Investigating the Interaction between TRAF1 and the Cellular Inhibitor of Apoptosis Protein 2 (cIAP2)

A fundamental family of adaptor proteins termed, tumor necrosis factor receptor (TNFR) -associated factors (TRAFs) are essential for signal transduction of various receptors. However, one particular member of the TRAF family, TRAF1 stands out for its ability to have opposing effects on NF-B activation downstream the TNFR and TLR signalling pathways. Previous studies have shown that TRAF1 is linked to an increased risk of rheumatoid arthritis (RA). Nonetheless, the mechanism concerning its role in RA is unclear. Autoimmune diseases such as RA and other inflammatory diseases are complex diseases that require the activation of multiple immune signalling pathways. In lymphocytes where TNFR pathway is predominant, TRAF1 recruits c-IAP2 to activate NF-B leading to survival and proliferation of these cells. In inflammatory cells like macrophages, TLR signalling pathway is more predominant in activating NF-B leading to the production of cytokines, where and TRAF1 inhibits this pathway through binding to the LUBAC complex. Since TRAF1 has opposing roles on NF-B activation downstream of TLR and TNF receptors, it is important to study the role of TRAF1 in regulating these pathways one at a time. This study aims to investigate the role of TRAF1 downstream of TNFR signalling pathway through studying its interaction with c-IAP2. We have developed mutated versions of TRAF1 and through the use of co-immunoprecipitation determined the exact amino acids that are responsible for the interaction between TRAF1 and cIAP2. Ultimately, we identified a version of TRAF1 that does not interact with cIAP2 while maintaining its interaction with other proteins such as TRAF2 and the LUBAC complex. Moreover, we have demonstrated for the first time that TRAFs direct interaction with cIAP2 protects it from proteasomal degradation. These results provide important insights into TRAF1/cIAP2 interaction, which may ultimately lead to development of new therapeutics that target it.