Specific receptor binding of renin on human mesangial cells in culture increases plasminogen activator inhibitor-1 antigen

Some proteases possess a membrane receptor that focalizes their proteolytic activity on the cell surface and may mediate a proliferative effect, such as urokinase on glomerular epithelial cells. Since some hypertensive states are associated with high concentrations of renin and proliferation of arteriolar smooth muscle cells, we asked whether renin, an aspartyl-protease, would bind to mesangial cells that are smooth-muscle derived cells, which would induce their proliferation The binding of I-125 labeled recombinant human renin (I-125-R) was studied on human primary mesangial cells and mesangial cells immortalized by transfection with SV40-T antigen. At 37 degrees C, the binding of I-125-R was time dependent and reached a plateau after two hours. I-125-R was found to bind in a saturable and specific manner with a K-d = 0.4 nM and 1 nM and 8,000 and 3,000 binding sites/cell, for primary and immortalized cells, respectively. When binding experiments were performed in the presence RO 42-5892, a synthetic inhibitor of renin, RO 43-5892 could inhibit the specific binding of labeled renin only at concentrations 1,000 times superior to the IC 50, indicating that the renin-mesangial receptor interaction did not depend on the active site of renin. Analysis by SDS-PAGE and autoradiography of cross-linking experiments of I-125-R bound to a membrane preparation showed a band of approximately 110 to 120 kDa, suggesting a Mr of 70 to 80 kDa for the renin receptor. Incubation of mesangial cells with 100 nM renin for 24 hours provoked a 100% increase of H-3 thymidine incorporation that was not accompanied by an increase of the cell number, even after a seven day period of incubation. However, the incubation of mesangial cells with renin for 24 hours induced a significant increase (170% of control, P = 0.04) of plasminogen activator inhibitor-1 (PAI1) antigen in the conditioned medium. In conclusion, we have shown that human mesangial cells in culture express a specific receptor for renin, and that the binding of renin increases H-3 thymidine incorporation independently of renin enzymatic activity. The absence of cell proliferation, the increase of H-3 thymidine incorporation and the increase of PAI1 antigen suggest that the binding of renin can induce mesangial cell activation, which is reflected by a change in the fibrinolytic capacity of the cells. The role of this receptor remains to be determined in nephropathies and hypertensive states associated with high plasma/tissue renin concentrations, hypertrophy of mesangial or smooth muscle cells and extracellular matrix remodeling.