β2-Adrenergic receptor regulate Toll-like receptor 4-induced late-phase NF-κB activation

Stimulation of Toll-like receptor 4 (TLR4) by lipopolysaccharide (LPS) triggers myeloid differentiation factor 88 (MyD88)-dependent early-phase NF-kappa B activation and Toll/IL-1 receptor domain-containing adaptor-inducing IFN-beta (TRIF)-dependent late-phase NF-kappa B activation. In a previous study, we have shown that beta(2)-adrenergic receptor (beta(2)AR) functions as a negative regulator of NF-kappa B activation through beta-arrestin 2 in the macrophage cell line RAW264 and that down-regulation Of beta(2)AR expression in response to LIPS is essential for NF-kappa B activation and expression of its target gene, inducible nitric oxide synthase (NOS II). Here, we demonstrate that beta(2)AR plays an important role in TRIF-dependent late-phase NF-kappa B activation. LPS-stimulated down-regulation was induced in MyD88-knockdown cells, but not in TRIF-knockdown cells, suggesting that NAR expression was down-regulated by the TRIF-dependent pathway. On the other hand, depletion Of beta(2)AR or beta-arrestin 2 expression by siRNA decreased cytoplasmic I kappa B alpha and abrogated late-phase I kappa B alpha degradation and NF-kappa B activation in response to LPS. Inducible nitric oxide synthase (NOS II) expression was increased continuously during 24 h of LPS stimulation in control cells, but decreased in beta(2)AR or beta-arrestin 2-knockdown cells after 6 h of LPS stimulation. These findings suggest that beta(2)AR functions not only as a negative regulator of NF-kappa B activation, but also as a stabilizing factor of the NF-kappa B/I kappa B alpha complex through cytoplasmic beta-arrestin 2, and that TRIF-dependent down-regulation Of beta(2)AR expression increases the level of cytoplasmic NF-kappa B/I kappa B alpha complex free from beta-arrestin 2, leading to continuous late-phase NF-kappa B activation. (C) 2008 Elsevier Ltd. All rights reserved.