Oncogenic mutations at the EGFR ectodomain structurally converge to remove a steric hindrance on a kinase-coupled cryptic epitope

TitleOncogenic mutations at the EGFR ectodomain structurally converge to remove a steric hindrance on a kinase-coupled cryptic epitope
Publication TypeJournal Article
Year of Publication2019
AuthorsOrellana, Laura, Thorne Amy H., Lema Rafael, Gustavsson Johan, Parisian Alison D., Hospital Adam, Cordeiro Tiago N., Bernadó Pau, Scott Andrew M., Brun-Heath Isabelle, Lindahl Erik, Cavenee Webster K., Furnari Frank B., and Orozco Modesto
JournalProceedings of the National Academy of Sciences
Date Published04/2019

EGFR cancer mutations display an astonishing tissue-specific asymmetry: in lung cancer, mutations target the intracellular kinase (KD), while in glioblastomas (GBMs), a variety of missense clusters and deletions concentrate at the ectodomain (ECD). Intriguingly, GBM-activating mutations share a paradoxical preference for inhibitors that bind the inactive kinase. By integrating simulations, small-angle X-ray scattering, and GBM models, we demonstrate that ECD mutants converge to a transition state characterized by a cryptic epitope, allosterically coupled to an intermediate kinase, and synergistically blocked by antibodies and inhibitors. Our findings indicate that apparently heterogeneous aberrations remove a similar steric restrain on KD activation. The diversity of structural tricks in ECD mutants to achieve the same conformational state constitutes a potent example of molecular mimicry and convergence.Epidermal growth factor receptor (EGFR) signaling is initiated by a large ligand-favored conformational change of the extracellular domain (ECD) from a closed, self-inhibited tethered monomer, to an open untethered state, which exposes a loop required for strong dimerization and activation. In glioblastomas (GBMs), structurally heterogeneous missense and deletion mutations concentrate at the ECD for unclear reasons. We explore the conformational impact of GBM missense mutations, combining elastic network models (ENMs) with multiple molecular dynamics (MD) trajectories. Our simulations reveal that the main missense class, located at the I-II interface away from the self-inhibitory tether, can unexpectedly favor spontaneous untethering to a compact intermediate state, here validated by small-angle X-ray scattering (SAXS). Significantly, such intermediate is characterized by the rotation of a large ECD fragment (N-TR1), deleted in the most common GBM mutation, EGFRvIII, and that makes accessible a cryptic epitope characteristic of cancer cells. This observation suggested potential structural equivalence of missense and deletion ECD changes in GBMs. Corroborating this hypothesis, our FACS, in vitro, and in vivo data demonstrate that entirely different ECD variants all converge to remove N-TR1 steric hindrance from the 806-epitope, which we show is allosterically coupled to an intermediate kinase and hallmarks increased oncogenicity. Finally, the detected extraintracellular coupling allows for synergistic cotargeting of the intermediate with mAb806 and inhibitors, which is proved herein.