A mutant EGF-receptor defective in ubiquitylation and endocytosis unveils a role for Grb2 in negative signaling.
Ligand-induced desensitization of the epidermal growth factor receptor (EGFR) is controlled by c-Cbl, a ubiquitin ligase that binds multiple signaling proteins, including the Grb2 adaptor. Consistent with a negative role for c-Cbl, here we report that defective Tyr1045 of EGFR, an inducible c-Cbl docking site, enhances the mitogenic response to EGF. Signaling potentiation is due to accelerated recycling of the mutant receptor and a concomitant defect in ligand-induced ubiquitylation and endocytosis of EGFR. Kinetic as well as morphological analyses of the internalization-defective mutant receptor imply that c-Cbl-mediated ubiquitylation sorts EGFR to endocytosis and to subsequent degradation in lysosomes. Unexpectedly, however, the mutant receptor displayed significant residual ligand-induced ubiquitylation, especially in the presence of an overexpressed c-Cbl. The underlying mechanism seems to involve recruitment of a Grb2 c-Cbl complex to Grb2-specific docking sites of EGFR, and concurrent acceleration of receptor ubiquitylation and desensitization. Thus, in addition to its well-characterized role in mediating positive signals, Grb2 can terminate signal transduction by accelerating c-Cbl-dependent sorting of active tyrosine kinases to destruction.
Waterman
Hadassa
H
Department of Biological Regulation, The Weizmann Institute of Science, Rehovot 76100, Israel.
Katz
Menachem
M
Rubin
Chanan
C
Shtiegman
Keren
K
Lavi
Sara
S
Elson
Ari
A
Jovin
Thomas
T
Yarden
Yosef
Y
D048868:Adaptor Proteins, Signal Transducing; D000818:Animals; D002460:Cell Line; D004705:Endocytosis; D066246:ErbB Receptors / Q000235:genetics* / Q000502:physiology; D051380:GRB2 Adaptor Protein; D006801:Humans; D009154:Mutation; D011506:Proteins / Q000502:physiology*; D011518:Proto-Oncogene Proteins / Q000378:metabolism; D050721:Proto-Oncogene Proteins c-cbl; D011817:Rabbits; D015398:Signal Transduction / Q000235:genetics; D014162:Transfection; D044767:Ubiquitin-Protein Ligases; D014452:Ubiquitins / Q000378:metabolism
D048868:Adaptor Proteins, Signal Transducing; D051380:GRB2 Adaptor Protein; C495948:GRB2 protein, human; D011506:Proteins; D011518:Proto-Oncogene Proteins; D014452:Ubiquitins; D050721:Proto-Oncogene Proteins c-cbl; D044767:Ubiquitin-Protein Ligases; D066246:ErbB Receptors; C067419:CBL protein, human