Abl Tyrosine Kinase Regulates Endocytosis of the Epidermal Growth Factor Receptor

Barbara Tanos,Ann Marie Pendergast

doi:10.1074/jbc.m603126200

Abstract

Signal attenuation from ligand-activated epidermal growth factor receptor (EGFR) is mediated in part by receptor endocytosis and trafficking to the lysosomal degradative compartment. Uncoupling the activated EGFR from endocytosis and degradation has emerged as a mechanism for oncogenic activation of the EGFR. The Abl nonreceptor tyrosine kinase is activated by ligand-stimulated EGFR, but the role of Abl in EGFR signaling has not been defined. Here we uncovered a novel role for the activated Abl kinase in the regulation of EGFR endocytosis. We show that activated Abl impairs EGFR internalization. Moreover, we show that activated Abl phosphorylates the EGFR primarily on tyrosine 1173, and that mutation of this site to phenylalanine restores ligand-dependent endocytosis of the EGFR in the presence of activated Abl. Furthermore, we show that activated Abl allows the ligand-activated EGFR to escape Cbl-dependent down-regulation by inhibiting the accumulation of Cbl at the plasma membrane in response to epidermal growth factor stimulation and disrupting the formation of the EGFR.Cbl complex without affecting Cbl protein stability. These findings reveal a novel role for Abl in promoting increased cell-surface expression of the EGFR and suggest that Abl/EGFR signaling may cooperate in human tumors.

Highlights

epidermal growth factor receptor (EGFR) signaling is associated with mutations of the EGFR itself or molecules required for receptor endocytosis [1, 3]
We identify tyrosine 1173 on the EGFR as the primary site phosphorylated by Abl, and we show that mutation of this site to phenylalanine restores normal ligand-induced EGFR internalization in the presence of kinase-active Abl-PP
Together these findings show that active Abl kinase negatively regulates EGFR internalization

Summary

Introduction

EGFR signaling is associated with mutations of the EGFR itself or molecules required for receptor endocytosis [1, 3]. EGFR internalization is inhibited in cells depleted of the Grb adaptor or by mutation of the Grb2-binding site on the receptor [9, 10, 12]. EGFR endocytosis is restored in Grb2-depleted cells by a chimeric protein that fuses the Grb Src homology 2 [2] domain to Cbl [10]. These findings show that in addition to a role in lysosomal sorting and degradation of the receptor, Cbl regulates EGFR internalization. We show that the activated Abl kinase phosphorylates the EGFR at specific sites and uncouples the receptor from ligand-mediated internalization. Abl and the EGFR may function synergistically in the pathogenesis of human tumors

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Conclusion