Most importantly, these mutants showed reduced virulence in mice [37]. Effect of FLC on genes involved in cell structure and maintenance Consequent to depletion of ergosterol and the concomitant accumulation of 14-methylated sterols, several plausible hypotheses on the mode of action of azoles were suggested by Vanden Bossche [32] two decades ago including alterations in membrane functions, synthesis and activity of membrane-bound enzymes, mitochondrial activities and uncoordinated activation of chitin synthesis. Transcript levels of several genes involving lipid and fatty
TSA HDAC in vivo acid metabolism decreased in the current study (Table 1), possibly in agreement with a remodelling of the cell membrane in
response to reduced ergosterol levels. Conversely, expression of PLB1, that encodes Plb1, a known virulence factor in C. neoformans, was increased 2.18-fold. Phospholipases cleave fatty acid moieties from larger lipid molecules, releasing arachidonic acid for the production of eicosanoids that are utilized by the pathogenic yeasts C. neoformans and C. albicans to produce immunomodulatory prostaglandins [38]. In addition, cell wall-linked cryptococcal Plb1 contributes to cell wall integrity and is a source of secreted enzyme [39]. It was also expected that exposure selleck inhibitor to FLC would affect genes responsible for cell wall integrity. Two chitin A-1210477 clinical trial synthase genes were found to be significantly up-regulated (2.20-fold for CHS2 and 3.62-fold for CHS7), concomitantly with down-regulated expression (4.35-fold) of the chitin deacetylase CDA3 (homolog to S. cerevisiae CDA2) (Table 1, next cell wall maintenance). In C. albicans, activation of chitin synthesis, which is mediated by the PKC-, Ca2+/calcineurin-, and HOG- cell wall signalling pathways, appears to be an adaptive response to caspofungin treatment. Hence, subculturing caspofungin-resistant cells in the absence of caspofungin resulted in wild-type levels of chitin content [40]. While this form of drug tolerance is rationally
accepted for a drug damaging the cell wall integrity (caspofungin is known to reduce β-glucan synthesis), it is also possible that exposure to azoles induces a salvage mechanism involving the up-regulation of chitin synthesis. Although known as a relatively minor cell wall component, chitin is thought to contribute significantly to cryptococcal wall strength and integrity [3]. Chitosan, the enzymatically deacetytaled form of chitin, helps to maintain cell integrity and is necessary for maintaining normal capsule width and retention of cell wall melanin [41]. Consistently, up-regulation was observed for BGL2 (2.61-fold) that encodes the glucantransferase (also termed glucosyltransferase) Bgl2, a major cell wall constituent described in a wide range of yeast species.