(49b) Integrated Feedback Regulation of the Epidermal Growth Factor Receptor in Non-Small Cell Lung Cancer
Activation of ErbB receptor tyrosine kinases initiates cell signaling pathways for differentiation, proliferation, and survival. Receptor activation simultaneously leads to up-regulation of molecular feedback regulators of ErbB signal duration and specificity, two of the most important of which are Spry2 and Mig6. Spry2, a member of a family of four Sprouty proteins, regulates the MAP kinase cascade at multiple levels while also regulating endocytosis of the epidermal growth factor receptor (EGFR/ErbB1). Mig6 is a pan-ErbB inhibitor that blocks dimerization-driven receptor kinase activation. The complete functionality of these regulators and how their activities are integrated to determine ErbB signaling dynamics is not fully understood. We examined how Spry2 and Mig6 function together in the context of non-small cell lung cancers (NSCLC) characterized by elevated expression of EGFR. In particular, we sought to answer the question of how Spry2 and Mig6 might differentially contribute to certain cancer phenotypes in NSCLC cells expressing wild-type EGFR or the recently discovered constitutively active EGFR mutants which confer cellular sensitivity to EGFR kinase inhibitors. The effects of shRNA-mediated knockdown or expression of Spry2 and Mig6 alone or in combination were examined in a panel of NSCLC cell lines with variable sensitivity to EGFR kinase inhibitors. We measured the effects of shRNA knockdown, reconstitution, and over-expression on EGFR endocytosis rate constants and the activities of downstream signaling pathways such as PI3K/AKT and ERK. Within this framework, we also measured cell death response to the specific EGFR tyrosine kinase inhibitor gefitinib. Results indicated that the roles of these feedback regulators are cell-context specific. More importantly, our findings suggest that these feedback regulators may contribute to sustained signaling from mutants receptors or function as tumor suppressors, depending on the context.