scholarly journals A role for complement receptor-like molecules in iron acquisition by Candida albicans.

1992 ◽  
Vol 175 (6) ◽  
pp. 1643-1651 ◽  
Author(s):  
M A Moors ◽  
T L Stull ◽  
K J Blank ◽  
H R Buckley ◽  
D M Mosser
Keyword(s):  
Candida Albicans ◽  
Human Serum ◽  
Iron Acquisition ◽  
Alternative Pathway ◽  
Protoporphyrin Ix ◽  
Surface Proteins ◽  
Pathogenic Potential ◽  
Opportunistic Fungal Pathogen ◽  
Iron Binding Proteins ◽  
Type 3

Candida albicans, an opportunistic fungal pathogen of humans, is dependent upon iron for growth. Consequently, human serum inhibits C. albicans growth due to the presence of high affinity iron-binding proteins that sequester serum iron, making it unavailable for use by the organism. We report that in the inhibitory environment of human serum, the growth of C. albicans can be restored by the addition of exogenous hemoglobin or heme, but not by protoporphyrin IX, the heme precursor that does not contain iron. We further report that C. albicans can utilize cell surface proteins that are homologues of the mammalian complement receptors (CR) to rosette complement-coated red blood cells (RBC) and obtain RBC-derived iron for growth. The ability of Candida to acquire RBC-derived iron under these conditions is dependent upon Candida-RBC rosetting mediated by CR-like molecules. Unopsonized RBC do not support Candida growth in serum, and restoration of Candida growth in serum by complement-opsonized RBC is inhibited by monoclonal antibodies to the human CR type 3 (CR3). In addition, activation of the human alternative pathway of complement by Candida leads to "bystander" deposition of C3 fragments on the surface of autologous, unopsonized RBC, generating the ligands necessary for Candida-RBC rosetting. These results suggest that C. albicans has evolved a unique strategy for acquiring iron from the host, which exploits the host complement system, and which may contribute to the pathogenic potential of the organism.

scholarly journals Deposition of C3b and iC3b onto particulate activators of the human complement system. Quantitation with monoclonal antibodies to human C3.

1985 ◽  
Vol 161 (6) ◽  
pp. 1414-1431 ◽  
Author(s):  
S L Newman ◽  
L K Mikus
Keyword(s):  
Monoclonal Antibodies ◽  
Serum Concentration ◽  
Human Serum ◽  
Molecular Form ◽  
Alternative Pathway ◽  
Classical Pathway ◽  
Sds Page ◽  
Predominant Form ◽  
Hemophilus Influenzae Type B ◽  
Type 3

Monoclonal antibodies were used to determine the number and molecular form of C3 bound to particulate activators of the complement (C) system by human serum. Sheep erythrocytes (E) coated with IgM (EIgM) and IgG (EIgG) were used to study activation of the classical pathway (CP). Yeast (Y), rabbit erythrocytes (ER), and five species of bacteria (Escherichia coli, Staphylococcus aureus, Streptococcus pneumoniae type 3, Streptococcus pyogenes, and Hemophilus influenzae type b) were used to study activation of the alternative pathway (AP). The deposition of C3b onto EIgM and EIgG incubated in C7-deficient human serum was dependent on the serum concentration. At all serum concentrations tested, there was complete conversion of C3b to iC3b. Kinetic analysis of C3b deposition and conversion to iC3b indicated that these events occurred almost simultaneously; the reaction was completed by 15 min. The deposition of C3 onto the AP activators ER and Y was also dependent on serum concentration, and ER, but not Y, required the presence of Mg-EGTA and thus the activation of only the AP. C3b deposition and conversion to iC3b on Y was complete in 15 min, with 82% of bound C3 converted to iC3b. For ER, maximum C3 deposition required 30 min in both the presence and absence of Mg-EGTA. However, after 1 h of incubation, 74% of bound C2 was iC3b in the absence of Mg-EGTA, compared with only 52% in the presence of Mg-EGTA. Thus, even on AP activators, a large portion of C3b may be converted to iC3b, and this conversion is probably controlled by elements on the particle's surface. Studies with the five species of bacteria yielded similar results. Approximately 3-5 X 10(4) molecules of C3 were bound per microorganism, with opsonization being completed in 30 min. Remarkably, only 16-28% of bound C3 was in the form of iC3b, even after 2 h of incubation. The presence or absence of Mg-EGTA, or the addition of purified CR1 to the reaction mixture, did not significantly effect the ratio of C3b to iC3b. Finally, SDS-PAGE and autoradiography of particle-bound 125I-C3 fragments confirmed that there was no conversion of iC3b to C3d,g or C3d. The data obtained about the opsonization of bacteria suggest that the predominant form of C3 that is encountered by inflammatory phagocytes may be C3b.

scholarly journals Cloning and Characterization of PRA1, a Gene Encoding a Novel pH-Regulated Antigen of Candida albicans

1998 ◽  
Vol 180 (2) ◽  
pp. 282-289 ◽  
Author(s):  
Maria Sentandreu ◽  
M. Victoria Elorza ◽  
Rafael Sentandreu ◽  
William A. Fonzi
Keyword(s):  
Cell Wall ◽  
Candida Albicans ◽  
Immunoblot Analysis ◽  
Surface Proteins ◽  
Cell Fractionation ◽  
Expression Library ◽  
Gene Encoding ◽  
Genes Encoding ◽  
Surface Localization ◽  
Opportunistic Fungal Pathogen

ABSTRACT Candida albicans is an opportunistic fungal pathogen of humans. The cell wall of the organism defines the interface between the pathogen and host tissues and is likely to play an essential and pivotal role in the host-pathogen interaction. The components of the cell wall critical to this interaction are undefined. Immunoscreening of a lambda expression library with sera raised against mycelial cell walls of C. albicans was used to identify genes encoding cell surface proteins. One of the positive clones represented a candidal gene that was differentially expressed in response to changes in the pH of the culture medium. Maximal expression occurred at neutral pH, with no expression detected below pH 6.0. On the basis of the expression pattern, the corresponding gene was designatedPRA1, for pH-regulated antigen. The protein predicted from the nucleotide sequence was 299 amino acids long with motifs characteristic of secreted glycoproteins. The predicted surface localization and N glycosylation of the protein were directly demonstrated by cell fractionation and immunoblot analysis. Deletion of the gene imparted a temperature-dependent defect in hypha formation, indicating a role in morphogenesis. The PRA1 protein was homologous to surface antigens of Aspergillus spp. which react with serum from aspergillosis patients, suggesting that thePRA1 protein may have a role in the host-parasite interaction during candidal infection.

scholarly journals Mannan-Specific Immunoglobulin G Antibodies in Normal Human Serum Accelerate Binding of C3 to Candida albicans via the Alternative Complement Pathway

1998 ◽  
Vol 66 (10) ◽  
pp. 4845-4850 ◽  
Author(s):  
Mason X. Zhang ◽  
Thomas R. Kozel
Keyword(s):  
Candida Albicans ◽  
Human Serum ◽  
Immunoglobulin G ◽  
Alternative Pathway ◽  
Normal Human Serum ◽  
Yeast Cells ◽  
Classical Pathway ◽  
Intact Antibody ◽  
Alternative Complement ◽  
Normal Human

ABSTRACT Candida albicans activates the classical and alternative complement pathways, leading to deposition of opsonic complement fragments on the cell surface. Our previous studies found that antimannan immunoglobulin G (IgG) in normal human serum (NHS) allows C. albicans to initiate the classical pathway. The purpose of this study was to determine whether antimannan IgG also plays a role in initiation of the alternative pathway. Pooled NHS was rendered free of classical pathway activity by chelation of serum Ca2+ with EGTA alone or in combination with immunoaffinity removal of antimannan antibodies. Kinetic analysis revealed a 6-min lag in detection of C3 binding to C. albicans incubated in EGTA-chelated NHS, compared to a 12-min lag in NHS that was both EGTA chelated and mannan absorbed. The 12-min lag was shortened to 6 min by addition of affinity-purified antimannan IgG. The accelerating effect of antimannan IgG on alternative pathway initiation was dose dependent and was reproduced in a complement binding reaction consisting of six purified proteins of the alternative pathway. Both Fab and F(ab′)2 fragments of antimannan IgG facilitated alternative pathway initiation in a manner similar to that observed with intact antibody. Immunofluorescence analysis showed that addition of antimannan IgG to EGTA-chelated and mannan-absorbed serum promoted an early deposition of C3 molecules on the yeast cells but had little or no effect on distribution of the cellular sites for C3 activation. Thus, antimannan IgG antibodies play an important regulatory role in interactions between the host complement system and C. albicans.

scholarly journals Serum Stimulates Growth of and Proteinase Secretion by Aspergillus fumigatus

2002 ◽  
Vol 70 (1) ◽  
pp. 19-26 ◽  
Author(s):  
Anna H. T. Gifford ◽  
Jodine R. Klippenstein ◽  
Margo M. Moore
Keyword(s):  
Aspergillus Fumigatus ◽  
Human Serum ◽  
Bovine Serum ◽  
Protein Concentration ◽  
Fold Increase ◽  
Dry Weight ◽  
Nutritional Factors ◽  
Fetal Bovine ◽  
Opportunistic Fungal Pathogen ◽  
Iron Binding Proteins

ABSTRACT Serum contains iron-binding proteins, which inhibit the growth of most pathogenic microorganisms, including fungi. The purpose of this research was to investigate the effect of serum on growth of the opportunistic fungal pathogen Aspergillus fumigatus. Supplementing minimal essential medium (MEM) with up to 80% human serum or up to 80% fetal bovine serum (FBS) stimulated growth and increased the amount of A. fumigatus dry biomass approximately fourfold. In addition, a 100-fold increase in proteinase secretion, as measured by azocasein hydrolysis, was observed when 10% human serum or 10% FBS was added to MEM. The fungal proteinases secreted in serum-containing media were shown to degrade 3H-labeled basal lamina proteins. The factor in serum that stimulated proteinase secretion was larger than 10 kDa and was 85% inactivated when the serum was heated for 30 min at 66°C. The proportions of proteinases of each catalytic class secreted by A. fumigatus in the presence of serum were different from the proportions secreted in media containing single proteins. Proteinase secretion did not result from increased protein concentration in the medium per se because bovine serum albumin (BSA) at a concentration equivalent to the concentration of serum produced only 20% of the proteinase activity per milligram (dry weight) that was produced by FBS. Addition of BSA plus 100 μM FeCl3 to MEM resulted in the same level of growth as addition of serum, indicating that a combination of nutritional factors in serum may stimulate growth. However, the level of proteinase secretion was still only 30% of the level observed with FBS. These data indicate that serum does not inhibit the growth of A. fumigatus and that the nutrients in serum result in high levels of proteinase secretion, potentially increasing the invasiveness of this species.

scholarly journals Candida albicans Hap43 Is a Repressor Induced under Low-Iron Conditions and Is Essential for Iron-Responsive Transcriptional Regulation and Virulence

2010 ◽  
Vol 10 (2) ◽  
pp. 207-225 ◽  
Author(s):  
Po-Chen Hsu ◽  
Cheng-Yao Yang ◽  
Chung-Yu Lan
Keyword(s):  
Candida Albicans ◽  
Iron Acquisition ◽  
Sufficient Conditions ◽  
Natural Resistance ◽  
Cluster Assembly ◽  
Healthy Human ◽  
Iron Sulfur Cluster ◽  
Content Type ◽  
Iron Deprivation ◽  
Opportunistic Fungal Pathogen

ABSTRACTCandida albicansis an opportunistic fungal pathogen that exists as normal flora in healthy human bodies but causes life-threatening infections in immunocompromised patients. In addition to innate and adaptive immunities, hosts also resist microbial infections by developing a mechanism of “natural resistance” that maintains a low level of free iron to restrict the growth of invading pathogens.C. albicansmust overcome this iron-deprived environment to cause infections. There are three types of iron-responsive transcriptional regulators in fungi; Aft1/Aft2 activators in yeast, GATA-type repressors in many fungi, and HapX/Php4 inSchizosaccharomyces pombeandAspergillusspecies. In this study, we characterized the iron-responsive regulator Hap43, which is theC. albicanshomolog of HapX/Php4 and is repressed by the GATA-type repressor Sfu1 under iron-sufficient conditions. We provide evidence that Hap43 is essential for the growth ofC. albicansunder low-iron conditions and forC. albicansvirulence in a mouse model of infection. Hap43 was not required for iron acquisition under low-iron conditions. Instead, it was responsible for repression of genes that encode iron-dependent proteins involved in mitochondrial respiration and iron-sulfur cluster assembly. We also demonstrated that Hap43 executes its function by becoming a transcriptional repressor and accumulating in the nucleus in response to iron deprivation. Finally, we found a connection between Hap43 and the global corepressor Tup1 in low-iron-induced flavinogenesis. Taken together, our data suggest a complex interplay among Hap43, Sfu1, and Tup1 to coordinately regulate iron acquisition, iron utilization, and other iron-responsive metabolic activities.

scholarly journals TUP1, CPH1 and EFG1 Make Independent Contributions to Filamentation in Candida albicans

Genetics ◽  
2000 ◽  
Vol 155 (1) ◽  
pp. 57-67 ◽  
Author(s):  
Burkhard R Braun ◽  
Alexander D Johnson
Keyword(s):  
Candida Albicans ◽  
Environmental Conditions ◽  
Target Genes ◽  
Single Cells ◽  
Filamentous Growth ◽  
Surface Proteins ◽  
Pathway Expression ◽  
Separate Pathway ◽  
The Common ◽  
Growth Pathway

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.

scholarly journals Identification and Characterization of TUP1-Regulated Genes in Candida albicans

Genetics ◽  
2000 ◽  
Vol 156 (1) ◽  
pp. 31-44 ◽  
Author(s):  
Burkhard R Braun ◽  
W Steven Head ◽  
Ming X Wang ◽  
Alexander D Johnson
Keyword(s):  
Candida Albicans ◽  
Systemic Infection ◽  
Subtractive Hybridization ◽  
Filamentous Growth ◽  
Surface Proteins ◽  
Infection Model ◽  
Ferric Reductase ◽  
Pathogenesis Related Protein ◽  
Plant Pathogenesis ◽  
Rnase T2

Abstract TUP1 encodes a transcriptional repressor that negatively controls filamentous growth in Candida albicans. Using subtractive hybridization, we identified six genes, termed repressed by TUP1 (RBT), whose expression is regulated by TUP1. One of the genes (HWP1) has previously been characterized, and a seventh TUP1-repressed gene (WAP1) was recovered due to its high similarity to RBT5. These genes all encode secreted or cell surface proteins, and four out of the seven (HWP1, RBT1, RBT5, and WAP1) encode putatively GPI-modified cell wall proteins. The remaining three, RBT2, RBT4, and RBT7, encode, respectively, an apparent ferric reductase, a plant pathogenesis-related protein (PR-1), and a putative secreted RNase T2. The expression of RBT1, RBT4, RBT5, HWP1, and WAP1 was induced in wild-type cells during the switch from the yeast form to filamentous growth, indicating the importance of TUP1 in regulating this process and implicating the RBTs in hyphal-specific functions. We produced knockout strains in C. albicans for RBT1, RBT2, RBT4, RBT5, and WAP1 and detected no phenotypes on several laboratory media. However, two animal models for C. albicans infection, a rabbit cornea model and a mouse systemic infection model, revealed that rbt1Δ and rbt4Δ strains had significantly reduced virulence. TUP1 appears, therefore, to regulate many genes in C. albicans, a significant fraction of which are induced during filamentous growth, and some of which participate in pathogenesis.

scholarly journals Copper Availability Influences the Transcriptomic Response of Candida albicans to Fluconazole Stress

2021 ◽  
Vol 11 (4) ◽  
Author(s):  
Elizabeth W Hunsaker ◽  
Chen-Hsin Albert Yu ◽  
Katherine J Franz
Keyword(s):  
Candida Albicans ◽  
Time Course ◽  
Transcriptional Response ◽  
Metal Homeostasis ◽  
Metal Availability ◽  
Drug Induced ◽  
Transcriptomic Response ◽  
Opportunistic Fungal Pathogen ◽  
Whole Transcriptome Analysis ◽  
Whole Transcriptome

Abstract The ability of pathogens to maintain homeostatic levels of essential biometals is known to be important for survival and virulence in a host, which itself regulates metal availability as part of its response to infection. Given this importance of metal homeostasis, we sought to address how the availability of copper in particular impacts the response of the opportunistic fungal pathogen Candida albicans to treatment with the antifungal drug fluconazole. The present study reports whole transcriptome analysis via time-course RNA-seq of C. albicans cells exposed to fluconazole with and without 10 µM supplemental CuSO4 added to the growth medium. The results show widespread impacts of small changes in Cu availability on the transcriptional response of C. albicans to fluconazole. Of the 2359 genes that were differentially expressed under conditions of cotreatment, 50% were found to be driven uniquely by exposure to both Cu and fluconazole. The breadth of metabolic processes that were affected by cotreatment illuminates a fundamental intersectionality between Cu metabolism and fungal response to drug stress. More generally, these results show that seemingly minor fluctuations in Cu availability are sufficient to shift cells’ transcriptional response to drug stress. Ultimately, the findings may inform the development of new strategies that capitalize on drug-induced vulnerabilities in metal homeostasis pathways.

scholarly journals Biology of Heme in Mammalian Erythroid Cells and Related Disorders

2015 ◽  
Vol 2015 ◽  
pp. 1-9 ◽  
Author(s):  
Tohru Fujiwara ◽  
Hideo Harigae
Keyword(s):  
Biosynthetic Pathway ◽  
Iron Acquisition ◽  
Protoporphyrin Ix ◽  
Erythroid Differentiation ◽  
Heme Biosynthesis ◽  
Erythroid Cells ◽  
Prosthetic Group ◽  
Expression Of Genes ◽  
Human Disorders ◽  
Pathway Regulation

Heme is a prosthetic group comprising ferrous iron (Fe2+) and protoporphyrin IX and is an essential cofactor in various biological processes such as oxygen transport (hemoglobin) and storage (myoglobin) and electron transfer (respiratory cytochromes) in addition to its role as a structural component of hemoproteins. Heme biosynthesis is induced during erythroid differentiation and is coordinated with the expression of genes involved in globin formation and iron acquisition/transport. However, erythroid and nonerythroid cells exhibit distinct differences in the heme biosynthetic pathway regulation. Defects of heme biosynthesis in developing erythroblasts can have profound medical implications, as represented by sideroblastic anemia. This review will focus on the biology of heme in mammalian erythroid cells, including the heme biosynthetic pathway as well as the regulatory role of heme and human disorders that arise from defective heme synthesis.

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