Tumor necrosis factor-alpha stimulates human Clara cell secretory protein production by human airway epithelial cells

Clara cell secretory protein (CCSP), or CC10, is an inhibitor of secretory phospholipase A2 which may be produced by phagocytic cells and by a variety of other cells in the airway. Tumor necrosis factor-alpha (TNF-alpha) is capable of activating phospholipases and inducing the expression of a variety of genes in the airway epithelium which may modulate the airway inflammatory response. Therefore, it was of interest to determine whether this proinflammatory cytokine could induce the production of a counterregulatory protein such as CCSP which might modulate the production of eicosanoid mediators in the airway. Using a human bronchial epithelial cell line (BEAS-2B), CCSP messenger RNA (mRNA) levels were detected by ribonuclease protection assay. TNF treatment of these cells increased CCSP mRNA levels in a time- and dose-dependent manner. The CCSP mRNA level increased in response to TNF-alpha (20 ng/ml) stimulation after 8 to 36 h with the peak increase at 18 h. Immunoblotting of CCSP protein released into the culture media demonstrated that TNF-alpha induced the synthesis and secretion of CCSP protein in a time-dependent manner over 8 to 18 h. The results of a CCSP reporter gene activity assay, nuclear run-on assay, and CCSP mRNA half-life assay indicated that the TNF-alpha-induced increases in CCSP gene expression are regulated at the post-transcriptional level. We conclude that TNF-alpha induces airway epithelial cell expression of human CCSP protein and may modulate airway inflammatory responses in this manner.