Transcriptional activation of the interleukin-8 gene by platelet-activating factor in human peripheral blood monocytes.

Interleukin-8 (IL-8) is a member of the chemokine family and a potent neutrophil chemoattractant and activator. It is produced by a variety of cell types during inflammation. In the present work, we examined the regulation of IL-8 gene expression in monocytes by the pro-inflammatory lipid mediator, platelet-activating factor (PAF). Stimulation of human peripheral blood monocytes with PAF augmented their release of IL-8. The enhancement of IL-8 secretion was associated with an increase in IL-8 mRNA expression. PAF induced a concentration- and time-dependent augmentation of IL-8 mRNA accumulation. The response was maximal at PAF concentrations of 10-100 nM. The increased mRNA expression was evident after 1.5 hr of stimulation and persisted for 6 hr. Stimulation of monocytes with PAF, followed by arrest of de novo transcription with actinomycin D, indicated that PAF only marginally increased the stability of IL-8 mRNA. However, in vitro nuclear transcription demonstrated that the enhancement of IL-8 mRNA expression occurred mainly at the transcriptional level. The PAF-induced increase in IL-8 mRNA levels could be blocked with a PAF receptor antagonist. These results show, for the first time, that IL-8 gene expression and protein production can be upregulated by PAF. This interaction could be important in the development and amplification of the inflammatory response.

Structure and metal-regulated expression of the gene encoding Xenopus laevis metallothionein-A.

To investigate the regulation of amphibian metallothionein(MT)-encoding genes, we have isolated and sequenced the XlMT-A gene encoding Xenopus laevis (Xl) MT-A. The gene displays an overall structure similar to that of mammalian MT, with three exons interrupted by two introns. The promoter region contains a typical TATA box and two metal regulatory elements (MRE) within the first 100 bp upstream from the transcription start point (tsp). The transition metal ion (Mc2+) inducibility of the promoter was studied by transient expression experiments in CV-1 African green monkey kidney cells, using different DNA fragments from the 5'-flanking region of XlMT-A fused to the bacterial cat reporter gene. The first 145 bp upstream from the tsp are sufficient to confer inducibility of cat by Cd2+. Constructs bearing only the most proximal MRE are not inducible by Me2+, thus suggesting that both MRE are required for Me2+ induction. Recognition sites for the transcription factors, AP-1 and AP-2, are located within the first 180 bp of the promoter region and these elements appear to be involved in controlling the constitutive basal level of expression of this MT.