A Novel TNF Receptor-Associated Factor 6 Binding Domain Mediates NF-κB Signaling by the Common Cytokine Receptor β Subunit

Abstract

GM-CSF, IL-3, and IL-5 are proinflammatory cytokines that control the production and function of myeloid and lymphoid cells. Their receptors are composed of a ligand-specific α subunit and a shared common signal-transducing β subunit (β common receptor or GM-CSFR β [βc]). The pleiotropic nature of biologic outcomes mediated by βc and the presence of large, uncharacterized regions of its cytoplasmic domain suggest that much remains to be learned about its downstream signaling pathways. Although some previous work has attempted to link βc with NF-κB activation, a definitive mechanism that mediates this pathway has not been described and, to date, it has not been clear whether the receptor can directly activate NF-κB. We demonstrate that NF-κB activation by βc is dependent on TNFR-associated factor 6 (TRAF6) and that association of TRAF6 with βc requires a consensus-binding motif found in other molecules known to interact with TRAF6. Furthermore, point mutation of this motif abrogated the ability of βc to mediate NF-κB activation and reduced the viability of an IL-3–dependent hematopoietic cell line. Because this receptor plays a key role in hematopoiesis and the βc cytoplasmic domain identified in this work mediates hematopoietic cell viability, this new pathway is likely to contribute to immune cell biology. This work is significant because it is the first description of a TRAF6-dependent signaling pathway associated with a type I cytokine receptor. It also suggests that TRAF6, a mediator of TNFR and TLR signaling, may be a common signaling intermediate in diverse cytokine receptor systems.