EGFR Activation and Conformational "Convergence": An Emerging Allosteric Model From Cancer Mutations.

Since its isolation nearly 50 years ago, the Epidermal Growth Factor Receptor (EGFR) has become one of the most extensively studied oncogenes. However, scarce data on the full-length receptor, together with its flexibility, has left critical aspects of its activation mechanism unresolved. This has hampered the interpretation of mutations, which are highly asymmetric, tissue-specific, and linked to antagonistic drug sensitivities. While in lung cancer, oncogenic mutations target the kinase and respond to type-I tyrosine kinase inhibitors (TKIs), in brain glioblastoma (GBM), highly heterogeneous mutations focus on the ectodomain (ECD) but share preferential responses to inhibitors that target intermediate active/inactive features in the kinase. Here, we recapitulate current structural and mutational data to shed light on how its extra- and intracellular domains are coupled, with a special focus on an ECD transition state in GBM. This intermediate, first detected by antibodies and later captured in simulations, is characterized by the flexible rotation of the same extracellular fragment deleted in the most frequent GBM mutation, EGFRvIII. The convergence of missense and deletion ECD changes to flexibilize or remove the same piece, hallmarked by a cryptic epitope, offers an explanation for shared drug responses. Based on these observations, we discuss a putative allosteric mechanism, where the extracellular and intracellular sides are tightly coupled in preformed dimers, and the rigidity of the ECD is key to preventing kinase activation. While GBM mutations bypass the steric blockade, lung cancer mutants directly enhance catalytic activity, stabilizing antagonistic states and explaining their opposite drug sensitivities.