Transcriptional analysis of the EhPgp1 promoter of Entamoeba histolytica multidrug-resistant mutant

A noncanonical GATA transcription factor of Entamoeba histolytica modulates genes involved in phagocytosis

In this paper, we explored the presence of GATA in Entamoeba histolytica and their function as regulators of phagocytosis-related genes. Bioinformatics analyses evidenced a single 579 bp sequence encoding for a protein (EhGATA), smaller than GATA factors of other organisms. EhGATA appeared phylogenetically close to Dictyostelium discoideum and Schistosoma mansoni GATA proteins. Its sequence predicts the presence of a zinc-finger DNA binding domain and an AT-Hook motif; it also has two nuclear localization signals. By transmission electron and confocal microscopy, anti-EhGATA antibodies revealed the protein in the cytoplasm and nucleus, and 65% of nuclear signal was in the heterochromatin. EhGATA recombinant protein and trophozoites nuclear extracts bound to GATA-DNA consensus sequence. By in silico scrutiny, 1,610 gene promoters containing GATA-binding sequences appeared, including Ehadh and Ehvps32 promoters, whose genes participate in phagocytosis. Chromatin immunoprecipitation assays showed that EhGATA interact with Ehadh and Ehvps32 promoters. In EhGATA-overexpressing trophozoites (NeoGATA), the Ehadh and Ehvps32 mRNAs amount was modified, strongly supporting that EhGATA could regulate their transcription. NeoGATA trophozoites exhibited rounded shapes, high proliferation rates, and diminished erythrophagocytosis. Our results provide new insights into the role of EhGATA as a noncanonical transcription factor, regulating genes associated with phagocytosis.

The Entamoeba histolytica TBP and TRF1 transcription factors are GAAC-box binding proteins, which display differential gene expression under different stress stimuli and during the interaction with mammalian cells

BACKGROUND

Entamoeba histolytica is the protozoan parasite responsible for human amebiasis. It causes up to 100,000 deaths worldwide each year. This parasite has two closely related basal transcription factors, the TATA-box binding protein (EhTBP) and the TBP-related factor 1 (EhTRF1). TBP binds to the canonical TATTTAAA-box, as well as to different TATA variants. TRF1 also binds to the TATTTAAA-box. However, their binding capacity to diverse core promoter elements, including the GAAC-element, and their role in gene regulation in this parasite remains unknown.

METHODS

EMSA experiments were performed to determine the binding capacity of recombinant TBP and TRF1 to TATA variants, GAAC and GAAC-like boxes. For the functional analysis under different stress stimuli (e.g. growth curve, serum depletion, heat-shock, and UV-irradiation) and during the interaction with mammalian cells (erythrocytes, MDCK cell monolayers, and hepatocytes of hamsters), RT-qPCR, and gene knockdown were performed.

RESULTS

Both transcription factors bound to the different TATA variants tested, as well as to the GAAC-boxes, suggesting that they are GAAC-box-binding proteins. The K _D values determined for TBP and TRF1 for the different TATA variants and GAAC-box were in the range of 10^-12 M to 10^-11 M. During the death phase of growth or in serum depletion, Ehtbp mRNA levels significantly increased, whereas the mRNA level of Ehtrf1 did not change under these conditions. Ehtrf1 gene expression was negatively regulated by UV-irradiation and heat-shock stress, with no changes in Ehtbp gene expression. Moreover, Ehtrf1 gene also showed a negative regulation during erythrophagocytosis, liver abscess formation, and a transient expression level increase at the initial phase of MDCK cell destruction. Finally, the Ehtbp gene knockdown displayed a drastic decrease in the efficiency of erythrophagocytosis in G3 trophozoites.

CONCLUSIONS

To our knowledge, this study reveals that these basal transcription factors are able to bind multiple core promoter elements. However, their immediate change in gene expression level in response to different stimuli, as well as during the interaction with mammalian cells, and the diminishing of erythrophagocytosis by silencing the Ehtbp gene indicate the different physiological roles of these transcription factors in E. histolytica.

A Novel Heat Shock Element (HSE) in Entamoeba histolytica that Regulates the Transcriptional Activation of the EhPgp5 Gene in the Presence of Emetine Drug

Transcriptional regulation of the multidrug resistance EhPgp5 gene in Entamoeba histolytica is induced by emetine stress. EhPgp5 overexpression alters the chloride-dependent currents that cause trophozoite swelling, diminishing induced programmed cell death (PCD) susceptibility. In contrast, antisense inhibition of P-glycoprotein (PGP) expression produces synchronous death of trophozoites and the enhancement of the biochemical and morphological characteristics of PCD induced by G418. Transcriptional gene regulation analysis identified a 59 bp region at position −170 to −111 bp promoter as putative emetine response elements (EREs). However, insights into transcription factors controlling EhPgp5 gene transcription are missing; to fill this knowledge gap, we used deletion studies and transient CAT activity assays. Our findings suggested an activating motif (−151 to −136 bp) that corresponds to a heat shock element (HSE). Gel-shift assays, UV-crosslinking, binding protein purification, and western blotting assays revealed proteins of 94, 66, 62, and 51 kDa binding to the EhPgp5 HSE that could be heat shock-like transcription factors that regulate the transcriptional activation of the EhPgp5 gene in the presence of emetine drug.

Regulation of serum-responsive transmembrane kinase EhTMKB1-9 by an unsaturated lipid, oleic acid in protistan parasite Entamoeba histolytica

Transmembrane kinases of Entamoeba histolytica are known to play a wide range of roles from virulence, phagocytosis, and proliferation to stress response. Transmembrane kinase EhTMKB1-9 is thought to be involved in early proliferative response and it was originally identified as a serum inducible gene. Ability to stimulate EhTMKB1 expression of serum starved cells resides in unsaturated fatty acids associated with albumin fraction of serum and the mechanism of stimulation follows activation of EhTMKB1-9 promoter. Gel shift assay showed the presence of proteins that bind to the specific site of EhTMKB1-9 upstream region and the concentration of these protein(s) go down on serum starvation, but level of binding protein(s) go up on serum or fatty acid replenishment. This increase in concentration of binding molecule(s) is due to new synthesis rather than activation of existing molecule(s) as a protein synthesis inhibitor blocked enhanced level of gel shifted material on replenishment. The stimulating activity resides in the fatty acyl chain, but not in the head group. Moreover, the fatty acid initiates signaling through class I PI3 kinases that result in activation of EhTMKB1-9 expression. These results suggest a novel mechanism of gene regulation in E. histolytica, and unsaturated fatty acids as potential new signaling molecules.

Transferrin regulates mRNA levels of a gene involved in iron utilization in Entamoeba histolytica

Entamoeba histolytica is a human pathogen, which can survive using haemoglobin (Hb) as only iron supply. Two probable haemophores (Ehhmbp26 and Ehhmbp45) are involved in iron acquisition in this parasite. However, mechanisms related to their transcriptional regulation have not been studied yet. In the present work, transcriptional profiles of both genes were evaluated in trophozoites cultures grown with different iron sources. ehhmbp26 gene was repressed totally by free iron, whereas ehhmbp45 gene showed clearly detectable mRNA levels. Expression profiles for both genes were significantly increased under iron privation condition. Interestingly, ehhmbp26 transcript was highly expressed by Holo-transferrin presence. This induction appears to be independent of direct contact between these proteins, because, in vitro assays evidenced that Ehhmbp26 protein was unable to bind this metalloprotein. Besides, in silico analysis of promoter nucleotide sequences of ehhmbp26 and ehhmbp45 genes revealed some distinctive core promoter elements described in E. histolytica and T-rich regions. Taking altogether these data suggest in E. histolytica dissimilar transcriptional mechanisms involved on iron acquisition control the expression of these genes, and they are unlike to those previously described for instance: in bacteria. Our findings evidenced this pathogen regulates the expression of ehhmbp26 and ehhmbp45 genes depending on the available iron supply, always ensuring the success of its infective process.

Serum-dependent selective expression of EhTMKB1-9, a member of Entamoeba histolytica B1 family of transmembrane kinases

Entamoeba histolytica transmembrane kinases (EhTMKs) can be grouped into six distinct families on the basis of motifs and sequences. Analysis of the E. histolytica genome revealed the presence of 35 EhTMKB1 members on the basis of sequence identity (≥95%). Only six homologs were full length containing an extracellular domain, a transmembrane segment and an intracellular kinase domain. Reverse transcription followed by polymerase chain reaction (RT-PCR) of the kinase domain was used to generate a library of expressed sequences. Sequencing of randomly picked clones from this library revealed that about 95% of the clones were identical with a single member, EhTMKB1-9, in proliferating cells. On serum starvation, the relative number of EhTMKB1-9 derived sequences decreased with concomitant increase in the sequences derived from another member, EhTMKB1-18. The change in their relative expression was quantified by real time PCR. Northern analysis and RNase protection assay were used to study the temporal nature of EhTMKB1-9 expression after serum replenishment of starved cells. The results showed that the expression of EhTMKB1-9 was sinusoidal. Specific transcriptional induction of EhTMKB1-9 upon serum replenishment was further confirmed by reporter gene (luciferase) expression and the upstream sequence responsible for serum responsiveness was identified. EhTMKB1-9 is one of the first examples of an inducible gene in Entamoeba. The protein encoded by this member was functionally characterized. The recombinant kinase domain of EhTMKB1-9 displayed protein kinase activity. It is likely to have dual specificity as judged from its sensitivity to different kinase inhibitors. Immuno-localization showed EhTMKB1-9 to be a surface protein which decreased on serum starvation and got relocalized on serum replenishment. Cell lines expressing either EhTMKB1-9 without kinase domain, or EhTMKB1-9 antisense RNA, showed decreased cellular proliferation and target cell killing. Our results suggest that E. histolytica TMKs of B1 family are functional kinases likely to be involved in serum response and cellular proliferation.

The presence of a vast array of putative transmembrane kinase genes suggests an extensive network of signaling systems in E. histolytica, particularly the ability to perceive signals from the extracellular environment and transduce these intracellularly. However, it has been very difficult to work with these molecules due to the presence of a large number of homologs. It is also not clear if these molecules are indeed protein kinases, as no kinase activity has yet been shown associated with these molecules. In this report, we show that EhTMKB1-9 is a protein kinase and it is one of the early serum-induced genes. It is a predominant EhTMKB1 molecule that is expressed in proliferating cells and its expression is modulated by serum. Cells containing a reduced level of EhTMKB1-9 or high level of a mutant protein result in decreased proliferation, target cell killing and adherence. The results presented in this report suggest that EhTMKB1-9 is an important signaling molecule likely to be involved in E. histolytica proliferation and virulence. We have also identified a serum starvation induced response where expression of EhTMKB1-18 was found to be induced.

Regulation of gene expression in protozoa parasites

Infections with protozoa parasites are associated with high burdens of morbidity and mortality across the developing world. Despite extensive efforts to control the transmission of these parasites, the spread of populations resistant to drugs and the lack of effective vaccines against them contribute to their persistence as major public health problems. Parasites should perform a strict control on the expression of genes involved in their pathogenicity, differentiation, immune evasion, or drug resistance, and the comprehension of the mechanisms implicated in that control could help to develop novel therapeutic strategies. However, until now these mechanisms are poorly understood in protozoa. Recent investigations into gene expression in protozoa parasites suggest that they possess many of the canonical machineries employed by higher eukaryotes for the control of gene expression at transcriptional, posttranscriptional, and epigenetic levels, but they also contain exclusive mechanisms. Here, we review the current understanding about the regulation of gene expression in Plasmodium sp., Trypanosomatids, Entamoeba histolytica and Trichomonas vaginalis.

Targets of the Entamoeba histolytica transcription factor URE3-BP

The Entamoeba histolytica transcription factor Upstream Regulatory Element 3-Binding Protein (URE3-BP) is a calcium-responsive regulator of two E. histolytica virulence genes, hgl5 and fdx1. URE3-BP was previously identified by a yeast one-hybrid screen of E. histolytica proteins capable of binding to the sequence TATTCTATT (Upstream Regulatory Element 3 (URE3)) in the promoter regions of hgl5 and fdx1. In this work, precise definition of the consensus URE3 element was performed by electrophoretic mobility shift assays (EMSA) using base-substituted oligonucleotides, and the consensus motif validated using episomal reporter constructs. Transcriptome profiling of a strain induced to produce a dominant-positive URE3-BP was then used to identify additional genes regulated by URE3-BP. Fifty modulated transcripts were identified, and of these the EMSA defined motif T[atg]T[tc][cg]T[at][tgc][tg] was found in over half of the promoters (54% p<0.0001). Fifteen of the URE3-BP regulated genes were potential membrane proteins, suggesting that one function of URE3-BP is to remodel the surface of E. histolytica in response to a calcium signal. Induction of URE3-BP leads to an increase in tranwell migration, suggesting a possible role in the regulation of cellular motility.

Programmed cell death in Entamoeba histolytica induced by the aminoglycoside G418

This study presents morphological and biochemical evidence of programmed cell death (PCD) in Entamoeba histolytica induced by exposure of trophozoites to the aminoglycoside antibiotic G418. Morphological characteristics of PCD, including cell shrinkage, reduced cellular volume, nuclear condensation, DNA fragmentation and vacuolization were observed, with preservation of trophozoite membrane integrity. PCD is orchestrated biochemically by alterations in intracellular ion fluxes. In G418-treated trophozoites, overproduction of reactive oxygen species (ROS), decreased intracellular K+, increased cytosolic calcium, and decreased intracellular pH levels were observed. However, externalization of phosphatidylserine was not detected. These results suggest that amoebae can undergo PCD under stress conditions, and that this PCD shares several properties with PCD reported in mammals and in a variety of unicellular organisms.

Structural and functional analysis of the Entamoeba histolytica EhrabB gene promoter

BACKGROUND

The Entamoeba histolytica EhrabB gene encodes for a Rab GTPase involved in phagocytosis. It is located at a virulence locus where the Ehcp112 gene is in the complementary strand at 332 bp of EhrabB start codon, suggesting a finely regulated transcription of both genes. However, the transcription regulation in this parasite is poorly understood.

RESULTS

To initiate the knowledge of EhrabB gene expression regulation, here we studied the structural characteristics of its gene promoter and its control transcription elements. In silico searches of the EhrabB 5'-flanking region revealed that it contains a motif similar to the upstream regulatory element 1 (URE1) of the E. histolytica hgl5 gene. It also has sequences with homology to C/EBP and GATA1 binding sites, and heat shock elements (HSE). Primer extension experiments revealed that EhrabB has at least four transcription initiation sites. The elements at the 5'-flanking region that drive EhrabB gene expression were detected and characterized using transitory transfected trophozoites with a plasmid carrying the CAT reporter gene. EhrabB transcription is negatively regulated by a sequence located between positions -491 to -428 with respect to the first transcription initiation site. We also showed that the URE1-like motif activates EhrabB transcription. In addition, heat shock activated the EhrabB promoter in episomal constructs and lead to an increase in de novo EhrabB transcription.

CONCLUSION

The data suggest that EhrabB transcription is controlled negatively by an unidentified sequence, but it is activated by an URE1-like motif. Our analyses also revealed the presence of activator HSE that function under stress.

Entamoeba histolytica EhPgp5 transcriptional activation depends on putative emetine response elements

The multidrug resistance EhPgp5 gene promoter is active in drug resistant clone C2 trophozoites and its activity increases when trophozoites are cultured in the presence of emetine, suggesting that the EhPgp5 gene shows an inducible drug dependent mechanism. We analyzed different promoter fragments to detect those regions that activate transcription in the presence of emetine. Trophozoites were transfected with p375Pgp5, p259Pgp5, p187Pgp5, and p76Pgp5 plasmids and incubated with different emetine concentrations. p375Pgp5 and p259Pgp5 plasmids were able to drive CAT expression in A and C2 trophozoites only in the presence of emetine. CAT activity was turned off in the absence of drug. Interestingly, no CAT activity was detected in the presence or in the absence of emetine with p187Pgp5 plasmid in which 59 bp were deleted at the 5' end of the EhPgp5 minimal promoter (p259Pgp5). These results suggest that the overexpression of the EhPgp5 gene is a consequence of transcriptional activation of the gene promoter by putative drug responsive elements, located within the -111 to -170 bp of the transcription initiation site.

Entamoeba histolytica: functional characterization of the -234 to -196 bp promoter region of the multidrug resistance EhPgp1 gene

The multidrug resistance EhPgp1 gene is constitutively expressed in drug resistant trophozoites from Entamoeba histolytica. It has been demonstrated that two CCAAT/enhancer binding sites located in the EhPgp1 gene promoter control its transcriptional activation. However, functional assays of the 5' end of its promoter showed that region from -234 to -196 bp (38 bp) is also important for the EhPgp1 gene transcription. Here, we demonstrated that in the 38 bp region putative cis-activator sequences are located. In silico analysis showed the presence of GATA1, Gal4, Nit-2, and C/EBP consensus sequences. Additionally, we identified three specific DNA-protein complexes, which were competed by a C/EBP, GATA1, and HOX oligonucleotides. Finally, we partially purified three proteins of 64.4, 56.7, and 27.4 kDa. Further investigations are currently in progress to determine the identity of these nuclear factors and how they are interacting with the EhPgp1 gene promoter.

Entamoeba histolytica TATA-box binding protein binds to different TATA variants in vitro

The ability of Entamoeba histolytica TATA binding protein (EhTBP) to interact with different TATA boxes in gene promoters may be one of the key factors to perform an efficient transcription in this human parasite. In this paper we used several TATA variants to study the in vitro EhTBP DNA-binding activity and to determine the TATA-EhTBP dissociation constants. The presence of EhTBP in complexes formed by nuclear extracts (NE) and the TATTTAAA oligonucleotide, which corresponds to the canonical TATA box for E. histolytica, was demonstrated by gel-shift assays. In these experiments a single NE-TATTTAAA oligonucleotide complex was detected. Complex was retarded by anti-EhTBP Igs in supershift experiments and antibodies also recognized the cross-linked complex in Western blot assays. Recombinant EhTBP formed specific complexes with TATA variants found in E. histolytica gene promoters and other TATA variants generated by mutation of TATTTAAA sequence. The dissociation constants of recombinant EhTBP for TATA variants ranged between 1.04 (+/-0.39) x 10(-11) and 1.60 (+/-0.37) x 10(-10) m. TATTTAAA and TAT_ _AAA motifs presented the lowest KD values. Intriguingly, the recombinant EhTBP affinity for TATA variants is stronger than other TBPs reported. In addition, EhTBP is more promiscuous than human and yeast TBPs, probably due to modifications in amino acids involved in TBP-DNA binding.

Collagen-induced STAT family members activation in Entamoeba histolytica trophozoites

The interaction of Entamoeba histolytica trophozoites with collagen type I and calcium induces a membrane to nuclei signaling. The transduction pathways involved in such phenomena are still poorly understood. Using a combination of immunoprecipitation assays, Western immunoblot analysis, electrophoretic mobility shift assays and immunocytochemistry we demonstrate here the expression, tyrosine phosphorylation, nuclear translocation and DNA binding of two members of the signal transducers and activators of transcription family of inducible transcription factors in the protozoan parasite E. histolytica. These results support the notion that the interaction of the extracellular matrix components with the parasite turns on a genetic program that facilitates the invasion of the host.

Cellular location and function of the P-glycoproteins (EhPgps) in Entamoeba histolytica multidrug-resistant trophozoites

We have studied the cellular location and the efflux pump function of the Entamoeba histolytica P-glycoproteins (EhPgps) in drug-sensitive and -resistant trophozoites. Polyclonal antibodies against the EhPgp384 polypeptide (375-759 amino acids) revealed a 147-kDa protein by Western blot. The band intensity correlated with the emetine-resistance of the trophozoites. Through the confocal microscope, using the anti-EhPgp384 and fluorescein secondary antibodies, the EhPgps were found in a complex vesicular network, in the plasma membrane and outside of the cells. Transmission electron microscopy assays confirmed that drug-resistant trophozoites presented four to five times more EhPgps than sensitive cells. Fluorescence co-localization experiments using rhodamine-123 (R123) and the anti-EhPgp384 antibodies suggested the interaction between EhPgps and the drug. R123 efflux kinetics evidenced that the emetine-resistant trophozoites displayed a drug efflux kinetic four times higher than the drug-sensitive trophozoites, which was reduced by verapamil in both cases. EhPgps may participate in avoiding drug accumulation in the trophozoites by two putative mechanisms: (1) the direct extrusion of the drug from the plasma membrane, and (2) an indirect transport mechanism in which the drug is trapped by EhPgps and concentrated within vesicles that drive the drug to the plasma membrane.

Ehp53, an Entamoeba histolytica protein, ancestor of the mammalian tumour suppressor p53

This paper reports the identification of Ehp53, a p53-like Entamoeba histolytica protein, which binds to the human p53 DNA consensus sequence (oli-p53). Monoclonal antibodies against p53 (Ab-1 and Ab-2) recognized a single 53 kDa spot in two-dimensional gels and inhibited the formation of complexes produced by E. histolytica nuclear extracts and oli-p53. Additionally, E. histolytica gene promoter sequences with high homology to oli-p53 formed complexes with nuclear proteins that were abolished by oli-p53. Ehp53 protein levels increased in UV-irradiated trophozoites. This protein was also detected in Entamoeba moshkovskii and Entamoeba invadens. By confocal microscopy, Ehp53 was located in the nuclei, EhkO organelles and cytoplasm. The Ehp53-encoding gene was cloned and its predicted amino acid sequence showed 30-54 % and 50-57 % homology with important domains of the human and the Drosophila melanogaster p53 proteins, respectively. This homology included the tetramerization domain, the nuclear export signal and a nuclear localization signal. Ehp53 also contains seven of the eight DNA-binding residues and two of the four Zn(2+)-binding sites described for p53. A recombinant Ehp53 was recognized by Ab-2. Ehp53 is believed to be the first p53-like protein found in protozoa and may be the evolutionary ancestor of the mammalian p53.

EhPgp5 mRNA stability is a regulatory event in the Entamoeba histolytica multidrug resistance phenotype

The multidrug resistance (MDR) phenotype in Entamoeba histolytica is characterized by the overexpression of the EhPgp5 gene in trophozoites grown in high drug concentrations. Here we evaluated the role of EhPgp5 mRNA stability on MDR using actinomycin D. EhPgp5 mRNA from trophozoites growing without emetine had a half-life of 2.1 h, which augmented to 3.1 h in cells cultured with 90 microM and to 7.8 h with 225 microM emetine. Polyadenylation sites were detected at 118-, 156-, and 189-nucleotide (nt) positions of the EhPgp5 mRNA 3'-untranslated region. Interestingly, trophozoites grown with 225 microM emetine exhibited an extra polyadenylation site at 19 nt. The 3'-untranslated region sequence is AU-rich and has putative consensus sequences for RNA-binding proteins. We detected a RNA-protein complex in a region that contains a polypyrimidine tract (142-159 nt) and a cytoplasmic polyadenylation element (146-154 nt). A longer poly(A) tail in the EhPgp5 mRNA was seen in trophozoites grown with 225 microM emetine. Emetine stress may affect factors involved in mRNA turnover, including polyadenylation/deadenylation proteins, which could induce changes in the EhPgp5 mRNA half-life and poly(A) tail length. Novel evidence on mechanisms participating in E. histolytica MDR phenotype is provided.

Calcium modulates promoter occupancy by the Entamoeba histolytica Ca2+-binding transcription factor URE3-BP

The Entamoeba histolytica upstream regulatory element 3-binding protein (URE3-BP) binds to the URE3 sequence of the Gal/GalNAc-inhibitable lectin hgl5 and ferredoxin 1 (fdx) gene promoters. This binding can be inhibited in vitro by addition of calcium. Two EF-hand motifs, which are associated with the ability to bind calcium, are present in the amino acid sequence of URE3-BP. Mutation of the second EF-hand motif in URE3-BP resulted in the loss of calcium inhibition of DNA binding as monitored by electrophoretic mobility shift assay. Chromatin immunoprecipitation assays revealed that URE3-BP was physically bound to the hgl5 and fdx promoters in vivo. Parasite intracellular calcium concentrations were altered by changes in extracellular calcium. Promoter occupancy was lost when intracellular calcium levels were increased by coordinate increases in extracellular calcium. Increased intracellular calcium also resulted in decreased levels of URE3-BP mRNA. Together these results demonstrate that changes in extracellular calcium result in changes in URE3-BP mRNA and in the ability of URE3-BP to bind to URE3-containing promoters. Modulation of URE3-BP by calcium may represent an important mechanism of control of gene expression in E. histolytica.

Multidrug resistance in the protozoan parasite Entamoeba histolytica

In this review we discuss the mechanisms and molecules involved in the multidrug resistance (MDR) of the protozoan parasite Entamoeba histolytica. Drug resistant mutants exhibited the main characteristics presented by the MDR mammalian cells. They showed cross-resistance to several unrelated drugs that is reverted by calcium channel blockers. MDR phenotype in E. histolytica is regulated at a transcriptional level by the EhPgp1 gene, which is constitutively expressed and by the EhPgp5 gene, whose expression is induced in the presence of the drug. Transcription factors participate in the expression regulation of these genes. After over transcription, the EhPgp genes are amplified, cooperating to produce the MDR phenotype. Post-transcriptional mechanisms such as mRNA stability seem to be involved in this phenomenon. As for other mdr gene products, the EhPGP5 protein functions as a chloride current inductor or as a regulator of cellular regulatory volume decrease.

Two CCAAT/enhancer binding protein sites are cis-activator elements of the Entamoeba histolytica EhPgp1 (mdr-like) gene expression

Here, we show the relevance of promoter regions (-74 to +24, -167 to -75 and -259 to -168 bp) in the transcriptional activation of the multidrug resistance gene EhPgp1 in Entamoeba histolytica, using mutated plasmids and transfection assays. We also demonstrate that both CCAAT/enhancer binding protein sites (-54 to -43 bp and -198 to -186 bp) are cis-activating elements of gene expression in the drug-resistant (clone C2) and -sensitive (clone A) trophozoites. Nuclear proteins from trophozoites of both clones and C/EBP sequences of the core promoter formed specific complexes, which were abolished by anti-human C/EBPbeta antibodies. UV cross-linking and Western blot assays revealed 25 and 65 kDa bands in urea treated and untreated proteins respectively. The nuclear factors that bind to C/EBP sites were semi-purified by affinity chromatography. They were immunodetected by anti-human C/EBPbeta antibodies and formed a specific complex with the C/EBP probe. The antibodies recognized proteins in the cytoplasm, nucleus and EhkO organelles in immunofluorescence and confocal microscopy experiments. Based on our results, we propose that the C/EBP site at -54 bp stabilizes the transcription pre-initiation complex, whereas the other site at -198 bp may be involved in the formation of a multiprotein complex, which provokes DNA folding and promotes the EhPgp1 gene transcription.

The Entamoeba histolytica EhPgp5 (MDR-like) protein induces swelling of the trophozoites and alters chloride-dependent currents in Xenopus laevis oocytes

Entamoeba histolytica, the protozoan responsible for human amoebiasis, presents the multidrug resistant phenotype due to the expression of the E. histolytica P-glycoproteins EhPgpl and EhPgp5. Here, we studied the protein EhPgp5 encoded by the EhPgp5 gene in emetine-sensitive trophozoites transfected with the pEhNEOPgp5 plasmid carrying the EhPgp5 gene. The transfected trophozoites increased their drug resistance slightly, but became bigger and globular. To investigate other EhPgp5 functions further, we microinjected the EhPgp5 mRNA in Xenopus laevis oocytes. Microinjected oocytes expressed EhPgp5 protein in their membranes and exhibited an ion current not present in the control oocytes. The antisense EhPgp5AS transcript, co-injected with the EhPgp5 mRNA, abolished the exogenous current, showing its specificity. Exogenous current was outward during depolarizing pulses. Reduction of the extracellular Cl- concentration displayed a reversible decrease of the current amplitude. Niflumic acid, 4,4-diisothiocyanatostilbene-2, 2'-disulfonic acid, and other Cl- channel blockers abolished the exogenous current, which was poorly modified by verapamil and changes in osmolarity of the medium. Our results suggest that the EhPgp5 protein could function as a Cl- current inductor and as a coadjuvant factor to avoid drug accumulation in the cell.

Identification of two Entamoeba histolytica sequence-specific URE4 enhancer-binding proteins with homology to the RNA-binding motif RRM

To study transcriptional regulation in the lower branching eukaryote Entamoeba histolytica, we have identified two sequence-specific DNA-binding proteins that recognize the upstream regulatory element URE4, an enhancer that regulates expression of the Gal/GalNAc lectin heavy subunit gene hgl5. A chromatographic purification of E. histolytica nuclear extracts by gel filtration, cation exchange, and sequence-specific DNA affinity chromatography led to a 700-fold increase in URE4 binding activity and the appearance of two dominant protein species with molecular masses of 28 and 18 kDa. These proteins, termed E. histolytica enhancer-binding proteins 1 and 2 (EhEBP1 and EhEBP2), were sequenced by tandem mass spectroscopy and their corresponding cDNA clones identified. Recombinant EhEBP1 and EhEBP2 were able to bind double-stranded oligonucleotides bearing the URE4 motif in a sequence-specific manner, and antibodies raised against EhEBP1 were able to interfere with the formation of URE4-protein complexes in crude nuclear extracts. Overexpression of EhEBP1 in E. histolytica trophozoites resulted in a 7-fold drop in promoter activity in transiently transfected reporter gene constructs when the URE4 motif was present, confirming its ability to specifically recognize the URE4 motif and suggesting that additional cofactors may be required for transcriptional activation by URE4. Further characterization and identification of binding partners for EhEBP1 and EhEBP2, the first proteins with demonstrated sequence-specific DNA binding activity to be identified in E. histolytica, should provide new insights into transcriptional regulation in this protozoan parasite.

An Entamoeba histolytica rab-like encoding gene and protein: function and cellular location

We identified here a 576 bp rab-like gene (EhrabB) in Entamoeba histolytica. EhrabB is located 332 bp upstream from the start codon of the Ehcp112 encoding gene, but is transcribed from the complementary strand. The EhrabB open reading frame predicts a 192 amino acid polypeptide (EhRabB) with 40-42% identity to Rab proteins, involved in vesicle docking regulation in endo and exocytic pathways of eukaryotic cells. Transcripts of 0.6 and 0.97 kb were detected by the EhrabB probe in northern blot assays. Using specific antibodies, EhRabB was located in small cytoplasmic vesicles by confocal microscopy. During phagocytosis, EhRabB was initially translocated to the plasma membrane and to the phagocytic mouths. The protein diminished after 10 min phagocytosis, suggesting that EhRabB could be participating in the regulation of the endocytosis process.

The genome of Entamoeba histolytica

Estimation of genome size of Entamoeba histolytica by different methods has failed to give comparable values due to the inherent complexities of the organism, such as the uncertain level of ploidy, presence of multinucleated cells and a poorly demarcated cell division cycle. The genome of E. histolytica has a low G+C content (22.4%), and is composed of both linear chromosomes and a number of circular plasmid-like molecules. The rRNA genes are located exclusively on some of the circular DNAs. Karyotype analysis by pulsed field gel electrophoresis suggests the presence of 14 conserved linkage groups and an extensive size variation between homologous chromosomes from different isolates. Several repeat families have been identified, some of which have been shown to be present in all the electrophoretically separated chromosomes. The typical nucleosomal structure has not been demonstrated, though most of the histone genes have been identified. Most Entamoeba genes lack introns, have short 3' and 5' untranslated regions, and are tightly packed. Promoter analysis revealed the presence of three conserved motifs and several upstream regulatory elements. Unlike typical eukaryotes, the transcription of protein coding genes is alpha-amanitin resistant. Expressed Sequence Tag analysis has identified a group of highly abundant polyadenylated RNAs which are unlikely to be translated. The Expressed Sequence Tag approach has also helped identify several important genes which encode proteins that may be involved in different biochemical pathways, signal transduction mechanisms and organellar functions.

Entamoeba histolytica : a novel cysteine protease and an adhesin form the 112 kDa surface protein

Here, we present evidence that a cysteine protease (EhCP112) and a protein with an adherence domain (EhADH112) form the Entamoeba histolytica 112 kDa adhesin. Immunoelectron microscopy and immunofluorescence assays using monoclonal antibodies (mAbAdh) revealed that, during phagocytosis, the adhesin is translocated from the plasma membrane to phagocytic vacuoles. mAbAdh inhibited 54% adherence, 41% phagocytosis, and 35% and 62% destruction of MDCK cell monolayers by live trophozoites and their extracts respectively. We cloned a 3587 bp DNA fragment (Eh112 ) with two open reading frames (ORFs) separated by a 188 bp non-coding region. The ORF at the 5' end (Ehcp112 ) encodes a protein with a cysteine protease active site, a transmembranal segment and an RGD motif. The second ORF (Ehadh112 ) encodes a protein recognized by mAbAdh with three putative transmembranal segments and four glycosylation sites. Northern blot, primer extension and Southern blot experiments revealed that Ehcp112 and Ehadh112 are two adjacent genes in DNA. Ehcp112 and Ehadh112 genes were expressed in bacteria. The recombinant peptides presented protease activity and inhibited adherence and phagocytosis, respectively, and both were recognized by mAbAdh. The EhCP112 and EhADH112 peptides could be joined by covalent or strong electrostatic forces, which are not broken during phagocytosis.

Physiology and molecular genetics of multidrug resistance in Entamoeba histolytica

Entamoeba histolytica presents the evolutionarily conserved multidrug-resistance (MDR) phenotype, discovered in mammalian cells. MDR cells overexpress the membrane P-glycoprotein, which excludes unrelated drugs from the cytoplasm. E. histolytica mutants exhibit cross-resistance to unrelated drugs, which are pumped out from the cytoplasm. In drug-resistant trophozoites, the constitutively expressed EhPg1 gene appears to be up-regulated by a C/EBP-like factor and a multiprotein complex that were not found in drug-sensitive trophozoites. The drug-induced EhPgp5 gene, on the other hand, appears to be up-regulated by AP-1 and HOX factors. Here we review the main physiological and molecular facts of the MDR phenotype in E. histolytica. Copyright 1999 Harcourt Publishers Ltd.

The novel core promoter element GAAC in the hgl5 gene of Entamoeba histolytica is able to direct a transcription start site independent of TATA or initiator regions

Entamoeba histolytica, an enteric protozoa, is the third leading parasitic cause of death worldwide. Investigation of the transcriptional machinery of this eukaryotic pathogen has revealed an unusual core promoter structure that consists of nonconsensus TATA and initiator regions and a novel third conserved core promoter sequence, the GAAC element. Mutation of this region in the hgl5 promoter decreases reporter gene expression and alters the transcription start site. Using positional analysis of this element, we have now demonstrated that it is able to direct a new transcription start site, 2-7 bases downstream of itself, independent of TATA and Inr regions. The GAAC region was also shown to control the rate of transcription via nuclear run on analysis and an amebic nuclear protein was demonstrated to specifically interact with this sequence. This is the first description in the eukaryotic literature of a third conserved core promoter element, distinct from TATA or initiator regions, that is able to direct a transcription start site. We have formulated two models for the role of the GAAC region: (i) the GAAC-binding protein is a part of the TFIID complex and (ii) the GAAC-binding protein functions to "tether" TATA-binding protein to the TATA box.

Transcriptional analysis of the EhPgp5 promoter of Entamoeba histolytica multidrug-resistant mutant

We report here the cloning and transcriptional characterization of the EhPgp5 multidrug resistance gene promoter isolated from the drug-resistant clone C2 of Entamoeba histolytica. The EhPgp5 promoter has the TATA-like motif at -31 base pairs; transcription initiates three nucleotides upstream from the ATG in trophozoites grown in 225 microM emetine (clone C2(225)), whereas in those grown without the drug (clone C2) a product with no open reading frame was detected. The promoter was active in transfected clone C2 trophozoites, its activity increased when trophozoites were cultured in 40 microM emetine, while it was turned off in the drug-sensitive clone A. The first -235 base pair kept full promoter activity, suggesting that it has important drug responsive elements. Gel shift assays detected the complex Ib in clone C2, which was augmented in clone C2(225). Competition experiments suggested that complex Ib may be constituted by HOX and AP-1 like factors in clone C2, whereas in clone C2(225), complex Ib was only competed by the HOX sequence. Complexes Ie, detected in clones A and C2 but not in C2(225), and Ia, present in all clones, were competed by the TATA box oligonucleotide. Our results suggest that proteins forming complexes Ib and Ie may be participating in the regulation of the EhPgp5 gene expression.