1 Department of Microbiology and Immunology, Georgetown University Medical Center, 312 SE Med. Dent. Building, 3900 Reservoir Rd, NW, Washington DC 20057, USA
2 Department of Medicine, INOVA Fairfax Hospital, Fairfax, VA, USA
Correspondence
Richard Calderone
calderor{at}georgetown.edu
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ABSTRACT |
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INTRODUCTION |
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Two-component signal transduction has been studied in both non-pathogenic and pathogenic fungi (Santos & Shiozaki, 2001). Of interest, the absence of these proteins in mammalian cells offers some degree of specificity in the development of antifungal drugs (Barrett & Hoch, 1998
; Koretke et al., 2000
). Two-component signal transduction proteins of C. albicans include three histidine kinases (Sln1p, Nik1p and Chk1p), two response regulator proteins (Ssk1p and Skn7p) and a phosphohistidine intermediate protein (Ypd1p) (Calera & Calderone, 1999b
; Santos & Shiozaki, 2001
). Sln1p, Ypd1p and Ssk1p are probably orthologues of the HOG1 MAP kinase pathway proteins [hyperosmotic glycerol] that in Saccharomyces cerevisiae are used for the adaptation of cells to osmotic stress (Hohmann, 2002
). In C. albicans these proteins have additional functions which include adaptation to oxidant stress, morphogenesis, virulence, adherence and cell wall biosynthesis (Alex et al., 1998
; Alonso-Monge et al., 1999
, 2003
; Bernhardt et al., 2001
; Calera et al., 1998
, 1999
, 2000a
, b
; Calera & Calderone, 1999a
; Chauhan et al., 2003
; Kruppa et al., 2003
, 2004b
; Li et al., 2002
; Nagahashi et al., 1998
; Selitrennikoff et al., 2001
; Singh et al., 2004
; Srikantha et al., 1998
; Torosantucci et al., 2002
; Yamada-Okabe et al., 1999
). All of the two-component genes except SKN7 have been implicated in the virulence of the organism in a haematogenously disseminated murine model. Deletions of nik1 or sln1 attenuate virulence, while deletion of chk1 abolishes virulence (Calera et al., 1999
; Yamada-Okabe et al., 1999
). Ssk1p, while not essential for adaptation to osmotic stress in C. albicans as it is in Saccharomyces cerevisiae, regulates adaptation to oxidant stress and the expression of cell wall proteins such as Als1p, Flo1p and Mnn4p (Chauhan et al., 2003
). Downregulation of Als1p (Kapteyn et al., 2000
) in the ssk1 mutant is offered as a partial explanation for the decreased adherence of the mutant to human oesophageal tissue in vitro (Li et al., 2002
). Of the histidine kinases of C. albicans, Chk1p and Nik1p are not found in Sac. cerevisiae (Santos & Shiozaki, 2001
). Nik1p of C. albicans, a homologue of Neurospora crassa nik1, is partially required for phenotypic switching and morphogenesis (Srikantha et al., 1998
; Santos & Shiozaki, 2001
). In addition to C. albicans, a nik1 orthologue has been reported in Aspergillus fumigatus (Pott et al., 2000
).
Chk1p is homologous to the Mak2p and Mak3p of Schizosaccharomyces pombe. In that organism, these proteins are used for adaptation to oxidant stress (Buck et al., 2001). C. albicans strains deleted of CHK1 have an altered cell wall phenotype characterized by a truncation of acid-stable cell wall mannan side chains, as well as a reduction in the amount of 1,3-
-glucan and an increase in the amount of 1,6-
-glucan (Kruppa et al., 2003
). The primary lesion of the chk1 null mutant has not been defined and is currently being investigated. That the mutant displays several changes in cell wall composition is often typical of fungal cell wall mutants. It would seem, therefore, that Chk1p is part of a signal pathway that regulates cell wall biosynthesis. The changes in cell wall composition may explain the reduced ability of the chk1 null mutant to adhere to human oesophageal tissue in vitro (Li et al., 2002
).
While a presumed pathway similar to the HOG MAP kinase of Sac. cerevisiae is postulated in C. albicans that includes Sln1p, Ypd1p and Ssk1p, the relationship of Chk1p to this pathway as well as with Nik1p is unknown. To determine the relationship of Chk1p to the HOG1 MAP kinase and to the other histidine kinases, a CHK1 promoter-lacZ reporter construct was used to transform wild-type and the null mutants in ssk1, sln1 and nik1 and measure expression of lacZ under stress conditions and in serum. Furthermore, the relationship of Chk1p to Hog1p was investigated by determining the phosphorylation of Hog1p using Western blotting in wild-type and the chk1 mutant as well as lacZ expression in the hog1 mutant of C. albicans.
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METHODS |
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Southern hybridization and PCR.
Verification of the correct integration of the CHK1prlacZ and Act1prlacZ cassettes in all transformants of CAI4 and mutants was accomplished by Southern hybridization using standard methods (Calera & Calderone, 1999a). For the CHK1-lacZ transformants, genomic DNA from all strains was digested with BclI and probed with the 550 bp fragment that is located at approximately 175 bp upstream of the KpnI restriction site (Fig. 1a
). For each transformant, two hybridizing bands of 4·9 and 5·6 kb were observed in Southern hybridizations (Fig. 1b
). The ACT1-lacZ transformants were restriction-digested with HindIII and probed with an 800 bp sequence derived from the ACT1 promoter (1210 to 410 bp, not shown). In addition to Southern analyses, two PCRs using primers P1P4, indicated in Fig. 1(a)
, bottom, were also used to confirm the correct integration of each cassette mentioned above. First, a 1·79 kb fragment was amplified with primer CHK5' (5'-GACACCTCCTAATAACTCAC-3'), located at
80 bp upstream of the 5' end of the CHK1 promoter corresponding to the KpnI restriction site and an StlacZ3' primer (5'-TTCTTGAGGAACTTGAGGTG-3') at
200 bp downstream of the lacZ start codon (Fig. 1a
, bottom, indicated as primer pair P1 and P2). The second PCR was performed using primers P3 (from pBSII KS+ vector) and P4 (CHKpr3', 5'-CTCGGCGATACTCTACTAC-3') at about 350 bp downstream of the KpnI site (Fig. 1a
, bottom, primer pair P3 and P4). This PCR fragment was 387 bp in size. Using the same strategy, ACT1-promoter-lacZ transformants were confirmed by two other PCRs. Primer ACT1pr5' (5'-GAGAGATTTGAAATGATCAG-3'), located at
198 bp upstream of 5' end of the ACT1 promoter-integrating site, and the StlacZ3' primer amplified a product of approximately 1·58 kb (data not shown). A second PCR utilizing the primers ACTpr3' (5'-TAGCACACACCCACAACAAC-3'),
590 bp downstream of the integrating site, and T3 resulted in a 617 bp PCR fragment (data not shown).
-Galactosidase assays.
Three transformants of CAI4 and each mutant strain were chosen for determinations of -galactosidase activity. Quantitative determinations of
-galactosidase activity were performed by measuring the hydrolysis of the substrate ONPG from broth cultures as described by Uhl & Johnson (2001)
using mid-exponential-phase cells obtained in the following manner. Fresh YNB medium (5 ml) with or without uridine was inoculated with 100 µl of an overnight culture of CAI4 or each transformant. Cultures were incubated at 30 °C with vigorous shaking for 3 h to achieve an OD600 of approximately 0·3. Cultures were then supplemented with 4 mM H2O2, 0·1 mM menadione (ViK3) or 1·5 M NaCl. With other cultures, cells were collected by centrifugation and resuspended in 10 % serum or M199 medium at pH 3·5. All cultures were then incubated at 30 °C. Control cultures consisted of cells without supplements and maintained at 30 °C in YNB. For other assays, cultures were shifted to 37 or 42 °C and expression was compared to cells grown at 30 °C. Cells incubated as described above under each condition were harvested at 10, 30 60 or 120 min for lacZ assays. The cells were collected and resuspended in 5 ml Z buffer (pH 7·0, 0·01 M sodium phosphate, supplemented with KCl, MgSO4 and
-mercaptoethanol) (Uhl & Johnson, 2001
). Then, triplicate samples of cells (0·8 ml per strain and for each growth condition) were permeabilized with 25 µl chloroform and 25 µl 0·1 % SDS. Cells were equilibrated at 37 °C for 5 min, 0·2 ml (4 mg ml1) of the ONPG substrate was added and the cells were mixed and incubated at 37 °C for 20 min. The reactions were stopped by the addition of 0·5 ml 1 M Na2CO3, cells were then centrifuged in a Sorvall Biofuge Pico for 5 min at 3000 r.p.m. and A420 was determined for each reaction. The units of
-galactosidase activity were determined by the following equation:
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Visual screens for C. albicans transformants were carried out by patching colonies onto X-Gal-modified medium (XMM) plates with 5 µl (1x106) mid-exponential-phase cells for each sample (Uhl & Johnson, 2001). XMM contained 1·7 g yeast nitrogen base (without amino acids), 20 g glucose, 5 g ammonium sulfate and 20 g agar in 930 ml H2O. After autoclaving, 70 ml 1 M potassium phosphate (pH 7·0) and 2 ml X-Gal (20 mg ml1) solution were added.
Phosphorylation of Hog1p.
The assay follows our protocol as described previously (Chauhan et al., 2003). The parental strain CAF2-1 and the chk1 null (CHK21) were grown in YPD medium supplemented with either 10 mM H2O2 or 1·5 M NaCl as described previously (Chauhan et al., 2003
). At designated times following incubation (t0t60 min), cells were collected, proteins extracted and equal amounts separated by SDS-PAGE. The electrophoresed proteins were then transferred to nylon membranes and first probed with a ScHog1p polyclonal antibody (anti-ScHog1; Santa Cruz Biotechnology). Subsequently, the blots were stripped and reacted with a phospho-p38 MAP kinase (Thr180/Tyr182) 28B10 mAb (anti-TGYp; Cell Signalling Technology Inc.). Blots were then developed as recommended by the manufacturer (Amersham Pharmacia Biotech).
In vitro sensitivity assays.
To determine the sensitivity of the mutants to oxidant or osmotic stress, we used in vitro drop plate assays containing 210 mM H2O2, 11·5 M NaCl or 0·1 mM menadione in YPD agar (Chauhan et al., 2003). To these media, inocula of 505x105 yeast cells of CAF2-1, CHK21 (chk1/chk1), CHK23 (chk1/CHK1) and, for comparison, two other histidine kinases, the sln1 and nik1 mutants, were spotted onto the agar media. Plates then were incubated at 30 °C for 48 h at which time growth was assessed at each cell concentration.
Statistical analysis.
To determine the significance of lacZ expression in different growth conditions or in strains, we used a non-parametric analysis-of-variance technique with multiple comparison tests (SAS 8.2, SAS Institute, Cary, NC, USA). All outcomes were considered statistically significant at P<0·05.
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RESULTS |
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-Galactosidase activity in CAI4 and mutant strains
-Galactosidase (CHK1-lacZ) activity in all strains was measured from cells grown in broth media (Fig. 2a, b
). In addition, essentially similar results were obtained with the agar plate X-Gal agar assays (data not shown). The level of
-galactosidase in each strain indicated in Fig. 2
is expressed as absorption units for cultures that reached a similar optical density in each of the growth conditions described in Methods. For all determinations represented in Fig. 2(ad)
, three clones of each transformant (mutants or CAI4) were assayed in triplicate and mean values for each of the three transformants are indicated. Experiments were repeated twice with similar results. We also measured the expression of ACT1-lacZ in mutant strains and CAI4 under all growth conditions to determine the changes in gene expression relative to CHK1-lacZ (data not shown). Thus, all data shown in Fig. 2(ad)
are normalized to the expression of ACT1-lacZ. Expression of ACT1-lacZ was similar for all strains under all growth conditions (P=0·76), although ACT1-lacZ expression was higher in all strains when cells were incubated in 10 % serum or 4 mM H2O2 (P<0·05) (data not shown). We measured the temporal expression of lacZ under all growth conditions and in each mutant at 0, 10, 30, 60 and 120 min and found that for all strains, lacZ expression was highest after 10 min incubation. For comparisons among strains and under each environmental condition, we have included expression data in Fig. 2(ad)
from both 10 and 120 min. In Fig. 2(a)
, lacZ expression of CAI4 is compared to the sln1 and nik1 mutants. At 10 min, the expression of lacZ in the sln1 mutant is lower than that of CAI4 under all growth conditions (P<0·05). However, expression of lacZ was not changed under any growth condition in CAI4 or either mutant. After 120 min under stress, expression of lacZ varied according to the strain and environmental growth conditions (Fig. 2b
). We observed that the expression of lacZ in CAI4 increased when cells were grown in 0·1 M menadione, 10 % serum, 4 mM H2O2, 1·5 M NaCl, pH 3·5, and at 37 °C (P<0·05). In the sln1 mutant, expression of lacZ was lower than in CAI4, again under all growth conditions (Fig. 2b
) (P<0·05). This observation indicates that Sln1p positively affects lacZ expression. On the other hand, lacZ expression in the nik1 mutant was similar to CAI4, except when cells were grown in the presence of 4 mM H2O2 or 1·5 M NaCl for 120 min (Fig. 2b
) (P<0·05).
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Phosphorylation of Hog1p in parental cells and the chk1 mutant
The lacZ reporter assays indicated that Ssk1p, Hog1p and Sln1p affect expression of CHK1-lacZ. To further define this interaction, we determined the phosphorylation of Hog1p in both CAF2-1 and the chk1 mutant (strain CHK21), since Hog1p is a MAP kinase that is downstream of Sln1p and Ssk1p in Sac. cerevisiae and, presumably, C. albicans. Both strains were stressed with either 10 mM H2O2 or 1·5 M NaCl and phosphorylation of Hog1p was measured. We knew from previous studies that Ssk1p is required for phosphorylation of Hog1p in cells under oxidant stress (Chauhan et al., 2003). In Fig. 3
(upper and lower panels), Hog1p is phosphorylated in CAF2-1 within 2 min after the shift to either stress condition. The phosphorylation signal then decreases by 60 min. In strain CHK21 the temporal phosphorylation of Hog1p is somewhat different. Under oxidative stress, phosphorylation of Hog1p persists, even at 60 min, while under osmotic stress, phosphorylation of Hog1p is delayed and a weak signal is first seen at 10 min which then persists for at least 60 min. Thus, under both types of stress, Chk1p is not required for phosphorylation of Hog1p, although minimal temporal changes occur in the chk1 mutant compared to wild-type cells.
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DISCUSSION |
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Chk1p is not found in Sac. cerevisiae, and while orthologues have been identified in Schizosaccharomyces pombe, Mak2p and Mak3p have not been assigned to a signal pathway (Buck et al., 2001). Based upon our current data, we postulate that the regulation of Chk1p by proteins of the HOG1 MAP seems likely, but the alignment of Chk1p within or downstream of this pathway remains uncertain. Sln1p and Ssk1p are both components of the HOG1 pathway, yet their effects on Chk1p transcription are opposite but reminiscent of their interactions in the Sac. cerevisiae HOG1 osmosensing pathway (Hohmann, 2002
). In that organism, in unstressed cells, the downstream Ssk1p is inactive (unable to bind to the MAPKKK of the HOG1 pathway), because Ssk1p is phosphorylated by the phosphohistidine intermediate protein, Ypd1p, via the histidine kinase, membrane receptor protein Sln1p. In osmotically stressed cells, Ssk1p is not phosphorylated and is able to activate the HOG1 MAP kinase pathway, which in turn results in an osmoadaptation. If SLN1 is deleted, then Ssk1p is constitutively active, since it is unphosphorylated in both stressed and unstressed cells; this leads to inviability in Sac. cerevisiae but not in C. albicans. Thus, in the C. albicans sln1 mutant, Ssk1p is presumably unphosphorylated and, hence, active, resulting in the downregulation of CHK1 transcription. Likewise, if SSK1 is deleted, then transcription of CHK1 increases. Support for the CHK1-lacZ expression profile in the ssk1 mutant has been demonstrated in previous studies by microarray analysis, since CHK1 transcription increases in the ssk1 mutant (Chauhan et al., 2003
). If this model of CHK1 regulation is correct, then Hog1p (downstream of Ssk1p) should likewise negatively regulate CHK1. In fact, the hog1 deletion mutant behaves similarly to the ssk1 mutant: CHK1 transcription is increased. The effects of the SLN1 or SSK1 deletions on CHK1 in C. albicans are observed in both stressed and unstressed cells, but the level of expression of CHK1p-lacZ is changed under some stress conditions at a specific time point.
We attempted to correlate the activity of Chk1p and Hog1p by Western blot analysis of phosphorylated and unphosphorylated Hog1p. Those data indicate that Chk1p is not required for Hog1p phosphorylation, although the deletion of CHK1 caused a minimal temporal change in phosphorylation of Hog1p. These data suggest that Chk1p is transcriptionally regulated but perhaps downstream of the HOG1 signal pathway.
The relationship of Nik1p to CHK1p-lacZ transcription is less apparent, since changes in the latter only occurred in a narrow range of growth conditions in the nik1 mutant. From previous microarray data with the ssk1 mutant, CHK1 transcription is increased, while NIK1 is unchanged compared to CAF2-1 (Chauhan et al., 2003). On the other hand, in the nik1, sln1 and chk1 mutants, the transcription profile of six mannosyl transferases increased similarly in each, and Western blotting profiles of acid-stable, but not acid-labile oligomannans were similar for each mutant (Kruppa et al., 2004b
), implying that the three histidine kinases may have cross-talking interactions in regard to some common activities.
Chk1p of C. albicans, and for that matter all fungi that have two-component signal transduction, is a functionally novel histidine kinase in that it regulates cell wall biosynthesis. We have shown that the chk1 mutant has profound changes in the composition of its cell wall, including levels of 1,3--glucan (about 50 % lower) and 1,6-
-glucan (about fourfold higher), as well as a truncation in the oligosaccharide side chains of the acid-stable mannan (Kruppa et al., 2003
, 2004b
). These changes have been confirmed by both biochemical and immunological determinations. Associated with the changes in cell wall structure is the reduced adherence of the mutant to human oesophageal tissues (Li et al., 2002
; Bernhardt et al., 2001
), increased sensitivity to human polymorphonucleocytes (Torosantucci et al., 2002
) and avirulence (Calera et al., 1999
). We now also show that the chk1 mutant is more sensitive to peroxide than parental cells in vitro using drop plate assays. More recently, Kruppa et al. (2004a)
have demonstrated that Chk1p may be a receptor for quorum sensing caused by the autoinducer farnesol. The chk1 mutant is refractory to farnesol in comparison to wild-type cells and the sln1, ssk1 and nik1 two-component mutants whose germination is inhibited by farnesol. This observation indicates a signalling pathway for Chk1p that does not include HOG1 two-component proteins. The Chk1p functions and relationship to the Hog1 pathway are summarized in Fig. 5
. It appears that Chk1p participates indirectly or directly in at least two signal pathways whose activation may depend upon the environmental signal, or Chk1p may be downstream of Hog1p and transcriptionally regulated via the HOG1 MAP kinase pathway.
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ACKNOWLEDGEMENTS |
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REFERENCES |
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Alonso-Monge, R., Navarro-García, F., Molero, G., Diez-Orejas, R., Gustin, M., Pla, J., Sanchez, M. & Nombela, C. (1999). Role of mitogen-activated protein kinase Hog1p in morphogenesis and virulence of Candida albicans. J Bacteriol 181, 30583068.
Alonso-Monge, R., Navarro-García, F., Roman, E., Negredo, A., Eisman, B., Nombela, C. & Pla, J. (2003). The Hog1 MAP kinase is essential in the oxidative stress response and chlamydospore formation in Candida albicans. Eukaryot Cell 2, 351361.
Barrett, J. F. & Hoch, J. (1998). Two-component signal transduction as a target for microbial anti-infective therapy. Antimicrob Agents Chemother 42, 15291536.
Berman, J. & Sudbery, P. E. (2002). Candida albicans: a molecular revolution built on lessons from budding yeast. Nature Rev 3, 918930.
Bernhardt, J., Herman, D., Sheridan, M. & Calderone, R. A. (2001). Adherence and invasion studies of Candida albicans strains utilizing in vitro models of esophageal candidiasis. J Infect Dis 184, 11701175.[CrossRef][Medline]
Bodey, G. P., Buckley, M., Sathe, Y. S. & Freirch, E. J. (1966). Quantitative relationship between circulating leukocytes and infections in patients with acute leukemia. Ann Intern Med 64, 328340.[Medline]
Buck, V., Quinn, J., Pine, T., Martin, H., Saldanka, J., Makino, K., Morgan, B. & Millar, J. B. A. (2001). Peroxide sensors for the fission yeast stress activated mitogen-activated kinase pathway. Mol Cell Biol 12, 407419.
Calderone, R. A. & Fonzi, W. A. (2001). Virulence factors of Candida albicans. Trends Microbiol 9, 327335.[CrossRef][Medline]
Calera, J. A. & Calderone, R. A. (1999a). Flocculation of hyphae is associated with a deletion in the putative CaHK1 two-component histidine kinase gene from Candida albicans. Microbiology 145, 14311442.[Medline]
Calera, J. A. & Calderone, R. A. (1999b). Histidine kinase, two-component signal transduction proteins of Candida albicans and the pathogenesis of candidosis. Mycoses 42, 4953.[CrossRef][Medline]
Calera, J. A., Cho, G. & Calderone, R. A. (1998). Identification of a putative histidine kinase two-component phosphorelay gene (CaCHK1) in Candida albicans. Yeast 14, 665674.[CrossRef][Medline]
Calera, J. A., Zhao, X.-J., Sheridan, M. & Calderone, R. A. (1999). Avirulence of Candida albicans CaHK1 mutants in a murine model of hematogenously disseminated candidiasis. Infect Immun 67, 42804284.
Calera, J. A., Zhao, X.-J. & Calderone, R. A. (2000a). Defective hyphal formation and avirulence caused by a deletion of the CSSK1 response regulator gene in Candida albicans. Infect Immun 68, 518525.
Calera, J. A., Herman, D. & Calderone, R. A. (2000b). Identification of YPD1, a gene of Candida albicans which encodes a two-component phospho-histidine intermediate protein. Yeast 16, 10531059.[CrossRef][Medline]
Chauhan, N., Inglis, D., Roman, E., Pla, J., Li, D., Calera, J. & Calderone, R. A. (2003). Candida albicans response regulator gene SSK1 regulates a subset of genes whose functions are associated with cell wall biosynthesis and adaptation to oxidative stress. Eukaryot Cell 2, 10181024.
Fonzi, W. A. & Irwin, M. Y. (1993). Isogenic strain construction and gene mapping in Candida albicans. Genetics 134, 717728.
Hohmann, S. (2002). Osmotic stress signaling and osmoadaptation in yeasts. Microbiol Mol Biol Rev 66, 300372.
Kapteyn, J. C., Hoyer, L. L., Hecht, J. E., Muller, W. H., Andel, A., Verkleij, A. J., Makarow, M., Van den Ende, H. & Klis, F. M. (2000). The cell wall architecture of Candida albicans wild-type cells and cell wall-deficient mutants. Mol Microbiol 35, 601611.[CrossRef][Medline]
Koretke, K. K., Lupas, A. N., Warren, P. V., Rosenberg, M. & Brown, J. R. (2000). Evolution of two-component signal transduction. Mol Biol Evol 17, 19561970.
Kruppa, M., Goins, T., Cutler, J. E. & 7 other authors (2003). The role of the Candida albicans histidine kinase (CHK1) gene in the regulation of cell wall mannan and glucan biosynthesis. FEMS Yeast Res 3, 289299.[CrossRef][Medline]
Kruppa, M., Krom, B., Chauhan, N., Bambach, A., Cihlar, R. & Calderone, R. (2004a). The two-component signal transduction protein, Chk1p, regulates quorum sensing in Candida albicans. Eukaryot Cell 3, 10621065.
Kruppa, M., Jabra-Rizk, M., Meiller, T. F. & Calderone, R. A. (2004b). The histidine kinases of Candida albicans: regulation of cell wall mannan biosynthesis. FEMS Yeast Res 4, 409416.[CrossRef][Medline]
Lengler, K. B., Davidson, R. C., D'Souza, C., Harashima, T., Shen, W.-C., Wang, P., Pan, X., Waugh, M. & Heitman, J. (2000). Signal transduction cascades regulating fungal development and virulence. Microbiol Mol Biol Rev 64, 746785.
Leuker, C. E., Hahn, A. & Ernst, J. F. (1992). -Galactosidase of Kluyveromyces lactis (Lac4p) as reporter of gene expression in Candida albicans and C. tropicalis. Mol Gen Genet 235, 235241.[CrossRef][Medline]
Li, D., Bernhardt, J. & Calderone, R. (2002). Temporal expression of the Candida albicans genes CHK1 and CSSK1, adherence and morphogenesis in a model of reconstituted human esophageal epithelial candidiasis. Infect Immun 70, 15581565.
Nagahashi, S., Mio, T., Ono, N., Yamada-Okabe, T., Arisawa, M., Bussey, H. & Yamada-Okabe, H. (1998). Isolation of CaSLN1 and CaNIK1, the genes for osmosensing histidine kinase homologues, from the pathogenic fungus Candida albicans. Microbiology 144, 425432.[Medline]
Navarro-Garcia, F., Sanchez, M., Nombela, C. & Pla, J. (2001). Virulence genes in the pathogenic yeast Candida albicans. FEMS Microbiol Rev 25, 245268.[CrossRef][Medline]
Pott, G. B., Miller, T. K., Bartlett, J. A., Palas, J. S. & Selitrennikoff, C. P. (2000). The isolation of FOS-1, a gene encoding a putative two-component histidine kinase from Aspergillus fumigatus. Fungal Genet Biol 31, 5567.[CrossRef][Medline]
Santos, J. L. & Shiozaki, K. (2001). Fungal histidine kinases. Sci Stke 98, RE1.
Selitrennikoff, C. P., Alex, L., Miller, T. K., Clemons, K., Simon, M. I. & Stevens, D. A. (2001). COS-1, a putative two-component histidine kinase of Candida albicans, is an in vivo virulence factor. Med Mycol 39, 6975.[Medline]
Singh, P., Chauhan, N., Ghosh, A., Dixon, F. & Calderone, R. (2004). The SKN7 of Candida albicans: mutant construction and phenotype analysis. Infect Immun 72, 23902394.
Srikantha, T. (1996). The sea pansy Renilla reniformis luciferase serves as a sensitive bioluminescent reporter for differential gene expression in Candida albicans. J Bacteriol 178, 121129.[Abstract]
Srikantha, T., Tsai, L., Daniels, K., Enger, L., Highley, K. & Soll, D. R. (1998). The two-component hybrid kinase regulator CaNIK1 of Candida albicans. Microbiology 144, 27152729.[Medline]
Torosantucci, A., Chiani, P., DeBernardis, F., Cassone, A., Calera, J. A. & Calderone, R. A. (2002). Deletion of the two-component histidine kinase gene (CHK1) of Candida albicans contributes to enhanced growth inhibition and killing by human neutrophils in vitro. Infect Immun 70, 985987.
Uhl, M. A. & Johnson, A. D. (2001). Development of Streptococcus thermophilus lacZ as a reporter gene for Candida albicans. Microbiology 147, 11891195.[Medline]
Wenzel, R. P. (1995). Nosocomial candidiasis: risk factors and attributable mortality. Clin Infect Dis 20, 15311534.[Medline]
Yamada-Okabe, T., Mio, T., Ono, N., Kashima, Y., Matsui, M., Arisawa, M. & Yamada-Okabe, H. (1999). Roles of three histidine kinase genes in hyphal development and virulence of the pathogenic fungus, Candida albicans. J Bacteriol 181, 72437247.
Received 14 April 2004;
revised 2 July 2004;
accepted 14 July 2004.
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