IDENTIFICATION OF NOVEL PROTEIN KINASES INVOLVED IN THE PROLIFERATION OF THYROID CANCER CELLS

This dissertation focuses on the study of different signaling mechanisms regulating thyroid carcinogenesis, with the aim of identifying new genes involved in thyroid tumors, thus potential targets for new anti-cancer therapeutics. Appended manuscripts II and III focus on the analysis of the role exerted by SOD3 (Superoxide dismutase 3) and components of the Sonic/Hedgehog signaling pathway in thyroid carcinomas. The main body of this dissertion (manuscript I), instead, describes a knock-down screening performed in the TPC1 thyroid cancer cell line with a library of siRNA targeting the entire complement of human protein kinases (kinome) and kinase-related proteins. Thyroid cancer is primarily associated to the oncogenic conversion of protein kinases (BRAF, RET, NTRK1, AKT). Thus, the aim of this screen was to identify novel protein kinases required to sustain viability of thyroid carcinoma cells and therefore involved in thyroid carcinogenesis. Through this screening, we identified 21 “down hits”, e.g. kinases whose knock-down reduced by 30% or more TPC1 cell viability. Most of these kinases were essential not only for the viability of TPC1 but also other thyroid cancer cell lines with different genetic backgrounds (RAS or BRAF mutations) but not normal thyroid cells. These kinases included components of several signaling pathways. In particular, we identified members of the EPH (ephrin receptors) family, namely EPHA2, EPHA4 and EPHB2, as overexpressed and functionally active in various thyroid cancer cell lines. These three EPH were also upregulated in human thyroid tumor specimens. Finally, functional assays proved that the expression of EPHA2, EPHA4 and EPHB2 is essential not only for thyroid cancer cell growth but also motility and invasiveness. In conclusion, our study strongly suggests that EPHA2, EPHA4 and EPHB2 activation plays an important role in human cancers derived from thyroid follicular epithelium