Synthetic peptides corresponding to a repetitive sequence of malarial histidine rich protein bind haem and inhibit haemozoin formation in vitro

Synthetic peptides containing a repetitive hexapeptide sequence (Ala-His-His-Ala-Ala-Asp) of malarial histidine-rich protein II were evaluated for binding with haem in vitro. The pattern of haem binding suggested that each repeat unit of this sequence provides one binding site for haem. Chloroquine inhibited the haem-peptide complex formation with preferential formation of a haem chloroquine complex. In vitro studies on haem polymerisation showed that none of the peptides could initiate haemozoin formation. However, they could inhibit haemozoin formation promoted by a malarial parasite extract, possibly by competitively binding free haem. These results indicate this hexapeptide sequence represents the haem binding site of the malarial histidine-rich protein and possibly the site of nucleation for haem polymerisation.

Hemozoin formation in malaria: a two-step process involving histidine-rich proteins and lipids

Major blood stage antimalarial drugs like chloroquine and artemisinin target the heme detoxification process of the malaria parasite. Hemozoin formation reactions in vitro using the Plasmodium falciparum histidine-rich protein-2 (Pfhrp-2), lipids, and auto-catalysis are slow and could not explain the speed of detoxification needed for parasite survival. Here, we show that malarial hemozoin formation is a coordinated two component process involving both lipids and histidine-rich proteins. Hemozoin formation efficiency in vitro is 1-2% with Pfhrp-2 and 0.25-0.5% with lipids. We added lipids after 9h in a 12h Pfhrp-2 mediated reaction that resulted in sixfold increase in hemozoin formation. However, a lipid mediated reaction in which Pfhrp-2 was added after 9h produced only twofold increase in hemozoin production compared to the reaction with Pfhrp-2 alone. Synthetic peptides corresponding to the Pfhrp-2 heme binding sequences, based on repeats of AHHAAD, neither alone nor in combination with lipids were able to generate hemozoin in vitro. These results indicate that hemozoin formation in malaria parasite involves both the lipids and the scaffolding proteins. Histidine-rich proteins might facilitate hemozoin formation by binding with a large number of heme molecules, and facilitating the dimer formation involving iron-carboxylate bond between two heme molecules, and lipids may then subsequently assist the mechanism of long chain formation, held together by hydrogen bonds or through extensive networking of hydrogen bonds.

Trypanosoma congolense procyclins: unmasking cryptic major surface glycoproteins in procyclic forms

In the tsetse fly, the protozoan parasite Trypanosoma congolense is covered by a dense layer of glycosylphosphatidylinositol (GPI)-anchored molecules. These include a protease-resistant surface molecule (PRS), which is expressed by procyclic forms early in infection, and a glutamic acid- and alanine-rich protein (GARP), which appears at later stages. Since neither of these surface antigens is expressed at intermediate stages, we investigated whether a GPI-anchored protein of 50 to 58 kDa, previously detected in procyclic culture forms, might constitute the coat of these parasites. We therefore partially purified the protein from T. congolense Kilifi procyclic forms, obtained an N-terminal amino acid sequence, and identified its gene. Detailed analyses showed that the mature protein consists almost exclusively of 13 heptapeptide repeats (EPGENGT). The protein is densely N glycosylated, with up to 13 high-mannose oligosaccharides ranging from Man(5)GlcNAc(2) to Man(9)GlcNAc(2) linked to the peptide repeats. The lipid moiety of the glycosylphosphatidylinositol is composed of sn-1-stearoyl-2-lyso-glycerol-3-HPO(4)-1-(2-O-acyl)-d-myo-inositol. Heavily glycosylated proteins with similar repeats were subsequently identified in T. congolense Savannah procyclic forms. Collectively, this group of proteins was named T. congolense procyclins to reflect their relationship to the EP and GPEET procyclins of T. brucei. Using an antiserum raised against the EPGENGT repeat, we show that T. congolense procyclins are expressed continuously in the fly midgut and thus form the surface coat of cells that are negative for both PRS and GARP.

Mechanism of malarial haem detoxification inhibition by chloroquine

The haem detoxification pathway of the malaria parasite Plasmodium falciparum is a potential biochemical target for drug development. Free haem, released after haemoglobin degradation, is polymerized by the parasite to form haemozoin pigment. Plasmodium falciparum histidine-rich protein-2 (Pfhrp-2) has been implicated as the catalytic scaffold for detoxification of haem in the malaria parasite. Previously we have shown that a hexapeptide repeat sequence (Ala-His-His-Ala-Ala-Asp), which appears 33 times in Pfhrp-2, may be the major haem binding site in this protein. The haem binding studies carried out by ourselves indicate that up to 18 equivalents of haem could be bound by this protein with an observed K(d) of 0.94 microM. Absorbance spectroscopy provides evidence that chloroquine is capable of extracting haem bound to Pfhrp-2. This was supported by the K(d) value, of 37 nM, observed for the haem-chloroquine complex. The native PAGE studies reveal that the formation of the haem-Pfhrp-2 complex is disrupted by chloroquine. These results indicate that chloroquine may be acting by inhibiting haem detoxification/binding to Pfhrp-2. Moreover, the higher affinity of chloroquine for haem than Pfhrp-2 suggests a possible mechanism of action for chloroquine; it may remove the haem bound to Pfhrp-2 and form a complex that is toxic to the parasite.

Artemisinin, an endoperoxide antimalarial, disrupts the hemoglobin catabolism and heme detoxification systems in malarial parasite

Endoperoxide antimalarials based on the ancient Chinese drug Qinghaosu (artemisinin) are currently our major hope in the fight against drug-resistant malaria. Rational drug design based on artemisinin and its analogues is slow as the mechanism of action of these antimalarials is not clear. Here we report that these drugs, at least in part, exert their effect by interfering with the plasmodial hemoglobin catabolic pathway and inhibition of heme polymerization. In an in vitro experiment we observed inhibition of digestive vacuole proteolytic activity of malarial parasite by artemisinin. These observations were further confirmed by ex vivo experiments showing accumulation of hemoglobin in the parasites treated with artemisinin, suggesting inhibition of hemoglobin degradation. We found artemisinin to be a potent inhibitor of heme polymerization activity mediated by Plasmodium yoelii lysates as well as Plasmodium falciparum histidine-rich protein II. Interaction of artemisinin with the purified malarial hemozoin in vitro resulted in the concentration-dependent breakdown of the malaria pigment. Our results presented here may explain the selective and rapid toxicity of these drugs on mature, hemozoin-containing, stages of malarial parasite. Since artemisinin and its analogues appear to have similar molecular targets as chloroquine despite having different structures, they can potentially bypass the quinoline resistance machinery of the malarial parasite, which causes sublethal accumulation of these drugs in resistant strains.

Posttranslational modification of the AU-rich element binding protein HuR by protein kinase Cdelta elicits angiotensin II-induced stabilization and nuclear export of cyclooxygenase 2 mRNA

The mRNA stabilizing factor HuR is involved in the posttranscriptional regulation of many genes, including that coding for cyclooxygenase 2 (COX-2). Employing RNA interference technology and actinomycin D experiments, we demonstrate that in human mesangial cells (hMC) the amplification of cytokine-induced COX-2 by angiotensin II (AngII) occurs via a HuR-mediated increase of mRNA stability. Using COX-2 promoter constructs with different portions of the 3' untranslated region of COX-2, we found that the increase in COX-2 mRNA stability is attributable to a distal class III type of AU-rich element (ARE). Likewise, the RNA immunoprecipitation assay showed AngII-induced binding of HuR to this ARE. Using the RNA pulldown assay, we demonstrate that the AngII-caused HuR assembly with COX-2 mRNA is found in free and cytoskeleton-bound polysomes indicative of an active RNP complex. Mechanistically, the increased HuR binding to COX-2-ARE by AngII is accompanied by increased nucleocytoplasmic HuR shuttling and depends on protein kinase Cdelta (PKCdelta), which physically interacts with nuclear HuR, thereby promoting its phosphorylation. Mapping of phosphorylation sites identified serines 221 and 318 as critical target sites for PKCdelta-triggered HuR phosphorylation and AngII-induced HuR export to the cytoplasm. Posttranslational modification of HuR by PKCdelta represents an important novel mode of HuR activation implied in renal COX-2 regulation.

Oncocytic ependymoma: a new morphological variant of high-grade ependymal neoplasm composed of mitochondrion-rich epithelioid cells

Oncocytomas are defined as tumors containing in excess of 50% large mitochondrion-rich cells, irrespective of histogenesis and dignity. Along the central neuraxis, oncocytomas are distinctly uncommon but relevant to the differential diagnosis of neoplasia marked by prominent cytoplasmic granularity. We describe an anaplastic ependymoma (WHO grade III) with a prevailing oncocytic component that was surgically resected from the right fronto-insular region of a 43-year-old female. Preoperative imaging showed a fairly circumscribed, partly cystic, contrast-enhancing mass of 2 cm × 2 cm × 1.7 cm. Histology revealed a biphasic neoplasm wherein conventional ependymal features coexisted with plump epithelioid cells replete with brightly eosinophilic granules. Whereas both components displayed an overtly ependymal immunophenotype, including positivity for S100 protein and GFAP, as well as "dot-like" staining for EMA, the oncocytic population also tended to intensely react with the antimitochondrial antibody 113-1. Conversely, failure to bind CD68 indicated absence of significant lysosomal storage. Negative reactions for both pan-cytokeratin (MNF 116) and low molecular weight cytokeratin (CAM 5.2), as well as synaptophysin and thyroglobulin, further assisted in ruling out metastatic carcinoma. In addition to confirming the presence of "zipper-like" intercellular junctions and microvillus-bearing cytoplasmic microlumina, electron microscopy allowed for the pervasive accumulation of mitochondria in tumor cells to be directly visualized. A previously not documented variant, oncocytic ependymoma, is felt to add a reasonably relevant novel item to the differential diagnosis of granule-bearing central nervous system neoplasia, in particular oncocytic meningioma, granular cell astrocytoma, as well as metastatic deposits by oncocytic malignancies from extracranial sites.

Identification of a fibronectin interaction site in the extracellular matrix protein ameloblastin

Mammalian teeth are composed of hydroxyapatite crystals that are embedded in a rich extracellular matrix. This matrix is produced by only two cell types, the mesenchymal odontoblasts and the ectodermal ameloblasts. Ameloblasts secrete the enamel proteins amelogenin, ameloblastin, enamelin and amelotin. Odontoblasts secrete collagen type I and several calcium-binding phosphoproteins including dentin sialophosphoprotein, dentin matrix protein, bone sialoprotein and osteopontin. The latter four proteins have recently been grouped in the family of the SIBLINGs (small integrin-binding ligand, N-linked glycoproteins) because they display similar gene structures and because they contain an RGD tripeptide sequence that binds to integrin receptors and thus mediates cell adhesion. We have prepared all the other tooth-specific proteins in recombinant form and examined whether they might also promote cell adhesion similar to the SIBLINGs. We found that only ameloblastin consistently mediated adhesion of osteoblastic and fibroblastic cells to plastic or titanium surfaces. The activity was dependent on the intact three-dimensional structure of ameloblastin and required de novo protein synthesis of the adhering cells. By deletion analysis and in vitro mutagenesis, the active site could be narrowed down to a sequence of 13 amino acid residues (VPIMDFADPQFPT) derived from exon 7 of the rat ameloblastin gene or exons 7-9 of the human gene. Kinetic studies and RNA interference experiments further demonstrated that this sequence does not directly bind to a cell surface receptor but that it interacts with cellular fibronectin, which in turn binds to integrin receptors. The identification of a fibronectin-binding domain in ameloblastin might permit interesting applications for dental implantology. Implants could be coated with peptides containing the active sequence, which in turn would recruit fibronectin from the patient's blood. The recruited fibronectin should then promote cell adhesion on the implant surface, thereby accelerating osseointegration of the implant.

Glycogen-rich pleomorphic xanthoastrocytoma with clear-cell features: confirmatory report of a rare variant with implications for differential diagnosis

Central nervous system space-occupying lesions with clear-cell features encompass a nosologically heterogeneous array, ranging from reactive histiocytic proliferations to neuroepithelial or meningothelial neoplasms of various grades and to metastases. In the face of such differential diagnostic breadth, recognizing cytoplasmic lucency as part of the morphological spectrum of some low grade gliomas will directly have an impact on patient care. We describe a prevailing clear-cell change in an epileptogenic left temporal pleomorphic xanthoastrocytoma surgically resected from a 36-year-old man. Mostly subarachnoid and focally calcified, the tumor was composed of fascicles of moderately atypical spindle cells with optically lucent cytoplasm that tended to intermingle with a desmoplastic mesh of reticulin fibers. Immunohistochemically, coexpression of S100 protein, vimentin, GFAP, and CD34 was noted. Conversely, neither punctate staining for EMA nor positivity for CD68 was seen. Mitotic activity was absent, and the MIB1 labeling index was 2-3% on average. Diastase-sensitive PAS-positive granula indicated clear-cell change to proceed from glycogen storage. Electron microscopy showed tumor cell cytoplasm to be largely obliterated by non-lysosomal-bound pools of glycogen, while hardly any fat vacuole was encountered. Neither ependymal-derived organelles nor annular lamellae suggesting oligodendroglial differentiation were detected. The latter differential diagnosis was further invalidated by lack of codeletion of chromosomal regions 1p36 and 19q13 on molecular genetic testing. By significantly interfering with pattern recognition as an implicit approach in histopathology, clear-cell change in pleomorphic xanthoastrocytoma is likely to suspend its status as a "classic", and to prompt more deductive differential diagnostic strategies to exclude look-alikes, especially clear-cell ependymoma and oligodendroglioma.

Post-translational signal peptide cleavage controls differential epitope recognition in the QP-rich domain of recombinant Theileria parva PIM

The presence of the schizont stage of the obligate intracellular parasites Theileria parva or T. annulata in the cytoplasm of an infected leukocyte results in host cell transformation via a mechanism that has not yet been elucidated. Proteins, secreted by the schizont, or expressed on its surface, are of interest as they can interact with host cell molecules that regulate host cell proliferation and/or survival. The major schizont surface protein is the polymorphic immunodominant molecule, PIM, which contains a large glutamine- and proline-rich domain (QP-rd) that protrudes into the host cell cytoplasm. Analyzing QP-rd generated by in vitro transcription/translation, we found that the signal peptide was efficiently cleaved post-translationally upon addition of T cell lysate or canine pancreatic microsomes, whereas signal peptide cleavage of a control protein only occurred cotranslationally and in the presence of microsomal membranes. The QP-rd of PIM migrated anomalously in SDS-PAGE and removal of the 19 amino acids corresponding to the predicted signal peptide caused a decrease in apparent molecular mass of 24kDa. The molecule was analyzed using monoclonal antibodies that recognize a set of previously defined PIM epitopes. Depending on the presence or the absence of the signal peptide, two conformational states could be demonstrated that are differentially recognized, with N-terminal epitopes becoming readily accessible upon signal peptide removal, and C-terminal epitopes becoming masked. Similar observations were made when the QP-rd of PIM was expressed in bacteria. Our observations could also be of relevance to other schizont proteins. A recent analysis of the proteomes of T. parva and T. annulata revealed the presence of a large family of potentially secreted proteins, characterized by the presence of large stretches of amino acids that are also particularly rich in QP-residues.

Leiomyomatoid angiomatous neuroendocrine tumor (LANT) of the pituitary: a distinctive biphasic neoplasm with primitive secretory phenotype and smooth muscle-rich stroma

We describe a hitherto undocumented variant of dimorphic pituitary neoplasm composed of an admixture of neurosecretory cells and profuse leiomyomatous stroma around intratumoral vessels. Radiologically perceived as a macroadenoma of 3.8 cm in diameter, this pituitary mass developed in an otherwise healthy 43-year-old female. At the term of a yearlong history of amenorrhea and progressive bitemporal visual loss, subtotal resection was performed via transsphenoidal microsurgery. Discounting mild hyperprolactinemia, there was no evidence of excess hormone production. Histologically, solid sheets, nests and cords of epithelial-looking, yet cytokeratin-negative cells were seen growing in a richly vascularized stroma of spindle cells. While strong immunoreactivity for NCAM, Synaptophysin and Chromogranin-A was detected in the former, the latter showed both morphological and immunophenotypic hallmarks of smooth muscle, being positive for vimentin, muscle actin and smooth muscle actin. Architectural patterns varied from monomorphous stroma-dominant zones through biphasic neuroendocrine-leiomyomatous areas, to pseudopapillary fronds along vascular cores. Only endothelia were labeled with CD34. Staining for S100 protein and GFAP, characteristics of sustentacular cells, as well as bcl-2 and c-kit was absent. Except for alpha-subunit, anterior pituitary hormones tested negative in tumor cells, as did a panel of peripheral endocrine markers, including serotonin, somatostatin, calcitonin, parathormone and vasoactive intestinal polypeptide. Mitotic activity was absent and the MIB-1 labeling index low (1-2%). While assignment of this lesion to any established neoplastic entity is not forthcoming, we propose it is being considered as a low-grade neuroendocrine tumor possibly related to null cell adenoma.

Differential gene and protein expression in abluminal sprouting and intraluminal splitting forms of angiogenesis

In adult skeletal muscle, abluminal sprouting or longitudinal splitting of capillaries can be initiated separately by muscle overload and elevated microcirculation shear stress respectively. In the present study, gene and protein expression patterns associated with the different forms of angiogenesis were examined using a targeted gene array (Superarray), validated by quantitative RT (reverse transcription)-PCR and immunoblots. Sprouting angiogenesis induced large changes in expression levels in genes associated with extracellular matrix remodelling, such as MMP-2 (matrix metalloproteinase-2), TIMP (tissue inhibitor of metalloproteinases), SPARC (secreted protein, acidic and rich in cysteine) and thrombospondin. Changes in neuropilin, midkine and restin levels, which may underpin changes in endothelial morphology, were seen during splitting angiogenesis. Up-regulation of VEGF (vascular endothelial growth factor), Flk-1, angiopoietin-2 and PECAM-1 (platelet/endothelial cell adhesion molecule-1) was seen in both forms of angiogenesis, representing a common angiogenic response of endothelial cells. In conclusion, the present study demonstrates that general angiogenic signals from growth factors can be influenced by the local microenvironment resulting in differing forms of capillary growth to produce a co-ordinated expansion of the vascular bed.

The European Hare (Lepus europaeus): A Picky Herbivore Searching for Plant Parts Rich in Fat

European hares of both sexes rely on fat reserves, particularly during the reproduc-tive season. Therefore, hares should select dietary plants rich in fat and energy. However, hares also require essential polyunsaturated fatty acids (PUFA) such as linoleic acid (LA) and alpha-linolenic acid (ALA) to reproduce and survive. Although hares are able to absorb PUFA selectively in their gastrointestinal tract, it is unknown whether this mechanism is sufficient to guarantee PUFA supply. Thus, diet selection may involve a trade-off between a preference for energy versus a preference for crucial nutrients, namely PUFA. We compared plant and nutrient availability and use by hares in an arable landscape in Austria over three years. We found that European hares selected their diet for high energy content (crude fat and crude protein), and avoided crude fibre. There was no evidence of a preference for plants rich in LA and ALA. We conclude that fat is the limiting resource for this herbivorous mammal, whereas levels of LA and ALA in forage are sufficiently high to meet daily requirements, especially since their uptake is enhanced by physiological mechanisms. Animals selected several plant taxa all year round, and preferences did not simply correlate with crude fat content. Hence, European hares might not only select for plant taxa rich in fat, but also for high-fat parts of preferred plant taxa. As hares preferred weeds/grasses and various crop types while avoiding cereals, we suggest that promoting heterogeneous habitats with high crop diversity and set-asides may help stop the decline of European hares throughout Europe.

Molecular characterisation of a predominant antigenic region of Giardia lamblia variant surface protein H7.

During infection, the intestinal protozoan parasite Giardia lamblia undergoes continuous antigenic variation which is determined by diversification of the parasite's major surface antigen, named VSP (variant surface protein). One member from this protein family, VSP H7, is expressed by G. lamblia clone GS/M-83-H7. In the present study, we characterised a highly antigenic portion of VSP H7 which is positioned inside a 130 amino acid C-terminal region of the protein. This region overlaps with a cysteine-rich motif that is rather conserved within the VSP family. Detailed molecular dissection of the antigenic portion monitored a 12 amino acid peptidyl structure which constitutes a non-conformational epitope of VSP H7. In the murine host, this epitope is recognised relatively early (before day 10 p.i.) during infection and stimulates a strong intestinal immunoglobulin A response. At late infective stages (after day 10 p.i.) this immune reaction is progressively complemented by reactions against 'late' antigenic epitopes which are also located inside the 130 amino acid antigenic portion but in closer proximity to the C-terminal end of VSP H7 than the 12 amino acid epitope. Both the high antigenicity and the conserved character suggest that the 12 amino acid epitope is a key factor within the immunological interplay between G. lamblia and the experimental murine host.