Adaptive tolerance to oxidative stress and the induction of antioxidant enzymatic activities in Candida albicans are independent of the Hog1 and Cap1-mediated pathways

Abstract

In the pathogenic yeast Candida albicans, the MAP-kinase Hog1 mediates an essential protective role against oxidative stress, a feature shared with the transcription factor Cap1. We analysed the adaptive oxidative response of strains with both elements altered. Pretreatment with gentle doses of oxidants or thermal upshifts (28-->37 and 37-->42 degrees C) improved survival in the face of high concentrations of oxidants (50 mM H(2)O(2) or 40 mM menadione), pointing to a functional cross-protective mechanism in the mutants. The oxidative challenge promoted a marked intracellular synthesis of trehalose, although hog1 (but not cap1) cells always displayed high basal trehalose levels. Hydrogen peroxide (H(2)O(2)) induced mRNA expression of the trehalose biosynthetic genes (TPS1 and TPS2) in the tested strains. Furthermore, oxidative stress also triggered a differential activation of various antioxidant activities, whose intensity was greater after HOG1 and CAP1 deletion. The pattern of activity was dependent on the oxidant dosage applied: low concentrations of H(2)O(2) (0.5-5 mM) clearly induced catalase and glutathione reductase (GR), whereas drastic H(2)O(2) exposure (50 mM) increased Mn-superoxide dismutase (SOD) isozyme-mediated SOD activity. These results firmly support the existence in C. albicans of both Hog1- and Cap1-independent mechanisms against oxidative stress.