Inhibition of IKK down-regulates antigen + IgE-induced TNF production by mast cells: A role for the IKK-IκB-NF-κB pathway in IgE-dependent mast cell activation

Mast cells (MC) are major effector cells for allergic diseases. Cross-linking of immunoglobulin E (IgE) and its high-affinity receptor, FcεRI, by antigen initiates a cascade of signaling events leading to nuclear factor (NF)-κB activation and tumor necrosis factor (TNF) production. Here, we demonstrated that inhibition of inhibitor of κB (IκB) kinase (IKK) by a peptide IKK inhibitor or by four individual chemical IKK inhibitors including 15-deoxyprostaglandin J₂, BMS-345541, SC-514, or sulindac significantly blocked IgE + trinitrophenyl (TNP)-induced TNF production by mouse bone marrow-derived MC (BMMC). Moreover, IgE + TNP induced a rapid phosphorylation of IKKα but not IKKβ in BMMC. IgE + TNP-induced phosphorylation of IKKα was accompanied with phosphorylation and degradation of IκBα, subsequent NF-κB activation, and TNF production. Inhibition of IKK by sulindac decreased IKKα phosphorylation, IκBα phosphorylation and degradation, NF-κB activation, and TNF production by BMMC. It is interesting that IgE + TNP stimulation also induced a prominent synthesis of IKKα and IκBα. Inhibition of NF-κB activity by pyrrolidine dithiocarbomate (PDTC) blocked IgE + TNP-induced IκBα synthesis. NF-κB activity and TNF production were also inhibited when PDTC was used even after IgE + TNP stimulation, suggesting a potential role for the newly synthesized IκBα in MC activation. In addition, IgE + TNP-induced IKKα and IκBα phosphorylation was inhibited by a protein kinase C (PKC) inhibitor Ro 31-8220. Taken together, our results support a role for the IKK-IκB-NF-κB pathway, which likely involves PKC in IgE-dependent TNF production by MC. Thus, IKK may serve as a new target for the regulation of MC function in allergy.