Autophosphorylation mutants of the EGF-receptor signal through auxiliary mechanisms involving SH2 domain proteins.

Many growth factors bind and activate receptors with intrinsic protein tyrosine kinase activity. Once activated these receptors undergo autophosphorylation allowing them to bind src homology 2 (SH2) domain proteins. We mutated or deleted all known autophosphorylation sites of the Epidermal Growth Factor-Receptor (EGF-receptor) and examined the effects of these mutations on gene expression, MAP kinase activation and mitogenesis. We find that the mutant receptors, although unable to bind SH2 domain proteins, are fully competent to activate all these signaling pathways. Our data indicates that these mutant receptors utilize several different compensatory mechanisms to overcome the lack of autophosphorylation sites. One mechanism is the use of tyrosine phosphorylated cellular proteins as surrogates for binding SH2 domain proteins. We find that all these mutant receptors can induce tyrosine phosphorylation of Shc which then acts as a binding site for the Grb2/Sos signaling complex. This data indicates that even though autophosphorylation mutants of the EGF-receptor cannot directly bind SH2 domain proteins, they are able to use auxiliary signals that result in activation of SH2 domain proteins crucial for mitogenesis.