Overexpression of genes involved in vesicular trafficking to the vacuole defends against lethal effects of oxidative damage.

Anticancer bleomycins and structurally-related analogs are oxidative agents that mimic ionizing radiation in many of their cellular effects. The current study was designed to better understand this class of radiomimetic and oxidative drugs, and how cells defend against them to become resistant. Based on some of the properties conferred by the b1m5-1 mutation of Saccharomyces cerevisiae, a multi-step cloning strategy was developed to search for genes that protect cells against oxidative damage and lethal effects of bleomycin treatments. The strategy employed blm5-1 mutant strains to search for genes that rescued the drug hypersensitivities conferred by the mutation, and utilized the inability of homozygous blm5-1 mutant diploid strains to grow at elevated temperatures. This approach identified the VPS3, VPS8 and PEP7 genes that function in vesicular trafficking between the endosome and the yeast vacuole via the carboxypeptidase Y (CpY) pathway. Mutant b1m5-1 strains possess several phenotypic characteristics consistent with CpY mutants, including reduced mitotic growth rates and sporulative abilities. However, blm5-1 strains were not found to be defective in the transport of CpY into the vacuole. We suggest that the ability of the VPS3, VPS8 and PEP7 genes to rescue lethal effects of oxidative damage resulted from the overexpression of these genes.