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Query: UMLS:C0024530 (malaria)
 44,886 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Complementary DNA clones encoding a protein highly homologous to the previously characterized long-chain acyl-CoA synthetase (LACS) in liver were isolated from rat brain cDNA libraries. This protein consists of 697 amino acids and has 64.7% identity with the rat liver LACS sequence. The brain protein and the liver LACS share essentially the same domain structure, having two regions similar to those of click beetle luciferase and a long discrete gap flanking the similar domains. A significant sequence similarity was found between the brain protein and malaria octapeptide-repeat antigen, suggesting a functional similarity. COS cells transfected with the cDNA for the brain protein expressed LACS activity with slightly different fatty acid specificity from that of the liver LACS. This new LACS is expressed predominantly in brain and, to a much lesser extent, in heart and adrenal. The 2.9- and 6.3-kb mRNAs coding for the brain enzyme are coregulated with the development of brain, suggesting the physiological importance of the enzyme in fatty acid metabolism in brain.
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PMID:Cloning and functional expression of a novel long-chain acyl-CoA synthetase expressed in brain. 156 43

Two genes encoding membrane antigens of Plasmodium falciparum were isolated by transient expression in mammalian cells and selection with human immune sera from African adults exposed to P. falciparum malaria. COS-7 cells were transfected with a plasmid expression library constructed from P. falciparum genomic DNA, and cells expressing reactive malaria antigens on their surface were enriched by adherence to antibody-coated dishes. One of the genes isolated is distinctive in that it does not contain repeat sequences typical of many malarial genes cloned by immunoscreening of bacterial expression libraries. The second gene apparently encodes a polymorphic version of the P. falciparum merozoite surface antigen Ag513, since the two sequences are identical in the 5' and 3' coding regions but diverge completely in the center. The COS-7 expression system provides an alternate means for cloning genes encoding malarial membrane antigens by using those antibodies in complex immune sera that bind membrane-associated, nondenatured molecules.
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PMID:Genes for Plasmodium falciparum surface antigens cloned by expression in COS cells. 169 28

The primary event in the pathogenesis of severe malaria in Plasmodium falciparum infection is thought to be adherence of trophozoite- and schizont-infected erythrocytes to capillary endothelium, a process called sequestration. Identifying the endothelial molecules used as receptors is an essential step in understanding this disease process. Recent work implicates the membrane glycoprotein CD36 (platelet glycoprotein IV; refs 2-5) and the multi-functional glycoprotein thrombospondin as receptors. Although CD36 has a widespread distribution on microvascular endothelium, it may not be expressed on all capillary beds where sequestration occurs, especially in the brain. The role of thrombospondin in cell adhesion, in vitro or in vivo, is less certain. We have noticed that some parasites bind to human umbilical-vein endothelial cells independently of CD36 or thrombospondin. To screen for alternative receptors, we have developed a novel cell-adhesion assay using transfected COS cells, which confirms that CD36 is a cell-adhesion receptor. In addition, we find that an endothelial-binding line of P. falciparum binds to COS cells transfected with a complementary DNA encoding intercellular adhesion molecule-1. As this molecule is widely distributed on capillaries and is inducible, this finding may be relevant to the pathogenesis of severe malaria.
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PMID:Intercellular adhesion molecule-1 is an endothelial cell adhesion receptor for Plasmodium falciparum. 247 84

The rotavirus glycoprotein VP7 has a cleavable signal peptide and is normally resident as an integral membrane protein in the ER of infected cells. A gene was constructed in which the VP7 H2 signal peptide was replaced by one from influenza hemagglutinin. COS cells transfected with this gene produced VP7 with the correct amino terminus, but the protein was rapidly secreted. Uncleaved VP7 from either precursor was not detected in cells after brief pulse-labeling, suggesting that the signal peptide was not acting as a temporary anchor; rather, it exerted its effect despite rapid cleavage. By splicing the H2 signal peptide onto another reporter protein, the malaria S-antigen, we demonstrated that H2 was necessary, but not itself sufficient, for targeting and retention. We propose that an interaction between the cleaved signal peptide and other downstream sequences in VP7 is required for retention of this protein in the ER as an integral membrane polypeptide.
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PMID:The signal peptide of the rotavirus glycoprotein VP7 is essential for its retention in the ER as an integral membrane protein. 253 41

To test whether the requirements for GPI-attachment are the same in mammalian cells and parasitic protozoa, we expressed the GPI-linked variant surface glycoprotein (VSG) of Trypanosoma brucei (T. brucei) in COS cells. Although large amounts of VSG were produced, only a small fraction became GPI-linked. This impaired processing is not due to the VSG ectodomain since replacement of the VSG GPI-signal with that of decay accelerating factor (DAF) produced GPI-linked VSG. Further, whereas fusion of the DAF GPI-signal to the COOH-terminus of human growth hormone (hGH) produces GPI-linked hGH, an analogous fusion using the VSG GPI-signal does not, indicating that the VSG GPI-signal functions poorly in mammalian cells. By constructing chimeric VSG-DAF GPI-signals and fusing them to the COOH-terminus of hGH, we show that of the two critical elements that comprise the GPI-signal--the cleavage/attachment site and the hydrophobic domain--the former is responsible for the impaired activity of the VSG GPI-signal in COS cells. To confirm this, we show that the VSG GPI-signal can be converted to a viable signal for mammalian cells by altering the amino acid configuration at the cleavage/attachment site. We also show that when fused to hGH, the putative GPI-signal from the malaria circumsporozoite (CS) protein produces low levels of GPI-anchored hGH, suggesting that the CS protein is indeed GPI-linked, but that the CS protein GPI-signal, like the VSG-signal, functions poorly in COS cells.
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PMID:The requirements for GPI-attachment are similar but not identical in mammalian cells and parasitic protozoa. 808 Dec 28

The general features of the glycosylphosphatidylinositol (GPI) signal have been conserved in evolution. To test whether the requirements for GPI attachment are indeed the same in mammalian cells and parasitic protozoa, we expressed the prototype GPI-linked protein of Trypanosoma brucei, the variant surface glycoprotein (VSG), in COS cells. Although large amounts of VSG were produced, only a small fraction became GPI linked. This impaired processing is not caused by the VSG ectodomain, since replacement of the VSG GPI signal with that of decay accelerating factor (DAF) produced GPI-linked VSG. Furthermore, whereas fusion of the DAF GPI signal to the COOH terminus of human growth hormone (hGH) produces GPI-linked hGH, an analogous hGH fusion using the VSG GPI signal does not, indicating that the VSG GPI signal functions poorly in mammalian cells. By constructing chimeric VSG-DAF GPI signals and fusing them to the COOH terminus of hGH, we show that of the two critical elements that comprise the GPI-signal--the cleavage/attachment site and the COOH terminal hydrophobic domain--the former is responsible for the impaired activity of the VSG GPI signal in COS cells. To confirm this, we show that the VSG GPI signal can be converted to a viable signal for mammalian cells by altering the amino acid configuration at the cleavage/attachment site. We also show that when fused to the COOH terminus of hGH, the putative GPI signal from the malaria circumsporozoite (CS) protein produces low levels of GPI-anchored hGH, suggesting that the CS protein is indeed GPI linked, but that the CS protein GPI signal, like the VSG-signal, functions poorly in COS cells. The finding that the requirements for GPI attachment are similar but not identical in parasitic protozoa and mammalian cells may allow for the development of selective inhibitors of GPI-anchoring that might prove useful as antiparasite therapeutics.
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PMID:Requirements for glycosylphosphatidylinositol attachment are similar but not identical in mammalian cells and parasitic protozoa. 816 50

In the past, several cell lines have been used as in vitro models for studying cytoadherence, which refers to the specific binding of Plasmodium falciparum-parasitized red blood cells (PRBC) to host endothelium of microvessels. These models include: (a) human cells, including human umbilical vein endothelial cells (HUVEC), C32 amelanotic melanoma cells and monocytes; (b) non-human cells transfected with human genes, including COS and CHO cells; and (c) purified candidate receptor molecules. However, endothelial cells from malaria target organs are rarely investigated. In this study, we describe the efficient isolation and characterization of human lung endothelial cells (HLEC). This is the first in vitro study of P. falciparum PRBC cytoadherence to human lung endothelium, one of the target organs during severe malaria. The endothelial nature of the HLEC lines was confirmed by the presence of the von Willebrand factor, anti-human platelet endothelial adhesion molecule-1 and E-selectin antigens as specific endothelial markers. After exposure of HLEC to human cytokines, FACScan analysis indicated the coexpression of PRBC receptors CD36, intercellular adhesion molecule-1 (ICAM-1), E-selectin and vascular cell adhesion molecule-1 (VCAM-1). The laboratory-adapted P. falciparum strains adhered specifically in vitro to these HLEC. The binding of PRBC could be inhibited with variable efficiency by various monoclonal antibodies (anti-CD36 > anti-ICAM-1 > anti-VCAM-1 > anti-E-selectin). Target organ specific cell lines such as HLEC expressing a variety of potential P. falciparum PRBC cytoadherence receptors may provide in vitro systems for studying the pathophysiology of severe malaria and identifying new therapeutic agents designed to directly block adhesive events involved in severe malaria.
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PMID:Primary culture of human lung microvessel endothelial cells: a useful in vitro model for studying Plasmodium falciparum-infected erythrocyte cytoadherence. 881 44

The presence of a signal sequence preceding the gene encoding a target antigen in a DNA vaccine should facilitate secretion of the in vivo translated antigen. The immune responses elicited upon injection with such a vector could differ from those induced by the same vector lacking a signal sequence. In the present study, the humoral responses elicited in mice immunized with two plasmids, either containing or lacking the human tissue plasminogen activator signal sequence, were compared. Both plasmids encode the chimeric antigen ZZN4, containing a malaria antigen Pf332-derived sequence (N4) linked to a bacterial fusion partner (ZZ). In vitro transfection of COS cells with each plasmid and treatment of the transfectants with brefeldin A confirmed that secretion of ZZN4 via the endoplasmic reticulum and Golgi pathway only occurred in cells transfected with the signal peptide-encoding plasmid. Repeated intramuscular injections of mice with either of the plasmids elicited comparable antibody responses to ZZN4 with regard to kinetics, specific IgG levels and persistence. These results indicate that in vivo transfection of muscle cells by either of these two plasmids generated comparable levels of antigen available for B-cell recognition and for uptake by antigen-presenting cells, despite the differential intracellular targeting of the encoded antigen. The relevance of these findings for the design of DNA vaccine vectors is discussed.
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PMID:Comparative study of DNA-based immunization vectors: effect of secretion signals on the antibody responses in mice. 927 Nov 70

The signal sequence trap method was used to isolate cDNAs corresponding to proteins containing secretory leader peptides and whose genes are expressed specifically in the salivary glands of the malaria vector Anopheles gambiae. Fifteen unique cDNA fragments, ranging in size from 150 to 550 bp, were isolated and sequenced in a first round of immunoscreening in COS-7 cells. All but one of the cDNAs contained putative signal sequences at their 5' ends, suggesting that they were likely to encode secreted or transmembrane proteins. Expression analysis by reverse transcription-PCR showed that at least six cDNA fragments were expressed specifically in the salivary glands. Fragments showing a high degree of similarity to D7 and apyrase, two salivary gland-specific genes previously found in Aedes aegypti, were identified. Of interest, three different D7-related cDNAs that are likely to represent a new gene family were found in An. gambiae. Moreover, three salivary gland-specific cDNA fragments that do not show similarity to known proteins in the databases were identified, and the corresponding full length cDNAs were cloned and sequenced. RNA in situ hybridization to whole female salivary glands showed patterns of expression that overlap only in part those observed in the culicine mosquito A. aegypti.
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PMID:Trapping cDNAs encoding secreted proteins from the salivary glands of the malaria vector Anopheles gambiae. 999 55

The pathophysiologic events leading to organ damage in Plasmodium falciparum malaria infections involve adhesion and sequestration of parasite-infected erythrocytes (PRBC) to the vascular endothelium and syncytiotrophoblast. Several potential receptors to which the PRBCs may bind have recently been identified, one of which is thrombomodulin (TM). TM has been implicated particularly in mediating sequestration of P. falciparum-infected erythrocytes in the placenta and brain, two sites of disease associated with high morbidity. In order to establish that binding of parasite-infected red blood cells to TM is dependent on its containing chondroitin-4-sulfate (CSA), we have mutated the CSA-attachment site of murine TM, and expressed this mutant form (TMsergly) in COS-7 cells. In cytoadhesion assays, we demonstrate that, in contrast to wild-type TM which contains CSA and supports the adhesion of 1466 PRBCs/mm2, TMser-gly does not contain CSA and adhesion of PRBCs to those cells expressing TMser-gly is entirely abrogated (200 PRBCs/mm2). These studies further confirm that the CSA of TM may play a role in the pathophysiology of malaria by providing a binding site for PRBCs.
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PMID:Plasmodium falciparum-infected erythrocytes: a mutational analysis of cytoadherence via murine thrombomodulin. 1036 58


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