The basidiomycete fungus Cryptococcus neoformans infects humans via inhalation of desiccated yeast cells or spores from the environment. In the absence of effective immune containment, the initial pulmonary infection often spreads to the central nervous system to result in meningoencephalitis. The fungus must therefore make the transition from the environment to different mammalian niches that include the intracellular locale of phagocytic cells and extracellular sites in the lung, bloodstream, and central nervous system. Recent studies provide insights into mechanisms of adaptation during this transition that include the expression of antiphagocytic functions, the remodeling of central carbon metabolism, the expression of specific nutrient acquisition systems, and the response to hypoxia. Specific transcription factors regulate these functions as well as the expression of one or more of the major known virulence factors of C. neoformans. Therefore, virulence factor expression is to a large extent embedded in the regulation of a variety of functions needed for growth in mammalian hosts. In this regard, the complex integration of these processes is reminiscent of the master regulators of virulence in bacterial pathogens.
The battle for iron between invading microorganisms and mammalian hosts is a pivotal determinant of the outcome of infection. The pathogenic fungus, Cryptococcus neoformans, employs multiple mechanisms to compete for iron during cryptococcosis, a disease primarily of immunocompromised hosts. In this study, we examined the role of endocytic trafficking in iron uptake by characterizing a mutant defective in the Sec1/Munc18 (SM) protein Vps45. This protein is known to regulate the machinery for vesicle trafficking and fusion via interactions with SNARE proteins. As expected, a vps45 deletion mutant was impaired in endocytosis and showed sensitivity to trafficking inhibitors. The mutant also showed poor growth on iron-limited media and a defect in transporting the Cfo1 ferroxidase of the high-affinity iron uptake system from the plasma membrane to the vacuole. Remarkably, we made the novel observation that Vps45 also contributes to mitochondrial function in that a Vps45-Gfp fusion protein associated with mitotracker, and a vps45 mutant showed enhanced sensitivity to inhibitors of electron transport complexes as well as changes in mitochondrial membrane potential. Consistent with mitochondrial function, the vps45 mutant was impaired in calcium homeostasis. To assess the relevance of these defects for virulence, we examined cell surface properties of the vps45 mutant and found increased sensitivity to agents that challenge cell wall integrity and to antifungal drugs. A change in cell wall properties was consistent with our observation of altered capsule polysaccharide attachment, and with attenuated virulence in a mouse model of cryptococcosis. Overall, our studies reveal a novel role for Vps45-mediated trafficking for iron uptake, mitochondrial function and virulence.
17The battle for iron between invading microorganisms and mammalian hosts is a 18 pivotal determinant of the outcome of infection. The pathogenic fungus, Cryptococcus 19 neoformans, employs multiple mechanisms to compete for iron during cryptococcosis, a 20 disease primarily of immunocompromised hosts. In this study, we examined the role of 21 endocytic trafficking in iron uptake by characterizing a mutant defective in the 22 Sec1/Munc18 (SM) protein Vps45. This protein is known to regulate the machinery for 23 vesicle trafficking and fusion via interactions with SNARE proteins. As expected, a 24 vps45 deletion mutant was impaired in endocytosis and showed sensitivity to trafficking 25 inhibitors. The mutant also showed poor growth on iron-limited media and a defect in 26 transporting the Cfo1 ferroxidase of the high-affinity iron uptake system from the plasma 27 membrane to the vacuole. Remarkably, we made the novel observation that Vps45 also 28 contributes to mitochondrial function in that a Vps45-Gfp fusion protein associated with 29 mitotracker, and a vps45 mutant showed enhanced sensitivity to inhibitors of electron 30 transport complexes as well as changes in mitochondrial membrane potential. Consistent 31 with mitochondrial function, the vps45 mutant was impaired in calcium homeostasis. To 32 assess the relevance of these defects for virulence, we examined cell surface properties of 33 the vps45 mutant and found increased sensitivity to agents that challenge cell wall 34 integrity and antifungal drugs. A change in cell wall properties was consistent with our 35 observation of altered capsule polysaccharide attachment, and with attenuated virulence 36 in a mouse model of cryptococcosis. Overall, our studies reveal a novel role for Vps45-37 mediated trafficking for iron uptake, mitochondrial function and virulence. 38 3 AUTHOR SUMMARY 39 Cryptococcus neoformans is a causative agent of cryptococcal meningitis, a 40 disease that is estimated to cause ~ 15% of AIDS-related deaths. In this context, 41 cryptococosis is the second most common cause of mortality in people with HIV/AIDS, 42 closely behind tuberculosis. Unfortunately, very few antifungal drugs are available to 43 treat this disease. However, understanding mechanisms involved in the pathogenesis of 44 C. neoformans can lead to new therapeutic avenues. In this study, we discovered a new 45 role for a regulatory protein involved in vesicle transport. Specifically, we found that the 46 Vps45 protein, which regulates vesicle fusion, participates in the trafficking of iron into 47 54 The pathogenic fungus Cryptococcus neoformans attacks immunocompromised 55 people to cause cryptococcosis, a particularly devastating disease in HIV/AIDS sufferers 56(1). Adaptations of the fungus to cause disease in mammalian hosts include the ability to 57 grow at 37 o C, to deliver key virulence components to the external milieu, and to acquire 58 nutrients for proliferation (2,3). In the latter case, iron plays a key role in the virulence 59 of C. neoformans as a...
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.