Extracellular Granzyme K mediates endothelial inflammation through the cleavage of Protease Activated Receptor-1

Granzymes are a family of serine proteases that were once thought to function exclusively as mediators of cytotoxic lymphocyte-induced target cell death. However, non-lethal roles for granzymes, including Granzyme K (GzK), have been recently proposed. As recent studies have observed elevated levels of GzK in plasma of patients diagnosed with sepsis, we hypothesized that extracellular GzK induces a pro-inflammatory response in endothelial cells. In the present study, extracellular GzK proteolytically activated Protease Activated Receptor-1 (PAR-1) leading to increased IL-6 and MCP-1 production in Human Umbilical Venous Endothelial Cells (HUVEC). Enhanced expression of ICAM-1 along with an increased capacity for adherence of THP-1 cells was also observed. Characterization of downstream pathways implicated the MAPK p38 pathway for ICAM-1 expression, and both the p38 and the ERK1/2 pathways in cytokine production. GzK also increased TNFα–induced inflammatory adhesion molecule expression. Furthermore, the physiological inhibitor of GzK, IαIp, significantly inhibited GzK activity in vitro. In summary, extracellular GzK is not cytotoxic but promotes a pro-inflammatory response in endothelial cells.Medicine, Faculty ofPathology and Laboratory Medicine, Department ofGraduat