An analysis of the molecular regulation of tumor necrosis factor-alpha expression in human mast cells
The objective of this study was to analyze the molecular regulation of tumour necrosis factor-alpha (TNF-α) gene expression in human cells. Allergic diseases (e.g., asthma) comprise one of the most prominent medical problems in Canada, and their incidence and severity are on the increase here as in most industrialized countries. Allergic responses are initiated by contact of allergens with specific IgE antibodies on mast cells, leading to cellular activation. Such activation induces mast cells to release very large amounts of the pro-inflammatory cytokine TNF-α which, by itself, mediates much of the cellular recruitment associated with the allergic late phase response (LPR). Most of the pathology of allergic diseases is directly attributable to the LPR. The molecular mechanism regulating TNF-α expression in mast cells, as opposed to that in macrophages (which can also produce an abundance of TNF-α) is poorly understood. My hypothesis is that if TNF-α were differentially regulated in mast cells, it might be possible to therapeutically manipulate its highly pathogenic contributions to allergic diseases without affecting the other roles of this cytokine in the body. I examined the kinetics of TNF-α gene transcription and protein expression in mast cell-differentiated KU812 cells which I stimulated with phorbol-12, 13-myristate acetate (PMA) and calcium ionophore A23187 (PMA and A23187 effectively mimic FcεRI stimulation of mast cells). RT-PCR and ELISA methods were used to detect TNF-α mRNA and protein, respectively. My results indicate that low levels of TNF-α is stored in the unstimulated cells (but not in the supernatant fluids), high levels of TNFα were secreted into the culture supernatants within 2 hr after stimulation. The critical regulatory elements in the human TNF-α promoter were studied. A human TNF -a gene promoter fragment (-625 to +19 bp relative to the transcription start site; TSS) was enzymatically digested from the 5' end inward and thereby I generated a series of promoter fragments of varying sizes. Each of these promoter fragments were placed immediately 5' to a cDNA encoding the marker protein luciferase. Then the constructs were transfected into differentiated KU812 cells and I assessed the TNF promoter-driven luciferase expression in the mast cells following PMA/A23187 challenge. A negative (-331 to -205) and several positive (-82 to +19, -131 to -82, -205 to -153) control regions were identified within the TNF-α promoter.