Molecular Mechanisms of Tyrosine Kinase Inhibitor Resistance Induced by Membranous/Cytoplasmic/Nuclear Translocation of Epidermal Growth Factor Receptor.

INTRODUCTION

The molecular mechanism underlying the induction of resistance to tyrosine kinase inhibitors (TKIs) via the membranous/cytoplasmic/nuclear translocation of EGFR has not yet been reported.

METHODS

We performed immunohistochemistry to detect the distribution of EGFR in lung adenocarcinoma specimens after TKI treatment and analyzed the relationship between different EGFR locations and patient survival duration. Mass spectrometry analysis and immunoprecipitation were performed to show the interaction of cytosolic EGFR with YY1 associated protein 1 (YAP) and salt inducible kinase 2 (SIK2). Dual-luciferase assays, immunoblotting, real-time polymerase chain reaction, and functional experiments were used to elucidate the role of EGFR cytoplasmic/nuclear translocation in Hippo pathway dysregulation.

RESULTS

Patients with advanced lung adenocarcinoma with membranous mutant EGFR (19del or 21 L858R) showed significantly longer progression-free survival than those with cytoplasmic mutant EGFR after gefitinib treatment. The concentration that inhibits 50% in PC-9 with cytoplasmic EGFR was higher than that in hunman non-small cell lung cancer 827 with membranous EGFR. During first-generation TKI resistance induction, membrane EGFR translocated to the cytoplasm/nucleus, accompanied by the Hippo pathway inhibition. Cytoplasmic EGFR and SIK2 interaction inhibited large tumor suppressor kinase 1 (LATS1) and macrophage stimulating 1 (MST1) interaction, promoting YAP nuclear translocation. However, cells with osimertinib-induced resistance also showed EGFR translocation and lower phospho-EGF receptor but did not show Hippo pathway inhibition. Moreover, osimertinib and erlotinib could restore sensitivity to each other in resistant cells.

CONCLUSIONS

Plasma/nuclear translocation of EGFR and inhibition of the Hippo pathway are some of the important mechanisms underlying the resistance induced by first-generation TKIs. Membrane/plasma translocation of EGFR induced by osimertinib may be another resistance phenomenon besides MNNG HOS transforming gene (c-MET) amplification, C797S mutation, and ERK pathway inhibition.