Close association of p38 and JNK with plasminogen-dependent upregulation of PAI-1 in rat astrocytes in vitro

As reported previously, stimulation of astrocytes with plasminogen (PLGn) remarkably enhances their production/release of plasminogen activator inhibitor-1 (PAI-1). In addition, both p38 mitogen-activated protein kinase (p38MAPK) and c-Jun N-terminal kinase (JNK) are activated in these astrocytes. However, it remains to be determined whether the MAPK activation is associated with the PAI-1 induction in PLGn-stimulated astrocytes. In the present study, we investigated the relationship between MAPK activity and PAI-1 induction in PLGn-stimulated astrocytes. PLGn stimulation led to definitive phosphorylation of three MAPKs: external signal regulated kinase (ERK), JNK and p38. These results suggest that all of these MAPKs, either alone or in combination, are involved in PAI-1 induction. To verify this association, an inhibition experiment was carried out by using inhibitors specific for each MAPK. The results of the immunoblotting analysis indicated that 20 μM SB203580 (the p38 inhibitor) or SP600125 (the JNK inhibitor) suppressed approximately 85% or 40% of PLGn-inducible PAI-1, respectively. Only 20% inhibition was achieved by pretreatment of astrocytes with 20 μM PD98059 (the inhibitor of MEK1/2, an upstream kinase of ERK). In conclusion, p38 and JNK were shown to be the major MAPKs involved in the signaling cascade leading to PAI-1 induction in astrocytes stimulated with PLGn.