51
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Abstract
Pathogenic fungi have become an increasingly common cause of systemic disease in healthy people and those with impaired immune systems. Although a vast number of fungal species inhabit our planet, just a small number are pathogens, and one feature that links many of them is the ability to differentiate morphologically from mould to yeast, or yeast to mould. Morphological differentiation between yeast and mould forms has commanded attention for its putative impact on the pathogenesis of invasive fungal infections. This review explores the current body of evidence linking fungal morphogenesis and virulence. The topics addressed cover work on phase-locked fungal cells, expression of phase-specific virulence traits and modulation of host responses by fungal morphotypes. The effect of morphological differentiation on fungal interaction with host cells, immune modulation and the net consequence on pathogenesis of disease in animal model systems are considered. The evidence argues strongly that morphological differentiation plays a vital role in the pathogenesis of fungal infection, suggesting that factors associated with this conversion process represent promising therapeutic targets.
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Affiliation(s)
- Peggy J Rooney
- Department of Medical Microbiology and Immunology, University of Wisconsin Medical School, Madison, Wisconsin, USA
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52
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Venancio EJ, Kyaw CM, Mello CV, Silva SP, Soares CMA, Felipe MSS, Silva-Pereira I. Identification of differentially expressed transcripts in the human pathogenic fungus Paracoccidioides brasiliensis by differential display. Med Mycol 2002; 40:45-51. [PMID: 11862980 DOI: 10.1080/mmy.40.1.45.51] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/20/2022] Open
Abstract
Paracoccidioides brasiliensis is a dimorphic human pathogenic fungus that is the causal agent of paracoccidioidomycosis, a systemic disease that predominantly affects rural communities in South and Central America. Dimorphism is a common characteristic of systemic human pathogenic fungi. Here we describe the use of differential display (DD) to isolate and identify differentially expressed genes of P. brasiliensis, in the two cell types, yeast (Y) and mycelium (M), as well as at different time intervals during temperature-induced M to Y transition. Using two oligo-deoxythymidine-anchored primers combined with 10 arbitrary ones, we were able to detect the presence of at least 20 differentially transcribed cDNA fragments. Some of these fragments were further analysed by reverse-northern blot and northern blot in order to confirm their differential expression. The M32, M51 and M73 cDNA fragments were specific for the mycelial form of P. brasiliensis. Furthermore, we found two cDNA fragments (M-Y1 and M-Y2) that were upregulated during M-Y transition. This method was efficient and useful in the detection of differentially expressed genes in P. brasiliensis.
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Affiliation(s)
- E J Venancio
- Universidade de Brasilia, Instituto de Biologia, Departamento de Biologia Celular, DF, Brasil
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53
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Singh P, Ghosh S, Datta A. Attenuation of virulence and changes in morphology in Candida albicans by disruption of the N-acetylglucosamine catabolic pathway. Infect Immun 2001; 69:7898-903. [PMID: 11705974 PMCID: PMC98888 DOI: 10.1128/iai.69.12.7898-7903.2001] [Citation(s) in RCA: 55] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023] Open
Abstract
A Candida albicans mutant with mutations in the N-acetylglucosamine (GlcNAc) catabolic pathway gene cluster, including the GlcNAc-6-phosphate deacetylase (DAC1), glucosamine-6-phosphate deaminase (NAG1), and GlcNAc kinase (HXK1) genes, was not able to grow on amino sugars, exhibited highly attenuated virulence in a murine systemic candidiasis model, and was less adherent to human buccal epithelial cells in vitro. No germ tubes were formed by the mutant after induction with GlcNAc, but the mutant exhibited hyperfilamentation under stress-induced filamentation conditions. In addition, the GlcNAc catabolic pathway played a vital role in determining the colony phenotype. Our results imply that this pathway is very important because of its diverse links with pathways involved in virulence and morphogenesis of the organism.
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Affiliation(s)
- P Singh
- School of Life Sciences, Jawaharlal Nehru University, New Delhi 110067, India
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54
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Rocha CR, Schröppel K, Harcus D, Marcil A, Dignard D, Taylor BN, Thomas DY, Whiteway M, Leberer E. Signaling through adenylyl cyclase is essential for hyphal growth and virulence in the pathogenic fungus Candida albicans. Mol Biol Cell 2001; 12:3631-43. [PMID: 11694594 PMCID: PMC60281 DOI: 10.1091/mbc.12.11.3631] [Citation(s) in RCA: 291] [Impact Index Per Article: 12.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022] Open
Abstract
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 Delta 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.
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Affiliation(s)
- C R Rocha
- Eukaryotic Genetics Group, Biotechnology Research Institute, National Research Council of Canada, Montreal, Quebec H4P 2R2, Canada
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55
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Leberer E, Harcus D, Dignard D, Johnson L, Ushinsky S, Thomas DY, Schröppel K. Ras links cellular morphogenesis to virulence by regulation of the MAP kinase and cAMP signalling pathways in the pathogenic fungus Candida albicans. Mol Microbiol 2001; 42:673-87. [PMID: 11722734 DOI: 10.1046/j.1365-2958.2001.02672.x] [Citation(s) in RCA: 225] [Impact Index Per Article: 9.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
The pathogenic fungus Candida albicans is capable of responding to a wide variety of environmental cues with a morphological transition from a budding yeast to a polarized filamentous form. We demonstrate that the Ras homologue of C. albicans, CaRas1p, is required for this morphological transition and thereby contributes to the development of pathogenicity. However, CaRas1p is not required for cellular viability. Deletion of both alleles of the CaRAS1 gene caused in vitro defects in morphological transition that were reversed by either supplementing the growth media with cAMP or overexpressing components of the filament-inducing mitogen-activated protein (MAP) kinase cascade. The induction of filament-specific secreted aspartyl proteinases encoded by the SAP4-6 genes was blocked in the mutant cells. The defects in filament formation were also observed in situ after phagocytosis of C. albicans cells in a macrophage cell culture assay and, in vivo, after infection of kidneys in a mouse model for systemic candidiasis. In the macrophage assay, the mutant cells were less resistant to phagocytosis. Moreover, the defects in filament formation were associated with reduced virulence in the mouse model. These results indicate that, in response to environmental cues, CaRas1p is required for the regulation of both a MAP kinase signalling pathway and a cAMP signalling pathway. CaRas1p-dependent activation of these pathways contributes to the pathogenicity of C. albicans cells through the induction of polarized morphogenesis. These findings elucidate a new medically relevant role for Ras in cellular morphogenesis and virulence in an important human infectious disease.
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Affiliation(s)
- E Leberer
- Eukaryotic Genetics Group, Biotechnology Research Institute, National Research Council of Canada, 6100 Royalmount Avenue, Montreal, Quebec H4P 2R2, Canada.
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56
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Zhan XL, Wishart MJ, Guan KL. Nonreceptor tyrosine phosphatases in cellular signaling: regulation of mitogen-activated protein kinases. Chem Rev 2001; 101:2477-96. [PMID: 11749384 DOI: 10.1021/cr000245u] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- X L Zhan
- Department of Molecular and Cell Biology, University of California at Berkeley, Berkeley, California 94720, USA.
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57
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Abstract
Candidiasis is a common infection of the skin, oral cavity and esophagus, gastrointestinal tract, vagina and vascular system of humans. Although most infections occur in patients who are immunocompromised or debilitated in some other way, the organism most often responsible for disease, Candida albicans, expresses several virulence factors that contribute to pathogenesis. These factors include host recognition biomolecules (adhesins), morphogenesis (the reversible transition between unicellular yeast cells and filamentous, growth forms), secreted aspartyl proteases and phospholipases. Additionally, 'phenotypic switching' is accompanied by changes in antigen expression, colony morphology and tissue affinities in C. albicans and several other Candida spp. Switching might provide cells with a flexibility that results in the adaptation of the organism to the hostile conditions imposed not only by the host but also by the physician treating the infection.
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Affiliation(s)
- R A Calderone
- Dept of Microbiology & Immunology, Georgetown University Medical Center, 20007, Washington, DC, USA.
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58
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Oh KB, Miyazawa H, Naito T, Matsuoka H. Purification and characterization of an autoregulatory substance capable of regulating the morphological transition in Candida albicans. Proc Natl Acad Sci U S A 2001; 98:4664-8. [PMID: 11274356 PMCID: PMC31891 DOI: 10.1073/pnas.071404698] [Citation(s) in RCA: 119] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/23/2000] [Indexed: 12/29/2022] Open
Abstract
The yeast Candida albicans has a distinguishing feature, dimorphism, which is the ability to switch between two morphological forms: a budding yeast form and a multicellular invasive filamentous form. This ability has been postulated to contribute to the virulence of this organism. Studies on the morphological transition from a filamentous to a budding yeast form in C. albicans have shown that this organism excretes an autoregulatory substance into the culture medium. This substance was extracted and purified by normal-phase and reversed-phase HPLC. The autoregulatory substance was structurally identified as 3,7,11-trimethyl-2,6,10-dodecatrienoate (farnesoic acid) by NMR and mass spectrometry. Growth experiments suggest that this substance does not inhibit yeast cell growth but inhibits filamentous growth. These findings have implications for developmental signaling by the fungus and might have medicinal value in the development of antifungal therapies.
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Affiliation(s)
- K B Oh
- Natural Products Research Institute, Seoul National University, 28, Yungun, Chongro, Seoul 110-460,
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59
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Sánchez-Martínez C, Pérez-Martín J. Dimorphism in fungal pathogens: Candida albicans and Ustilago maydis--similar inputs, different outputs. Curr Opin Microbiol 2001; 4:214-21. [PMID: 11282479 DOI: 10.1016/s1369-5274(00)00191-0] [Citation(s) in RCA: 92] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
Abstract
The ability to switch between a yeast-like form and a filamentous form is an extended characteristic among several fungi. In pathogenic fungi, this capacity has been correlated with virulence because along the infection process, dimorphic transitions are often required. Two well-known organisms for which dimorphism have been studied are the pathogenic fungi Candida albicans and Ustilago maydis, which infect mammals and corn, respectively. In both cases, several signal transduction pathways have been defined. Not surprisingly, these pathways are similar to the well-known pathways involved in the pseudohyphal differentiation that some Saccharomyces cerevisiae diploid strains show when nutrients are starved. However, in spite of similarities at the molecular level, strikingly, fungi use similar pathways to respond to environmental inputs, but with differing outcomes.
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Affiliation(s)
- C Sánchez-Martínez
- Department of Microbial Biotechnology, Centro Nacional de Biotecnología (CSIC), Cantoblanco 28049, Madrid, Spain
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60
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Navarro-García F, Sánchez M, Nombela C, Pla J. Virulence genes in the pathogenic yeast Candida albicans. FEMS Microbiol Rev 2001; 25:245-68. [PMID: 11250036 DOI: 10.1111/j.1574-6976.2001.tb00577.x] [Citation(s) in RCA: 110] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022] Open
Abstract
In recent years, the incidence of fungal infections has been rising all over the world. Although the amount of research in the field of pathogenic fungi has also increased, there is still a need for the identification of reliable determinants of virulence. In this review, we focus on identified Candida albicans genes whose deletant strains have been tested in experimental virulence assays. We discuss the putative relationship of these genes to virulence and also outline the use of new different systems to examine the precise effect in virulence of different genes.
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Affiliation(s)
- F Navarro-García
- Departamento de Microbiología II, Facultad de Farmacia, Universidad Complutense de Madrid, Spain
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61
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Staib P, Kretschmar M, Nichterlein T, Köhler G, Morschhäuser J. Expression of virulence genes in Candida albicans. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2001; 485:167-76. [PMID: 11109103 DOI: 10.1007/0-306-46840-9_23] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/18/2023]
Affiliation(s)
- P Staib
- Zentrum für Infektionsforschung, Universität Würzburg, Germany
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62
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Navarro-García F, Eisman B, Román E, Nombela C, Pla J. Signal transduction pathways and cell-wall construction inCandida albicans. Med Mycol 2001. [DOI: 10.1080/mmy.39.1.87.100] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/20/2022] Open
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63
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Abstract
Pseudohyphal growth in both haploid and diploid strains of Saccharomyces cerevisiae reflects concerted changes in different cellular processes: budding pattern, cell elongation and cell adhesion. These changes are triggered by environmental signals and are controlled by several pathways which act in parallel. Nitrogen deprivation, and possibly other stresses, activate a MAP kinase cascade which has the transcription factor Ste12 as its final target. A cAMP-dependent pathway, in which the protein kinase Tpk2 plays a specific role, is also required for the morphogenetic switch. Both pathways contribute to modulate the expression of the MUC1/FLO11 gene which encodes a cell-surface flocculin required for pseudohyphal and invasive growth. The MAP kinase cascade could also control the activity of the cyclin/Cdc28 complexes which affect both the budding pattern of yeast and cell elongation. A further protein which stimulates filamentous growth in S. cerevisiae is Phd1; although its mode of action is unknown, it may be regulated by a cAMP-dependent protein kinase, as occurs with the homologous protein Efg1 from Candida albicans, which is required for the formation of true hyphae. Morphogenesis in different yeast genera share common elements, but there are also important differences. Although a complete picture cannot yet be drawn, partial models may be proposed for the interaction of the regulatory pathways, both in the case of S. cerevisiae and in that of C. albicans.
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Affiliation(s)
- J M Gancedo
- Instituto de Investigaciones Biomédicas 'Alberto Sols', CSIC-UAM, Arturo Duperier 4, 28029 Madrid, Spain.
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64
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Lengeler KB, Davidson RC, D'souza C, Harashima T, Shen WC, Wang P, Pan X, Waugh M, Heitman J. Signal transduction cascades regulating fungal development and virulence. Microbiol Mol Biol Rev 2000; 64:746-85. [PMID: 11104818 PMCID: PMC99013 DOI: 10.1128/mmbr.64.4.746-785.2000] [Citation(s) in RCA: 652] [Impact Index Per Article: 27.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Cellular differentiation, mating, and filamentous growth are regulated in many fungi by environmental and nutritional signals. For example, in response to nitrogen limitation, diploid cells of the yeast Saccharomyces cerevisiae undergo a dimorphic transition to filamentous growth referred to as pseudohyphal differentiation. Yeast filamentous growth is regulated, in part, by two conserved signal transduction cascades: a mitogen-activated protein kinase cascade and a G-protein regulated cyclic AMP signaling pathway. Related signaling cascades play an analogous role in regulating mating and virulence in the plant fungal pathogen Ustilago maydis and the human fungal pathogens Cryptococcus neoformans and Candida albicans. We review here studies on the signaling cascades that regulate development of these and other fungi. This analysis illustrates both how the model yeast S. cerevisiae can serve as a paradigm for signaling in other organisms and also how studies in other fungi provide insights into conserved signaling pathways that operate in many divergent organisms.
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Affiliation(s)
- K B Lengeler
- Departments of Genetics, Pharmacology and Cancer Biology, Microbiology, and Medicine, Howard Hughes Medical Institute, Duke University Medical Center, Durham, North Carolina 27710, USA
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65
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Lengeler KB, Davidson RC, D'souza C, Harashima T, Shen WC, Wang P, Pan X, Waugh M, Heitman J. Signal transduction cascades regulating fungal development and virulence. Microbiol Mol Biol Rev 2000. [PMID: 11104818 DOI: 10.1023/a:1024123915158] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 04/18/2023] Open
Abstract
Cellular differentiation, mating, and filamentous growth are regulated in many fungi by environmental and nutritional signals. For example, in response to nitrogen limitation, diploid cells of the yeast Saccharomyces cerevisiae undergo a dimorphic transition to filamentous growth referred to as pseudohyphal differentiation. Yeast filamentous growth is regulated, in part, by two conserved signal transduction cascades: a mitogen-activated protein kinase cascade and a G-protein regulated cyclic AMP signaling pathway. Related signaling cascades play an analogous role in regulating mating and virulence in the plant fungal pathogen Ustilago maydis and the human fungal pathogens Cryptococcus neoformans and Candida albicans. We review here studies on the signaling cascades that regulate development of these and other fungi. This analysis illustrates both how the model yeast S. cerevisiae can serve as a paradigm for signaling in other organisms and also how studies in other fungi provide insights into conserved signaling pathways that operate in many divergent organisms.
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Affiliation(s)
- K B Lengeler
- Departments of Genetics, Pharmacology and Cancer Biology, Microbiology, and Medicine, Howard Hughes Medical Institute, Duke University Medical Center, Durham, North Carolina 27710, USA
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66
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Schröppel K, Sprösser K, Whiteway M, Thomas DY, Röllinghoff M, Csank C. Repression of hyphal proteinase expression by the mitogen-activated protein (MAP) kinase phosphatase Cpp1p of Candida albicans is independent of the MAP kinase Cek1p. Infect Immun 2000; 68:7159-61. [PMID: 11083847 PMCID: PMC97832 DOI: 10.1128/iai.68.12.7159-7161.2000] [Citation(s) in RCA: 35] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Cpp1p is a putative mitogen-activated protein (MAP) kinase phosphatase that suppresses Candida albicans hyphal formation at 25 degrees C through its probable substrate, the Cek1p filamentation MAP kinase. Here we report that expression of the serum-induced genes SAP4-6 and HYR1 increased several fold in hyphal forms of a cpp1/cpp1 null mutant, while the rate and extent of hyphal development up to 5 h were normal. Therefore, we provide evidence that Cpp1p represses hyphal gene expression by acting through a Cek1p-independent mechanism. SAP4-6 and HYR1 transcripts were undetectable in a null mutant of another key regulator of filamentation, Efg1p; thus, Efg1p and Cpp1p oppose each other during the expression of these genes in hyphal forms.
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Affiliation(s)
- K Schröppel
- Institute of Clinical Microbiology, Immunology and Hygiene, University of Erlangen, 91054 Erlangen, Germany.
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67
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Schweizer A, Rupp S, Taylor BN, Röllinghoff M, Schröppel K. The TEA/ATTS transcription factor CaTec1p regulates hyphal development and virulence in Candida albicans. Mol Microbiol 2000; 38:435-45. [PMID: 11069668 DOI: 10.1046/j.1365-2958.2000.02132.x] [Citation(s) in RCA: 184] [Impact Index Per Article: 7.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
The temporal and spatial expression of stage-specific genes during morphological development of fungi and higher eukaryotes is controlled by transcription factors. In this study, we report the cloning and functional analysis of the Candida albicans TEC1 (CaTEC1) gene, a new member of the TEA/ATTS family of transcription factors that regulates C. albicans virulence. The promoters of the type 4, 5 and 6 proteinase isogenes (SAP4-6) contain repetitive TEA/ATTS consensus sequence motifs. This finding suggests a possible role for a homologue of Saccharomyces cerevisiae TEC1 during the activation of proteinase gene expression in C. albicans. CaTEC1 is predominantly expressed in the hyphal form of C. albicans. In vitro, serum-induced hyphal formation as well as evasion from MPhi after phagocytosis is suppressed in catec1/catec1 mutant cells. Furthermore, expression of the proteinase isogenes SAP4-6 is no longer inducible in these mutant cells. The deletion of the CaTEC1 gene attenuates virulence of C. albicans in a systemic model of murine candidiasis, although both mutant and revertant cells that were prepared from infected tissues or the vaginal mucosa grew in a hyphal morphology in vivo. CaTEC1 complements the pseudohyphal and invasive growth defect of haploid and diploid S. cerevisiae tec1/tec1 mutant cells and strongly activates the promoter of FLO11, a gene required for pseudohyphal growth. This study provides the first evidence pointing to an essential role for a member of the TEA/ATTS transcription factor family that had so far only been ascribed to function during development as a virulence regulator in microbial pathogenesis.
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Affiliation(s)
- A Schweizer
- Institute of Clinical Microbiology, Immunology and Hygiene, University of Erlangen, Wasserturmstrasse 3, 91054 Erlangen, Germany
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68
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Fekete-Forgács K, Gyüre L, Lenkey B. Changes of virulence factors accompanying the phenomenon of induced fluconazole resistance in Candida albicans. Mycoses 2000; 43:273-9. [PMID: 11036397 DOI: 10.1046/j.1439-0507.2000.00587.x] [Citation(s) in RCA: 54] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
We investigated a fluconazole-sensitive (MICflu = 5 micrograms ml-1) clinical isolate and a fluconazole-resistant (MICflu > 80 micrograms ml-1) laboratory mutant Candida albicans strain developed from the sensitive one. We studied putative virulence factors including germination, adherence ability to either buccal epithelial cells or acrylate surface, the secreted aspartic proteinase, and the extracellular phospholipase activity of the two strains as well as their growth. The fluconazole-resistant strain proved to be superior to the original strain in all the virulence traits tested. The higher virulence of the fluconazole-resistant strain was also supported by a mouse model. These results suggest that the development of fluconazole resistance can be accompanied by serious morphological and physiological changes: several putative virulence traits, moreover the in vivo virulence can increase simultaneously.
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Affiliation(s)
- K Fekete-Forgács
- Department of Microbiology and Biotechnology, Kossuth Lajos University, Debrecen, Hungary
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69
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Abstract
The ability to undergo morphological change has been reported as an advantageous trait in fungal pathogenesis. Here we demonstrate that Candida glabrata ATCC2001, like diploid Saccharomyces cerevisiae strains, forms elongated chains of pseudohyphal cells on solid nitrogen starvation media (SLAD). Constrictions were apparent between adjoining cells; no parallel-sided hyphae were seen and pseudohyphae invaded the agar. When SLAD was supplemented with ammonium sulfate both C. glabrata and diploid S. cerevisiae strains lost their ability to undergo pseudohyphal growth. However, on this media C. glabrata yeast cells invaded the agar in a similar fashion to the invasive growth mode exhibited by haploid strains of S. cerevisiae cultured on rich media such as YPD. C. glabrata was not capable of invading YPD demonstrating that the process of filamentation is distinct in these two fungi. To our knowledge this is the first report to demonstrate that C. glabrata can undergo morphological change and grow as an invasive filamentous organism.
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Affiliation(s)
- C Csank
- Eukaryotic Genetics Group, National Research Council of Canada, Biotechnology Research Institute, Montreal, Quebec
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70
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Ernst JF. Transcription factors in Candida albicans - environmental control of morphogenesis. MICROBIOLOGY (READING, ENGLAND) 2000; 146 ( Pt 8):1763-1774. [PMID: 10931884 DOI: 10.1099/00221287-146-8-1763] [Citation(s) in RCA: 215] [Impact Index Per Article: 9.0] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Affiliation(s)
- Joachim F Ernst
- Institut für Mikrobiologie, Heinrich-Heine-Universität, Universitätsstr. 1/26.12, D-40225 Düsseldorf, Germany1
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71
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Affiliation(s)
- MI Borges-Walmsley
- Divn of Infection and Immunity, Institute of Biomedical and Life Sciences, University of Glasgow, Glasgow, UK G12 8QQ
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72
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Timpel C, Zink S, Strahl-Bolsinger S, Schröppel K, Ernst J. Morphogenesis, adhesive properties, and antifungal resistance depend on the Pmt6 protein mannosyltransferase in the fungal pathogen candida albicans. J Bacteriol 2000; 182:3063-71. [PMID: 10809683 PMCID: PMC94490 DOI: 10.1128/jb.182.11.3063-3071.2000] [Citation(s) in RCA: 88] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Protein mannosyltransferases (Pmt proteins) initiate O glycosylation of secreted proteins in fungi. We have characterized PMT6, which encodes the second Pmt protein of the fungal pathogen Candida albicans. The residues of Pmt6p are 21 and 42% identical to those of C. albicans Pmt1p and S. cerevisiae Pmt6p, respectively. Mutants lacking one or two PMT6 alleles grow normally and contain normal Pmt enzymatic activities in cell extracts but show phenotypes including a partial block of hyphal formation (dimorphism) and a supersensitivity to hygromycin B. The morphogenetic defect can be suppressed by overproduction of known components of signaling pathways, including Cek1p, Cph1p, Tpk2p, and Efg1p, suggesting a specific Pmt6p target protein upstream of these components. Mutants lacking both PMT1 and PMT6 are viable and show pmt1 mutant phenotypes and an additional sensitivity to the iron chelator ethylenediamine-di(o-hydroxyphenylacetic acid). The lack of Pmt6p significantly reduces adherence to endothelial cells and overall virulence in a mouse model of systemic infection. The results suggest that Pmt6p regulates a more narrow subclass of proteins in C. albicans than Pmt1p, including secreted proteins responsible for morphogenesis and antifungal sensitivities.
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Affiliation(s)
- C Timpel
- Institut für Mikrobiologie, Biologisch-Medizinisches Forschungszentrum, D-40225 Düsseldorf, Germany
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73
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Braun BR, Johnson AD. TUP1, CPH1 and EFG1 make independent contributions to filamentation in candida albicans. Genetics 2000; 155:57-67. [PMID: 10790384 PMCID: PMC1461068 DOI: 10.1093/genetics/155.1.57] [Citation(s) in RCA: 203] [Impact Index Per Article: 8.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
The common fungal pathogen, Candida albicans, can grow either as single cells or as filaments (hyphae), depending on environmental conditions. Several transcriptional regulators have been identified as having key roles in controlling filamentous growth, including the products of the TUP1, CPH1, and EFG1 genes. We show, through a set of single, double, and triple mutants, that these genes act in an additive fashion to control filamentous growth, suggesting that each gene represents a separate pathway of control. We also show that environmentally induced filamentous growth can occur even in the absence of all three of these genes, providing evidence for a fourth regulatory pathway. Expression of a collection of structural genes associated with filamentous growth, including HYR1, ECE1, HWP1, ALS1, and CHS2, was monitored in strains lacking each combination of TUP1, EFG1, and CPH1. Different patterns of expression were observed among these target genes, supporting the hypothesis that these three regulatory proteins engage in a network of individual connections to downstream genes and arguing against a model whereby the target genes are regulated through a central filamentous growth pathway. The results suggest the existence of several distinct types of filamentous forms of C. albicans, each dependent on a particular set of environmental conditions and each expressing a unique set of surface proteins.
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Affiliation(s)
- B R Braun
- Department of Microbiology, University of California, San Francisco, California 94143-0414, USA
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74
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Abstract
The magnitude and duration of signalling through mitogen- and stress-activated kinases are critical determinants of biological effect. This reflects a balance between the activities of upstream activators and a complex regulatory network of protein phosphatases. These mitogen-activated protein kinase phosphatases include both dual-specificity (threonine/tyrosine) and tyrosine-specific enzymes, and recent evidence suggests that a single mitogen-activated protein kinase isoform may be acted upon by both classes of protein phosphatase. In both cases, substrate selectivity is determined by specific protein-protein interactions mediated through noncatalytic amino-terminal mitogen-activated protein kinase binding domains. Future challenges include the determination of exactly how this network of protein phosphatases interacts selectively with mitogen-activated protein kinase signalling complexes to achieve precise regulation of these key pathways in mammalian cells.
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Affiliation(s)
- S M Keyse
- Molecular Pharmacology Unit, Imperial Cancer Research Fund, Biomedical Research Centre, Level 5, Ninewells Hospital, Dundee, DD1 9SY, UK.
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75
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Leng P, Sudbery PE, Brown AJ. Rad6p represses yeast-hypha morphogenesis in the human fungal pathogen Candida albicans. Mol Microbiol 2000; 35:1264-75. [PMID: 10712706 DOI: 10.1046/j.1365-2958.2000.01801.x] [Citation(s) in RCA: 37] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Rad6p plays important roles in post-replication DNA repair, chromatin organization, gene silencing and meiosis. In this study, we show that Rad6p also regulates yeast-hypha morphogenesis in the human pathogen Candida albicans. CaRAD6 gene and cDNAs were isolated and characterized revealing that the gene carries two 5'-proximal introns. CaRad6p shows a high degree of sequence similarity to Rad6 proteins from fungi to man (60-83% identity), and it suppresses the UV sensitivity and lack of induced mutagenesis displayed by a Saccharomyces cerevisiae rad6 mutant. In C. albicans, CaRAD6 expression is induced in response to UV, and CaRad6p depletion confers UV sensitivity, confirming that Rad6p serves a role in protecting this fungus against UV damage. CaRAD6 overexpression inhibits hyphal development, whereas CaRad6p depletion enhances hyphal growth. Also, CaRAD6 mRNA levels decrease during the yeast-hypha transition. These effects are dependent on Efg1p, but not Cph1p, indicating that CaRad6p acts specifically through the Efg1p morphogenetic signalling pathway to repress yeast-hypha morphogenesis.
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Affiliation(s)
- P Leng
- Department of Molecular and Cell Biology, University of Aberdeen, Institute of Medical Sciences, Foresterhill, Aberdeen AB25 2ZD, UK
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76
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Calera JA, Zhao XJ, Calderone R. Defective hyphal development and avirulence caused by a deletion of the SSK1 response regulator gene in Candida albicans. Infect Immun 2000; 68:518-25. [PMID: 10639412 PMCID: PMC97171 DOI: 10.1128/iai.68.2.518-525.2000] [Citation(s) in RCA: 123] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022] Open
Abstract
In a previous study, we reported the isolation and characterization of the two-component response regulator SSK1 gene of Candida albicans. This gene is a structural but not a functional homolog of the SSK1 and mcs4(+) genes of Saccharomyces cerevisiae and Schizosaccharomyces pombe, respectively. In the present study, we have constructed and phenotypically characterized Deltassk1 mutants of C. albicans. The results confirmed our previous observation that CaSSK1, unlike SSK1 or mcs4(+), does not regulate cellular responses to either osmotic or oxidative stress. Instead, Deltassk1 null strains showed severely reduced hyphal formation on serum agar and were totally defective in hyphal development on other solid media, such as medium 199 (pH 7.5) and Spider medium. In contrast, under conditions of low nitrogen availability on solid media, Deltassk1 null strains dramatically hyperinvaded the agar. However, while forming germ tubes and hyphae in liquid media similar to those of the wild type, Deltassk1 null strains flocculated in a manner similar to that of Deltachk1 two-component histidine kinase mutants, which we have previously described. Finally, virulence studies indicated that SSK1 is essential for the pathogenesis of C. albicans, suggesting that the Ssk1p response regulator could be a good target for antifungal therapy.
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Affiliation(s)
- J A Calera
- Department of Microbiology and Immunology, Georgetown University Medical Center, Washington, DC 20007-2197, USA.
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77
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Cho T, Hamatake H, Hagihara Y, Kaminishi H. Inhibitors of protein phosphorylation including the retinoblastoma protein induce germination of Candida albicans. Med Mycol 2000; 38:41-5. [PMID: 10746226 DOI: 10.1080/mmy.38.1.41.45] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/20/2022] Open
Abstract
It has been previously shown that the induction of germination in Candida albicans occurs following its cessation of growth as a yeast. Similarly, mammalian cells undergo a differentiation process that is preceded by a growth cessation associated with a hypophosphorylation of proteins of the retinoblastoma gene family. It is postulated that a similar type of mechanism may be operative in C. albicans and protein phosphorylation inhibitors: forskolin (stimulates cyclic adenosine monophosphate production), okadaic acid (phosphatase inhibitor) and D-erythro-sphingosine (retinoblastoma protein phosphorylation inhibitor) have been used to further strengthen this hypothesis. Okadaic acid (1-1000 nM) and D-erythro-sphingosine (100 microM) significantly inhibited the growth of yeast cells of C. albicans. D-Erythro-sphingosine at 1000 microM was candidicidal. Forskolin did not significantly affect growth. Exponentially grown C. albicans pretreated with forskolin (10 microM), okadaic acid (1000 nM) or D-erythro-sphingosine (100 microM) readily germinated. In comparison, when these inhibitors were incorporated in the same medium, germination of exponentially grown cells did not occur. These results suggest that protein dephosphorylation may be necessary at an early stage of the yeast-hyphae transition in C. albicans.
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Affiliation(s)
- T Cho
- Department of Oral Microbiology, Fukuoka Dental College, Japan.
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78
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Calderone R, Suzuki S, Cannon R, Cho T, Boyd D, Calera J, Chibana H, Herman D, Holmes A, Jeng HW, Kaminishi H, Matsumoto T, Mikami T, O'Sullivan JM, Sudoh M, Suzuki M, Nakashima Y, Tanaka T, Tompkins GR, Watanabe T. Candida albicans : adherence, signaling and virulence. Med Mycol 2000. [DOI: 10.1080/mmy.38.s1.125.137] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/19/2022] Open
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79
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Sonneborn A, Bockmühl DP, Gerads M, Kurpanek K, Sanglard D, Ernst JF. Protein kinase A encoded by TPK2 regulates dimorphism of Candida albicans. Mol Microbiol 2000; 35:386-96. [PMID: 10652099 DOI: 10.1046/j.1365-2958.2000.01705.x] [Citation(s) in RCA: 163] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
External signals induce the switch from a yeast to a hyphal growth form in the fungal pathogen Candida albicans. We demonstrate here that the catalytic subunit of a protein kinase A (PKA) isoform encoded by TPK2 is required for internal signalling leading to hyphal differentiation. TPK2 complements the growth defect of a Saccharomyces cerevisiae tpk1-3 mutant and Tpk2p is able to phosphorylate an established PKA-acceptor peptide (kemptide). Deletion of TPK2 blocks morphogenesis and partially reduces virulence, whereas TPK2 overexpression induces hyphal formation and stimulates agar invasion. The defective tpk2 phenotype is suppressed by overproduction of known signalling components, including Efg1p and Cek1p, whereas TPK2 overexpression reconstitutes the cek1 but not the efg1 phenotype. The results indicate that PKA activity of Tpk2p is an important contributing factor in regulating dimorphism of C. albicans.
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Affiliation(s)
- A Sonneborn
- Institut für Mikrobiologie, Heinrich-Heine-Universität Düsseldorf, Universitätsstr. 1/Geb. 26.12, D-40225 Düsseldorf, Germany
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80
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Sharkey LL, McNemar MD, Saporito-Irwin SM, Sypherd PS, Fonzi WA. HWP1 functions in the morphological development of Candida albicans downstream of EFG1, TUP1, and RBF1. J Bacteriol 1999; 181:5273-9. [PMID: 10464197 PMCID: PMC94032 DOI: 10.1128/jb.181.17.5273-5279.1999] [Citation(s) in RCA: 147] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The morphological plasticity of Candida albicans is an important determinant of pathogenicity, and nonfilamentous mutants are avirulent. HWP1, a hypha-specific gene, was identified in a genetic screen for developmentally regulated genes and encodes a cell surface protein of unknown function. Heterozygous and homozygous deletions of HWP1 resulted in a medium-conditional defect in hyphal development. HWP1 expression was blocked in a Deltaefg1 mutant, reduced in an Deltarbf1 mutant, and derepressed in a Deltatup1 mutant. Therefore, HWP1 functions downstream of the developmental regulators EFG1, TUP1, and RBF1. Mutation of CPH1 had no effect on HWP1 expression, suggesting that the positive regulators of hyphal development, CPH1 and EFG1, are components of separate pathways with different target genes. The expression of a second developmentally regulated gene, ECE1, was similarly regulated by EFG1. Since ECE1 is not required for hyphal development, the regulatory role of EFG1 apparently extends beyond the control of cell shape determinants. However, expression of ECE1 was not influenced by TUP1, suggesting that there may be some specificity in the regulation of morphogenic elements during hyphal development.
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Affiliation(s)
- L L Sharkey
- Department of Microbiology and Immunology, Georgetown University, Washington, D.C. 20007, USA
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81
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Abstract
Candida albicans undergoes reversible morphogenetic transitions between budding, pseudohyphal and hyphal growth forms that promote the virulence of this pathogenic fungus. The regulatory networks that control morphogenesis are being elucidated; however, the primary signals that trigger morphogenesis remain obscure, and the physiological outputs of these networks are complex.
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Affiliation(s)
- A J Brown
- Dept of Molecular and Cell Biology, Institute of Medical Sciences, University of Aberdeen, Foresterhill, Aberdeen, UK AB25 2ZD.
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82
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Alonso-Monge R, Navarro-García F, Molero G, Diez-Orejas R, Gustin M, Pla J, Sánchez M, Nombela C. Role of the mitogen-activated protein kinase Hog1p in morphogenesis and virulence of Candida albicans. J Bacteriol 1999; 181:3058-68. [PMID: 10322006 PMCID: PMC93760 DOI: 10.1128/jb.181.10.3058-3068.1999] [Citation(s) in RCA: 288] [Impact Index Per Article: 11.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The relevance of the mitogen-activated protein (MAP) kinase Hog1p in Candida albicans was addressed through the characterization of C. albicans strains without a functional HOG1 gene. Analysis of the phenotype of hog1 mutants under osmostressing conditions revealed that this mutant displays a set of morphological alterations as the result of a failure to complete the final stages of cytokinesis, with parallel defects in the budding pattern. Even under permissive conditions, hog1 mutants displayed a different susceptibility to some compounds such as nikkomycin Z or Congo red, which interfere with cell wall functionality. In addition, the hog1 mutant displayed a colony morphology different from that of the wild-type strain on some media which promote morphological transitions in C. albicans. We show that C. albicans hog1 mutants are derepressed in the serum-induced hyphal formation and, consistently with this behavior, that HOG1 overexpression in Saccharomyces cerevisiae represses the pseudodimorphic transition. Most interestingly, deletion of HOG1 resulted in a drastic increase in the mean survival time of systemically infected mice, supporting a role for this MAP kinase pathway in virulence of pathogenic fungi. This finding has potential implications in antifungal therapy.
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Affiliation(s)
- R Alonso-Monge
- Departamento de Microbiología II, Facultad de Farmacia, Universidad Complutense de Madrid, E-28040 Madrid, Spain
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83
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Wiltshire C, Black S, Brown AJ. Over-expression of Candida albicans mitochondrial ribosomal protein S9 (MrpS9p) disturbs mitochondrial function in Saccharomyces cerevisiae. Yeast 1999; 15:139-43. [PMID: 10029992 DOI: 10.1002/(sici)1097-0061(19990130)15:2<139::aid-yea347>3.0.co;2-5] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022] Open
Abstract
A Candida albicans mitochondrial ribosomal protein S9 (MRPS9) cDNA was identified in a screen for sequences whose expression induce galactose lethality in Saccharomyces cerevisiae. MRPS9 appears to encode a protein of 346 amino acids with an N-terminal mitochondrial targeting sequence and an internal S9 signature that is conserved amongst eukaryotic mitochondrial and prokaryotic ribosomal protein S9 sequences. Expression of a GAL1-CaMRPS9 fusion in S. cerevisiae caused the slow development of a galactose-negative phenotype upon repeated subculturing, and this correlated with an increased frequency of petite mutant formation. Therefore, over-expression of CaMRPS9 interferes with S. cerevisiae mitochondrial function, which accounts for the inhibition of growth on galactose.
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Affiliation(s)
- C Wiltshire
- Department of Molecular and Cell Biology, University of Aberdeen, U.K
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84
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Abstract
Two regulatory pathways govern filamentation in the pathogenic fungus Candida albicans. Recent virulence studies of filamentation regulatory mutants argue that both yeast and filamentous forms have roles in infection. Filamentation control pathways seem closely related in C. albicans and in Saccharomyces cerevisiae, thus permitting speculation about C. albicans filamentation genes not yet discovered.
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Affiliation(s)
- A P Mitchell
- Department of Microbiology, Institute of Cancer Research, Columbia University, 701 West 168th Street, New York, NY 10032, USA.
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85
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Abstract
Many members of the fungal kingdom have a distinguishing feature, dimorphism, which is the ability to switch between two morphological forms: a cellular yeast form and a multicellular invasive filamentous form. At least three pathways are involved in regulating the transition between these two forms in the budding yeast Saccharomyces cerevisiae, and evidence is now emerging that homologous signalling modules are involved in regulating filament formation and virulence in a range of human and plant fungal pathogens. Strikingly, components used to signal sexual differentiation in the response to mating pheromones are often reutilized to regulate dimorphic development, suggesting an ancient link between these processes.
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Affiliation(s)
- H D Madhani
- Whitehead Institute for Biomedical Research, Nine Cambridge Center, MA 02142, USA.
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86
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Csank C, Schröppel K, Leberer E, Harcus D, Mohamed O, Meloche S, Thomas DY, Whiteway M. Roles of the Candida albicans mitogen-activated protein kinase homolog, Cek1p, in hyphal development and systemic candidiasis. Infect Immun 1998; 66:2713-21. [PMID: 9596738 PMCID: PMC108260 DOI: 10.1128/iai.66.6.2713-2721.1998] [Citation(s) in RCA: 280] [Impact Index Per Article: 10.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023] Open
Abstract
Extracellular signal-regulated protein kinase (ERK, or mitogen-activated protein kinase [MAPK]) regulatory cascades in fungi turn on transcription factors that control developmental processes, stress responses, and cell wall integrity. CEK1 encodes a Candida albicans MAPK homolog (Cek1p), isolated by its ability to interfere with the Saccharomyces cerevisiae MAPK mating pathway. C. albicans cells with a deletion of the CEK1 gene are defective in shifting from a unicellular budding colonial growth mode to an agar-invasive hyphal growth mode when nutrients become limiting on solid medium with mannitol as a carbon source or on glucose when nitrogen is severely limited. The same phenotype is seen in C. albicans mutants in which the homologs (CST20, HST7, and CPH1) of the S. cerevisiae STE20, STE7, and STE12 genes are disrupted. In S. cerevisiae, the products of these genes function as part of a MAPK cascade required for mating and invasiveness of haploid cells and for pseudohyphal development of diploid cells. Epistasis studies revealed that the C. albicans CST20, HST7, CEK1, and CPH1 gene products lie in an equivalent, canonical, MAPK cascade. While Cek1p acts as part of the MAPK cascade involved in starvation-specific hyphal development, it may also play independent roles in C. albicans. In contrast to disruptions of the HST7 and CPH1 genes, disruption of the CEK1 gene adversely affects the growth of serum-induced mycelial colonies and attenuates virulence in a mouse model for systemic candidiasis.
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Affiliation(s)
- C Csank
- Eukaryotic Genetics Group, National Research Council of Canada, Biotechnology Research Institute, Montreal, Quebec H4P 2R2
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87
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Cutler JE. The Candida albicans phosphomannan complex in Candida-host interactions. RESEARCH IN IMMUNOLOGY 1998; 149:299-308; discussion 507-9. [PMID: 9720948 DOI: 10.1016/s0923-2494(98)80754-2] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
Affiliation(s)
- J E Cutler
- Department of Microbiology, Montana State University, Bozeman 59717-3520, USA
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