Structure and expression of the hsp 70 gene family of Leishmania major

Leishmania: Responding to environmental signals and challenges without regulated transcription

Here we describe the non-canonical control of gene expression in Leishmania, a single-cell parasite that is responsible for one of the major neglected tropical diseases. We discuss the lack of regulated RNA synthesis, the post-transcriptional gene regulation including RNA stability and regulated translation. We also show that genetic adaptations such as mosaic aneuploidy, gene copy number variations and DNA sequence polymorphisms are important means for overcoming drug challenge and environmental diversity. These mechanisms are discussed in the context of the unique flow of genetic information found in Leishmania and related protists.

No stress--Hsp90 and signal transduction in Leishmania

SUMMARY Hsp90 (a.k.a. Hsp83) plays a significant role in the life cycle control of the protozoan parasite Leishmania donovani. Rather than protecting Leishmania spp. against adverse and stressful environs, Hsp90 is required for the maintenance of the motile, highly proliferative insect stage, the promastigote. However, Hsp90 is also essential for survival and proliferation of the intracellular mammalian stage, the amastigote. Moreover, recent evidence shows Hsp90 and other components of large multi-chaperone complexes as substrates of stage-specific protein phosphorylation pathways, and thus as likely effectors of the signal transduction pathways in Leishmania spp. Future efforts should be directed towards the identification of the protein kinases and the critical phosphorylation sites as targets for novel therapeutic approaches.

The Hsp90-Sti1 interaction is critical for Leishmania donovani proliferation in both life cycle stages

The heat shock protein 90 plays a pivotal role in the life cycle control of Leishmania donovani promoting the fast-growing insect stage of this parasite. Equally important for insect stage growth is the co-chaperone Sti1. We show that replacement of Sti1 is only feasible in the presence of additional Sti1 transgenes indicating an essential role. To better understand the impact of Sti1 and its interaction with Hsp90, we performed a mutational analysis of Hsp90. We established that a single amino acid exchange in the Leishmania Hsp90 renders that protein resistant to the inhibitor radicicol (RAD), yet does not interfere with its functionality. Based on this RAD-resistant Hsp90, we established a combined chemical knockout/gene complementation (CKC) approach. We can show that Hsp90 function is required in both insect and mammalian life stages and that the Sti1-binding motif of Hsp90 is crucial for proliferation of insect and mammalian stages of the parasite. The Sti1-binding motif in Leishmania Hsp90 is suboptimal - optimizing the motif increased initial intracellular proliferation underscoring the importance of the Hsp90-Sti1 interaction for this important parasitic protozoan. The CKC strategy we developed will allow the future analysis of more Hsp90 domains and motifs in parasite viability and infectivity.

Identification of the HSP70-II gene in Leishmania braziliensis HSP70 locus: genomic organization and UTRs characterization

Background

The heat stress suffered by Leishmania sp during its digenetic life-cycle is a key trigger for its stage differentiation. In Leishmania subgenera two classes of HSP70 genes differing in their 3' UTR were described. Although the presence of HSP70-I genes was previously suggested in Leishmania (Viannia) braziliensis, HSP70-II genes had been reluctant to be uncovered.

Results

Here, we report the existence of two types of HSP70 genes in L. braziliensis and the genomic organization of the HSP70 locus. RT-PCR experiments were used to map the untranslated regions (UTR) of both types of genes. The 3' UTR-II has a low sequence identity (55-57%) when compared with this region in other Leishmania species. In contrast, the 5' UTR, common to both types of genes, and the 3' UTR-I were found to be highly conserved among all Leishmania species (77-81%). Southern blot assays suggested that L. braziliensis HSP70 gene cluster may contain around 6 tandemly-repeated HSP70-I genes followed by one HSP70-II gene, located at chromosome 28. Northern blot analysis indicated that levels of both types of mRNAs are not affected by heat shock.

Conclusions

This study has led to establishing the composition and structure of the HSP70 locus of L. braziliensis, complementing the information available in the GeneDB genome database for this species. L. braziliensis HSP70 gene regulation does not seem to operate by mRNA stabilization as occurs in other Leishmania species.

A postgenomic view of the heat shock proteins in kinetoplastids

The kinetoplastids Leishmania major, Trypanosoma brucei and Trypanosoma cruzi are causative agents of a diverse spectrum of human diseases: leishmaniasis, sleeping sickness and Chagas' disease, respectively. These protozoa possess digenetic life cycles that involve development in mammalian and insect hosts. It is generally accepted that temperature is a triggering factor of the developmental programme allowing the adaptation of the parasite to the mammalian conditions. The heat shock response is a general homeostatic mechanism that protects cells from the deleterious effects of environmental stresses, such as heat. This response is universal and includes the synthesis of the heat-shock proteins (HSPs). In this review, we summarize the salient features of the different HSP families and describe their main cellular functions. In parallel, we analyse the composition of these families in kinetoplastids according to literature data and our understanding of genome sequence data. The genome sequences of these parasites have been recently completed. The HSP families described here are: HSP110, HSP104, group I chaperonins, HSP90, HSP70, HSP40 and small HSPs. All these families are widely represented in these parasites. In particular, kinetoplastids possess an unprecedented number of members of the HSP70, HSP60 and HSP40 families, suggesting key roles for these HSPs in their biology.

Genomic organization and expression of the HSP70 locus in New and Old World Leishmania species

Heat shock is believed to be a developmental inductor of differentiation in Leishmania. Furthermore, heat shock genes are extensively studied as gene models to decipher mechanisms of gene regulation in kinetoplastids. Here, we describe the organization and expression of the HSP70 loci in representative Leishmania species (L. infantum, L. major, L. tropica, L. mexicana, L. amazonensis and L. braziliensis). With the exception of L. braziliensis, the organization of the HSP70 loci was found to be well conserved among the other Leishmania species. Two types of genes, HSP70-I and HSP70-II, were found to be present in these Leishmania species except for L. braziliensis that lacks HSP70-II gene. Polymorphisms in the HSP70 locus allow the differentiation of the Old and New World species within the subgenus Leishmania. A notable discrepancy between our data and those of the L. major genome database in relation to the gene copy number composing the L. major HSP70 locus was revealed. The temperature-dependent accumulation of the HSP70-I mRNAs is also conserved among the different Leishmania species with the exception of L. braziliensis. In spite of these differences, analysis of the HSP70 synthesis indicated that the HSP70 mRNAs are also preferentially translated during heat shock in L. braziliensis.

AUG-proximal nucleotides regulate protein synthesis in Leishmania tropica

Gene expression in the Leishmania is controlled post-transcriptionally, and is likely to be impacted by both 5' and 3' untranslated regions (UTRs). We have investigated the effects of trinucleotides in the AUG-proximal region (APR) (i.e. positions -3 to -1 upstream of an AUG) on two reporter genes in the context of an endogenous intergenic region of Leishmania tropica. The effects of APRs on protein expression were determined in stable transfectants in vivo. Three APRs, namely, C(-3)C(-2)C(-1), ACC and GCC, yielded robust translation, whereas GTA produced low amounts of proteins. A purine at -3 of an APR was not crucial for efficient translation. Steady-state level of reporter mRNA did not correlate directly with the amount of protein detected. Polysome analysis revealed that APRs modulate translation, at least in part, by influencing mRNA association with ribosomes. An analysis of genomic UTRs in L. major showed that (i) the consensus APR is N(-3)N(-2)C(-1) (where N = any nucleotide), and (ii) the most frequently used APRs include ACA, ACC, ATC, GCC, GCG, GTC and CAC, some of which were translation enhancers in our experimental studies.

Construction of a bacterial artificial chromosome library, determination of genome size, and characterization of an Hsp70 gene family in Phytophthora nicotianae

The oomycete plant pathogen Phytophthora nicotianae causes diseases on a wide range of plant species. To facilitate isolation and functional characterization of pathogenicity genes, we have constructed a large-insert bacterial artificial chromosome (BAC) library using nuclear DNA from P. nicotianae H1111. The library contains 10,752 clones with an average insert size of 90 kb and is free of mitochondrial DNA. The quality of the library was verified by hybridization with 37 genes, all of which resulted in the identification of multiple positive clones. The library is estimated to be 10.6 haploid genome equivalents based on hybridization of 23 single-copy genes and the genome size of P. nicotianae was estimated to be 95.5 Mb. Hybridization with a nuclear repetitive DNA probe revealed that 4.4% of clones in the library contained 28S rDNA. Hybridization of total genomic DNA to the library indicated that at least 39% of the BAC library contains repetitive DNA sequences. A BAC pooling strategy was developed for efficient library screening. The library was used to identify and characterize BAC clones containing an Hsp70 gene family whose four members were identified to be clustered within approximately 18 kb in the P. nicotianae genome based on the physical mapping of eight BACs spanning a genomic region of approximately 186 kb. The BAC library created provides an invaluable resource for the isolation of P. nicotianae genes and for comparative genomics studies.

Identification of a putative regulatory element in the 3'-untranslated region that controls expression of HSP70 in Leishmania infantum

The regulation of HSP70 gene expression in Leishmania infantum, in contrast to most eukaryotes, occurs by mechanisms that operate exclusively at the post-transcriptional level. During the normal growth of L. infantum promastigotes at 26 degrees C the mRNAs derived from the sixth gene of the HSP70 locus are more abundant than the mRNAs derived from the other five HSP70 genes, but only the latter transcripts accumulate after incubation at 37 degrees C. Here, it was found that the full-length 3'untranslated region (UTR) and downstream sequences of the HSP70 genes are necessary for a correct polyadenylation of both types of transcripts and responsible for the differences in the steady-state levels of the transcripts. Also, it was found that the addition of the 3'-UTR-I (common to the first five genes of the L. infantum HSP70 gene cluster) to a reporter gene is sufficient to achieve an accumulation of the corresponding transcripts at 37 degrees C. This effect was, furthermore, found to be strand dependent. A progressive shortening of the 1063-base 3'-UTR-I has shown that the temperature-dependent accumulation was lost after deletion of 364-nucleotides from the 3' end. In addition, the accumulation of reporter transcripts at 37 degrees C was not observed in a plasmid construct containing an internal deletion (region 699-816) of the 3'-UTR-I. Thus, our data suggest that RNAs derived from L. infantum HSP70 genes 1-5 contain a cis-acting sequence that functions as a positive element during heat shock.

Xanthine phosphoribosyltransferase from Leishmania donovani. Molecular cloning, biochemical characterization, and genetic analysis

Xanthine phosphoribosyltransferase (XPRT) from Leishmania donovani is a unique enzyme that lacks a mammalian counterpart and is, therefore, a potential target for antiparasitic therapy. To investigate the enzyme at the molecular and biochemical level, a cDNA encoding the L. donovani XPRT was isolated by functional complementation of a purine auxotroph of Escherichia coli that also harbors deficiencies in the prokaryotic phosphoribosyltransferase (PRT) activities. The cDNA was then used to isolate the XPRT genomic clone. XPRT encodes a 241-amino acid protein exhibiting approximately 33% amino acid identity with the L. donovani hypoxanthine-guanine phosphoribosyltransferase (HGPRT) and significant homology with other HGPRT family members. Southern blot analysis revealed that XPRT was a single copy gene that co-localized with HGPRT within a 4.3-kilobase pair (kb) EcoRI fragment, implying that the two genes arose as a result of an ancestral duplication event. Sequencing of this EcoRI fragment confirmed that HGPRT and XPRT were organized in a head-to-tail arrangement separated by an approximately 2.2-kb intergenic region. Both the 3.2-kb XPRT mRNA and XPRT enzyme were significantly up-regulated in Deltahgprt and Deltahgprt/Deltaaprt L. donovani mutants. Genetic obliteration of the XPRT locus by targeted gene replacement indicated that XPRT was not an essential gene under most conditions and that the Deltaxprt null strain was competent of salvaging all purines except xanthine. XPRT was overexpressed in E. coli and the recombinant protein purified to homogeneity. Kinetic analysis revealed that the XPRT preferentially phosphoribosylated xanthine but could also recognize hypoxanthine and guanine. K(m) values of 7.1, 448.0, and >100 microM and k(cat) values of 3.5, 2.6, and approximately 0.003 s(-1) were calculated for xanthine, hypoxanthine, and guanine, respectively. The XPRT gene and XPRT protein provide the requisite molecular and biochemical reagents for subsequent studies to validate XPRT as a potential therapeutic target.

Immune response against heat shock proteins in infectious diseases

Heat shock proteins (hsp) are conserved molecules that play an important role in protein folding and assembly and in translocation of proteins between different compartments. Under stress, hsp synthesis is drastically increased, representing a mechanism essential for cell survival. During infection or inflammation, numerous hsp are overexpressed. Not surprisingly, hsp represent dominant antigens in many infectious and autoimmune diseases that induce strong humoral and cellular immune responses. There is substantial evidence that hsp are dominant immune targets in a number of diseases, to the benefit or detriment of man. Nevertheless, findings also exist which argue against a universal role for hsp as target antigens in disease situations. It is suggested that hsp mainly serve as 'early' targets in the immune response, thus providing support for anti-infectious or autoaggressive immune responses directed against unique pathogen- or disease-associated antigens, respectively.

Should I stay or should I go now? A stochastic model of stage differentiation in Theileria annulata

The events that initiate and determine stage differentiation of protozoan parasites are not fully understood. In this article, Brian Shiels suggests that for differentiation to the merozoite in Theileria annulata the process is predetermined by the parasite, but can be initiated and modulated by changes to the extracellular environment. Shiels proposes a mechanism operating on the basis of factors that regulate gene expression reaching a commitment threshold. Similarities across protozoan and higher eukaryotic differentiation systems lead Shiels to speculate that the T. annulata model may be of relevance to other parasites.

Role of heat shock proteins in protection from and pathogenesis of infectious diseases

Increased synthesis of heat shock proteins (hsp) occurs in prokaryotic and eukaryotic cells when they are exposed to stress. By increasing their hsp content, cells protect themselves from lethal assaults, primarily because hsp interfere with the uncontrolled protein unfolding that occurs under stress. However, hsp are not produced only by stressed cells; some hsp are synthesized constitutively and perform important housekeeping functions. Accordingly, hsp are involved in the assembly of molecules which play important roles in the immune system. It is not surprising that due to their wide distribution and their homology among different species, hsp represent target antigens of the immune response. Frequent confrontation of the immune system with conserved regions of hsp which are shared by various microbial pathogens can potentiate antimicrobial immunity. However, long-term confrontation of the immune system with hsp antigens which are similar in the host and invaders may convert the immune response against these host antigens and promote autoimmune disease. This review provides an overview of the role of hsp in immunity with a focus on infectious and autoimmune diseases.

The 3' untranslated region of the hsp 70 genes maintains the level of steady state mRNA in Trypanosoma brucei upon heat shock

An increase in the transcriptional efficiency at elevated temperatures is a characteristic of transcription of heat shock protein (hsp) coding genes in most eukaryotes analyzed to date. The regulatory mechanism for hsp 70 genes expression in Trypanosoma brucei does not follow the conventional transcriptional induction mechanism. The hsp 70 locus of T.brucei appears in a permanently activated state, and transcriptional induction of hsp 70 genes by heat shock does not occur in this organism. Therefore, the differential expression of the hsp 70 genes in trypanosomes is, to a large extent, post-transcriptionally controlled. Mechanisms of post-transcriptional control of the hsp 70 gene expression were investigated. Procyclic trypanosomes were normally maintained at approximately 25 degreesC. Incubation of procyclic trypanosomes at 41 degreesC drastically reduced the steady state mRNA levels of many protein coding genes. In contrast, the expression of the hsp 70 genes is either maintained at a high level or is up-regulated. The hsp 70 intergenic region promoter together with its 3' splice acceptor sites and the 5' untranslated region (UTR) are not sufficient to maintain or up-regulate the mRNA level of a reporter gene upon heat shock. However, addition of the 3' UTR of hsp 70 genes to a reporter gene, driven by different promoters, maintained a high level expression of the mRNA during heat shock. These results suggested that the 3' UTR of the hsp 70 genes is primarily responsible for the maintenance of mRNA level during heat shock, while mRNA containing the 3' UTR from many other genes may be rapidly degraded by heat shock induced processes.

Molecular characterization of the heat-inducible LmSTI1 protein of Leishmania major

We have recently isolated a cDNA encoding the Leishmania major homologue of the yeast stress-inducible protein STI1. Southern blot analyses indicate that this protein is encoded by a single copy gene in L. major and that this gene is highly conserved throughout the Leishmania genus. The STI1 gene is constitutively expressed in both L. major promastigotes and amastigotes however, STI1 transcript levels can be upregulated in promastigotes by a shift in culture temperature from 26 to 37 degrees C. Upregulation of transcript was detectable within 5' of heat shock and continued to increase for a further 8 h before returning to constitutive levels. In addition, biosynthetic incorporation of [35S]methionine followed by immunoprecipitation revealed an increase in the level of nascent STI1 protein synthesized when promastigote cultures were shifted from 26 to 37 degrees C. The L. major STI1 protein and the heat shock proteins Hsp83 and Hsp70 form a salt-sensitive complex in L. major promastigotes as evidenced by co-immunoprecipitation using an antiserum specific for L. major STI1. Furthermore, this complex can be reconstituted in vitro by adding recombinant STI1 containing an amino-terminal histidine tag to promastigote lysate and subsequent purification using metal chelate affinity chromatography.

Leishmania major Hsp100 is required chiefly in the mammalian stage of the parasite

In Leishmania major a 100-kDa heat shock protein, Hsp100, is abundant in the intracellular amastigote stage which persists in the mammalian host. A replacement of both clpB alleles which encode Hsp100 does not affect promastigote viability under standard culture conditions but impairs thermotolerance in vitro. In experimental infections of BALB/c inbred mice, the lack of Hsp100 in the gene replacement mutants results in a markedly delayed lesion development compared with that in infections with wild-type L. major. Overexpression of exogenous clpB gene copies can partly restore virulence to the gene replacement mutants. Genetic-selection experiments also reveal a strong pressure for Hsp100 expression in the mammalian stage. This requirement for Hsp100 was also observed in in vitro infection experiments with mouse peritoneal macrophages. These experiments indicated a role for Hsp100 during the development from the promastigote to the amastigote stage. Our results suggest an important role for this parasite heat shock protein during the initial stages of a mammalian infection.

Transcription of the Leishmania major Hsp70-I gene locus does not proceed through the noncoding region

Primary transcripts in kinetoplastid protozoa are generally assumed to be multicistronic. We have analyzed the transcription in the gene locus which encodes the 70-kDa heat shock protein by using nuclear run-on analysis. We find that RNA synthesis in the Hsp70-I gene locus either is terminated or pauses within the intergenic region approximately 250 nt downstream of the polyadenylation site. We therefore propose a discontinuous mode of transcription in the Hsp70 genes of Leishmania major.

Leishmania major: molecular cloning, sequencing, and expression of the heat shock protein 60 gene reveals unique carboxy terminal peptide sequences

Heat shock proteins (HSP) in the size range of M(r) 60,000 are major targets of the immune response in vivo. The leishmania heat-inducible proteins of M(r) 65-67,000 are expressed at relatively high levels in infected macrophages (Infection and Immunity 1993, 61, 3265-3272) and may be important targets of the host response. To facilitate further studies concerned with these proteins, the HSP60 gene of Leishmania major was cloned, sequenced, and expressed. A lambdaEMBL-3 L. major genomic library was screened with a PCR-generated DNA probe derived from a highly conserved region of the leishmania HSP60 gene. A single clone that hybridized strongly was characterized. Sequence analysis revealed an open reading frame of 1770 bp encoding a putative polypeptide of 589 amino acids with a predicted size of M(r) 64,790 and with the highest degree of amino acid sequence similarity (56%) to HSP60 from Trypanosoma cruzi. Less extensive amino acid sequence similarity (48%) was observed between that leishmania HSP60 and the corresponding human protein. Notably, significant regions of sequence dissimilarity between the leishmania and human proteins were identified principally within the carboxy-terminal regions of the proteins. The entire coding region of the leishmania HSP60 gene was subcloned into the pET-3a vector and expressed in Escherichia coli. Purified recombinant protein was used to examine sera from patients with tegumentary leishmaniasis from Colombia for the presence of antibodies to HSP60. Unlike sera from healthy, uninfected controls, sera from patients reacted strongly with recombinant leishmania HSP60. This recognition had specificity in that these same sera showed little or no reactivity with either recombinant mycobacterial HSP65 or recombinant human HSP60. These findings indicate that patients with tegumentary forms of leishmaniasis have humoral responses to leishmania HSP60. Further studies of this protein will clarify its importance as a target of the immune response and as a potential antigen for serodiagnosis.

Analysis of post-transcriptional regulation operating on transcription products of the tandemly linked Leishmania infantum hsp70 genes

The genomic organization and expression of the hsp70 genes of Leishmania infantum were examined. In the cluster there are at least six copies of the hsp70 genes arranged in a head-to-tail tandem of 3. 8-kilobase repetition units. The hsp70 gene copy (gene 6) located at the 3' end of the tandem has a 3'-untranslated region highly divergent in sequence relative to the 3'-untranslated region of the rest of hsp70 gene copies (genes 1-5). Nuclease S1 protection assays indicated that the steady-state level of the mRNAs derived from gene 6 is about 50-fold more abundant than the transcript level derived from genes 1-5. Nuclear run-on assays showed, however, that all hsp70 genes are transcribed at similar rates. Thus, it is likely that the differences in the steady-state levels of the transcripts from the hsp70 genes should be associated with variations in their processing or maturation rates. While the abundance of the mRNAs derived from hsp70 genes 1-5 is increased by heat shock, the hsp70 gene 6 mRNA level remains unaffected. Our data showed that ongoing protein synthesis is required for the maintenance of the heat inducement, depicting, thus, a post-transcriptional mechanism of positive regulation involving a labile protein factor that would be either induced or activated during heat shock.

Detection of polymorphism in the Trypanosoma cruzi TcP2 beta gene family by single strand conformational analysis (SSCA)

Single strand conformation analysis (SSCA) is a technique that has been used to detect point mutations. We explored its usefulness in the analysis of four different members of the Trypanosoma cruzi TcP2 beta gene family and its suitability for detection of polymorphism in different parasite strains. The availability of primers covering a 97-bp sequence at the 5' end of the genes allowed assessment of the effect of a single base substitution, while the analysis of a 321 bp long sequence permitted the evaluation of sequences differing in several bases. PCR products were analysed under four different electrophoretic conditions: with or without the addition of 10% glycerol in a 6% polyacrylamide gel run at room temperature or at 4 degrees C. Shifts in mobility were radically dependent on the migration condition. Both 97-bp and 321-bp amplicons were best resolved at 4 degrees C, without glycerol. Amplification products derived from total genomic DNA showed a pattern that resembled closely a combination of the products derived from the cloned genes. The results herein demonstrate the usefulness of SSCA to differentiate forms of a complex protozoan gene family, and to scan its polymorphic nature. Furthermore, due to the remarkable sensitivity of the technique it can generate genomic markers, such as Sequence Tagged Sites (STS), of great need in the T. cruzi genome project.

The developmental expression of Leishmania donovani A2 amastigote-specific genes is post-transcriptionally mediated and involves elements located in the 3'-untranslated region

Leishmania donovani is a protozoan parasite that exists as a free-living promastigote in the sandfly insect vector and as an amastigote inside the mammalian host macrophage phagolysosome compartment. The L. donovani A2 genes have been described previously as developmentally expressed in amastigotes but can be induced experimentally in promastigotes by a combination of pH and temperature shifts, conditions that mimic the phagolysosomal compartment of the macrophage cell. Considering the importance of the amastigote stage in human infections, we have examined the molecular basis for amastigote stage-specific gene expression. Our results provide evidence that A2 developmental expression during the promastigote-to-amastigote cytodifferentiation is mediated through differential RNA stability and involves the A2 mRNA 3'-untranslated region. The site of processing in the 3'-untranslated region was a major factor for the accumulation of A2 mRNAs in cells incubated under phagolysosomal conditions. The stability of reporter gene transcripts bearing the A2 3'-untranslated region was increased in cells incubated at low pH, further confirming the importance of pH shift as an inducer for A2 expression. These observations contribute to defining the mechanism of amastigote-specific gene regulation in L. donovani. We also demonstrate the feasibility of using the A2 locus to express heterologous genes differentially in the amastigote form of the L. donovani parasite.

Developmental changes in the expression of Leishmania chagasi gp63 and heat shock protein in a human macrophage cell line

The ability of the protozoan Leishmania chagasi to infect a vertebrate host depends on its ability to survive intracellularly in a mammalian macrophage. Novel patterns of gene expression are probably important for conversion from the extracellular promastigote to the obligate intracellular amastigote parasite form. We found that the human macrophage-like cell line U937 provided an in vitro model of phagocytosis of L. chagasi promastigotes and intracellular conversion to amastigotes, allowing examination of parasite protein and RNA expression. The Leishmania surface protease gp63 assumed three isoforms during stage conversion, and a 64-kDa form of gp63 not present in promastigotes became the most prominent form in amastigotes. gp63 RNAs derived from the three different classes of msp genes (mspS, mspL, and mspC) were also differentially expressed. Infectious promastigotes contained mRNAs from mspS and mspC genes, whereas converting parasites expressed only mspL and mspC mRNAs. Sequence analysis of clones from an amastigote cDNA library confirmed the presence of gp63 mRNAs only from mspL and mspC class genes in tissue-derived amastigotes. Finally, 24 h after phagocytosis, there was a transient increase in the level of hsp70 and hsp90 proteins that subsequently decreased to baseline; this increase was not due to heat shock alone. We conclude that a unique pattern of selected L. chagasi proteins and RNAs is induced following phagocytosis by macrophages.

Structural and functional characterization of the Leishmania amazonensis ribosomal RNA promoter

The promoter region of the ribosomal RNA (rRNA) genes of Leishmania amazonensis was characterised and the transcription start point, defined by primer extension, was shown to be a T residue, 1048 nucleotides upstream of the beginning of the 18S sequence. A repetitive element of 60 bp was identified in the intergenic spacer. This element did not show sequence similarity with the region around the transcription start point. Conserved sequences were found in the external transcribed spacer of L. amazonensis, Trypanosoma cruzi and Crithidia fasciculata rRNA genes, 150 nucleotides downstream of the transcription start point. These sequences might be involved in processing events of the rRNA precursor molecule. The general organisation of the gene resembles the pattern observed for the ribosomal cistron in eukaryotic cells. Constructs containing the L. amazonensis promoter region upstream of the chloramphenicol acetyltransferase (cat) gene were able to drive the expression of the reporter gene in transient transfection experiments. CAT expression could be detected even when no trans-splicing acceptor sequence was added to the constructs, although its presence enhanced 5-fold the level of CAT activity. Species-specificity of the RNA polymerase I promoter activity was also demonstrated since constructs containing the L. amazonensis promoter region were unable to drive CAT expression when transfected into the related trypanosomatids, T. cruzi, C. fasciculata and Endotrypanum schaudini.

Post-transcriptional control of hsp70 mRNA in Trypanosoma brucei

The control of hsp70 mRNA levels was investigated using transgenic bloodstream and procyclic trypanosomes. Heat shock of procyclic and bloodstream trypanosomes caused no significant change in overall protein synthesis, but led to a 2-3-fold increase in the relative hsp70 mRNA level in bloodstream trypanosomes. Incubation of procyclic trypanosomes at 35 degrees C for up to 18 h increased the level of hsp70 mRNA only marginally. The expression of actin and hsp70 mRNAs was markedly reduced in late log phase procyclic trypanosomes but PARP mRNA levels remained constant. Measurements of phleomycin-binding-protein RNAs bearing 3'- and 5'-untranslated regions from the actin, PARP or hsp70 loci indicated that both the heat-shock and cell-density effects were mediated by the untranslated regions. No significant promoter activity was detected in the different hsp70 locus intergenic regions in transient assays.

Lack of serological specificity of recombinant heat shock protein of Leishmania donovani

In order to identify a specific recombinant antigen of Leishmania donovani with potential use for diagnosis, a cDNA library was constructed in lambda ZAP II expression vector. On screening the cDNA library using pooled sera from Indian patients with kala azar, 20 antibody reactive clones were identified. These were subcloned into pBluescript phagemid by an in vivo excision procedure. The molecular weights of the expressed recombinant proteins varied from 15 to 70 kDa and the cDNA insert sizes varied from 0.5 kb to the largest size of approximately 2.0 kb which was designated as the E2b clone. The nucleotide sequencing revealed that 50% of the clones had sequence homology to the heat shock protein gene of L. donovani. The serological studies conducted with the kala azar positive sera and sera from healthy laboratory workers using the recombinant protein from the E2b clone and having sequence homology to Ldhsp 70, indicated that although all the kala azar sera was positive, 12 of 20 healthy individuals also showed antibodies against the recombinant hsp70, indicating that this antigen is not suitable for serological diagnosis of kala azar.

Molecular comparison of the mitochondrial and cytoplasmic hsp70 of Trypanosoma cruzi, Trypanosoma brucei and Leishmania major

We compared the expression and localization of the mitochondrial and cytoplasmic hsp70 of the protozoans Trypanosoma cruzi, Trypanosoma brucei and Leishmania major. The mitochondrial protein is encoded by multiple mRNA in all species, while the cytoplasmic protein is encoded by a single mRNA. In all three species, the mitochondrial hsp70 is concentrated in the kinetoplast, a submitochondrial structure that houses the unusual DNA (kDNA) that characterizes this group of organisms, while the cytoplasmic protein is distributed throughout the cell. These results suggest that, in all kinetoplastid species, mt-hsp70 has a specific function in kDNA biology, possibly in the processes of kDNA replication, RNA editing or kinetoplast structure.

Protein trafficking in kinetoplastid protozoa

The kinetoplastid protozoa infect hosts ranging from invertebrates to plants and mammals, causing diseases of medical and economic importance. They are the earliest-branching organisms in eucaryotic evolution to have either mitochondria or peroxisome-like microbodies. Investigation of their protein trafficking enables us to identify characteristics that have been conserved throughout eucaryotic evolution and also reveals how far variations, or alternative mechanisms, are possible. Protein trafficking in kinetoplastids is in many respects similar to that in higher eucaryotes, including mammals and yeasts. Differences in signal sequence specificities exist, however, for all subcellular locations so far examined in detail--microbodies, mitochondria, and endoplasmic reticulum--with signals being more degenerate, or shorter, than those of their higher eucaryotic counterparts. Some components of the normal array of trafficking mechanisms may be missing in most (if not all) kinetoplastids: examples are clathrin-coated vesicles, recycling receptors, and mannose 6-phosphate-mediated lysosomal targeting. Other aspects and structures are unique to the kinetoplastids or are as yet unexplained. Some of these peculiarities may eventually prove to be weak points that can be used as targets for chemotherapy; others may turn out to be much more widespread than currently suspected.

High constitutive levels of heat-shock proteins in human-pathogenic parasites of the genus Leishmania

We have analysed the transcription of three heat-shock genes, HSP70, HSP83 and ClpB, in the protozoan parasite Leishmania. All three heat-shock genes are transcribed constitutively and not heat-inducibly. However, we find that two major heat-shock proteins, HSP70 and HSP83, are synthesized at elevated rates during heat stress. We conclude that the cellular stress response in Leishmaniae is regulated exclusively on a post-transcriptional level much in contrast with all other eukaryotes examined so far. The induced synthesis of HSP70 and HSP83, however, does not increase the steady-state level of either protein significantly. This is compensated by high constitutive levels of both proteins: HSP70 and HSP83 make up 2.1% and 2.8%, respectively, of the total protein in unstressed Leishmania promastigotes. Also, HSP70 is a strictly cytoplasmic protein in Leishmania and does not relocate into the nucleus during heat stress, as it does in other eukaryotes examined in the past.

A member of the ClpB family of stress proteins is expressed during heat shock in Leishmania spp

We have identified and isolated the Leishmania major homologue to the bacterial ClpB gene and to the yeast Hsp104 gene. ClpB in Leishmania major is a single-copy gene and encodes a low-abundance mRNA which is induced several-fold during a heat stress. We raised antibodies against the product of the recombinant gene and show that the leishmanial ClpB encodes a predominantly cytoplasmic protein of approx. 100 kDa which is detectable in Leishmania promastigotes of various species after exposure to elevated temperatures. We, therefore, term this protein Hsp100.

The hsp70 gene family of Neurospora crassa: cloning, sequence analysis, expression, and genetic mapping of the major stress-inducible member

The gene encoding the major heat shock-inducible member of the HSP70 family of Neurospora crassa was cloned and characterized. The 5' nontranscribed region shows the presence of consensus sequence motifs resembling the classical heat shock elements found in many heat shock-responsive eukaryotic promoters, as well as metal-responsive-element sequences. The coding region of the gene contains four introns with boundaries and internal consensus motifs typical of genes of filamentous fungi. None of the other stress-inducible hsp70 genes of fungal origin have, so far, been reported to contain introns. The sequence adjoining the transcriptional initiation zone shows the presence of prominent CT-rich stretches, characteristic of highly expressed fungal genes. The deduced amino acid sequence corresponds to a 646-residue polypeptide, with a calculated molecular mass of 70,561 Da and an average pI of 6.01, exhibiting strong sequence homology with many other eukaryotic HSP70s, with typical HSP70 family signatures 1 and 2 and a bipartite nuclear targeting sequence. Experiments with primer extension revealed the presence of one minor and two major transcriptional start sites. This gene, designated hsps-1, was mapped to a locus on the left arm of linkage group II, in close proximity to the AR-30 translocation breakpoint.

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.

Response of Leishmania chagasi promastigotes to oxidant stress

At the onset of infection, Leishmania promastigotes are phagocytized by mammalian macrophages. They must survive despite exposure to toxic oxidants such as hydrogen peroxide (H2O2) and superoxide (.O2-) generated during phagocytosis. We investigated the effects of these oxidants on Leishmania chagasi promastigotes and promastigote mechanisms for oxidant resistance. According to spin trapping and electron paramagnetic resonance spectrometry, .O2- could be generated by exposure of promastigotes to the redox-cycling compound menadione. Incubation in either menadione or H2O2 caused a concentration-dependent loss of promastigote viability. However, incubation in sublethal concentrations of H2O2 or menadione caused a stress response in promastigotes. This oxidant-induced response was associated with an increase in the amount of heat shock protein hsp70. Induction of a stress response by exposure of promastigotes either to heat shock or to sublethal oxidants (H2O2 or menadione) caused promastigotes to become more resistant to H2O2 toxicity. Sublethal menadione also caused promastigotes to become more virulent in a BALB/c mouse model of leishmaniasis. We previously correlated H2O2 cytotoxicity for promastigotes with the formation of hydroxyl radical (.OH) from H2O2. However, according to electron paramagnetic resonance spectrometry, the increase in H2O2 resistance after exposure to sublethal oxidants was not associated with diminished generation (i.e., scavenging) of .OH. These data suggest that there is a cross-protective stress response that occurs after exposure of L. chagasi promastigotes to heat shock or to sublethal H2O2 or .O2-, exposures that also occur during natural infection. This response results in increased resistance to H2O2 toxicity and increased virulence for a mammalian host.

A regulatory role for the 5' and 3' untranslated regions in differential expression of hsp83 in Leishmania

Exposure of Leishmania promastigotes to temperatures typical of mammals result in a stress response, which is accompanied by an increase in the steady state level of heat shock transcripts and their translation. Accumulation of the heat shock protein (hsp83) mRNA occurs due to differential decay rates at the altered temperatures, while transcription is unaffected. A similar pattern of post-transcriptional regulation was observed for a transfected chloramphenicol acetyltransferase (CAT) gene, which was flanked at both ends by intergenic regions (IR) of hsp83. Shortening the 5' untranslated region (UTR) by 100 nts produced an active CAT enzyme, but abolished the temperature-dependent regulation of the CAT-hsp83 mRNA turn-over. The 3' UTR is also involved in the temperature-dependent degradation of hsp83 mRNA, since exchange of the hsp83 3' UTR with a parallel fragment from a non-heat shock gene abolished the differential turn-over of CAT mRNA. Thus, the regulated decay of hsp83 mRNA is controlled by sequence or conformational elements present in both upstream and downstream UTRs. Like the endogenous hsp83, translation of CAT mRNA which contained hsp83 UTRs was higher at 35 degrees C. This was observed only with transcripts in which stability increased at elevated temperatures. Modifications which abolished the temperature dependence of CAT mRNA decay, eliminated its elevated translation at the higher temperatures. The correlation suggests a mechanistic link between the translational machinery and mRNA stability.

The structure, organization, and expression of the Leishmania donovani gene encoding trypanothione reductase

Trypanothione reductase (TR) is an NADPH-dependent flavoprotein oxidoreductase central to thiol metabolism in the trypanosomatids. We report here the cloning by expression of the Leishmania donovani gene. It is single copy, expresses a 2.6-kb transcript and a 52-kDa protein and is located on a 1.1-Mbp chromosome. The 491 amino acid sequence has 76% similarity to Crithidia fasciculata and 67% similarity to Trypanosoma cruzi, Trypanosoma congolense and Trypanosoma brucei TR. Residues recognising the adenosine pyrophosphate moiety of NADPH and FAD, and residues in the catalytic site segment (A47-A67) involving electron transfer from TR to trypanothione disulphide (T(S)2) were completely conserved. Thus inhibitors of TR are likely to be active against the enzyme from all the parasitic trypanosomatids. Two peptide inserts (39-47, 131-140) seen in other TR genes and a C-terminal extension of 19 residues were also present. When the gene was introduced back into L. donovani at high copy number using the pTEX expression vector, we detected elevated expression of TR RNA and a 14-fold increase in TR activity. Transfection and overexpression of the TR gene will facilitate studies of gene function and of the dependence of trypanosomatids on TR for protection against oxidative stress.

Conservation of heat-shock proteins in Trypanosoma cruzi

Heat shock is an integral part of the life cycle of Trypanosoma cruzi. Here, Edson Rondinelli reviews the parasite's response to stress.

Sequence and genomic organization of the hsp70 genes of Leishmania amazonensis

The sequence and genomic organization of hsp70 genes in Leishmania amazonensis were examined. Maps of overlapping cosmid clones revealed that seven L. amazonensis hsp70 genes are organized into a 24-kb locus containing 3.5-kb tandem repeats. Cosmids covering a different chromosomal region indicated that an eighth hsp70 sequence is located at a distant site. Southern blot data suggested the existence of additional hsp70 genes or pseudogenes. One complete 3.5-kb genomic repeat unit, including coding and intergenic regions, was sequenced. The predicted L. amazonensis HSP70 protein had approximately 95% sequence identity with Leishmania donovani or Leishmania major HSP70, 81-85% identity with trypanosome HSP70, and 68 or 72% identity with human HSP70 or HSP70 cognate, respectively. The GGMP tetrapeptide repeat found in other trypanosomatid HSP70 proteins is absent from the L. amazonensis sequence. Intergenic sequences of L. amazonensis and L. major differed mainly in the presence of short gaps in the L. amazonensis sequence. Potential regulatory heat shock elements were identified in the upstream sequence. Several cDNA clones were also isolated, and two different poly(A) addition sites 100 nucleotides apart were identified.

Expression of 65- and 67-kilodalton heat-regulated proteins and a 70-kilodalton heat shock cognate protein of Leishmania donovani in macrophages

Heat shock protein (HSP) expression was examined in murine bone marrow-derived macrophages infected with stationary-phase promastigotes of Leishmania donovani. Immunoblotting performed with a rabbit polyclonal antiserum raised against HSP60 from Heliothis virescens (moth) revealed the de novo appearance of 65- and 67-kDa proteins in leishmania-infected macrophages. A third protein of 60 kDa, which represented murine HSP60, was also detected, and its expression did not change in response to infection. In contrast, expression of the novel 65- and 67-kDa proteins in infected cells was coordinately regulated and, at 24 h of infection, reached maximal levels of 52 to 100% increases above initial levels determined at 3 h. Proteins which had identical electrophoretic mobilities and were similarly regulated in response to heat were also detected in promastigotes. The appearance of these proteins in macrophages was specific to leishmania infection in that neither protein was detected in noninfected cells either in the basal state or following several treatments, including (i) infection with Yersinia pseudotuberculosis, (ii) phagocytosis of Staphylococcus aureus, (iii) NaAsO2 treatment, and (iv) heat shock. Expression of the 65- and 67-kDa heat-regulated Leishmania proteins was also observed to be selective, in that as their concentration was increasing, the abundance of the Leishmania surface protease gp63 in infected cells was noted to decrease. Murine HSP60 but not the Leishmania heat-regulated proteins was also recognized by a distinct rabbit antiserum raised against human HSP60, suggesting the presence of specific determinants within these Leishmania proteins. A monoclonal antibody that recognizes both mammalian HSP70 and HSP70 from plasmodia detected single isoforms of both Leishmania and murine HSP70 in infected cells, and the level of neither protein changed during infection. Moreover, although a murine HSP of 73 kDa was induced in response to both heat shock and NaAsO2 treatment, it was not induced to detectable levels by infection. The rapid and relatively high level of expression of inducible HSP60-related proteins of L. donovani and Leishmania HSP70 in infected macrophages suggests that these proteins are involved in pathogenesis and may be important targets of the immune response.

Leishmaniases of the New World: current concepts and implications for future research

Recent epidemiologic studies indicate that leishmaniasis in the Americas is far more abundant and of greater public health importance than was previously recognized. The disease in the New World is caused by a number of different parasite species that are capable of producing a wide variety of clinical manifestations. The outcome of leishmanial infection in humans is largely dependent on the immune responsiveness of the host and the virulence of the infecting parasite strain. This article reviews current concepts of the clinical forms, immunology, pathology, laboratory diagnosis, and treatment of the disease as well as aspects of its epidemiology and control. Recommendations for future research on the disease and its control are made.

Coupling of poly(A) site selection and trans-splicing in Leishmania

Intergenic regions of polycistronic pre-mRNAs of trypanosomatid protozoans are the sites of two processing reactions: polyadenylation of the upstream gene and trans-splicing of the capped miniexon to the downstream gene. Their close proximity and the lack of consensus motifs at poly(A) sites led us to test whether poly(A) site selection is governed by the location of the downstream splice acceptor in the DHFR-TS locus of Leishmania major. Whenever the position of the downstream splice site was altered, the poly(A) site was shifted 400-500 nucleotides upstream of the new splice site. In contrast, when the wild-type poly(A) site was eliminated, the downstream splice site was unaffected, and polyadenylation was maintained 200-500 nucleotides upstream of the splice site. In a second set of experiments, T7 RNA polymerase expressed in Leishmania was used to direct the synthesis of artificial pre-RNAs in vivo whose expression was found to require the presence of a downstream splice acceptor. We conclude that poly(A) site selection in Leishmania is specified by the position of the downstream splice acceptor and propose a scanning model for poly(A) site selection after splice site recognition.

Intergenic sequences from the heat-shock protein 83-encoding gene cluster in Leishmania mexicana amazonensis promote and regulate reporter gene expression in transfected parasites

Regulation of expression from hsp83 gene cluster encoding heat-shock protein (HSP) 83 of the protozoan parasite Leishmania mexicana amazonensis (L.m.a) was examined. The first gene from this cluster, along with 8 kb of flanking sequences, was cloned, and intergenic region (IR) sequences were found upstream from the cluster. L.m.a. parasites were electroporated with a plasmid (pICI) in which the chloramphenicol acetyltransferase (CAT)-encoding gene (cat) was cloned between two IRs derived from an internal repeat unit of the hsp83 cluster, resulting in CAT activity at 26 degrees C. Exposure of cells transfected with this plasmid to a 35 degrees C heat shock led to an increase in CAT activity, within a range similar to that observed for the accumulation of hsp83 steady-state mRNA at 35 degrees C. S1 analysis of the hsp83 mRNA showed that the major part of the IR was transcribed and mostly present as 3' non-translated extensions. Deletion analysis of the flanking regions indicated that the presence of IR sequences, both upstream and downstream from cat, was critical to its expression. Partial deletions that removed the original AG splice acceptor site (leaving 289 bp upstream) and downstream IR sequences (leaving 200 bp) did not eliminate CAT activity. However, this combined deletion altered the effect of temperature on cat expression in transfected cells, as compared with the activity measured in cells transfected with the original plasmid.

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.

Mapping of a visceral leishmaniasis-specific immunodominant B-cell epitope of Leishmania donovani Hsp70

We have shown that a member of the 70-kDa heat shock protein (Hsp70) family is a major target of the humoral immune response during Leishmania donovani infection. A recombinant fusion protein was recognized by sera from 92% (35 of 38) of patients with visceral leishmaniasis, including representatives from each of the major regions where it is endemic. Serological analysis of recombinant Hsp70, expressed by a series of deletion constructs, identified the carboxy-terminal region as the immunodominant site. This region, which is the most evolutionarily divergent part of the molecule, was recognized by all sera from patients with visceral leishmaniasis which exhibited an anti-Hsp70 response. Purified recombinant L. donovani Hsp70 was not recognized by sera from patients with cutaneous leishmaniasis, Chagas' disease, leprosy, malaria, or schistosomiasis. To determine the regions involved in antibody recognition, a series of overlapping peptides were synthesized on polyethylene pins by the Pepscan method, and a hexamer, EADDRA, was identified by the visceral leishmaniasis serum samples as an immunodominant B-cell epitope.

Regulation of hsp70 expression in Trypanosoma cruzi by temperature and growth phase

The steady-state level of the hsp70 mRNAs of Trypanosoma cruzi cultured at different temperatures and growth conditions has been analyzed by Northern blotting. We show that only one size class of hsp70 mRNA, of about 2.2 kb, is transcribed from the hsp70 cluster and that its transcription is constitutive at 28 degrees C. However, after a heat shock treatment at 37 degrees C for 2 h of logarithmically growing parasites, the abundance of the hsp70 mRNA increased about 4-fold. A similar increase was observed at 28 degrees C when the parasite culture reached the stationary phase of growth. On the other hand, a heat shock at 42 degrees C did not change the steady state level of the 2.2-kb size class of hsp70 mRNA. However, accumulation of transcripts of high molecular weight was detected when stationary growing parasites were cultured at 42 degrees C for 2 h. Also at 37 degrees C the steady state level of the alpha- and beta-tubulin mRNAs of logarithmically growing parasites exhibited a slight increase but only after a period of 24 h. Analysis by one-dimensional immunoblots of the Hsp70 levels showed that at 37 degrees C the abundance of the protein was 4-fold higher than at 28 degrees C. Immunoblots of high-resolution two-dimensional gel electrophoresis showed, moreover, that various isoforms of this protein are constitutively expressed at 28 degrees C and that some of them have a specific pattern of induction at 37 degrees C. We observed, moreover, that the heat shock induces the expression of a series of proteins while it causes repression of others.

The chromosomes of Leishmania

Chromosome size polymorphisms occur in Leishmania such that each strain of a given species has a distinctive molecular karyotype. Despite this variability, the chromosomal similarities among closely related strains of Leishmania are sufficiently characteristic to permit classification of unidentified clinical isolates. Mechanisms generating chromosome size polymorphisms are related to chromosomal evolution. In this review, Geoffrey Lighthall and Suzanne Giannini explain that the chromosomal profiles of members of different species may be diverging from a conserved 'consensus' karyotype at different rates, and present a current understanding of the genomic organization of Leishmania with emphasis on chromosomal elements.

Leishmaniasis epidemiology: all down to the DNA

Application of quantitative methods to the study of leishmaniasis epidemiology has allowed Dye (1992) to pinpoint important biological parameters which, if they could be accurately measured in the field, would contribute most to our knowledge of the spread of disease and key targets for control. Three areas in which laboratory-based research could impact most on leishmaniasis epidemiology were highlighted by Dye (1992): (i) the development of accurate diagnostic tools which can distinguish between current and past infection; (ii) to determine the underlying molecular/genetic basis to virulence polymorphisms in the parasite and study these in the context of field epidemiological studies; and (iii) to provide the molecular tools to measure genetic variation in resistance to infection in humans and in reservoir hosts of disease. This paper describes current progress in attaining these goals, highlighting first the work on isolation and field application of genomic and kDNA probes for species-specific diagnosis, and the development of PCR-based assays which can be performed under field conditions. At a more preliminary stage, studies are described in which variability in the major molecular determinants of virulence (lipophosphoglycan, GP63, and members of the HSP70 family of stress proteins) identified through studies of laboratory models of infection, is being measured in primary field isolates of Leishmania peruviana. To complete the picture, current progress in identifying and cloning the genes which control host resistance to leishmanial infection is described, along with field studies of multicase families of human disease in which linkage analysis using marker genes from the chromosomal regions bearing these genes can be used to find evidence for their role in determining disease phenotypes in man. The projected view from these studies is that the future of leishmaniasis epidemiology will be all down to the DNA.

Recombinant Leishmania Hsp90 and Hsp70 are recognized by sera from visceral leishmaniasis patients but not Chagas' disease patients

Approximately 70% of the cDNA clones identified by immunoscreening Leishmania donovani expression libraries with serum from a patient with visceral leishmaniasis (kala-azar) were found to encode the highly conserved Hsp90 and Hsp70 members of the heat shock protein family. Recombinant fusion proteins containing the C-terminal portions of L. donovani Hsp90 and Hsp70 were used as target antigens in enzyme-linked immunosorbent assays of various sera. Sera from four patients with visceral leishmaniasis recognized recombinant Leishmania Hsp90 and Hsp70, while sera from seven patients with Chagas' disease did not, despite the fact that Trypanosoma cruzi Hsp90 and Hsp70 share more than 80% amino acid identity with their counterparts in Leishmania spp. Thus, Leishmania Hsp90 and Hsp70 elicit strong humoral responses and are potential candidates for specific serodiagnostic assays capable of distinguishing between L. donovani and T. cruzi infections.

Hydrogen peroxide-mediated toxicity for Leishmania donovani chagasi promastigotes. Role of hydroxyl radical and protection by heat shock

Leishmania must survive despite exposure to the toxic oxidant hydrogen peroxide (H2O2) during phagocytosis by macrophages. We investigated the mechanism of H2O2 toxicity for L. donovani chagasi promastigotes, and factors responsible for their relative H2O2 resistance. There was a dose-dependent toxic effect of H2O2 for promastigotes isolated during logarithmic phase of growth. In contrast, stationary phase promastigotes were less susceptible to H2O2 toxicity, and more infectious for BALB/c mice. By spin trapping we found that hydroxyl radical (.OH) was generated after exposure of promastigotes to H2O2, and the amount of .OH was greater with log-phase than with stationary-phase promastigotes. .OH was generated after the addition of H2O2 to the cytosol but not the membranes of fractionated promastigotes, and the magnitude of .OH was greater in log than in stationary promastigote cytosol. Deferoxamine inhibition suggested that intracellular promastigote iron catalyzes .OH formation via the Fenton reaction. Furthermore, exposure of log-phase promastigotes to heat shock induced a relative H2O2-resistant state, which was not associated with a decrease in .OH formation but which required ongoing transcription. Thus, growth to stationary phase and heat shock both induce a state of relative H2O2 resistance, but these are probably due to different resistance mechanisms.