Interleukin 6 is a negative regulator of the acute phase alpha 1-inhibitor III gene.

The broad-range proteinase inhibitor alpha 1-inhibitor III (alpha 1I3), a member of the complement C3/alpha 2-macroglobulin protein family, is the prototype of a negatively regulated acute phase protein. During an acute inflammatory reaction alpha 1I3 plasma protein and liver mRNA concentrations are decreased three- to fourfold in rats, and in chronic inflammations the protein concentration is reduced between ten- and 20-fold. In search of a cell culture model to study the regulation of the alpha 1I3 gene by mediators of inflammation, five well-established rat hepatoma cell lines were examined. All five lines constitutively expressed the gene, a marker for a highly differentiated hepatic phenotype, although at less than one-tenth the level of its expression in vivo. In the three hepatoma lines FAZA, FTO2B and FAO1, alpha 1I3 mRNA was decreased by treatment with interleukin 6 (IL6) and glucocorticoids. Among these lines untreated FAO1 cells produced the highest constitutive concentrations of alpha 1I3 mRNA and in FAO1 cells alpha 1I3 mRNA concentrations were decreased up to fourfold in a dose-responsive and time-dependent manner after treatment with IL6 alone or with combinations of IL6 and the synthetic glucocorticoid dexamethasone. Thus, IL6 alone was sufficient to negatively regulate alpha 1I3 mRNA levels in hepatoma cells with similar characteristics as occur during an inflammatory response in the liver. A number of other acute phase mRNA species, including alpha 1-acid glycoprotein, T2-kininogen, gamma-fibrinogen and alpha 2-macroglobulin were induced to higher levels by the same hormonal treatments in FAO1 cells. The fourfold reduction of alpha 1I3 mRNA concentrations in FAO1 cells could be reversed by treatment with 1 microM of a water-soluble derivative of forskolin, an activator of the cyclic AMP pathway. Thus, the effect of IL6 on the expression of the alpha 1I3 gene may involve the activation of the cyclic AMP pathway. In contrast, T2 kininogen mRNA levels were not altered by treatment of FAO1 cells with forskolin, suggesting that IL6 may act on this gene through a different mechanism.