INDUCTION OF UROKINASE-TYPE PLASMINOGEN-ACTIVATOR RECEPTOR BY IL-1-BETA

Extensive tissue remodeling occurs in survivors of acute lung injury, leading to nearly normal histology and physiology in the majority of i ndividuals, whereas others suffer significant impairment due to the de velopment of pulmonary fibrosis. Alveolar epithelial cells play a cent ral role in the repair process. They are strategically located to dire ctly participate in the solubilization of intraalveolar fibrin deposit s, and have the capacity to promote fibrinolysis. We have previously r eported that interleukin-1 beta (IL-1 beta), an important inflammatory mediator in acute lung injury, upregulates urokinase-type plasminogen activator expression by human A549 cells (1). In this work, we show t hat IL-1 beta increases cell-surface plasmin generation, mediated in p art by increased expression of urokinase receptor (u-PAR). Northern bl ot analyses demonstrated that IL-1 beta rapidly induces accumulation o f u-PAR messenger RNA (mRNA) in a dose-dependent fashion, and that thi s effect is blocked by actinomycin. The IL-1 beta-mediated increase in u-PAR mRNA is inhibited by: (1) the relatively specific protein kinas e C (PKC) inhibitors 1-(5-isoquinoline sulfonyl)-2-methylpiperazine (H 7) and calphostin C; and (2) prolonged pretreatment of cells with phor bol myristate acetate (PMA), suggesting that PKC is an important compo nent of the signaling pathway. Okadaic acid, an inhibitor of serine/th reonine phosphatases, markedly potentiates the effect of IL-1 beta on u-PAR mRNA levels. In contrast, dexamethasone, in concentrations as lo w as 10(-8) M, completely blocks the IL-1 beta-mediated increase in u- PAR mRNA. Half-life experiments show that dexamethasone has no effect on u-PAR mRNA stability. Aldosterone, at concentrations in which it bi nds primarily to the mineralocorticoid receptor, has no effect on u-PA R expression, suggesting that the glucocorticoid effect is due to a tr ansrepressive mechanism. In summary, IL-1 beta increases cell-surface plasmin generation in A549 cells by coordinately upregulating urokinas e and u-PAR expression. Transcriptional activation of the u-PAR gene i nvolves PKC-dependent mechanisms, and glucocorticoid suppression is pr obably due to interactions between the glucocorticoid receptor and ano ther transcriptional activating system such as activator protein-1(AP- 1) and/or nuclear factor-kappa B (NF-kappa B).