An atypical ABC transporter is involved in antifungal resistance and host interactions in the pathogenic fungus Cryptococcus neoformans

Abstract

ATP-binding cassette (ABC) transporters represent one of the largest protein superfamilies. Functionally diverse, ABC transporters have been implicated in many aspects of microbial physiology. The genome of the human fungal pathogen Cryptococcus neoformans encodes 54 putative ABC transporters and the majority of them remain uncharacterized. In a previous genetic screen for fungal regulators of phagocytosis, we identified an uncharacterized gene, CNAG_06909, that modulates host interactions. This gene encodes a half-size ABC transporter of the PDR-type, and phenotypic studies of a strain with this gene deleted revealed an altered antifungal susceptibility profile, including hypersensitivity to fluconazole (FLC). This gene, which we have named PDR6, localizes to the endoplasmic reticulum (ER) and plasma membrane (PM), and when absent, less ergosterol is observed in the PM. Additionally, we observed that the pdr6{Delta} strain displays a reduction in secreted polysaccharide capsular material. These changes to the cellular surface may explain the observed increased uptake by macrophages and the reduced intracellular survival. Finally, studies in mice demonstrate that Pdr6 function is required for normal progression of cryptococcal infection. Taken together, this study demonstrates a novel dual role for PDR transporters in C. neoformans, which could represent a potential target for antifungal therapeutics. Furthermore, the atypical half-size transporter encoded by PDR6 is conserved in many fungal pathogens, but absent in model non-pathogenic fungi. Hence, this study provides for the first time, a function for this unique group of fungal half-size PDR transporters that, although conserved, remain largely understudied. IMPORTANCEConserved across all kingdoms of life, ABC transporters comprise one of the largest protein families. They are associated with multidrug resistance, affecting aspects such as resistance to antimicrobials or anti-cancer drugs. Despite their importance, they are understudied in fungal pathogens. In the environmental fungus Cryptococcus neoformans, a leading cause of fungal infections, only a few ABC transporters have been studied. Here we characterize an atypical, half-size, ABC transporter of the PDR-type, that affects both antifungal resistance and host-pathogen interactions. PDR-type transporters are only present in fungi and plants, and this subgroup of half-size transporters is conserved in fungal pathogens, yet their function was completely unknown. Because the current treatments for cryptococcal infection are suboptimal, understanding the mechanisms of antifungal resistance and the host interactions that drive the infection is critical to improve the management of this disease. Here we provide insights into these important aspects of cryptococcal pathogenesis.