Roles for Stress Response and Cell Wall Biosynthesis Pathways in Caspofungin Tolerance in Cryptococcus neoformans

Abstract

Limited antifungal diversity and availability are growing problems for the treatment of fungal infections in the face of increasing drug resistance. The echinocandins, one of the newest classes of antifungal drugs, inhibit production of a crucial cell wall component. However, these compounds do not effectively inhibit the growth of the opportunistic fungal pathogen Cryptococcus neoformans , despite potent inhibition of the target enzyme in vitro . Therefore, we performed a forward genetic screen to identify cellular processes that mediate the relative tolerance of this organism to the echinocandin drug caspofungin. Through these studies, we identified 14 genetic mutants that enhance caspofungin antifungal activity. Rather than directly affecting caspofungin antifungal activity, these mutations seem to prevent the activation of various stress-induced compensatory cellular processes. For example, the pfa4 Δ mutant has defects in the palmitoylation and localization of many of its target proteins, including the Ras1 GTPase and the Chs3 chitin synthase, which are both required for caspofungin tolerance. Similarly, we have confirmed the link between caspofungin treatment and calcineurin signaling in this organism, but we suggest a deeper mechanism in which caspofungin tolerance is mediated by multiple pathways downstream of calcineurin function. In summary, we describe here several pathways in C. neoformans that contribute to the complex caspofungin tolerance phenotype in this organism.

A Mechanosensitive Channel Governs Lipid Flippase-Mediated Echinocandin Resistance in Cryptococcus neoformans

“…neoformans, and this organism shows innate resistance to echinocandins. Neither the FKS1 expression level nor β-1,3-glucan synthase localization changed after caspofungin treatment (15). These studies suggest that C.…”

“…Recently, Pianalto et al performed a forward genetic screen to identify cellular processes that mediate the relative tolerance to caspofungin and found several pathways contributing to caspofungin resistance in C. neoformans (15). Mutants of the calcineurin A catalytic and B regulatory subunits ( cna1 Δ or cnb1 Δ) were hypersensitive to caspofungin (15, 22).…”

“…neoformans (15). Mutants of the calcineurin A catalytic and B regulatory subunits ( cna1 Δ or cnb1 Δ) were hypersensitive to caspofungin (15, 22). Calcineurin is a known multifunctional regulator in fungi that influences fungal virulence and stress responses (23, 24).…”

Calcineurin A Is Essential in the Regulation of Asexual Development, Stress Responses and Pathogenesis in Talaromyces marneffei

“…In Candida tropicalis, it has been shown that calcineurin is essential for tolerance of azoles, caspofungin, anidulafungin, and cell wall-perturbing agents (Chen et al, 2014). Similarly, in Cryptococcus neoformans, caspofungin tolerance is mediated by multiple pathways downstream of calcineurin function (Pianalto et al, 2019). This study showed that the T. marneffei cnaA mutant displays defects in the hyphal and the yeast cell wall and that the cnaA gene is important for cell wall integrity.…”

DNA Methylation Changes Induced by Cold in Psychrophilic and Psychrotolerant Naganishia Yeast Species

“…In S. cerevisiae mutants, it was demonstrated that delocalized chitin in lateral walls can increase to as much as 20% of the wall components, as cell wall stress response (e.g., cells characterized by a deficit of other wall components as b-glucan, mannan, O-linked glycans, and GPI anchors) [59]. In Cryptococcus neoformans mutants, the defect in the palmitoylation and localization of a few target genes, including Chs3 chitin synthase, reduced their viability when subjected to antifungal activity stress (caspofungin tolerance) [60]. The alteration of the synthesis of chitin could therefore be associated to an increase or a reduction of cell duplication as well as to the lack of wall components due to reduction of proteins/enzymes synthesis.…”