¹Department of Biochemistry and Biophysics, University of Pennsylvania School of Medicine, Philadelphia, PA, USA

Correspondence: Professor MA Lemmon, Department of Biochemistry and Biophysics, University of Pennsylvania School of Medicine, 809C Stellar-Chance Laboratories, 422 Curie Boulevard, Philadelphia, PA 19104-6059, USA. E-mail: mlemmon@mail.med.upenn.edu

²These authors contributed equally to this work.

Received 17 March 2006; Revised 19 July 2006; Accepted 19 July 2006; Published online 4 September 2006.

Abstract

Several somatic mutations within the tyrosine kinase domain of epidermal growth factor receptor (EGFR) have been identified that predict clinical response of non-small-cell lung carcinoma (NSCLC) patients to gefitinib. To test the hypothesis that these mutations cause constitutive EGF receptor signaling, and to investigate its mechanistic basis, we expressed representative examples in a null background and analysed their biochemical properties. Each mutation caused significant EGF-independent tyrosine phosphorylation of EGFR, and allowed the receptor to promote Ba/F3 cell mitogenesis in the absence of EGF, arguing that these are oncogenic mutations. Active mutated receptors are present at the cell surface and are fully competent to bind EGF. Recent structural studies show that the inactive EGFR tyrosine kinase domain is autoinhibited by intramolecular interactions between its activation loop and C helix. We find that mutations predicted to disrupt this autoinhibitory interaction (including several that have not been described in NSCLC) elevate EGF-independent tyrosine kinase activity, thus providing new insight into how somatic mutations activate EGFR and other ErbB family members.