MET overexpression and activation favors invasiveness in a model of anaplastic thyroid cancer

// Cyril Garcia 1, 2, 3, 4 , Camille Buffet 1, 2, 3 , Laila El Khattabi 1, 2, 3, 5 , Marthe Rizk-Rabin 1, 2, 3 , Karine Perlemoine 1, 2, 3 , Bruno Ragazzon 1, 2, 3 , Jerome Bertherat 1, 2, 3, 6 , Francoise Cormier 1, 2, 3, * and Lionel Groussin 1, 2, 3, 6, * 1 INSERM Unite 1016, Institut Cochin, Paris, France 2 Centre National de la Recherche Scientifique, Unite Mixte de Recherche 8104, Institut Cochin, Paris, France 3 Universite Paris Descartes, Sorbonne Paris Cite, Paris, France 4 Hopital d’Instruction des Armees BEGIN, Saint-Mande, France 5 Cytogenetics Laboratory, APHP, Cochin Hospital, Paris, France 6 Department of Endocrinology, APHP, Cochin Hospital, Paris, France * These authors contributed equally to this work Correspondence to: Lionel Groussin, email: lionel.groussin@aphp.fr Keywords: thyroid cancer; MET amplification; cell invasion; PHA665752; MET targeting Received: August 08, 2018      Accepted: March 04, 2019      Published: March 19, 2019 ABSTRACT In thyroid cancers, MET receptor overexpression has been associated with higher risk of metastatic progression. In this study, it was shown that the anaplastic thyroid cancer (ATC)-derived TTA1 cell line overexpressed MET. By using FISH and relative quantification by qPCR, it was demonstrated that this overexpression resulted from a MET amplification with more than 20 copies. As expected, MET overexpression led to its constitutive activation and upregulated signaling towards the MAPK, PI3K/AKT, STAT3 and NF-κB pathways. Since the usual feature of MET -amplified cell lines is the "MET addiction" for their cell proliferation, the effect of the highly selective ATP competitive MET inhibitor PHA665752 was analyzed. While PHA665752 strongly inhibited the MAPK pathway, it did not reduce cell proliferation in TTA1 cells (IC 50 = 4100 nM). This resistance to PHA665752 of the TTA1 cell line was demonstrated to be related to EGFR-MET functional cross-talk and PI3K/AKT and NF-κB signaling. Nevertheless, PHA665752 suppressed the anchorage-independent growth capacity of the TTA1 cell line and reduced cell migration and invasion in a transwell assay. The role of activated MET in these neoplastic properties of the TTA1 cells was also proved with si-MET-RNA targeting. Thus, this work highlights the TTA1 cell line as the first model of MET amplification in an ATC cell line, which leads to MET constitutive activation and underlies its neoplastic properties. Besides being a useful model for MET inhibitors screening, the TTA1 cell line also supports the argument for searching for MET amplification in ATC, as it could have therapeutic implications.