The E3 ubiquitin ligases HOIP and cIAP1 are recruited to the TNFR2 signaling complex and mediate TNFR2-induced canonical NF-κB signaling.

Tumor Necrosis Factor (TNF) is a proinflammatory cytokine that elicits its action by binding to two cell surface TNF receptors (TNFR), TNFR1 and TNFR2, which are expressed by many different cell types. Stimulation of TNFR1 activates canonical NF-κB signaling, leading to the NF-κB dependent expression of a large number of genes. Canonical NF-κB signaling requires the assembly of a TNFR1 signaling complex at the cell membrane, whose formation is regulated by different protein ubiquitination events. In this context, recruitment of the Linear Ubiquitin Chain Assembly Complex (LUBAC) to TNFR1 plays an important role by mediating M1-linked polyubiquitination of specific NF-κB signaling proteins. In contrast to TNFR1, much less is known about the role of ubiquitination in TNFR2 signaling. Here we demonstrate that specific TNFR2 stimulation rapidly triggers M1- and K63-linked polyubiquitination at the TNFR2 signaling complex. In agreement, TNFR2 stimulation induces the recruitment of HOIP, a LUBAC component and the only known E3 ubiquitin ligase for M1-polyubiquitination, to the TNFR2 signaling complex. Also cIAP1, a E3 ubiquitin ligase able to modify proteins with K63-polyubiquitin chains, was recruited to the TNFR2 signaling complex. Treatment of cells with a cIAP antagonist inhibited the recruitment of HOIP and prevented HOIP-mediated M1-ubiquitination of the TNFR2 signaling complex, indicating that HOIP recruitment to the TNFR2 relies on cIAPs. Finally, we show that both HOIP and cIAP1 are required for TNFR2-induced canonical NF-κB activation. Together, our findings demonstrate an important role for M1- and K63-linked polyubiquitination in TNFR2 signaling.