达MCT-1的细胞对基因毒性的敏感性较低。此外，基因毒性应激诱导的核MCT-1的分布与γ-H2AX的出现适度吻合。在整个损伤修复过程中，与显示染色体断裂/间隙和微小染色体片段增加的对照相比，异位表达MCT-1的细胞显示出许多更大的染色体和多个染色体融合。光谱核型分析精确地鉴定出异位表达MCT-1的细胞中获得了一条额外的14号染色体拷贝以及复杂的基因组组织，包括已易位到衍生染色体6 [der(6)] 和9 [der(9)] 的染色体片段的额外拷贝。总之，MCT-1失调p53-p21网络并损害了与致癌染色体异常密切相关的损伤检查点。
