Yang Jer-Yen, Zong Cong S, Xia Weiya, Wei Yongkun, Ali-Seyed Mohamed, Li Zheng, Broglio Kristine, Berry Donald A, Hung Mien-Chie
Department of Molecular and Cellular Oncology, University of Texas M. D. Anderson Cancer Center, Unit 108, Houston, TX 77030, USA.
Mol Cell Biol. 2006 Oct;26(19):7269-82. doi: 10.1128/MCB.00172-06.
Gene amplification and protein overexpression of MDM2, which is often found in certain types of cancers, indicate that MDM2 plays an important role in tumorigenesis. Interestingly, several clinical reports have demonstrated that amplification of the MDM2 gene correlates with the metastatic stage. Using an antibody array assay, we identified E-cadherin as an MDM2-binding protein and confirmed that E-cadherin is a substrate for the MDM2 E3 ubiquitin ligase. We demonstrate that MDM2 interacts in vivo with E-cadherin, resulting in its ubiquitination and degradation. This regulation appears to be clinically relevant, as we found a significant correlation between high MDM2 and low E-cadherin protein levels in resected tumor specimens recovered from breast cancer patients with lymph node metastases. Ectopic expression of MDM2 in breast cancer cells was found to disrupt cell-cell contacts and enhance cell motility and invasive potential. We found that E-cadherin and MDM2 colocalized on the plasma membrane and in the early endosome, where ubiquitin moieties were attached to E-cadherin. Blocking endocytosis with dominant-negative mutants of dynamin abolished the association of MDM2 with E-cadherin, prevented E-cadherin degradation, and attenuated cell motility as observed by fluorescence microscopy. Thus, we provide evidence to support a novel role for MDM2 in regulating cell adhesions by a mechanism that involves degrading and down-regulating the expression of E-cadherin via an endosome pathway. This novel MDM2-regulated pathway is likely to play a biologically relevant role in cancer metastasis.
MDM2的基因扩增和蛋白过表达在某些类型的癌症中经常出现，这表明MDM2在肿瘤发生中起重要作用。有趣的是，一些临床报告表明MDM2基因的扩增与转移阶段相关。使用抗体阵列分析，我们鉴定出E-钙黏蛋白是一种MDM2结合蛋白，并证实E-钙黏蛋白是MDM2 E3泛素连接酶的底物。我们证明MDM2在体内与E-钙黏蛋白相互作用，导致其泛素化和降解。这种调节似乎具有临床相关性，因为我们在从有淋巴结转移的乳腺癌患者切除的肿瘤标本中发现，高MDM2水平与低E-钙黏蛋白水平之间存在显著相关性。发现MDM2在乳腺癌细胞中的异位表达会破坏细胞间接触并增强细胞运动性和侵袭潜能。我们发现E-钙黏蛋白和MDM2共定位于质膜和早期内体中，在那里泛素部分附着于E-钙黏蛋白。用发动蛋白的显性负性突变体阻断内吞作用消除了MDM2与E-钙黏蛋白的结合，阻止了E-钙黏蛋白的降解，并通过荧光显微镜观察到减弱了细胞运动性。因此，我们提供证据支持MDM2通过一种机制调节细胞黏附的新作用，该机制涉及通过内体途径降解和下调E-钙黏蛋白的表达。这种新的MDM2调节途径可能在癌症转移中发挥生物学相关作用。
