miR-199a-3p displays tumor suppressor functions in papillary thyroid carcinoma

// Emanuela Minna 1,* , Paola Romeo 1,* , Loris De Cecco 2 , Matteo Dugo 2 , Giuliana Cassinelli 3 , Silvana Pilotti 4 , Debora Degl’Innocenti 1 , Cinzia Lanzi 3 , Patrizia Casalini 5 , Marco A. Pierotti 6 , Angela Greco 1 and Maria Grazia Borrello 1 1 Molecular Mechanisms Unit, Department of Experimental Oncology and Molecular Medicine, Fondazione IRCCS Istituto Nazionale dei Tumori, Milan, Italy 2 Functional Genomics Core Facility, Fondazione IRCCS Istituto Nazionale dei Tumori, Milan, Italy 3 Molecular Pharmacology Unit, Department of Experimental Oncology and Molecular Medicine, Fondazione IRCCS Istituto Nazionale dei Tumori, Milan, Italy 4 Department of Pathology, Fondazione IRCCS Istituto Nazionale dei Tumori, Milan, Italy 5 Molecular Targeting Unit, Department of Experimental Oncology and Molecular Medicine, Fondazione IRCCS Istituto Nazionale dei Tumori, Milan, Italy 6 Scientific Directorate, Fondazione IRCCS Istituto Nazionale dei Tumori, Milan, Italy * These authors contributed equally to the work Correspondence: Maria Grazia Borrello, email: // Keywords : miR-199a-3p, Papillary thyroid carcinoma, microRNA, RET/PTC, MET, oncogene Received : January 28, 2014 Accepted : March 15, 2014 Published : March 16, 2014 Abstract Thyroid cancer incidence is rapidly increasing. Papillary Thyroid Carcinoma (PTC), the most frequent hystotype, usually displays good prognosis, but no effective therapeutic options are available for the fraction of progressive PTC patients. BRAF and RET/PTC are the most frequent driving genetic lesions identified in PTC. We developed two complementary in vitro models based on RET/PTC1 oncogene, starting from the hypothesis that miRNAs modulated by a driving PTC-oncogene are likely to have a role in thyroid neoplastic processes. Through this strategy, we identified a panel of deregulated miRNAs. Among these we focused on miR-199a-3p and showed its under-expression in PTC specimens and cell lines. We demonstrated that miR-199a-3p restoration in PTC cells reduces MET and mTOR protein levels, impairs migration and proliferation and, more interesting, induces lethality through an unusual form of cell death similar to methuosis, caused by macropinocytosis dysregulation. Silencing MET or mTOR, both involved in survival pathways, does not recapitulate miR-199a-3p-induced cell lethality, thus suggesting that the cooperative regulation of multiple gene targets is necessary. Integrated analysis of miR-199a-3p targets unveils interesting networks including HGF and macropinocytosis pathways. Overall our results indicate miR-199a-3p as a tumor suppressor miRNA in PTC.