Glucocorticosteroids have a wide variety of effects which result in the long-term dampening of inflammatory responses. An important site of steroid action may be on the control of the activator protein-1 (AP-1) binding to deoxyribonucleic acid (DNA). AP-1 is a proinflammatory transcription factor composed of a heterodimer of Fos and Jun proto-oncogenes, which can be induced by phorbol esters and various cytokines. We have examined the hypothesis that dexamethasone may inhibit inflammation via an effect on AP-1 activation in human lung tissue. The effect of dexamethasone on the phorbol ester and cytokine activation of AP-1 and its monomers was examined in human lung tissue obtained from transplantation donors. AP-1 activation was measured by its ability to bind DNA, its localization in the nucleus by Western blotting, and the levels of fos and jun messenger ribonucleic acids (mRNAs) using Northern blotting. The phorbol ester, phorbol myristate acetate (PMA), caused a significant 2-3 fold increase in AP-1 DNA binding, which was sustained for 24 h and completely attenuated by co-incubation with dexamethasone. Dexamethasone alone caused a 40% decrease in AP-1 DNA binding. Dexamethasone modulated the expression of both c-jun and c-fos mRNA and produced long-term (24 h) 40% reduction in both mRNAs when compared to control tissues. PMA induced a rapid and prolonged increase in c-Fos and c-Jun nuclear localization, which was not attenuated by co-incubation with dexamethasone.(ABSTRACT TRUNCATED AT 250 WORDS)