Presence of heat shock protein in chronic periapical pathology of pulpal origin

In order to establish whether tissues damaged by Chronic Periapical Pathology (CPP) of endodontic origin produced heat shock protein (HSP) capable of attracting reactive lymphocytes, paraffin sections of samples from the oral cavity of 10 patients with CPP were incubated with commercially available anti-HSP monoclonal antibodies. Antibodies were evidenced employing the alkaline phosphatase immunoenzymatic method (DAKO). HSP was found in the lamina propria infiltrated by lymphocytes, in six of the ten samples. These results suggest that HSP may be one of the lymphocyte recruiting factors in the damaged area and opens new possibilities for further research.

Host response and Histoplasma capsulatum/macrophage molecular interactions

Histoplasma capsulatum is the etiological agent of histoplasmosis, a chronic respiratory infection that is generally asymptomatic in healthy individuals, but severe or fatal in patients who are immunosuppressed or otherwise debilitated. H. capsulatum is found as a mould in soil and becomes a pathogenic yeast in the mammalian host. The first line of defense that H. capsulatum faces during host invasion is the attack of polymorphonuclear neutrophils and resident macrophages. In animal models, once phagocytosed, H. capsulatum is not killed by fusion of the phago-lysosomes, instead it multiplies within non-activated macrophages and destroys them. Upon induction of cell-mediated immunity, cytokines activate macrophages and destroy the yeast cells. Some aspects of the fungus-macrophage interaction have been elucidated, and it is clear that some of the mechanisms by which H. capsulatum escapes the lethal effects of this very hostile environment, involve the regulation of specific genes. Recently, using the differential display reverse transcriptase polymerase chain reaction technique, a number of H. capsulatum genes that are induced after the yeasts are ingested by macrophages have been identified. However, the mechanisms that underlie the capacity of H. capsulatum to adapt to the new environmental conditions present in macrophages remain to be clarified.

CAMP is involved in transcriptional regulation of delta9-desaturase during Histoplasma capsulatum morphogenesis

We have characterized the promoter region of the delta9-desaturase gene from two different strains of the dimorphic fungus Histoplasma capsulatum. Desaturase transcription is regulated in the two phases of growth: it is transcribed in the yeast phase at 37 degrees C, while it is inactive in the mycelial phase at 25 degrees C. Phase transition can be induced by shifting the temperature from 25 to 37 degrees C or by adding cAMP to the growth medium. We have identified a stress-responsive cis element (STRE) responsive to cyclic AMP (cAMP)-signaling pathway and demonstrated that this element acts in H. capsulatum. We have also identified an element, hereafter called DRE (Desaturase Regulatory Element), present in the promoters of the H. capsulatum and S. cerevisiae delta9-desaturase gene. We show that this element is necessary but not sufficient to regulate transcription of the H. capsulatum delta9-desaturase gene.

Mucor rouxii delta9-desaturase gene is transcriptionally regulated during cell growth and by low temperature

Unsaturated fatty acids are essential lipid components of Mucor rouxii. Gamma-linolenic acid (GLA) is synthesized via the desaturase enzymes: delta9-desaturase catalyzes mono-unsaturated fatty acids that are utilized as substrate for GLA biosynthesis. We cloned and characterized a M. rouxii gene highly homologous to delta9-desaturase genes. This sequence encodes for a protein of 452 amino acids and contains two introns of 60 and 61 nucleotides. Delta9-desaturase of M. rouxii is expressed during cell growth when cells are subjected to temperature shifts. At 30 degrees C, the mRNA level of late log phase is about 6.4-fold higher than that of early log phase. A shift from 30 to 15 degrees C induced transcription of delta9-desaturase gene in both early and late log phases. However, the pattern of increased transcription by cold induction varied depending on growth conditions: transcription of late log phase is higher than that of early log phase. These results indicate that cell growth and low temperature influence the expression of delta9-desaturase gene and fatty acid composition of M. rouxii.

Stress proteins in fungal diseases

Heat shock proteins (hsps) are ubiquitous families of proteins, found in all organisms studied so far. They are highly conserved across the species barrier and serve fundamental functions in cell physiology. The term 'heat shock' was adopted because of the early observation of the heat-inducible nature of these proteins, although, as it is now realized that they can be induced by a variety of stressful stimuli, it is probably more appropriate to call them 'stress proteins'. The nomenclature of many hsps, for example hsp90, hsp70 and hsp60, reflects the approximate molecular mass of hsps within each of these families. For many bacterial and parasitic infections, hsps were first recognized as immunodominant antigens on immunoblots of extracts from the organism probed with immune sera, or in T-cell proliferation assays. They have now been identified in a range of fungal pathogens, again often linked to an immune response. In this symposium, we review the association of hsps with humoral immunity to candidosis and aspergillosis, cellular immunity to histoplasmosis, and the identification of hsp70 in another dimorphic fungus, Paracoccidioides brasiliensis. Finally, the crucial role of the membrane in setting the temperature of the heat shock response in yeasts is discussed.

An homologue of the human 100-kDa protein (p100) is differentially expressed by Histoplasma capsulatum during infection of murine macrophages

Using differential display reverse transcription-PCR (DDRT-PCR) we have identified several sequences that are specifically expressed by Histoplasma capsulatum during infection of murine macrophages (MPhi). Here, we report the characterization of a clone, pHc12, identified as a differentially expressed gene 1 hour after infection of MPhi. Screening of a cDNA library of H. capsulatum allowed us to isolate a clone, pHc12-E, that contains the complete coding sequence. We show that after infection the level of transcription of this gene increases about 5 fold. Analysis of its sequence revealed the presence of an open reading frame of 890 aa (ORF890) that shares respectively 30 and 33% identity with human and Caenorhabditis elegans p100 kD and rat p105 kD co-activator proteins. Using the two-dimensional Hydrophobic Cluster Analysis (HCA) method, we showed that H. capsulatum ORF890 and p100 kD co-activator proteins are clearly related. The H. capsulatum protein consists of a four-fold repeated module (domains I to IV) like the p100 kD co-activator proteins, whose three-dimensional (3D) structure is related to staphylococcal thermonuclease, followed by a modified fifth "hybrid" domain which partially resembles the structure of the tudor domain found in multiple copies in the Drosophila melanogaster tudor protein. These data strongly suggest that ORF890 is homologous to human p100 kD and that this protein, named Hcp100, may play an essential role during infection by co-activating the expression of specific genes.

Does the membrane's physical state control the expression of heat shock and other genes?

Membranes provide the structural framework that divides cells from their environment and that, in eukaryotic cells, permits compartmentation. They are not simply passive barriers that are liable to be damaged during environmental challenge or pathological states, but are involved in cellular responses and in modulating intracellular signalling. Recent data show that the expression of several genes, particularly those that respond to changes in temperature, ageing or disease, is influenced and/or controlled by the membrane's physical state.

Identification and isolation by DDRT-PCR of genes differentially expressed by Histoplasma capsulatum during macrophages infection

Establishment of infection and disease implies modifications in the genetic programmes of the cell systems that are involved and the differential expression of genes in both parasite and host. In order to identify and isolate relevant genes of the fungus, Histoplasma capsulatum, in which expression is specifically induced during its interaction with murine macrophages (Mphi), we performed a comparative analysis of the pattern of gene expression of the fungus before and after exposure to, and internalization into Mphi by using differential display reverse transcriptase-PCR (DDRT-PCR). Using a limited set of primer combinations, six cDNA fragments of H. capsulatum were identified and isolated; five representing fungal genes in which expressions were enhanced during Mphi infection, whereas one mRNA fragment was down-regulated. Slot blots followed by Northern blot analyses confirmed that the transcripts detected with cDNA clones were over expressed after 1 h of Mphi infection, whereas no transcripts were detected with mRNA purified from H. capsulatum before infection. Sequence analyses and database searches revealed no significant homology to any known sequence for five of these clones. One of the clones showed homology to the rat p105 kD protein, and to the p100 kD co-activator proteins of human and Caenorhabditis elegans. To our knowledge, this is the first experimental evidence that specific genes are differentially expressed by a fungal pathogen when it is exposed to, and phagocytosed by Mphi. Furthermore, these results show that the DDRT-PCR procedure has adequate sensitivity to detect fungal genes induced during parasite-host interaction to identify potential new targets that can be used to develop new antifungal drugs.

Highly increased TNF sensitivity of tumor cells expressing the yeast delta 9-desaturase gene

L929 and WEHI tumor cell lines were genetically modified to constitutively express the Saccharomyces cerevisiae Ole 1 gene, coding for the delta 9-desaturase enzyme. These cells exhibit an increased ratio of monounsaturated fatty acids in their membrane phospholipids paralleled by an overall decrease in the membrane molecular order and a highly increased tumor necrosis factor-alpha (TNF) sensitivity. The TNF-alpha signaling cascade involves events, like receptor clustering and cleavage of membrane constituent lipid molecules by phospholipases, which are influenced by the physical state of cellular membranes. We discuss the possible involvement of non-bilayer forming lipids in the control of signaling mechanisms leading to TNF cytotoxicity.

Bimoclomol: a nontoxic, hydroxylamine derivative with stress protein-inducing activity and cytoprotective effects

Preservation of the chemical architecture of a cell or of an organism under changing and perhaps stressful conditions is termed homeostasis. An integral feature of homeostasis is the rapid expression of genes whose products are specifically dedicated to protect cellular functions against stress. One of the best known mechanisms protecting cells from various stresses is the heat-shock response which results in the induction of the synthesis of heat-shock proteins (HSPs or stress proteins). A large body of information supports that stress proteins--many of them molecular chaperones--are crucial for the maintenance of cell integrity during normal growth as well as during pathophysiological conditions, and thus can be considered "homeostatic proteins." Recently emphasis is being placed on the potential use of these proteins in preventing and/or treating diseases. Therefore, it would be of great therapeutic benefit to discover compounds that are clinically safe yet able to induce the accumulation of HSPs in patients with chronic disorders such as diabetes mellitus, heart disease or kidney failure. Here we show that a novel cytoprotective hydroxylamine derivative, [2-hydroxy-3-(1-piperidinyl) propoxy]-3-pyridinecarboximidoil-chloride maleate, Bimoclomol, facilitates the formation of chaperone molecules in eukaryotic cells by inducing or amplifying expression of heat-shock genes. The cytoprotective effects observed under several experimental conditions, including a murine model of ischemia and wound healing in the diabetic rat, are likely mediated by the coordinate expression of all major HSPs. This nontoxic drug, which is under Phase II clinical trials, has enormous potential therapeutic applications.

Effects of membrane fatty acids on thermal and oxidative injury in the human premonocytic line U937

Heat shock (HS) proteins (HSP) function as molecular chaperones and protect cells from thermal and oxidative injury. The signals leading to HSP synthesis, i.e. the "cellular thermometer(s)," are still a matter of debate. In the human premonocytic line U937, we investigated the effects of specific modification of membrane fatty acid (FA) composition by incubation with various saturated and unsaturated fatty acids (UFA) on the HS response and on hydrogen peroxide (H2O2)-induced cell death. FA readily incorporated into U937 cell membranes. UFA did not modulate the HS response but potentiated H2O2-mediated damage, while pre-exposure to HS protected the UFA-treated cells from this increased H2O2 toxicity.

Modulation of lipid unsaturation and membrane fluid state in mammalian cells by stable transformation with the delta9-desaturase gene of Saccharomyces cerevisiae

The composition and physical state of membrane lipids determine the dynamic nature of membranes, which in turn, could directly be linked to the activity of various membrane-associated cellular functions. To better understand the molecular basis of different membrane-related phenomena we established a novel strategy to alter unsaturation of mammalian cell membranes with an identical genetic background. We transfected L929 mouse fibroblastoid cells with DNA constructs containing the Delta9-fatty acid desaturase gene (Ole1) of S. cerevisiae under the control of desaturase promoters derived either from wild type or mutant strains of the dimorphic fungus H. capsulatum.

An AP1 element is involved in transcriptional regulation of delta9-desaturase gene of Histoplasma capsulatum

We have characterized a region of the promoter of a cloned delta9-desaturase gene (Ole1) of Histoplasma capsulatum, a dimorphic pathogenic fungus of humans. The product of the delta9-desaturase gene is involved in regulating membrane fluid state in animal cells and microorganisms. To identify sequences critical for Ole1 expression in both the saprobic mycelial and parasitic yeast phases of this organism, we performed a deletion analysis. Evidence is presented that a 240 nt region of the proximal promoter is involved in a phase-specific binding in vitro. By sequence analysis we have identified one likely regulatory element that coincides with an AP1 binding site (TGACTAA) that is located at -740 nt of 5'-upstream from the ATG. Using gel mobility shift assays, we show that this cis-acting element binds nuclear proteins extracted from the yeast and mycelial phases of H. capsulatum that may participate in control of expression of the delta9-desaturase gene.

Cellular immune responses to recombinant heat shock protein 70 from Histoplasma capsulatum

Heat shock protein (hsp) 70 from several microbes is antigenic in mammals. In this study we sequenced and expressed the gene encoding this protein from Histoplasma capsulatum to study its immunological activity. The deduced amino acid sequence of the gene demonstrated 71 and 76% identity to hsp7O from humans and Saccharomyces cerevisiae, respectively. A cDNA was synthesized by reverse transcription-PCR and was expressed in Escherichia coli. Recombinant protein reacted with a mouse monoclonal antibody raised against human hsp7O. Splenocytes from C57BL/6 mice immunized with recombinant hsp7O emulsified in adjuvant, but not yeast cells, reacted in vitro to the antigen. Recombinant hsp7O elicited a cutaneous delayed-type hypersensitivity response in mice immunized with protein or with viable yeast cells. Mice were injected with recombinant hsp7O and challenged intranasally with a sublethal inoculum of yeast cells. Vaccination did not confer protection in this model. Thus, recombinant hsp7O can induce a cell-mediated immune response but does not induce a protective response.

Membrane lipid perturbation modifies the set point of the temperature of heat shock response in yeast

Addition of a saturated fatty acid (SFA) induced a strong increase in heat shock (HS) mRNA transcription when cells were heat-shocked at 37 degrees C, whereas treatment with an unsaturated fatty acid (UFA) reduced or eliminated the level of HS gene transcription at 37 degrees C. Transcription of the delta 9-desaturase gene (Ole1) of Histoplasma capsulatum, whose gene product is responsible for the synthesis of UFA, is up-regulated in a temperature-sensitive strain. We show that when the L8-14C mutant of Saccharomyces cerevisiae, which has a disrupted Ole1 gene, is complemented with its own Ole1 coding region under control of its own promoter or Ole1 promoters of H. capsulatum, the level of HS gene transcription depends on the activity of the promoters. Fluorescence anisotropy of mitochondrial membranes of completed strains corresponded to the different activity of the Ole1 promoter used. We propose that the SFA/UFA ratio and perturbation of membrane lipoprotein complexes are involved in the perception of rapid temperature changes and under HS conditions disturbance of the preexisting membrane physical state causes transduction of a signal that induces transcription of HS genes.

A temperature-sensitive strain of Histoplasma capsulatum has an altered delta 9-fatty acid desaturase gene

We have isolated and characterized the delta 9-desaturase gene (Ole1), which codes for a key enzyme involved in regulating membrane fluidity in animal cells and microorganisms, from two strains of Histoplasma capsulatum, one that is temperature-tolerant (G217B) and the other temperature-susceptible (Downs). These pathogenic fungi are dimorphic in that they undergo a morphologic transition from the mycelial to yeast-like form when the temperature of incubation is switched from 25 to 37 degrees C or when they infect a susceptible host. The coding sequences of the two genes, both containing an intron of 93 nucleotides, are virtually identical and analogous to the delta 9-desaturase gene of Saccharomyces cerevisiae and those of the rat, mouse and human. Ole1 transcription of the thermotolerant G217B and thermosensitive Downs strains is similar in yeast phase cells and during the temperature shift down from 34, 37, or 40 to 25 degrees C (yeast-to-mycelia transition). Nevertheless, the delta 9-desaturase gene is transcriptionally inactive in mycelia of G217B at 25 degrees C while it is actively transcribed in the Downs strain at the same temperature. These results are in agreement with the finding that membranes of the Downs strain have a higher level of oleic acid. The differential expression of delta 9-desaturase genes is discussed in relationship to differences in thermosensitivity in the fungal isolates and in regulating the level of expression of heat shock genes.

Hsp70 in parasites: as an inducible protective protein and as an antigen

The heat shock (HS) response is a general homeostatic mechanism that protects cells and the entire organism from the deleterious effects of environmental stresses. It has been demonstrated that heat shock proteins (HSP) play major roles in many cellular processes, and have a unique role in several areas of cell biology, from chronic degenerative diseases to immunology, from cancer research to interaction between host and parasites. This review deals with the hsp70 gene family and with its protein product, hsp70, as an antigen when pathogens infect humans. Members of HSP have been shown to be major antigens of many pathogenic organisms when they experience a major temperature shift upwards at the onset of infection and become targets for host B and T cells.

Morphological transition in the human fungal pathogen Histoplasma capsulatum

Considerable information has accumulated recently about specific genes of Histoplasma capsulatum that are expressed during the process of adaptation when the organism undergoes morphological transition at the onset of infection. The study of these genes is crucial to identify targets for the development of novel antifungal agents.

The Histoplasma capsulatum cdc2 gene is transcriptionally regulated during the morphologic transition

To understand the molecular mechanisms that control the reversible morphologic transition from mycelia to yeast in dimorphic fungi, we have isolated and characterized a cdc2 gene from Histoplasma capsulatum. This organism is a dimorphic pathogenic fungus that grows as a filamentous saprobic mold in soil and as a unicellular pathogenic yeast in human tissue. The cloned gene, whose protein product has a high degree of homology with other members of the cdc2 family, is split into four exons and three introns of 95, 52 and 85 nucleotides. Analyses of cDNA clones confirm the presence of the eukaryotic splice donor (GT) and acceptor (AG) sites. The spliced gene codes for a protein of 324 amino acids (aa) with a predicted molecular mass of 36.9 kDa. The H. capsulatum cdc2 product has 71% aa identity with Saccharomyces cerevisiae and 70% with Schizosaccharomyces pombe. The deduced protein contains the sequence, PSTAIRE, that is normally found in most p34cdc2 proteins. H. capsulatum cdc2 is transcriptionally regulated during the morphologic mycelium<==>yeast transitions and is more actively transcribed in the yeast than in the mycelial phase.

The biology of the heat shock response in parasites

The heat shock response is a general homeostatic mechanism that protects cells and the entire organism from the deleterious effects of environmental stress. It has been shown that heat shock proteins play major roles in many cellular processes and have a unique role in several areas of cell biology, from chronic degenerative diseases to immunology and from cancer research to interactions between host and parasite. In this review, Bruno Maresca and Luisella Carratu deal with some of the unique characteristics of the heat shock response in parasitic organisms.

Molecular cloning and expression of hsp82 gene of the dimorphic pathogenic fungus Histoplasma capsulatum

We have cloned a nucleotide sequence from Histoplasma capsulatum G222B corresponding to a heat inducible hsp82 gene, and determined its entire sequence and the flanking regions. During the temperature-controlled mycelium-to-yeast phase transition the gene is more actively transcribed at 37 degrees C in the temperature tolerant and mouse-virulent G222B strain, while 34 degrees C is the optimum for transcription in the temperature sensitive and mouse-avirulent Downs strain.

Mitochondrial activity and heat-shock response during morphogenesis in the pathogenic fungus Histoplasma capsulatum

Changes in temperature and a variety of other stimuli coordinately induce transcription of a specific set of heat-shock genes in all organisms. In the human fungal pathogen Histoplasma capsulatum, a temperature shift from 25 to 37 degrees C acts not only as a signal that causes transcription of heat-shock genes, but also triggers a morphological mycelium- to yeast-phase transition. The temperature-induced morphological transition may be viewed as a heat-shock response followed by cellular adaptation to a higher temperature. We have found that by inducing thermotolerance, i.e., an initial incubation at 34 degrees C, the thermosensitive attenuated Downs strain of H. capsulatum can be made to resemble those of the more temperature-tolerant G222B strain with respect to mitochondrial ATPase activity and electron transport efficiency at elevated temperatures. Furthermore, if the heat-shock response is first elicited by preincubation at milder temperatures or stress, transcription of heat-shock mRNA in mycelial cells of Downs strain that shifted to 37 degrees C proceeds at rates comparable to those of the virulent strains.

The intron-containing hsp82 gene of the dimorphic pathogenic fungus Histoplasma capsulatum is properly spliced in severe heat shock conditions

We have isolated and characterized a heat-inducible gene, hsp82, from the dimorphic pathogenic fungus Histoplasma capsulatum, which is a filamentous mold at 25 degrees C and a unicellular yeast at 37 degrees C. This gene, which has a high degree of homology with other members of the hsp82 gene family, is split into three exons and two introns of 122 and 86 nucleotides, respectively. Contrary to what has been demonstrated in Drosophila melanogaster, Saccharomyces cerevisiae, and other organisms, hsp82 mRNA in H. capsulatum is properly spliced during the severe heat conditions of 37 to 40 degrees C in the temperature-sensitive Downs strain. Splicing accuracy was also observed at 42 degrees C in the temperature-tolerant G222B strain, which showed no evidence of accumulation of primary transcripts. Furthermore, the intron containing the beta-tubulin gene is also properly spliced at the upper temperature range, suggesting that the lack of a block in splicing may be a general phenomenon in this organism.

Acquired thermotolerance following heat shock protein synthesis prevents impairment of mitochondrial ATPase activity at elevated temperatures in Saccharomyces cerevisiae

The complex molecular response of cells to sudden temperature changes is a well-characterized phenomenon. Although it is clear that the induction of heat shock proteins provides protection from heat in all of the organisms so far tested, very little is known about the role that this set of proteins plays in cellular homeostasis. Recently, putative roles for hsp60 and hsp70-like proteins have been proposed in Saccharomyces cerevisiae. hsp70-like proteins have been shown to be necessary for translocation of precursor polypeptides into mitochondria and endoplasmic reticulum, while hsp60 is required for the assembly of precursor polypeptides into oligomeric complexes following incorporation into the mitochondrial matrix. In this paper, we report that a brief temperature shock (44 degrees C) impairs coupling of oxidative phosphorylation in S. cerevisiae as measured indirectly by the Cl-CCP/oligomycin assay. Furthermore, at high temperature oligomycin stimulates rather than inhibits oxygen uptake under nonthermotolerant conditions. Pretreatment of cells for a short period of time at 37 degrees C, prior to exposure to higher temperatures rescues the capacity to maintain coupling between oxidative phosphorylation and electron transport. Inhibition of cytoplasmic RNA or protein synthesis during heat shock prevents the protection of this mitochondrial activity. We propose that one of the roles of the induction of heat shock proteins (or related activities) is to protect mitochondrial ATPase activity under conditions of further increase in temperature.

Dimorphism in Histoplasma capsulatum: a model for the study of cell differentiation in pathogenic fungi

Several fungi can assume either a filamentous or a unicellular morphology in response to changes in environmental conditions. This process, known as dimorphism, is a characteristic of several pathogenic fungi, e.g., Histoplasma capsulatum, Blastomyces dermatitidis, and Paracoccidioides brasiliensis, and appears to be directly related to adaptation from a saprobic to a parasitic existence. H. capsulatum is the most extensively studied of the dimorphic fungi, with a parasitic phase consisting of yeast cells and a saprobic mycelial phase. In culture, the transition of H. capsulatum from one phase to the other can be triggered reversibly by shifting the temperature of incubation between 25 degrees C (mycelia) and 37 degrees C (yeast phase). Mycelia are found in soil and never in infected tissue, in contrast to the yeast phase, which is the only form present in patients. The temperature-induced phase transition and the events in establishment of the disease state are very likely to be intimately related. Furthermore, the temperature-induced phase transition implies that each growth phase is an adaptation to two critically different environments. A fundamental question concerning dimorphism is the nature of the signal(s) that responds to temperature shifts. So far, both the responding cell component(s) and the mechanism(s) remain unclear. This review describes the work done in the last several years at the biochemical and molecular levels on the mechanisms involved in the mycelium to yeast phase transition and speculates on possible models of regulation of morphogenesis in dimorphic pathogenic fungi.

Purification of membranes and identification of phase-specific proteins of the dimorphic pathogenic fungus Histoplasma capsulatum

Plasma membrane vesicles from the yeast and mycelial phases of Histoplasma capsulatum have been purified and characterized. The method of purification involved differential centrifugation of ballistically fractured cells followed by sedimentation through discontinuous sucrose density gradient and equilibrium centrifugation. Purity of the preparation was assessed by electron microscopy. The protein composition of the membrane preparations from the yeast and mycelial phases of the fungus was analyzed by polyacrylamide gels. A comparison of the two morphologic phases revealed quantitative and qualitative differences in the expressions of several membrane-specific proteins. Physical differences in the appearance of the membranes were also observed by electron micrography of membrane preparations. Alteration in membrane fluidity may be one of the many causes for differences in the appearance of membrane vesicles in the two phases.

Heat shock 70 gene is differentially expressed in Histoplasma capsulatum strains with different levels of thermotolerance and pathogenicity

The response to heat shock has been examined in two strains of the dimorphic pathogenic fungus Histoplasma capsulatum, which differ considerably in thermotolerance and pathogenicity. The gene for the 70 kD heat shock protein (hsp70) was isolated using a Drosophila hsp70 gene to screen a cosmid library of the DNA from the temperature-sensitive Downs strain (low level of thermotolerance for mice). Using the cloned gene as a probe, we have measured the transcription of the endogenous hsp70 gene at 25 degrees C and in response to temperature shift to 34 degrees, 37 degrees and 40 degrees C, temperatures that trigger the mycelial to yeast phase transition in this fungus. The gene is constitutively transcribed at low levels, both in the yeast and the mycelial stages. Synthesis of hsp70 mRNA was transiently increased 1 to 3 h after the temperature shifts. By Northern analysis, peak levels of transcription were shown to occur at 34 degrees C in the Downs strain and at 37 degrees C in the more pathogenic G222B strain. Our results are consistent with reports in which it has been shown that heat shock gene expression is part of temperature adaptation and probably developmental processes. The low levels of transcription of the hsp70 gene in the Downs strain at 37 degrees C correlate with its greater temperature sensitivity and low level of virulence.

Incidence of histoplasmin skin test reactivity in Somalia: an epidemiological study

Histoplasmosis is an important systemic mycotic infection with a wide geographic distribution. Its occurrence has been mostly studied in the US (6) and in Central America (6), but very little is known about its distribution in Africa, where a specific variant exists. Skin test surveys in the Democratic Republic of Somali indicate that Histoplasma capsulatum or a closely related agent has a focus in this east African country.

Correlation between pathogenicity and temperature sensitivity in different strains of Histoplasma capsulatum

We compared the mycelial to yeast transitions of the Downs strain of Histoplasma capsulatum (low level of virulence) with those of G184A and G222B, two more virulent strains having different levels of pathogenicity for mice. When the morphological transitions are initiated by a temperature shift from 25 degrees to 37 degrees C, all three strains undergo similar physiological changes, but these are less severe in G184A and G222B than in the Downs strain. The transitions from mycelial to yeast morphology in both of the more virulent strains are also one-third more rapid than in Downs. We also find that the differences in temperature sensitivity of the three strains can be correlated with the temperature required for complete uncoupling of oxidative phosphorylation. The differences in sensitivity to elevated temperatures extend to the growth of yeast cells of all three strains. Considered together, our results suggest that sensitivity to elevated temperatures may be a key factor accounting for differences in virulence and that uncoupling of oxidative phosphorylation may be the primary event in the morphological transition in all three strains.

Irreversible block of the mycelial-to-yeast phase transition of Histoplasma capsulatum

p-Chloromercuriphenylsulfonic acid (PCMS), a sulfhydryl inhibitor, prevented the mycelial-to-yeast transition of the dimorphic fungal pathogen, Histoplasma capsulatum. The effect of PCMS was specific for the mycelial-to-yeast transformation; it had no effect on growth of either the yeast or mycelial forms or on the yeast-to-mycelial transition. The failure of PCMS-treated mycelia to transform to yeast was permanent and irreversible. PCMS-treated mycelia could not infect mice but could stimulate resistance to infection by a pathogenic strain of Histoplasma capsulatum. These results suggest a new general strategy for vaccine development in diseases caused by dimorphic pathogens.

Purification and characterization of a cysteine dioxygenase from the yeast phase of Histoplasma capsulatum

A cysteine dioxygenase, cysteine oxidase (EC 1.13.11.20), has been purified from the cytosolic fraction of yeast phase cells of the dimorphic fungus Histoplasma capsulatum. The cysteine oxidase is an iron-containing dioxygenase with a molecular weight of 10500 (+/- 1500) and is present only in the yeast phase of the fungus. The enzyme is highly specific for L-cysteine, with a Km of 2 X 10(-5) M in vitro. The product of cysteine oxidation is cysteinesulfinic acid, as analyzed by thin-layer chromatography and mass spectroscopy. To our knowledge, this is the first cysteine oxidase isolated from a fungus, and it probably plays an important role in the mycelial to yeast phase transition of H. capsulatum during which redox potential and cysteine levels are crucial factors.

Role of cysteine in regulating morphogenesis and mitochondrial activity in the dimorphic fungus Histoplasma capsulatum

Three stages can be distinguished in the temperature-induced mycelial-to-yeast phase transition of Histoplasma capsulatum. Stage one is characterized by a progressive decrease in the respiration rate and in the intracellular concentrations of cysteine and other amino acids. By stage two, respiration has ceased completely and free cysteine has fallen to low levels. Exogenous cysteine is required during the second stage for activation of mitochondrial respiration (stage three) and completion of the morphological transition. Mitochondria isolated from cells in the second stage show no respiration with NADH, succinate, or other substrates unless they are first incubated with cysteine. In addition, a novel, cytosolic cysteine oxidase appears during the latter part of the second stage. In stage three, the respiration rate rises, intracellular concentrations of free cysteine and other amino acids increase to levels characteristic of yeast, and the morphological transition is completed. The results support the idea that alterations in cysteine metabolism play a key role in this differentiation process.

Temperature- and cyclic nucleotide-induced phase transitions of Histoplasma capsulatum

The transition from yeast to mycelia of Histoplasma capsulatum could be accomplished by shifting the temperature of incubation from 37 to 25 degrees C. It was accompanied by many changes in cellular metabolism, including changes in respiration, intracellular cyclic adenosine 3',5'-monophosphate (cAMP) levels, and activities of two enzymes specific for the yeast phase, cystine reductase (EC 1.6.4.1) and cysteine oxidase (EC 1.13.11.20). Even at 37 degrees C, the yeast to mycelial transition could be induced by cAMP and agents which raise the intracellular levels of cAMP (theophylline, acetylsalicylic acid, prostaglandin E1, and nerve growth factor). During this morphogenesis the same pattern of changes occurred as in the temperature-induced transition. Therefore, these changes were not simply dependent on a shift in temperature, but rather were part of the process of the phase transition.

Respiration in the yeast and mycelial phases of Histoplasma capsulatum

Respiration in the yeast and mycelial phases of Histoplasma capsulatum proceeds via a cytochrome system and an alternate oxidase, both present constitutively. The mycelial cytochrome system is distinguished by an additional partial shunt around the antimycin-sensitive site.

Cystine reductase in the dimorphic fungus Histoplasma capsulatum

Organo-sulfur compounds favor the transition of mycelia of Histoplasma capsulatum to the yeast form (6, 8). Investigation of the role of cystine in the transition revealed that the two phases concentrated this amino acid at comparable rates and that mutants defective in the uptake of cystine were still able to undergo the transition normally. Uptake of cystine is therefore probably not a requirement for transition to or maintenance of the yeast phase. Both phases contained a reduced nicotinamide adenine dinucleotide phosphate-dependent glutathione reductase; but a reduced nicotinamide adenine dinucleotide-dependent cystine reductase was detectable only in the yeast phase. The cystine reductase appeared early in the transition of mycelium to yeast. Treatment of mycelia with p-chloromercuriphenylsulfonic acid, which prevented the transition to yeast, had no effect on cystine uptake but strongly inhibited the cystine reductase. These results suggest that cystine reductase may provide reduced sulfhydryl groups involved in the transition of mycelium to yeast.