FAIM-L Is an IAP-Binding Protein That Inhibits XIAP Ubiquitinylation and Protects from Fas-Induced Apoptosis
Moubarak, Rana S.
Planells Ferrer, Laura
Segura Ginard, Miguel Francisco
Marqués Fernàndez, Fernando
Solé Serra, Carme
Llecha Cano, Núria
López Soriano, Joaquin
Yuste Mateos, Víctor J. (Víctor José)
Comella i Carnicé, Joan Xavier
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The neuronal long isoform of Fas Apoptotic Inhibitory Molecule (FAIM-L) protects from death receptor (DR)-induced apoptosis, yet its mechanism of protection remains unknown. Here, we show that FAIM-L protects rat neuronal Type II cells from Fas-induced apoptosis. XIAP has previously emerged as a molecular discriminator that is upregulated in Type II and downregulated in Type I apoptotic signaling. We demonstrate that FAIM-L requires sustained endogenous levels of XIAP to protect Type II cells as well as murine cortical neurons from Fas-induced apoptosis. FAIM-L interacts with the BIR2 domain of XIAP through an IAP-binding motif, the mutation of which impairs the antiapoptotic function of FAIM-L. Finally, we report that FAIM-L inhibits XIAP auto-ubiquitinylation and maintains its stability, thus conferring protection from apoptosis. Our results bring new understanding of the regulation of endogenous XIAP by a DR antagonist, pointing out at FAIM-L as a promising therapeutic tool for protection from apoptosis in pathological situations where XIAP levels are decreased.