Mechanistic Insights into R776H Mediated Activation of Epidermal Growth Factor Receptor Kinase

Significance Statement

Epidermal growth factor receptor (EGFR) is a receptor tyrosine kinase that is frequently mutated in a variety of human cancers. Researchers from the University of Georgia characterized a novel recurrent oncogenic mutation (R776H) in the hinge region of EGFR kinase domain through a combination of cell-based assays and molecular dynamics simulations. The authors show that the R776H mutation activates the kinase domain by enhancing EGFR dimerization, a critical step in EGFR activation, and the mutant form preferentially adopts the acceptor position in the asymmetric dimer. The authors also demonstrate that the asymmetric dimer can phosphorylate monomeric EGFR, providing insights into lateral phosphorylation and downstream signaling. Using molecular modeling and molecular dynamics simulations, the authors propose a mechanistic model in which loss of key auto-inhibitory interactions with the regulatory αC-helix results in constitute activation. These findings have implications for the design of mutant-specific EGFR inhibitors for personalized cancer therapy

About the author

Dr. Natarajan Kannan is an Associate Professor in the Department of Biochemistry & Molecular Biology and Institute of Bioinformatics at the University of Georgia, Athens, GA. He obtained his PhD at the Indian Institute of Science, Bangalore in 2001, and post-doctoral training at University of California, San Diego and Cold Spring Harbor Laboratory, New York. Dr. Kannan is a Georgia Cancer Coalition Distinguished Cancer Scholar.

About the author

Zheng Ruan is a PhD student at The University of Georgia in Athens, GA. He finished his undergraduate study at Huazhong Agricultural University, Wuhan, China. ZhengRuan’s current research focuses on understanding the dynamics and functions of protein kinases using computational and experimental approaches.

Journal Reference

Biochemistry. 2015;54(27):4216-25.

Ruan Z, Kannan N.

Department of Biochemistry & Molecular Biology and ^‡Institute of Bioinformatics, University of Georgia, Athens, Georgia, United States

Abstract

The epidermal growth factor receptor (EGFR) kinase is activated by a variety of mutations in human cancers. R776H is one such recurrent mutation (R752H in another numbering system) in the αC-β4 loop of the tyrosine kinase domain that activates EGFR in the absence of the activating EGF ligand. However, the mechanistic details of how R776H contributes to kinase activation are not well understood. Here using cell-based cotransfection assays, we show that the R776H mutation activates EGFR in a dimerization-dependent manner by preferentially adopting the acceptor position in the asymmetric dimer. The acceptor function, but not the donor function, is enhanced for the R776H mutant, supporting the “superacceptor” hypothesis proposed for oncogenic mutations in EGFR. We also find that phosphorylation of monomeric EGFR is increased by R776H mutation, providing insights into EGFR lateral phosphorylation and oligomerization. On the basis of molecular modeling and molecular dynamics simulation, we propose a model in which loss of key autoinhibitory αC-helix capping interaction and alteration of coconserved cis regulatory interactions between the kinase domain and the flanking regulatory segments contribute to mutational activation. Since the R776 equivalent position is mutated in ErbB2 and ErbB4, our studies have implications for understanding kinase mutational activation in other ErbB family members as well.

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Figure legend

Background: DNA sequences of EGFR with the R776 codon highlighted in red. Upper left panel: WT EGFR adopts αC-helix “out” conformation, whereas R776H favors αC-helix “in” conformation. Right panel: R776H mutant adopts the “acceptor” position in the asymmetric dimer. Lower left panel: R776H mutant exerts lateral phosphorylation of monomeric EGFR.