Keleti J, Quezado M M, Abaza M M, Raffeld M, Tsokos M
Pediatric Tumor Biology-Ultrastructural Pathology Section, Laboratory of Pathology, National Cancer Institute, National Institutes of Health, Bethesda, MD, USA.
Am J Pathol. 1996 Jul;149(1):143-51.
MDM2 gene overexpression has been implicated in the pathogenesis of human neoplasia via inhibition of the p53 tumor-suppressor function. To investigate the potential involvement of the MDM2 oncogene in the pathogenesis of childhood rhabdomyosarcoma (RMS) we studied MDM2 abnormalities in six RMS cell lines in correlation with the p53 status. Three showed overexpression of MDM2 mRNA and protein, one with concomitant MDM2 gene amplification. All three lacked p53 mutation and expressed low levels of p53 mRNA but exhibited elevated p53 proteins. Double immunostaining revealed that the overexpressed MDM2 and p53 proteins were co-localized to the same cell nuclei. Furthermore, the two proteins were physically associated, as shown by co-immunoprecipitation and Western blot analysis. The half-life of the p53 protein was prolonged in the MDM2-expressing RMS cells. The extended half-life wildtype p53 protein and its complex formation with the elevated MDM2 suggest that the underlying mechanism for p53 protein accumulation in these cell lines is p53 stabilization by an overabundant MDM2 protein. The overexpressed MDM2 protein had a short half-life. The three remaining RMS cell lines exhibited low MDM2 mRNA and protein levels and carried p53 mutations. This study suggest that MDM2 overexpression represents an alternative mechanism for p53 inactivation in a subset of childhood RMS without p53 mutations. The results further indicate that the elevated MDM2 protein is responsible for wildtype p53 protein accumulation via stabilization.
MDM2基因的过表达通过抑制p53肿瘤抑制功能参与了人类肿瘤的发病机制。为了研究MDM2癌基因在儿童横纹肌肉瘤（RMS）发病机制中的潜在作用，我们研究了6种RMS细胞系中的MDM2异常情况，并与p53状态进行关联分析。其中3种细胞系显示MDM2 mRNA和蛋白过表达，其中1种伴有MDM2基因扩增。这3种细胞系均无p53突变，p53 mRNA表达水平较低，但p53蛋白水平升高。双重免疫染色显示，过表达的MDM2和p53蛋白共定位于同一细胞核。此外，免疫共沉淀和蛋白质印迹分析表明这两种蛋白存在物理相互作用。在表达MDM2的RMS细胞中，p53蛋白的半衰期延长。野生型p53蛋白半衰期的延长及其与升高的MDM2形成复合物表明，这些细胞系中p53蛋白积累的潜在机制是p53被过量的MDM2蛋白稳定化。过表达的MDM2蛋白半衰期较短。其余3种RMS细胞系显示MDM2 mRNA和蛋白水平较低，并携带p53突变。本研究表明，MDM2过表达是儿童RMS中一部分无p53突变的肿瘤中p53失活的另一种机制。结果进一步表明，升高的MDM2蛋白通过稳定化作用导致野生型p53蛋白积累。
