The activated protein C (APC) pathway has been suggested to be a common link between coagulation and inflammation. APC may function to restore hemostasis via modulation of cytokine expression. We investigated the effect of APC on the endothelial expression of monocyte chemoattractant protein-1 (MCP-1), a chemokine that is controlled by the activation of central proinflammatory transcription factors, such as nuclear factor-kappa B (NF-kappaB). We found that human APC (2.5-10 micro g/ml) upregulated the amount of MCP-1-mRNA in human umbilical vein endothelial cells (HUVEC) and caused a time- and dose-dependent increase in MCP-1 protein production (p <0.001 for APC 2.5 micro g/ml at 4 up to 24 h). In this cell culture model MCP-1 induced an improvement of cell migration and wound repair after injury to endothelial monolayers. After stimulation of MCP-1-mRNA-transcription with TNF-alpha (0.1-1 ng/ml), HUVEC's were washed and an inhibitor of gene transcription, Actinomycin D (1 micro g/ml), was added in the presence or absence of APC. HUVEC's receiving APC contained more MCP-1-mRNA than controls after one hour and up to eight hours suggesting an inhibitory effect of APC on MCP-1-mRNA degradation (with APC: 753 +/- 56 atto mol of MCP-1-mRNA per ml of cell lysate vs. 263 +/- 60 atto mol/ml without APC at t =4 h; p <0.001). Electrophoretic mobility shift assays revealed that APC attenuated NF-kappaB DNA-binding capacity implying that NF-kappaB may not be involved in the upregulatory effect of APC on MCP-1 production. The ability of APC to upregulate the production of MCP-1, most likely by increasing the stability of MCP-1-mRNA rather than by transcriptional activation via NF-B, identifies a novel immunomodulatory pathway, by which APC may control the local inflammatory reaction, thereby initiating wound repair and modulating the extent of endothelial injury.