The ubiquitously expressed protein, β-arrestin2, is a multifunctional signaling molecule. It was originally identified as a negative regulator of GPCR signaling.28 It has been CH5424802 purchase demonstrated that β-arrestin2 is able to bind to NF-κB inhibitor IκBα in the cytoplasm to inhibit NF-κB activity.29, 30 In this work, we further investigated the function of β-arrestin2 in NF-κB signaling. HEK293 cells cotransfected with TGR5, β-arrestin2, and IκBα were challenged with TGR5

agonist 23(S)-mCDCA, then the cell extracts were subjected to immunoprecipitantion. TGR5 activation enhanced β-arrestin2 interaction with IκBα (Fig. 5A). These results were also confirmed in mouse livers. TGR5 ligand administration increased β-arrestin2 interaction with IκBα in WT, but not in TGR5−/− mouse livers (Fig. 5B). Knockdown of β-arrestin2 abolished the inhibition of TGR5 activation on NF-κB transactivity and its target gene expression induced by p65 overexpression (Fig. 5C-E). Adriamycin order These results indicate that TGR5 inhibits NF-κB in a β-arrestin2-dependent manner. GPCRs comprise the largest protein family of transmembrane receptors that sense molecules outside the cell and activate inside signal-transduction pathways through agonist binding to an orthosteric binding site. GPCRs regulate cell migration, proliferation, differentiation, and survival and play

a major role in the development and progression of many diseases, such as inflammatory selleck chemicals diseases and cancer.31, 32 Many GPCRs induce NF-κB activation,33, 34 whereas only a few GPCRs inhibit NF-κB-mediated inflammation.35 Two GPCRs, the A2A and A2B adenosine receptors, suppress the NF-κB pathway in a specific gene- and cell-type–dependent manner.35-37 Activation of β2-adrenergic receptor, a subtype of GPCRs, inhibits NF-κB activity by means of β-arrestin interaction with IκBα.29 Our data show that TGR5 is a potential suppressor

of NF-κB-dependent inflammatory response. TGR5 activation is able to enhance β-arrestin2 interaction with IκBα. TGR5 antagonizing NF-κB signaling was abolished by the expression of anti-β-arrestin2 siRNA (Fig. 5). These results suggest that TGR5 inhibits NF-κB in a β-arrestin2-dependent manner, and the inhibition of NF-κB-mediated inflammation by some GPCRs could share the same mechanism. It is interesting to study the mechanism of the TGR5-dependent β-arrestin2–IκBα interaction. We ruled out the possibility that TGR5 may interact with β-arrestin2. We also ruled out another possibility that activation of TGR5 may reduce the interaction of casein kinase II and β-arrestin2 and thus enhance the β-arrestin2–IκBα interaction.29 It will be interesting to continue the study in future work. We noted that TGR5 activation repressed specific sets of NF-κB target genes, but not all the target genes, in response to LPS in vitro and in vivo. This phenomenon has also been observed for bile acid nuclear receptor farnesoid X receptor.