The DNA Damage Response Gene DDR48 Regulates Sterol Synthesis Genes to Confer Antifungal Resistance to the Pathogenic Fungus \u3ci\u3eHistoplasma capsulatum\u3c/i\u3e
Histoplasma capsulatum is a dimorphic fungal pathogen that is endemic to the Ohio, Missouri, and Mississippi river valley regions. The fungus grows as a mold at environmental temperatures (25C) and transforms into a unicellular yeast upon inhalation by a mammalian host (37C). The mold to yeast shift is required for pathogenicity in host organisms, where the potentially fatal disease, histoplasmosis, can present. This study aims to characterize the DNA damage response protein DDR48 and the role that it plays in combating cellular stressors in H. capsulatum. We found that DDR48 is expressed strongly in the mold phase but expressed only at basal levels in the yeast phase. However, DDR48 expression is significantly upregulated in the yeast phase under stressful conditions, like antifungal stress. We found that wild-type H. capsulatum yeast exposed to the antifungal drugs ketoconazole or Amphotericin-B upregulated DDR48 expression (assayed via qRT-PCR) at least 4-fold. The mold growth form, however, showed no significant change in expression of DDR48 under these conditions. Additionally, the DDR48 knockout mutant previously created in our lab was significantly more sensitive to these antifungal drugs. The knockout cells also experienced dysregulation of their membrane sterol synthesis genes, indicating a potential role of DDR48 in conferring antifungal resistance to H. capsulatum by acting as a regulator of membrane maintenance and integrity. Research is ongoing to further elucidate the role of DDR48 in the stress response pathway of this common human pathogen
