Dimerization and the signal transduction pathway of a smallin‐frame deletion in the epidermal growth factor receptor

Abstract

A short, in-frame deletional mutant (E746-A750del) is one of the major mutant forms of epidermal growth factor receptor (EGFR) and has been reported to be a determinant of response to EGFR tyrosine kinase inhibitors such as gefitinib and erlotinib. However, the biological and pharmacological functions of mutational EGFR remain unclear. To clarify these biological functions of deletional EGFR, we examined the cellular response to EGF ligand stimulation. Dimerization and phosphorylation of EGFR were observed without any ligand stimulation in the 293(D) cells transfected with deletional EGFR as compared with those transfected with wild-type EGFR (293(W) cells). When the 293(D) cells were exposed to gefitinib, an immunoblotting analysis revealed remarkable inhibition of AKT phosphorylation but not phospho-p44/42 MAPK. To examine the cellular response in a lung cancer cell line intrinsically expressing deletional EGFR, phospho-EGFR, and downstream reactions were monitored under EGF stimulation with a beads-based mulitiplex assay. EGFR and its downstream proteins were constitutively phosphorylated in the PC-9 cells without any ligand stimulation as compared with A549 lung cancer cells expressing wild-type EGFR. In conclusion, deletional EGFR is constitutively active and phosphorylates p44/42 MAPK and AKT in the cells, although the fact that the EGFR phosphorylation in the PC-9 cells is still modulated by EGF stimulation cannot be ignored. Gefitinib-inhibited phospho-AKT predominantly in deletional EGFR expressing cells.

Combined Treatment with Silibinin and Epidermal Growth Factor Receptor Tyrosine Kinase Inhibitors Overcomes Drug Resistance Caused by T790M Mutation

“…Activating mutations in the EGFR gene confer increased EGFR activity even under serum-free conditions (3,32). One study showed that this phenomenon results from EGF-independent dimerization of mutant EGFR (33). Consistent with previous studies, EGFR dimers were observed in cells harboring EGFR mutations under basal conditions and even under serum-free conditions, but not in cells with wild-type EGFR (Supplementary Fig.…”

EGF-independent activation of cell-surface EGF receptors harboring mutations found in gefitinib-sensitive lung cancer

“…Moreover, Greulich et al (2005) found that several of the EGFR mutants studied here can transform NIH 3T3 cells. Thus, from our own studies and those published recently by other groups Jiang et al, 2005;Chen et al, 2006;Sakai et al, 2006), it appears that the EGFR mutations identified in gefitinibresponsive lung cancer patients are oncogenic. The response to gefitinib and other EGFR inhibitors of patients expressing these mutants is therefore likely to reflect the dependence of their tumors on constitutive EGFR signaling per se, rather than any alteration in the response of mutated EGFR to the inhibitors.…”

SLK-mediated phosphorylation of paxillin is required for focal adhesion turnover and cell migration

“…Despite the fact that SLK activity does not seem to be affected by EGF stimulation in 293 cells, it may be because 293 do not express very high levels of endogenous EGFR [70,172]. Therefore, the increased paxillin S250 phosphorylation seen in the MDA-MB-231 cell line in may in fact be the result of an alternative mechanism of SLK activation, possibly the activation of EGFR.…”