Copper homeostasis in fungal pathogenesis

About This Grant

SUMMARY Copper (Cu) is an essential trace element and a catalytic cofactor for a variety of enzymes involved in cell growth, development, and stress resistance. Fungal systems have been instrumental in identifying mechanisms of Cu utilization and homeostasis in diverse eukaryotic cells. The experiments in this proposal will use a relevant fungal model system to explore Cu homeostasis in microbial physiology and pathogenesis. Cryptococcus neoformans is an opportunistic fungal pathogen that is responsible for >100,000 deaths annually, especially among patients with poorly treated HIV infection. This pathogenic microorganism is an outstanding model to study rapid cellular adaptations between high and low Cu states. This fungus has sophisticated transcriptional and post-transcriptional Cu regulatory mechanisms to adapt to Cu overload and Cu limitation in biologically relevant niches. C. neoformans first infects the host lung where it is engulfed by alveolar macrophages and experiences toxic Cu bombardment within the phagolysosome. In immunocompromised hosts, this fungus disseminates through the bloodstream to the central nervous system where it causes lethal disease, and where it encounters extreme Cu starvation. Failure to acquire Cu, or to adapt to low bioavailable brain Cu levels, results in defective fungal survival in the host. Therefore, during the infection cycle this microorganism must be able to rapidly transition from a Cu-resistant state during toxic Cu exposure to a Cu-foraging state during Cu limitation. The C. neoformans Cuf1 transcription factor is the primary regulator of the cellular response to both high and low Cu levels. We and our prior collaborators therefore characterized the Cuf1- dependent transcriptome and used this data to define conserved and novel mechanisms of eukaryotic copper biology. These studies identified important cellular responses to Cu limitation (increasing Cu import) as well as to Cu excess (inducing Cu detoxification processes). In the experiments outlined in this proposal, we will build upon this rigorous experimental foundation to explore new intersections between Cu homeostasis and microbial pathogenesis. These include (SA1) exploring our new observations regarding the roles of Cu homeostasis and Cu-containing enzymes in cell wall/cell membrane function; and (SA2) defining the impact of failed copper regulation on microbial pathogenesis. Together, these studies will advance new concepts for how microbial cells acquire the essential metal ion Cu, invoke adaptive responses to Cu toxicity, and regulate these processes to mediate interactions with the infected host.