IMPAIRED SHP2-MEDIATED ERK ACTIVATION CONTRIBUTES TO GEFITINIB SENSITIVITY OF LUNG CANCER CELLS WITH EGFR- ACTIVATING MUTATIONS

Most non-small cell lung cancers (NSCLC) display elevated expression of epidermal growth factor receptor (EGFR), but response to EGFR kinase inhibitors is predominantly limited to NSCLC harboring EGFR-activating mutations. These mutations are associated with increased activity of survival pathways including PI3K/AKT and STAT3/5. We report that EGFR-activating mutations also surprisingly lead to decreased ability to activate ERK compared to wild-type EGFR. In NSCLC cells and mouse embryonic fibroblasts expressing mutant EGFR, this effect on ERK correlates with decreased EGFR internalization and reduced phosphorylation of SHP2, a tyrosine phosphatase required for the full activation of ERK. We further demonstrate that ERK activation levels impact cellular response to gefitinib. NSCLC cells with EGFR mutation display reduced gefitinib sensitivity when ERK activation is augmented by expression of constitutively active mutants of MEK. Conversely, in an NSCLC cell line expressing wild-type EGFR, gefitinib treatment along with or following MEK inhibition increases death response compared to treatment with gefitinib alone. Our results demonstrate that EGFR-activating mutations may promote some survival pathways but simultaneously impair others. This multivariate alteration of the network governing cellular respons