<b>A TALE OF TWO </b><b><i>HAP1</i></b><b> OHNOLOGS, </b><b><i>HAP1A</i></b><b> AND </b><b><i>HAP1B</i></b><b>: ROLE IN ERGOSTEROL GENE REGULATION AND STEROL HOMEOSTASIS IN </b><b><i>CANDIDA GLABRATA</i></b><b> UNDER AZOLE AND HYPOXIC CONDITIONS</b>
Creators: name: Saha, Debasmita
Publisher: name: Purdue University Graduate School
Year: 2024
Subjects: classificationCode: 310702
subject: Infectious agents
classificationCode: 310705
subject: Mycology
classificationCode: 310505
subject: Gene expression (incl. microarray and other genome-wide approaches)

description: <i>Candida glabrata</i> is a member of the gut microbiota that can become an opportunistic pathogen under certain conditions. It is known for its inherent resistance to azole antifungal drugs and its ability to rapidly develop resistance during treatment. However, the regulatory mechanisms that enable this commensal organism to survive in low-oxygen environments, such as the gut, and to develop antifungal resistance when it becomes pathogenic, are not fully understood. In this study, we demonstrate for the first time the roles of two zinc cluster transcription factors in <i>C. glabrata</i>, Hap1A and Hap1B, in contributing to azole drug resistance in both laboratory strains and drug-resistant clinical isolates, adaptation to hypoxia, and resistance to other antifungal drugs like polyenes and echinocandins under specific conditions.Azole drugs, which target the Erg11 protein, are widely used to treat <i>Candida</i> infections. The regulation of azole-induced <i>ERG</i> gene expression and activation of drug efflux pumps in <i>C. glabrata</i> has primarily been linked to the zinc cluster transcription factors Upc2A and Pdr1. Here, we investigated the roles of <i>S. cerevisiae</i> Hap1 orthologs, Hap1A and Hap1B, in <i>C. glabrata</i> as direct regulators of <i>ERG</i> genes upon azole exposure.Our research shows that deleting <i>HAP1</i> in the yeast model <i>S. cerevisiae</i> increases sensitivity to fluconazole due to the failure to induce <i>ERG11 </i>expression in the <i>hap1Δ</i> mutant compared to the wild-type strain. Although <i>C. glabrata</i> is closely related to <i>S. cerevisiae</i>, a whole genome duplication (WGD) event allowed <i>C. glabrata</i> to retain two HAP1 ohnologs, while <i>S. cerevisiae</i> lost one copy. Through phylogenetic and syntenic analyses, we identified Hap1A and Hap1B in <i>C. glabrata</i> as ohnologs of Hap1 in <i>S. cerevisiae</i>, which is known to regulate <i>ERG</i> gene expression under both aerobic and hypoxic conditions. Interestingly, deleting <i>HAP1B</i> in <i>C. glabrata</i> increased sensitivity to both triazole and imidazole drugs, similar to Hap1 in <i>S. cerevisiae</i>, while deleting <i>HAP1A </i>did not affect azole sensitivity.Gene expression analysis revealed that the increased azole sensitivity in the <i>hap1BΔ </i>strain was due to reduced azole-induced <i>ERG</i> gene expression, leading to lower total endogenous ergosterol levels. Additionally, the loss of <i>HAP1B</i> in <i>C. glabrata</i> clinical isolates like SM1 and BG2, as well as in drug-resistant strains like SM3, also led to increased azole hypersusceptibility. While it was already known that losing <i>UPC2A</i> in <i>C. glabrata</i> increases azole sensitivity, our study is the first to demonstrate that the combined loss of both <i>HAP1B </i>and <i>UPC2A</i> makes <i>C. glabrata</i> strains even more sensitive to azoles than losing either gene alone. Additionally, we show that the loss of both <i>HAP1B </i>and the H3K4 histone methyltransferase <i>SET1</i> increases azole hypersensitivity more than the loss of either gene alone.Interestingly, the Hap1A protein is barely detectable under aerobic conditions but is specifically induced under hypoxia, where it plays a crucial role in repressing <i>ERG</i> genes. In the absence of Hap1A, Hap1B compensates by acting as a transcriptional repressor. Our RNA sequencing analysis further showed that losing both <i>HAP1A</i> and <i>HAP1B</i> not only affects genes in the ergosterol biosynthesis pathway but also upregulates iron transport-related genes <i>FET3 </i>and <i>FTR1</i>. Moreover, we found that the hypoxic growth defect caused by the loss of both <i>HAP1A</i> and <i>HAP1B</i> is exacerbated when treated with the echinocandin caspofungin and the cell wall-damaging agent calcofluor white, indicating that these Hap1 ohnologs contribute to maintaining cell wall integrity under hypoxic conditions. Since <i>HAP1A</i> transcript levels remain stable under aerobic conditions, we suspect that Hap1A expression is regulated post-transcriptionally.Furthermore, we discovered that the simultaneous loss of both HAP1A and HAP1B leads to increased hypersensitivity to the polyene antifungal drug amphotericin B, though the exact mechanism behind this phenotype remains unclear. Altogether, our study is the first to show that Hap1A and Hap1B have evolved distinct roles, enabling <i>C. glabrata</i> to adapt to specific host and environmental conditions.