An alternative EGFR activation by patient-derived R252C mutation promotes cancer progression.

Mutations in the extracellular or intracellular domains of epidermal growth factor receptor (EGFR) are implicated in the development of various cancers. While the intracellular mutations of EGFR have been extensively studied, the function of extracellular mutations remains poorly understood. In this study, we identify an EGFR mutant (EGFR R252C) in a patient with multifocal lung cancer and glioma, in which arginine (R) 252 is mutated to cysteine (C) in the EGFR extracellular domain. This mutation promotes C252-C252 disulfide-mediated EGFR dimerization and induces a conformational change of EGFR, leading to absent autophosphorylation and enhanced direct interaction between EGFR and extracellular signal-regulated protein kinase 1/2 (ERK1/2). Importantly, EGFR directly phosphorylates ERK1/2 at threonine (T) 202 / tyrosine (Y) 204 and activates ERK1/2, thereby promoting tumor cell proliferation and tumor growth in vivo. Afatinib, a second-generation EGFR tyrosine kinase inhibitor, effectively suppresses primary tumor growth and extends progression-free survival in the patient with multifocal lung cancer and glioma driven by EGFR R252C. Our finding elucidates the activation mechanism of this extracellular EGFR mutation and demonstrates the efficacy of afatinib in treating lung cancer or glioma patients with this variant.