RESUMO
HIV is a major public health issue, and infection of CD4(+) T lymphocytes is one of its key features. Whereas several cellular proteins have been identified that facilitate viral infection and replication, the role of hemichannels in these processes has not been fully characterized. We now show that the HIV isolates, R5 and X4, induced a transient-early (5-30 min) and a later, persistent (48-120 h) opening of Panx1 hemichannels, which was dependent on the binding of HIV to CD4 and CCR5/CXCR4 receptors. Blocking Panx1 hemichannels by reducing their opening or protein expression inhibited HIV replication in CD4(+) T lymphocytes. Thus, our findings demonstrate that Panx1 hemichannels play an essential role in HIV infection.
Assuntos
Linfócitos T CD4-Positivos/virologia , Conexinas/fisiologia , HIV/fisiologia , Proteínas do Tecido Nervoso/fisiologia , Conexina 43/fisiologia , Humanos , Receptores CCR5/fisiologia , Receptores CXCR4/fisiologia , Replicação ViralRESUMO
Gap junctional communication between microglia was investigated at rat brain stab wounds and in primary cultures of rat and mouse cells. Under resting conditions, rat microglia (FITC-isolectin-B4-reactive cells) were sparsely distributed in the neocortex, and most (95%) were not immunoreactive for Cx43, a gap junction protein subunit. At brain stab wounds, microglia progressively accumulated over several days and formed aggregates that frequently showed Cx43 immunoreactivity at interfaces between cells. In primary culture, microglia showed low levels of Cx43 determined by Western blotting, diffuse intracellular Cx43 immunoreactivity, and a low incidence of dye coupling. Treatment with the immunostimulant bacterial lipopolysaccharide (LPS) or the cytokines interferon-gamma (INF-gamma) or tumor necrosis factor-alpha (TNF-alpha) one at a time did not increase the incidence of dye coupling. However, microglia treated with INF-gamma plus LPS showed a dramatic increase in dye coupling that was prevented by coapplication of an anti-TNF-alpha antibody, suggesting the release and autocrine action of TNF-alpha. Treatment with INF-gamma plus TNF-alpha also greatly increased the incidence of dye coupling and the Cx43 levels with translocation of Cx43 to cell-cell contacts. The cytokine-induced dye coupling was reversibly inhibited by 18 alpha-glycyrrhetinic acid, a gap junction blocker. Cultured mouse microglia also expressed Cx43 and developed dye coupling upon treatment with cytokines, but microglia from homozygous Cx43-deficient mice did not develop significant dye coupling after treatment with either INF-gamma plus LPS or INF-gamma plus TNF-alpha. This report demonstrates that microglia can communicate with each other through gap junctions that are induced by inflammatory cytokines, a process that may be important in the elaboration of the inflammatory response.
Assuntos
Conexina 43/metabolismo , Junções Comunicantes/efeitos dos fármacos , Interferon gama/farmacologia , Microglia/efeitos dos fármacos , Fator de Necrose Tumoral alfa/farmacologia , Animais , Lesões Encefálicas/metabolismo , Comunicação Celular/efeitos dos fármacos , Conexina 43/deficiência , Junções Comunicantes/metabolismo , Masculino , Camundongos , Camundongos Knockout , Microglia/metabolismo , Ratos , Ratos Sprague-DawleyRESUMO
Gap junction channels are sites of cytoplasmic communication between contacting cells. In vertebrates, they consist of protein subunits denoted connexins (Cxs) which are encoded by a gene family. According to their Cx composition, gap junction channels show different gating and permeability properties that define which ions and small molecules permeate them. Differences in Cx primary sequences suggest that channels composed of different Cxs are regulated differentially by intracellular pathways under specific physiological conditions. Functional roles of gap junction channels could be defined by the relative importance of permeant substances, resulting in coordination of electrical and/or metabolic cellular responses. Cells of the native and specific immune systems establish transient homo- and heterocellular contacts at various steps of the immune response. Morphological and functional studies reported during the last three decades have revealed that many intercellular contacts between cells in the immune response present gap junctions or "gap junction-like" structures. Partial characterization of the molecular composition of some of these plasma membrane structures and regulatory mechanisms that control them have been published recently. Studies designed to elucidate their physiological roles suggest that they might permit coordination of cellular events which favor the effective and timely response of the immune system.
Assuntos
Comunicação Celular/fisiologia , Junções Comunicantes/fisiologia , Timo/fisiologia , Animais , Conexinas/fisiologia , Células Epiteliais , Matriz Extracelular , Humanos , Imunidade Celular , Camundongos , RNA Mensageiro , Timo/citologiaRESUMO
Gap junction channels are sites of cytoplasmic communication between contacting cells. In vertebrates, they consist of protein subunits denoted connexins (Cxs) which are encoded by a gene family. According to their Cx composition, gap junction channels show different gating and permeability properties that define which ions and small molecules permeate them. Differences in Cx primary sequences suggest that channels composed of different Cxs are regulated differentially by intracellular pathways under specific physiological conditions. Functional roles of gap junction channels could be defined by the relative importance of permeant substances, resulting in coordination of electrical and/or metabolic cellular responses. Cells of the native and specific immune systems establish transient homo- and heterocellular contacts at various steps of the immune response. Morphological and functional studies reported during the last three decades have revealed that many intercellular contacts between cells in the immune response present gap junctions or "gap junction-like" structures. Partial characterization of the molecular composition of some of these plasma membrane structures and regulatory mechanisms that control them have been published recently. Studies designed to elucidate their physiological roles suggest that they might permit coordination of cellular events which favor the effective and timely response of the immune system
Assuntos
Humanos , Conexinas/fisiologia , Junções Comunicantes/fisiologia , Sistema Imunitário/citologia , Sistema Imunitário/fisiologia , Células da Medula Óssea/citologia , Comunicação Celular/fisiologia , Imunidade Celular/fisiologia , Células Estromais/fisiologiaRESUMO
Because hepatocytes communicate via gap junctions, it has been proposed that Ca2+ waves propagate through this pathway and in the process activate Ca2+-dependent cellular responses. We testedthis hypothesis by measuring vasopressin-induced glycogenolysis in short-term cultures of rat hepatocytes. A 15-min vasopressin (10(-8) M) stimulation induced a reduction of glycogen content that reached a maximum 1-3 h later. Gap junction blockers, octanol or 18alpha-glycyrrhetinic acid, reduced the effect by 70%. The glycogenolytic response induced by Ca2+ ionophore 8-bromo-A-21387, which acts on each hepatocyte, was not affected by gap junction blockers. Moreover, the vasopressin-induced glycogenolysis was lower (70%) in dispersed than in reaggregated hepatocytes and in dispersed hepatocytes was not affected by gap junction blockers. In hepatocytes reaggregated in the presence of a synthetic peptide homologous to a domain of the extracellular loop 1 of the main hepatocyte gap junctional protein, vasopressin-induced glycogenolysis and incidence of dye coupling were drastically reduced. Moreover, gap junctional communication was detected between reaggregated cells, suggesting that hepatocytes with different vasopressin receptor densities become coupled to each other. The vasopressin-induced effect was not affected by suramin, ruling out ATP as a paracrine mediator. We propose that gap junctions allow for a coordinated vasopressin-induced glycogenolytic response despite the heterogeneity among hepatocytes.