RET/PTC1-Driven Neoplastic Transformation and Proinvasive Phenotype of Human Thyrocytes Involve Met Induction and β-Catenin Nuclear Translocation

• Published in: Neoplasia (New York, N.Y.) N.Y.), 2009-01, Vol.11 (1), p.10-21
• Main Authors: Cassinelli, Giuliana, Favini, Enrica, Degl'Innocenti, Debora, Salvi, Alessandro, De Petro, Giuseppina, Pierotti, Marco A., Zunino, Franco, Borrello, Maria Grazia, Lanzi, Cinzia
• Format: Article
• Language: English
• Subjects: Active Transport, Cell Nucleus; Animals; beta Catenin - metabolism; beta Catenin - physiology; Cell Adhesion - genetics; Cell Nucleus - metabolism; Cell Proliferation; Cell Transformation, Neoplastic - genetics; Cells, Cultured; Gene Expression Regulation, Neoplastic; Humans; Mice; Neoplasm Invasiveness; NIH 3T3 Cells; Phenotype; Proto-Oncogene Proteins - genetics; Proto-Oncogene Proteins - metabolism; Proto-Oncogene Proteins - physiology; Proto-Oncogene Proteins c-met; Proto-Oncogene Proteins c-ret - genetics; Proto-Oncogene Proteins c-ret - metabolism; Proto-Oncogene Proteins c-ret - physiology; Receptors, Growth Factor - genetics; Receptors, Growth Factor - metabolism; Receptors, Growth Factor - physiology; Thyroid Gland - metabolism; Thyroid Gland - pathology; Up-Regulation - physiology
• ISSN: 1476-5586; 1522-8002; 1476-5586; 1522-8002
• DOI: 10.1593/neo.08916

Activation of the RET gene by chromosomal rearrangements generating RET/PTC oncogenes is a frequent, early, and causative event in papillary thyroid carcinoma (PTC). We have previously shown that, in human primary thyrocytes, RET/PTC1 induces a transcriptional program including the MET proto-oncogene. In PTCs, β-catenin is frequently mislocated to the cytoplasm nucleus. We investigated the interplay between Ret/ptc1 signaling and Met in regulating the proinvasive phenotype and β-catenin localization in cellular models of human PTC. Here, we show that Met protein is expressed and is constitutively active in human thyrocytes exogenously expressing RET/PTC1 as well as a mutant (Y451F) devoid of the main Ret/ptc1 multidocking site. Both in transformed thyrocytes and in the human PTC cell line TPC-1, Ret/ptc1-Y451-dependent signaling and Met cooperated to promote a proinvasive phenotype. Accordingly, gene/functional silencing of either RET/PTC1 or MET abrogated early branching morphogenesis in TPC-1 cells. The same effect was obtained by blocking the common downstream effector Akt. Y451 of Ret/ptc1 was required to promote proliferation and nuclear translocation of β-catenin, suggesting that these oncogene-driven effects are Met-independent. Pharmacologic inhibition of Ret/ptc1 and Met tyrosine kinases by the multitarget small molecule RPI-1 blocked cell proliferation and invasive ability and dislocated β-catenin from the nucleus. Altogether, these results support that Ret/ptc1 cross talks with Met at transcriptional and signaling levels and promotes β-catenin transcriptional activity to drive thyrocyte neoplastic transformation. Such molecular network, promoting disease initiation and acquisition of a proinvasive phenotype, highlights new options to design multitarget therapeutic strategies for PTCs.