ABSTRACT
In the present study, we investigated whether apigenin significantly affects tumor necrosis factor-alpha (TNF-alpha)-induced production and gene expression of MUC5AC mucin in airway epithelial cells. Confluent NCI-H292 cells were pretreated with apigenin for 30 min and then stimulated with TNF-alpha for 24 h or the indicated periods. The MUC5AC mucin gene expression and mucin protein production were measured by reverse transcription - polymerase chain reaction (RT-PCR) and enzyme-linked immunosorbent assay (ELISA), respectively. Apigenin significantly inhibited MUC5AC mucin production and down-regulated MUC5AC gene expression induced by TNF-alpha in NCI-H292 cells. To elucidate the action mechanism of apigenin, effect of apigenin on TNF-alpha-induced nuclear factor kappa B (NF-kappaB) signaling pathway was also investigated by western blot analysis. Apigenin inhibited NF-kappaB activation induced by TNF-alpha. Inhibition of inhibitory kappa B kinase (IKK) by apigenin led to the suppression of inhibitory kappa B alpha (IkappaBalpha) phosphorylation and degradation, p65 nuclear translocation. This, in turn, led to the down-regulation of MUC5AC protein production in NCI-H292 cells. Apigenin also has an influence on upstream signaling of IKK because it inhibited the expression of adaptor protein, receptor interacting protein 1 (RIP1). These results suggest that apigenin can regulate the production and gene expression of mucin through regulating NF-kappaB signaling pathway in airway epithelial cells.