Transcriptional regulation of plasminogen activator inhibitor-1 expression in human synovial fibroblasts by prostaglandin E 2: mediation by protein kinase A and role of interleukin-1

Abstract

Differential expression of PAI-1 in connective tissues has been associated etiologically with some forms of arthritis. Our objective was to delineate the mechanisms by which PGE 2 and IL-lβ, inflammatory mediators commonly found at sites of inflammation, regulate the expression and synthesis of PAI-1 in human synoviocytes. PGE 2 (and PGE 1) inhibited PAI-1 mRNA expression and secretion in a dose-dependent manner with an IC 50 (for antigen secretion) of 4.6 × 10 -10M and 8.7 x 10″IOM, respectively. Cyclic AMP agonists forskolin, Sp-cAMP, and IBMX mimic the effects of the PGE s. rhIL-1β stimulated the secretion of PAI-1 in a dose-dependent fashion under basal culture conditions; the effect was reversed by actinomycin D and the protein kinase inhibitors H7 and staurosporine but not KT-5720. PMA, an activator of protein kinase C, transiently increased (maximum 3 h) the expression of PAI-1 mRNA by approximately 10-fold, especially the 3.2kb species. However, there was no significant increase in PAI-1 antigen secreted into the culture medium after PMA (100–300 nM) treatment. The half-life (t 1/2) of PAI-1 mRNA, both the 3.2 and 2.2 transcripts was about 9.6 h (mean n= 3) and PGE 2 has no affect on the stability of both messages. PGE 2 reduced the rate of PAI-1 gene transcription as judged by run-off assays. The NSAID naproxen (30μg/ml) induced the expression of PAI-1 mRNA over basal levels and superinduced the inhibitor's expression above rhIL-1β stimulated levels. Our results suggest that PGE 2 suppresses PAI-1 expression and synthesis by activation of the cAMP/PKA system and inhibition of the rate of gene transcription. Data concerning the activation of PKC suggest that the expression, synthesis and release of the PAI-1 may be differentially regulated in normal human synoviocytes.