REGULATION OF EXPRESSION OF THE RAT SERINE-PROTEASE-INHIBITOR-2.3 GENE BY GLUCOCORTICOIDS AND INTERLEUKIN-6 - A COMPLEX AND UNUSUAL INTERPLAY BETWEEN POSITIVE AND NEGATIVE CIS-ACTING ELEMENTS

The rat serine protease inhibitor 2.3 gene (spi 2.3) is almost complet ely silent in normal animals and is transiently expressed during acute inflammation. It encodes a potential anti-elastase which is likely to play a major physiological role for the host defense. Two well-known inflammatory mediators, glucocorticoids and interleukin-6 (IL-6) activ ate the spi 2.3 promoter and increase steady-state levels of mRNA in c ultured hepatocytes. GC activation is mediated by a single glucocortic oid-response element which seems to act autonomously. A unique array o f four functional IL-6-response sites was identified in the spi 2.3 pr omoter. Three of them (C-II-IV) bear structural identity to the CCAAT/ enhancer-binding-protein-binding site consensus sequence, whereas the forth closely resembles the consensus kappa B nuclear factor recogniti on motif. The C-IV element, which is the most active, contains the mot if 5'-CTGGGA and binds the IL-6-inducible acute-phase response factor present in liver nuclear extracts from inflamed rats. Both basal and I L-6-dependent activities of each individual cytokine-response element tested separately are strongly down regulated by a recently identified regulatory sequence [Le Cam, A. & Legraverend, C. (1995) Eur. J. Bioc hem. 231, 620-627], located in the 3' untranslated region of the spi 2 .3 gene. However, this repressor element does not significantly affect overall IL-6-dependent spi 2.3 promoter activity. This suggests that, in the context of the active gene in vivo, all four IL-6-response sit es, which are largely redundant, cooperate to overcome the strong repr essive effect of the 3' untranslated region silencer and are needed to bring about a maximal IL-6 response. These data reveal a novel type o f regulation of an acute-phase gene involving different classes of IL- 6-response elements controlled by a repressor and acting in conjunctio n with a glucocorticoid-response element.