Lipid Rafts and Caveolin-1 Coordinate Interleukin-1β (IL-1β)-dependent Activation of NFκB by Controlling Endocytosis of Nox2 and IL-1β Receptor 1 from the Plasma Membrane

Recent evidence suggests that signaling by the proinflammatory cytokine interleukin-1 beta (IL-1 beta) is dependent on reactive oxygen species derived from NADPH oxidase. Redox signaling in response to IL-1 beta is known to require endocytosis of its cognate receptor (IL-1R1) following ligand binding and the formation of redox-active signaling endosomes that contain Nox2 (also called redoxosomes). The consequent generation of reactive oxygen species by redoxosomes is responsible for the downstream recruitment of IL-1R1 effectors (IRAK, TRAF6, and I kappa B kinase kinases) and ultimately for activation of the transcription factor NF kappa B. Despite this knowledge of the signaling events that occur downstream of redoxosome formation, an understanding of the mechanisms that coordinate the genesis of redoxosomes following IL-1 beta stimulation has been lacking. Here, we demonstrate that lipid rafts play an important role in this process. We show that Nox2 and IL-1R1 localize to plasma membrane lipid rafts in the unstimulated state and that IL-1 beta signals caveolin-1-dependent endocytosis of both proteins into the redoxosome. We also show that inhibiting lipid raft-mediated endocytosis prevents NF kappa B activation. Finally, we demonstrate that Vav1, a Rac1 guanine exchange factor and activator of Nox2, is recruited to lipid rafts following IL-1 beta stimulation and that it is required for NF kappa B activation. Our results fill in an important mechanistic gap in the understanding of early IL-1R1 and Nox2 signaling events that control NF kappa B activation, a redox-dependent process important in inflammation.