Mechanism for activation of mutated epidermal growth factor receptors in lung cancer

Significance This is a unique report of receptor tyrosine kinase (RTK) “superacceptor” activity in which mutated EGFRs associated with lung cancer preferentially adopt the “acceptor” or “receiver” position in the presence of WT epidermal growth factor receptor (EGFR) or ErbB-2. The mechanism of superacceptor activity is defined by biochemical reconstitution data in combination with the first crystal structure of the L834R/T766M (L858R/T790M in alternate numbering) mutant EGFR kinase asymmetric dimer in an active conformation. The data imply that mutant/wild-type interactions play a key role in tumorigenesis as well as sensitivity of cells to various EGFR tyrosine kinase inhibitors, which could be therapeutically important. Notably, none of the previous studies involving mutated EGFR have studied the contribution of WT EGFRs in heterogeneous cell populations, although in nearly all instances wild-type EGFR alleles are preserved within EGFR mutant tumor cells. The initiation of epidermal growth factor receptor (EGFR) kinase activity proceeds via an asymmetric dimerization mechanism in which a “donor” tyrosine kinase domain (TKD) contacts an “acceptor” TKD, leading to its activation. In the context of a ligand-induced dimer, identical wild-type EGFR TKDs are thought to assume the donor or acceptor roles in a random manner. Here, we present biochemical reconstitution data demonstrating that activated EGFR mutants found in lung cancer preferentially assume the acceptor role when coexpressed with WT EGFR. Mutated EGFRs show enhanced association with WT EGFR, leading to hyperphosphorylation of the WT counterpart. Mutated EGFRs also hyperphosphorylate the related erythroblastic leukemia viral oncogene (ErbB) family member, ErbB-2, in a similar manner. This directional “superacceptor activity” is particularly pronounced in the drug-resistant L834R/T766M mutant. A 4-Å crystal structure of this mutant in the active conformation reveals an asymmetric dimer interface that is essentially the same as that in WT EGFR. Asymmetric dimer formation induces an allosteric conformational change in the acceptor subunit. Thus, superacceptor activity likely arises simply from a lower energetic cost associated with this conformational change in the mutant EGFR compared with WT, rather than from any structural alteration that impairs the donor role of the mutant. Collectively, these findings define a previously unrecognized mode of mutant-specific intermolecular regulation for ErbB receptors, knowledge of which could potentially be exploited for therapeutic benefit.