Rab7 Activity Affects Epidermal Growth Factor:Epidermal Growth Factor Receptor Degradation by Regulating Endocytic Trafficking from the Late Endosome

Steven J Bahr,Brian P Ceresa

doi:10.1074/jbc.m504175200

Abstract

The epidermal growth factor receptor (EGFR) is a member of the receptor tyrosine kinase family. Ligand (epidermal growth factor or EGF) binding to the EGFR results in the coordinated activation and integration of biochemical signaling events to mediate cell growth, migration, and differentiation. One mechanism the cell utilizes to orchestrate these events is ligand-mediated endocytosis through the canonical clathrin-mediated endocytic pathway. Identification of proteins that regulate the intracellular movement of the EGF.EGFR complex is an important first step in dissecting how specificity of EGFR signaling is conferred. We examined the role of the small molecular weight guanine nucleotide-binding protein (G-protein) rab7 as a regulator of the distal stages of the endocytic pathway. Through the transient expression of activating and inactivating mutants of rab7 in HeLa cells, we have determined that rab7 activity directly correlates with the rate of radiolabeled EGF and EGFR degradation. Furthermore, when inhibitory mutants of rab7 are expressed, the internalized EGF.EGFR complex accumulates in high-density endosomes that are characteristic of the late endocytic pathway. Thus, we conclude that rab7 regulates the endocytic trafficking of the EGF.EGFR complex by regulating its lysosomal degradation.

Highlights

In the resting state, the epidermal growth factor receptor (EGFR) exists as a monomeric, single membrane spanning protein
In addition to the signaling events initiated by ligand binding, EGFR stimulation triggers the internalization of the ligand-receptor complex via the canonical clathrin-mediated endocytic pathway [6]
There is literature indicating that dynamin coordinates EGFR endocytosis [13], rab5 has a role in mediating entry of the receptor into the early endosome (16 –18), and rab11 facilitates EGFR recycling to the plasma membrane [19]

Summary

Introduction

The EGFR exists as a monomeric, single membrane spanning protein. Binding of its ligand to the extracellular domain of the receptor induces dimerization of the receptor and stimulation of its intrinsic kinase domain This kinase transphosphorylates a number of carboxyl-terminal tyrosine residues in the cytoplasmic portion of the receptor that serve as docking sites for the Src homology 2 domains of downstream signaling effectors [2, 3]. Expression of inhibitory forms of rab have been implicated in slowing endocytic trafficking of proteins such as low density lipoprotein, vesicular stomatitis virus, mannose 6-phosphate receptor, and angiotensin II type 1A receptor [21,22,23,24]. It is unclear if functional rab is needed for normal EGF1⁄7EGFR endocytic trafficking

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Conclusion