A Major Role for Capsule-Independent Phagocytosis-Inhibitory Mechanisms in Mammalian Infection by Cryptococcus neoformans

Department of Biochemistry and Biophysics, University of California, San Francisco, San Francisco, CA 94158-2200, USA.
Cell host & microbe (Impact Factor: 12.33). 03/2011; 9(3):243-51. DOI: 10.1016/j.chom.2011.02.003
Source: PubMed


The antiphagocytic polysaccharide capsule of the human fungal pathogen Cryptococcus neoformans is a major virulence attribute. However, previous studies of the pleiotropic virulence determinant Gat201, a GATA family transcription factor, suggested that capsule-independent antiphagocytic mechanisms exist. We have determined that Gat201 controls the mRNA levels of ∼1100 genes (16% of the genome) and binds the upstream regions of ∼130 genes. Seven Gat201-bound genes encode for putative and known transcription factors--including two previously implicated in virulence--suggesting an extensive regulatory network. Systematic analysis pinpointed two critical Gat201-bound genes, GAT204 (a transcription factor) and BLP1, which account for much of the capsule-independent antiphagocytic function of Gat201. A strong correlation was observed between the quantitative effects of single and double mutants on phagocytosis in vitro and on host colonization in vivo. This genetic dissection provides evidence that capsule-independent antiphagocytic mechanisms are pivotal for successful mammalian infection by C. neoformans.

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    • "Other fungal proteins have been described to be involved for capsule-independent antiphagocytic processes. For example, App1 might manipulate host CD11b for evasion of phagocytosis (Stano et al., 2009), while Gat201 transcription factor regulates gene expression of antiphagocytic proteins of unknown mechanism (Chun et al., 2011). Other examples of immunomodulation exist but for some studies it is hard to differentiate from a response that originated as a reaction to a more fragile pathogen or de facto immunomodulatory properties. "
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    ABSTRACT: Cryptococcus neoformans is a fungal pathogen that causes almost half a million deaths each year. It is believed that most humans are infected with C. neoformans, possibly in a form that survives through latency in the lung and can reactivate to cause disease if the host becomes immunosuppressed. C. neoformans has a remarkably sophisticated intracellular survival capacities yet it is a free-living fungus with no requirement for mammalian virulence whatsoever. In this review, we discuss the tools that C. neoformans possesses to achieve survival, latency and virulence within its host. Some of these tools are mechanisms to withstand starvation and others aim to protect against microbicidal molecules produced by the immune system. Furthermore, we discuss how these tools were acquired through evolutionary pressures and perhaps accidental stochastic events, all of which combined to produce an organism with an unusual and unique intracellular pathogenic strategy.
    Advances in applied microbiology 03/2014; 87:1-41. DOI:10.1016/B978-0-12-800261-2.00001-3 · 2.74 Impact Factor
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    • "and CNAG03401.2 have unknown functions [34], [68], [69], [70], [71]. To determine if any of these GATA factors play a negative role in nitrogen catabolism, we tested the gat201Δ, gat204Δ, bwc2Δ, cir1Δ, CNAG04263.2Δ "
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    ABSTRACT: Nitrogen source utilization plays a critical role in fungal development, secondary metabolite production and pathogenesis. In both the Ascomycota and Basidiomycota, GATA transcription factors globally activate the expression of catabolic enzyme-encoding genes required to degrade complex nitrogenous compounds. However, in the presence of preferred nitrogen sources such as ammonium, GATA factor activity is inhibited in some species through interaction with co-repressor Nmr proteins. This regulatory phenomenon, nitrogen metabolite repression, enables preferential utilization of readily assimilated nitrogen sources. In the basidiomycete pathogen Cryptococcus neoformans, the GATA factor Gat1/Are1 has been co-opted into regulating multiple key virulence traits in addition to nitrogen catabolism. Here, we further characterize Gat1/Are1 function and investigate the regulatory role of the predicted Nmr homolog Tar1. While GAT1/ARE1 expression is induced during nitrogen limitation, TAR1 transcription is unaffected by nitrogen availability. Deletion of TAR1 leads to inappropriate derepression of non-preferred nitrogen catabolic pathways in the simultaneous presence of favoured sources. In addition to exhibiting its evolutionary conserved role of inhibiting GATA factor activity under repressing conditions, Tar1 also positively regulates GAT1/ARE1 transcription under non-repressing conditions. The molecular mechanism by which Tar1 modulates nitrogen metabolite repression, however, remains open to speculation. Interaction between Tar1 and Gat1/Are1 was undetectable in a yeast two-hybrid assay, consistent with Tar1 and Gat1/Are1 each lacking the conserved C-terminus regions present in ascomycete Nmr proteins and GATA factors that are known to interact with each other. Importantly, both Tar1 and Gat1/Are1 are suppressors of C. neoformans virulence, reiterating and highlighting the paradigm of nitrogen regulation of pathogenesis.
    PLoS ONE 03/2012; 7(3):e32585. DOI:10.1371/journal.pone.0032585 · 3.23 Impact Factor
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    • "Systematic analysis yielded two critical Gat201-bound genes, GAT204 (a transcription factor) and BLP1, which account for most of the capsule-independent antiphagocytic function of Gat201. A strong correlation was observed between the quantitative effects of single and double mutants on phagocytosis in vitro and on host colonization in vivo (Chun et al., 2011), and thus, it is believed that Gat201 could be a regulator of virulence because the gat201 mutant is avirulent in mice (Liu et al., 2008). "
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    ABSTRACT: After inhalation of infectious particles, Cryptococcus neoformans resides in the alveolar spaces, where it can survive and replicate in the extracellular environment. This yeast has developed different mechanisms to avoid internalization by phagocytic cells, the main one being a polysaccharide capsule around the cell body, which inhibits the uptake of the yeast by macrophages. In addition, capsule-independent mechanisms have also been described, such as the production of antiphagocytic proteins. Despite these mechanisms, phagocytosis can occur in the presence of opsonins, and once C. neoformans is internalized, multiple outcomes are possible, including pathogen killing or intracellular replication and escape from macrophages. For this reason, C. neoformans is considered a facultative intracellular pathogen. As alveolar macrophages are the first component of the host immune system to confront C. neoformans, the outcome of this interaction could determine the degree of infection, producing either a severe disseminated disease or a latency state. In this review, we will tackle the complexity of the interaction between C. neoformans and macrophages, including the phagocytic avoidance mechanisms and all the possible outcomes that have been described for this interaction. Finally, we will discuss the consequences of the different outcomes for the type of infection produced in the host.
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