RESUMO
The discovery of dendritic cell (DC)-specific intercellular adhesion molecule (ICAM)-3-grabbing nonintegrin (DC-SIGN) as a DC-specific ICAM-3 binding receptor that enhances HIV-1 infection of T cells in trans has indicated a potentially important role for adhesion molecules in AIDS pathogenesis. A related molecule called DC-SIGNR exhibits 77% amino acid sequence identity with DC-SIGN. The DC-SIGN and DC-SIGNR genes map within a 30-kb region on chromosome 19p13.2-3. Their strong homology and close physical location indicate a recent duplication of the original gene. Messenger RNA and protein expression patterns demonstrate that the DC-SIGN-related molecule is highly expressed on liver sinusoidal cells and in the lymph node but not on DCs, in contrast to DC-SIGN. Therefore, we suggest that a more appropriate name for the DC-SIGN-related molecule is L-SIGN, liver/lymph node-specific ICAM-3-grabbing nonintegrin. We show that in the liver, L-SIGN is expressed by sinusoidal endothelial cells. Functional studies indicate that L-SIGN behaves similarly to DC-SIGN in that it has a high affinity for ICAM-3, captures HIV-1 through gp120 binding, and enhances HIV-1 infection of T cells in trans. We propose that L-SIGN may play an important role in the interaction between liver sinusoidal endothelium and trafficking lymphocytes, as well as function in the pathogenesis of HIV-1.
Assuntos
Antígenos CD , Antígenos de Diferenciação , Moléculas de Adesão Celular/metabolismo , Proteína gp120 do Envelope de HIV/metabolismo , HIV-1/fisiologia , Lectinas Tipo C , Lectinas/fisiologia , Fígado/metabolismo , Receptores de Antígenos/fisiologia , Receptores de HIV/fisiologia , Receptores Virais/fisiologia , Animais , Sequência de Bases , Linhagem Celular , Células Cultivadas , Mapeamento Cromossômico , DNA Complementar , Células Dendríticas , Endotélio/citologia , Éxons , HIV-1/metabolismo , Humanos , Lectinas/genética , Lectinas/metabolismo , Camundongos , Camundongos Endogâmicos BALB C , Dados de Sequência Molecular , Polimorfismo Genético , Receptores de Antígenos/genética , Receptores de Antígenos/metabolismo , Receptores de Superfície Celular/genética , Receptores de Superfície Celular/metabolismo , Receptores de HIV/genética , Receptores de HIV/metabolismoRESUMO
The intracellular protozoan parasite Toxoplasma gondii shares with other members of the Apicomplexa a common set of apical structures involved in host cell invasion. Micronemes are apical secretory organelles releasing their contents upon contact with host cells. We have identified a transmembrane micronemal protein MIC6, which functions as an escorter for the accurate targeting of two soluble proteins MIC1 and MIC4 to the micronemes. Disruption of MIC1, MIC4, and MIC6 genes allowed us to precisely dissect their contribution in sorting processes. We have mapped domains on these proteins that determine complex formation and targeting to the organelle. MIC6 carries a sorting signal(s) in its cytoplasmic tail whereas its association with MIC1 involves a lumenal EGF-like domain. MIC4 binds directly to MIC1 and behaves as a passive cargo molecule. In contrast, MIC1 is linked to a quality control system and is absolutely required for the complex to leave the early compartments of the secretory pathway. MIC1 and MIC4 bind to host cells, and the existence of such a complex provides a plausible mechanism explaining how soluble adhesins act. We hypothesize that during invasion, MIC6 along with adhesins establishes a bridge between the host cell and the parasite.
Assuntos
Moléculas de Adesão Celular/metabolismo , Estrutura Terciária de Proteína , Proteínas de Protozoários/metabolismo , Toxoplasma/metabolismo , Toxoplasmose/fisiopatologia , Animais , Moléculas de Adesão Celular/genética , Linhagem Celular , Chlorocebus aethiops , Retículo Endoplasmático/metabolismo , Fibroblastos , Marcação de Genes , Complexo de Golgi/metabolismo , Humanos , Immunoblotting , Microscopia de Fluorescência , Sinais Direcionadores de Proteínas , Transporte Proteico , Proteínas de Protozoários/genética , Proteínas Recombinantes/metabolismo , Toxoplasma/genética , Toxoplasma/patogenicidade , Toxoplasma/ultraestrutura , Transfecção , Células VeroRESUMO
Adhesion of erythrocytes infected with the malaria parasite Plasmodium falciparum to human host receptors is a process associated with severe malarial pathology. A number of in vitro cell lines are available as models for these adhesive processes, including Chinese hamster ovary (CHO) cells which express the placental adhesion receptor chondroitin-4-sulphate (CSA) on their surface. CHO-745 cells, a glycosaminoglycan-negative mutant CHO cell line lacking CSA and other reported P. falciparum adhesion receptors, are often used for recombinant expression of host receptors and for receptor binding studies. In this study we show that P. falciparum-infected erythrocytes can be easily selected for adhesion to an endogenous receptor on the surface of CHO-745 cells, bringing into question the validity of using these cells as a tool for P. falciparum adhesin expression studies. The adhesive interaction between CHO-745 cells and parasitized erythrocytes described here is not mediated by the known P. falciparum adhesion receptors CSA, CD36, or ICAM-1. However, we found that CHO-745-selected parasitized erythrocytes bind normal human IgM and that adhesion to CHO-745 cells is inhibited by protein A in the presence of serum, but not in its absence, indicating a non-specific inhibitory effect. Thus, protein A, which has been used as an inhibitor for a recently described interaction between infected erythrocytes and the placenta, may not be an appropriate in vitro inhibitor for understanding in vivo adhesive interactions.
Assuntos
Eritrócitos/parasitologia , Malária Falciparum/parasitologia , Plasmodium falciparum/fisiologia , Animais , Antígenos CD36/metabolismo , Células CHO , Adesão Celular/fisiologia , Sulfatos de Condroitina/metabolismo , Cricetinae , Cricetulus , Eritrócitos/fisiologia , Humanos , Imunoglobulina M/metabolismo , Molécula 1 de Adesão Intercelular/metabolismo , Malária Falciparum/fisiopatologia , Proteína Estafilocócica A/metabolismoRESUMO
The paucity of human cell lines expressing defined receptors for the cytoadhesion of erythrocytes infected with the human malarial parasite Plasmodium falciparumhas hampered the investigation of this important virulence property. Here, we investigate a permanent cell line derived from a human, malignant schwannoma, termed HMS-97, and show that this cell line expresses chondroitin-4-sulfate as the only surface receptor to which P. falciparum-infected erythrocytes can cytoadhere. Other common receptors for parasite adhesion, including CD36, vascular cellular adhesion molecule-1 (VCAM), intercellular adhesion molecule-1 (ICAM-1), and E-selectin are absent. Thus, HMS-97 cells are a useful tool for the study of P. falciparum adhesion to chondoitin-4-sulfate, the main receptor for parasite sequestration in the placenta. As chondoitin-4-sulfate can be readily cleaved from the cells, HMS-97 cells are also an ideal system for expressing recombinant adhesion receptors and studying their function in binding assays.