An Unusual U2AF2 Inhibits Splicing and Attenuates the Virulence of the Human Protozoan Parasite Entamoeba histolytica

E. histolytica is the etiological agent of intestinal amebiasis and liver abscesses, which still poses public health threat globally. Metronidazole is the drug of choice against amebiasis. However, metronidazole-resistant amoebic clinical isolates and strains have been reported recently, challenging the efforts for amebiasis eradication. In search of alternative treatments, E. histolytica transcriptomes have shown the association of genes involved in RNA metabolism with the virulence of the parasite. Among the upregulated genes in amoebic liver abscesses are the splicing factors EhU2AF2 and a paralog of EhSF3B1. For this reason and because EhU2AF2 contains unusual KH-QUA2 (84KQ) motifs in its lengthened C-terminus domain, here we investigated how the role of EhU2AF2 in pre-mRNA processing impacts the virulence of the parasite. We found that 84KQ is involved in splicing inhibition/intron retention of several virulence and non-virulence-related genes. The 84KQ domain interacts with the same domain of the constitutive splicing factor SF1 (SF1KQ), both in solution and when SF1KQ is bound to branchpoint signal RNA probes. The 84KQ–SF1KQ interaction prevents splicing complex E to A transition, thus inhibiting splicing. Surprisingly, the deletion of the 84KQ domain in EhU2AF2 amoeba transformants increased splicing and enhanced the in vitro and in vivo virulence phenotypes. We conclude that the interaction of the 84KQ and SF1KQ domains, probably involving additional factors, tunes down Entamoeba virulence by favoring intron retention.

Entamoeba histolytica: the over expression of a mutated EhRabB protein produces a decrease of in vitro and in vivo virulence

Vesicular trafficking, which is implicated in secretion of cytolytic molecules as well as in phagocytosis, plays an important role in the pathogenic mechanism of Entamoeba histolytica, the protozoan parasite causative of human amoebiasis. Thus, Rab GTPases, that are key regulators of vesicle trafficking, should be considered as molecules involved in the parasite virulence. EhRabB is a Rab protein located in cytoplasmic vesicles that are translocated to phagocytic mouths during ingestion of target cells, suggesting that this Rab protein is involved in phagocytosis. To prove this hypothesis, we over expressed the wild type EhrabB gene and a mutant gene encoding for a protein (RabBN118I) unable to bind guanine nucleotides and therefore constitutively inactive. The over expression of the mutated protein in E. histolytica trophozoites provoked a dominant negative effect, reflected in a significant decrease of both phagocytosis and cytopathic effect as well as in a failure to produce hepatic abscesses in hamsters. These results confirm that EhRabB is involved in phagocytosis and virulence of E. histolytica.

Thermal Properties of Mineralized and Non Mineralized Type I Collagen in Bone

The research about the structural stability of bone, as a composite material, compromises a complete understanding of the interaction between the mineral and organic phases. The thermal stability of human bone and type I collagen extracted from human bone by different methods was studied in order to understand the interactions between the mineral and organic phases when is affected by a degradation/combustion process. The experimental techniques employed were calorimetry and infrared spectroscopy (FTIR) techniques. The extracted type I collagens result to have a bigger thermal stability with a Tmax at 500 and 530 Celsius degrees compared with the collagen present in bone with Tmax at 350 Celsius degrees. The enthalpy value for the complete degradation/combustion process were similar for all the samples, being 8.4 +- 0.11 kJ/g for recent bones diminishing with the antiquity, while for extracted collagens were 8.9 +- 0.07 and 7.9 +-1.01 kJ/g. These findings demonstrate that the stability loss of type I collagen is due to its interactions with the mineral phase, namely carbonate hydroxyapatite. This cause a change in the molecular properties of the collagen during mineralization, specifically in its cross-links and other chemical interactions, which have a global effect over the fibers elasticity, but gaining tensile strength in bone as a whole tissue. We are applying this characterization to analyze the diagenetic process of bones with archaeological interest in order to identify how the environmental factors affect the molecular structure of type I collagen. In bone samples that proceed from an specific region with the same environmental conditions, the enthalpy value per unit mass was found to diminish exponentially with respect to the bone antiquity.

Microstructure and Thermal Expansion Properties of Ostrich Eggshell

Textures of calcite crystals from ostrich (Struthio camelus) eggshells were examined with X ray diffractometry (XRD), transmission and scanning electron microscopy (TEM, SEM), and the thermal stability by thermal expansion analysis (TEA). Results showed that textures vary through the thickness of the eggshell and that expansion properties and thermal behaviour are unusual. Crystals from ostrich eggshell are arranged in two main configurations or layers; the outer layer with the c-axis of crystals oriented perpendicular to the eggshell surface and the inner layer with the c-axes of the crystals arranged almost parallel to eggshell surface; thermal expansion analysis show high stability through a wide range of temperatures until a steep growth near 450-460°C. These results show that the manipulation of crystal texture and properties is under biological control and a better understanding of this biological phenomenon will provide more and better data for improving new synthetic composite materials.

The crystal structure of FeInGe2O7

A new iron indium germanate has been prepared as polycrystalline powder material which crystallizes in the monoclinic system (S.G. C2/m, No. 12). The structure was characterized by X-ray powder diffraction and Rietveld refinement of the resulting diffraction pattern. The cell parameters are a = 6.5124(4) Å, b = 8.5914(5) Å, c = 4.8936(3) Å, β = 102.683(2)°, V = 267.12(3) Å3 and Z = 2. The structure contains R+3 cations (R=Fe, In) almost equally distributed in distorted RO6 octahedral sites. These octahedra are joined by edge sharing forming a hexagonal arrangement on the ab planes. The RO6 octahedra layers are held together by sheets of isolated Ge2O7 diorthogroups constituted by a double tetrahedra sharing a common vertex. This compound has the thortveitite structure and keeps a strong relationship with the FeYGe2O7 germanate, which presents two R+3 sites with six-coordinated (R=Fe) and seven-coordinated (R=Y) oxygens, corresponding to the different symmetry given by the monoclinic space group P21/m (No. 11)

The crystal structure of InYGe2O7 germanate

A new indium yttrium germanate presenting the thortveitite structure with symmetry described by the space group C2/m (No. 12) has been prepared by high temperature solid state reaction as polycrystalline powder material. This crystallizes in the monoclinic system, with cell parameters a = 6.8286(1) Å, b = 8.8836(2) Å, c = 4.9045(1) Å, β= 101.8340(7)º, V = 291.195(9) Å3 and Z = 2. The structure was characterized by X-ray powder diffraction and Rietveld refinement of the diffraction pattern. The In3+ and Y+3 cations occupy the same octahedral site forming a hexagonal arrangement on the ab planes. In their turn, the hexagonal arrangements of InO6/YO6 octahedral layers are held together by sheets of isolated diorthogroups constituted by a double tetrahedra sharing a common vertex. In this compound, the Ge2O7 diorthogroup shows the C2h symmetry implying a Ge-O-Ge angle of 180º, being an important feature of the thortveitite structure, which has been controversial in some reported papers. A remarkable photo-luminescence effect (in comparison with glass) was observed when the sample was irradiated with α-particles beam during the RBS experiments employed to analyze the chemical stoichiometry.

Functional characterization of EhADH112: an Entamoeba histolytica Bro1 domain-containing protein

EhADH112 is part of the EhCPADH complex, a protein involved in key events of the Entamoeba histolytica host invasion. EhADH112 participates in trophozoite adherence to target cells and in phagocytosis. We report here the finding of two EhADH112 homologues in the E. histolytica genome (EhADH112-like proteins). EhADH112 and its relatives have a Bro1 domain at their amino-terminus and a consensus context for phosphorylation by Src-tyrosine kinases, both involved in signal transduction processes in other organisms. Our findings associate EhADH112 to supplementary functions related to those reported for the Alix/AIP1 family. To elucidate the precise function of EhADH112, we studied the phenotypes displayed by trophozoites transfected with the Ehadh112 full gene. Transfected trophozoites overexpressed a 78 kDa protein, which was mainly targeted to the EhCPADH complex. Moreover, these trophozoites exhibited enhanced phagocytic rates, providing further evidence of EhADH112 contribution to adhesion and phagocytosis activities.

Entamoeba histolytica: structural and functional analysis of the Ehadh112 gene promoter

The Entamoeba histolytica Ehcp112 and Ehadh112 genes that encode the EhCPADH complex are separated by a non-coding 188pb region. Their proximity suggests a coordinated expression regulation for both genes. Here, we studied the structure and function of 996 bp (p996CAT) upstream the ATG start codon of the Ehadh112 gene. The p996CAT plasmid drove CAT transcription with a 78% of the activity showed by actin promoter. Deletion of 330 bp at the 5' end of p966CAT to produce the p776CAT plasmid, decreased activity to 40% in relation to actin promoter and to 50% of p996CAT, suggesting the presence of a silencer in this region. Interestingly, deletion of other 297 bp to the p776CAT to generate the p469CAT plasmid, augmented activity in 2.5-fold compared with p776CAT construction, showing the presence of a proximal enhancer promoter. Transcription initiation sites (-69 and -150 bp), TATA like box, GAAC, and Inr elements, as well as putative DNA binding motifs, were mapped in the -1 to -469 bp core promoter region.

The Entamoeba histolytica Ehcp112 gene has a distal and weak promoter

Ehcp112 encodes the Entamoeba histolytica EhCP112 cysteine protease that is part of the EhCPADH complex. By in silico analysis we identified putative transcription factor-binding sites along 837 bp upstream the Ehcp112 gene ATG codon. A TATA-like motif (TATATAAA) was located at -36 to -29 bp, a GAAC box (GAACC) was found at -10 to -14 bp and an Inr sequence (TTCAAC) at -8 to -2 bp. These tripartite promoter elements are in non-canonical positions, downstream the transcription initiation site (-280 bp). We cloned four Ehcp112 promoter fragments in pBSCAT-ACT plasmid to obtain pI (355 bp), pII (681 bp), pIII (833 bp), and pIV (554 bp) constructs. In transfected trophozoites, only pIII drove CAT activity with 44% efficiency in relation to actin promoter activity. Our results showed the presence of a distal and weak promoter in the Ehcp112 gene. The active DNA region is inside the open reading frame of the Ehrab B gene, suggesting that expression of both genes could be coordinately regulated.

Structural characterization of SmMn2GeO7 single microcrystals by electron microscopy

Single microcrystals of the new compound samarium dimanganese germanium oxide, SmMn2GeO7, were grown using the flux method in a double spherical mirror furnace (DSMF). The micrometric crystals were observed and chemically analysed with scanning electron microscopy (SEM) and X-ray energy dispersive spectroscopy (EDX). The structural characterization and chemical analysis of these crystals were also carried out using transmission electron microscopy (TEM) and high-resolution transmission electron microscopy (HRTEM), together with electron-energy-loss spectroscopy (EELS). We found that the new quaternary compound crystallizes in the orthorhombic system with the point group mmm (D2h), space group Immm (No. 71) and cell parameters a=8.30 (10), b=8.18 (10), c=8.22 (10) A and V=558.76 A3.

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.

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.

Entamoeba histolytica: DNA carrier vesicles in nuclei and kinetoplast-like organelles (EhkOs)

Entamoeba histolytica, the protozoan responsible for human amoebiasis, has a complex genome, whose linear chromosomes and DNA circles have so far eluded detailed analysis. We report the detection by transmission electron microscopy of nuclear vesicles (0.05-0.3 microm in diameter) carrying DNA in E. histolytica trophozoites. In late anaphase many of these nuclear vesicles were found to be organized in structures of approximately 2.5 x 1 microm, in association with chromosomes and microtubules. In glutaraldehyde-fixed and detergent-treated trophozoites, nuclear vesicles displayed a non-membranous envelope. Binding of phosphotungstate stain and recognition by serum from patients with systemic lupus erythematosus indicated that these vesicles contain DNA. Similar DNA carrier vesicles were found in the cytoplasm and in the E. histolytica kinetoplast-like organelle (EhkO). By Feulgen staining, we detected DNA carrier vesicles entering or leaving the nuclei, suggesting a structural relationship between the nuclear vesicles and the vesicles present in the EhkOs.

Specific detection of Entamoeba histolytica DNA by hemolysin gene targeted PCR

Diagnostic differentiation of pathogenic Entamoeba histolytica from non-pathogenic Entamoeba dispar is of great clinical importance. We have developed and evaluated a new polymerase chain reaction (PCR) assay (haemo-PCR) based on the novel E. histolytica hemolysin gene HLY6. The specificity of this assay was confirmed by analyzing different Entamoeba species, faeces samples, human and bacterial DNA, and digestion of amplification products with appropriate restriction enzymes. The sensitivity was confirmed by serial dilutions of E. histolytica HM-1:IMSS DNA in the excess of human DNA. Totally, 45 clinical samples were analyzed by the haemo-PCR assay including amoebic liver abscess (ALA) fluids from 23 patients suspected for amoebiasis, four faeces samples containing E. histolytica and E. dispar, and positive and negative controls. The results were compared with those obtained with PCRs for cystein-rich surface protein (P30) and small subunit ribosomal RNA (ssu rRNA) genes. The haemo-PCR gave a positive result in 18 (89%) ALA fluids compared with 14 (77%) and five (28%) by PCR for p30, and ssu rRNA, respectively. PCR products were obtained only from specimens containing E. histolytica DNA. The haemo-PCR assay was therefore found to be a valuable diagnostic tool for identification of E. histolytica infections both in faeces and ALA samples.

Circular and linear DNA molecules in the Entamoeba histolytica complex molecular karyotype

Entamoeba histolytica genome was analysed by pulsed field gel electrophoresis under conditions to separate linear chromosomes in the 170-1400 kb range. We identified linear DNA molecules of 227, 366, 631, 850, 1112 and 1361 kb (mean sizes obtained by three different methods) and we estimated their reorientation times and migration velocities at various experimental conditions. DNA shift mobility assays, using ethidium bromide, suggested that bands migrating at 227 and 631 kb contain linear and circular DNA, whereas a band at 436 kb has only circular DNA. We obtained a regression equation relating sizes of supercoiled DNA molecules with their migration velocities during a pulse at constant electric field and temperature. We also developed a computer program (EHPATTERNS) that predicts the migration per pulse and the resolution order of circular and linear E. histolytica DNA at different pulse times and constant driving and frictional forces. The simulation showed that linear DNA molecules frequently co-migrate with circular molecules, but circular molecules change when the pulse time varies. This molecular mixture generates broad bands and difficulties in the interpretation of the molecular karyotype of E. histolytica.

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.

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.

Entamoeba histolytica: signaling through G proteins

The intracellular signaling pathways of Entamoeba histolytica are largely unknown. Although the expression of guanine nucleotide binding proteins (G proteins) is expected from functional studies, their biochemical characterization remains elusive in this protozoan. Using a combination of biochemical and immunological studies, we provide strong evidence for the presence of a Gs protein in amoeba. Our results strengthen our understanding of the signal transduction mechanisms in E. histolytica as potential sites of a new therapeutic strategy.

Family responses to HIV/AIDS in Mexico

This paper presents findings from a qualitative study of household and community responses to HIV/AIDS in Mexico. Fieldwork took place in two contrasting settings: (a) Ciudad Netzahualcóyotl, a socially marginalized urban community and (b) the homosexual community of Mexico City, a sexually marginalized social network. 113 in-depth interviews were conducted with people with HIV/AIDS, their relatives and members of their social networks. This paper describes findings from interviews conducted with family members of persons with AIDS. Four stages of response are identified and characterized within each community: (i) life before AIDS, (ii) life during the discovery of AIDS, (iii) living with a person with AIDS and (iv) surviving those who have died from AIDS. The social marginalization of both communities is central in explaining how families respond to the disease. In Ciudad Netzahualcoyotl, social support derives from a local culture of kinship. In the gay community, on the other hand, solidarity arises out of friendship. Between social support and discrimination, many more "ambivalent" behaviours (neither fully supportive nor discriminating) are displayed by family members and friends. Fear, pre-existing family conflicts and prejudice nurture these negative responses. Family responses and the processes to which they give rise, also differ depending on whether or not a male or female household member is affected. Policy recommendations are made concerning how best to promote positive family and household responses to persons with HIV/AIDS and how to inhibit negative ones.

AIDS-related illness trajectories in Mexico: findings from a qualitative study in two marginalized communities

This paper describes findings from a recent study examining how people affected directly and indirectly by the HIV/AIDS epidemic cope with HIV-related illness in Mexico. One-hundred-and-thirteen in-depth interviews were conducted with key informants in two contrasting communities: Ciudad Netzahualcóyotl (an economically marginalized community) and the gay community in Mexico City (a sexually marginalized community). This paper describes the AIDS-related wellness/illness careers or trajectories followed by individuals in both communities, and identifies critical points for material and emotional intervention. This career comprises four stages: (1) life before infection; (2) life surrounding the discovery of seropositivity; (3) living as an HIV-positive person; and (4) facing death. Comparisons are drawn between the processes of adjustment and coping found in both communities. In Ciudad Netzahualcóyotl, wellness/illness careers are closely linked to prevailing poverty and oppression, as well as the sense of urgency in which local people live their lives. In the case of the gay community, wellness/illness careers are associated with the intolerance and social repression faced by homosexual men. The paper concludes by suggesting possible interventions to improve the lives of people with HIV/AIDS in Mexico today.

Conceptual bases and methodology for the evaluation of women's and providers' perception of the quality of antenatal care in the WHO Antenatal Care Randomised Controlled Trial

In this paper, we describe the conceptual bases and methodology used to assess women's and providers' perception of the quality of antenatal care, as part of a large randomised trial in four developing countries. Information has been obtained by applying both qualitative and quantitative methodologies. The focus group discussions and in-depth interviews have contributed useful insights into the cultural milieu in which care is provided, users' and providers' expectations, and their concept of quality. Based on these findings, we developed two standardised questionnaires, one being administered to a representative sample of pregnant women (n = 1600) and the other for all care providers. In this paper we present some of the findings of the focus group discussions and in-depth interviews with women in one country as an example of the kind of information we have obtained. Women expressed their point of view concerning a reduced number of visits, type of provider, information that they get during clinical encounters and interpersonal relations with health professionals. The qualitative information, together with the data we obtain from the surveys, will highlight the aspects that will have be to considered if the new model of care is to be introduced on a routine basis.

The pyruvate:ferredoxin oxidoreductase enzyme is located in the plasma membrane and in a cytoplasmic structure in Entamoeba

This work investigated the cellular location of the pyruvate:ferredoxin oxidoreductase (PFO) enzyme in Entamoeba. A 1.9 kb fragment located at the 3' end of the Ehpfo gene was cloned in the pRSETB vector and expressed. The recombinant peptide was purified and inoculated in rabbits. By Western blot assays the antibodies detected a single 130 kDa band in all E. histolytica strains tested and in E. moshkovskii. By immunofluorescence, the antibodies showed the presence of PFO in the plasma membrane and in a cytoplasmic structure that appeared as a ring or as a compact small body in E. histolytica strains. In E. invadens and E. moshkovskii (strains FIC and Laredo) PFO was located in the plasma membrane showing different fluorescence patterns. Immunofluorescence on E. histolytica synchronized cultures showed that the cytoplasmic structure appeared in 85, 60, 20 and 10% of the trophozoites in mitosis, G1, S and G2 phases, respectively. By in situ hybridization the Ehpfo gene was found in the nuclei and the trophozoites of the clone A, strain HM1:IMSS, differed in the Ehpfo gene content.

Comparison of DNA migrations in two clamped homogeneous electric field chambers of different sizes. Relation between sample thickness and electrophoresis time

We present here a method to compare the mathematical descriptions of DNA migration per pulse as a function of pulse time. It is based on obtaining robust estimates and variances of DNA reorientation time, migration velocities during and after DNA reorientation; and on the statistical comparisons of these estimates. We demonstrated an equal description for the migration per pulse of each DNA molecule separated under identical conditions in clamped homogeneous electric field (CHEF) and miniCHEF chambers. However, miniCHEF resolved the patterns in shorter times, because it uses thinner samples. The relationship between sample thickness and CHEF run time is also presented.

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.

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

We present here the cloning and characterization of the EhPgp1 multidrug resistance gene promoter isolated from the Entamoeba histolytica drug-resistant mutant clone C2. The EhPgp1 promoter lacks the typical TATA box and the transcriptional initiation sequences described for other E. histolytica promoters. The major transcription initiation site of the EhPgp1 gene was located at the ATG start codon. The EhPgp1 core promoter located within the first 244 base pairs showed a higher chloramphenicol acetyltransferase expression in the transfected trophozoites of clone C2 than in those of the sensitive clone A. Gel shift assays revealed three specific DNA-protein complexes (Ia, IIa, and IIIc) using nuclear extracts from clone C2, whereas three main complexes (If, IIf, and IIg) were limited to clone A. Competition assays suggested the presence of C/EBP-like and OCT-like proteins in complexes Ia and IIa, respectively, probably involved in the expression of the EhPgp1 gene, whereas complex IIIc was competed by GATA-1, C/EBP, OCT, and HOX oligonucleotides. Thus, differential DNA-protein complexes may be formed by transcriptional factors involved in the regulation of the EhPgp1 gene expression.