Abstract
This study aimed to investigate the expression of tumour necrosis factor receptor (TNF-R) at the gene and surface level, and its shedding in human lung tissue and a pulmonary epithelial cell line, A549. Levels of gene expression of TNF-R were evaluated by Northern blot analysis. Human lung tissue expressed both type I and type II TNF-R gene, while A549 cells expressed only type I TNF-R gene. Phorbol ester upregulated and TNF-alpha down-regulated the TNF-R gene expression in A549 cells. Consistent with these modulations of TNF-R gene expression, 125I-TNF binding capacities were increased with phorbol ester stimulation and decreased with TNF stimulation after 24 h in A549 cells. The shedding of TNF-R from A549 cells was investigated using enzyme-linked immunosorbent assay (ELISA) for soluble type I TNF-R. Not only lung tissues but also A549 cells spontaneously released soluble type I TNF-R into the culture medium. Both phorbol ester and TNF stimulation accelerated the shedding of soluble TNF-R from A549 cells. These results suggest that type I TNF-R gene expression and shedding of soluble TNF-R are differentially regulated in A549 cells. We conclude that tumour necrosis factor receptor surface expression is regulated, at least in part, at the gene expression level and shedding of soluble tumour necrosis factor receptor is modulated by inflammatory mediators, such as tumour necrosis factor in A549 cells.
