Disruption of the UPC2 Gene Enhances Fluconazole Antifungal Activity by Inhibiting HAC1 mRNA Splicing in Candida albicans

Azole resistance in Candida albicans is an increasing clinical challenge. Upc2 is a key transcription factor regulating ergosterol biosynthesis, but its additional roles in azole tolerance remain unclear. This study investigated whether Upc2 contributes to azole resistance through pathways beyond ergosterol synthesis. Chemical sensitivity screening, RNA sequencing, flow cytometry, and molecular assays were performed to compare wild-type C. albicans and the upc2Δ/upc2Δ mutant under fluconazole (FLC) treatment. The UPC2 gene deletion affected physiological processes that are dependent on the calcineurin signaling pathway and led to an overall negative enrichment trend in the unfolded protein response (UPR) pathway gene set. Mechanistically, the UPC2 gene deletion impaired unconventional splicing of HAC1 mRNA, leading to accumulation of unfolded proteins and phenotypically its deletion enhanced sensitivity of C. albicans to FLC in planktonic growth, hyphal development, and biofilm formation. Our findings reveal that Upc2 regulates proteostasis in C. albicans, and its absence enhances FLC efficacy by disrupting the UPR pathway. Targeting Upc2-mediated UPR signaling may represent a promising strategy to combat azole resistance.