REGULATION OF PLASMINOGEN ACTIVATION BY INTERLEUKIN-6 IN HUMAN LUNG FIBROBLASTS

We determined that exposure of cultured lung fibroblasts (HEL-299) to recombinant human interleukin-6 (0-400 ng/ml) resulted in a dose- and time-dependent increase in secreted and cell lysate PAI-1 and total tP A levels (maximal increase of 2.6-fold and 1.7-fold, respectively). Sp ecificity of this response was indicated when increases in PAI-1 level s were inhibited by neutralizing polyclonal antibodies to IL-6, but no t with non-specific antibodies. Inhibition of the response to IL-6 by cycloheximide and alpha-amanitin indicates that increases in PAI-1 are dependent on both protein and RNA synthesis. The addition of IL-6 to HEL-299 cells also stimulated a dose- and time-dependent increase in s teady-state PAI-1 mRNA levels (3.8 to 15.1 pg/mu g total RNA by 24 h). A rapid increase (5-6-fold) in PAI-1 mRNA levels was found between 3 and 12 h. Nuclear run-on assays using a maximum dose of IL-6 showed th at IL-6 increases a 4-fold rate of transcription of the PAI-1 gene. We further showed that LPS induces a 70% increase in secreted IL-6 and a 50% increase in PAT-I protein levels. Increasing doses of anti-IL-6 c ompletely blocked the effect of LPS on PAI-1 while non-specific antibo dies had no effect. These studies suggest an autocrine role for IL-6 i n regulating localized proteolysis and modulating tissue remodeling du ring acute inflammatory conditions by fibroblasts.