Binding of death receptor 3 (DR3) to intracellular TRADD and TRAF2 is independent of its natural ligand, TL1A.

The TNF‑like cytokine TL1A is a key regulator of immune responses through engagement of its receptor, death receptor 3 (DR3), and has emerged as a therapeutic target in inflammatory diseases. Prevailing models propose that TL1A binding initiates recruitment of adaptor proteins to DR3, leading to downstream signaling. Here, we investigated proximal DR3 signaling events and found that the adaptor proteins TRADD and TRAF2 associate with DR3 independently of TL1A stimulation in both TF‑1 cells and primary human CD4+ T cells. In contrast, TL1A stimulation was strictly required for activation of NF‑κB signaling, including IκBα degradation and downstream ubiquitination events. These findings indicate that DR3 can exist in a preassembled adaptor complex prior to ligand engagement and suggest a revised model in which TL1A binding confers signaling competence rather than initiating adaptor recruitment. We propose a structurally informed, hypothesis‑generating model in which ligand engagement promotes higher‑order organization of prebound signaling components to enable downstream signal transduction. Together, our results refine current understanding of TL1A/DR3 signaling by decoupling adaptor assembly from ligand‑dependent signal activation.