Increased mdm-2 expression in a p53-independent manner blocks UV-induced cell cycle arrest and apoptosis in human osteosarcoma cells
Increased mdm-2 expression in a p53-independent manner blocks UV-induced cell cycle arrest and apoptosis in human osteosarcoma cells
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DOI：
10.1159/000073842
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发表时间：
2003-11-01
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影响因子：
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通讯作者：
McMasters, KM
中科院分区：
文献类型：
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作者：
Dong, YB;Yang, HL;McMasters, KM
DNA损伤导致p53水平升高，这是启动p53介导的细胞周期阻滞和/或凋亡所必需的。P53与MDM-2形成一个反馈控制回路：P53可以反激活MDM-2基因，而高水平的MDM-2抑制P53的反激活，促进P53的快速降解。在本研究中，我们研究了内源性MDM-2和p53在紫外线诱导的MDM-2过表达细胞系DNA损伤后的相互作用。本研究使用了一种人类骨肉瘤细胞系（OsACL，它含有野生型p53并过表达MDM-2蛋白）。本研究表明，在紫外线处理后，尽管存在高水平的内源性MDM-2，但OsACL细胞中的p53水平升高；然而，使用p53报告系统的CAT检测显示该p53是转录失活的。虽然p53的转激活受到抑制，但紫外线照射后MDM-2水平明显升高。Northern blot分析显示，MDM-2蛋白水平的升高是MDM-2 mRNA水平升高的结果，可能是由于转录增加所致。细胞周期分析显示，OsACL细胞对紫外线诱导的凋亡具有明显的抗性。用反义mdm-2质粒转染OsACL细胞可下调mdm-2的表达，增加紫外线诱导的细胞凋亡。综上所述，MDM-2过表达可通过抑制p53转录活性来阻断紫外线诱导的细胞周期阻滞和凋亡。此外，紫外线照射后OsACL细胞中MDM-2的表达增加似乎与p53无关的机制有关。版权所有(C) 2003 S. Karger AG，巴塞尔。
DNA damage results in an increase in p53 levels, which is required to initiate a p53-mediated cell cycle arrest and/or apoptosis. P53 and MDM-2 form a feedback control loop: while p53 can transactivate the mdm-2 gene, high levels of MDM-2 inhibit p53 transactivation as well as promote rapid degradation of P53. In the present study, we investigated the interaction between endogenous MDM-2 and p53 following UV-induced DNA damage in an MDM-2 overexpression cell line. A human osteosarcoma cell line (OsACL, which contains wild-type p53 and overexpresses MDM-2 protein) was used in this study. Here we show that following UV treatment, p53 levels increased in the OsACL cells despite the presence of high-level endogenous MDM-2; however, CAT assays using a p53 reporter system revealed that this P53 was transcriptionally inactive. Although p53 transactivation was inhibited, MDM-2 levels rose markedly following UV irradiation. Northern blot analysis revealed that the increase in MDM-2 protein levels was a result of increased levels of mdm-2 mRNA, possibly due to increased transcription. Cell cycle analysis revealed that OsACL cells were markedly resistant to UV-induced apoptosis. Transfection of OsACL cells with an anti-sense mdm-2 plasmid dowregulated MDM-2 expression and increased UV-induced apoptosis. In conclusion, MDM-2 overexpression can block UV-induced cell cycle arrest and apoptosis by inhibiting p53 transcriptional activity. Furthermore, increased expression of MDM-2 in OsACL cells following UV irradiation appears to be related to p53-independent mechanisms. Copyright (C) 2003 S. Karger AG, Basel.