AP-1 mediated signal transduction in thrombin-induced regulation of PAL-1 expression in human mesangial cells

Objective To evaluate activator protein-1 (AP-1) mediated mechanisms in thr ombin-induced qlasminogen activator inhibitor-1 (PAI-1) expression in cultu red human glomerular mesangial cells (MCs). Methods Electrophoretic mobility shift assay (EMSA) was employed to assess AP-1 DNA-binding activity, and Western blot hybridization was used for quan tification of c-fos and c-jun, two subunits of AP-1 dimers. PAI-1 activity and mRNA expression were analysed by the fibrin plate assay and Northern hy bridization, respectively. Results Thrombin concentration enhanced PAI-1 activity in the supernatant a nd stimulated PAI-1 mRNA expression in cultured MCs. PAI-1 activity was blo cked by hirudin, a specific inhibitor of thrombin. Further study demonstrat ed that thrombin promoted AP-1 DNA-binding activity but exerted little effe ct on c-fos or c-jun. Curcumin (AP-1 inhibitor), staurosporine (PKC inhibit or), and genistein (PTK inhibitor) all reduced AP-l-mediated PAI-1 mRNA exp ression induced by thrombin in cultured MCs. Conclusion The present study indicates that in cultured human MCs, thrombin stimulates PAI-1 expression through an AP-1 signal pathway, which may be m ediated by PKC and PTK.