Increased nuclear envelope permeability and Pep4p-dependent degradation of nucleoporins during hydrogen peroxide-induced cell death

The death of yeast treated with hydrogen peroxide (H2O2) shares a number of morphological and biochemical features with mammalian apoptosis. In this study, we report that the permeability of yeast nuclear envelopes (NE) increased during H2O2-induced cell death. Similar phenomena have been observed during apoptosis in mammalian tissue culture cells. Increased NE permeability in yeast was temporally correlated with an increase in the production of reactive-oxygen species (ROS). Later, after ROS levels began to decline and viability was lost, specific nuclear pore complex (NPC) proteins (nucleoporins) were degraded. Although caspases are responsible for the degradation of mammalian nucleoporins during apoptosis, the deletion of the metacaspase gene YCA1 had no effect on the stability of yeast nucleoporins. Instead, Pep4p, a vacuolar cathepsin D homolog, was responsible for the proteolysis of nucleoporins. Coincident with nucleoporin degradation, a Pep4p-EGFP reporter migrated out of the vacuole in H2O2-treated cells. We conclude that increases in ROS and NPC permeability occur relatively early during H2O2-induced cell death. Later, Pep4p migrates out of vacuoles and degrades nucleoporins after the cells are effectively dead.