In rat aortic smooth muscle cells (RASMC), exposure to lipopolysaccharide (LPS) resulted in NF-κB-DNA binding, degradation of IκB-α, -β and -ε and increased activity of both α and β isoforms of inhibitory kappa B kinase (IKK). Expression of dominant-negative (DN)-IKK-α, IKK-β and NF-κB-inducing kinase (NIK) abolished LPS-stimulated NF-κB reporter activity, suggesting that activation of a NIK/IKK-dependent pathway is indispensable for NF-κB activation by LPS in this cell type. The tyrosine phosphatase inhibitor, pervanadate, abolished LPS-stimulated NF-κB-DNA-binding activity. However, the effect of pervanadate was shown to be mediated by excess hydrogen peroxide (H2O2) present in the reaction mix. Preincubation of RASMC with H2O2 inhibited LPS-stimulated IKK kinase activity and downstream NF-κB-DNA binding activity. H2O2 also strongly stimulated p38 MAP kinase activity in RASMCs. Effective inhibition of this pathway using SB203580 did not reverse the effects of H2O2 on LPS-stimulated IKK/NF-κB signalling. These studies show that hydrogen peroxide-mediated inhibition of LPS-stimulated NF-κB activation in RASMC occurs upstream of IKK. The inhibitory effect of H2O2 is not due to tyrosine phosphatase inhibition, it is mediated by H2O2 through a mechanism which is independent of any cross-talk involving MAP kinase homologues.
- hydrogen peroxide
- rat aortic smooth muscle cells
- inhibitory kappa B kinase