Biology subjects

Palmer, G. E.

Publications and source records attributed to Palmer, G. E..

4 recordsLinked to original sources

bioRxiv2026

Loss of the high-affinity vacuolar Ca2+ pump Pmc1p confers echinocandin tolerance in Candida albicans through enhancing calcineurin-based responses.

Signaling through the calcium-activated calcineurin phosphatase promotes fungal survival of stressful conditions including those imposed by antifungal medications. Calcium is an essential secondary messenger that regulates diverse cellular processes in eukaryotes; however, it is also profoundly toxic and cytoplasmic concentrations must be tightly controlled. In fungi, the vacuole serves as a major calcium reservoir with the H+-exchanger Vcx1p and P-type ATPase Pmc1p sequestering intracellular calcium. Upon stimulation, these stores can be released through the Yvc1p ion channel to create transient cytoplasmic pulses that activate calcium-dependent responses. Despite the importance of calcineurin signaling in sustaining fungal viability upon antifungal insult, the contribution of many other proteins responsible for intracellular calcium homeostasis during antifungal exposure remains poorly understood. Here, we investigated whether Yvc1p, Vcx1p, and Pmc1p influence Candida albicans capacity to endure exposure to the first-line echinocandin antifungals. Our results demonstrate that loss of Pmc1p function confers high-levels of tolerance, with pmc1?/? mutant cells sustaining less damage, surviving and capable of proliferation in the presence of supra-MIC concentrations of the echinocandins. Moreover, this phenotype is dependent upon elevated signaling through the calcineurin pathway. Finally, we demonstrate that at least a subset of drugs previously identified as echinocandin antagonists activate calcineurin signaling in a Pmc1-dependent manner to drive echinocandin tolerance. These findings reveal how genetic or pharmacological modulation of calcium homeostasis can have profound consequences on the outcome of C. albicans - echinocandin interaction.

microbiology↗

bioRxiv2025

A screen to identify antifungal antagonists reveals a variety of pharmacotherapies induce echinocandin tolerance in Candida albicans.

Through screening a comprehensive collection of drugs approved for human use, we identified over 20 that oppose the antifungal activity of the echinocandins upon the infectious yeast, Candida albicans. More detailed evaluation of five such drugs, including the atypical antipsychotic aripiprazole and the tyrosine kinase inhibitor ponatinib, indicated they promote C. albicans survival following exposure to the echinocandin antifungals. The activity of the five selected antagonists was dependent upon the Mkc1p MAPK pathway, however, ponatinib was paradoxically shown to suppress phosphorylation and therefore activation of Mkc1p itself. Components of several other signaling pathways are also required, including those of calcineurin and casein kinase-2, suggesting the observed antagonism required much of the cell wall stress responses previously described for C. albicans. Transcriptome analysis revealed that the antagonists stimulated the expression of genes involved in xenobiotic and antifungal resistance, and suppressed the expression of genes associated with hyphal growth. Thus, the echinocandin antagonistic drugs modulate C. albicans physiology in ways that could impact its pathogenicity and/or response to therapeutic intervention. Finally, a mutant lacking the Efg1p transcription factor, which has a central role in the activation of C. albicans hyphal growth was found to have intrinsically high levels of echinocandin tolerance, suggesting a link between modulation of morphogenesis related signaling and echinocandin tolerance. ImportanceWe report a substantial number of previously unknown drug interactions that modulate the echinocandin sensitivity of one of the most prevalent human fungal pathogens, Candida albicans. The echinocandins are the first line therapy for treating disseminated and often lethal Candida infections, that account for >75% of invasive fungal infections in the U.S.. For largely unknown reasons, a substantial number of patients with invasive candidiasis fail to respond to treatment with these drugs. The finding of this study suggest that co-administered medications have the potential to influence the therapeutic outcomes of invasive fungal infections through modulating antifungal drug tolerance and/or fungal pathogenicity. The potential for echinocandin antagonistic medications to influence therapeutic outcomes is discussed.

microbiology↗

bioRxiv2024

The atypical antipsychotic aripiprazole alters the outcome of disseminated Candida albicans infections.

Invasive fungal infections (IFIs) impose an enormous clinical, social, and economic burden on humankind. For many IFIs, [≥] 30% of patients fail therapy with existing antifungal drugs, including the widely used azole class. We previously identified a collection of 13 approved medications that antagonize azole activity. While gain-of-function mutants resulting in antifungal resistance are often associated with reduced fitness and virulence, it is currently unknown how exposure to azole antagonistic drugs impact C. albicans physiology, fitness, or virulence. In this study, we examined how exposure to azole antagonists affected C. albicans phenotype and capacity to cause disease. We discovered that most of the azole antagonists had little impact on fungal growth, morphology, stress tolerance, or gene transcription. However, aripiprazole had a modest impact on C. albicans hyphal growth and increased cell wall chitin content. It also worsened the outcome of disseminated infections in mice at human equivalent concentrations. This effect was abrogated in immunosuppressed mice, indicating an additional impact of aripiprazole on host immunity. Collectively, these data provide proof-of-principle that unanticipated drug-fungus interactions have the potential to influence the incidence and outcomes of invasive fungal disease. ImportanceAs natural inhabitants of the gastrointestinal and reproductive tracts, Candida sp. are routinely exposed to medications consumed by their human host. This study provides new insight into how drugs can modulate the physiology, fitness, and pathogenicity of Candida albicans - one of the most important human fungal pathogens. These results provide a proof of principle that co-administered medications consumed by at-risk patients may influence the initiation and/or outcome of life-threatening fungal disease.

microbiology↗

bioRxiv2020

Mutations in TAC1B: a novel genetic determinant of clinical fluconazole resistance in C. auris

Candida auris has emerged as a multidrug-resistant pathogen of great clinical concern. Approximately 90% of clinical C. auris isolates are resistant to fluconazole, the most commonly prescribed antifungal agent, yet it remains unknown what mechanisms underpin this fluconazole resistance. To identify novel mechanisms contributing to fluconazole resistance in C. auris, the fluconazole-susceptible C. auris clinical isolate AR0387 was passaged in media supplemented with fluconazole to generate derivative strains which had acquired increased fluconazole resistance in vitro. Comparative analysis of comprehensive sterol profiles, [3H]-fluconazole uptake, sequencing of C. auris genes homologous to genes known to contribute to fluconazole resistance in other species of Candida, and the relative expression of C. auris ERG11, CDR1, and MDR1 were performed. All fluconazole-evolved derivative strains were found to have acquired mutations in the zinc-cluster transcription factor-encoding gene, TAC1B, and a corresponding increase in CDR1 expression relative to the parental clinical isolate, AR0387. Mutations in TAC1B were also identified in a set of 304 globally distributed C. auris clinical isolates representing each of the four major clades. Introduction of the most common mutation found among fluconazole-resistant clinical isolates of C. auris into the fluconazole-susceptible isolate AR0387, was confirmed to increase fluconazole resistance by 8-fold, and the correction of the same mutation in a fluconazole-resistant isolate, AR0390, decreased fluconazole MIC by 16-fold. Taken together, these data demonstrate that C. auris can rapidly acquire resistance to fluconazole in-vitro, and that mutations in TAC1B significantly contribute to clinical fluconazole resistance. IMPORTANCECandida auris is an emerging multidrug-resistant pathogen of global concern, known to be responsible for outbreaks on six continents and commonly resistant to antifungals. While the vast majority of clinical C. auris isolates are highly resistant to fluconazole, an essential part of the available antifungal arsenal, very little is known about the mechanisms contributing to resistance. In this work, we show that mutations in the transcription factor TAC1B significantly contribute to clinical fluconazole resistance. These studies demonstrate that mutations in TAC1B can arise rapidly in vitro upon exposure to fluconazole, and that a multitude of resistance-associated TAC1B mutations are present among the majority of fluconazole-resistant C. auris isolates from a global collection and appear specific to a subset of lineages or clades. Thus, identification of this novel genetic determinant of resistance significantly adds to the understanding of clinical antifungal resistance in C. auris.

microbiology↗