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

Heat shock proteins in Varroa destructor exposed to heat stress and in-hive acaricides

Varroa destructor is one of the major pests that affect honeybees around the world. Chemical treatments are common to control varroosis, but mites possess biochemical adaptive mechanisms to resist these treatments, enabling them to survive. So far, no information is available regarding whether these pesticides can induce the expression of heat shock protein (Hsp) as a common protective mechanism against tissue damage. The aims of this study were to determine differences in heat shock tolerance between mites collected from brood combs and phoretic ones, and to examine patterns of protein expression of Hsp70 that occur in various populations of V. destructor after exposure to acaricides commonly employed in beekeeping, such as flumethrin, tau-fluvalinate and coumaphos. Curiously, mites obtained from brood cells were alive at 40 °C, unlike phoretic mites that reached 100% mortality, demonstrating differential thermo-tolerance. Heat treatment induced Hsp70 in mites 4 × more than in control mites and no differences in response were observed in phoretic versus cell-brood-obtained mites. Dose-response assays were carried out at increasing acaricide concentrations. Each population showed a different stress response to acaricides despite belonging to the same geographic region. In one of them, coumaphos acted as a hormetic stressor. Pyrethroids also induced Hsp70, but mite population seemed sensitive to this treatment. We concluded that Hsp70 could represent a robust biomarker for measuring exposure of V. destructor to thermal and chemical stress, depending on the acaricide class and interpopulation variability. This is relevant because it is the first time that stress response is analyzed in this biological model, providing new insight in host-parasite-xenobiotic interaction.

Ultrastructural and physiological changes induced by different stress conditions on the human parasite Trypanosoma cruzi

Trypanosoma cruzi is the etiological agent of Chagas disease. The life cycle of this protozoan parasite is digenetic because it alternates its different developmental forms through two hosts, a vector insect and a vertebrate host. As a result, the parasites are exposed to sudden and drastic environmental changes causing cellular stress. The stress response to some types of stress has been studied in T. cruzi, mainly at the molecular level; however, data about ultrastructure and physiological state of the cells in stress conditions are scarce or null. In this work, we analyzed the morphological, ultrastructural, and physiological changes produced on T. cruzi epimastigotes when they were exposed to acid, nutritional, heat, and oxidative stress. Clear morphological changes were observed, but the physiological conditions varied depending on the type of stress. The maintenance of the physiological state was severely affected by heat shock, acidic, nutritional, and oxidative stress. According to the surprising observed growth recovery after damage by stress alterations, different adaptations from the parasite to these harsh conditions were suggested. Particular cellular death pathways are discussed.

Investigating the Chaperone Properties of a Novel Heat Shock Protein, Hsp70.c, from Trypanosoma brucei

The neglected tropical disease, African Trypanosomiasis, is fatal and has a crippling impact on economic development. Heat shock protein 70 (Hsp70) is an important molecular chaperone that is expressed in response to stress and Hsp40 acts as its co-chaperone. These proteins play a wide range of roles in the cell and they are required to assist the parasite as it moves from a cold blooded insect vector to a warm blooded mammalian host. A novel cytosolic Hsp70, from Trypanosoma brucei, TbHsp70.c, contains an acidic substrate binding domain and lacks the C-terminal EEVD motif. The ability of a cytosolic Hsp40 from Trypanosoma brucei J protein 2, Tbj2, to function as a co-chaperone of TbHsp70.c was investigated. The main objective was to functionally characterize TbHsp70.c to further expand our knowledge of parasite biology. TbHsp70.c and Tbj2 were heterologously expressed and purified and both proteins displayed the ability to suppress aggregation of thermolabile MDH and chemically denatured rhodanese. ATPase assays revealed a 2.8-fold stimulation of the ATPase activity of TbHsp70.c by Tbj2. TbHsp70.c and Tbj2 both demonstrated chaperone activity and Tbj2 functions as a co-chaperone of TbHsp70.c. In vivo heat stress experiments indicated upregulation of the expression levels of TbHsp70.c.

The heat shock proteins of Trypanosoma cruzi

Trypanosoma cruzi is the causal agent of Chagas' disease, a debilitating disorder affecting millions of people in several countries. A flagellated protozoan parasite, T. cruzi has a complex life cycle that involves infecting an insect and a mammalian host. During its life cycle, the parasite undergoes several kinds of stress, prominent among which is heat stress. To deal with this environmental challenge, molecular chaperones and proteases, also known as heat shock proteins (HSPs), are induced as part of the stress response. Several families of HSPs are synthesized by T. cruzi, including members of the major HSP classes such as HSP70, HSP90, HSP100, HSP40, chaperonins and small HSPs, and these proteins show conserved and unique features. In this review we describe these proteins and the corresponding gene expression patterns and discuss their relevance to the biology of the parasite.

Assessment of the viability of Cryptosporidium parvum oocysts with the induction ratio of hsp70 mRNA production in manure

Determining the presence of viable Cryptosporidium parvum oocysts in complex environmental matrices in hygiene control can prevent the contamination of water resources and food with this pathogen. This study assessed the induction ratio of hsp70 mRNA production by heat shock in different oocysts as a marker of viability. Using different procedures for (m)RNA extraction directly from manure and reverse transcription real-time qPCR, this study found slightly increased hsp70 mRNA contents in viable oocysts that were heat shock induced at 45°C for 20 min compared to not induced oocysts (1.6 fold induction in average). Prolonging the heat shock treatment to 2h did not further increase the copy numbers. Heat shock by consecutive stimuli, such as freezing and then heating, did not yield significantly higher copy numbers than the 45°C treatment. There was a certain background level of hsp70 mRNA in viable oocysts that were not exposed to heat shock, indicating a constitutive production of the transcripts in the oocysts. The production of hsp70 mRNA induced by heat shock in oocysts aged for 9 months that exhibited reduced viability was lower than in fresher oocysts (induction ratio<1.2). No production of hsp70 mRNA by heat shock was detected in 12 months old oocysts that were not viable in the excystation test. Oocysts inactivated at 75°C for 30 min were not able to respond to heat shock, and low amount of copies were occasionally measured only in total RNA extracts, but not in mRNA extracts that were purified directly with an oligo (dT)25 based system. The induction ratio of hsp70 mRNA varied according to the viability of the organisms in a sample. Copy numbers of β-tubulin mRNA in viable oocysts were lower than hsp70 mRNA, therefore the latter is more suitable to detect low numbers of oocysts by RT-qPCR.

Characterization of heat shock protein 70 gene fromHaemonchus contortusand its expression and promoter analysis inCaenorhabditis elegans

Haemonchus contortusinfections in small ruminants are of major economic importance worldwide. Heat shock proteins (HSPs) are a family of molecular chaperones that play important roles in the process of invasion and survival of nematodes. Although HSP70 has been identified in several parasitic nematodes, little is known of its distribution and function inHaemonchus contortus. The aims of this study were to characterize HSP70 fromHaemonchus contortus(designed as Hc-hsp70), express Hc-hsp70 and analyse the promoter activity inCaenorhabditis elegans. Bioinformatic analysis revealed that the open reading frame of the Hc-hsp70 cDNA encodes a 646-amino acid peptide, which is highly conserved in comparison to HSP70 in other nematodes. Phylogenetic analysis indicated thatH. contortusis closely related toCaenorhabditis. The 5′-flanking region promoted green fluorescence protein (GFP) expression in the intestine in all larval stages and adult with 2 expression patterns inC. elegans. Expression of Hc-hsp70 mRNA transcripts inC. elegansincreased following 2, 4, 6 h of heat shock and peaked at 4 h. However, its expression induced down-regulation ofhsp-1ofC. elegans. These results suggest that theH. contortushsp70 might have a similar function to that ofC. elegans hsp-1.

Severe heat shock induces nucleolar accumulation of mRNAs in Trypanosoma cruzi

Several lines of evidence have shown that, besides its traditional function in ribosome biogenesis, the nucleolus is also involved in regulating other cellular processes such as mRNA metabolism, and that it also plays an important role as a sensor and coordinator of the stress response. We have recently shown that a subset of RNA Binding Proteins and the poly(A)+ RNA are accumulated into the Trypanosoma cruzi nucleolus after inducing transcription inhibition with Actinomycin D. In this study, we investigated the behaviour of the T. cruzi mRNA population in parasites subjected to severe heat shock, an environmental stress that also decreases the rate of RNA synthesis. We found that the bulk of poly(A)+ RNA is reversibly accumulated into the nucleolus when exposing T. cruzi epimastigote forms to severe heat shock. However, the Hsp70 mRNA was able to bypass such nucleolar accumulation. Together, these data reinforce the idea about the involvement of the T. cruzi nucleolus in mRNA metabolism during an environmental stress response. Interestingly, T. brucei procyclic forms did not induce nucleolar accumulation of poly(A)+ RNA under such stress condition, suggesting that different trypanosomatids have adopted different responses to deal with the same stress conditions.

Proteomic analysis of Trypanosoma cruzi epimastigotes subjected to heat shock

Trypanosoma cruzi is exposed to sudden temperature changes during its life cycle. Adaptation to these variations is crucial for parasite survival, reproduction, and transmission. Some of these conditions may change the pattern of genetic expression of proteins involved in homeostasis in the course of stress treatment. In the present study, the proteome of T. cruzi epimastigotes subjected to heat shock and epimastigotes grow normally was compared by two-dimensional gel electrophoresis followed by mass spectrometry for protein identification. Twenty-four spots differing in abundance were identified. Of the twenty-four changed spots, nineteen showed a greater intensity and five a lower intensity relative to the control. Several functional categories of the identified proteins were determined: metabolism, cell defense, hypothetical proteins, protein fate, protein synthesis, cellular transport, and cell cycle. Proteins involved in the interaction with the cellular environment were also identified, and the implications of these changes are discussed.

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.

Characterization of TcSTI-1, a homologue of stress-induced protein-1, in Trypanosoma cruzi

The life cycle of the protozoan Trypanosoma cruzi exposes it to several environmental stresses in its invertebrate and vertebrate hosts. Stress conditions are involved in parasite differentiation, but little is known about the stress response proteins involved. We report here the first characterization of stress-induced protein-1 (STI-1) in T. cruzi (TcSTI-1). This co-chaperone is produced in response to stress and mediates the formation of a complex between the stress proteins HSP70 and HSP90 in other organisms. Despite the similarity of TcSTI-1 to STI-1 proteins in other organisms, its expression profile in response to various stress conditions, such as heat shock, acidic pH or nutrient starvation, is quite different. Neither polysomal mRNA nor protein levels changed in exponentially growing epimastigotes cultured under any of the stress conditions studied. Increased levels of TcSTI-1 were observed in epimastigotes subjected to nutritional stress in the late growth phase. Co-immunoprecipitation assays revealed an association between TcSTI-1 and TcHSP70 in T. cruzi epimastigotes. Immunolocalization demonstrated that TcSTI-1 was distributed throughout the cytoplasm and there was some colocalization of TcSTI-1 and TcHSP70 around the nucleus. Thus, TcSTI-1 associates with TcHSP70 and TcSTI-1 expression is induced when the parasites are subjected to stress conditions during specific growth phase.

Trypanosoma cruzi: modulation of HSP70 mRNA stability by untranslated regions during heat shock

Gene regulation in trypanosomatids occurs mainly by post-transcriptional mechanisms modulating mRNA stability and translation. We have investigated heat shock protein (HSP) 70 gene regulation in Trypanosoma cruzi, the causal agent of Chagas' disease. The HSP70 mRNA's half-life increases after heat shock, and the stabilization is dependent on protein synthesis. In a cell-free RNA decay assay, a U-rich region in the 3' untranslated region (UTR) is a target for degradation, which is reduced when in the presence of protein extracts from heat shocked cells. In a transfected reporter gene assay, both the 5'- and 3'-UTRs confer temperature-dependent regulation. Both UTRs must be present to increase mRNA stability at 37 degrees C, indicating that the 5'- and 3'-UTRs act cooperatively to stabilize HSP70 mRNA during heat shock. We conclude that HSP70 5'- and 3'-UTRs regulate mRNA stability during heat shock in T. cruzi.

Characterising the KMP-11 and HSP-70 recombinant antigens' humoral immune response profile in chagasic patients

BACKGROUND

Antigen specificity and IgG subclass could be significant in the natural history of Chagas' disease. The relationship between the different stages of human Chagas' disease and the profiles of total IgG and its subclasses were thus analysed here; they were directed against a crude T. cruzi extract and three recombinant antigens: the T. cruzi kinetoplastid membrane protein-11 (rKMP-11), an internal fragment of the T. cruzi HSP-70 protein 192-433, and the entire Trypanosoma rangeli HSP-70 protein.

METHODS

Seventeen Brazilian acute chagasic patients, 50 Colombian chronic chagasic patients (21 indeterminate and 29 cardiopathic patients) and 30 healthy individuals were included. Total IgG and its subtypes directed against the above-mentioned recombinant antigens were determined by ELISA tests.

RESULTS

The T. cruzi KMP-11 and T. rangeli HSP-70 recombinant proteins were able to distinguish both acute from chronic chagasic patients and infected people from healthy individuals. Specific antibodies to T. cruzi crude antigen in acute patients came from IgG3 and IgG4 subclasses whereas IgG1 and IgG3 were the prevalent isotypes in indeterminate and chronic chagasic patients. By contrast, the specific prominent antibodies in all disease stages against T. cruzi KMP-11 and T. rangeli HSP-70 recombinant antigens were the IgG1 subclass.

CONCLUSION

T. cruzi KMP-11 and the T. rangeli HSP-70 recombinant proteins may be explored together in the immunodiagnosis of Chagas' disease. Polarising the IgG1 subclass of the IgG response to T. cruzi KMP-11 and T. rangeli HSP-70 recombinant proteins could have important biological effects, taking into account that this is a complement fixing antibody.

Molecular characterization and expression of three heat shock protein70 genes from the carmine spider mite, Tetranychus cinnabarinus (Boisduval)

Three heat shock protein 70 (Hsp70) cDNAs were isolated from the carmine spider mite, Tetranychus cinnabarinus. They were tentatively named as TCHsp70-1, TCHsp70-2 and TCHsp70-3. Structural analyses showed that all of the three TCHsp70 cDNAs held the full open reading frame (ORF). Putative protein sequences and a phylogenetic tree suggested that TCHsp70-1 and TCHsp70-3 were cytoplasm HSP70 and TCHsp70-2 was endoplasmic reticulum HSP70. Comparison of deduced amino acid sequences of TCHsp70-1 and TCHsp70-3 showed 84.78% identity, TCHsp70-1 and TCHsp70-2 showed 57.33% identity, TCHsp70-2 and TCHsp70-3 showed 58.26% identity. Real-time comparative quantitative PCR revealed that the relative expression of TCHsp70-2 was lower than TCHsp70-1 and TCHsp70-3 at each temperature tested. TCHsp70-1 and TCHsp70-3 shared a similar expression pattern after cold and heat shock compared with their expression at normal temperature (26 degrees C), but the mRNA expression of TCHsp70-1 was significantly higher and lower than that of TCHsp70-3 at cold and heat shock temperatures (except for 34 degrees C), respectively. This result possibly indicated the expression patterns of TCHsp70 were affected by their location in different cellular compartments. The results also indicated that three TCHsp70s, especially TCHsp70-1 and TCHsp70-3, may play an important role in mediating tolerance to cold, thermal stress for Tetranychus cinnabarinus.

Expression patterns of three heat shock protein 70 genes among developmental stages of the red flour beetle, Tribolium castaneum (Coleoptera: Tenebrionidae)

Three genes were identified encoding heat shock protein 70's in Tribolium castaneum (Herbst) and they were tentatively named as tchsp70 I, tchsc70 II, and tchsp70 III. Comparison of deduced amino acid sequences of tchsp70 I and tchsc70 II showed 99% identity. However, the amino acid sequence of tchsp70 III was only 58.5% identical to those of tchsp70 I and tchsc70 II. Stage-specific expression patterns of the tchsp70 were investigated in young larvae, old larvae, pupae, and adults of T. castaneum exposed for 1 h to 23 degrees C (control) or 40 degrees C (heat-shock). Northern blot and real-time quantitative PCR analyses were carried out to determine mRNA levels in each life stage. Transcripts of all three genes were detected by Northern blotting, and the sizes were 2.4- 2.2-, and 2.3-kb for tchsp70 I, tchsc70 II, and tchsp70 III, respectively. A 1.1- to 2.0-fold increased expression of tchsp70 I mRNA was found in heat-shocked developmental stages compared with the control. The expression of tchsc70 II mRNA among developmental stages was similar between heat-shocked and control insects, and the expression of tchsp70 III mRNA varied among developmental stages. Results suggest that the expression of tchsp70 I gene is heat-inducible, tchsc70 II is constitutive, and tchsp70 III is developmentally regulated in T. castaneum.

Role of calreticulin from parasites in its interaction with vertebrate hosts

Although parasites range from protozoan to complex, evolutionary advanced arthropods, in general, a hallmark of parasite life cycles is their ability to adapt to changes in temperature, pH and host defense strategies. Calreticulin, a calcium-binding protein, highly conserved and multifunctional, is present in every cell of higher organisms, except erythrocytes. The surprising array of calreticulin-associated functions include lectin-like chaperoning, calcium storage and signaling, modulation of gene expression, cell adhesion, enhancement of phagocytosis of C1q or collectin opsonized apoptotic cells, inhibition of angiogenesis and tumoral growth, inhibition of perforin pore formation in T and NK cells, and inhibition of C1q-dependent complement activation. Likewise, calreticulin is present in a wide spectrum of sub cellular compartments. Parasite calreticulin shows a surprisingly high degree of conservation within the framework of its functional domains. Its role within the parasite/host relationship needs to be assessed further, in particular with regard to its impact on parasite infectivity, by helping to evade from its hosts' immune response. With special emphasis on calreticulin from Trypanosoma cruzi, the intracellular protozoan agent of American trypanosomiasis (Chagas' disease), we wish to exemplify and highlight the various implications of parasite calreticulin, within the pathophysiology of parasite-mediated human and animal disease.

Cloning and sxpression of mitochondrial heat shock protein 70 of Trypanosoma congolense and potential use as a diagnostic antigen

The ability to use mitochondrial heat shock protein 70 (MTP) of Trypanosoma congolense as a diagnostic antigen was examined. One cDNA clone was obtained by immunoscreening of a T. congolense procyclic form (PCF) cDNA library with monoclonal antibody (MAb) 10F9. The cDNA clone contained an open reading frame of 1,977 bp encoding a polypeptide consisting of 659 amino acids. Southern blotting analysis indicated that there were at least three copies of the MTP gene in the haploid genome. Interference of the MTP RNA resulted in complete inhibition, which indicated that MTP is essential at the PCF stage. Northern and Western blotting analyses revealed that MTP is expressed both in the bloodstream form (BSF) and in PCF. The B-cell epitope recognized by MAb 10F9 was located within 206 amino acids from the C terminus. Depending on the conditions of protein extraction, MTP was cleaved into smaller polypeptides by endogenous proteases. However, the C-terminal epitope of MTP was preserved with a high degree of antigenicity, even after cleavage. Antibody detection by enzyme-linked immunosorbent assay with the truncated recombinant MTP revealed that anti-MTP antibodies exist in experimentally infected mouse sera. Thus, MTP may be useful as an antigen for the serodiagnosis of primary T. congolense infection.

Cloning and characterization of a member of the hsp70 gene family from Locusta migratoria, a highly thermotolerant insect

A complementary deoxyribonucleic acid (cDNA) and the corresponding gene segment encoding a member of the 70-kDa heat shock protein (Hsp70) family have been cloned and sequenced from Locusta migratoria, the African migratory locust. These animals are noted for their thermotolerance, which can exceed temperatures of 50 degrees C. Conceptually translated, the sequence shows a 654-residue protein with theoretical molecular weight of 71.4 kDa, which more closely resembles the mammalian Hsp70 (84-85% similarity) than Hsp70 from other insects, with approximately 75% similarity to the sequence from the fruit fly. Comparisons of cDNA and genomic sequences show that the gene contains 2 introns, a 245-bp intron located in the 5' untranslated region and a 91-bp intron in the coding region. Transcript abundance, as estimated by Northern blot analysis and reverse transcription-polymerase chain reaction, shows that heat shock treatment (45 degrees C for 3 hours) does not elevate hsp70 messenger ribonucleic acid levels in fat bodies or in neural tissues. Immunological assays of Hsp70 show that the protein is constitutively expressed, with a modest, approximately 2-fold induction after a 3-hour heat shock in fat body preparations. Although this sequence could be an hsc70 rather than an hsp70, it was the only cDNA isolated from heat-shocked tissue. Whatever the formal designation, such modest induction and constitutive expression may be ideally suited as an adaptation to the locust's chronic exposure to heat shock temperatures and the consequent demand for chaperone proteins.

Production of amastigotes from metacyclic trypomastigotes of Trypanosoma cruzi

Attempts to recreate all the developmental stages of Trypanosoma cruzi in vitro have thus far been met with partial success. It is possible, for instance, to produce trypomastigotes in tissue culture and to obtain metacyclic trypomastigotes in axenic conditions. Even though T. cruzi amastigotes are known to differentiate from trypomastigotes and metacyclic trypomastigotes, it has only been possible to generate amastigotes in vitro from the tissue-culture-derived trypomastigotes. The factors and culture conditions required to trigger the transformation of metacyclic trypomastigotes into amastigotes are as yet undetermined. We show here that pre-incubation of metacyclic trypomastigotes in culture (MEMTAU) medium at 37 degrees C for 48 h is sufficient to commit the parasites to the transformation process. After 72 h of incubation in fresh MEMTAU medium, 90% of the metacyclic parasites differentiate into forms that are morphologically indistinguishable from normal amastigotes. SDS-PAGE, Western blot and PAABS analyses indicate that the transformation of axenic metacyclic trypomastigotes to amastigotes is associated with protein, glycoprotein and antigenic modifications. These data suggest that (a) T. cruzi amastigotes can be obtained axenically in large amounts from metacyclic trypomastigotes, and (b) the amastigotes thus obtained are morphological, biological and antigenically similar to intracellular amastigotes. Consequently, this experimental system may facilitate a direct, in vitro assessment of the mechanisms that enable T. cruzi metacyclic trypomastigotes to transform into amastigotes in the cells of mammalian hosts.

HSP70 from Trypanosoma cruzi is endowed with specific cell proliferation potential leading to apoptosis

The Trypanosoma cruzi HSP70 recombinant protein has the capacity to stimulate splenocytes or lymph node cells from naive mice in a non-haplotype-restricted way. The proliferative response is abolished by proteinase K digestion and by specific anti-HSP70 antibodies. The induced stimulation index was maximal after 24 h of incubation with the protein. This stimulation leads to cell death in a Fas-Fas ligand-independent way. The phenotype of the expanded cells was CD3(+) TCRalphass(+) CD4(+). HSP70-responsive cells express a broad range of cytokines including IFN-gamma, IL-2 and tumor necrosis factor-alpha. After 48 h of incubation with HSP70 there was a significant increase in relative intracellular levels of CD3 TCRalphass receptors. The expanded CD4(+) cell population expressed CD25; however, in contrast to concanavalin A-treated culture, delayed CD44 expression was observed.

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.

The stability and maturation of the H2A histone mRNAs from Trypanosoma cruzi are implicated in their post-transcriptional regulation

We have recently described that the Trypanosoma cruzi histone H2A genes are actively transcribed as two sized classes of polyadenylated transcripts and that they differ in the 3'-UTRs due to the insertion of a partial SINE sequence in the 3'-end of some of H2A gene units. The expression of the H2A genes in the non-replicative trypomastigote forms is very low, whereas in the replicative forms, there is significant and constitutive transcription of the H2A genes probably regulated in a posttranscriptional way and associated to DNA replication. The data presented in this paper reveal that in epimastigotes, the steady-state levels of the H2A mRNAs are determined by controlling the stability of the messengers in the cytoplasm, most likely mediated by a nuclease attack. The data also indicate that there must be an additional control, associated to the parasite growth phase, which may act at the maturation step of the transcripts. The data suggest, moreover; that the cytoplasmic level of the H2A protein might be involved in the regulation of its own synthesis by controlling translation of existing messengers.

Molecular characterization of KMP11 from Trypanosoma cruzi: a cytoskeleton-associated protein regulated at the translational level

Kinetoplasmid membrane protein-11 (KMP11) is present in a wide range of trypanosomatids. In the present paper, we show that the T. cruzi KMP11 gene is organized in a cluster formed by four gene units arranged in a head-to-tail tandem manner located on a chromosome of about 1900 kb. Northern blot analyses indicated that the steady-state level of mature KMP11 transcripts of 0.52 kb is high and similar in the three forms of the parasite. The KMP11 mRNAs have a half-life of about 16 h whose steady-state level is strongly downregulated when the parasites reach the stationary growth phase. The T. cruzi KMP11 sequence presents a significant homology with the amino-terminal third of the cytoskeleton-associated protein CIP1 from Arabidopsis thaliana. Western blot and immunoelectron microscopy studies showed that KMP11 is present in the cytoskeleton structure. Because the strong downregulation observed in the de novo synthesis of KMP11 protein in parasites treated with vinblastine is not accompanied by a significant fall in the steady-state level of KMP11 mRNAs, regulatory control of the protein at the translational level is suggested.

Expression of alpha- and beta-tubulin genes during growth of Trypanosoma cruzi epimastigotes

The expression of tubulin genes was studied during the growth of epimastigotes of Trypanosoma cruzi. Northern blot analysis showed that there was a decrease in the levels of alpha- and beta-tubulin mRNAs as epimastigotes changed from the logarithmic to the stationary phase. The changes were associated with a similar decrease in the rates of transcription for both of these genes as measured by run-on assays using permeabilized parasites. In contrast to these results, ubiquitin transcription increased slightly. The levels of alpha-tubulin protein per parasite also decreased in stationary compared with logarithmic phase epimastigotes, in close agreement with the decrease in transcription. However, beta-tubulin protein levels did not change significantly. Our results thus indicated that during the growth of epimastigotes, the expression of alpha-tubulin is controlled partially at the transcriptional level. On the other hand, the experiments also suggested that beta-tubulin expression is controlled at a post-transcriptional level.

Bradyzoite development in Toxoplasma gondii and the hsp70 stress response

Toxoplasma gondii is a well-described ubiquitous Apicomplexan protozoan parasite that is an important opportunistic pathogen. The factors affecting the transition of tachyzoites to the latent bradyzoite stage remain to be defined. The induction of bradyzoite development in vitro has been linked to temperature, pH, mitochondrial inhibitors, sodium arsenite, and many of the other stressors associated with heat shock protein (hsp) induction. There is evidence for other organisms that hsps are developmentally regulated. Therefore, we examined whether hsp induction is an early event in bradyzoite differentiation. Extracellular and intracellular T. gondii cells, after exposure to pH 8.1 or 7.1, were analyzed for the expression of inducible hsp70 by using monoclonal antibody C92F3A-5 (specific to hsp70). Western blotting demonstrated that a 72-kDa protein reactive with C92F3A-5 (hsp70), which we believe is part of the hsp70 family, is induced during bradyzoite development. By immunofluorescence and immunoelectron microscopy, we were able to demonstrate that hsp70 staining colocalized to T. gondii expressing bradyzoite-specific antigens and the presence of hsp70 in bradyzoites isolated from mouse brain. Quercetin, a bioflavonoid which inhibits the synthesis of hsp90, hsp70, and hsp27, suppresses the induction of bradyzoite development in vitro. Reverse transcription-PCR with conserved hsp70 primers demonstrated an increase in hsp70 in T. gondii on exposure to conditions which induce bradyzoite formation. A T. gondii hsp70 was subsequently cloned and sequenced by using this amplified fragment. We believe our evidence suggests that hsps are important in the process of bradyzoite differentiation.

Control mechanisms of the H2A genes expression in Trypanosoma cruzi

In a previous report we have described that the T. cruzi histone H2A gene is encoded in two independent gene clusters located in a single chromosome. In the present paper we show that both gene cluster are actively transcribed as two sized classes of polyadenylated mRNAs demonstrating, moreover, the existence of alternative splicing sites and microheterogeneities at the polyadenylation site. We also describe that while the expression of the H2A genes in the non replicative trypomastigote forms is only residual, in the replicative forms there is constitutive transcription of these genes and that the transcription is not associated to DNA replication. The data show, moreover, that in the replicative forms the steady state levels of the H2A mRNAs are controlled at a post-transcriptional level which is associated to DNA replication.

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.

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.

Antioxidant defense mechanisms in parasitic protozoa

Many of the parasitic protozoa, such as Entamoeba histolytica, Giardia, Trypanosoma, Leishmania, and Plasmodium, are considered to be anaerobes because they can be grown in vitro only under conditions of reduced oxygen tension. However, these parasitic protozoa have been found to be aerotolerant or microaerophilic, and also to consume oxygen to a certain extent. Furthermore, these organisms are highly susceptible to exogenous reactive oxygen species, such as hydrogen peroxide. They must, therefore, detoxify both oxygen and free radical products of enzymatic reactions. However, they lack some or all of the usual antioxidant defense mechanisms present in aerobic or other aerotolerant cells, such as catalase, superoxide dismutase, reduced glutathione, and the glutathione-recycling enzymes glutathione peroxidase and glutathione reductase. Instead, they possess alternative mechanisms for detoxification similar to those known to exist in certain prokaryotes. Although the functional aspects of these alternative mechanisms are yet to be understood completely, they could provide new insights into the biochemical peculiarities of these enigmatic pathogens.

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.

A 69 kDa immunodominant antigen of Trypanosoma (Nannomonas) congolense is homologous to immunoglobulin heavy chain binding protein (BiP)

An immunodominant antigen in Trypanosoma congolense-infected cattle is a 69 kDa protein which is conserved among species and developmental stages of African trypanosomes. Immunoscreening of a cDNA expression library identified a 2.35 kbp clone which contains a complete open reading frame encoding a protein of 653 amino acids with a predicted molecular mass of 71 kDa. Protein sequence analyses revealed 45-65% identity with hsp70s from a broad range of organisms, the highest homology being with the mammalian BiP (immunoglobulin heavy chain binding protein). The 69 kDa trypanosome protein shares with other BiP-related molecules two characteristics that are associated with their localization in the endoplasmic reticulum and their function as chaperonins, i.e., a hydrophobic N-terminal signal sequence and a conserved C-terminal tetrapeptide (X)DEL. Divergence between the 69 kDa antigen and other BiP-homologues occurs in the C-terminal region. This may be responsible for the high immunogenicity of the trypanosome protein. The gene for the 69 kDa antigen appears to be present as a cluster of several copies which are not organized in tandem repeats. It is expressed in all developmental stages of T. congolense, but the specific mRNA levels are higher in metacyclics than in other stages.

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.

Mapping of antigenic determinants of the T. cruzi hsp70 in chagasic and healthy individuals

In the present paper we describe the analysis of the immunological recognition by sera of healthy individuals and chagasic patients of the Trypanosoma cruzi heat shock 70 kDa protein. By a Falcon Assay Screening Test, using as antigen an ATP-agarose purified T. cruzi hsp70, it has been found that the sera of infected patients as well as of that of healthy individuals show reactivity against the hsp70 protein but that the reactivity of the sera of patients is in general significantly higher than that of healthy individuals. The analysis of the reactivity of the chagasic sera against a collection of peptides covering 92% of the protein has shown that more than 50% of the peptides gave a positive response but only against a few peptides did we observe high reactivity in a wide spectrum of sera. Only four peptides (numbers 9, 12, 14 and 47) were recognized by all sera tested with high reactivity values. The sera of healthy individuals also showed reactivity against a large percentage of peptides but with lower values. It was observed that particular peptides showing high reactivity against the sera of healthy donors also show high reactivity against patients' sera. However, the general pattern of reactivity against the peptides is different in chagasic and healthy sera. The immunodominant peptides map in the highly conserved as well as in the less conserved part of the hsp70 molecule. The 1/3 C-terminal, being the least conserved part of the molecule, seems to be the least immunogenic. Mapping of the epitopes led to the identification of particular immunogenic motifs within individual peptides.