Browsing by Subject "SACCHAROMYCES-CEREVISIAE"
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Item Open Access Defects in intracellular trafficking of fungal cell wall synthases lead to aberrant host immune recognition.(PLoS pathogens, 2018-06-04) Esher, Shannon K; Ost, Kyla S; Kohlbrenner, Maria A; Pianalto, Kaila M; Telzrow, Calla L; Campuzano, Althea; Nichols, Connie B; Munro, Carol; Wormley, Floyd L; Alspaugh, J AndrewThe human fungal pathogen, Cryptococcus neoformans, dramatically alters its cell wall, both in size and composition, upon entering the host. This cell wall remodeling is essential for host immune avoidance by this pathogen. In a genetic screen for mutants with changes in their cell wall, we identified a novel protein, Mar1, that controls cell wall organization and immune evasion. Through phenotypic studies of a loss-of-function strain, we have demonstrated that the mar1Δ mutant has an aberrant cell surface and a defect in polysaccharide capsule attachment, resulting in attenuated virulence. Furthermore, the mar1Δ mutant displays increased staining for exposed cell wall chitin and chitosan when the cells are grown in host-like tissue culture conditions. However, HPLC analysis of whole cell walls and RT-PCR analysis of cell wall synthase genes demonstrated that this increased chitin exposure is likely due to decreased levels of glucans and mannans in the outer cell wall layers. We observed that the Mar1 protein differentially localizes to cellular membranes in a condition dependent manner, and we have further shown that the mar1Δ mutant displays defects in intracellular trafficking, resulting in a mislocalization of the β-glucan synthase catalytic subunit, Fks1. These cell surface changes influence the host-pathogen interaction, resulting in increased macrophage activation to microbial challenge in vitro. We established that several host innate immune signaling proteins are required for the observed macrophage activation, including the Card9 and MyD88 adaptor proteins, as well as the Dectin-1 and TLR2 pattern recognition receptors. These studies explore novel mechanisms by which a microbial pathogen regulates its cell surface in response to the host, as well as how dysregulation of this adaptive response leads to defective immune avoidance.Item Open Access HDAC genes play distinct and redundant roles in Cryptococcus neoformans virulence.(Scientific reports, 2018-03-26) Brandão, Fabiana; Esher, Shannon K; Ost, Kyla S; Pianalto, Kaila; Nichols, Connie B; Fernandes, Larissa; Bocca, Anamélia L; Poças-Fonseca, Marcio José; Alspaugh, J AndrewThe human fungal pathogen Cryptococcus neoformans undergoes many phenotypic changes to promote its survival in specific ecological niches and inside the host. To explore the role of chromatin remodeling on the expression of virulence-related traits, we identified and deleted seven genes encoding predicted class I/II histone deacetylases (HDACs) in the C. neoformans genome. These studies demonstrated that individual HDACs control non-identical but overlapping cellular processes associated with virulence, including thermotolerance, capsule formation, melanin synthesis, protease activity and cell wall integrity. We also determined the HDAC genes necessary for C. neoformans survival during in vitro macrophage infection and in animal models of cryptococcosis. Our results identified the HDA1 HDAC gene as a central mediator controlling several cellular processes, including mating and virulence. Finally, a global gene expression profile comparing the hda1Δ mutant versus wild-type revealed altered transcription of specific genes associated with the most prominent virulence attributes in this fungal pathogen. This study directly correlates the effects of Class I/II HDAC-mediated chromatin remodeling on the marked phenotypic plasticity and virulence potential of this microorganism. Furthermore, our results provide insights into regulatory mechanisms involved in virulence gene expression that are likely shared with other microbial pathogens.