Interplay between Ret and Fap-1 regulates CD95-mediated apoptosis in medullary thyroid cancer cells

• Published in: Biochemical pharmacology 2011-10, Vol.82 (7), p.778-788
• Main Authors: Nicolini, Valentina, Cassinelli, Giuliana, Cuccuru, Giuditta, Bongarzone, Italia, Petrangolini, Giovanna, Tortoreto, Monica, Mondellini, Piera, Casalini, Patrizia, Favini, Enrica, Zaffaroni, Nadia, Zunino, Franco, Lanzi, Cinzia
• Format: Article
• Language: English
• Subjects: agonists; Animals; Antineoplastic Agents - pharmacology; Apoptosis; Biological and medical sciences; Carcinoma, Medullary - metabolism; Carcinoma, Medullary - pathology; Carcinoma, Neuroendocrine; Caspase 8; Caspase 8 - metabolism; caspases; CD95; cell growth; Cell Line, Tumor; cell membranes; death; Endocrinopathies; Enzyme Activation; Fap-1; fas Receptor - physiology; Female; Gastroenterology. Liver. Pancreas. Abdomen; Gene Expression Regulation; growth retardation; Humans; Indoles - pharmacology; Life Sciences; Malignant tumors; Medical sciences; Medullary thyroid cancer; MEN2B; Mice; Mice, SCID; mutants; Neoplasm Transplantation; NIH 3T3 Cells; Non tumoral diseases. Target tissue resistance. Benign neoplasms; oncogene proteins; Pharmaceutical sciences; Pharmacology; Pharmacology. Drug treatments; phenotype; Phosphorylation; Protein Tyrosine Phosphatase, Non-Receptor Type 13 - physiology; Proto-Oncogene Proteins c-ret - antagonists & inhibitors; Proto-Oncogene Proteins c-ret - physiology; RET oncogene; RNA interference; Stomach. Duodenum. Small intestine. Colon. Rectum. Anus; thyroid neoplasms; Thyroid Neoplasms - metabolism; Thyroid Neoplasms - pathology; Thyroid. Thyroid axis (diseases); Transplantation, Heterologous; Tumor Burden; Tumors; tyrosine
• ISSN: 0006-2952; 1873-2968
• DOI: 10.1016/j.bcp.2011.06.037

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.