Background: The resistance of lung cancer to epidermal growth factor receptor-tyrosine kinase inhibitor (EGFR-TKI) is one of the unconquered frontiers in chemotherapy. Mitogen-inducible gene 6 (Mig-6) is known to inhibit the kinase activity of epidermal growth factor receptor (EGFR). Similarly, numerous studies of mouse models suggested tumor suppressive function of Mig-6 in lung cancer. On the contrary, the results of clinical investigations revealed that lung cancer patients with elevated expression of Mig-6 are associated with a poor prognosis. More recent work showed that unlike wild type (WT) EGFR, mutant EGFR phosphorylates Mig-6 and phosphorylated Mig-6 negatively regulates the degradation of EGFR mutants in lung adenocarcinoma. Here, we tried to untangle the controversies surrounding Mig-6 function as a protagonist or an antagonist of EGFR-TKI resistant lung cancer.
Methods: We compared the expression and phosphorylation status of Mig-6 in the EGFR-TKI resistant lung adenocarcinoma (PC9/GR cells) to EGFR-TKI sensitive lung adenocarcinoma (PC9 cells). We investigated the function of Mig-6 by either depletion or overexpression of Mig-6 in those cells and evaluated the efficacy of combining of Mig-6 knock-down and EGFR-TKI treatment in PC9/GR. The correlation between Mig-6 expressions and the prognoses of lung adenocarcinoma was examined by The Cancer Genome Atlas (TCGA) data and clinical samples.
Results: Our results indicated that the expression of Mig-6 was significantly increased in PC9/GR cells compared to that of PC9 cells. The significant portion of Mig-6 existed as a phosphorylated form in PC9 and PC9/GR cells. Moreover, overexpression of Mig-6 significantly increased the cell proliferation, invasion and epithelial mesenchymal transition (EMT) in PC9 cells. Combination of Mig-6 knock-down and EGFR-TKI treatment significantly overcame the EGFR-TKI resistance of PC9/GR cells. In addition, our analyses of clinical samples confirmed that high Mig-6 expressions positively correlate with a poor prognosis and EGFR-TKI resistance in lung adenocarcinoma.
Conclusion: Our findings reinforce scientific notion of Mig-6 as an oncoprotein in the context of EGFR-TKI resistant lung adenocarcinoma. We propose that targeting Mig-6 may be a promising strategy to overcome the EGFR-TKI resistance in lung cancer.
Keywords: Chemotherapy resistance; EGFR-TKI; Lung adenocarcinoma; Mig-6.