Glycoconjugate expression on the cell wall of tps1/tps1 trehalose-deficient Candida albicans strain and implications for its interaction with macrophages

Abstract

The yeast Candida albicans has developed a variety of strategies to resist macrophage killing. In yeasts, accumulation of trehalose is one of the principal defense mechanisms under stress conditions. The gene-encoding trehalose-6-phosphate synthase (TPS1), which is responsible for trehalose synthesis, is induced in response to oxidative stress, as in phagolysosomes. Mutants unable to synthesize trehalose are sensitive to oxidative stress in vitro. In mice, the TPS1-deficient strain, tps1/tps1, displays a lower infection rate than its parental strain (CAI4). We have previously demonstrated the reduced binding capacity of tps1/tps1 and its lower resistance to macrophages. At the same time, its outer cell wall layer was seen to be altered. In this study, we show that depending on the culture conditions, the tps1/tps1 strain regulates the carbohydrate metabolism in a different way to CAI4, as reflected by the enhanced β-mannosylation of cell wall components, especially at the level of the 120 kDa glycoprotein species, accessible at the cell surface of tps1/tps1 when cultured in liquid medium, but not on solid medium. This leads to changes in its surface properties, as revealed by decreased hydrophobicity, and the lower levels of ERK1/2 phosphorylation and tumor necrosis factor-α (TNF-α) production in macrophages, thus increasing the resistance to these cells. In contrast, in solid medium, in which over-glycosylation was less evident, tps1/tps1 showed similar macrophage interaction properties to CAI4, but was less resistant to killing, confirming the protective role of trehalose. Thus, the lack of trehalose is compensated by an over-glycosylation of the cell wall components in the tps1/tps1 mutant, which reduces susceptibility to killing.