Decreased levels of Prx1 are associated with proteasome impairment and mitochondrial dysfunction in the yeast Saccharomyces cerevisiae

Abstract

In previous studies we reported the S-glutathionylation at Cys residues (C76 and C221) of the α5 subunit of the 20S catalytic unit of the yeast proteasome, later mutated to Ser residues. Notably, the strain with the α5-C76S mutation exhibited a reduced chronological life span when grown in glucose as the carbon source. In the present study, we aimed to explore the interplay between mitochondria and the proteasome, considering the α5-C76S-mutated strain as a model of proteasomal impairment. For this purpose, we focused on the growth of the C76S strain in glycerol/ethanol as the carbon source. C76S strain exhibited poor growth and morphological alterations under these conditions, while the proteasomal activity was significantly decreased. We observed decreased activity of the 30S and 26S complexes in the C76S strain, which were accompanied by increased pool of poly-ubiquitinylated proteins. Regarding mitochondrial function, O₂ consumption and the concentration of total cellular ATP were significantly increased in the C76S strain. However, levels of peroxiredoxin-1 (Prx1), an important mitochondrial Cys-based peroxidase, were reduced in the C76S strain. In parallel, H₂O₂ release by mitochondrial respiration was augmented as well as decreased GSH/GSSG ratios, an important parameter of oxidative stress. These findings suggest that, despite increased O₂ consumption and ATP production, the mitochondria from the C76S strain promotes an increased oxidative stress most probably due to decreased Prx1 levels. DNA fragmentation and increased cytoplasmic cytochrome C, two apoptotic markers, were observed in the C76S strain. To assess the role of Prx1 in the survival of the C76S strain, we overexpressed this peroxiredoxin in both wild type and C76S strains, which resulted in the partial recovery of the C76S strain phenotype and proteasome activity. The relationship between decreased Prx1 concentration and proteasome impairment remains under investigation.