title: Interplay between Ret and Fap-1 regulates CD95-mediated apoptosis in medullary thyroid cancer cells.
abstract: Emerging evidence suggests that Ret oncoproteins expressed in medullary thyroid cancer (MTC) might evade the pro-apoptotic function of the dependence receptor proto-Ret by directly impacting the apoptosis machinery. Identification of the molecular determinants of the interplay between Ret signaling and apoptosis might provide a relevant contribution to the optimization of Ret-targeted therapies. Here, we describe the cross-talk between Ret-M918T oncogenic mutant responsible for type 2B multiple endocrine syndrome (MEN2B), and components of death receptor-mediated extrinsic apoptosis pathway. In the human MEN2B-type MTC cell line MZ-CRC-1 expressing Ret-M918T, Ret was found associated with Fap-1, known as inhibitor of the CD95 death receptor trafficking to the cell membrane, and with procaspase-8, the initiator pro-form caspase in the extrinsic apoptosis pathway. Cell treatment with the anti-tumor Ret kinase inhibitor RPI-1 inhibited tyrosine phosphorylation of procaspase-8, likely inducing its local activation, followed by downregulation of both Ret and Fap-1, and translocation of CD95 into lipid rafts. According to the resulting increase of CD95 cell surface expression, the CD95 agonist antibody CH11 enhanced RPI-1-induced cell growth inhibition and apoptosis. RET RNA interference downregulated Fap-1 protein in MZ-CRC-1 cells, whereas exogenous RET-M918T upregulated Fap-1 in HEK293 cells. Overall, these data indicate that the Ret oncoprotein exerts opposing controls on Fap-1 and CD95, increasing Fap-1 expression and decreasing CD95 cell surface expression. The functional interplay of the Ret mutant with the extrinsic apoptosis pathway provides a mechanism possibly contributing to MTC malignant phenotype and a rational basis for novel therapeutic strategies combining Ret inhibitors and CD95 agonists.
authors: Molecular Pharmacology Unit, Department of Experimental Oncology and Molecular Medicine, Fondazione IRCCS Istituto Nazionale dei Tumori, Milan, Italy.
authors: Valentina
authors: V
authors: Nicolini
authors: Giuliana
authors: G
authors: Cassinelli
authors: Giuditta
authors: G
authors: Cuccuru
authors: Italia
authors: I
authors: Bongarzone
authors: Giovanna
authors: G
authors: Petrangolini
authors: Monica
authors: M
authors: Tortoreto
authors: Piera
authors: P
authors: Mondellini
authors: Patrizia
authors: P
authors: Casalini
authors: Enrica
authors: E
authors: Favini
authors: Nadia
authors: N
authors: Zaffaroni
authors: Franco
authors: F
authors: Zunino
authors: Cinzia
authors: C
authors: Lanzi
mesh_terms: D000818:Animals; D000970:Antineoplastic Agents / Q000494:pharmacology; D017209:Apoptosis; D018276:Carcinoma, Medullary / Q000378:metabolism / Q000473:pathology*; D018278:Carcinoma, Neuroendocrine; D053181:Caspase 8 / Q000378:metabolism; D045744:Cell Line, Tumor; D004789:Enzyme Activation; D005260:Female; D005786:Gene Expression Regulation; D006801:Humans; D007211:Indoles / Q000494:pharmacology; D051379:Mice; D016513:Mice, SCID; D041681:NIH 3T3 Cells; D009368:Neoplasm Transplantation; D010766:Phosphorylation; D054595:Protein Tyrosine Phosphatase, Non-Receptor Type 13 / Q000502:physiology*; D051096:Proto-Oncogene Proteins c-ret / Q000037:antagonists & inhibitors / Q000502:physiology*; D013964:Thyroid Neoplasms / Q000378:metabolism / Q000473:pathology*; D014183:Transplantation, Heterologous; D047368:Tumor Burden; D019014:fas Receptor / Q000502:physiology*
chemical_list: D000970:Antineoplastic Agents; D007211:Indoles; C477359:RPI-1 compound; D019014:fas Receptor; D051096:Proto-Oncogene Proteins c-ret; C099282:RET protein, human; C516742:PTPN13 protein, human; D054595:Protein Tyrosine Phosphatase, Non-Receptor Type 13; D053181:Caspase 8