. The pathogenic fungus Cryptococcus neoformans causes life-threatening infections in AIDS patients and therefore poses a major threat to the >34 million people worldwide who are infected with HIV. The related species Cryptococcus gattii has recently emerged as a primary pathogen of immunocompetent people. The long-term goal of this project is to acquire knowledge that will lead to new strategies to combat fungal infections. In particular, we want to establish a detailed understanding of the factors required for pathogen growth in mammalian hosts and identify useful targets for therapy. In this regard, iron availability is a key indicator of the host environment as well as an essential nutrient for pathogen proliferation. In addition, mammals actively withhold iron from pathogens in a process termed nutritional immunity, and pathogens must therefore aggressively compete for iron. Iron is particularly important for the pathogenesis of C. neoformans because the availability of this metal not only influences growth but also the size of the polysaccharide capsule that is the major virulence factor. To fill gaps in our understanding of the mechanisms by which fungal pathogens compete for iron, the first specific aim is to determine the molecular functions of cell surface proteins that support iron acquisition from heme. These proteins each contribute to robust growth on heme and include a secreted mannoprotein that is a candidate heme-binding protein as well as three ferric reductases. A second specific aim will characterize the intracellular machinery for heme trafficking and processing. An insertional mutagenesis screen identified 25 genes in which mutations caused growth defects on heme, and some of these genes encode intracellular trafficking machinery. This result led to the hypothesis that heme is acquired by endocytosis and transported to the vacuole for iron extraction and recycling. Mutants with defects at specific steps in known and candidate transport functions will be constructed and tested for their ability to process heme. A final specific aim will evaluate the role of heme and iron acquisition functions in the virulence of C. neoformans. Mutants lacking combinations of iron acquisition functions will be tested in mouse inhalation models of cryptococcosis and the proliferation of the mutants in macrophages will be examined in the context of different iron sources. These studies will provide a comprehensive view of the relative importance of specific host iron sources and fungal uptake strategies during cryptococcosis. !
of this project comes from the pressing need to control fungal infections in humans with impaired immune systems. In particular, the 34 million or more people infected with HIV have a high chance of succumbing to fungal diseases. The research will specifically examine the potential to control these infections by targeting the abiliy of fungal pathogens to acquire iron as a vital nutrient during infection.
|Saikia, Sanjay; Oliveira, Debora; Hu, Guanggan et al. (2014) Role of ferric reductases in iron acquisition and virulence in the fungal pathogen Cryptococcus neoformans. Infect Immun 82:839-50|
|Janbon, Guilhem; Ormerod, Kate L; Paulet, Damien et al. (2014) Analysis of the genome and transcriptome of Cryptococcus neoformans var. grubii reveals complex RNA expression and microevolution leading to virulence attenuation. PLoS Genet 10:e1004261|
|Kronstad, James W; Hu, Guanggan; Jung, Won Hee (2013) An encapsulation of iron homeostasis and virulence in Cryptococcus neoformans. Trends Microbiol 21:457-65|
|Cadieux, Brigitte; Lian, Tianshun; Hu, Guanggan et al. (2013) The Mannoprotein Cig1 supports iron acquisition from heme and virulence in the pathogenic fungus Cryptococcus neoformans. J Infect Dis 207:1339-47|
|Kronstad, James W; Cadieux, Brigitte; Jung, Won Hee (2013) Pathogenic yeasts deploy cell surface receptors to acquire iron in vertebrate hosts. PLoS Pathog 9:e1003498|
|Hu, Guanggan; Caza, Melissa; Cadieux, Brigitte et al. (2013) Cryptococcus neoformans requires the ESCRT protein Vps23 for iron acquisition from heme, for capsule formation, and for virulence. Infect Immun 81:292-302|
|Kronstad, Jim; Saikia, Sanjay; Nielson, Erik David et al. (2012) Adaptation of Cryptococcus neoformans to mammalian hosts: integrated regulation of metabolism and virulence. Eukaryot Cell 11:109-18|
|Jung, Won Hee; Kronstad, James W (2011) Iron influences the abundance of the iron regulatory protein Cir1 in the fungal pathogen Cryptococcus neoformans. FEBS Lett 585:3342-7|
|Kronstad, James W; Attarian, Rodgoun; Cadieux, Brigitte et al. (2011) Expanding fungal pathogenesis: Cryptococcus breaks out of the opportunistic box. Nat Rev Microbiol 9:193-203|
|Jung, Won Hee; Kronstad, James W (2011) The iron-responsive, GATA-type transcription factor Cir1 influences mating in Cryptococcus neoformans. Mol Cells 31:73-7|
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