α-Melanocyte-Stimulating Hormone Inhibits Tumor Necrosis Factor α-Stimulated MUC5AC Expression in Human Nasal Epithelial Cells

Mucin hypersecretion is an important clinical feature of several respiratory diseases, including asthma, cystic fibrosis, nasal allergy, rhinitis, and sinusitis. It has been shown that alpha-melanocyte-stimulating hormone (alpha-MSH), a proopiomelanocortin (POMC)-derived peptide, has immunomodulatory activities by inhibiting NF-kappa B activation induced by proinflammatory cytokines such as TNF-alpha. Because MUC5AC expression is known to be up-regulated by TNF-alpha via NF-kappa B activation, we evaluated the inhibitory effect of alpha-MSH on MUC5AC gene expression induced by TNF-alpha in normal human nasal epithelial (NHNE) cells. Melanocortin-1-receptor (MC-1R) was detected by RT-PCR, Western blotting, and immunofluorescent labeling in NHNE cells. alpha-MSH suppressed NF-kappa B/p65 phosphorylation induced by TNF-alpha as well as IkB-alpha degradation in a dose-dependent manner, as assessed by Western blotting. In addition, alpha-MSH inhibited TNF-alpha-induced nuclear translocation of NF-kappa B and NF-kappa B luciferase activity. Real-time quantitative PCR data showed that alpha-MSH inhibited TNF-alpha-induced expression of MUC5AC, and this effect of alpha-MSH was neutralized by knockdown of MC-1R using MC-1R shRNA lentivirus. Analyses using RT-PCR and Western blotting showed the expression of POMC and two key enzymes in the POMC processing, proprotein convertases (PC) 1 and PC2, and 7B2, which is required for enzymatic activity of PC2, in normal human nasal mucosa. We conclude that alpha-MSH down-regulates MUC5AC expression by inhibiting TNF-alpha-induced NF-kappa B activity through MC-1R stimulation in NHNE cells and that normal human nasal mucosa possesses the POMC processing machinery. Therefore, alpha-MSH may be a promising candidate to decrease mucin overproduction initiated by NF-kappa B activation.