Use of the acute phase serum amyloid A2 (SAA2) gene promoter in the analysis of pro- and anti-inflammatory mediators: differential kinetics of SAA2 promoter induction by IL-1 beta and TNF-alpha compared to IL-6.

A cytokine responsive construct, pGL2-SAA2pt, was generated by cloning the acute phase promoter of human serum amyloid A2 (SAA2) upstream of a luciferase reporter gene. The construct responds to the inflammatory mediators MoCM, IL-1 beta, TNF-alpha, and IL-6 in a manner that closely mimics the response of the endogenous SAA2 gene to such stimuli: i.e. single treatments induce transcriptional activation by IL-1 beta and TNF-alpha to a greater extent than by IL-6 at 12-24 h. However, timecourse experiments show that the kinetics of induction generated by IL-1 beta and TNF-alpha are quite distinct from IL-6, IL-6 having a much greater effect at 3-6 h. IL-1 beta and TNF-alpha synergize with IL-6 to give a 10-fold increase in transcriptional readout over single cytokine treatments. The kinetics of this synergistic response resembles that generated by IL-6 alone. The IL-1 receptor antagonist, hIL-1ra, can specifically block the IL-1 beta driven transcriptional activation of pGL2-SAA2pt, but not that driven by TNF-alpha or IL-6. Furthermore, in synergistic cytokine combinations, it blocks only the IL-1 beta driven component indicating that the effect is biological and not attributable to toxicity. Consequently assays utilizing pGL2-SAA2pt will be useful both for the investigation of the kinetics of inflammatory signalling in a cytokine specific manner, and for the evaluation of the pro- and anti-inflammatory properties of novel natural and synthetic molecules.