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The GET Pathway Modulates Azole Susceptibility through Sterol Metabolic Remodeling and Protein Trafficking in Filamentous Fungi

ABSTRACT: Azole antifungals are widely used to control fungal infection, yet resistance mechanisms beyond drug efflux and target modification remain insufficiently understood. Here, we identified the Guided Entry of Tail-anchored proteins (GET) pathway as a conserved regulator of azole susceptibility in Neurospora crassa and Aspergillus fumigatus. Deletion or dysfunction of the core GET components Get-3 or Get-4 confers resistance to multiple azoles without impairing hyphal growth or sporulation. Mechanistically, GET deficiency neither reduced intracellular accumulation nor altered drug efflux and target expression or total ergosterol levels. Instead, GET-deficient strains displayed significantly reduced accumulation of the toxic sterol intermediate 14α-methyl-3,6-diol under azole stress, indicating a potential bypass of azole-induced sterol toxicity. Proximity labeling and functional validation indicated that GET deficiency perturbs the trafficking of multiple azole-resistance-associated proteins, including the key tail-anchored protein transporter Emp-47 and mitochondrial Cox subunits Cox-4 and Cox-15, which deletion enhanced azole resistance. Transcriptomic and functional analysis further revealed that GET disruption altered the expression of some azole resistance-associated genes, which involve in membrane transport, metabolism, and cell wall organization, independent of canonical stress pathways. In this study, a total of 17 new genes that modulate azole susceptibility were identified. Collectively, our findings uncover a non-classical mechanism of azole resistance mediated by GET-dependent protein trafficking and metabolic adaptation, conserved across filamentous fungi.

ORGANISM(S): Neurospora crassa

PROVIDER: GSE328637 | GEO | 2026/04/23

REPOSITORIES: GEO

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Project description:In Candida albicans, the transcription factor Upc2 is central to the regulation of ergosterol biosynthesis. UPC2-activating mutations contribute to azole resistance, whereas disruption increases azole susceptibility. In the present study, we investigated the relationship of UPC2 to fluconazole susceptibility, particularly in azole-resistant strains. In addition to the reduced fluconazole MIC previously observed with UPC2 disruption, we observed a lower minimum fungicidal concentration (MFC) for a upc2M-NM-^T/M-NM-^T mutant than for its azole-susceptible parent, SC5314. Moreover, the upc2M-NM-^T/M-NM-^T mutant was unable to grow on a solid medium containing 10 M-BM-5g/ml fluconazole and exhibited increased susceptibility and a clear zone of inhibition by Etest. Time-kill analysis showed higher fungistatic activity against the upc2M-NM-^T/M-NM-^T mutant than against SC5314. UPC2 disruption in strains carrying specific resistance mutations also resulted in reduced MICs and MFCs. UPC2 disruption in a highly azole resistant clinical isolate containing multiple resistance mechanisms likewise resulted in a reduced MIC and MFC. This mutant was unable to grow on a solid medium containing 10 M-BM-5g/ml fluconazole and exhibited increased susceptibility and a clear zone of inhibition by Etest. Time-kill analysis showed increased fungistatic activity against the upc2M-NM-^T/M-NM-^T mutant in the resistant background. Microarray analysis showed attenuated induction by fluconazole of genes involved in sterol biosynthesis, iron transport, or iron homeostasis in the absence of UPC2. Taken together, these data demonstrate that the UPC2 transcriptional network is universally essential for azole resistance in C. albicans and represents an attractive target for enhancing azole antifungal activity. We examined the genome-wide gene expression profiles of the wild-type parent strain SC5314 and its upc2M-NM-^T/M-NM-^T derivative in response to fluconazole in order to identify genes whose expression in response to fluconazole is influenced by Upc2.

Project description:Azole antifungal agents such as fluconazole exhibit fungistatic activity against Candida albicans. Strategies to enhance azole antifungal activity would be therapeutically appealing. In an effort to identify transcriptional pathways that influence fluconazole susceptibility, we sought to identify transcription factors (TFs) involved in this process. From a collection of C. albicans strains disrupted for genes encoding TFs (Homann et al., PLoS Genet. 2009;5:e1000783), four exhibited a marked reduction in minimum fungicidal concentration (MFC) in both RPMI and YPD media. One of these, UPC2, has been previously characterized with regard to its role in azole susceptibility. Of mutants representing the three remaining TF genes of interest, one (CAS5) was unable to recover from fluconazole exposure at concentrations as low as 2 M-BM-5g/mL after 72 hours in YPD medium. This mutant also showed reduced susceptibility and a clear zone of inhibition by Etest, was unable to grow on solid media containing 10 M-BM-5g/mL fluconazole, and exhibited increased susceptibility by time-kill analysis. CAS5 disruption in highly azole-resistant clinical isolates exhibiting multiple resistance mechanisms did not alter susceptibility. However, CAS5 disruption in strains with specific resistance mutations in ergosterol biosynthesis or efflux pumps resulted in a moderate reduction in MIC and MFC. Genome-wide transcriptional analysis was performed in the presence of fluconazole and was consistent with the suggested role of CAS5 in cell wall organization while also suggesting a role in iron transport and homeostasis. These findings suggest that Cas5 regulates a transcriptional network that influences susceptibility of C. albicans to fluconazole. Further delineation of this transcriptional network may identify targets for potential co-therapeutic strategies to enhance the activity to the azole class of antifungals. We examined the genome-wide gene expression profiles of the wild-type parent strain SC5314 and its cas5M-NM-^T/M-NM-^T derivative in response to fluconazole in order to identify genes whose expression in response to fluconazole is influenced by Cas5.

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The GET Pathway Modulates Azole Susceptibility through Sterol Metabolic Remodeling and Protein Trafficking in Filamentous Fungi

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