Role of proteases in red blood cell target cell destruction by cells transformed by Rous sarcoma virus mutants

The tumor induced RBC cytotoxicity assay has been used to explore the mechanism by which Rous sarcoma virus mutant transformed chick embryo fibroblasts and mouse 3T3 cells cause the cytolysis of RBC in vitro. All Rous sarcoma virus and viral mutant transformed cells were cytolytic for RBC. Three mutant viruses, tsGl251, rASV1702, and rASV157, appeared to cause quantitatively less cytolysis after transformation of chick embryo fibroblasts than other virally transformed cells. This decreased cytolytic activity may be correlated with decreased in vivo tumorigenicity. Temperature sensitive mutant transformed chick embryo fibroblasts and mouse 3T3, which were phenotypically normal and which secrete little if any plasminogen activator at non-permissive temperatures, were cytolytic at non-permissive temperatures. In addition, inhibitors of plasminogen activator and plasmin were ineffective inhibitors of cytotoxicity. The only effective inhibitor of cytotoxicity for both transformed chick embryo fibroblasts and mouse 3T3 cells was leupeptin. In Rous sarcoma virus transformed mouse 3T3 cells, the leupeptin inhibitable enzyme appears to be a plasma membrane enzyme.