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

Area of Science:

• Molecular Biology
• Structural Biology
• Cancer Research

Background:

• Epidermal growth factor receptor (EGFR) signaling is crucial for cell growth and is often dysregulated in glioblastomas (GBMs).
• EGFR activation involves a conformational change in its extracellular domain (ECD) from a closed to an open state.
• GBMs exhibit heterogeneous mutations in the EGFR ECD, but their structural and functional impact remains unclear.

Purpose of the Study:

• To investigate the conformational effects of missense mutations in the EGFR ECD in glioblastomas.
• To understand how different EGFR ECD mutations converge to a common oncogenic state.
• To explore potential therapeutic strategies targeting this common intermediate state.

Main Methods:

• Utilized elastic network models (ENMs) and molecular dynamics (MD) simulations to study EGFR ECD conformational changes.
• Employed small-angle X-ray scattering (SAXS) for experimental validation of simulated intermediate states.
• Conducted fluorescence-activated cell sorting (FACS), in vitro, and in vivo experiments to assess epitope accessibility and oncogenicity.

Main Results:

• GBM-associated missense mutations in the EGFR ECD can promote spontaneous untethering to a compact intermediate state.
• This intermediate state involves the rotation of the N-TR1 fragment, exposing a cryptic epitope (806-epitope) characteristic of cancer cells.
• Both missense and deletion mutations (like EGFRvIII) converge to remove steric hindrance from the 806-epitope, which is allosterically coupled to an intermediate kinase and increased oncogenicity.

Conclusions:

• Structural and functional equivalence exists between different classes of EGFR ECD mutations in GBMs, all leading to the exposure of the 806-epitope.
• The exposed 806-epitope is linked to an intermediate kinase conformation associated with increased oncogenicity.
• Synergistic cotargeting of this intermediate state with antibodies (mAb806) and inhibitors presents a promising therapeutic strategy for GBMs.