Signaling through Adenylyl Cyclase Is Essential for Hyphal Growth and Virulence in the Pathogenic Fungus Candida albicans (original) (raw)
Related papers
Molecular Biology of the Cell, 2001
The human fungal pathogen Candida albicans switches from a budding yeast form to a polarized hyphal form in response to various external signals. This morphogenetic switching has been implicated in the development of pathogenicity. We have cloned the CaCDC35 gene encoding C. albicans adenylyl cyclase by functional complementation of the conditional growth defect of Saccharomyces cerevisiae cells with mutations in Ras1p and Ras2p. It has previously been shown that these Ras homologues regulate adenylyl cyclase in yeast. The C. albicans adenylyl cyclase is highly homologous to other fungal adenylyl cyclases but has less sequence similarity with the mammalian enzymes. C. albicans cells deleted for both alleles of CaCDC35 had no detectable cAMP levels, suggesting that this gene encodes the only adenylyl cyclase in C. albicans. The homozygous mutant cells were viable but grew more slowly than wild-type cells and were unable to switch from the yeast to the hyphal form under all environmental conditions that we analyzed in vitro. Moreover, this morphogenetic switch was completely blocked in mutant cells undergoing phagocytosis by macrophages. However, morphogenetic switching was restored by exogenous cAMP. On the basis of epistasis experiments, we propose that CaCdc35p acts downstream of the Ras homologue CaRas1p. These epistasis experiments also suggest that the putative transcription factor Efg1p and components of the hyphal-inducing MAP kinase pathway depend on the function of CaCdc35p in their ability to induce morphogenetic switching. Homozygous cacdc35⌬ cells were unable to establish vaginal infection in a mucosal membrane mouse model and were avirulent in a mouse model for systemic infections. These findings suggest that fungal adenylyl cyclases and other regulators of the cAMP signaling pathway may be useful targets for antifungal drugs.
Fungal Adenylyl Cyclase Integrates CO2 Sensing with cAMP Signaling and Virulence
Current Biology, 2005
The ascomycete Candida albicans is the most common fungal pathogen in immunocompromised patients [1]. Its ability to change morphology, from yeast to filamentous forms, in response to host environmental cues is important for virulence [2-5]. Filamentation is mediated by second messengers such as cyclic adenosine 3′,5′-monophosphate (cAMP) synthesized by adenylyl cyclase [4]. The distantly related basidiomycete Cryptococcus neoformans is an encapsulated yeast that predominantly infects the central nervous system in immunocompromised patients [6-8]. Similar to the morphological change in C. albicans, capsule biosynthesis in C. neoformans, a major virulence attribute, is also dependent upon adenylyl cyclase activity [7]. Here we demonstrate that physiological concentrations of CO 2 /HCO 3 induce filamentation in C. albicans by direct stimulation of cyclase activity. Furthermore, we show that CO 2 /HCO 3 equilibration by carbonic anhydrase is essential for pathogenesis of C. albicans in niches where the available CO 2 is limited. We also demonstrate that adenylyl cyclase from C. neoformans is sensitive to physiological concentrations of CO 2 /HCO 3-. These data demonstrate that the link between cAMP signaling and CO 2 /HCO 3 sensing is conserved in fungi and reveal CO 2 sensing to be an important mediator of fungal pathogenesis. Novel therapeutic agents could target this pathway at several levels to control fungal infections.
2021
ABSTRACTMicrobial pathogens grow in a wide range of different morphologies that provide distinct advantages for virulence. In the fungal pathogen Candida albicans, adenylyl cyclase (Cyr1) is thought to be a master regulator of the switch to invasive hyphal morphogenesis and biofilm formation. However, faster growing cyr1Δ/Δ pseudorevertant (PR) mutants were identified that form hyphae in the absence of cAMP. Isolation of additional PR mutants revealed that their improved growth was due to loss of one copy of BCY1, the negative regulatory subunit of protein kinase (A) from the left arm of chromosome 2. Furthermore, hyphal morphogenesis was improved in some of PR mutants by multigenic haploinsufficiency resulting from loss of large regions of the left arm of chromosome 2, including global transcriptional regulators. Interestingly, hyphal-associated genes were also induced in a manner that was independent of cAMP. This indicates that basal protein kinase A activity is an important prer...
Molecular Microbiology, 2011
The adenylyl cyclase Cyr1 plays a pivotal role in regulating virulence traits in the human fungal pathogen Candida albicans. Although a diverse range of signals are known to activate Cyr1, it remains unclear how low activity is maintained in the absence of stimuli. To uncover negative regulatory elements, we designed a genetic screen to identify mutations in Cyr1 that increase its catalytic activity. We found such a mutant carrying a single Glu1541 to Lys substitution in a conserved motif C-terminal to the catalytic domain. This E1541K mutation caused constitutive filamentous growth, hypersensitivity to stress, resistance to farnesol and overproduction of riboflavin. The mutant phenotype depends on Cap1 and Ras1, two known positive regulators of Cyr1, and the filamentous growth requires Hgc1, a key promoter of hyphal growth. Strikingly, expressing a truncated version of the mutant protein lacking the entire region N-terminal to the catalytic domain in cyr1D cells caused a fivefold increase in the cellular cAMP level. Such cells exhibited dramatic enlargement, cytokinetic defects, G1 arrest and impaired hyphal development. Thus, our studies have revealed novel regulatory elements in Cyr1 that normally repress Cyr1 activity to prevent the toxicity of unregulated high cAMP levels.
Transcription Profiling of Cyclic AMP Signaling in Candida albicans
Molecular Biology of the Cell, 2004
We used transcription profiling in Candida albicans to investigate cellular regulation involving cAMP. We found that many genes require the adenylyl cyclase Cdc35p for proper expression. These include genes encoding ribosomal subunit proteins and RNA polymerase subunit proteins, suggesting that growth could be controlled in part by cAMP-mediated modulation of gene expression. Other genes influenced by loss of adenylyl cyclase are involved in metabolism, the cell wall, and stress response and include a group of genes of unknown function that are unique to C. albicans. The profiles generated by loss of the adenylyl cyclase regulator Ras1p and a downstream effector Efg1p were also examined. The loss of Ras1p function disturbs the expression of a subset of the genes regulated by adenylyl cyclase, suggesting both that the primary role of Ras1p in transcriptional regulation involves its influence on the function of Cdc35p and that there are Ras1p independent roles for Cdc35p. The transcription factor Efg1p is also needed for the expression of many genes; however, these genes are distinct from those modulated by Cdc35p with the exception of a class of hyphal-specific genes. Therefore transcription profiling establishes that cAMP plays a key role in the overall regulation of gene expression in C. albicans, and enhances our detailed understanding of the circuitry controlling this regulation.
Human serum potently induces hyphal development of the polymorphic fungal pathogen Candida albicans, a phenotype that contributes critically to infections. The fungal adenylyl cyclase Cyr1p is a key component of the cAMP/PKA-signaling pathway that controls diverse infection-related traits, including hyphal morphogenesis. However, identity of the serum hyphal inducer(s) and its fungal sensor remain unknown. Our initial analyses of active serum fractions revealed signs of bacterial peptidoglycan (PGN)-like molecules. Here, we show that several purified and synthetic muramyl dipeptides (MDPs), subunits of PGN, can strongly promote C. albicans hyphal growth. Analogous to PGN recognition by the mammalian sensors Nod1 and Nod2 through their leucine-rich-repeat (LRR) domain, we show that MDPs activate Cyr1p by directly binding to its LRR domain.
2011
Paracoccidioides brasiliensis is a human pathogenic fungus that switches from a saprobic mycelium to a pathogenic yeast. Consistent with the morphological transition being regulated by the cAMP-signalling pathway, there is an increase in cellular cAMP levels both transiently at the onset (< 24 h) and progressively in the later stages (> 120 h) of the transition to the yeast form, and this transition can be modulated by exogenous cAMP. We have cloned the cyr1 gene encoding adenylate cyclase (AC) and established that its transcript levels correlate with cAMP levels. In addition, we have cloned the genes encoding three Ga (Gpa1-3), Gb (Gpb1) and Gg (Gpg1) G proteins. Gpa1 and Gpb1 interact with one another and the N-terminus of AC, but neither Gpa2 nor Gpa3 interacted with Gpb1 or AC. The interaction of Gpa1 with Gpb1 was blocked by GTP, but its interaction with AC was independent of bound nucleotide. The transcript levels for gpa1, gpb1 and gpg1 were similar in mycelium, but there was a transient excess of gpb1 during the transition, and an excess of gpa1 in yeast. We have interpreted our findings in terms of a novel signalling mechanism in which the activity of AC is differentially modulated by Gpa1 and Gpb1 to maintain the signal over the 10 days needed for the morphological switch.
cAMP-PKA pathway to induce morphogenesis in Candida albicans
2000
Tel: +32 16 321512 Fax: +32 16 321979 Email: patrick.vandijck@bio.kuleuven.ac.be key-words: GPCR/signal transduction/yeast-to-hyphae/nutrient sensing/methionine Running title: GPCR-induced morphogenesis in C. albicans 2 Abstract We investigated the role in cell morphogenesis and pathogenicity of the Candida albicans GPR1 gene, encoding the G protein coupled receptor Gpr1. Deletion of C. albicans GPR1 has only minor effects in liquid hypha-inducing media but results in strong defects in the yeast-to-hypha transition on solid hypha-inducing media. Addition of cAMP, expression of a constitutively active allele of the Gα protein Gpa2 or of the catalytic protein kinase A subunit TPK1 restores the wild type phenotype of the CaGPR1-deleted strain. Overexpression of HST7, encoding a component of the Mitogen-Activated Protein Kinase (MAPK) pathway, does not suppress the defect in filamentation. These results indicate that CaGpr1 functions upstream in the cAMP-
Transcription profiling of cyclic AMP signalling in Candida albicans
2000
We used transcription profiling in Candida albicans to investigate cellular regulation involving cAMP. We found that many genes require the adenylyl cyclase Cdc35p for proper expression. These include genes encoding ribosomal subunit proteins and RNA polymerase subunit proteins, suggesting that growth could be controlled in part by cAMP-mediated modulation of gene expression. Other genes influenced by loss of adenylyl cyclase