The permissive role of glucocorticoids on interleukin-1 stimulation of angiotensinogen gene transcription is mediated by an interaction between inducible enhancers

The acute-phase activation of the rat angiotensinogen (rAT) gene in liver cells is a transcriptional event mediated through an interleukin-1-inducible, NFκB-binding, cis-acting element (the acute-phase response element [APRE]). Using a cell culture model for the acute-phase response, we showed that the Increase in angiotensinogen mRNA in H35 rat hepatoma cells requires costimulation with glucocorticoids and cytokines. Stably transfected rAT promoter-luciferase reporter genes were also activated by cytokines only in the presence of glucocorticoids. This permissive role of glucocorticoids is dependent on the expression of functional glucocorticoid receptors, because in HepG2 cells naturally deficient in such receptors, rAT gene-luciferase reporter constructs responded to interleukin-1 only when cotransfected with an expression vector for the glucocorticoid receptor. Point mutations in the two rAT gene glucocorticoid response elements located adjacent to the APRE led to loss of interleukin-1 inducibility. Induction of luciferase activity in transfected cells occurred even in the presence of cyclobeximide, demonstrating that this synergistic response did not depend on new protein synthesis. Thus, a direct interaction between the interleukin-1-inducible NFκB-binding APRE and glucocorticoid response elements, located in cis, underlies the acute-phase activation of the rAT gene.