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

Cyril Garcia,Karine Perlemoine,Jérôme Bertherat,Marthe Rizk-Rabin,Bruno Ragazzon,Françoise Cormier,Laila El Khattabi,Camille Buffet,Lionel Groussin

doi:10.18632/oncotarget.26798

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 (IC50 = 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.

Highlights

Follicular cells-derived thyroid cancers are the most frequent endocrine tumors with an increasing incidence worldwide [1, 2]
No hepatocyte growth factor (HGF) mRNA expression could be demonstrated by qRT-PCR in TTA1 cells compared to the high level of expression in the HGF-producing HL60 cell line [14], indicating that MET constitutive activation in the TTA1 cell line was not dependent on the co-expression of its ligand
In follicular cells-derived thyroid cancers, this mutation was found in 6% of the 53 PTC, 10% of the 21 FTC, but none of the 17 anaplastic thyroid cancer (ATC) studied [23]

Summary

Introduction

Follicular cells-derived thyroid cancers are the most frequent endocrine tumors with an increasing incidence worldwide [1, 2]. Thyroid tumors can be classified into well-differentiated (papillary and follicular thyroid carcinoma (PTC and FTC)), poorly differentiated, and undifferentiated (anaplastic) carcinoma (PDTC and ATC). PTC is the most frequent histotype accounting for 85% of thyroid cancers with a good clinical prognosis [3]. Progress in the identification of genetic alterations underlying the pathogenesis of thyroid carcinoma provides a basis for the development of targeted therapies for resistant and iodine-refractory cancers [6,7,8]. Tyrosine-kinase receptor genes rearrangements (RET/ PTC, NRTK...), RAS (N-RAS, H-RAS, K-RAS) and BRAF activating mutations are frequent and mutually exclusive driver molecular abnormalities leading to a constitutive activation of the MAPK pathway in PTC [9, 10]. Gene amplifications are additional genomic events in thyroid cancers, with, essentially, copy-number gains of genes encoding receptor tyrosine-kinases (RTK), such as EGFR, PDGFRA, PDGFRB, VEFGR, KIT and MET [9]

Methods

Results

Conclusion