Antibody-induced dimerization activates the epidermal growth factor receptor tyrosine kinase.
The relationship between epidermal growth factor receptor (EGF-R) protein tyrosine kinase activation and ligand-induced receptor dimerization was investigated using several bivalent anti-EGF-R antibodies directed against various receptor epitopes. In A431 membrane preparations and permeabilized cells, all antibodies were able to activate the EGF-R tyrosine kinase, as measured by EGF-R autophosphorylation and phosphorylation of other substrates on tyrosine residues. EGF-R tyrosine kinase activation correlated strongly with the induction of EGF-R dimerization. (i) Both processes specifically occurred in a narrow antibody concentration range; (ii) both processes required the presence of detergent; and (iii) both processes depended on antibody bivalence since monovalent Fab fragments were inactive yet regained full activity after cross-linking by a second bivalent antibody. These data demonstrate that antibody bivalence is essential and sufficient for EGF-R activation and that activation occurs regardless of the EGF-R epitope recognized. Finally, EGF-R dimerization was shown not to depend on receptor autophosphorylation since it still occurred in the absence of ATP. Also, partial inhibition of the tyrosine kinase activity by the specific EGF-R tyrosine kinase inhibitor tyrphostin AG 213 did not affect formation of EGF-R dimers. Taken together these results demonstrate that induction of EGF-R dimerization is sufficient and in case of antibody action, essential, for activation of the EGF-R tyrosine kinase and thus provide strong support for an intermolecular mechanism of EGF-R tyrosine kinase activation.
Spaargaren
M
M
Hubrecht Laboratory, Netherlands Institute for Developmental Biology, Utrecht.
Defize
L H
LH
Boonstra
J
J
de Laat
S W
SW
D000911:Antibodies, Monoclonal; D002460:Cell Line; D002462:Cell Membrane / Q000201:enzymology; D003902:Detergents / Q000737:chemistry; D004789:Enzyme Activation; D066246:ErbB Receptors / Q000378:metabolism*; D006801:Humans; D015394:Molecular Structure; D010766:Phosphorylation; D011485:Protein Binding; D011505:Protein-Tyrosine Kinases / Q000378:metabolism*; D011940:Receptor Aggregation; D013329:Structure-Activity Relationship
D000911:Antibodies, Monoclonal; D003902:Detergents; D066246:ErbB Receptors; D011505:Protein-Tyrosine Kinases