The RING Finger of c-Cbl Mediates Desensitization of the Epidermal Growth Factor Receptor

Hadassa Waterman,Gil Levkowitz,Yosef Yarden,Iris Alroy

doi:10.1074/jbc.274.32.22151

Hadassa Waterman, Gil Levkowitz + Show 2 more

Open Access

https://doi.org/10.1074/jbc.274.32.22151

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Abstract

Ligand-induced activation of surface receptors, including the epidermal growth factor receptor (EGFR), is followed by a desensitization process involving endocytosis and receptor degradation. c-Cbl, a tyrosine phosphorylation substrate shared by several signaling pathways, accelerates desensitization by recruiting EGFR and increasing receptor polyubiquitination. Here we demonstrate that the RING type zinc finger of c-Cbl is essential for ubiquitination and subsequent desensitization of EGFR. Mutagenesis of a single cysteine residue impaired the ability of c-Cbl to enhance both down-regulation and ubiquitination of EGFR in living cells, although the mutant retained binding to the activated receptor. Consequently, the mutant form of c-Cbl acquired a dominant inhibitory function and lost the ability to inhibit signaling downstream to EGFR. In vitro reconstitution of EGFR ubiquitination implies that the RING finger plays an essential direct role in ubiquitin ligation. Our results attribute to the RING finger of c-Cbl a causative role in endocytic sorting of EGFR and desensitization of signal transduction.

Highlights

We have reported recently that c-Cbl can accelerate the rate of EGFR1 degradation by increasing conjugation of polyubiquitin to an endocytosed epidermal growth factor receptor (EGFR) [1]
Noteworthy is the fact that the two other family members of c-Cbl carry an intact RING fingers (RFs) [8, 9], but oncogenic Cbl variants are defective in the RF [10, 11]
To substantiate the effect on down-regulation, we examined the effect of C381A-Cbl on EGFR degradation and ubiquitination

Summary

Introduction

We have reported recently that c-Cbl can accelerate the rate of EGFR1 degradation by increasing conjugation of polyubiquitin to an endocytosed EGFR [1]. Mutagenesis of the RING Finger Impairs Cbl-induced Downregulation of EGFR—The recently reported ability of c-Cbl to enhance degradation of the EGFR [1] and the platelet-derived growth factor receptor [3] can explain the phenotype of Sli-1 mutant worms [2], but they leave open the mechanism underlying increased ubiquitination and degradation.

Results

Conclusion