Induction of interleukin‐1β production in human dermal fibroblasts by interleukin‐1α and tumor necrosis factor‐α. Involvement of protein kinase‐dependent and adenylate cyclase‐dependent regulatory pathways

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Abstract
It has previously been demonstrated that interleukin-1 (IL-1) is expressed in a variety of fibroblast cell lines. In this study, we investigated the mechanisms involved in the regulation of IL-1β production by cultured human dermal fibroblasts. We have shown that IL-1β is constitutively expressed as a cell-associated form, with no soluble form detectable in control cell or in stimulated cell supernatants. IL-1α and tumor necrosis factor-α (TNF-α) exerted a dose-depdent stimulation on the production of the cell-associated IL-1β, as estimated using a specific enzyme linked immunosorbent assay (ELISA). As expected, this effect was accompanied by a huge release of prostaglandin E2 (PGE2) and a transient rise in intracellular cyclic AMP. Furthermore, IL-1β production was elevated to a lesser extent by the addition of increasing concentrations of the protein kinase C activator phorbol myristate acetate or by low concentration (0.001 μg/ml) of PGE2. In contrast, higher concentrations (0.1 and 1. μg/ml) of PGE2, as well as exogenous dibutyryl-cyclic AMP, were clearly inhibitory. H7, an inhibitor of protein kinases also reduced the stimulatory effect of IL-1α and TNF-α. Together with the results obtained with phorbol myristate acetate, these data suggest that protein kinase C may play a role in the upregulation of IL-1β expression in normal skin fibroblasts. The addition of indomethacin not only suppressed prostaglandin synthesis, but also dramatically reduced cyclic AMP formation, probably because the PGE2-induced stimulation of adenylate cyclase was abolished. This resulted in a strong potentiation of the stimulatory effect of IL-1α and TNF-α, supporting the role of both the cyclooxygenase and adenylate cyclase pathways in the endogenous downregulation of IL-1β induction by the two cytokines studied.

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