Capsule Enlargement in Cryptococcus neoformans Is Dependent on Mitochondrial Activity.
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ABSTRACT:
SUBMITTER: Trevijano-Contador N
PROVIDER: S-EPMC5534456 | biostudies-other | 2017
REPOSITORIES: biostudies-other
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Project description:Microbial capsules are important virulence traits that mediate cell-host interactions and provide protection against host immune defense mechanisms. Cryptococcus neoformans is a yeast-like fungus that is capable of synthesizing a complex polysaccharide (PS) capsule that is required for causing disease. Microscopic visualization of capsule enlargement is difficult, because the capsule is a highly hydrated structure with an index of refraction that is very close to that of aqueous medium. In this study, we took advantage of the capsular reaction ("quellung" effect) produced by IgM monoclonal antibody (MAb) 13F1 to increase the refraction index difference between capsule and medium such that we visualized the capsule using differential interference contrast (DIC) microscopy. Time-lapse size measurements allowed us to quantify the growth rate of the capsule relative to that of the cell body. The increase in capsule volume per unit of time was consistent with a logistic variable slope model in which the capsule's final size was proportional to the rate of its growth. The rate of capsule growth (0.3 to 2.5 µm(3)/min) was at least 4-fold faster than the rate of cell body growth (0.1 to 0.3 µm(3)/min), and there was large cell-to-cell variation in the temporal kinetics of capsule and cellular growth. Previous to the first cellular replication event, both the capsule and cell body enlarged simultaneously, and their differences showed monotonic growth, which was affected only by its rate of volume increase per unit of time. Using these results, we provide an updated model for cryptococcal capsule biogenesis.
| S-EPMC3811331 | biostudies-literature
Project description:The human pathogenic fungus Cryptococcus neoformans has a distinctive polysaccharide (PS) capsule that enlarges during infection. The capsule is essential for virulence, but the mechanism for capsular growth is unknown. In the present study, we used dynamic light scattering (LS) analysis of capsular PS and optical tweezers (OT) to explore the architecture of the capsule. Analysis of capsular PS from cells with small and large capsules by dynamic LS revealed a linear correlation between PS effective diameter and microscopic capsular diameter. This result implied that capsule growth was achieved by the addition of molecules with larger effective diameter, such that some molecules can span the entire diameter of the capsule. Measurement of polystyrene bead penetration of C. neoformans capsules by using OT techniques revealed that the outer regions were penetrable, but not the inner regions. Our results provide a mechanism for capsular enlargement based on the axial lengthening of PS molecules and suggest a model for the architecture of a eukaryotic microbial capsule.
| S-EPMC2633523 | biostudies-literature
Project description:Microbial capsules are important for virulence, but their architecture and physical properties are poorly understood. The human pathogenic fungus Cryptococcus neoformans has a large polysaccharide capsule that is necessary for virulence and is the target of protective antibody responses. To study the C. neoformans capsule we developed what we believe is a new approach whereby we probed the capsular elastic properties by applying forces using polystyrene beads manipulated with optical tweezers. This method allowed us to determine the Young's modulus for the capsule in various conditions that affect capsule growth. The results indicate that the Young's modulus of the capsule decreases with its size and increases with the Ca(2+) concentration in solution. Also, capsular polysaccharide manifests an unexpected affinity for polystyrene beads, a property that may function in attachment to host cells and environmental structures. Bead probing with optical tweezers provides a new, nondestructive method that may have wide applicability for studying the effects of growth conditions, immune components, and drugs on capsular properties.
| S-EPMC2726329 | biostudies-literature
Project description:The human fungal pathogen Cryptococcus neoformans is characterized by its ability to induce a distinct polysaccharide capsule in response to a number of host-specific environmental stimuli. The induction of capsule is a complex biological process encompassing regulation at multiple steps, including the biosynthesis, transport, and maintenance of the polysaccharide at the cell surface. By precisely regulating the composition of its cell surface and secreted polysaccharides, C. neoformans has developed intricate ways to establish chronic infection and dormancy in the human host. The plasticity of the capsule structure in response to various host conditions also underscores the complex relationship between host and parasite. Much of this precise regulation of capsule is achieved through the transcriptional responses of multiple conserved signaling pathways that have been coopted to regulate this C. neoformans-specific virulence-associated phenotype. This review focuses on specific host stimuli that trigger the activation of the signal transduction cascades and on the downstream transcriptional responses that are required for robust encapsulation around the cell.
| S-EPMC3416491 | biostudies-literature
Project description:Cryptococcus neoformans is an opportunistic fungal pathogen that causes serious human disease in immunocompromised populations. Its polysaccharide capsule is a key virulence factor which is regulated in response to growth conditions, becoming enlarged in the context of infection. We used microarray analysis of cells stimulated to form capsule over a range of growth conditions to identify a transcriptional signature associated with capsule enlargement. The signature contains 880 genes, is enriched for genes encoding known capsule regulators, and includes many uncharacterized sequences. One uncharacterized sequence encodes a novel regulator of capsule and of fungal virulence. This factor is a homolog of the yeast protein Ada2, a member of the Spt-Ada-Gcn5 Acetyltransferase (SAGA) complex that regulates transcription of stress response genes via histone acetylation. Consistent with this homology, the C. neoformans null mutant exhibits reduced histone H3 lysine 9 acetylation. It is also defective in response to a variety of stress conditions, demonstrating phenotypes that overlap with, but are not identical to, those of other fungi with altered SAGA complexes. The mutant also exhibits significant defects in sexual development and virulence. To establish the role of Ada2 in the broader network of capsule regulation we performed RNA-Seq on strains lacking either Ada2 or one of two other capsule regulators: Cir1 and Nrg1. Analysis of the results suggested that Ada2 functions downstream of both Cir1 and Nrg1 via components of the high osmolarity glycerol (HOG) pathway. To identify direct targets of Ada2, we performed ChIP-Seq analysis of histone acetylation in the Ada2 null mutant. These studies supported the role of Ada2 in the direct regulation of capsule and mating responses and suggested that it may also play a direct role in regulating capsule-independent antiphagocytic virulence factors. These results validate our experimental approach to dissecting capsule regulation and provide multiple targets for future investigation.
| S-EPMC3234223 | biostudies-literature
Project description:A remarkable aspect of the interaction of Cryptococcus neoformans with mammalian hosts is a consistent increase in capsule volume. Given that many aspects of the interaction of C. neoformans with macrophages are also observed with amoebae, we hypothesized that the capsule enlargement phenomenon also had a protozoan parallel. Incubation of C. neoformans with Acanthamoeba castellanii resulted in C. neoformans capsular enlargement. The phenomenon required contact between fungal and protozoan cells but did not require amoeba viability. Analysis of amoebae extracts showed that the likely stimuli for capsule enlargement were protozoan polar lipids. Extracts from macrophages and mammalian serum also triggered cryptococcal capsular enlargement. C. neoformans capsule enlargement required expression of fungal phospholipase B, but not phospholipase C. Purified phospholipids, in particular, phosphatidylcholine, and derived molecules triggered capsular enlargement with the subsequent formation of giant cells. These results implicate phospholipids as a trigger for both C. neoformans capsule enlargement in vivo and exopolysaccharide production. The observation that the incubation of C. neoformans with phospholipids led to the formation of giant cells provides the means to generate these enigmatic cells in vitro. Protozoan- or mammalian-derived polar lipids could represent a danger signal for C. neoformans that triggers capsular enlargement as a non-specific defense mechanism against potential predatory cells. Hence, phospholipids are the first host-derived molecules identified to trigger capsular enlargement. The parallels apparent in the capsular response of C. neoformans to both amoebae and macrophages provide additional support for the notion that certain aspects of cryptococcal virulence emerged as a consequence of environmental interactions with other microorganisms such as protists.
| S-EPMC3102711 | biostudies-literature
Project description:Cryptococcus neoformans is an opportunistic basidiomycete pathogen that is a major etiological agent of fungal meningoencephalitis leading to more than 180,000 deaths worldwide annually. For this pathogen, the polysaccharide capsule is a key virulence factor, which interferes with the phagocytosis by host innate immune cells, but its complex signaling networks remain elusive. In this study, we systematically analyzed capsule biosynthesis and signaling networks by using C. neoformans transcription factor (TF) and kinase mutant libraries under diverse capsule-inducing conditions, such as Dulbecco’s Modified Eagle’s (DME), Littman’s medium (LIT) and fetal bovine serum (FBS) medium. We found that deletion of GAT201, YAP1, BZP4, and ADA2 consistently causes capsule production defects in all tested media, indicating that they are capsule-regulating core TFs. Epistatic and expression analysis showed that Yap1 and Ada2 control Gat201 upstream, whereas Bzp4 and Gat201 regulate capsule production independently. We next searched for potential upstream kinases and found that mutants deleted of PKA1, BUD32, POS5, IRE1 or CDC2801 showed reduced capsule production under all three capsule induction conditions, whereas mutants deleted of HOG1 and IRK5 displayed enhanced capsule production. Notably, Pka1 and Irk5 controls induction of GAT201 and BZP4, respectively, under capsule induction condition. Finally, we monitored transcriptome profiles governed by Bzp4, Gat201, and Ada2 under capsule-inducing condition and demonstrated that these TFs regulate redundant and unique sets of downstream target genes. In conclusion, this study provides further insight into the complex regulatory mechanism of capsule production related signaling pathways in C. neoformans.
2022-10-18 | GSE208163 | GEO
Project description:Cryptococcus neoformans is a prevalent human fungal pathogen that must survive within various tissues in order to establish a human infection. We have identified the C. neoformans Rim101 transcription factor, a highly conserved pH-response regulator in many fungal species. The rim101 multiply sign in circle mutant strain displays growth defects similar to other fungal species in the presence of alkaline pH, increased salt concentrations, and iron limitation. However, the rim101 multiply sign in circle strain is also characterized by a striking defect in capsule, an important virulence-associated phenotype. This capsular defect is likely due to alterations in polysaccharide attachment to the cell surface, not in polysaccharide biosynthesis. In contrast to many other C. neoformans capsule-defective strains, the rim101 multiply sign in circle mutant is hypervirulent in animal models of cryptococcosis. Whereas Rim101 activation in other fungal species occurs through the conserved Rim pathway, we demonstrate that C. neoformans Rim101 is also activated by the cAMP/PKA pathway. We report here that C. neoformans uses PKA and the Rim pathway to regulate the localization, activation, and processing of the Rim101 transcription factor. We also demonstrate specific host-relevant activating conditions for Rim101 cleavage, showing that C. neoformans has co-opted conserved signaling pathways to respond to the specific niche within the infected host. These results establish a novel mechanism for Rim101 activation and the integration of two conserved signaling cascades in response to host environmental conditions.
| S-EPMC2824755 | biostudies-literature
Project description:The cryptococcal capsule is a critical virulence factor of an important pathogen, but little is known about how it is associated with the cell or released into the environment. Two mutants lacking PBX1 and PBX2 were found to shed reduced amounts of the capsule polysaccharide glucuronoxylomannan (GXM). Nuclear magnetic resonance, composition, and physical analyses showed that the shed material was of normal mass but was slightly enriched in xylose. In contrast to previous reports, this material contained no glucose. Notably, the capsule fibers of pbx? mutant cells grown under capsule-inducing conditions were present at a lower than usual density and were loosely attached to the cell wall. Mutant cell walls were also defective, as indicated by phenotypes including abnormal cell morphology, reduced mating filamentation, and altered cell integrity. All observed phenotypes were shared between the two mutants and exacerbated in a double mutant. Consistent with a role in surface glycan synthesis, the Pbx proteins localized to detergent-resistant membrane domains. These results, together with the sequence motifs in the Pbx proteins, suggest that Pbx1 and Pbx2 are redundant proteins that act in remodeling the cell wall to maintain normal cell morphology and precursor availability for other glycan synthetic processes. Their absence results in aberrant cell wall growth and metabolic imbalance, which together impact cell wall and capsule synthesis, cell morphology, and capsule association. The surface changes also lead to increased engulfment by host phagocytes, consistent with the lack of virulence of pbx mutants in animal models.
| S-EPMC4060484 | biostudies-literature
Project description:UnlabelledThe fungal pathogen Cryptococcus neoformans has several virulence factors, among which the most important is a polysaccharide capsule. The size of the capsule is variable and can increase significantly during infection. In this work, we investigated the relationship between capsular enlargement and the cell cycle. Capsule growth occurred primarily during the G1 phase. Real-time visualization of capsule growth demonstrated that this process occurred before the appearance of the bud and that capsule growth arrested during budding. Benomyl, which arrests the cells in G2/M, inhibited capsule growth, while sirolimus (rapamycin) addition, which induces G1 arrest, resulted in cells with larger capsule. Furthermore, we have characterized a mutant strain that lacks a putative G1/S cyclin. This mutant showed an increased capacity to enlarge the capsule, both in vivo (using Galleria mellonella as the host model) and in vitro. In the absence of Cln1, there was a significant increase in the production of extracellular vesicles. Proteomic assays suggest that in the cln1 mutant strain, there is an upregulation of the glyoxylate acid cycle. Besides, this cyclin mutant is avirulent at 37°C, which correlates with growth defects at this temperature in rich medium. In addition, the cln1 mutant showed lower intracellular replication rates in murine macrophages. We conclude that cell cycle regulatory elements are involved in the modulation of the expression of the main virulence factor in C. neoformans.ImportanceCryptococcus neoformans is a pathogenic fungus that has significant incidence worldwide. Its main virulence factor is a polysaccharide capsule that can increase in size during infection. In this work, we demonstrate that this process occurs in a specific phase of the cell cycle, in particular, in G1. In agreement, mutants that have an abnormal longer G1 phase show larger capsule sizes. We believe that our findings are relevant because they provide a link between capsule growth, cell cycle progression, and virulence in C. neoformans that reveals new aspects about the pathogenicity of this fungus. Moreover, our findings indicate that cell cycle elements could be used as antifungal targets in C. neoformans by affecting both the growth of the cells and the expression of the main virulence factor of this pathogenic yeast.
| S-EPMC4056547 | biostudies-literature