CX3CR1 promotes recruitment of human glioma-infiltrating microglia/macrophages (GIMs)

The transmembrane chemokine CX3CL1 and its receptor CX3CR1 are thought to be involved in the trafficking of immune cells during an immune response and in the pathology of various human diseases including cancer. However, little is known about the expression and function of CX3CR1 in human glioma-infiltrating microglia/macrophages (GIMs), representing the major cellular stroma component of highly malignant gliomas. Here, we show that CX3CR1 is overexpressed at both the mRNA and protein level in solid human astrocytomas of different malignancy grades and in glioblastomas. CX3CR1 was localized in ionized calcium-binding adapter molecule 1 (Iba1) and CD11b/c positive GIMs in situ as shown by fluorescence microscopy. In accordance with this, freshly isolated human GIM-enriched fractions separated by CD11b MACS technology displayed high Iba1 and CX3CR1 mRNA expression levels in vitro. Moreover, cultured human GIMs responded to CX3CL1-triggered activation of CX3CR1 with adhesion and migration in vitro. Besides an increase in motility, CX3CL1 also enhanced expression of matrix metalloproteases 2, 9, and 14 in GIM fractions in vitro. These data indicate that the CX3CL1/CX3CR1 system has a crucial tumor-promoting role in human glioblastomas via its impact on glioma-infiltrating immune subsets.     

Spinal CX3CL1/CX3CR1 May Not Directly Participate in the Development of Morphine Tolerance in Rats

CX3CL1 (fractalkine), the sole member of chemokine CX3C family, is implicated in inflammatory and neuropathic pain via activating its receptor CX3CR1 on neural cells in spinal cord. However, it has not been fully elucidated whether CX3CL1 or CX3CR1 contributes to the development of morphine tolerance. In this study, we found that chronic morphine exposure did not alter the expressions of CX3CL1 and CX3CR1 in spinal cord. And neither exogenous CX3CL1 nor CX3CR1 inhibitor could affect the development of morphine tolerance. The cellular localizations of spinal CX3CL1 and CX3CR1 changed from neuron and microglia, respectively, to all the neural cells during the development of morphine tolerance. A microarray profiling revealed that 15 members of chemokine family excluding CX3CL1 and CX3CR1 were up-regulated in morphine-treated rats. Our study provides evidence that spinal CX3CL1 and CX3CR1 may not be involved in the development of morphine tolerance directly.

     

CX3CL1/CX3CR1 and CCL2/CCR2 Chemokine/Chemokine Receptor Complex in Patients with AMD

Purpose

The chemokine receptors CX3CR1 and CCR2 have been implicated in the development of age-related macular degeneration (AMD). The evidence is mainly derived from experimental cell studies and murine models of AMD. The purpose of this study was to investigate the association between expression of CX3CR1 and CCR2 on different leukocyte subsets and AMD. Furthermore we measured the plasma levels of ligands CX3CL1 and CCL2.

Methods

Patients attending our department were asked to participate in the study. The diagnosis of AMD was based on clinical examination and multimodal imaging techniques. Chemokine plasma level and chemokine receptor expression were measured by flow-cytometry.

Results

A total of 150 participants were included. We found a significantly lower expression of CX3CR1 on CD8⁺ T cells in the neovascular AMD group compared to the control group (p = 0.04). We found a significant positive correlation between CCR2 and CX3CR1 expression on CD8⁺ cells (r = 0.727, p = 0.0001). We found no difference in plasma levels of CX3CL1 and CCL2 among the groups.

Conclusions

Our results show a down regulation of CX3CR1 on CD8⁺ cells; this correlated to a low expression of CCR2 on CD8⁺ cells. Further studies are needed to elucidate the possible role of this cell type in AMD development.     

Eotaxin-3/CC chemokine ligand 26 is a functional ligand for CX3CR1

Eotaxin-3/CCL26 is a functional ligand for CCR3 and abundantly produced by IL-4-/IL-13-stimulated vascular endothelial cells. CCL26 also functions as a natural antagonist for CCR1, CCR2, and CCR5. In this study, we report that CCL26 is yet a functional ligand for CX3CR1, the receptor for fractalkine/CX3CL1, which is expressed by CD16(+) NK cells, cytotoxic effector CD8(+) T cells, and CD14(low)CD16(high) monocytes. Albeit at relatively high concentrations, CCL26 induced calcium flux and chemotaxis in mouse L1.2 cells expressing human CX3CR1 but not mouse CX3CR1 and competed with CX3CL1 for binding to CX3CR1. In chemotaxis assays using human PBMCs, CCL26 attracted not only eosinophils but also CD16(+) NK cells, CD45RA(+)CD27(-)CD8(+) T cells, and CD14(low)CD16(high) monocytes. Intraperitoneal injection of CCL26 into mice rapidly recruited mouse eosinophils and intravenously transferred human CD16(+) NK cells into the peritoneal cavity. IL-4-stimulated HUVECs produced CCL26 and efficiently induced adhesion of cells expressing CX3CR1. Real-time PCR showed that skin lesions of psoriasis consistently contained CX3CL1 mRNA but not CCL26 mRNA, whereas those of atopic dermatitis contained CCL26 mRNA in all samples but CX3CL1 mRNA in only about half of the samples. Nevertheless, the skin lesions from both diseases consistently contained CX3CR1 mRNA at high levels. Thus, CCL26 may be partly responsible for the recruitment of cells expressing CX3CR1 in atopic dermatitis particularly when the expression of CX3CL1 is low. Collectively, CCL26 is another agonist for CX3CR1 and may play a dual role in allergic diseases by attracting eosinophils via CCR3 and killer lymphocytes and resident monocytes via CX3CR1.     

IL-15 alters expression and function of the chemokine receptor CX3CR1 in human NK cells

The chemokine receptor CX3CR1 is thought to regulate inflammation in part by modulating NK cell adhesion, migration, and killing in response to its ligand CX3CL1 (fractalkine). Recent reports indicate that IL-15, which is essential for development and survival of NK cells, may negatively regulate CX3CR1 expression, however, the effects of the cytokine on human NK cell CX3CR1 expression and function have not been fully delineated. Here, we demonstrate that short term culture in IL-15 decreases surface expression of CX3CR1 on cultured CD56+ cells from human blood resulting in diminished chemotaxis and calcium flux in response to CX3CL1. Cells cultured long term in IL-15 (more than five days) completely lost surface expression as well as mRNA and protein for CX3CR1. The effect was specific since mRNA for CCR5 was increased and mRNA for CXCR4 was unchanged in these cells by IL-15. Thus, exogenous IL-15 is a negative regulator of CX3CR1 expression and function in human CD56+ NK cells. The data imply that the use of IL-15 alone to expand NK cells ex vivo for immunotherapy may produce cells impaired in their ability to traffic to sites of inflammation.     

MicroRNA-424 regulates the expression of CX3CL1 (fractalkine) in human microvascular endothelial cells during Rickettsia rickettsii infection

Cytokines and chemokines trigger complex intracellular signaling through specific receptors to mediate immune cell recruitment and activation at the sites of infection. CX3CL1 (Fractalkine), a membrane-bound chemokine also capable of facilitating intercellular interactions as an adhesion molecule, contributes to host immune responses by virtue of its chemoattractant functions. Published studies have documented increased CX3CL1 expression in target tissues in a murine model of spotted fever rickettsiosis temporally corresponding to infiltration of macrophages and recovery from infection. Because pathogenic rickettsiae primarily target vascular endothelium in the mammalian hosts, we have now determined CX3CL1 mRNA and protein expression in cultured human microvascular endothelial cells (HMECs) infected in vitro with Rickettsia rickettsii. Our findings reveal 15.5 ± 4.0-fold and 12.3 ± 2.3-fold increase in Cx3cl1 mRNA expression at 3 h and 24 h post-infection, coinciding with higher steady-state levels of the corresponding protein in comparison to uninfected HMECs. Since CX3CL1 is a validated target of microRNA (miR)-424-5p (miR-424) and our earlier findings demonstrated robust down-regulation of miR-424 in R. rickettsii-infected HMECs, we further explored the possibility of regulation of CX3CL1 expression during rickettsial infection by miR-424. As expected, R. rickettsii infection resulted in 87 ± 5% reduction in miR-424 expression in host HMECs. Interestingly, a miR-424 mimic downregulated R. rickettsii-induced expression of CX3CL1, whereas an inhibitor of miR-424 yielded a converse up-regulatory effect, suggesting miR-424-mediated regulation of CX3CL1 during infection. Together, these findings provide the first evidence for the roles of a host microRNA in the regulation of an important bifunctional chemokine governing innate immune responses to pathogenic rickettsiae.     

Protective roles of the fractalkine/CX3CL1-CX3CR1 interactions in alkali-induced corneal neovascularization through enhanced antiangiogenic factor expression

Macrophages accumulate during the course of corneal neovascularization, but its mechanisms and roles still remain elusive. To address these points, we herein examined corneal neovascularization after alkali injury in mice deficient in fractalkine receptor/CX3CR1, which is normally expressed by macrophages. After alkali injury, the mRNA expression of CX3CR1 was augmented along with accumulation of F4/80-positive macrophages and Gr-1-positive neutrophils in the corneas. Compared with wild-type mice, CX3CR1-deficient mice exhibited enhanced corneal neovascularization 2 wk after injury, as evidenced by enlarged CD31-positive areas. Concomitantly, the accumulation of F4/80-positive macrophages, but not Gr-1-positive neutrophils, was markedly attenuated in CX3CR1-deficient mice compared with wild-type mice. The intraocular mRNA expression of vascular endothelial growth factor (VEGF) was enhanced to similar extents in wild-type and CX3CR1-deifient mice after the injury. However, the mRNA expression of antiangiogenic factors, thrombospondin (TSP) 1, TSP-2, and a disintegrin and metalloprotease with thrombospondin (ADAMTS) 1, was enhanced to a greater extent in wild-type than CX3CR1-deificient mice. A double-color immunofluorescence analysis demonstrated that F4/80-positive cells also expressed CX3CR1 and ADAMTS-1 and that TSP-1 and ADAMTS-1 were detected in CX3CR1-positive cells. CX3CL1 enhanced TSP-1 and ADAMTS-1, but not VEGF, expression by peritoneal macrophages. Moreover, topical application of CX3CL1 inhibited corneal neovascularization at 2 wk, along with enhanced intraocular expression of TSP-1 and ADAMTS-1 but not VEGF. Thus, these observations indicate that accumulation of CX3CR1-positive macrophages intraocularly can dampen alkali-induced corneal neovascularization by producing antiangiogenic factors such as TSP-1 and ADAMTS-1 and suggest the potential therapeutic efficacy of using CX3CL1 against alkali-induced corneal neovascularization.     

The antimicrobial peptide,human β-defensin-1, potentiates in vitro osteoclastogenesis via activation of the p44/42 mitogen-activated protein kinases

Previous studies have demonstrated increased expression and raised levels of human β-defensin (hBD)-1 in gingival tissue and crevicular fluid of patients with chronic periodontitis and peri-implantitis, oral bone-resorbing diseases caused by enhanced osteoclastogenesis. Therefore, we aimed to investigate the effect of hBD-1 on osteoclast formation and function and to elucidate the involved signaling pathway in vitro. Human peripheral blood mononuclear cells (PBMCs) were first incubated with various doses of hBD-1 and cell viability was assayed by MTT. PBMCs were treated with macrophage-colony stimulating factor and receptor activator of nuclear factor kappa-B ligand (RANKL) in the presence or absence of non-toxic doses of hBD-1. In vitro osteoclastogenesis was analyzed by tartrate-resistant acid phosphatase (TRAP) staining, osteoclast-specific gene expression, and a resorption pit assay. Involvement of mitogen-activated protein kinases (MAPKs) was studied by immunoblotting and specific MAPK inhibitors. HBD-1 potentiated induction of in vitro osteoclastogenesis by RANKL, as shown by significantly increased number of TRAP-positive multinuclear cells and resorption areas on the dentin slices, and further up-regulated expressions of osteoclast-specific genes compared to those by RANKL treatment (p < 0.05). However, hBD-1 treatment without RANKL failed to induce formation of osteoclast-like cells. A significant and further increase in transient phosphorylation of the p44/42 MAPKs was demonstrated by hBD-1 co-treatment (p < 0.05), consistent with the inhibitory effect by pretreatment with U0126 or PD98059 on hBD-1-enhanced osteoclastogenesis. Collectively, hBD-1 potentiates the induction of in vitro osteoclastogenesis by RANKL via enhanced phosphorylation of the p44/42 MAPKs.     

Involvement of CX3CL1/CX3CR1 Signaling in Spinal Long Term Potentiation

The long-term potentiation (LTP) of spinal C-fiber-evoked field potentials is considered as a fundamental mechanism of central sensitization in the spinal cord. Accumulating evidence has showed the contribution of spinal microglia to spinal LTP and pathological pain. As a key signaling of neurons-microglia interactions, the involvement of CX3CL1/CX3CR1 signaling in pathological pain has also been investigated extensively. The present study examined whether CX3CL1/CX3CR1 signaling plays a role in spinal LTP. The results showed that 10-trains tetanic stimulation (100 Hz, 2s) of the sciatic nerve (TSS) produced a significant LTP of C-fiber-evoked field potentials lasting for over 3 h in the rat spinal dorsal horn. Blockade of CX3CL1/CX3CR1 signaling with an anti-CX3CR1 neutralizing antibody (CX3CR1 AB) markedly suppressed TSS-induced LTP. Exogenous CX3CL1 significantly potentiated 3-trains TSS-induced LTP in rats. Consistently, spinal LTP of C-fiber-evoked field potentials was also induced by TSS (100 Hz, 1s, 4 trains) in all C57BL/6 wild type (WT) mice. However, in CX3CR1^-/- mice, TSS failed to induce LTP and behavioral hypersensitivity, confirming an essential role of CX3CR1 in spinal LTP induction. Furthermore, blockade of IL-18 or IL-23, the potential downstream factors of CX3CL1/CX3CR1 signaling, with IL-18 BP or anti-IL-23 neutralizing antibody (IL-23 AB), obviously suppressed spinal LTP in rats. These results suggest that CX3CL1/CX3CR1 signaling is involved in LTP of C-fiber-evoked field potentials in the rodent spinal dorsal horn.     

Inhibition of CX3CL1 (fractalkine) improves experimental autoimmune myositis in SJL/J mice

Idiopathic inflammatory myopathy is a chronic inflammatory muscle disease characterized by mononuclear cell infiltration in the skeletal muscle. The infiltrated inflammatory cells express various cytokines and cytotoxic molecules. Chemokines are thought to contribute to the inflammatory cell migration into the muscle. We induced experimental autoimmune myositis (EAM) in SJL/J mice by immunization with rabbit myosin and CFA. In the affected muscles of EAM mice, CX3CL1 (fractalkine) was expressed on the infiltrated mononuclear cells and endothelial cells, and its corresponding receptor, CX3CR1, was expressed on the infiltrated CD4 and CD8 T cells and macrophages. Treatment of EAM mice with anti-CX3CL1 mAb significantly reduced the histopathological myositis score, the number of necrotic muscle fibers, and infiltration of CD4 and CD8 T cells and macrophages. Furthermore, treatment with anti-CX3CL1 mAb down-regulated the mRNA expression of TNF-alpha, IFN-gamma, and perforin in the muscles. Our results suggest that CX3CL1-CX3CR1 interaction plays an important role in inflammatory cell migration into the muscle tissue of EAM mice. The results also point to the potential therapeutic usefulness of CX3CL1 inhibition and/or blockade of CX3CL1-CX3CR1 interaction in idiopathic inflammatory myopathy.     

Fibroblast Growth Factor Receptor 1 Activation in Mammary Tumor Cells Promotes Macrophage Recruitment in a CX3CL1-Dependent Manner

Tumor formation is an extensive process requiring complex interactions that involve both tumor cell-intrinsic pathways and soluble mediators within the microenvironment. Tumor cells exploit the intrinsic functions of many soluble molecules, including chemokines and their receptors, to regulate pro-tumorigenic phenotypes that are required for growth and progression of the primary tumor. Previous studies have shown that activation of inducible FGFR1 (iFGFR1) in mammary epithelial cells resulted in increased proliferation, migration, and invasion in vitro and tumor formation in vivo. These studies also demonstrated that iFGFR1 activation stimulated recruitment of macrophages to the epithelium where macrophages contributed to iFGFR1-mediated epithelial cell proliferation and angiogenesis. The studies presented here further utilize this model to identify the mechanisms that regulate FGFR1-induced macrophage recruitment. Results from this study elucidate a novel role for the inflammatory chemokine CX3CL1 in FGFR1-induced macrophage migration. Specifically, we illustrate that activation of both the inducible FGFR1 construct in mouse mammary epithelial cells and endogenous FGFR in the triple negative breast cancer cell line, HS578T, leads to expression of the chemokine CX3CL1. Furthermore, we demonstrate that FGFR-induced CX3CL1 is sufficient to recruit CX3CR1-expressing macrophages in vitro. Finally, blocking CX3CR1 in vivo leads to decreased iFGFR1-induced macrophage recruitment, which correlates with decreased angiogenesis. While CX3CL1 is a known target of FGF signaling in the wound healing environment, these studies demonstrate that FGFR activation also leads to induction of CX3CL1 in a tumor setting. Furthermore, these results define a novel role for CX3CL1 in promoting macrophage recruitment during mammary tumor formation, suggesting that the CX3CL1/CX3CR1 axis may represent a potential therapeutic approach for targeting breast cancers associated with high levels of tumor-associated macrophages.     

The CC chemokine MCP-1 stimulates surface expression of CX3CR1 and enhances the adhesion of monocytes to fractalkine/CX3CL1 via p38 MAPK

The membrane-anchored form of CX3CL1 has been proposed as a novel adhesion protein for leukocytes. This functional property of CX3CL1 is mediated through CX3CR1, a chemokine receptor expressed predominantly on circulating white blood cells. Thus far, it is still uncertain at what stage of the trafficking process CX3CR1 becomes importantly involved and how the CX3CR1-dependent adhesion of leukocytes is regulated during inflammation. The objective of this study was to examine the functional effects of chemokine stimulation on CX3CR1-mediated adhesion of human monocytes. Consistent with previous reports, our data indicate that the activity of CX3CR1 on resting monocytes is sufficient to mediate cell adhesion to CX3CL1. However, the basal, nonstimulated adhesion activity is low, and we hypothesized that like the integrins, CX3CR1 may require a preceding activation step to trigger firm leukocyte adhesion. Compatible with this hypothesis, stimulation of monocytes with MCP-1 significantly increased their adhesion to immobilized CX3CL1, under both static and physiological flow conditions. The increase of the adhesion activity was mediated through CCR2-dependent signaling and obligatory activation of the p38 MAPK pathway. Stimulation with MCP-1 also induced a rapid increase of CX3CR1 protein on the cell surface. Inhibition of the p38 MAPK pathway prevented this increase of CX3CR1 surface expression and blunted the effect of MCP-1 on cell adhesion, indicating a causal link between receptor surface density and adhesion activity. Together, our data suggest that a chemokine signal is required for firm CX3CR1-dependent adhesion and demonstrate that CCR2 is an important regulator of CX3CL1-dependent leukocyte adhesion.     

The chemokine CX3CL1 regulates NK cell activity in vivo

In vitro, chemokines can both activate and induce migration of NK cells. However, little is known about how chemokines influence NK cell activity in vivo. We studied the role of CX(3)CL1 and its receptor, CX(3)CR1, in modulating NK cell activity in an established in vivo model of tumour cell clearance. Radiolabelled YAC-1 target cells intravenously injected into C57BL/6 mice rapidly localize to the lungs and are cleared by NK cells. In mice pre-treated with blocking anti-CX(3)CL1 or anti-CX(3)CR1 Ab, target cell clearance decreased by four- to fivefold (p<0.001). In vitro, we found no effect of anti-CX(3)CL1 or anti-CX(3)CR1 Ab on NK lysis of target cells. We further examined adhesion of NK cells to Py-4-1 endothelial cells. NK cell binding to activated endothelial monolayers was significantly inhibited by anti-CX(3)CR1 Ab or soluble CX(3)CL1 (p<0.001). These studies identify a critical role for CX(3)CL1 in modulating NK cell activity in vivo.     

CX3CL1 RNA干扰慢病毒载体的构建包装与鉴定

摘要 目的：构建包装趋化因子CX3C的配体1（CX3CL1）RNA干扰慢病毒载体。方法：参考目的基因CX3CL1序列,设计PCR引物扩增相应的干扰序列,然后将干扰序列连接至pLVX-shRNA2酶切后的线性化载体上,通过酶切及测序鉴定获得阳性克隆,即为构建成功的pLVX-shRNA2-CX3CL1慢病毒干扰载体。将构建好的慢病毒干扰载体同慢病毒包装载体共同转染293T细胞,收集上清,纯化浓缩后即为pLVX-shRNA2-CX3CL1慢病毒。最后将慢病毒感染BMSCs细胞,QPCR检测慢病毒的干扰效率。结果：经过酶切能切出大小约为6500bp和1350bp的两条带,获得与预期结果相一致的DNA片段,并通过测序验证了序列的准确性,成功构建CX3CL1 RNA慢病毒干扰载体。然后经过包装、纯化浓缩后得到pLVX-shRNA2-CX3CL1慢病毒。QPCR结果表明干扰组明显抑制了CX3CL1mRNA的表达,干扰效率在70%以上。结论：成功构建包装CX3CL1干扰慢病毒载体,并证实其显著沉默了BMSCs细胞CX3CL1的表达,为CX3CL1在BMSCs移植的大鼠缺血性脑卒中炎症反应的机制研究奠定基础。     

Hydrogen sulfide inhibits the development of atherosclerosis with suppressing CX3CR1 and CX3CL1 expression

Hydrogen sulfide, as a novel gaseous mediator, has been suggested to play a key role in atherogenesis. However, the precise mechanisms by which H(2)S affects atherosclerosis remain unclear. Therefore, the present study aimed to investigate the potential role of H(2)S in atherosclerosis and the underlying mechanism with respect to chemokines (CCL2, CCL5 and CX3CL1) and chemokine receptors (CCR2, CCR5, and CX3CR1) in macrophages. Mouse macrophage cell line RAW 264.7 or mouse peritoneal macrophages were pre-incubated with saline or NaHS (50 μM, 100 μM, 200 μM), an H(2)S donor, and then stimulated with interferon-γ (IFN-γ) or lipopolysaccharide (LPS). It was found that NaHS dose-dependently inhibited IFN-γ or LPS-induced CX3CR1 and CX3CL1 expression, as well as CX3CR1-mediated chemotaxis in macrophages. Overexpression of cystathionine γ-lyase (CSE), an enzyme that catalyzes H(2)S biosynthesis resulted in a significant reduction in CX3CR1 and CX3CL1 expression as well as CX3CR1-mediated chemotaxis in stimulated macrophages. The inhibitory effect of H(2)S on CX3CR1 and CX3CL1 expression was mediated by modulation of proliferators-activated receptor-γ (PPAR-γ) and NF-κB pathway. Furthermore, male apoE(-/-) mice were fed a high-fat diet and then randomly given NaHS (1 mg/kg, i.p., daily) or DL-propargylglycine (PAG, 10 mg/kg, i.p., daily). NaHS significantly inhibited aortic CX3CR1 and CX3CL1 expression and impeded aortic plaque development. NaHS had a better anti-atherogenic benefit when it was applied at the early stage of atherosclerosis. However, inhibition of H(2)S formation by PAG increased aortic CX3CR1 and CX3CL1 expression and exacerbated the extent of atherosclerosis. In addition, H(2)S had minimal effect on the expression of CCL2, CCL5, CCR2 and CCR5 in vitro and in vivo. In conclusion, these data indicate that H(2)S hampers the progression of atherosclerosis in fat-fed apoE(-/-) mice and downregulates CX3CR1 and CX3CL1 expression on macrophages and in lesion plaques.     

CX3CL1 induces cell migration and invasion through ICAM-1 expression in oral squamous cell carcinoma cells

Human oral squamous cell carcinoma (OSCC) has been associated with a relatively low survival rate over the years and is characterized by a poor prognosis. C-X3-C motif chemokine ligand 1 (CX3CL1) has been involved in advanced migratory cells. Overexpressed CX3CL1 promotes several cellular responses related to cancer metastasis, including cell movement, migration and invasion in tumour cells. However, CX3CL1 controls the migration ability, and its molecular mechanism in OSCC remains unknown. The present study confirmed that CX3CL1 increased cell movement, migration and invasion. The CX3CL1-induced cell motility is upregulated through intercellular adhesion molecule-1 (ICAM-1) expression in OSCC cells. These effects were significantly suppressed when OSCC cells were pre-treated with CX3CR1 monoclonal antibody (mAb) and small-interfering RNA (siRNA). The CX3CL1-CX3CR1 axis activates promoted PLCβ/PKCα/c-Src phosphorylation. Furthermore, CX3CL1 enhanced activator protein-1 (AP-1) activity. The CX3CR1 mAb and PLCβ, PKCα, c-Src inhibitors reduced CX3CL1-induced c-Jun phosphorylation, c-Jun translocation into the nucleus and c-Jun binding to the ICAM-1 promoter. The present results reveal that CX3CL1 induces the migration of OSCC cells by promoting ICAM-1 expression through the CX3CR1 and the PLCβ/PKCα/c-Src signal pathway, suggesting that CX3CL1-CX3CR1-mediated signalling is correlated with tumour motility and appealed to be a precursor for prognosis in human OSCC.     

Respiratory syncytial virus G protein and G protein CX3C motif adversely affect CX3CR1+ T cell responses

Interactions between fractalkine (CX3CL1) and its receptor, CX3CR1, mediate leukocyte adhesion, activation, and trafficking. The respiratory syncytial virus (RSV) G protein has a CX3C chemokine motif that can bind CX3CR1 and modify CXCL1-mediated responses. In this study, we show that expression of the RSV G protein or the G protein CX3C motif during infection is associated with reduced CX3CR1+ T cell trafficking to the lung, reduced frequencies of RSV-specific, MHC class I-restricted IFN-gamma-expressing cells, and lower numbers of IL-4- and CX3CL1-expressing cells. In addition, we show that CX3CR1+ cells constitute a major component of the cytotoxic response to RSV infection. These results suggest that G protein and the G protein CX3C motif reduce the antiviral T cell response to RSV infection.