Preligand assembly domain-mediated ligand-independent association between TRAIL receptor 4 (TR4) and TR2 regulates TRAIL-induced apoptosis

Abstract

Tumor necrosis factor (TNF)-related apoptosis-inducing ligand (TRAIL) is a cytokine with potential therapeutic value against cancers because of its selective cytotoxicity to many transformed, but not normal, cells. The ''decoy receptors'' TRAIL-R3 (TR3) and TRAIL-R4 (TR4) were believed to negatively regulate TRAIL-induced cytotoxicity by competing for ligand binding with TRAIL-R1 (TR1) and TRAIL-R2 (TR2). Here, we show that inhibition of TRAILinduced apoptosis by TR4 critically depends on its association with TR2 via the NH 2-terminal preligand assembly domain overlapping the first partial cysteine-rich domain of both receptors. By contrast, ligand binding by TR4 is dispensable for its apoptosis inhibitory function, thereby excluding the possibility that TR4 was a ''decoy'' to inhibit apoptosis by binding up TRAIL. In primary CD8 ؉ T cells, which express only TR2 and TR4 and are resistant to TRAIL-induced apoptosis, stimulation with phorbol myristate acetate abrogated the ligand-independent interaction between TR2 and TR4 and enhanced their sensitivity to TRAIL-induced apoptosis. Hence, whereas most TNF receptors normally form only homotrimeric complexes, the preligand assembly domains in TR2 and TR4 permit mixed complex formation as a means to regulate apoptosis induction. We propose that TR4 is a ''regulatory'' rather than ''decoy'' receptor that inhibits apoptosis signaling by TRAIL through this previously uncharacterized ligand-independent mechanism. decoy receptors T he regulation of cell death by members of the TNF family plays a critical role in immune function and homeostasis (1). TRAIL is a TNF-like cytokine that selectively induces apoptosis in many tumor cells, but not in normal cells. Administration of recombinant TRAIL or antibodies against TR2 in several experimental tumor models exhibited potent antitumor activity with minimal hepatic toxicity (2-6). Moreover, recombinant TRAIL or agonist TRAIL receptor antibody often synergizes with chemotherapy or radiation to induce tumor-cell apoptosis (7-10). This unique property of TRAIL has prompted many to vaunt it as a potential therapeutic agent against malignant diseases. Despite its potency against tumor cells, the physiological function of TRAIL is largely unknown, although some reports have implicated TRAIL to be involved in tumor surveillance (11), target cell killing by various immune effector cells (12,13), and the regulation of innate immune responses (14).TRAIL binds to five distinct TNF receptor (TNFR)-like receptors, TR1 (TRAIL-R1͞DR4), TR2 (TRAIL-R2͞DR5͞ Killer͞Trick), TR3 (TRAIL-R3͞DcR1͞LIT͞TRID), TR4 (TRAIL-R4͞DcR2͞TRUNDD), and the soluble receptor osteoprotegerin (OPG). OPG is a soluble receptor that also binds another TNF-like cytokine called TRANCE͞RANK-L and may have a more prominent role in bone and myeloid cell development than in regulating TRAIL-induced apoptosis. The four membrane-anchored TRAIL receptors contain two complete cysteine-rich domains (CRDs) for ligand binding that are preceded at the NH 2 termini by a highly conserved...

New insights into apoptosis signaling by Apo2L/TRAIL

“…A preligand assembly domain (PLAD), located in the first CRD of the receptor, mediates the association between monomers. Subsequently, PLAD-dependent association has been reported for DR4 and DR5 (Clancy et al, 2005). Overexpression experiments suggest that the ECDs of DR4 and DR5 can interact either with each other or with the ECD of DcR2; the latter may disrupt the formation of DR4 or DR5 homotrimers.…”

Enforced covalent trimerization increases the activity of the TNF ligand family members TRAIL and CD95L

“…Furthermore, in the human system TRAILR1 and TRAILR2, which are differentially dependent on ligand cross-linking for activation, are also differentially regulated by TRAILR4. 19,20 Second, the transformation of receptor occupancy by ligand into DISC formation and further to activation of apoptotic caspases could be non-linear and receptor-specific. Taken together, fusion with the TNC domain did not overcome the requirement of hCD95L and hTRAIL for secondary cross-linking to become properly active ( Figure 7c and d).…”

p53-Mediated upregulation of DcR1 impairs oxaliplatin/TRAIL-induced synergistic anti-tumour potential in colon cancer cells

“…On the other hand, some chemotherapeutic drugs involve, at least partially, the engagement of death domain-containing receptors to trigger cell death (Micheau et al, 1999). Recent evidence indicates that both tumour and normal cells can acquire resistance to TRAIL-induced killing by upregulating either of the two antagonistic receptors, DcR1 and DcR2, which do not transfer any apoptotic signal (Davidovich et al, 2004;Clancy et al, 2005;Merino et al, 2006), indicating that the four TRAIL receptors are involved for regulating TRAIL-induced apoptosis (Kelley and Ashkenazi, 2004;Bouralexis et al, 2005;Merino et al, 2007).…”