Project description:Iron sequestration by host iron-binding proteins is an important mechanism of resistance to microbial infections. Inside oral epithelial cells, iron is stored within the ferritin, and is therefore usually not accessible to pathogenic microbes. We observed that the ferritin concentration within oral epithelial cells was directly related to their susceptibility to damage by the human pathogenic fungus Candida albicans. Thus, we hypothesized that host ferritin may be used as an iron source by this organism. A screen of C. albicans mutants lacking components of each of the three iron acquisition systems revealed that only the reductive pathway is involved in iron utilization from ferritin by this organism. Transcriptional profiling of wild-type and hyphal-defective C. albicans strains suggested that the C. albicans invasin-like protein Als3 plays a role in ferritin binding.
Project description:Eukaryotic cell growth is coordinated in response to nutrient availability, growth factors, and environmental stimuli, enabling cell–cell interactions that promote survival. The rapamycin-sensitive Tor1 protein kinase, which is conserved from yeasts to humans, participates in a signaling pathway central to cellular nutrient responses. To gain insight into Tor-mediated processes in human fungal pathogens, we have characterized Tor signaling in Candida albicans. Global transcriptional profiling revealed evolutionarily conserved roles for Tor1 in regulating the expression of genes involved in nitrogen starvation responses and ribosome biogenesis. Interestingly, we found that in C. albicans Tor1 plays a novel role in regulating the expression of several cell wall and hyphal specific genes, including adhesins and their transcriptional repressors Nrg1 and Tup1. In accord with this transcriptional profile, rapamycin induced extensive cellular aggregation in an adhesin-dependent fashion. Moreover, adhesin gene induction and cellular aggregation of rapamycin-treated cells were strongly dependent on the transactivators Bcr1 and Efg1. These findings support models in which Tor1 negatively controls cellular adhesion by governing the activities of Bcr1 and Efg1. Taken together, these results provide evidence that Tor1-mediated cellular adhesion might be broadly conserved among eukaryotic organisms.
Project description:We perform microarray analysis of HUVECs upon stimulation with virulent wildtype C. albicans strain SC5314 or its efg1/efg1 cph1/cph1 hyphal-deficient derivative strain CAN34 to compare the gene expression profiles elicited from HUVECs in response to these strains. In addition, these responses are compared to that of TNF-alpha induced responses to determine which responses are Candida-specific. Keywords: comparison of host response to different Candida albicans morphologies
Project description:The fungus Candida albicans is part of the human microbiome and mainly colonises the GI tract of healthy individuals. However, when the balance in the GI tract is disturbed, the fungus can switch from a commensal to a virulent lifestyle and can turn into a life-threatening pathogen. Life in the host is characterised by a constant struggle for nutrients, essential trace elements such as iron, copper and zinc are particularly important. To protect itself from pathogens, the human host has developed a strategy to limit the availability of trace elements, this strategy is also described as nutritional immunity. C. albicans has developed a whole range of counter-strategies to obtain sufficient trace elements. In this manuscript, we have characterised the transcription factor Orf19.217, which acts at the interface between trace element scavenging and acquisition and is therefore particularly important in adaptation to life in the host. According to its identified function, we named the transcription factor Irf1, Iron-dependent Regulator of Filamentation. The transcription factor was previously identified in a systematic screen of genes whose overexpression contributes to morphological changes in C. albicans. We have comprehensively investigated the function of Irf1 using state-of-the-art functional genomics approaches, including ChIP-seq, transcriptomics and bioinformatics analyses. Analysis of the Irf1 gene-regulatory network indicates that the transcription factor is involved in the regulation of genes important for iron uptake. Using phenotypic analysis, we confirmed that Irf1 acts in a pathway parallel to known iron uptake regulators and is also required for hyphal formation induced by iron deficiency, a process that allows the fungus to access more viable body niches. Through epistasis experiments, we were also able to identify downstream effectors of Irf1 that are involved in this process. Our study provides new insights into how C. albicans adapts to iron deficiency and establish a direct functional link between hyphal formation and iron uptake.
Project description:The fungus Candida albicans is part of the human microbiome and mainly colonises the GI tract of healthy individuals. However, when the balance in the GI tract is disturbed, the fungus can switch from a commensal to a virulent lifestyle and can turn into a life-threatening pathogen. Life in the host is characterised by a constant struggle for nutrients, essential trace elements such as iron, copper and zinc are particularly important. To protect itself from pathogens, the human host has developed a strategy to limit the availability of trace elements, this strategy is also described as nutritional immunity. C. albicans has developed a whole range of counter-strategies to obtain sufficient trace elements. In this manuscript, we have characterised the transcription factor Orf19.217, which acts at the interface between trace element scavenging and acquisition and is therefore particularly important in adaptation to life in the host. According to its identified function, we named the transcription factor Irf1, Iron-dependent Regulator of Filamentation. The transcription factor was previously identified in a systematic screen of genes whose overexpression contributes to morphological changes in C. albicans. We have comprehensively investigated the function of Irf1 using state-of-the-art functional genomics approaches, including ChIP-seq, transcriptomics and bioinformatics analyses. Analysis of the Irf1 gene-regulatory network indicates that the transcription factor is involved in the regulation of genes important for iron uptake. Using phenotypic analysis, we confirmed that Irf1 acts in a pathway parallel to known iron uptake regulators and is also required for hyphal formation induced by iron deficiency, a process that allows the fungus to access more viable body niches. Through epistasis experiments, we were also able to identify downstream effectors of Irf1 that are involved in this process. Our study provides new insights into how C. albicans adapts to iron deficiency and establish a direct functional link between hyphal formation and iron uptake.
Project description:Candida yeasts causing human infections are spread across the yeast phylum with Candida glabrata being related to Saccharomyces cerevisiae, Candida krusei grouping to Pichia spp., and Candida albicans, Candida parapsilosis and Candida tropicalis belonging to the CTG-clade. The latter lineage contains yeasts with an altered genetic code translating CUG codons as serine using a serine-tRNA with a mutated anticodon. It has been suggested that the CTG-clade CUG codons are mistranslated to a small extent as leucine due to mischarging of the serine-tRNA(CAG). The mistranslation was suggested to result in variable surface proteins explaining fast host adaptation and pathogenicity. Here, we re-assessed this potential mistranslation by high-resolution mass spectrometry-based proteogenomics of multiple CTG-clade yeasts, various C. albicans strains, isolated from colonized and from infected human body sites, and C. albicans grown in yeast and hyphal forms.
Project description:Candida albicans is an important fungal pathogen in humans. Several virulence factors of C. albicans have been reported, including a morphological transition from yeast to filamentous forms (hyphae and pseudohyphae). Mss11 is a transcriptional activator required for hyphal formation. To reveal the potential target genes of Mss11, DNA microarray analysis was performed to compare wild type and mss11-deleted mutant.