NUCLEAR SERINE-PROTEASE ACTIVITY CONTRIBUTES TO BILE ACID-INDUCED APOPTOSIS IN HEPATOCYTES

Glycodeoxycholate (GDC) induces apoptosis in hepatocytes by a mechanis m associated with DNA cleavage by endonucleases. In many models of apo ptosis, proteolysis is required prior to DNA cleavage. Our aims were t o determine if enhanced proteolysis is a mechanism causing GDC-mediate d apoptosis. In cultured rat hepatocytes exposed to 50 mu M GDC for 4 h, nonlysosomal proteolysis increased by 65% compared with controls. T he serine protease inhibitor N alpha-p-tosyl-L-lysine chloromethyl ket one (TLCK; 100 mu M) reduced cell death from apoptosis by 75% after 4 h of treatment with GDC. TLCK also inhibited DNA fragmentation. There was a twofold increase in nuclear serinelike protease activity during GDC-induced apoptosis accompanied by a 2.5-fold reduction in nonnuclea r serine protease activity, suggesting translocation of the protease f rom the cytosol to the nucleus. Zn2+, an inhibitor of apoptosis, also inhibited nonlysosomal proteolysis and nuclear serinelike protease act ivity. These novel data suggest that nonlysosomal serinelike protease activity contributes to hepatocyte apoptosis. These data may be import ant in understanding apoptosis in other cell types and in providing in sight into the mechanisms of liver injury during cholestasis.