The MET proto-oncogene plays crucial roles in cell growth and proliferation, epithelial-mesenchymal (EMT) transition, invasion/metastasis and drug resistance in a broad range of malignancies. In non–small cell lung cancer (NSCLC), aberrant MET signaling can occur through a number of mechanisms that include MET or HGF protein overexpression, MET gene amplification, MET gene mutation or aberrations in downstream signaling or regulatory components. Among the various MET alterations, recurrent MET exon 14 skipping (METΔ14) mutations occur in approximately 3%-5% of NSCLC, and recently emerged as an actionable oncogenic driver. Moreover, METΔ14 was found to be mutually exclusive with other recognized drivers, which further supports its potential oncogenic role.

In the current study, we sought to perform an array of experiments to determine the intrinsic tumorigenic role of METΔ14 in NSCLC. We firstly established several METΔ14 NSCLC cell models using a CRISPR gene editing system. Using these models, we dissected the biochemical events underlying METΔ14 oncogenic activity. Through combining a biotin-labeled receptor internalization assay and fluorescence imaging analysis of receptor endocytic trafficking we identified that METΔ14 decreases ligand-dependent receptor internalization and lysosomal degradation but does not affect a recycling process. Our results indicate that METΔ14 does not affect receptor dimerization but impairs receptor endocytic degradation, which eventually leads to an extended activation of HGF/MET signaling. In subsequent functional analyses, we identified that METΔ14 significantly increases HGF-dependent cell scatter, migration and invasion capacity in vitro as well as metastasis in vivo compared to wild-type MET. In order to define the underlying mechanisms we pursued further experiments and demonstrate that METΔ14 increases cell movement at least partially via regulation of the PI3K/Akt-GTPase Rac1 pathway. Accordingly, METΔ14 significantly increased the HGF-dependent activation of the Rac1 and cell ruffling formation whereas Rac1 knockdown contrastively repressed HGF/METΔ14-mediated Rac1 activation and cell invasion. Separately, the PI3K inhibitor, LY294002 repressed HGF/METΔ14-mediated Rac1 activity and cell movement. Therefore, these data demonstrate that METΔ14 increases cell movement, at least partially via regulation of the PI3K/Akt-Rac1 pathway.

We finally tested the effect of a recently developed potent MET inhibitor, MGCD516, and found that MGCD516 significantly inhibited METΔ14-mediated PI3K/Akt and MAPK activation, repressed Rac1 activation and cell invasion. These results suggested that MET inhibition with agents such as MGCD516 might be potent therapeutic options for METΔ14-mutated NSCLC patients.

Citation Format: Feng Wang, Elaine Shum, Roman Perez-Soler, Haiying Cheng, Balazs Halmos. MET exon 14 skipping mutation promotes metastasis via activation of the PI3K/Akt-Rac1 pathway in non-small cell lung cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 2740.