Histidine kinase, two‐component signal transduction proteins of Candida albicans and the pathogenesis of candidosis (original) (raw)
Related papers
Frontiers in Microbiology
ObjectivesThe histidine kinase (HK) CHK1 and other protein kinases in Candida albicans are key players in the development of hyphae. This study is designed to determine the functional roles of the S_Tkc domain (protein kinase) and the GAF domain of C. albicans CHK1 in hyphal formation and mucosal invasion.MethodsThe domain mutants CHK25 (ΔS_TkcCHK1/Δchk1) and CHK26 (ΔS_TkcΔgafCHK1/Δchk1) were first constructed by the his1-URA3-his1 method and confirmed by sequencing and Southern blots. A mouse tongue infection model was used to evaluate the hyphal invasion and fungal loads in each domain mutant, full-gene deletion mutant CHK21 (chk1Δ/chk1Δ), re-constituted strain CHK23 (chk1Δ/CHK1), and wild type (WT) from day 1 to day 5. The degree of invasion and damage to the oral mucosa of mice in each strain-infected group was evaluated in vivo and compared with germ tube rate and hyphal formation in vitro.ResultWhen compared with severe mucosal damage and massive hyphal formation in WT- or CHK...
Microbiology, 1999
In Candida albicans, three putative histidine kinase genes have been described thus far, including CaSLNI, CaNIKlICOSl and CaHKl. The encoded proteins for C. albicans, CaSlnlp and CaNiklp, which are similar to S l n l p from Saccharomyces cerevisiae and Nik-1 from Neurospora crassa, seem to function in osmoregulation and morphogenesis, respectively. Recently, the isolation of CaHKl, a putative histidine kinase gene from C. albicans has been reported. In addition t o the histidine and aspartyl domains located at its C-terminus as previously described, it is shown here that the N-terminal domain o f Cahklp contains a P-loop motif and a sequence which shows significant homology with the seven C-terminal domains of serinekhreonine kinases. The Ser/Thrhomologous domains of Cahklp could, in fact, correspond to its sensor sequence. CaHKl has been mapped to chromosome 2 and gene deletion studies were undertaken to understand its function. Acahkl mutants are phenotypically different from any other histidine kinase mutants thus far described either in C. albicans or in any other yeast or filamentous fungus. This study demonstrates that Acahkl mutants flocculate extensively in a genedosage-dependent manner under conditions which induce germ-tube formation, such as growth in medium 199 (pH 7.5). The flocculation occurs by an interaction along the hyphal surfaces, probably because of the altered expression o f one or more hyphal-cell-surface components in the Acahkl mutants. These results indicate that CaHKl could be involved in regulating their expression.
Proceedings of the National Academy of Sciences, 1998
Two-component histidine kinases recently have been found in eukaryotic organisms including fungi, slime molds, and plants. We describe the identification of a gene, COS1, from the opportunistic pathogen Candida albicans by using a PCR-based screening strategy. The sequence of COS1 indicates that it encodes a homolog of the histidine kinase Nik-1 from the filamentous fungus Neurospora crassa. COS1 is also identical to a gene called CaNIK1 identified in C. albicans by low stringency hybridization using CaSLN1 as a probe [Nagahashi, S., Mio, T., Yamada-Okabe, T., Arisawa, M., Bussey, H. & Yamada-Okabe, H. (1998) Microbiol. 44, 425-432].
Functional Studies on the Histidine Kinase CaNik1p from Candida albicans
2013
I am very grateful to the Egyptian government and the DAAD for the financial support of my studies. In addition, I thank the graduate school of HZI, Braunschweig for financing attendance at conferences and for organizing workshops, scientific courses, and retreats, which altogether improved not only my scientific experience, but also my research skills. To my parents, I say "You might think you were in Egypt far away from me, but I would say you were always in my mind. With your continuous support and prayers for me, I was always on the right track." Zu Deutschland wollte ich "Herzlichen Dank für die Gastfreundschaft" sagen.
Fems Yeast Research, 2003
The human pathogen Candida albicans encodes at least three putative two-component histidine kinase signal transduction proteins, including Chk1p and a response regulator protein (Cssk1p). Strains deleted in CHK1 are avirulent in a murine model of hematogenously disseminated disease. The specific function of Chk1p has not been established, but hyphae of the chk1 mutant exhibit extensive flocculation while yeast forms are less adherent to reconstituted human esophageal tissue, indicating that this protein may regulate cell surface properties. Herein, we analyze glucan, mannan and chitin profiles in strains deleted in chk1 (CHK21) compared to a genereconstituted strain (CHK23) and a parental strain CAF2. Total alkali-soluble hexose from the cell wall of the chk1 mutant (strain CHK21) was significantly reduced. Western blots of cell wall extracts from CHK21, CHK23 and CAF2 reacted with a Mab to the acidstable mannan fraction revealed extensive staining of lower molecular mass species in strain CHK21 only. FACE (fluorophore assisted carbohydrate electrophoresis) was used to characterize the oligosaccharide side chains of L-eliminated (O-linked), acid-hydrolyzed (acidlabile phosphomannan) and acetolysis (acid-stable mannan) extracted fractions of total mannan. The profiles of O-linked as well as the acid-labile oligosaccharides were similar in both CAF2 and CHK21, but the acid-stable oligosaccharide side chains were significantly truncated. We also characterized the L-glucan from each strain using NMR, and found that both the degree of polymerization and the ratio of (1-3)/(1-6) linkages was lower in CHK21 relative to wild-type cells. The sensitivity of CHK21 to antifungal drugs and inhibitors was unaffected. In summary, our data have identified a new function for a histidine kinase two-component signal protein in a human pathogenic fungus. ß 2002 Published by Elsevier Science B.V. on behalf of the Federation of European Microbiological Societies. 1567-1356 / 02 / $22.00 ß 2002 Published by Elsevier Science B.V. on behalf of the Federation of European Microbiological Societies. PII: S 1 5 6 7 -1 3 5 6 ( 0 2 ) 0 0 1 6 4 -2
Fems Yeast Research, 2003
The human pathogen Candida albicans encodes at least three putative two-component histidine kinase signal transduction proteins, including Chk1p and a response regulator protein (Cssk1p). Strains deleted in CHK1 are avirulent in a murine model of hematogenously disseminated disease. The specific function of Chk1p has not been established, but hyphae of the chk1 mutant exhibit extensive flocculation while yeast forms are less adherent to reconstituted human esophageal tissue, indicating that this protein may regulate cell surface properties. Herein, we analyze glucan, mannan and chitin profiles in strains deleted in chk1 (CHK21) compared to a genereconstituted strain (CHK23) and a parental strain CAF2. Total alkali-soluble hexose from the cell wall of the chk1 mutant (strain CHK21) was significantly reduced. Western blots of cell wall extracts from CHK21, CHK23 and CAF2 reacted with a Mab to the acidstable mannan fraction revealed extensive staining of lower molecular mass species in strain CHK21 only. FACE (fluorophore assisted carbohydrate electrophoresis) was used to characterize the oligosaccharide side chains of L-eliminated (O-linked), acid-hydrolyzed (acidlabile phosphomannan) and acetolysis (acid-stable mannan) extracted fractions of total mannan. The profiles of O-linked as well as the acid-labile oligosaccharides were similar in both CAF2 and CHK21, but the acid-stable oligosaccharide side chains were significantly truncated. We also characterized the L-glucan from each strain using NMR, and found that both the degree of polymerization and the ratio of (1-3)/(1-6) linkages was lower in CHK21 relative to wild-type cells. The sensitivity of CHK21 to antifungal drugs and inhibitors was unaffected. In summary, our data have identified a new function for a histidine kinase two-component signal protein in a human pathogenic fungus. ß 2002 Published by Elsevier Science B.V. on behalf of the Federation of European Microbiological Societies. 1567-1356 / 02 / $22.00 ß 2002 Published by Elsevier Science B.V. on behalf of the Federation of European Microbiological Societies. PII: S 1 5 6 7 -1 3 5 6 ( 0 2 ) 0 0 1 6 4 -2
Eukaryotic Cell, 2014
Prokaryotes and lower eukaryotes, such as yeasts, utilize two-component signal transduction pathways to adapt cells to environmental stress and to regulate the expression of genes associated with virulence. One of the central proteins in this type of signaling mechanism is the phosphohistidine intermediate protein Ypd1. Ypd1 is reported to be essential for viability in the model yeast Saccharomyces cerevisiae. We present data here showing that this is not the case for Candida albicans. Disruption of YPD1 causes cells to flocculate and filament constitutively under conditions that favor growth in yeast form. To determine the function of Ypd1 in the Hog1 mitogen-activated protein kinase (MAPK) pathway, we measured phosphorylation of Hog1 MAPK in ypd1⌬/⌬ and wild-type strains of C. albicans. Constitutive phosphorylation of Hog1 was observed in the ypd1⌬/⌬ strain compared to the wild-type strain. Furthermore, fluorescence microscopy revealed that green fluorescent protein (GFP)-tagged Ypd1 is localized to both the nucleus and the cytoplasm. The subcellular segregation of GFP-tagged Ypd1 hints at an important role(s) of Ypd1 in regulation of Ssk1 (cytosolic) and Skn7 (nuclear) response regulator proteins via phosphorylation in C. albicans. Overall, our findings have profound implications for a mechanistic understanding of two-component signaling pathways in C. albicans, and perhaps in other pathogenic fungi.
Infection and Immunity, 1998
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. Candida albicans, an opportunistic fungal pathogen, is the major causative agent of thrush and other forms of candidiasis. Diploid C. albicans alternates between a yeast form and mycelial and pseudomycelial forms but does not have a sexual cycle. Physiological temperatures, pH, and serum can promote the emergence of true hyphae from yeast cells in vitro, yet both these forms, as well as pseudohyphae, may be found in infected tissues (for a review, see reference 32). The roles of these different morphologies in pathogenesis have been controversial, but recently, hyphal differentiation has been found to be linked to systemic virulence (22, 26) and the ability of C. albicans cells to evade macrophages (26). Filamentous forms are also better than yeast forms at invading epithelial cells (7) and agar surfaces in vitro (5, 12, 34). This may be the result of both the mechanical advantages of hyphal forms in the penetration of solid substrates (11) and the production of hyphaspecific hydrolytic enzymes such as some of the secreted aspartyl proteinases which also appear to contribute to virulence (14, 40). Baker's yeast, Saccharomyces cerevisiae, is also able to switch
The Candida albicans histidine kinase Chk1p: Signaling and cell wall mannan
Fungal Genetics and Biology, 2009
Several published functions associated with the CHK1 histidine kinase of Candida albicans resemble those of the MAPK Cek1p and its cognate receptor Sho1p (SSU81). To explore this further, we have compared mutants lacking the proteins mentioned above and have constructed a double sho1/ chk1Δ null mutant to determine relationships among these proteins. We observed that the sensitivity to Congo red (CR), calcofluor white (CW), as well as clumping of cells, was slightly increased in the double mutant compared to the single chk1Δ or sho1Δ mutants. However, Cek1p phosphorylation via Sho1p, which occurs during log phase growth in the presence or absence of CR in Wt cells, does not require Chk1p. These data suggest that Chk1p and Sho1p are components of parallel but independent signal pathways. In addition, bulk mannan of strains was analyzed by GPC/MS and NMR. Compared to Wt and a CHK1 gene-reconstituted strain (CHK23) that contained, high, intermediate and low Mw mannan species, we found that the mannan of strains CHK21 (chk1Δ null), the cek1Δ null, and the double mutant consisted only of low Mw mannan. The sho1Δ null mutant only demonstrated a reduced intermediate type of mannan. Alcian blue binding was lower in cek1Δ, chk1Δ, and the double sho1/chk1Δ null mutant lacking high and intermediate Mw mannan than in the sho1Δ null which had a partial loss of intermediate Mw mannan only. We conclude that the Chk1p HK is part of a functionally similar but parallel pathway to the Sho1p-Cek1p pathway that confers resistance to the cell wall inhibitors CR and CW. However, a functional relationship in mannan biosynthesis of Chk1p and Cek1p exists that only partially requires Sho1p.