Effect of type-1 plasminogen activator inhibitor on human leukocyte elastase

When human leukocyte elastase (HLE) activity (1.0 microgram/ml) was analysed in the presence of PAI-1 (0.15.0 micrograms/ml), HLE activity, measured with the low molecular weight paranitroanilide substrate L-pyroglutamyl-prolyl-L-valine-p-nitroanilide was increased time and dose dependently (a plateau of stimulation was reached after 30 minutes) with a simultaneous decrease in PAI-1 inhibitory activity. This effect was neither influenced by the presence of vitronectin nor heparin. When PAI-1 was converted into its latent form by incubation for 48 hours at 37 degrees C or incubated with an excess of recombinant t-PA to convert free PAI-1 into t-PA-PAI-1 complexes, the stimulatory effect of both the latent and the complexed form of PAI-1 was significantly greater than that of the active form. Analysing HLE PAI-1 interaction on a molecular level using SDS-PAGE, no SDS stable complex formation between HLE and PAI-1 could be observed but lower molecular weight cleavage products of PAI-1 were generated. The stimulatory effect of PAI-1 on HLE activity was not restricted to the low molecular weight pNA-substrate but was also revealed using a natural substrate assay (bovine neck ligament elastin solubilization). Therefore interaction of HLE and PAI-1 seems not to be restricted just to decrease PAI-1 activity but would simultaneously also increase HLE activity, thereby supporting enzymatic activity necessary for migration of leukocytes, dissolution of blood clots and tissue remodelling.