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

Valentina Nicolini (1) , Giuliana Cassinelli (1) , Giuditta Cuccuru (1) , Italia Bongarzone (1) , Giovanna Petrangolini (1) , Monica Tortoreto (1) , Piera Mondellini (1) , Patrizia Casalini (1) , Enrica Favini (1) , Nadia Zaffaroni (1) , Franco Zunino (1) , Cinzia Lanzi (1)

1 Department of Experimental Oncology and Molecular Medicine

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. RNA interference downregulated Fap-1 protein in MZ-CRC-1 cells, whereas exogenous -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.

Mots clés: RET oncogene; Medullary thyroid cancer; Fap-1; CD95; MEN2B; Caspase 8

Domaines: Pharmacologie

Valentina Nicolini, Giuliana Cassinelli, Giuditta Cuccuru, Italia Bongarzone, Giovanna Petrangolini, et al.. Interplay between Ret and Fap-1 regulates CD95-mediated apoptosis in medullary thyroid cancer cells. Biochemical Pharmacology, 2011, 82 (7), pp.778. ⟨10.1016/j.bcp.2011.06.037⟩. ⟨hal-00723638⟩