PROTEASES IN RENAL-CELL DEATH - CALPAINS MEDIATE CELL-DEATH PRODUCED BY DIVERSE TOXICANTS

The role of proteases in renal cell death has received limited investi gation. Calpains are non-lysosomal cysteine proteases that are Ca+2 ac tivated. Calpain inhibitors that block the active site of calpains (ca lpain inhibitor I and 2) or the Ca+2 binding domain of calpains (PD150 606) decreased calpain activity in rabbit renal proximal tubule (RPT) suspensions. The inhibition of calpain activity decreased cell death p roduced by the diverse toxicants antimycin A (mitochondrial inhibitor) , tetrafluroethyl-L-cysteine (nephrotoxic halocarbon), bromohydroquino ne (nephro-toxic quinone), t-butylhydroperoxide (model oxidant)and ion omycin (Ca+2 ionophore). In summary, calpains appear to play a common and critical role in cell injury produced by diverse toxicants with di fferent mechanisms of action. The general cysteine protease inhibitor trans-epoxysuccinyl-L-leucylamido (4-guanidino)-butane (E-64) decrease d antimycin A- and tetrafluoroethyl-L-cysteine-induced cell death but had no effect on bromohydroquinone- or t-butylhydroperoxide-induced ce ll death. Serine/cysteine protease inhibitors (antipain, leupeptin) we re not cytoprotective to RPT exposed to any of the toxicants. The cyto protection associated with E-64 correlated with inhibition of lysosoma l cathepsins and E-64 was only cytoprotective after some cell death ha d occurred. Since some cell death occurred prior to the E-64 cytoprote ctive effect, lysosomal cathepsins may be released from dying cells an d subsequently target the remaining viable cells.