Erg4A and Erg4B Are Required for Conidiation and Azole Resistance via Regulation of Ergosterol Biosynthesis in Aspergillus fumigatus

Abstract

Ergosterol, a fungus-specific sterol enriched in cell plasma membranes, is an effective antifungal drug target. However, current knowledge of the ergosterol biosynthesis process in the saprophytic human fungal pathogen Aspergillus fumigatus remains limited. In this study, we found that two endoplasmic reticulumlocalized sterol C-24 reductases encoded by both erg4A and erg4B homologs are required to catalyze the reaction during the final step of ergosterol biosynthesis. Loss of one homolog of Erg4 induces the overexpression of the other one, accompanied by almost normal ergosterol synthesis and wild-type colony growth. However, double deletions of erg4A and erg4B completely block the last step of ergosterol synthesis, resulting in the accumulation of ergosta-5,7,22,24(28)-tetraenol, a precursor compound of ergosterol. Further studies indicate that erg4A and erg4B are required for conidiation but not for hyphal growth. Importantly, the Δerg4A Δerg4B mutant still demonstrates wild-type virulence in a compromised mouse model but displays remarkable increased susceptibility to antifungal azoles. Our data suggest that inhibitors of Erg4A and Erg4B may serve as effective candidates for adjunct antifungal agents with azoles.IMPORTANCE Knowledge of the ergosterol biosynthesis pathway in the human opportunistic pathogen A. fumigatus is useful for designing and finding new antifungal drugs. In this study, we demonstrated that the endoplasmic reticulum-localized sterol C-24 reductases Erg4A and Erg4B are required for conidiation via regulation of ergosterol biosynthesis. Moreover, inactivation of both Erg4A and Erg4B results in hypersensitivity to the clinical guideline-recommended antifungal drugs itraconazole and voriconazole. Therefore, our finding indicates that inhibition of Erg4A and Erg4B might be an effective approach for alleviating A. fumigatus infection.

Aspergillus fumigatus Mitochondrial Acetyl Coenzyme A Acetyltransferase as an Antifungal Target

“…5B, the ROS level in P alcA ::erg10A mutant was significantly higher than in the WT (P Ͻ 0.001) in repression medium, whereas no difference was observed in inducing medium, suggesting that higher intercellular ROS level in P alcA ::erg10A mutant may account for the increased sensitivity toward oxidative stresses. Previous study has shown that sterol C-24 reductase ERG4A/B is involved in cell wall integrity in A. fumigatus (36). Similarly, as shown in Fig.…”

“…Indeed, widely used antifungal drugs such as azoles, allylamines, and polyenes target ergosterol and its biosynthesis. Of the approximately 20 enzymes involved in ergosterol synthesis, only ERG3 (C-5 sterol desaturase), ERG4 (C-24 sterol reductase), ERG11 (lanosterol 14-␣-demethylase), and ERG25 (C-4 methyl sterol oxidase) have been genetically characterized in the human opportunistic pathogen A. fumigatus (27,36,40,41). The physiological functions of the other enzymes involved in ergosterol biosynthesis are yet to be explored, including acetyl-CoA acetyl- on August 5, 2020 by guest http://aem.asm.org/ transferase ERG10, which is the initial enzyme in the mevalonate and ergosterol biosynthesis pathway.…”

TheAspergillus fumigatustranscription factor AceA is involved not only in Cu but also in Zn detoxification through regulating transporters CrpA and ZrcA

“…Moreover, A. fumigatus is thermotolerant and can survive on a broad range of environmental niches (Haines, 1995;Seyedmousavi et al, 2015). Notably, it is one of the most prevalent airborne fungal pathogens, causing severe (usually fatal) invasive aspergillosis in immune compromised individuals (Ellett, Jorgensen, Frydman, Jones, & Irimia, 2017;Hillmann et al, 2015;Long, Xu, Zeng, Sang, & Lu, 2017;Throckmorton, Lim, Kontoyiannis, Zheng, & Keller, 2016). It has been identified that the virulence determinants of A. fumigatus are dependent on both fungal biological characteristics and host immune status (Cai et al, 2016).…”

A sphingolipid synthesis‐related protein OrmA in Aspergillus fumigatus is responsible for azole susceptibility and virulence

“…Azoles, the first-line-used antifungals in clinic due to their limited side effects, damage the cell membrane through preventing the synthesis of ergosterol, a key component of fungal plasma membranes. Moreover, ergosterols are special lipids located in the cell membrane, which can regulate membrane fluidity and permeability (Bard et al, 1993;Kodedova & Sychrova, 2015;Long, Xu, Zeng, Sang, & Lu, 2017). It has been reported that sterols, along with sphingolipids, form membrane outer niches to support conformational functions of membrane proteins as well as serve as a platform for establishment of signalling molecules (Hinrichs, Klappe, Hummel, & Kok, 2004;Mongrand et al, 2004;Pasrija, Prasad, & Prasad, 2005).…”