43 research outputs found
Human cytomegalovirus subverts the functions of monocytes, impairing chemokine-mediated migration and leukocyte recruitment.
No full textDespite their role in innate and adaptive immunity, during human cytomegalovirus (HCMV) infection, monocytes are considered to be an important target of infection, a site of latency, and vehicles for virus dissemination. Since chemokine receptors play crucial roles in monocyte activation and trafficking, we investigated the effects of HCMV on their expression and function. By using endotheliotropic strains of HCMV, we obtained high rates (roughly 50%) of in vitro-infected monocytes but only restricted viral gene expression. At 24 h after infection, while the chemokine receptors CX3CR and CCR7 were unaffected, CCR1, CCR2, CCR5, and CXCR4 were downmodulated on the cell surface and retained intracellularly. Structural components of the viral particles, but not viral gene expression or soluble factors released from infected cells, accounted for the changed localization of the receptor molecules and for the block of chemokine-driven migration. HCMV-infected monocytes indeed became unresponsive to inflammatory and homeostatic chemokines, although the basal cell motility and responsiveness to N-formyl-Met-Leu-Phe were unaffected or slightly increased. The production of inflammatory mediators responsible for the recruitment of other immune cells was also hampered by HCMV. Whereas endothelial and fibroblast cells infected by HCMV efficiently recruited leukocytes, infected monocytes were unable to recruit lymphocytes, monocytes, and neutrophils. Our data further highlight the complex level of interference exerted by HCMV on the host immune system
Funktion und Regulation des Chemokinrezeptors CXCR7
No full textDer Chemokinrezeptor CXCR7 spielt eine essentielle Rolle bei der normalen Entwicklung und fördert die Initiation und Progression verschiedener pathologischer Prozesse wie Krebs und Autoimmunerkrankungen. Er ist ein atypischer Rezeptor, der nicht an G-Proteine koppelt und als effektiver Scavenger für SDF-1 agiert. Der zweite SDF-1-bindende Chemokinrezeptor CXCR4 aktiviert intrazelluläre Signalkaskaden über G-Proteine und vermittelt so physiologisch und pathologisch relevante Zellmigrationsprozesse. Indem er als Scavenger für SDF-1 agiert, moduliert CXCR7 den CXCR4-SDF-1-Signalweg. Um die Funktionen von CXCR7 besser zu verstehen und die strukturellen Domänen zu definieren, welche die entgegengesetzten Effekte der beiden SDF-1-Rezeptoren regulieren, wurden Tail swap-Mutanten und weitere Rezeptorchimären erzeugt. Diese Rezeptoren wurden in HEK293 oder CHO-K1 Zellen exprimiert und es wurde das Rezeptortrafficking, die Bindung, Internalisierung und Degradation von SDF-1, die G-Protein Kopplung und die Aktivierung von MAP-Kinasen untersucht. Die Ergebnisse bestätigen, dass CXCR7 ein effektiver Scavenger für SDF-1 ist und weisen darauf hin, dass diese Funktion aufgrund von starker Rezeptordegradation strengen Regulationsmechanismen wie de novo Synthese und Rezeptorrecycling unterliegt. Des Weiteren konnte gezeigt werden, dass die C-terminale Domäne von CXCR7 eine entscheidende Rolle bei der Regulation der Rezeptorfunktion spielt und dass diese regulatorische Funktion durch umfangreiche C-terminale Phosphorylierungen von Serin- und Threonin-Resten vermittelt wird
CCR2 acts as scavenger for CCL2 during monocyte chemotaxis.
No full textBackgroundLeukocyte migration is essential for effective host defense against invading pathogens and during immune homeostasis. A hallmark of the regulation of this process is the presentation of chemokines in gradients stimulating leukocyte chemotaxis via cognate chemokine receptors. For efficient migration, receptor responsiveness must be maintained whilst the cells crawl on cell surfaces or on matrices along the attracting gradient towards increasing concentrations of agonist. On the other hand agonist-induced desensitization and internalization is a general paradigm for chemokine receptors which is inconsistent with the prolonged migratory capacity.Methodology/principal findingsChemotaxis of monocytes was monitored in response to fluorescent CCL2-mCherry by time-lapse video microscopy. Uptake of the fluorescent agonist was used as indirect measure to follow the endogenous receptor CCR2 expressed on primary human monocytes. During chemotaxis CCL2-mCherry becomes endocytosed as cargo of CCR2, however, the internalization of CCR2 is not accompanied by reduced responsiveness of the cells due to desensitization.Conclusions/significanceDuring chemotaxis CCR2 expressed on monocytes internalizes with the bound chemoattractant, but cycles rapidly back to the plasma membrane to maintain high responsiveness. Moreover, following relocation of the source of attractant, monocytes can rapidly reverse their polarization axis organizing a new leading edge along the newly formed gradient, suggesting a uniform distribution of highly receptive CCR2 on the plasma membrane. The present observations further indicate that during chemotaxis CCR2 acts as scavenger consuming the chemokine forming the attracting cue
