TUMOR-NECROSIS-FACTOR-ALPHA INDUCES MUCIN HYPERSECRETION AND MUC-2 GENE-EXPRESSION BY HUMAN AIRWAY EPITHELIAL-CELLS

Tumor necrosis factor-alpha (TNF-alpha) is a multifunctional, proinfla mmatory cytokine that is capable of activating a diverse number of tar get genes within multiple cell types. Little information is known rega rding the role of TNF-alpha in the regulation of human airway mucin hy persecretion and MUG-2 gene expression. To assess the effect of TNF-al pha exposure on mucin secretion, human airway organ cultures and prima ry cultures of human airway epithelial cells were stimulated with 20 n g/ml of recombinant human TNF-alpha and mucin secretion quantitated by an enzyme-linked immunosorbent assay using a specific monoclonal anti body directed against human airway mucin. Significant increases in muc in secretion from human airway organ cultures were initially detected at 1 h, peaked at 8 h, and persisted for 24 h. The TNF-alpha-mediated mucin hypersecretion at 8 h was concentration dependent. Significant i ncreases in mucin secretion from primary cultures of human airway epit helial cells were initially detected at 4 h, peaked at 48 h, and persi sted for 72 h after stimulation with 20 ng/ml of recombinant human TNF -alpha. The TNF-alpha-mediated mucin hypersecretion at 48 h from prima ry cultures of human airway epithelial cells was inhibited by coincuba tion with soluble 55 kD, type I TNF receptors. Using reverse transcrip tion-polymerase chain reaction and a human pulmonary mucoepidermoid ca rcinoma cell line (NCI-H292), increases in MUG-2 steady-state mRNA lev els were first detectable after 30 min of TNF-alpha stimulation and pe rsisted for 24 h. Cycloheximide did not inhibit TNF-alpha-mediated MUG -2 mRNA expression at 1 h, suggesting that new protein translation was not required. In addition, TNF-alpha-mediated MUG-2 gene expression w as inhibited by calphostin C and genistein, suggesting that signal tra nsduction was dependent on both protein kinase C and tyrosine kinases. These data suggest that human airway epithelial cell mucin hypersecre tion and MUC-2 gene expression may be regulated by proinflammatory cyt okines, such as TNF-alpha. Consequently, TNF-alpha-mediated mucin hype rsecretion and MUG-2 gene expression might contribute to the pathogene sis of human inflammatory airway disorders, such as asthma.