Iron‐regulated transcription and capsule formation in the fungal pathogen Cryptococcus neoformans

Abstract

SummaryCryptococcus neoformans is the leading cause of fungal meningitis in humans. Production of a polysaccharide capsule is a key virulence property for the fungus and capsule synthesis is regulated by iron levels. Given that iron acquisition is an important aspect of virulence for many pathogens, we employed serial analysis of gene expression (SAGE) to examine the transcriptome under iron-limiting and iron-replete conditions. Initially, we demonstrated by SAGE and Northern analysis that iron limitation results in an elevated transcript level for the CAP60 gene that is required for capsule production. We also identified genes encoding putative components for iron transport and homeostasis, including the FTR1 (iron permease) gene, with higher transcript levels in the lowiron condition. An FTR1 disruption mutant grows more slowly than wild-type cells in low-iron medium, and shows delayed growth and altered capsule regulation in iron-replete medium. Iron deprivation also resulted in elevated SAGE tags for putative extracellular mannoproteins and the GPI8 gene encoding a glycosylphosphatidylinositol (GPI ) transamidase.The GPI8 gene appears to be essential while disruption of the CIG1 gene encoding a mannoprotein resulted in impaired growth in low-iron medium and altered capsule response to the iron-replete condition. Additionally, we found that iron-replete conditions led to elevated transcripts for genes for iron storage, nitrogen metabolism, glycolysis, mitochondrial function, lipid metabolism and calmodulincalcineurin signalling. Overall, these studies provide the first view of the C. neoformans transcriptional response to different iron levels.

Mevalonate governs interdependency of ergosterol and siderophore biosyntheses in the fungal pathogen Aspergillus fumigatus

“…We speculated that this expression pattern reflects an increased demand for mevalonate as a precursor for TAFC biosynthesis, which is induced by iron starvation. Consistent with this hypothesis, genome-wide transcription profiling data do not indicate that iron availability has any effect on the expression of genes encoding HMG-CoA reductase in fungal species that do not produce siderophores (e.g., Saccharomyces cerevisiae, Cryptococcus neoformans, and Candida albicans) or that produce non-mevalonate-derived siderophores (e.g., Ustilago maydis) (12)(13)(14)(15).…”

Altered Immune Response Differentially Enhances Susceptibility to Cryptococcus neoformans and Cryptococcus gattii Infection in Mice Expressing the HIV-1 Transgene

“…C. neoformans can acquire iron bound to the major carrier transferrin by a reductive iron uptake pathway (69). Because growth of C. neoformans at high iron concentrations results in cells with thinner capsules (30) and lower expression of the CAP60 gene that is required for capsule production (70), increased availability of iron from the ferritin carrier may have contributed to the lack of capsule thickening during the course of cryptococcal infection in the Tg mice. However, despite the absence of capsule thickening during infection by both species, the capsule thickness of C. neoformans remained greater than that of C. gattii in the Tg mice and may have contributed to its enhanced systemic dissemination to the liver and spleen, which was also observed in the non-Tg mice.…”

Role of Ferric Reductases in Iron Acquisition and Virulence in the Fungal Pathogen Cryptococcus neoformans

“…All strains were maintained on YPD medium (1% yeast extract, 2% peptone, 2% glucose). Yeast nitrogen base low-iron medium (YNB-LIM) (YNB [pH 7.2] plus 150 M bathophenanthroline disulfonate [BPS]) and defined low-iron medium (LIM) were prepared as described previously (7,25,26) and used as iron-limiting media, supplemented as indicated, for phenotypic characterization. YNB low-copper medium (YNB-LCM) (YNB [pH 7.2] plus 100 M bathocuproine disulfonate [BCS]) was prepared similarly to YNB-LIM.…”