The Toxicity of a Novel Antifungal Compound Is Modulated by Endoplasmic Reticulum-Associated Protein Degradation Components

Abstract

iIn a search for new antifungal compounds, we screened a library of 4,454 chemicals for toxicity against the human fungal pathogen Aspergillus fumigatus. We identified sr7575, a molecule that inhibits growth of the evolutionary distant fungi A. fumigatus, Cryptococcus neoformans, Candida albicans, and Saccharomyces cerevisiae but lacks acute toxicity for mammalian cells. To gain insight into the mode of inhibition, sr7575 was screened against 4,885 S. cerevisiae mutants from the systematic collection of haploid deletion strains and 977 barcoded haploid DAmP (decreased abundance by mRNA perturbation) strains in which the function of essential genes was perturbed by the introduction of a drug resistance cassette downstream of the coding sequence region. Comparisons with previously published chemogenomic screens revealed that the set of mutants conferring sensitivity to sr7575 was strikingly narrow, affecting components of the endoplasmic reticulum-associated protein degradation (ERAD) stress response and the ER membrane protein complex (EMC). ERAD-deficient mutants were hypersensitive to sr7575 in both S. cerevisiae and A. fumigatus, indicating a conserved mechanism of growth inhibition between yeast and filamentous fungi. Although the unfolded protein response (UPR) is linked to ERAD regulation, sr7575 did not trigger the UPR in A. fumigatus and UPR mutants showed no enhanced sensitivity to the compound. The data from this chemogenomic analysis demonstrate that sr7575 exerts its antifungal activity by disrupting ER protein quality control in a manner that requires ERAD intervention but bypasses the need for the canonical UPR. ER protein quality control is thus a specific vulnerability of fungal organisms that might be exploited for antifungal drug development.

Squaring the EMC – how promoting membrane protein biogenesis impacts cellular functions and organismal homeostasis

“…A chemical toxicity screen identified EMC subunits (EMC1 to EMC6) and ERAD factors (i.e. UBC7, CUE1, HRD1/3, UBX4, RPN4) as having underlying hypersensitivity to the cytotoxic antifungal compound sr7575 (Raj et al, 2015). Functional associations between the EMC and the human ERAD machinery, i.e.…”

A phenotypic small-molecule screen identifies halogenated salicylanilides as inhibitors of fungal morphogenesis, biofilm formation and host cell invasion

“…However, these drugs have serious side effects such as nephrotoxicity and/or create complications such as resistance and interactions with other commonly prescribed drugs. There are currently a limited number of novel antifungal molecules on the drug discovery pipelines and most of them target the same cellular processes as azoles and echinocandins 5 – 7 . Thus, these molecules will most likely face the same limitations in term of resistance and toxicity.…”

Integrated transcriptional analysis of the cellular and extracellular vesicle RNA content of Candida auris in response to caspofungin

“…EMC is a conserved protein complex of the ER that is necessary for homeostasis, and membrane protein biogenesis (59). EMC1 has been linked to antifungal resistance, as deletion of EMC1 led to an increased sensitivity to the sr7575 drug in S. cerevisiae (60). We hypothesized that this transcript could be transferred between cells upon caspofungin treatment, which is supported by our data showing that caspofungin-treated C. auris produces more EVs.…”