MDM2 Promotes Cell Motility and Invasiveness by Regulating E-Cadherin Degradation

Abstract

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.

We thank Jiandong Chen (H. Lee Moffitt Comprehensive Cancer Center and Research Institute, Tampa, FL), Mark A. McNiven, and Alexandre Benmerah for their generosity in providing the expression plasmids. We thank Guillermina Lozano for the knockout MEF cells. We also thank Dipak K Giri, Peter Zhou, and Lei Shen for their early contributions to this work and Ulrich Hermanto and Jeng C. Cheng for editing the manuscript.

This work was supported by grants from NIH P01 CA 099031 and M. D. Anderson Cancer Center Core Grant CA16672 and was also partially supported by the National Breast Cancer Foundation and the Patel Memorial Breast Cancer Research Foundation.