The fungal pathogen Cryptococcus neoformans causes a high incidence of life-threatening infections in AIDS patients and this fungus therefore poses a major threat to the >40 million people worldwide who are infected with HIV. In addition, the related species C. gattii has recently emerged as a primary pathogen of immunocompetent people. Our long-term goal is to acquire knowledge that will lead to new strategies to combat fungal infections. In particular, we want to develop a detailed understanding of the factors required for growth of pathogens in mammalian hosts in order to identify key targets to block infection. In this regard, iron availability is an important indicator of the host environment as well as an essential nutrient for pathogens. Therefore, we plan to investigate iron regulation and acquisition in C. neoformans, as a model for understanding the role of iron in fungal pathogenesis. Iron levels are particularly important for the pathogenesis of C. neoformans because availability influences the size of the polysaccharide capsule that is the major virulence factor of the fungus. Our hypothesis is that the influence of iron on virulence and growth occurs through a network controlled by the master iron-responsive regulator Cir1 (Cryptococcus iron regulator). We believe that the characterization of Cir1 and this network will identify mechanisms of iron acquisition that are essential for C. neoformans to cause disease. Our first specific aim is to characterize the key functions of Cir1. We will specifically determine whether Cir1 directly binds iron and whether the protein binds the promoter regions of target genes encoding iron uptake functions. This work will include proteomic approaches to identify regulatory factors that interact with Cir1. These factors may participate in the regulation of target genes for iron acquisition and other functions relevant to virulence. Our second specific aim will characterize the role of the Hap transcription factor complex in iron acquisition from heme. The expression of the HAP genes is regulated by Cir1 and we have preliminary data that these genes are required for heme use. Our third specific aim will employ transcriptional profiling to examine the role of Cir1 in the use of iron sources (heme and transferrin) that are abundant in the host. Finally, we will construct mutants that are defective in genes encoding candidate functions for the use of heme and transferrin during infection. Likely targets (e.g., heme oxygenase) have been identified and we anticipate that our microarray work in aim 3 will identify additional functions. At the conclusion of this work, we will have a deeper understanding of the regulatory network that links iron to virulence, and we will know the functions that C. neoformans uses to steal iron from the host during infection. This information will highlight the key iron-related functions that can be targeted to treat Cryptococcal disease.

Public Health Relevance

The relevance of this project comes from the pressing need to control fungal infections in humans with impaired immune systems. In particular, the 40 million or more people infected with HIV have a high chance of succumbing to fungal disease. The research will specifically examine the potential to control infections by targeting the ability of fungal pathogens to acquire the nutrient iron during infection.

National Institute of Health (NIH)
National Institute of Allergy and Infectious Diseases (NIAID)
Research Project (R01)
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Special Emphasis Panel (ZRG1-IDM-B (02))
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Duncan, Rory A
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University of British Columbia
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V6 1-Z3
Rizzo, Juliana; Colombo, Ana C; Zamith-Miranda, Daniel et al. (2018) The putative flippase Apt1 is required for intracellular membrane architecture and biosynthesis of polysaccharide and lipids in Cryptococcus neoformans. Biochim Biophys Acta Mol Cell Res 1865:532-541
Attarian, Rodgoun; Hu, Guanggan; Sánchez-León, Eddy et al. (2018) The Monothiol Glutaredoxin Grx4 Regulates Iron Homeostasis and Virulence in Cryptococcus neoformans. MBio 9:
Caza, Mélissa; Hu, Guanggan; Nielson, Erik David et al. (2018) The Sec1/Munc18 (SM) protein Vps45 is involved in iron uptake, mitochondrial function and virulence in the pathogenic fungus Cryptococcus neoformans. PLoS Pathog 14:e1007220
Bairwa, Gaurav; Hee Jung, Won; Kronstad, James W (2017) Iron acquisition in fungal pathogens of humans. Metallomics 9:215-227
Hu, Guanggan; Caza, Mélissa; Bakkeren, Erik et al. (2017) A P4-ATPase subunit of the Cdc50 family plays a role in iron acquisition and virulence in Cryptococcus neoformans. Cell Microbiol 19:
Do, Eunsoo; Hu, Guanggan; Caza, Mélissa et al. (2016) The ZIP family zinc transporters support the virulence of Cryptococcus neoformans. Med Mycol 54:605-15
Do, Eunsoo; Park, Minji; Hu, Guanggan et al. (2016) The lysine biosynthetic enzyme Lys4 influences iron metabolism, mitochondrial function and virulence in Cryptococcus neoformans. Biochem Biophys Res Commun 477:706-711
Ding, Hao; Mayer, François L; Sánchez-León, Eddy et al. (2016) Networks of fibers and factors: regulation of capsule formation in Cryptococcus neoformans. F1000Res 5:
Jung, Won Hee; Sham, Anita; White, Rick et al. (2016) Correction: Iron Regulation of the Major Virulence Factors in the AIDS-Associated Pathogen Cryptococcus neoformans. PLoS Biol 14:e1002410
Caza, Mélissa; Hu, Guanggan; Price, Michael et al. (2016) The Zinc Finger Protein Mig1 Regulates Mitochondrial Function and Azole Drug Susceptibility in the Pathogenic Fungus Cryptococcus neoformans. mSphere 1:

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