Lobetyolin, lobetyol and methyl linoleate were reported to be derived from
C. pilosula6 and there are some reports with regard to the biological effects of lobetyolin, lobetyol and methyl linoleate
7,8. However, as aforementioned in introduction, there are no reports about the potential effects of lobetyolin, lobetyol and methyl linoleate on mucin secretion, production and gene expression from airway epithelial cells. Among the twenty one or more MUC genes coding human mucins reported, MUC5AC was mainly expressed in goblet cells in the airway surface epithelium
2,12. PMA was reported to stimulate the endogenous activator of protein kinase C (PKC), diacylglycerol
13 and to be an inflammatory stimulant that can control a gene transcription
14, cell growth and differentiation
15. PMA also can induce
MUC5AC gene expression in NCI-H292 cells. In brief, PMA activates a type of PKC isoforms. This activates matrix metalloproteinases, which cleave pro-epidermal growth factor receptor (pro-EGFR) ligands from the cell surface to become mature EGFR ligands. These ligands bind to the EGFR, provoking the phosphorylation of its intracellular tyrosine kinase. This leads to activation of MEK leading to ERK activation. Following is the activation of the transcription factor, Sp1, and binding of the factor to specific sites with the
MUC5AC gene promoter. Eventually, the promoter is activated and produced the gene transcription and translation to MUC5AC mucin protein
14. Based on these reports, we investigated the effects of lobetyolin, lobetyol and methyl linoleate on PMA-induced MUC5AC mucin secretion, production and gene expression from NCI-H292 cells, a human pulmonary mucoepidermoid cell line. As shown in results, lobetyolin, lobetyol and methyl linoleate decreased MUC5AC mucin gene expression stimulated by PMA (
Figure 1). Next, we tried to examine whether the three compounds regulate the production of MUC5AC mucin proteins, since the three compounds affect the transcriptional level of gene expression. As a result, lobetyol and methyl linoleate suppressed PMA-induced MUC5AC mucin production from NCI-H292 cells. However, lobetyolin did not affect mucin production (
Figure 2). Finally, we checked whether the three compounds affect the secretion step of MUC5AC mucin, because the production and secretion of airway mucin can be controlled separately. As can be seen in
Figure 3, methyl linoleate suppressed the secretion of MUC5AC mucin induced by PMA. However, lobetyolin and lobetyol did not affect mucin secretion. These results suggest that, among the three natural products, only methyl linoleate showed the consistent inhibitory activities on secretion, production and gene expression of airway MUC5AC mucin, by directly acting on airway epithelial cells. The underlying mechanism of action of methyl linoleate on MUC5AC secretion, production and gene expression are not clear at present, although we are investigating whether methyl linoleate act as potential regulators of the mitogen-activated protein kinase cascade after ligand binding to the EGFR and/or potential regulators of nuclear factor kB signaling pathway, in mucin-producing NCI-H292 cells. Taken together, the inhibitory action of methyl linoleate on airway mucin secretion, production and gene expression might explain, at least in part, the folk use of
C. pilosula, as an anti-inflammatory and anti-allergic agent for pulmonary inflammatory diseases, in traditional folk medicine. We suggest it is valuable to find the natural products that have specific inhibitory effects on mucin secretion, production and gene-in view of both basic and clinical sciences-and the result from this study suggests a possibility of developing methyl linoleate as a candidate for the new efficacious mucoregulators for pulmonary diseases, although further studies are required.