ABSTRACT
The membrane cytoskeleton linker ezrin participates in several functions downstream of the receptor Met in response to Hepatocyte Growth Factor (HGF) stimulation. Here we report a novel interaction of ezrin with a HECT E3 ubiquitin ligase, WWP1/Aip5/Tiul1, a potential oncogene that undergoes genomic amplification and overexpression in human breast and prostate cancers. We show that ezrin binds to the WW domains of WWP1 via the consensus motif PPVY(477) present in ezrin's C-terminus. This association results in the ubiquitylation of ezrin, a process that requires an intact PPVY(477) motif. Interestingly ezrin ubiquitylation does not target the protein for degradation by the proteasome. We find that ezrin ubiquitylation by WWP1 in epithelial cells leads to the upregulation of Met level in absence of HGF stimulation and increases the response of Met to HGF stimulation as measured by the ability of the cells to heal a wound. Interestingly this effect requires ubiquitylated ezrin since it can be rescued, after depletion of endogenous ezrin, by wild type ezrin but not by a mutant of ezrin that cannot be ubiquitylated. Taken together our data reveal a new role for ezrin in Met receptor stability and activity through its association with the E3 ubiquitin ligase WWP1. Given the role of Met in cell proliferation and tumorigenesis, our results may provide a mechanistic basis for understanding the role of ezrin in tumor progression.
Subject(s)
Cytoskeletal Proteins/metabolism , Proto-Oncogene Proteins c-met/metabolism , Ubiquitin-Protein Ligases/metabolism , Ubiquitination/physiology , Breast Neoplasms/genetics , Breast Neoplasms/metabolism , Cell Line, Tumor , Cell Membrane/metabolism , Cytoskeletal Proteins/genetics , Female , Gene Expression Regulation, Neoplastic , Humans , Male , Prostatic Neoplasms/genetics , Prostatic Neoplasms/metabolism , Proteasome Endopeptidase Complex/genetics , Proteasome Endopeptidase Complex/metabolism , Proto-Oncogene Proteins c-met/genetics , Tumor Cells, Cultured , Ubiquitin-Protein Ligases/geneticsABSTRACT
The highly related ERM (Ezrin, Radixin, Moesin) proteins provide a regulated linkage between the membrane and the underlying actin cytoskeleton. They also provide a platform for the transmission of signals in responses to extracellular cues. Studies in different model organisms and in cultured cells have highlighted the importance of ERM proteins in the generation and maintenance of specific domains of the plasma membrane. A central question is how do ERM proteins coordinate actin filament organization and membrane protein transport/stability with signal transduction pathways to build up complex structures? Through their interaction with numerous partners including membrane proteins, actin cytoskeleton and signaling molecules, ERM proteins have the ability to organize multiprotein complexes in specific cellular compartments. Likewise, ERM proteins participate in diverse functions including cell morphogenesis, endocytosis/exocytosis, adhesion and migration. This review focuses on aspects still poorly understood related to the function of ERM proteins in epithelial cell adhesion and migration.
Subject(s)
Cell Movement , Cytoskeletal Proteins/metabolism , Cytoskeleton/metabolism , Membrane Proteins/metabolism , Microfilament Proteins/metabolism , Actins/metabolism , Animals , Biomarkers, Tumor/genetics , Biomarkers, Tumor/metabolism , Caenorhabditis elegans , Cell Adhesion , Cell Membrane/metabolism , Cytoskeletal Proteins/genetics , Drosophila melanogaster , Epithelial Cells/cytology , Epithelial Cells/metabolism , Gene Expression , Humans , Intercellular Junctions/physiology , Membrane Proteins/genetics , Mice , Microfilament Proteins/genetics , Models, Molecular , Neoplasms/genetics , Neoplasms/metabolism , Protein Interaction Domains and Motifs , Signal TransductionABSTRACT
In the degradative pathway, the progression of cargos through endosomal compartments involves a series of fusion and maturation events. The HOPS (homotypic fusion and protein sorting) complex is part of the machinery that promotes the progression from early to late endosomes and lysosomes by regulating the exchange of small GTPases. We report that an interaction between subunits of the HOPS complex and the ERM (ezrin, radixin, moesin) proteins is required for the delivery of EGF receptor (EGFR) to lysosomes. Inhibiting either ERM proteins or the HOPS complex leads to the accumulation of the EGFR into early endosomes, delaying its degradation. This impairment in EGFR trafficking observed in cells depleted of ERM proteins is due to a delay in the recruitment of Rab7 on endosomes. As a consequence, the maturation of endosomes is perturbed as reflected by an accumulation of hybrid compartments positive for both early and late endosomal markers. Thus, ERM proteins represent novel regulators of the HOPS complex in the early to late endosomal maturation.
