Functional characterization of two new STAT3 mutations associated with hyper-IgE syndrome in a Mexican cohort.

Hyper-IgE syndrome (HIES) is an immunodeficiency disorder that is characterized by distinctive immunologic and non-immunologic manifestations. Although mutations in signal transducer and activator of transcription 3 (STAT3) have been associated with HIES, the exact nature of the relationship is unknown. Here, we characterized the functional activity of STAT3 and its mutations in 11 Mexican patients with autosomal dominant HIES. STAT3 phosphorylation was evaluated by flow cytometry, and in silico analyses were performed to estimate the impact of allelic mutations on the DNA binding and SH2 domains of the STAT3 protein. Electrophoretic mobility shift assays were used to assess whether the STAT3 mutants could bind to the consensus oligonucleotide target in vitro. Two novel mutations [g.58891A>T (Asn395Tyr) and g.59078A>T (Asn425Tyr)] as well as one possible somatic mosaicism were found in several of the patients who bore some remarkable features. However, there were no direct correlations between genotypes and HIES clinical features. STAT3 phosphorylation was found to be lower in the patient cohort than in healthy controls. Moreover, the mutated STAT3 proteins could bind to the Sp1, but not to the STAT3, consensus sequence. From these functional studies, the STAT3 mutations found in our patient cohort were concluded to be deleterious for normal STAT3 function.

A functional study of nucleocytoplasmic transport signals of the EhNCABP166 protein from Entamoeba histolytica.

EhNCABP166 is an Entamoeba histolytica actin-binding protein that localizes to the nucleus and cytoplasm. Bioinformatic analysis of the EhNCABP166 amino acid sequence shows the presence of 3 bipartite nuclear localization signals (NLS) and a nuclear export signal (NES). The present study aimed to investigate the functionality of these signals in 3 ways. First, we fused each potential NLS to a cytoplasmic domain of ehFLN to determine whether the localization of this domain could be altered by the presence of the NLSs. Furthermore, the localization of each domain of EhNCABP166 was determined. Similarly, we generated mutations in the first block of bipartite signals from the domains that contained these signals. Additionally, we added an NES to 2 constructs that were then evaluated. We confirmed the intranuclear localization of EhNCABP166 using transmission electron microscopy. Fusion of each NLS resulted in shuttling of the cytoplasmic domain to the nucleus. With the exception of 2 domains, all of the evaluated domains localized within the nucleus. A mutation in the first block of bipartite signals affected the localization of the domains containing an NLS. The addition of an NES shifted the localization of these domains to the cytoplasm. The results presented here establish EhNCABP166 as a protein containing functional nuclear localization signals and a nuclear export signal.

Identification and evaluation of inhibitors of the EhGEF1 protein from Entamoeba histolytica.

The Dbl family of guanine nucleotide exchange factors (GEFs) is made up of a vast array of members that participate in the activation of the Rho family of small GTPases. Dbl-family proteins promote the exchange of guanosine diphosphate/guanosine triphosphate (GDP/GTP) in their target molecules, resulting in the activation of a variety of signaling pathways involved in diverse cellular events, such as actin-cytoskeleton remodeling, cellular invasion, cell movement, and other functions. It has been reported that members of the Dbl family have important roles in several cellular events in Entamoeba histolytica. These include activation of the actin cytoskeleton, cytokinesis, capping, uroid formation, cellular proliferation, erythrophagocytosis, cell migration, and chemotaxis. Here, we report the identification and testing of inhibitors of the E. histolytica guanine nucleotide exchange factor 1 (EhGEF1) protein (the research compounds 2BYRF, 2BY05, 2BYT6, 2BYLX, and 2BYPD), which decreased the in vitro ability of the protein to exchange GDP/GTP at its target GTPases, EhRacG and EhRho1, by 14.9-85.2%. Interestingly, the drug 1,1'-(1,2-phenylene)-bis-(1H-pyrrole-2,5-dione), which completely inhibits the GEF activity of the Trio protein in human cells, decreases the GEF activity of the EhGEF1 protein on the EhRacG and EhRho1 GTPases by 55.7% and 3.2%, respectively. The identification and evaluation of such inhibitors opens up the possibility of obtaining a new pharmacological tool to study the function of amoeba GEF proteins, their roles in various Rho GTPase-mediated signaling pathways, and the repercussions of modulating their activities with respect to several mechanisms related to E. histolytica pathogenesis.

H2A.Z overexpression suppresses senescence and chemosensitivity in pancreatic ductal adenocarcinoma.

Pancreatic ductal adenocarcinoma (PDAC) is one of the most intractable and devastating malignant tumors. Epigenetic modifications such as DNA methylation and histone modification regulate tumor initiation and progression. However, the contribution of histone variants in PDAC is unknown. Here, we demonstrated that the histone variant H2A.Z is highly expressed in PDAC cell lines and PDAC patients and that its overexpression correlates with poor prognosis. Moreover, all three H2A.Z isoforms (H2A.Z.1, H2A.Z.2.1, and H2A.Z.2.2) are highly expressed in PDAC cell lines and PDAC patients. Knockdown of these H2A.Z isoforms in PDAC cell lines induces a senescent phenotype, cell cycle arrest in phase G2/M, increased expression of cyclin-dependent kinase inhibitor CDKN2A/p16, SA-ß-galactosidase activity and interleukin 8 production. Transcriptome analysis of H2A.Z-depleted PDAC cells showed altered gene expression in fatty acid biosynthesis pathways and those that regulate cell cycle and DNA damage repair. Importantly, depletion of H2A.Z isoforms reduces the tumor size in a mouse xenograft model in vivo and sensitizes PDAC cells to gemcitabine. Overexpression of H2A.Z.1 and H2A.Z.2.1 more than H2A.Z.2.2 partially restores the oncogenic phenotype. Therefore, our data suggest that overexpression of H2A.Z isoforms enables cells to overcome the oncoprotective barrier associated with senescence, favoring PDAC tumor grow and chemoresistance. These results make H2A.Z a potential candidate as a diagnostic biomarker and therapeutic target for PDAC.

Entamoeba histolyticaEhGEF1 structure and mutational analysis: New specific residues critical for function.

This paper reports the EhGEF1-EhRacG and EhGEF1-EhRho1 molecular complexes from Entamoeba histolytica. The not conserved amino acids Gln201,Tyr299, Gln302, Lys312, Asn313, Phe314 and Ile324 were localized, by means of an in silico computational analysis, at the interface of the exposed face from the DH domain of EhGEF1, which are important to establish the contact with its target GTPases EhRacG and EhRho1. Functional studies of nucleotide exchange of Phe314Ala mutant showed a decrement of 80% on EhRacG GTPase; in contrast the Ile324Ala mutant exhibited a reduction of 77%, specifically on EhRho1; meanwhile the Gln302Ala mutant showed a reduction of approximately 50% on the exchange activity for both GTPases. Moreover, the functional studies of the protein EhGEF1 mutants in the conserved residues Thr194Ala, Asn366Ala and Glu367Ala indicated that contrary to what has been reported for other systems, the mutation of these residues did not alter considerably its catalytic activity.

Expressed var genes are found in Plasmodium falciparum subtelomeric regions.

The antigenic variation and cytoadherence of Plasmodium falciparum-infected erythrocytes are modulated by a family of variant surface proteins encoded by the var multigene family. The var genes occur on multiple chromosomes, often in clusters, and 50 to 150 genes are estimated to be present in the haploid parasite genome. Transcripts from var genes have been previously mapped to internal chromosome positions, but the generality of such assignments and the expression sites and mechanisms that control switches of var gene expression are still in early stages of investigation. Here we describe investigations of closely related var genes that occur in association with repetitive elements near the telomeres of P. falciparum chromosomes. DNA sequence analysis of one of these genes (FCR3-varT11-1) shows the characteristic two-exon structure encoding expected var features, including three variable Duffy binding-like (DBL) domains, a transmembrane sequence, and a carboxy-terminal segment thought to anchor the protein product in knobs at the surface of the parasitized erythrocyte. FCR3-varT11-1 cross-hybridizes with var genes located close to the telomeres of many other P. falciparum chromosomes, including a transcribed gene (FCR3-varT3-1) in chromosome 3 of the P. falciparum FCR3 line. The relatively high level transcription from this gene shows that the polymorphic chromosome ends of P. falciparum, which have been proposed to be transcriptionally silent, can be active expression sites for var genes. The pattern of the FCR3-varT11-1 and FCR3-varT3-1 genes are variable between different P. falciparum lines, presumably due to DNA rearrangements. Thus, recombination events in subtelomeric DNA may have a role in the expression of novel var forms.

Compartmentalization of genes coding for immunodominant antigens to fragile chromosome ends leads to dispersed subtelomeric gene families and rapid gene evolution in Plasmodium falciparum.

Recent studies on the chromosome structure of Plasmodium falciparum have led to two observations: chromosome breakage occurs frequently in subtelomeric regions and the genes coding for a number of immunodominant parasite proteins are located in these fragile chromosomal segments. Toward understanding the biological significance of these observations, we have been studying the variability of a number of these telomeric genes in parasite lines isolated in different regions of the world. In this report, we present evidence that the telomeric location of the resa and the gbp genes of P. falciparum has allowed their dispersion to other chromosomes and eventual alteration. In the first example it is shown that the resa gene has been dispersed to subtelomeric positions on chromosomes 1, 2, 11 and 14 in clinical isolates from West African patients, giving rise to new parasite genotypes and gene linkage groups. Cloning and molecular analysis of the newly detected resa-related sequences reveal that two of the members of the family have diverged from the ancestral copy on chromosome 1, while the third member on chromosome 14 is very homologous to the ancestral copy indicating that it arose from a recent translocation event. In the second example, we show that the gbp genes form a dispersed gene family that maps to at least three different chromosome extremities. The data suggest that the compartmentalization of P. falciparum antigen genes to the chromosome ends lead to gene families scattered on several chromosome extremities. We propose that the generation of segmental aneuploidy is a specific mechanism of genome adaptation of P. falciparum to its host environment. We present a model to explain the duplicative translocation of chromosome termini.

Characterisation of PfSec61, a Plasmodium falciparum homologue of a component of the translocation machinery at the endoplasmic reticulum membrane of eukaryotic cells.

Plasmodium falciparum secretes several proteins that cause changes in the erythrocyte membrane enabling it to survive within red blood cells. Little is known of the mechanisms involved in the secretion and targeting of parasite polypeptides to the various cell compartments. The P. falciparum gene homologous to the mammalian Sec61alpha, gene, which encodes a component of the translocation pore in the endoplasmic reticulum of eukaryotic cells, was characterised to investigate the translocation process in the parasite. PfSec61 is present as a unique copy in the parasite genome and was mapped to chromosome 13. It encodes a 40 kDa polypeptide, as shown by immunoblotting and immunoprecipitation of [35S]methionine metabolically-labelled parasite extracts. The deduced amino acid sequence of PfSec61 is 87% similar to the mammalian polypeptide, and the two proteins give similar hydropathy plots. These results strongly suggest that PfSec61 has the same topological orientation and functional role as Sec61alpha. Anti-PfSec61 antibodies were used to investigate the cellular location and kinetics of expression of the polypeptide in the parasite. Immunofluorescence confocal microscopy showed that PfSec61 was located in the parasite cytoplasm, close to the nucleus, in a position consistent with its being in the endoplasmic reticulum.

Trypanosoma cruzi 5S rRNA genes: molecular cloning, structure and chromosomal organization.

To further study the ribosomal RNA genetic system in Trypanosoma cruzi, the 5S rRNA gene family was characterized. We found that this gene family is reiterated about 1600 times per diploid nuclei and is mostly organized as a tandem repeat of 481 base pairs. These gene clusters were assigned to two chromosomes of about 1500 and 1400 kilobase pairs. We found that the 5S rRNA-coding region is comprised of 120 nucleotides, and contains the well-known internal control regions of eukaryotic RNA polymerase III. The two gene-spacer regions analysed exhibit a putative signal for transcription termination and six sites homologous to the consensus sequence for the binding of transcription factor Sp1.

EhNCABP166: a nucleocytoplasmic actin-binding protein from Entamoeba histolytica.

The actin cytoskeleton consists of multiple actin binding proteins (ABPs) that participate cooperatively in different cellular functions such as the maintenance of polarity and cell motility as well as the invasion of target cells and regulation of gene expression, among others. Due to the important role of ABPs in the pathogenesis of Entamoeba histolytica, the role of a new nucleocytoplasmic ABP from E. histolytica named EhNCABP166 was investigated. The EhNCABP166 gene encodes a protein with an estimated molecular weight of 166kDa. Structurally, this peptide is composed of two CH domains arranged in tandem at the N-terminus of the protein, followed by an alpha-helical region containing a number of different domains with a low level of homology. Two (Bin1/Amphiphysin/Rvs167) (BAR) domains, one GTPase-binding/formin 3 homology (GBD/FH3) domain, three Bcl2-associated athanogene (BAG) domains, one basic-leucine zipper (bZIP) domain and one poly(A)-binding protein C-terminal (PABC) domain were also present. Molecular and biochemical studies showed that the EhNCABP166 protein is transcribed and translated in trophozoites of E. histolytica. It was also shown that the CH domains are functional and bind to F-actin, whereas the BAR and GBD/FH3 domains interact in vitro and in vivo with different families of GTPases such as Rho and Ras, and with different phosphoinositides. These findings suggest that these domains have the conserved functional properties described in other eukaryotic systems. These domains also interacted with additional GTPase and lipid targets that have not been previously described. Finally, cellular studies showed that EhNCABP166 is localized to the cytoplasm and nucleus of E. histolytica and that it has an important role in phagocytosis, proliferation, and motility of E. histolytica.

Recombinant scorpine: a multifunctional antimicrobial peptide with activity against different pathogens.

Scorpine is an antimicrobial peptide whose structure resembles a hybrid between a defensin and a cecropin. It exhibits antibacterial activity and inhibits the sporogonic development of parasites responsible for murine malaria. In this communication we report the production of scorpine in a heterelogous system, using a specific vector containing its cloned gene. The recombinantly expressed scorpine (RScp) in (Anopheles gambie) cells showed antibacterial activity against (Bacillus subtilis) and (Klebsiella pneumoniae), at 5 and 10 microM, respectively. It also produced 98% mortality in sexual stages of (Plasmodium berghei) at 15 microM and 100% reduction in (Plasmodium falciparum) parasitemia at 5 microM. RScp also inhibited virus dengue-2 replication in C6/36 mosquito cells. In addition, we generated viable and fertile transgenic (Drosophila) that overexpresses and correctly secretes RScp into the insect hemolymph, suggesting that the generation of transgenic mosquitoes resistant to different pathogens may be viable.

Separation and mapping of chromosomes of parasitic protozoa.

Many protozoan parasites represent an important group of human pathogens. Pulsed Field Gradient Gel Electrophoresis (PFGE) analysis has been an important tool for fundamental genetic studies of parasites like Trypanosoma, Leishmania, Giardia or the human malaria parasite Plasmodium falciparum. We present PFGE conditions allowing a high resolution separation of chromosomes ranging from 500 to 4000 kb within a two day electrophoresis run. In addition, we present conditions for separating large chromosomes (2000-6000 kb) within 36 hr. We demonstrate that the application of two dimensional PFGE (2D-PFGE) technique to parasite karyotypes is a very useful method for the analysis of dispersed gene families and comparative studies of the intrachromosomal genome organization.

Trypanosoma cruzi ribosomal RNA genes: a review.

Our research work group has been interested in the study of the ribosomal RNA and 5S gene systems from Trypanosoma cruzi. Our contributions span from the general description of a multifragmented molecular system, to the sequence analysis of some ribosomal RNA coding regions. From the latter, we have constructed phylogenetic trees of the Trypanosomatidae family, and our data indicate that the molecular inferences do not sustain the traditional classification of these species. Our published findings are here reviewed along with recent unpublished observations of ribosomal RNA and 5S gene structures.

Antigenic variation in malaria: in situ switching, relaxed and mutually exclusive transcription of var genes during intra-erythrocytic development in Plasmodium falciparum.

Members of the Plasmodium falciparum var gene family encode clonally variant adhesins, which play an important role in the pathogenicity of tropical malaria. Here we employ a selective panning protocol to generate isogenic P.falciparum populations with defined adhesive phenotypes for CD36, ICAM-1 and CSA, expressing single and distinct var gene variants. This technique has established the framework for examining var gene expression, its regulation and switching. It was found that var gene switching occurs in situ. Ubiquitous transcription of all var gene variants appears to occur in early ring stages. However, var gene expression is tightly regulated in trophozoites and is exerted through a silencing mechanism. Transcriptional control is mutually exclusive in parasites that express defined adhesive phenotypes. In situ var gene switching is apparently mediated at the level of transcriptional initiation, as demonstrated by nuclear run-on analyses. Our results suggest that an epigenetic mechanism(s) is involved in var gene regulation.

Karyotype analysis of virulent Plasmodium falciparum strains propagated in Saimiri sciureus: strain adaptation leads to deletion of the RESA gene.

The squirrel monkey, Saimiri sciureus, is an important experimental model for the study of the human malaria parasite Plasmodium falciparum. A detailed karyotype analysis of four different P. falciparum strains propagated in S. sciureus was done using various subtelomeric antigen gene probes. We observed deletion of the complete RESA gene from chromosome 1 in all four strains. Interestingly, a loss of RESA was observed immediately upon adaptation to the squirrel monkey, suggesting that this DNA rearrangement is fundamental for the P. falciparum infection of S. sciureus erythrocytes. However, a RESA-specific gene probe hybridized with chromosome 1 of wild isolates from 28 different patients, indicating that this gene is maintained during infection of humans.

Plasmodium falciparum domain mediating adhesion to chondroitin sulfate A: a receptor for human placental infection.

Malaria during the first pregnancy causes a high rate of fetal and neonatal death. The decreasing susceptibility during subsequent pregnancies correlates with acquisition of antibodies that block binding of infected red cells to chondroitin sulfate A (CSA), a receptor for parasites in the placenta. Here we identify a domain within a particular Plasmodium falciparum erythrocyte membrane protein 1 that binds CSA. We cloned a var gene expressed in CSA-binding parasitized red blood cells (PRBCs). The gene had eight receptor-like domains, each of which was expressed on the surface of Chinese hamster ovary cells and was tested for CSA binding. CSA linked to biotin used as a probe demonstrated that two Duffy-binding-like (DBL) domains (DBL3 and DBL7) bound CSA. DBL7, but not DBL3, also bound chondroitin sulfate C (CSC) linked to biotin, a negatively charged sugar that does not support PRBC adhesion. Furthermore, CSA, but not CSC, blocked the interaction with DBL3; both CSA and CSC blocked binding to DBL7. Thus, only the DBL3 domain displays the same binding specificity as PRBCs. Because protective antibodies present after pregnancy block binding to CSA of parasites from different parts of the world, DBL-3, although variant, may induce cross-reactive immunity that will protect pregnant women and their fetuses.