Induction of Apoptosis by X-linked Ectodermal Dysplasia Receptor via a Caspase 8-dependent Mechanism

Suwan K Sinha,Preet M Chaudhary

doi:10.1074/jbc.m407363200

Abstract

X-linked ectodermal dysplasia receptor (XEDAR) is a recently isolated member of the tumor necrosis factor receptor family that is highly expressed during embryonic development and binds to ectodysplasin-A2 (EDA-A2). In this report, we demonstrate that although XEDAR lacks a death domain, it nevertheless induces apoptosis in an EDA-A2-dependent fashion. The apoptosis-inducing ability of XEDAR is dependent on the activation of caspase 8 and can be blocked by its genetic and pharmacological inhibitors. Although XEDAR-induced apoptosis can be blocked by dominant-negative Fas-associated death domain (FADD) protein and FADD small interfering RNA, XEDAR does not directly bind to FADD, tumor necrosis factor receptor-associated death domain (TRADD) protein, or RIP1. Instead, XEDAR signaling leads to the formation of a secondary complex containing FADD, caspase 8, and caspase 10, which results in caspase activation. Thus, XEDAR belongs to a novel class of death receptors that lack a discernible death domain but are capable of activating apoptosis in a caspase 8- and FADD-dependent fashion. XEDAR may represent an early stage in the evolution of death receptors prior to the emergence of the death domain and may play a role in the induction of apoptosis during embryonic development and adult life.

Highlights

The death receptors of the tumor necrosis factor receptor (TNFR)1 superfamily and their ligands have been recognized to play a crucial role in the normal development and regulation of immune and inflammatory response [1, 2]
Recombinant EDA-A2 Induces Apoptosis in 293F Cells Expressing X-linked ectodermal dysplasia receptor (XEDAR)—To facilitate the characterization of XEDAR signaling, we recently generated a subclone of 293F, designated 293FLAG-XEDAR, with stable expression of the NH2-terminal FLAG epitope-tagged XEDAR-L isoform [19]
SiRNA-mediated silencing of tumor necrosis factor receptor-associated death domain (TRADD) expression failed to significantly block EDA-A2- or TNF␣-induced apoptosis in 293FLAG-XEDAR cells, while silencing of caspase 8 effectively did so (Fig. 6, D and E). These results argue against the involvement of TRADD in EDA-A2induced apoptosis and suggest that its role in TNFR1-induced apoptosis may need re-examination

Summary

Introduction

The death receptors of the tumor necrosis factor receptor (TNFR) superfamily and their ligands have been recognized to play a crucial role in the normal development and regulation of immune and inflammatory response [1, 2]. Unlike TNFR1, signaling via Fas, DR4, and DR5 delivers a strong and rapid proapoptotic signal [3, 8, 9] Ligand binding to these receptors leads to DD-mediated recruitment of FADD directly without the involvement of TRADD (8 –10). Unlike most TNFR family receptors, XEDAR is a type III transmembrane protein (lacking an NH2-terminal signal peptide) that bears 32% sequence homology with EDAR in the extracellular ligand-binding domain [17]. Two predominant alternatively spliced isoforms of XEDAR have been described, XEDAR-s and XEDAR-L, which differ from each other by the presence of a 21-amino acid linker in the juxtamembrane region of the cytoplasmic domain [19] Both XEDAR isoforms lack a death do-. Induction of Apoptosis by XEDAR main and have been shown to signal mainly via TRAF6 and TRAF3 to activate the NF-␬B and JNK pathways [17, 19]

Methods

Results

Conclusion