Glucosamine suppresses the nuclear factor-κB signaling via the <i>O</i> -linked- <i>N</i> -acetylglucosamine modification of inhibitor of κB kinase β in human synovial MH7A cells

We previously demonstrated that glucosamine (GlcN) exerts anti-inflammatory effects through the inhibition of nuclear factor-κB (NF-κB) signaling, possibly via O-linked-N-acetylglucosamine (O-GlcNAc) modification. In this study, we examined the effects of GlcN and alloxan (an inhibitor of O-linked-N-acetylglucosamine transferase) on NF-κB signaling molecules in interleukin (IL)-1β-stimulated human synovial MH7A cells. GlcN-induced O-GlcNAc modification of NF-κB and markedly inhibited IL-1β-induced nuclear translocation of the NF-κB, and phosphorylation of p65 subunit. GlcN also suppressed IL-1β-induced phosphorylation and degradation of inhibitor of κB (IκB). Moreover, GlcN promoted O-GlcNAc modification of IκB kinase (IKK) β, which phosphorylates IκBα, and concurrently inhibited its phosphorylation (activation). Notably, the effects of GlcN on NF-κB, IκBα, and IKKβ were reversed by alloxan. Finally, the inhibitory effect of GlcN on IL-8 production was eliminated in IKKβ-knockdown cells. Collectively, these findings indicate that O-GlcNAc modification of IKKβ is a key mediator of GlcN-induced suppression of NF-κB signaling and inflammatory cytokine production.