TRAF2 is a biologically important necroptosis suppressor.

Area of Science:

• Cellular Biology
• Immunology
• Molecular Biology

Background:

• Tumor necrosis factor α (TNFα) initiates necroptosis via the necrosome complex, involving RIPK1 and RIPK3.
• Mixed lineage kinase-domain-like (MLKL) is phosphorylated by RIPK3, leading to its oligomerization and cell death.
• TNF receptor-associated factor 2 (TRAF2) has been linked to apoptosis suppression.

Purpose of the Study:

• To investigate the role of TRAF2 in TNFα-induced necroptotic signaling.
• To elucidate the mechanism by which TRAF2 regulates necroptosis.
• To determine the in vivo significance of TRAF2 in necroptosis and organismal survival.

Main Methods:

• Utilized mouse fibroblasts to assess TNFα-driven necrosome formation and RIPK3-MLKL association upon TRAF2 disruption.
• Examined TRAF2-MLKL interactions and the effect of TNFα-induced deubiquitination.
• Generated TRAF2 knockout mice, including crosses with RIPK3 knockout mice, to evaluate in vivo lethality and necroptosis markers.
• Administered decoy receptors to assess their protective effects against TRAF2 deficiency-induced mortality.

Main Results:

• TRAF2 disruption in fibroblasts enhanced TNFα-induced necrosome formation and RIPK3-MLKL association, promoting necroptosis.
• TRAF2 constitutively binds MLKL, a process reversed by TNFα via deubiquitination; C-terminal TRAF2 is crucial for MLKL interaction.
• TRAF2 knockout in adult mice led to rapid lethality with increased hepatic necrosome assembly.
• TRAF2 knockout on a RIPK3 knockout background caused delayed mortality, with elevated intestinal caspase-8 activity.
• Combined decoy receptor treatment (TNFR1-Fc, Fas-Fc, DR5-Fc) prevented death in TRAF2 KO mice; TNFR1-Fc and IFNAR1-Fc offered partial protection in combined TRAF2/RIPK3 KO mice.

Conclusions:

• TRAF2 acts as a significant suppressor of necroptosis both in vitro and in vivo.
• TRAF2 inhibits TNFα-induced necroptosis by interacting with MLKL, thereby preventing its activation.
• These findings reveal a novel regulatory mechanism of necroptosis and highlight TRAF2 as a potential therapeutic target.