Search tips
Search criteria

Results 1-21 (21)

Clipboard (0)

Select a Filter Below

more »
Year of Publication
more »
1.  Two-Component Histidine Phosphotransfer Protein Ypd1 Is Not Essential for Viability in Candida albicans 
Eukaryotic Cell  2014;13(4):452-460.
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 ypd1Δ/Δ and wild-type strains of C. albicans. Constitutive phosphorylation of Hog1 was observed in the ypd1Δ/Δ 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.
PMCID: PMC4000104  PMID: 24489039
2.  MicroRNA-145 targets MUC13 and suppresses growth and invasion of pancreatic cancer 
Oncotarget  2014;5(17):7599-7609.
Pancreatic cancer has a poor prognosis due to late diagnosis and ineffective therapeutic multimodality. MUC13, a transmembrane mucin is highly involved in pancreatic cancer progression. Thus, understanding its regulatory molecular mechanisms may offer new avenue of therapy for prevention/treatment of pancreatic cancer. Herein, we report a novel microRNA (miR-145)-mediated mechanism regulating aberrant MUC13 expression in pancreatic cancer. We report that miR-145 expression inversely correlates with MUC13 expression in pancreatic cancer cells and human tumor tissues. miR-145 is predominantly present in normal pancreatic tissues and early Pancreatic Ductal Adenocarcinoma (PDAC) precursor lesions (PanIN I) and is progressively suppressed over the course of development from PanIN II/III to late stage poorly differentiated PDAC. We demonstrate that miR-145 targets 3′ untranslated region of MUC13 and thus downregulates MUC13 protein expression in cells. Interestingly, transfection of miR-145 inhibits cell proliferation, invasion and enhances gemcitabine sensitivity. It causes reduction of HER2, P-AKT, PAK1 and an increase in p53. Similar results were found when MUC13 was specifically inhibited by shRNA directed at MUC13. Additionally, intratumoral injections of miR-145 in xenograft mice inhibited tumor growth via suppression of MUC13 and its downstream target, HER2. These results suggest miR-145 as a novel regulator of MUC13 in pancreatic cancer.
PMCID: PMC4202147  PMID: 25277192
Pancreatic cancer; MUC13; MicroRNA; Tumor suppressor; Diagnostics; Therapeutics
3.  Novel Curcumin Loaded Magnetic Nanoparticles for Pancreatic Cancer Treatment 
Molecular cancer therapeutics  2013;12(8):1471-1480.
Curcumin (CUR), a naturally occurring polyphenol derived from the root of Curcuma longa, has demonstrated potent anti-cancer and cancer prevention activity in a variety of cancers. However, the clinical translation of curcumin has been significantly hampered due to its extensive degradation, suboptimal pharmacokinetics and poor bioavailability. To address these clinically relevant issues, we have developed a novel curcumin loaded magnetic nanoparticle (MNP-CUR) formulation. Herein, we have evaluated the in vitro and in vivo therapeutic efficacy of this novel MNP-CUR formulation in pancreatic cancer. Human pancreatic cancer cells (HPAF-II and Panc-1) exhibited efficient internalization of the MNP-CUR formulation in a dose dependent manner. As a result, the MNP-CUR formulation effectively inhibited growth of HPAF-II and Panc-1 cells in cell proliferation and colony formation assays. The MNP-CUR formulation suppressed pancreatic tumor growth in an HPAF-II xenograft mice model and improved mice survival by delaying tumor growth. The growth inhibitory effect of MNP-CUR formulation was correlated with the suppression of PCNA, Bcl-xL, Mcl-1, MUC1, Collagen I and enhanced membrane β-catenin expression. MNP-CUR formulation did not show any sign of hemotoxicity and was stable after incubation with human serum proteins. Additionally, the MNP-CUR formulation improved serum bioavailability of curcumin in mice up to 2.5 fold as compared to free curcumin. Biodistribution studies demonstrate that a significant amount of MNP-CUR formulation was able to reach the pancreatic xenograft tumor(s) which suggests its clinical translational potential. In conclusion, this study suggests that our novel MNP-CUR formulation can be valuable for the treatment of pancreatic cancer.
PMCID: PMC3965353  PMID: 23704793
magnetic nanoparticles; curcumin; chemoprevention; pancreatic cancer; nanomedicine
4.  Role of Novel Multidrug Efflux Pump Involved in Drug Resistance in Klebsiella pneumoniae 
PLoS ONE  2014;9(5):e96288.
Multidrug resistant Klebsiella pneumoniae have caused major therapeutic problems worldwide due to the emergence of the extended-spectrum β-lactamase producing strains. Although there are >10 major facilitator super family (MFS) efflux pumps annotated in the genome sequence of the K. pneumoniae bacillus, apparently less is known about their physiological relevance.
Principal Findings
Insertional inactivation of kpnGH resulting in increased susceptibility to antibiotics such as azithromycin, ceftazidime, ciprofloxacin, ertapenem, erythromycin, gentamicin, imipenem, ticarcillin, norfloxacin, polymyxin-B, piperacillin, spectinomycin, tobramycin and streptomycin, including dyes and detergents such as ethidium bromide, acriflavine, deoxycholate, sodium dodecyl sulphate, and disinfectants benzalkonium chloride, chlorhexidine and triclosan signifies the wide substrate specificity of the transporter in K. pneumoniae. Growth inactivation and direct fluorimetric efflux assays provide evidence that kpnGH mediates antimicrobial resistance by active extrusion in K. pneumoniae. The kpnGH isogenic mutant displayed decreased tolerance to cell envelope stressors emphasizing its added role in K. pneumoniae physiology.
Conclusions and Significance
The MFS efflux pump KpnGH involves in crucial physiological functions besides being an intrinsic resistance determinant in K. pneumoniae.
PMCID: PMC4019481  PMID: 24823362
5.  Mitochondrial Two-Component Signaling Systems in Candida albicans 
Eukaryotic Cell  2013;12(6):913-922.
Two-component signal transduction pathways are one of the primary means by which microorganisms respond to environmental signals. These signaling cascades originated in prokaryotes and were inherited by eukaryotes via endosymbiotic lateral gene transfer from ancestral cyanobacteria. We report here that the nuclear genome of the pathogenic fungus Candida albicans contains elements of a two-component signaling pathway that seem to be targeted to the mitochondria. The C. albicans two-component response regulator protein Srr1 (stress response regulator 1) contains a mitochondrial targeting sequence at the N terminus, and fluorescence microscopy reveals mitochondrial localization of green fluorescent protein-tagged Srr1. Moreover, phylogenetic analysis indicates that C. albicans Srr1 is more closely related to histidine kinases and response regulators found in marine bacteria than are other two-component proteins present in the fungi. These data suggest conservation of this protein during the evolutionary transition from endosymbiont to a subcellular organelle. We used microarray analysis to determine whether the phenotypes observed with a srr1Δ/Δ mutant could be correlated with gene transcriptional changes. The expression of mitochondrial genes was altered in the srr1Δ/Δ null mutant in comparison to their expression in the wild type. Furthermore, apoptosis increased significantly in the srr1Δ/Δ mutant strain compared to the level of apoptosis in the wild type, suggesting the activation of a mitochondrion-dependent apoptotic cell death pathway in the srr1Δ/Δ mutant. Collectively, this study shows for the first time that a lower eukaryote like C. albicans possesses a two-component response regulator protein that has survived in mitochondria and regulates a subset of genes whose functions are associated with the oxidative stress response and programmed cell death (apoptosis).
PMCID: PMC3675996  PMID: 23584995
6.  Adhesins in Human Fungal Pathogens: Glue with Plenty of Stick 
Eukaryotic Cell  2013;12(4):470-481.
Understanding the pathogenesis of an infectious disease is critical for developing new methods to prevent infection and diagnose or cure disease. Adherence of microorganisms to host tissue is a prerequisite for tissue invasion and infection. Fungal cell wall adhesins involved in adherence to host tissue or abiotic medical devices are critical for colonization leading to invasion and damage of host tissue. Here, with a main focus on pathogenic Candida species, we summarize recent progress made in the field of adhesins in human fungal pathogens and underscore the importance of these proteins in establishment of fungal diseases.
PMCID: PMC3623432  PMID: 23397570
7.  Candida glabrata Pwp7p and Aed1p are required for Adherence to Human Endothelial Cells 
FEMS yeast research  2011;11(7):595-601.
Candida glabrata owes its success as a pathogen, in part, to a large repertoire of adhesins present on the cell surface. Our current knowledge of C. glabrata adhesins and their role in the interaction between host and pathogen is limited to work with only a single family of epithelial adhesins (Epa proteins). Here we report identification and characterization of a family of glycosylphosphatidylinositol (GPI) anchored cell wall proteins in C. glabrata. These proteins are absent in both S. cerevisiae and C. albicans suggesting that C. glabrata has evolved different mechanism(s) for interaction with host cells. In the current study we present data on the characterization of Pwp7p (PA14 domain containing Wall Protein) and Aed1p (Adherence to Endothelial cells) of this family in the interaction of C. glabrata with Human Umbilical Vein Endothelial Cells (HUVECs). Deletion of C. glabrata genes PWP7 and AED1 results in significant reduction in adherence to endothelial cells compared to the wild type parent. These data indicate that C. glabrata utilizes these proteins for adherence to endothelial cells in vitro. This also represents the first evidence that C. glabrata utilizes adhesins other than Epa proteins.
PMCID: PMC3202042  PMID: 21726406
Candida; GPI; adhesin; PWP7; AED1; AED2
9.  Curcumin-loaded magnetic nanoparticles for breast cancer therapeutics and imaging applications 
The next generation magnetic nanoparticles (MNPs) with theranostic applications have attracted significant attention and will greatly improve nanomedicine in cancer therapeutics. Such novel MNP formulations must have ultra-low particle size, high inherent magnetic properties, effective imaging, drug targeting, and drug delivery properties. To achieve these characteristic properties, a curcumin-loaded MNP (MNP-CUR) formulation was developed.
MNPs were prepared by chemical precipitation method and loaded with curcumin (CUR) using diffusion method. The physicochemical properties of MNP-CUR were characterized using dynamic light scattering, transmission electron microscopy, and spectroscopy. The internalization of MNP-CUR was achieved after 6 hours incubation with MDA-MB-231 breast cancer cells. The anticancer potential was evaluated by a tetrazolium-based dye and colony formation assays. Further, to prove MNP-CUR results in superior therapeutic effects over CUR, the mitochondrial membrane potential integrity and reactive oxygen species generation were determined. Magnetic resonance imaging capability and magnetic targeting property were also evaluated.
MNP-CUR exhibited individual particle grain size of ~9 nm and hydrodynamic average aggregative particle size of ~123 nm. Internalized MNP-CUR showed a preferential uptake in MDA-MB-231 cells in a concentration-dependent manner and demonstrated accumulation throughout the cell, which indicates that particles are not attached on the cell surface but internalized through endocytosis. MNP-CUR displayed strong anticancer properties compared to free CUR. MNP-CUR also amplified loss of potential integrity and generation of reactive oxygen species upon treatment compared to free CUR. Furthermore, MNP-CUR exhibited superior magnetic resonance imaging characteristics and significantly increased the targeting capability of CUR.
MNP-CUR exhibits potent anticancer activity along with imaging and magnetic targeting capabilities. This approach can be extended to preclinical and clinical use and may have importance in cancer treatment and cancer imaging in the future. Further, if these nanoparticles can functionalize with antibody/ligands, they will serve as novel platforms for multiple biomedical applications.
PMCID: PMC3356199  PMID: 22619526
magnetic nanoparticles; drug delivery systems; magnetic resonance imaging; nanomedicine; cancer therapeutics; biomedical applications
10.  Candida albicans SRR1, a Putative Two-Component Response Regulator Gene, Is Required for Stress Adaptation, Morphogenesis, and Virulence▿† 
Eukaryotic Cell  2011;10(10):1370-1374.
We report here the identification and characterization of a previously uncharacterized, two-component response regulator gene (orf19.5843) from Candida albicans. Because of its apparent functions in stress adaptation, we have named this gene SRR1 (stress response regulator 1). Disruption of SRR1 causes defects in hyphal development, reduced resistance to stress, and severe virulence attenuation in the mouse model of disseminated candidiasis.
PMCID: PMC3187061  PMID: 21841121
11.  Loss of CD127 & increased immunosenescence of T cell subsets in HIV infected individuals 
Background & objectives:
HIV infection is characterized by a perturbation in T cell homeostasis, leading to alteration in T cell subsets. In addition to alteration in differentiation, HIV infection also leads to change in T cell survival and regenerative capacity, as suggested by differential expression of CD127 and CD57. We evaluated the expression patterns of CD127 and CD57 on CD4 and CD8 effector, memory and naïve T cell subsets in HIV-infected and uninfected individuals.
We characterized T cell subsets based on expression of these markers, and compared their expression pattern in HIV infected subjects and uninfected controls. We further assessed therapy generated changes in these subsets and expression of CD127 and CD57 on them.
There was a generalized decrease in naïve CD4 and CD8 T cells in HIV infected subjects. These changes in T cell subset distribution were related to antigen load. CD127 expression was significantly reduced in T cells from HIV infected subject. In association to this, HIV infected subjects had higher percentage of T cell subsets expressing CD57. Increased CD57 and reduced CD127 expression correlated with plasma viraemia and CD8 T cell activation state. Incomplete restoration of T cell subset proportions was observed, despite suppression of viral replication and increase in CD4 T cell counts. Further, the improvement was more pronounced in CD127 expression.
Interpretation & conclusions:
HIV infected subjects have reduced T cell regenerative capacity along with increased senescence, highlighting decreased proliferation and effector activities.
PMCID: PMC3284107  PMID: 22310831
CD57; CD127; HIV-1 viral load; T cell activation; T cell subset
12.  Interaction of curcumin nanoformulations with human plasma proteins and erythrocytes 
Recent studies report curcumin nanoformulation(s) based on polylactic-co-glycolic acid (PLGA), β-cyclodextrin, cellulose, nanogel, and dendrimers to have anticancer potential. However, no comparative data are currently available for the interaction of curcumin nanoformulations with blood proteins and erythrocytes. The objective of this study was to examine the interaction of curcumin nanoformulations with cancer cells, serum proteins, and human red blood cells, and to assess their potential application for in vivo preclinical and clinical studies.
The cellular uptake of curcumin nanoformulations was assessed by measuring curcumin levels in cancer cells using ultraviolet-visible spectrophotometry. Protein interaction studies were conducted using particle size analysis, zeta potential, and Western blot techniques. Curcumin nanoformulations were incubated with human red blood cells to evaluate their acute toxicity and hemocompatibility.
Cellular uptake of curcumin nanoformulations by cancer cells demonstrated preferential uptake versus free curcumin. Particle sizes and zeta potentials of curucumin nanoformulations were varied after human serum albumin adsorption. A remarkable capacity of the dendrimer curcumin nanoformulation to bind to plasma protein was observed, while the other formulations showed minimal binding capacity. Dendrimer curcumin nanoformulations also showed higher toxicity to red blood cells compared with the other curcumin nanoformulations.
PLGA and nanogel curcumin nanoformulations appear to be very compatible with erythrocytes and have low serum protein binding characteristics, which suggests that they may be suitable for application in the treatment of malignancy. These findings advance our understanding of the characteristics of curcumin nanoformulations, a necessary component in harnessing and implementing improved in vivo effects of curcumin.
Video abstract
PMCID: PMC3225220  PMID: 22128249
nanoparticle; curcumin; chemotherapy; cellular uptake; protein binding; hemocompatibility
13.  Late presenters to HIV care and treatment, identification of associated risk factors in HIV-1 infected Indian population 
BMC Public Health  2010;10:416.
Timely access to antiretroviral therapy is a key to controlling HIV infection. Late diagnosis and presentation to care diminish the benefits of antiretrovirals and increase risk of transmission. We aimed to identify late presenters in patients sent for first CD4 T cell count after HIV diagnosis, for therapy initiation evaluation. Further we aimed at identifying patient factors associated with higher risk of late presentation.
Retrospective data collection and analysis was done for 3680 subjects visiting the laboratory for CD4 T cell counts between 2001 and 2007. We segregated the patients on basis of their CD4 T cell counts after first HIV diagnosis. Factors associated with risk of late presentation to CD4 T cell counts after HIV diagnosis were identified using univariate analysis, and the strength of association of individual factor was assessed by calculation of odds ratios.
Of 3680 subjects, 2936 (83.37%) were defined as late presenters. Late testing varied among age groups, transmission categories, and gender. Males were twice as likely to present late as compared to females. We found significant positive association of heterosexual transmission route (p < 0.001), and older age groups of 45 years and above (p = 0.0004) to late presentation. Female sex, children below 14 years of age and sexual contact with HIV positive spouse were associated with significantly lower risks to presenting late. Intravenous drug users were also associated with lower risks of late presentation, in comparison to heterosexual transmission route.
The study identifies HIV infected population groups at a higher risk of late presentation to care and treatment. The risk factors identified to be associated with late presentation should be utilised in formulating targeted public health interventions in order to improve early HIV diagnosis.
PMCID: PMC2912818  PMID: 20626905
14.  Goa1p of Candida albicans Localizes to the Mitochondria during Stress and Is Required for Mitochondrial Function and Virulence▿ †  
Eukaryotic Cell  2009;8(11):1706-1720.
Using a Tn7 transposon library of Candida albicans, we have identified a mutant that exhibited sensitivity in drop plate assays to oxidants such as menadione and hydrogen peroxide. To verify the role of the mutated gene in stress adaptation, null mutants were constructed and phenotypically characterized. Because of its apparent functions in growth and oxidant adaptation, we have named the gene GOA1. Goa1p appears to be unique to the CTG subclade of the Saccharomycotina, including C. albicans. Mutants of C. albicans lacking goa1 (strain GOA31) were more sensitive to 6 mM H2O2 and 0.125 mM menadione than the wild type (wt) or a gene-reconstituted (GOA32) strain. The sensitivity to oxidants correlated with reduced survival of the GOA31 mutant in human neutrophils and avirulence compared to control strains. Other phenotypes of GOA31 include reduced growth and filamentation in 10% serum, Spider, and SLAD agar media and an inability to form chlamydospores. Since Goa1p has an N-terminal mitochondrion localization site, we also show that green fluorescent protein-tagged Goa1p shows a mitochondrionlike distribution during oxidant or osmotic stress. Further, the inability of GOA31 to grow in medium containing lactate, ethanol, or glycerol as the sole carbon source indicates that the mitochondria are defective in the mutant. To determine how Goa1p contributes to mitochondrial function, we compared the wt, GOA32, and GOA31 strains for mitochondrial electrical membrane potential, respiration, and oxidative phosphorylation. We now show that GOA31, but not the wt or GOA32, had decreased respiration and mitochondrial membrane potential such that mutant cells are unable to drive oxidative phosphorylation. This is the first report in C. albicans of a respiratory defect caused by a loss of mitochondrial membrane potential.
PMCID: PMC2772395  PMID: 19717740
15.  Transcriptional profiling of the Candida albicans Ssk1p receiver domain point mutants and their virulence 
FEMS yeast research  2008;8(5):756-763.
The Ssk1p response regulator of Candida albicans is required for oxidant adaptation, survival in human neutrophils, and virulence in a disseminated murine model of candidiasis. The activities of the Ssk1p are signaled through the HOG1 MAP kinase pathway (HOG=hyperosmotic glycerol). Further, we have previously shown that the amino acid residues D556 and D513 of the Ssk1p receiver domain are critical to the activities of the Ssk1p in oxidant stress adaptation and morphogenesis. Herein, we use transcriptional profiling to explain the oxidant sensitivity and defect in morphogenesis of two point mutants (D556N and D513K, respectively) compared to a WT strain. In the D556N mutant compared to WT cells during oxidative stress (5mM H2O2), a down regulation of genes associated with redox homeostasis and oxidative stress occurred that accounted for about 5% of all gene changes, including among others, SOD1 (superoxide dismutase), CAP1 (transcription factor required for some forms of oxidant adaptation), and three genes encoding glutathione biosynthesis proteins (GLR1, GSH1, and GSH2). Mutant SSK26 (D513K) was not sensitive to peroxide but was impaired in its yeast to hyphal transition. We noted down regulation of genes associated with morphogenesis and cell elongation. Virulence of each mutant was also evaluated in a rat vaginitis model of candidiasis. Clearance of the SSK1 null mutant (strain SSK21) and SSK25 from the vaginal canal was significantly greater than wild type (CAF2-1) or the D513K mutant (D513K), indicating that a specific change in a single amino acid of the Ssk1p may alter the ability of this strain to colonize the rat vaginal mucosa.
PMCID: PMC2576740  PMID: 18616606
response regulator; two-component proteins; point mutants
17.  The Ssk1p Response Regulator and Chk1p Histidine Kinase Mutants of Candida albicans Are Hypersensitive to Fluconazole and Voriconazole▿  
Antimicrobial Agents and Chemotherapy  2007;51(10):3747-3751.
Hypersensitivity to the triazoles fluconazole and voriconazole associated with two-component signal transduction proteins has not been reported in Candida albicans. Herein, we show that strains of C. albicans lacking the response regulator Ssk1p or the Chk1p histidine kinase signal transduction proteins are hypersensitive to fluconazole and voriconazole compared to wild-type (wt) as well as gene-reconstituted strains, reflecting an increased hypersensitivity to these drugs of about 16- to 500-fold. In comparison to wt cells, both mutants had elevated levels of fluconazole accumulation and reduced viability upon incubation with either drug, suggesting that in the absence of Ssk1p or Chk1p, fluconazole and voriconazole have significantly increased fungicidal effects on C. albicans.
PMCID: PMC2043284  PMID: 17664325
18.  Virulence and Karyotype Analyses of rad52 Mutants of Candida albicans: Regeneration of a Truncated Chromosome of a Reintegrant Strain (rad52/RAD52) in the Host 
Infection and Immunity  2005;73(12):8069-8078.
The virulence of Candida albicans mutants lacking one or both copies of RAD52, a gene involved in homologous recombination (HR), was evaluated in a murine model of hematogenously disseminated candidiasis. In this study, the virulence of the rad52Δ mutant was dependent upon the inoculum concentration. Mice survived at a cell inoculum of 1 × 106, but there was a decrease in survival time at dosages of 1.5 × 106 and especially at 3 × 106 cells per animal. The heterozygote RAD52/rad52 behaved like wild type, whereas a reintegrant strain was intermediate in its ability to cause death compared to these strains and to the avirulent rad52/rad52 null at inocula of 1 × 106 and 1.5 × 106 cells. A double mutant, lig4/lig4/rad52/rad52, was avirulent at all inocula used. PCR analysis of the RAD52 and/or LIG4 loci showed that all strains recovered from animals matched the genotype of the inoculated strains. Analysis of the electrophoretical karyotypes indicated that the inoculated, reintegrant strain carried a large deletion in one copy of chromosome 6 (the shortest homologue, or Chr6b). Interestingly, truncated Chr6b was regenerated in all the strains recovered from moribund animals using the homologue as a template. Further, regeneration of Chr6b was paralleled by an increase in virulence that was still lower than that of wild type, likely because of the persistent loss of heterozygosity in the regenerated region. Overall, our results indicate that systemic candidiasis can develop in the absence of HR, but simultaneous elimination of both recombination pathways, HR and nonhomologous end-joining, suppresses virulence even at very high inocula.
PMCID: PMC1307084  PMID: 16299301
19.  The Two-Component Signal Transduction Protein Chk1p Regulates Quorum Sensing in Candida albicans 
Eukaryotic Cell  2004;3(4):1062-1065.
Regulation of hyphal morphogenesis in Candida albicans can occur through quorum sensing (QS). A QS signal, farnesol, is produced during high-density growth and inhibits morphogenesis. However, the signal transduction pathway that regulates QS is unknown. Here, we show that a C. albicans mutant lacking Chk1p but not either the Sln1p or the Nik1p histidine kinase is refractory to the inhibitory effect of farnesol both in cell suspension and during the formation of a biofilm. This study is the first to demonstrate a role for a two-component signal transduction protein in QS by a eukaryotic organism.
PMCID: PMC500889  PMID: 15302838
20.  SKN7 of Candida albicans: Mutant Construction and Phenotype Analysis  
Infection and Immunity  2004;72(4):2390-2394.
The SKN7 two-component response regulator gene of Candida albicans was deleted, and the phenotype of the mutant was established. This mutant exhibited impaired growth on Spider agar and 10% serum agar compared to wild-type and gene-reconstituted strains. The skn7 mutant was sensitive to H2O2 in vitro, but its virulence was only mildly attenuated. A comparison of the Skn7p and Ssk1p response regulators of C. albicans is discussed.
PMCID: PMC375215  PMID: 15039366
21.  Candida albicans Response Regulator Gene SSK1 Regulates a Subset of Genes Whose Functions Are Associated with Cell Wall Biosynthesis and Adaptation to Oxidative Stress 
Eukaryotic Cell  2003;2(5):1018-1024.
Ssk1p of Candida albicans is a putative response regulator protein of the Hog1 two-component signal transduction system. In Saccharomyces cerevisiae, the phosphorylation state of Ssk1p determines whether genes that promote the adaptation of cells to osmotic stress are activated. We have previously shown that C. albicans SSK1 does not complement the ssk1 mutant of S. cerevisiae and that the ssk1 mutant of C. albicans is not sensitive to sorbitol. In this study, we show that the C. albicans ssk1 mutant is sensitive to several oxidants, including hydrogen peroxide, t-butyl hydroperoxide, menadione, and potassium superoxide when each is incorporated in yeast extract-peptone-dextrose (YPD) agar medium. We used DNA microarrays to identify genes whose regulation is affected by the ssk1 mutation. RNA from mutant cells (strain CSSK21) grown in YPD medium for 3 h at 30°C was reverse transcribed and then compared with similarly prepared RNA from wild-type cells (CAF2). We observed seven genes from mutant cells that were consistently up regulated (three-fold or greater compared to CAF2). In S. cerevisiae, three (AHP1, HSP12, and PYC2) of the seven genes that were up regulated provide cells with an adaptation function in response to oxidative stress; another gene (GPH1) is regulated under stress conditions by Hog1p. Three other genes that are up regulated encode a cell surface protein (FLO1), a mannosyl transferase (MNN4-4), and a putative two-component histidine kinase (CHK1) that regulates cell wall biosynthesis in C. albicans. Of the down-regulated genes, ALS1 is a known cell adhesin in C. albicans. Verification of the microarray data was obtained by reverse transcription-PCR for HSP12, AHP1, CHK1, PYC2, GPH1, ALS1, MNN4-4, and FLO1. To further determine the function of Ssk1p in the Hog1p signal transduction pathway in C. albicans, we used Western blot analysis to measure phosphorylation of Hog1p in the ssk1 mutant of C. albicans when grown under either osmotic or oxidative stress. We observed that Hog1p was phosphorylated in the ssk1 mutant of C. albicans when grown in a hyperosmotic medium but was not phosphorylated in the ssk1 mutant when the latter was grown in the presence of hydrogen peroxide. These data indicate that C. albicans utilizes the Ssk1p response regulator protein to adapt cells to oxidative stress, while its role in the adaptation to osmotic stress is less certain. Further, SSK1 appears to have a regulatory function in some aspects of cell wall biosynthesis. Thus, the functions of C. albicans SSK1 differ from those of S. cerevisiae SSK1.
PMCID: PMC219380  PMID: 14555484

Results 1-21 (21)