Rho kinase is required for CCR7-mediated polarization and chemotaxis of T lymphocytes

Dysregulation of miR-193a serves as a potential contributor to MS pathogenesis via affecting RhoA and Rock1

BACKGROUND

Multiple sclerosis (MS) is one of the most common neurological diseases that cause chronic inflammation of the central nervous system and demyelination of the myelin sheath. At present, microRNAs (miRNAs) are considered not only a diagnostic and prognostic indicator of diseases but also a new goal in gene therapy. This study aims to find a simple, non-invasive, valuable biomarker for early detection and potential treatment of MS.

METHODS

In the present study, 30 patients with MS were included. The qRT-PCR method was performed to evaluate the expression level of miR-193a, RhoA, and ROCK1. Besides, western blotting was performed to determine the expression level of RhoA and ROCK1 at protein levels. Moreover, we aimed to clarify the possible correlation between miR-193a-5p and its-regulated target genes so that miR-193a-5p mimic was transfected into MS-derived cultured PBMSs, and the expression level of RhoA and ROCK1 were then evaluated by qRT-PCR and Western blotting. In the final step, the correlation between miR-193a-5p and clinicopathological features of patients was investigated.

RESULTS

Results showed that miR-193a was decreased while RhoA and ROCK1 were up-regulated in PBMCs obtained from patients with MS compared to the control group. It was also revealed that miR-193a transfection reduced RhoA and ROCK1 expression at mRNA and protein levels. The results from the Chi-square analysis showed that down-regulation of miR-193a was associated with increased CRP level, CSF IgG positivity, and MSSS (Multiple Sclerosis Severity Score), suggesting miR-193a is a potential diagnostic and prognostic indicator.

CONCLUSION

We implied that miR-193a could modulate RhoA and ROCK 1 expression in MS patients, in which its down-regulation leads to increased expression of RhoA and ROCK1 and poor prognosis of patients with MS. Therefore, miR-193a and its associated targets could serve potential prognostic, diagnostic, and therapeutic efficacy in MS patients.

Role of casein kinase 1 in the amoeboid migration of B-cell leukemic and lymphoma cells: A quantitative live imaging in the confined environment

The migratory properties of leukemic cells are commonly associated with their pathological potential and can significantly affect the disease progression. While the research in immunopathology mostly employed powerful indirect methods such as flow cytometry, these cells were rarely observed directly using live imaging microscopy. This is especially true for the malignant cells of the B-cell lineage, such as those originating from chronic lymphocytic leukemia (CLL) and mantle cell lymphoma (MCL). In this study, we employed open-source image analysis tools to automatically and quantitatively describe the amoeboid migration of four B-cell leukemic and lymphoma cell lines and primary CLL cells. To avoid the effect of the shear stress of the medium on these usually non-adherent cells, we have confined the cells using a modified under-agarose assay. Surprisingly, the behavior of tested cell lines differed substantially in terms of basal motility or response to chemokines and VCAM1 stimulation. Since casein kinase 1 (CK1) was reported as a regulator of B-cell migration and a promoter of CLL, we looked at the effects of CK1 inhibition in more detail. Migration analysis revealed that CK1 inhibition induced rapid negative effects on the migratory polarity of these cells, which was quantitatively and morphologically distinct from the effect of ROCK inhibition. We have set up an assay that visualizes endocytic vesicles in the uropod and facilitates morphological analysis. This assay hints that the effect of CK1 inhibition might be connected to defects in polarized intracellular transport. In summary, 1) we introduce and validate a pipeline for the imaging and quantitative assessment of the amoeboid migration of CLL/MCL cells, 2) we provide evidence that the assay is sensitive enough to mechanistically study migration defects identified by the transwell assay, and 3) we describe the polarity defects induced by inhibition or deletion of CK1ε.

Cellular Electrical Impedance as a Method to Decipher CCR7 Signalling and Biased Agonism

The human C-C chemokine receptor type 7 (CCR7) has two endogenous ligands, C-C chemokine ligand 19 (CCL19) and CCL21, displaying biased agonism reflected by a pronounced difference in the level of β-arrestin recruitment. Detecting this preferential activation generally requires the use of separate, pathway-specific label-based assays. In this study, we evaluated an alternative methodology to study CCR7 signalling. Cellular electrical impedance (CEI) is a label-free technology which yields a readout that reflects an integrated cellular response to ligand stimulation. CCR7-expressing HEK293 cells were stimulated with CCL19 or CCL21, which induced distinct impedance profiles with an apparent bias during the desensitisation phase of the response. This discrepancy was mainly modulated by differential β-arrestin recruitment, which shaped the impedance profile but did not seem to contribute to it directly. Pathway deconvolution revealed that Gαi-mediated signalling contributed most to the impedance profile, but Gαq- and Gα12/13-mediated pathways were also involved. To corroborate these results, label-based pathway-specific assays were performed. While CCL19 more potently induced β-arrestin2 recruitment and receptor internalisation than CCL21, both chemokines showed a similar level of Gαi protein activation. Altogether, these findings indicate that CEI is a powerful method to analyse receptor signalling and biased agonism.

Biphasic effect of mechanical stress on lymphocyte activation

Mechanical forces can modulate the immune response, mostly described as promoting the activation of immune cells, but the role and mechanism of pathological levels of mechanical stress in lymphocyte activation have not been focused on before. By an ex vivo experimental approach, we observed that mechanical stressing of murine spleen lymphocytes with 50 mmHg for 3 h induced the nuclear localization of NFAT1, increased C-Jun, and increased the expression of early activation marker CD69 in resting CD8+ cells. Interestingly, 50 mmHg mechanical stressing induced the nuclear localization of NFAT1; but conversely decreased C-Jun and inhibited the expression of CD69 in lymphocytes under lipopolysaccharide or phorbol 12-myristate 13-acetate/ionomycin stimulation. Additionally, we observed similar changes trends when comparing RNA-seq data of hypertensive and normotensive COVID-19 patients. Our results indicate a biphasic effect of mechanical stress on lymphocyte activation, which provides insight into the variety of immune responses in pathologies involving elevated mechanical stress.

Investigation of Fascin1, a Marker of Mature Dendritic Cells, Reveals a New Role for IL-6 Signaling in CCR7-Mediated Chemotaxis

Migration of mature dendritic cells (DCs) to lymph nodes is critical for the initiation of adaptive immunity. CCR7, a G-protein-coupled receptor for CCL19/21 chemokines, is known to be essential for chemotaxis of mature DCs, but the molecular mechanism linking inflammation to chemotaxis remains unclear. We previously demonstrated that fascin1, an actin-bundling protein, increases chemotaxis of mature mouse DCs. In this article, we demonstrated that fascin1 enhanced IL-6 secretion and signaling of mature mouse DCs. Furthermore, we demonstrated that IL-6 signaling is required for chemotaxis. Blockage of IL-6 signaling in wild-type DCs with an anti-IL-6 receptor α (IL-6Rα) Ab inhibited chemotaxis toward CCL19. Likewise, knockout of IL-6Rα inhibited chemotaxis of bone marrow-derived DCs. The addition of soluble IL-6Rα and IL-6 rescued chemotaxis of IL-6Rα knockout bone marrow-derived DCs, underscoring the role of IL-6 signaling in chemotaxis. We found that IL-6 signaling is required for internalization of CCR7, the initial step of CCR7 recycling. CCR7 recycling is essential for CCR7-mediated chemotaxis, explaining why IL-6 signaling is required for chemotaxis of mature DCs. Our results have identified IL-6 signaling as a new regulatory pathway for CCR7/CCL19-mediated chemotaxis and suggest that rapid migration of mature DCs to lymph nodes depends on inflammation-associated IL-6 signaling.

CXCL5 Modified Nanoparticle Surface Improves CXCR2+ Cell Selective Internalization

Driving nanomaterials to specific cell populations is still a major challenge for different biomedical applications. Several strategies to improve cell binding and uptake have been tried thus far by intrinsic material modifications or decoration with active molecules onto their surface. In the present work, we covalently bound the chemokine CXCL5 on fluorescently labeled amino-functionalized SiO₂ nanoparticles to precisely targeting CXCR2⁺ immune cells. We synthesized and precisely characterized the physicochemical features of the modified particles. The presence of CXCL5 on the surface was detected by z-potential variation and CXCL5-specific electron microscopy immunogold labeling. CXCL5-amino SiO₂ nanoparticle cell binding and internalization performances were analyzed in CXCR2⁺ THP-1 cells by flow cytometry and confocal microscopy. We showed improved internalization of the chemokine modified particles in the absence or the presence of serum. This internalization was reduced by cell pre-treatment with free CXCL5. Furthermore, we demonstrated CXCR2⁺ cell preferential targeting by comparing particle uptake in THP-1 vs. low-CXCR2 expressing HeLa cells. Our results provide the proof of principle that chemokine decorated nanomaterials enhance uptake and allow precise cell subset localization. The possibility to aim at selective chemokine receptor-expressing cells can be beneficial for the diverse pathological conditions involving immune reactions.

The Mechanobiology of the Actin Cytoskeleton in Stem Cells during Differentiation and Interaction with Biomaterials

An understanding of the cytoskeleton's importance in stem cells is essential for their manipulation and further clinical application. The cytoskeleton is crucial in stem cell biology and depends on physical and chemicals signals to define its structure. Additionally, cell culture conditions will be important in the proper maintenance of stemness, lineage commitment, and differentiation. This review focuses on the following areas: the role of the actin cytoskeleton of stem cells during differentiation, the significance of cellular morphology, signaling pathways involved in cytoskeletal rearrangement in stem cells, and the mechanobiology and mechanotransduction processes implicated in the interactions of stem cells with different surfaces of biomaterials, such as nanotopography, which is a physical cue influencing the differentiation of stem cells. Also, cancer stem cells are included since it is necessary to understand the role of their mechanical properties to develop new strategies to treat cancer. In this context, to study the stem cells requires integrated disciplines, including molecular and cellular biology, chemistry, physics, and immunology, as well as mechanobiology. Finally, since one of the purposes of studying stem cells is for their application in regenerative medicine, the deepest understanding is necessary in order to establish safety protocols and effective cell-based therapies.

β-Arrestin-2-Dependent Signaling Promotes CCR4-mediated Chemotaxis of Murine T-Helper Type 2 Cells

Allergic asthma is a complex inflammatory disease that leads to significant healthcare costs and reduction in quality of life. Although many cell types are implicated in the pathogenesis of asthma, CD4+ T-helper cell type 2 (Th2) cells are centrally involved. We previously reported that the asthma phenotype is virtually absent in ovalbumin-sensitized and -challenged mice that lack global expression of β-arrestin (β-arr)-2 and that CD4+ T cells from these mice displayed significantly reduced CCL22-mediated chemotaxis. Because CCL22-mediated activation of CCR4 plays a role in Th2 cell regulation in asthmatic inflammation, we hypothesized that CCR4-mediated migration of CD4+ Th2 cells to the lung in asthma may use β-arr-dependent signaling. To test this hypothesis, we assessed the effect of various signaling inhibitors on CCL22-induced chemotaxis using in vitro-polarized primary CD4+ Th2 cells from β-arr2-knockout and wild-type mice. Our results show, for the first time, that CCL22-induced, CCR4-mediated Th2 cell chemotaxis is dependent, in part, on a β-arr2-dependent signaling pathway. In addition, we show that this chemotactic signaling mechanism involves activation of P-p38 and Rho-associated protein kinase. These findings point to a proinflammatory role for β-arr2-dependent signaling and support β-arr2 as a novel therapeutic target in asthma.

RhoA Drives T-Cell Activation and Encephalitogenic Potential in an Animal Model of Multiple Sclerosis

T-cells are known to be intimately involved in the pathogenesis of multiple sclerosis (MS) and its animal model experimental autoimmune encephalomyelitis (EAE). T-cell activation is controlled by a range of intracellular signaling pathways regulating cellular responses such as proliferation, cytokine production, integrin expression, and migration. These processes are crucial for the T-cells’ ability to mediate inflammatory processes in autoimmune diseases such as MS. RhoA is a ubiquitously expressed small GTPase well described as a regulator of the actin cytoskeleton. It is essential for embryonic development and together with other Rho GTPases controls various cellular processes such as cell development, shaping, proliferation, and locomotion. However, the specific contribution of RhoA to these processes in T-cells in general, and in autoreactive T-cells in particular, has not been fully characterized. Using mice with a T-cell specific deletion of the RhoA gene (RhoA^fl/flLckCre⁺), we investigated the role of RhoA in T-cell development, functionality, and encephalitogenic potential in EAE. We show that lack of RhoA specifically in T-cells results in reduced numbers of mature T-cells in thymus and spleen but normal counts in peripheral blood. EAE induction in RhoA^fl/flLckCre⁺ mice results in significantly reduced disease incidence and severity, which coincides with a reduced CNS T-cell infiltration. Besides presenting reduced migratory capacity, both naïve and autoreactive effector T-cells from RhoA^fl/flLckCre⁺ mice show decreased viability, proliferative capacity, and an activation profile associated with reduced production of Th1 pro-inflammatory cytokines. Our study demonstrates that RhoA is a central regulator of several archetypical T-cell responses, and furthermore points toward RhoA as a new potential therapeutic target in diseases such as MS, where T-cell activity plays a central role.

Switching between individual and collective motility in B lymphocytes is controlled by cell-matrix adhesion and inter-cellular interactions

Lymphocytes alternate between phases of individual migration across tissues and phases of clustering during activation and function. The range of lymphocyte motility behaviors and the identity of the factors that govern them remain elusive. To explore this point, we here collected unprecedented statistics pertaining to cell displacements, cell:matrix and cell:cell interactions using a model B cell line as well as primary human B lymphocytes. At low cell density, individual B lymphocytes displayed a high heterogeneity in their speed and diffusivity. Beyond this intrinsic variability, B lymphocytes adapted their motility to the composition of extra-cellular matrix, adopting slow persistent walks over collagen IV and quick Brownian walks over fibronectin. At high cell density, collagen IV favored the self-assembly of B lymphocytes into clusters endowed with collective coordination, while fibronectin stimulated individual motility. We show that this behavioral plasticity is controlled by acto-myosin dependent adhesive and Arp2/3-dependent protrusive actin pools, respectively. Our study reveals the adaptive nature of B lymphocyte motility and group dynamics, which are shaped by an interplay between and cell:matrix and cell:cell interactions.

Biased signaling of G protein-coupled receptors - From a chemokine receptor CCR7 perspective

Chemokines (chemotactic cytokines) and their associated G protein-coupled receptors (GPCRs) work in a concerted manner to govern immune cell positioning in time and space. Promiscuity of both ligands and receptors, but also biased signaling within the chemokine system, adds to the complexity of how the cell-based immune system is controlled. Bias comes in three forms; ligand-, receptor- and tissue-bias. Biased signaling is increasingly being recognized as playing an important role in contributing to the fine-tuned coordination of immune cell chemotaxis. In the current review we discuss the recent findings related to ligand- and tissue-biased signaling of CCR7 and summarize what is known about bias at other chemokine receptors. CCR7 is expressed by a subset of T-cells and by mature dendritic cells (DCs). Together with its two endogenous ligands CCL19 and CCL21, of which the carboxy terminal tail of CCL21 displays an extraordinarily strong glycosaminoglycan (GAG) binding, CCR7 plays a central role in coordinating the meeting between mature antigen presenting DCs and naïve T-cells which normally takes place in the lymph nodes (LNs). This process is a prerequisite for the initiation of an antigen-specific T-cell mediated immune response. Thus CCR7 and its ligands are key players in initiating cell-based immune responses. CCL19 and CCL21 display differential interaction- and docking-modes for CCR7 leading to stabilization of different CCR7 conformations and hereby preferential activation of distinct intracellular signaling pathways (i.e. ligand bias). In general CCL19 seems to generate a strong temporal signal, whereas CCL21 generates a weaker, but more persistent signal. Tissue differential expression of these two ligands, and the generation of a third ligand "tailless-CCL21", through DC specific protease activity (tissue bias), orchestrates DC and T-cell LN homing and priming, with each ligand serving overlapping, but also distinct roles.

Beyond Chemoattraction: Multifunctionality of Chemokine Receptors in Leukocytes

The word chemokine is a combination of the words chemotactic and cytokine, in other words cytokines that promote chemotaxis. Hence, the term chemokine receptor refers largely to the ability to regulate chemoattraction. However, these receptors can modulate additional leukocyte functions, as exemplified by the case of CCR7 which, apart from chemotaxis, regulates survival, migratory speed, endocytosis, differentiation and cytoarchitecture. We present evidence highlighting that multifunctionality is a common feature of chemokine receptors. Based on the activities that they regulate, we suggest that chemokine receptors can be classified into inflammatory (which control both inflammatory and homeostatic functions) and homeostatic families. The information accrued also suggests that the non-chemotactic functions controlled by chemokine receptors may contribute to optimizing leukocyte functioning under normal physiological conditions and during inflammation.

Stimulation of osteoclast migration and bone resorption by C-C chemokine ligands 19 and 21

Osteoclasts are responsible for the bone erosion associated with rheumatoid arthritis (RA). The upregulation of the chemokines CCL19 and CCL21 and their receptor CCR7 has been linked to RA pathogenesis. The purpose of this study was to evaluate the effects of CCL19 and CCL21 on osteoclasts and to reveal their underlying mechanisms. The expression of CCL19, CCL21 and CCR7 was higher in RA patients than in osteoarthritis patients. In differentiating osteoclasts, tumor necrosis factor-α, interleukin-1β and lipopolysaccharide stimulated CCR7 expression. CCL19 and CCL21 promoted osteoclast migration and resorption activity. These effects were dependent on the presence of CCR7 and abolished by the inhibition of the Rho signaling pathway. CCL19 and CCL21 promoted bone resorption by osteoclasts in an in vivo mice calvarial model. These findings demonstrate for the first time that CCL19, CCL21 and CCR7 play important roles in bone destruction by increasing osteoclast migration and resorption activity. This study also suggests that the interaction of CCL19 and CCL21 with CCR7 is an effective strategic focus in developing therapeutics for alleviating inflammatory bone destruction.

Role of ROCK2 in CD4+ cells in allergic airways responses in mice

BACKGROUND

Rho kinases (ROCKs) contribute to allergic airways disease. ROCKs also play a role in lymphocyte proliferation and migration.

OBJECTIVE

To determine the role of ROCK2 acting within CD4+ cells in allergic airways responses.

METHODS

ROCK2-haploinsufficient (ROCK2+/- ) and wild-type mice were sensitized with ovalbumin (OVA). ROCK2+/- mice then received either CD4+ cells from ROCK2-sufficient OVA TCR transgenic (OT-II) mice or saline i.v. 48 h before challenge with aerosolized OVA. Wild-type mice received saline before challenge. Allergic airways responses were measured 48 h after the last challenge. Allergic airways responses were also assessed in mice lacking ROCK2 only in CD4+ cells (ROCK2CD4Cre mice) vs. control (CD4-Cre and ROCK2flox/flox ) mice.

RESULTS

OVA-induced increases in bronchoalveolar lavage lymphocytes, eosinophils, IL-13, IL-5, and eotaxin were reduced in ROCK2+/- vs. wild-type mice, as were airway hyperresponsiveness and mucous hypersecretion. In ROCK2+/- mice, adoptive transfer with CD4+ cells from OT-II mice restored effects of OVA on lymphocytes, eosinophils, IL-13, IL-5, and mucous hypersecretion to wild-type levels, whereas eotaxin and airway hyperresponsiveness were not affected. ROCK2 inhibitors reduced IL-13-induced release of eotaxin from airway smooth muscle (ASM), similar to effects of these inhibitors on ASM contractility. Despite the ability of adoptive transfer to restore allergic airways inflammation in ROCK2-insufficient mice, allergic inflammation was not different in ROCK2CD4Cre vs. control mice.

CONCLUSION

ROCK2 contributes to allergic airways responses likely via effects within ASM cells and within non-lymphocyte cells involved in lymphocyte activation and migration into the airways.

The RacGAP protein FilGAP is a negative regulator of chemokine-promoted lymphocyte migration

Rho family small GTPases regulate lymphocyte migration induced by chemokines. However, how lymphocyte migration is regulated by Rho GTPases remains to be elucidated. Here, we identified FilGAP, a Rac-specific GAP, as a negative regulator of lymphocyte polarization and migration. Depletion of FilGAP in mouse pro-B BAF cells increased cellular elongation and membrane protrusion after stimulation of the cells with SDF-1α, which caused increased migration speed. Although FilGAP is detectable both at the front and rear of polarized cells, FilGAP appears to be concentrated at the tip of retracting lamellae of moving lymphocytes. Moreover, depletion of FilGAP increased activation of Rac at the front of polarized cells. Thus, FilGAP may inhibit lamellae extension at the front of moving lymphocytes.

Common and biased signaling pathways of the chemokine receptor CCR7 elicited by its ligands CCL19 and CCL21 in leukocytes

Chemokines are pivotal regulators of cell migration during continuous immune surveillance, inflammation, homeostasis, and development. Chemokine binding to their 7-transmembrane domain, G-protein-coupled receptors causes conformational changes that elicit intracellular signaling pathways to acquire and maintain an asymmetric architectural organization and a polarized distribution of signaling molecules necessary for directional cell migration. Leukocytes rely on the interplay of chemokine-triggered migration modules to promote amoeboid-like locomotion. One of the most important chemokine receptors for adaptive immune cell migration is the CC-chemokine receptor CCR7. CCR7 and its ligands CCL19 and CCL21 control homing of T cells and dendritic cells to areas of the lymph nodes where T cell priming and the initiation of the adaptive immune response occur. Moreover, CCR7 signaling also contributes to T cell development in the thymus and to lymphorganogenesis. Although the CCR7-CCL19/CCL21 axis evolved to benefit the host, inappropriate regulation or use of these proteins can contribute or cause pathobiology of chronic inflammation, tumorigenesis, and metastasis, as well as autoimmune diseases. Therefore, it appears as the CCR7-CCL19/CCL21 axis is tightly regulated at numerous intersections. Here, we discuss the multiple regulatory mechanism of CCR7 signaling and its influence on CCR7 function. In particular, we focus on the functional diversity of the 2 CCR7 ligands, CCL19 and CCL21, as well as on their impact on biased signaling. The understanding of the molecular determinants of biased signaling and the multiple layers of CCR7 regulation holds the promise for potential future therapeutic intervention.

T Lymphocyte Migration: An Action Movie Starring the Actin and Associated Actors

The actin cytoskeleton is composed of a dynamic filament meshwork that builds the architecture of the cell to sustain its fundamental properties. This physical structure is characterized by a continuous remodeling, which allows cells to accomplish complex motility steps such as directed migration, crossing of biological barriers, and interaction with other cells. T lymphocytes excel in these motility steps to ensure their immune surveillance duties. In particular, actin cytoskeleton remodeling is a key to facilitate the journey of T lymphocytes through distinct tissue environments and to tune their stop and go behavior during the scanning of antigen-presenting cells. The molecular mechanisms controlling actin cytoskeleton remodeling during T lymphocyte motility have been only partially unraveled, since the function of many actin regulators has not yet been assessed in these cells. Our review aims to integrate the current knowledge into a comprehensive picture of how the actin cytoskeleton drives T lymphocyte migration. We will present the molecular actors that control actin cytoskeleton remodeling, as well as their role in the different T lymphocyte motile steps. We will also highlight which challenges remain to be addressed experimentally and which approaches appear promising to tackle them.

Chemokine receptor 7 promotes tumor migration and invasiveness via the RhoA/ROCK pathway in metastatic squamous cell carcinoma of the head and neck

Metastatic squamous cell carcinoma of the head and neck (SCCHN) has been shown to express chemokine receptor 7 (CCR7), which can activate signaling pathways to promote invasion and survival of SCCHN cells. We hypothesized that the RhoA/Rho-associated kinase (ROCK) pathway is involved in the CCR7-induced invasion and migration of metastatic SCCHN cells. Thus, using migration, matrigel invasion and scrape wound-healing assays, we elucidated the role of RhoA in mediating CCR7-associated cellular mobility. Pull-down assays and western blotting were used to measure RhoA and its downstream expression. Immunohistochemical staining and analysis were useful in identifying the correlation between CCR7 and RhoA expression and clinicopathological factors. The results showed that inhibition of RhoA/ROCK reduced the tumor cell migration and invasiveness induced by CCL19. Activated RhoA, proline-rich tyrosine kinase-2 (Pyk2) and cofilin induced by CCL19 were elevated, and increased RhoA, Pyk2 and cofilin activity was eliminated by CCR7mAb, RhoA/ROCK and Pyk2 inhibitors, indicating involvement of the RhoA/ROCK-Pyk2-cofilin cascade. In summary, CCR7 via RhoA/ROCK-Pyk2 cofilin pathway promotes invasion and migration of metastatic SCCHN cells.

Treatment with a rho kinase inhibitor improves survival from graft-versus-host disease in mice after MHC-haploidentical hematopoietic cell transplantation

Acute graft-versus-host disease (GVHD) is a major complication of allogeneic hematopoietic cell transplantation (HCT) and the main cause of nonrelapse mortality during the first 100 days post-transplant. Although GVHD can be prevented by extensive removal of mature donor T cells from the donor hematopoietic stem cell population, doing so eliminates any potential allogeneic graft-versus-tumor (GVT) effect also mediated by donor T cells and results in unacceptable rates of cancer relapse. One potential solution to this problem of separating GVHD development from a GVT response is to prevent T cell-mediated GVHD in the intestinal tract (IT) while preserving systemic antihost alloreactivity of donor T cells that target residual tumor cells expressing host alloantigens. We examined the ability of the anti-inflammatory rho kinase inhibitor, fasudil, given orally and intraperitoneally, to prevent GVHD in a C3H → B6C3F1 mouse model of MHC-haploidentical bone marrow transplantation. Fasudil-treated recipients of anti-thy-1 mAb + C' treated bone marrow (ATBM) cells plus T cells had a 73% 90-day survival compared with 25% among untreated ATBM + T cell recipients (P < .0001). Severe initial weight loss was similar in the 2 groups, but less diarrhea was observed among treated animals, and fasudil-treated survivors recovered more weight than untreated survivors. Skin inflammation occurred and resolved between weeks 2 and 8 with similar severity and kinetics in both treated and untreated surviving animals, indicating persistent alloreactivity. Day 10 post-transplantation splenocytes from fasudil-treated mice, containing mature donor T cells, and day 98 splenocytes, containing mature donor and de novo thymus-derived T cells, exhibited alloreactivity against host parental antigens, as assessed by in vitro IFN-γ production and rounds of allostimulated proliferation, respectively. These data support the idea that targeted treatment of the IT with rho kinase inhibitors can ameliorate lethal GVHD while preserving systemic alloreactivity. The results also suggest that similar mechanisms of IT-specific tolerance or resistance to GVHD operate in fasudil-treated and untreated long-term survivors of allogeneic ATBM + T cells.

The prognostic values of leukocyte Rho kinase activity in acute ischemic stroke

Objective. It has been reported that leukocyte ROCK activity is elevated in patients after ischemic stroke, but it is unclear whether leukocyte ROCK activity is associated with clinical outcomes following acute stroke events. The objective of this study is to investigate if leukocyte ROCK activity can predict the outcomes in patients with acute ischemic stroke. Materials and Methods. We enrolled 110 patients of acute ischemic stroke and measured the leukocyte ROCK activity and plasma level of inflammatory cytokines to correlate the clinical outcomes of these patients. Results. The leukocyte ROCK activity at 48 hours after admission in acute ischemic stroke patients was higher as compared to a risk-matched population. The leukocyte ROCK activity significantly correlated with National Institute of Health Stroke Scale (NIHSS) difference between admission and 90 days after stroke event. Kaplan-Meier survival estimates showed lower stroke-free survival during follow-up period in patients with high leukocyte ROCK activity or plasma hsCRP level. Leukocyte ROCK activity independently predicted the recurrent stroke in patients with atherosclerotic stroke. Conclusions. This study shows elevated leukocyte ROCK activity in patients with ischemic stroke as compared to risk-matched subjects and is an independent predictor for recurrent stroke.

Jak3 enables chemokine-dependent actin cytoskeleton reorganization by regulating cofilin and Rac/Rhoa GTPases activation

We have previously shown that Jak3 is involved in the signaling pathways of CCR7, CCR9 and CXCR4 in murine T lymphocytes and that Jak3^−/− lymphocytes display an intrinsic defect in homing to peripheral lymph nodes. However, the molecular mechanism underlying the defective migration observed in Jak3^−/− lymphocytes remains elusive. Here, it is demonstrated for the first time, that Jak3 is required for the actin cytoskeleton reorganization in T lymphocytes responding to chemokines. It was found that Jak3 regulates actin polymerization by controlling cofilin inactivation in response to CCL21 and CXCL12. Interestingly, cofilin inactivation was not precluded in PTX- treated cells despite their impaired actin polymerization. Additionally, Jak3 was required for small GTPases Rac1 and RhoA activation, which are indispensable for acquisition of the migratory cell phenotype and the generation of a functional leading edge and uropod, respectively. This defect correlates with data obtained by time-lapse video-microscopy showing an incompetent uropod formation and impaired motility in Jak3-pharmacologically inhibited T lymphocytes. Our data support a new model in which Jak3 and heterotrimeric G proteins can use independent, but complementary, signaling pathways to regulate actin cytoskeleton dynamics during cell migration in response to chemokines.

Insights into the mechanism for dictating polarity in migrating T-cells

This review is focused on mechanisms of chemokine-induced polarization of T-lymphocytes. Polarization involves, starting from spherical cells, formation of a morphologically and functionally different rear (uropod) and front (leading edge). This polarization is required for efficient random and directed T-cell migration. The addressed topics concern the specific location of cell organelles and of receptors, signaling molecules, and cytoskeletal proteins in chemokine-stimulated polarized T-cells. In chemokine-stimulated, polarized T-cells, specific proteins, signaling molecules and organelles show enrichment either in the rear, the midzone, or the front; different from the random location in spherical resting cells. Possible mechanisms involved in this asymmetric location will be discussed. A major topic is also the functional role of proteins and cell organelles in T-cell polarization and migration. Specifically, the roles of adhesion and chemokine receptors, cytoskeletal proteins, signaling molecules, scaffolding proteins, and membrane microdomains in these processes will be discussed. The polarity which is established during contact formation of T-cells with antigen-presenting cells is not discussed in detail.

Molecular mechanisms deployed by virally encoded G protein-coupled receptors in human diseases

G protein-coupled receptors (GPCRs) represent the largest family of cell surface molecules involved in signal transduction. Surprisingly, open reading frames for multiple GPCRs were hijacked in the process of coevolution between Herpesviridae family viruses and their human and mammalian hosts. Virally encoded GPCRs (vGPCRs) evolved as parts of viral genomes, and this evolution allowed the power of host GPCR signaling circuitries to be harnessed in order to ensure viral replicative success. Phylogenetically, vGPCRs are distantly related to human chemokine receptors, although they feature several unique characteristics. Here, we describe the molecular mechanisms underlying vGPCR-mediated viral pathogenesis. These mechanisms include constitutive activity, aberrant coupling to human G proteins and β-arrestins, binding and activation by human chemokines, and dimerization with other GPCRs expressed in infected cells. The likely structural basis for these molecular events is described for the two closest viral homologs of human GPCRs. This information may aid in the development of novel targeted therapeutic strategies against viral diseases.

Actin depolymerization-based force retracts the cell rear in polarizing and migrating cells

In migrating cells, the relative importance of myosin II contractility for cell rear retraction varies [1-12]. However, in myosin II-inhibited polarizing cells, actin organization is compromised [13-18]; thus it remains unclear whether myosin II is simply required for correct actin arrangement or also directly drives rear retraction [9]. Ascaris sperm cells lack actin and associated motors, and depolymerization of major sperm protein is instead thought to pull the cell rear forward [19, 20]. Opposing views exist on whether actin could also have this function [19, 20] and has not been directly experimentally sought. We probe function at high temporal resolution in polarizing fibroblasts that establish migration by forming the cell rear first [9, 15, 21]. We show that in cells with correctly organized actin, that actin filament depolymerization directly drives retraction of the rear margin to polarize cells and spatially accounts for most cell rear retraction during established migration. Myosin II contractility is required early, to form aligned actin bundles that are needed for polarization, and also later to maintain bundle length that ensures directed protrusion at the cell front. Our data imply a new mechanism: actin depolymerization-based force retracts the cell rear to polarize cells with no direct contribution from myosin II contractility.

In vivo analysis of uropod function during physiological T cell trafficking

Migrating lymphocytes acquire a polarized phenotype with a leading and a trailing edge, or uropod. Although in vitro experiments in cell lines or activated primary cell cultures have established that Rho-p160 coiled-coil kinase (ROCK)-myosin II-mediated uropod contractility is required for integrin de-adhesion on two-dimensional surfaces and nuclear propulsion through narrow pores in three-dimensional matrices, less is known about the role of these two events during the recirculation of primary, nonactivated lymphocytes. Using pharmacological antagonists of ROCK and myosin II, we report that inhibition of uropod contractility blocked integrin-independent mouse T cell migration through narrow, but not large, pores in vitro. T cell crawling on chemokine-coated endothelial cells under shear was severely impaired by ROCK inhibition, whereas transendothelial migration was only reduced through endothelial cells with high, but not low, barrier properties. Using three-dimensional thick-tissue imaging and dynamic two-photon microscopy of T cell motility in lymphoid tissue, we demonstrated a significant role for uropod contractility in intraluminal crawling and transendothelial migration through lymph node, but not bone marrow, endothelial cells. Finally, we demonstrated that ICAM-1, but not anatomical constraints or integrin-independent interactions, reduced parenchymal motility of inhibitor-treated T cells within the dense lymphoid microenvironment, thus assigning context-dependent roles for uropod contraction during lymphocyte recirculation.

Dynamic reorganization of flotillins in chemokine-stimulated human T-lymphocytes

Background

Different types of membrane microdomains (rafts) have been postulated to be present in the rear and front of polarized migrating T-lymphocytes. Disruption of rafts by cholesterol sequestration prevents T-cell polarization and migration. Reggie/flotillin-1 and -2 are two highly homologous proteins that are thought to shape membrane microdomains. We have previously demonstrated the enrichment of flotillins in the uropod of human neutrophils. We have now investigated mechanisms involved in chemokine-induced flotillin reorganization in human T-lymphocytes, and possible roles of flotillins in lymphocyte polarization.

Results

We studied flotillin reorganization and lateral mobility at the plasma membrane using immunofluorescence staining and FRAP (fluorescence recovery after photobleaching). We show that flotillins redistribute early upon chemokine stimulation, and form very stable caps in the uropods of human peripheral blood T-lymphocytes, colocalizing with the adhesion molecule PSGL-1 and activated ezrin/radixin/moesin (ERM) proteins. Chemokine-induced formation of stable flotillin caps requires integrity and dynamics of the actin cytoskeleton, but is not abolished by inhibitors suppressing Rho-kinase or myosin II activity. Tagged flotillin-2 and flotillin-1 coexpressed in T-lymphocytes, but not singly expressed proteins, colocalize in stable caps at the tips of uropods. Lateral mobility of coexpressed flotillins at the plasma membrane is already partially restricted in the absence of chemokine. Incubation with chemokine results in almost complete immobilization of flotillins. Capping is abolished when wild-type flotillin-1 is coexpressed with a mutant of flotillin-2 (G2A) that is unable to interact with the plasma membrane, or with a deletion mutant of flotillin-2 that lacks a putative actin-binding domain. Wild-type flotillin-2 in contrast forms caps when coexpressed with a mutant of flotillin-1 unable to interact with membranes. Transfection of T-lymphocytes with flotillin-2-G2A reduces cell polarization and uropod recruitment of endogenous flotillin-1 and PSGL-1.

Conclusions

Our data suggest that stable flotillin cap formation in the rear of polarized T-lymphocytes requires flotillin heterooligomer formation, as well as direct F-actin interactions of flotillin-2 and raft/membrane association of flotillin-2, but not -1. Our data also implicate flotillin-rich actin-dependent membrane microdomains in T-lymphocyte uropod formation.

Mechanisms of force generation and force transmission during interstitial leukocyte migration

For innate and adaptive immune responses it is essential that inflammatory cells use quick and flexible locomotion strategies. Accordingly, most leukocytes can efficiently infiltrate and traverse almost every physiological or artificial environment. Here, we review how leukocytes might achieve this task mechanistically, and summarize recent findings on the principles of cytoskeletal force generation and transduction at the leading edge of leukocytes. We propose a model in which the cells switch between adhesion-receptor-mediated force transmission and locomotion modes that are based on cellular deformations, but independent of adhesion receptors. This plasticity in migration strategies allows leukocytes to adapt to the geometry and molecular composition of their environment.

Two-photon microscopy analysis of leukocyte trafficking and motility

During the last several years, live tissue imaging, in particular using two-photon laser microscopy, has advanced our understanding of leukocyte trafficking mechanisms. Studies using this technique are revealing distinct molecular requirements for leukocyte migration in different tissue environments. Also emerging from the studies are the ingenious infrastructures for leukocyte trafficking, which are produced by stromal cells. This review summarizes the recent imaging studies that provided novel mechanistic insights into in vivo leukocyte migration essential for immunosurveillance.

In vivo imaging and quantitative analysis of leukocyte directional migration and polarization in inflamed tissue

Directional migration of transmigrated leukocytes to the site of injury is a central event in the inflammatory response. Here, we present an in vivo chemotaxis assay enabling the visualization and quantitative analysis of subtype-specific directional motility and polarization of leukocytes in their natural 3D microenvironment. Our technique comprises the combination of i) semi-automated in situ microinjection of chemoattractants or bacteria as local chemotactic stimulus, ii) in vivo near-infrared reflected-light oblique transillumination (RLOT) microscopy for the visualization of leukocyte motility and morphology, and iii) in vivo fluorescence microscopy for the visualization of different leukocyte subpopulations or fluorescence-labeled bacteria. Leukocyte motility parameters are quantified off-line in digitized video sequences using computer-assisted single cell tracking. Here, we show that perivenular microinjection of chemoattractants [macrophage inflammatory protein-1alpha (MIP-1alpha/Ccl3), platelet-activating factor (PAF)] or E. coli into the murine cremaster muscle induces target-oriented intravascular adhesion and transmigration as well as polarization and directional interstitial migration of leukocytes towards the locally administered stimuli. Moreover, we describe a crucial role of Rho kinase for the regulation of directional motility and polarization of transmigrated leukocytes in vivo. Finally, combining in vivo RLOT and fluorescence microscopy in Cx3CR1(gfp/gfp) mice (mice exhibiting green fluorescent protein-labeled monocytes), we are able to demonstrate differences in the migratory behavior of monocytes and neutrophils.Taken together, we propose a novel approach for investigating the mechanisms and spatiotemporal dynamics of subtype-specific motility and polarization of leukocytes during their directional interstitial migration in vivo.

Rho kinase as a therapeutic target in the treatment of asthma and chronic obstructive pulmonary disease

Asthma is a complex inflammatory disease of the airways involving reversible bronchoconstriction. Chronic obstructive pulmonary disease is typified by inflammation and airflow limitation that has an irreversible component. There is now substantial evidence that Rho kinase is involved in many of the pathways that contribute to the pathologies associated with these respiratory diseases including bronchoconstriction, airway inflammation, airway remodelling, neuromodulation and exacerbations due to respiratory tract viral infection. Indeed the Rho kinase inhibitor Y-27632 causes bronchodilatation and reduces pulmonary eosinophilia trafficking and airways hyperresponsiveness. Furthermore, accumulating evidence suggests that inhibition of Rho kinase could have a major beneficial impact on symptoms and disease progression in asthma and COPD by modulating several other systems and processes. Thus, the Rho kinase pathway may indeed be a worthwhile therapeutic target in the treatment of asthma and chronic obstructive pulmonary disease.

Chemoattract receptor signaling and its role in lymphocyte motility and trafficking

Intravital microscopy has provided extraordinary glimpses of lymphocytes crossing high endothelial venules, detailed the movements and interactions of lymphocytes within lymph organs, and recorded lymphocytes crossing the lymphatic endothelium into the efferent lymph. Helping to orchestrate these movements are signals generated by the engagement of chemoattractants with their cognate receptors. Chemokines present on high endothelial venules and within lymph organs, and the high levels of sphingosine l-phosphate in the lymph, provide signposts to help guide lymphocytes and provide intracellular signals that affect lymphocyte polarity and motility. Within lymph nodes, T and B lymphocytes migrate along networks of fibroblastic reticular cells and follicular dendritic, respectively, which provide an adhesive platform and solid phased chemokines. Illustrating the importance of chemoattractant receptors in these processes, lymphocytes that lack CXCR4, CXCR5, CCR7 or S1PR1, or which lack crucial signaling molecules activated by these receptors, exhibit defects in lymph node entrance, positioning, polarity, motility, and/or lymph node egress. This review will focus on the contributions of in vivo imaging of lymphocytes from various mouse mutants to our understanding of the roles chemoattractants play in lymphocyte entrance into and exit from lymph nodes, and in coordinating and facilitating the movements of lymphocytes within lymph nodes.

How chemokines invite leukocytes to dance

A prominent activity of the chemokine system is the regulation of leukocyte trafficking. Here we summarize recent findings on the initial steps in chemokine receptor-induced signal transduction in leukocytes. In particular, we discuss the potential influences of the formation of oligomers of ligand and receptor and of coupling between chemokine signals and regulators of the cytoskeleton, such as small GTPases.

The actin cytoskeleton in T cell activation

T cell cytoarchitecture differs dramatically depending on whether the cell is circulating within the bloodstream, migrating through tissues, or interacting with antigen-presenting cells. The transition between these states requires important signaling-dependent changes in actin cytoskeletal dynamics. Recently, analysis of actin-regulatory proteins associated with T cell activation has provided new insights into how T cells control actin dynamics in response to external stimuli and how actin facilitates downstream signaling events and effector functions. Among the actin-regulatory proteins that have been identified are nucleation-promoting factors such as WASp, WAVE2, and HS1; severing proteins such as cofilin; motor proteins such as myosin II; and linker proteins such as ezrin and moesin. We review the current literature on how signaling pathways leading from diverse cell surface receptors regulate the coordinated activity of these and other actin-regulatory proteins and how these proteins control T cell function.

Therapeutic potential of RhoA/Rho kinase inhibitors in pulmonary hypertension

A burgeoning body of evidence suggests that RhoA/Rho kinase (ROCK) signalling plays an important role in the pathogenesis of various experimental models of pulmonary hypertension (PH), including chronic hypoxia-, monocrotaline-, bleomycin-, shunt- and vascular endothelial growth factor receptor inhibition plus chronic hypoxia-induced PH. ROCK has been incriminated in pathophysiologic events ranging from mediation of sustained abnormal vasoconstriction to promotion of vascular inflammation and remodelling. In addition, the 3-hydroxy-3-methylglutaryl CoA reductase inhibitors, statins, which inhibit activation of RhoA by preventing post-translational isoprenylation of the protein and its translocation to the plasma membrane ameliorate PH in several different rat models, and may also be effective in PH patients. Also, phosphorylation of RhoA and prevention of its translocation to the plasma membrane are involved in the protective effect of the type 5-PDE inhibitor, sildenafil, against hypoxia- and bleomycin-induced PH. Collectively, these and other observations indicate that independent of the cause of PH, activation of the RhoA/ROCK pathway serves as a point of convergence of various signalling cascades in the pathogenesis of the disease. We propose that ROCK inhibitors and other drugs that inhibit this pathway might be useful in the treatment of various forms of PH.

The inhaled Rho kinase inhibitor Y-27632 protects against allergen-induced acute bronchoconstriction, airway hyperresponsiveness, and inflammation

Recently, we have shown that allergen-induced airway hyperresponsiveness (AHR) after the early (EAR) and late (LAR) asthmatic reaction in guinea pigs could be reversed acutely by inhalation of the Rho kinase inhibitor Y-27632. The present study addresses the effects of pretreatment with inhaled Y-27632 on the severity of the allergen-induced EAR and LAR, the development of AHR after these reactions, and airway inflammation. Using permanently instrumented and unrestrained ovalbumin (OA)-sensitized guinea pigs, single OA challenge-induced EAR and LAR, expressed as area under the lung function (pleural pressure, P(pl)) time-response curve, were measured, and histamine PC(100) (provocation concentration causing a 100% increase of P(pl)) values were assessed 24 h before, and at 6 and 24 h after, the OA challenge (after the EAR and LAR, respectively). Thirty minutes before and 8 h after OA challenge, saline or Y-27632 (5 mM) was nebulized. After the last PC(100) value, bronchoalveolar lavage (BAL) was performed, and the inflammatory cell profile was determined. It was demonstrated that inhalation of Y-27632 before allergen challenge markedly reduced the immediate allergen-induced peak rise in P(pl), without significantly reducing the overall EAR and LAR. Also, pretreatment with Y-27632 considerably protected against the development of AHR after the EAR and fully prevented AHR after the LAR. These effects could not be explained by a direct effect of Y-27632 on the histamine responsiveness, because of the short duration of the acute bronchoprotection of Y-27632 (<90 min). In addition, Y-27632 reduced the number of total inflammatory cells, eosinophils, macrophages, and neutrophils recovered from the BAL. Altogether, inhaled Y-27632 protects against acute allergen-induced bronchoconstriction, development of AHR after the EAR and LAR, and airway inflammation in an established guinea pig model of allergic asthma.

T cell activation and the cytoskeleton: you can't have one without the other

More than a quarter of a century has passed since the observation that T cells rapidly polarize their actin and microtubule cytoskeletal systems toward antigen-presenting cells during activation. Since this initial discovery, several receptors on T cells (e.g., T cell receptor [TCR], co-receptors, integrins, and chemokine receptors) have been identified to regulate these two cytoskeletal networks through complex signaling pathways, which are still being elucidated. There is now an undeniable body of biochemical, pharmacological, and genetic evidence indicating that regulators of actin and microtubule dynamics are crucial for T cell activation and effector functions. In fact, the actin cytoskeleton participates in the initial clustering of TCR-major histocompatibility complex or peptide complexes, formation and stabilization of the immune synapse, integrin-mediated adhesion, and receptor sequestration, whereas both the actin and microtubule cytoskeletons regulate the establishment of cell polarity, cell migration, and directed secretion of cytokines and cytolytic granules. Over the past several years, we have begun to more thoroughly understand the contributions of specific actin-regulatory and actin-nucleating proteins that govern these processes. Herein, we discuss our current understanding of how activating receptors on T lymphocytes regulate the actin and microtubule cytoskeletons, and how in turn, these distinct but integrated cytoskeletal networks coordinate T cell immune responses.

Age-related defects in moesin/ezrin cytoskeletal signals in mouse CD4 T cells

Cytoskeletal proteins of the ezrin-radixin-moesin (ERM) family contribute to T cell activation in response to Ag, and also to T cell polarization in response to connective tissue matrix proteins and chemokine gradients. Previous work has shown that T cells from aged mice are defective in their ability to develop molecular linkages between surface macromolecules and the underlying cytoskeletal framework, both for proteins that move to the synapse and those that are excluded from the site of T cell-APC interaction. T cells from aged mice also show defective cytoskeletal rearrangements and lamellipodia formation when placed in contact with slides coated with Abs to the TCR/CD3 complex. In this study, we show that old CD4 T cells differ from young CD4 T cells in several aspects of ERM biochemistry, including ERM phosphorylation and ERM associations with CD44, CD43, and EBP50. In addition, CD4 T cells from aged mice show defects in the Rho GTPase activities known to control ERM function.

Rho kinase as potential therapeutic target for cardiovascular diseases: opportunities and challenges

Rho kinase (ROCK) belongs to a family of Ser/Thr protein kinases that are activated via interaction with the small GTP-binding protein RhoA. Growing evidence suggests that RhoA and ROCK participate in a variety of important physiological functions in vasculature including smooth muscle contraction, cell proliferation, cell adhesion and migration, and many aspects of inflammatory responses. As these processes mediate the onset and progression of cardiovascular disease, modulation of the Rho/ROCK signalling pathway is a potential strategy for targeting an array of cardiovascular indications. Two widely employed ROCK inhibitors, fasudil and Y-27632, have provided preliminary but compelling evidence supporting the potential cardiovascular benefits of ROCK inhibition in preclinical animal disease models and in the clinic. This review summarises the molecular biology of ROCK and its biological functions in smooth muscle, endothelium and other vascular tissues. In addition, there will be a focus on recent progress demonstrating the benefits of ROCK inhibition in several animal models of cardiovascular diseases. Finally, recent progress in the identification of novel ROCK inhibitors and challenges associated with their development for clinical use will be discussed.

The selective Rho-kinase inhibitor Fasudil is protective and therapeutic in experimental autoimmune encephalomyelitis

We studied the role of fasudil, a selective Rho-kinase inhibitor, in experimental autoimmune encephalomyelitis (EAE). Both parenteral and oral administration of fasudil prevented the development of EAE induced by proteolipid protein (PLP) p139-151 in SJL/J mice. Specific proliferation of lymphocytes to PLP was significantly reduced, together with a downregulation of interleukin (IL)-17 and a marked decrease of the IFN-gamma/IL-4 ratio. Immunohistochemical examination also disclosed a marked decrease of inflammatory cell infiltration, and attenuated demyelination and acute axonal transaction. These results may provide a rationale of selective blockade of Rho-kinase by oral use of fasudil as a new therapy for multiple sclerosis.

Opposite fate of endocytosed CCR7 and its ligands: recycling versus degradation

The chemokine receptor CCR7 and its ligands CCL19 and CCL21 play a crucial role for the homing of lymphocytes and dendritic cells to secondary lymphoid tissues. Nevertheless, how CCR7 senses the gradient of chemokines and how migration is terminated are poorly understood. In this study, we demonstrate that CCR7(-GFP) is endocytosed into early endosomes containing transferrin receptor upon CCL19 binding, but less upon CCL21 triggering. Internalization of CCR7 was independent of lipid rafts but relied on dynamin and Eps15 and was inhibited by hypertonic sucrose, suggesting clathrin-dependent endocytosis. After chemokine removal, internalized CCR7 recycled back to the plasma membrane and was able to mediate migration again. In contrast, internalized CCL19 was sorted to lysosomes for degradation, showing opposite fate for endocytosed CCR7 and its ligand.

Chemoattractant receptor signaling and the control of lymphocyte migration

This review focuses on mechanisms by which chemoattractant receptors activate downstream signaling pathways in lymphocytes. An emphasis is placed on heterotrimeric G protein signaling with a discussion of the specific heterotrimeric G-proteins involved in lymphocyte chemotaxis and motility and the role of regulator of G protein signaling (RGS) proteins in controlling the activation of downstream effectors. Also considered are those direct downstream effectors known to function in lymphocyte chemotaxis and/or motility. The consequences of targeting genes suspected, known, or serendipitously found to be involved in chemokine receptor signaling pathways form much of a basis for the review. When needed for clarification, reference to studies of chemoattractant signaling in model organisms and in neutrophils will be compared and contrasted to studies in lymphocytes. Finally, the emergence of tools to image lymphocyte in vitro and in vivo will be mentioned as they are increasing helpful for the analysis of lymphocyte trafficking and amendable to the study of chemokine receptor signaling.

Chemokines CCL19 and CCL21 promote activation-induced cell death of antigen-responding T cells

Secondary lymphoid organs (SLOs) provide a niche for the initiation and regulation of T-cell responses, but the mechanisms have been poorly understood. We investigated the influence of chemokines CCL19 and CCL21 constitutively expressed in SLOs on activation-induced cell death (AICD) of CD4+ T cells. When paucity of lymph node T cells (plt) mutant mice lacking expression of CCL19/CCL21 were primed with OVA/CFA, both expansion of OVA-responding CD4+ T cells in the draining lymph nodes and an in vitro recall response were prolonged as compared with responses in wild-type (WT) mice. The apoptotic cell frequency among OVA-responding CD4+ T cells was similarly low in plt/plt and WT mice during the clonal expansion phase. However, during the clonal contraction phase, the frequency never increased in plt/plt mice, whereas in WT mice it continuously increased to a peak 18 days after immunization. The presence of CCL19/CCL21 during the in vitro stimulation of CD4+ T cells with anti-CD3 plus anti-CD28 significantly enhanced in vitro AICD induction of the restimulated T cells, partially through enhancing expression of Fas ligand. Our results suggest that CCL19/CCL21 produced by stromal cells and antigen-presenting cells regulate CD4+ T-cell immune responses in SLOs by promoting AICD.

The Multiple Personalities of the Chemokine Receptor CCR7 in Dendritic Cells

CCR7 was described initially as a potent leukocyte chemotactic receptor that was later shown to be responsible of directing the migration of dendritic cells (DCs) to the lymph nodes where these cells play an important role in the initiation of the immune response. Recently, a variety of reports have indicated that, apart from chemotaxis, CCR7 controls the cytoarchitecture, the rate of endocytosis, the survival, the migratory speed, and the maturation of the DCs. Some of these functions of CCR7 and additional ones also have been described in other cell types. Herein we discuss how this receptor may contribute to modulate the immune response by regulating different functions in DCs. Finally, we also suggest a possible mechanism whereby CCR7 may control its multiple tasks in these cells.