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 proteo lytic activity on the cell surface and may mediate a proliferative eff ect, such as urokinase on glomerular epithelial cells. Since some hype rtensive states are associated with high concentrations of renin and p roliferation 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 bindi ng of I-125 labeled recombinant human renin (I-125-R) was studied on h uman primary mesangial cells and mesangial cells immortalized by trans fection with SV40-T antigen. At 37 degrees C, the binding of I-125-R w as time dependent and reached a plateau after two hours. I-125-R was f ound to bind in a saturable and specific manner with a K-d = 0.4 nM an d 1 nM and 8,000 and 3,000 binding sites/cell, for primary and immorta lized cells, respectively. When binding experiments were performed in the presence RO 42-5892, a synthetic inhibitor of renin, RO 43-5892 co uld inhibit the specific binding of labeled renin only at concentratio ns 1,000 times superior to the IC 50, indicating that the renin-mesang ial receptor interaction did not depend on the active site of renin. A nalysis by SDS-PAGE and autoradiography of cross-linking experiments o f I-125-R bound to a membrane preparation showed a band of approximate ly 110 to 120 kDa, suggesting a Mr of 70 to 80 kDa for the renin recep tor. Incubation of mesangial cells with 100 nM renin for 24 hours prov oked a 100% increase of H-3 thymidine incorporation that was not accom panied by an increase of the cell number, even after a seven day perio d of incubation. However, the incubation of mesangial cells with renin for 24 hours induced a significant increase (170% of control, P = 0.0 4) of plasminogen activator inhibitor-1 (PAI1) antigen in the conditio ned medium. In conclusion, we have shown that human mesangial cells in culture express a specific receptor for renin, and that the binding o f renin increases H-3 thymidine incorporation independently of renin e nzymatic activity. The absence of cell proliferation, the increase of H-3 thymidine incorporation and the increase of PAI1 antigen suggest t hat the binding of renin can induce mesangial cell activation, which i s reflected by a change in the fibrinolytic capacity of the cells. The role of this receptor remains to be determined in nephropathies and h ypertensive states associated with high plasma/tissue renin concentrat ions, hypertrophy of mesangial or smooth muscle cells and extracellula r matrix remodeling.