Mucin-5AC (716-724)

In this study, we investigated whether wogonin significantly affects MUC5AC mucin gene expression and production in human airway epithelial cells. Confluent NCI-H292 cells were pretreated with wogonin for 30 min and then stimulated with tumor necrosis factor-α (TNF-α) for 24 h or the indicated periods. The MUC5AC mucin gene expression and mucin protein production were measured by RT-PCR and ELISA, respectively. We found that incubation of NCI-H292 cells with wogonin significantly inhibited mucin production and down-regulated MUC5AC gene expression induced by TNF-α in a dose-dependent fashion. To elucidate the action mechanism of wogonin, effect of wogonin on TNF-α-induced NF-κB signaling pathway was investigated by western blot analysis. Wogonin inhibited NF-κB activation induced by TNF-α. Inhibition of IKK by wogonin led to the suppression of IκB phosphorylation and degradation, p65 nuclear translocation and NF-κB-regulated gene expression. This, in turn, led to the down-regulation of MUC5AC protein production in NCI-H292 cells. Wogonin also inhibited the gene products involved in cell survival (Bcl-2) and proliferation (cyclooxygenase-2). These results suggest that wogonin inhibits the NF-κB signaling pathway, which may explain its role in the inhibition of MUC5AC mucin gene expression and production.

Airway mucus secretion is an essential innate immune response for host protection. However, overproduction and hypersecretion of mucus, mainly composed of MUC5AC, are significant risk factors in asthma and chronic obstructive pulmonary disease (COPD) patients. Previously, we reported that verproside, a catalpol derivative iridoid glycoside isolated from Pseudolysimachion rotundum var. subintegrum, is a potent anti-asthmatic candidate drug in vivo. However, the molecular mechanisms underlying the pharmacological actions of verproside remain unknown. Here, we found that verproside significantly reduces the expression levels of tumor necrosis factor alpha (TNF-α)-induced MUC5AC mRNA and protein by inhibiting both nuclear factor kappa B (NF-κB) transcriptional activity and the phosphorylation of its upstream effectors such as IκB kinase (IKK)β, IκBα, and TGF-β-activated kinase 1 (TAK1) in NCI-H292 cells. Moreover, verproside attenuated TNF-α-induced MUC5AC transcription more effectively when combined with an IKK (BAY11-7082) or a TAK1 (5z-7-oxozeaenol) inhibitor than when administered alone. Importantly, we demonstrated that verproside negatively modulates the formation of the TNF-α-receptor (TNFR) 1 signaling complex [TNF-RSC; TNFR1-recruited TNFR1-associated death domain protein (TRADD), TNFR-associated factor 2 (TRAF2), receptor-interacting protein kinase 1 (RIP1), and TAK1], the most upstream signaling factor of NF-κB signaling. In silico molecular docking studies show that verproside binds between TRADD and TRAF2 subunits. Altogether, these results suggest that verproside could be a good therapeutic candidate for treatment of inflammatory airway diseases such as asthma and COPD by blocking the TNF-α/NF-κB signaling pathway.

Alpha-melanocyte stimulating hormone (alpha-MSH) has pigmentary, anti-inflammatory, antipyretic, and general immunomodulatory roles. It can oppose several cytokines including tumor necrosis factor-alpha in a number of tissues, including skin. We have previously shown that alpha-MSH can inhibit tumor necrosis factor-alpha stimulated intercellular adhesion molecule 1 upregulation and nuclear factor kappaB (NFkappaB) transcription factor activation in melanocyte and melanoma cells. It is thought, however, that this MSH biology may also extend to other cells of the skin and in this study we extend our work to keratinocytes. We have investigated in detail the ability of three alpha-MSH peptides to inhibit tumor necrosis factor alpha stimulated NFkappaB activation in nonpigmentary HaCaT keratinocytes (alpha-MSH, L-Lys-L-Pro-L-Val, and L-Lys-L-Pro-D-Val) and two adrenocorticotropic hormone (ACTH) peptides (1-17 and 1-39), reported to be present in skin tissue. NFkappaB/p65 activation was analyzed by electrophoretic mobility shift assay and immunofluorescent microscopy. alpha-MSH, L-Lys-L-Pro-L-Val, and L-Lys-L-Pro-D-Val all significantly inhibited tumor necrosis factor alpha stimulated NFkappaB activation, whereas ACTH 1-17 and 1-39 did not, in the HaCaT keratinocytes. MSH peptides and ACTH 1-39 were effective, however, at inhibiting NFkappaB activation in normal human keratinocytes. Immunolabeling of inhibitor kappaBalpha of NFkappaB (IkappaBalpha) revealed an abnormal localization to the nucleus of HaCaT cells, which was unaffected by MSH/ACTH peptides. In contrast, normal human keratinocytes showed a normal IkappaBalpha distribution that responded to MSH/ACTH with nuclear translocation. Our data support previous work on the role of MSH/ACTH peptides as immunomodulatory/anti-inflammatory regulators, and extend this work to keratinocytes identifying a novel IkappaBalpha mechanism and extends findings to ACTH peptides, identifying an abnormal IkappaBalpha mechanism in the immortal HaCaT versus normal keratinocyte.