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.     

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.     

The chemokine CX3CL1 reduces migration and increases adhesion of neurons with mechanisms dependent on the beta1 integrin subunit

Fractalkine/CX3CL1 and its specific receptor CX3CR1 are constitutively expressed in several regions of the CNS and are reported to mediate neuron-microglial interaction, synaptic transmission, and neuronal protection from toxic insults. CX3CL1 is released both by neuronal and astrocytic cells, whereas CX3CR1 is mainly expressed by microglial cells and neurons. Microglial cells efficiently migrate in response to CX3CL1, whereas no evidence is reported to date on CX3CL1-induced neuronal migration. For this reason, we have investigated in vitro the effects of CX3CL1 on basal migration of neurons and of the microglial and astrocytic populations, all these cells being obtained from the hippocampus and the cerebellum of newborn rats. We report that CX3CL1 stimulates microglial cell migration but efficiently reduces basal neuronal movement, regardless of the brain source. The effect of CX3CL1 is pertussis toxin (PTX) sensitive and PI3K dependent on hippocampal neurons, while it is PTX sensitive, PI3K dependent, and ERK dependent on cerebellar granules. Interestingly, CX3CL1 also increases neuron adhesion to the extracellular matrix component laminin, with mechanisms dependent on PTX-sensitive G proteins, and on the ERK and PI3K pathways. Both the reduction of migration and the increase of neuron adhesion require the activation of the beta(1) and alpha(6) integrin subunits with the exception of cerebellar neuron migration, which is only dependent on the beta(1) subunit. More importantly, in neurons, CX3CL1/CXCL12 cotreatment abolished the effect mediated by a single chemokine on chemotaxis and adhesion. In conclusion, our findings indicate that CX3CL1 reduces neuronal migration by increasing cell adhesion through integrin-dependent mechanisms in hippocampal and cerebellar neurons.     

Apoptosis Signal-Regulating Kinase 1 Is Involved in WISP-1–Promoted Cell Motility in Human Oral Squamous Cell Carcinoma Cells

Oral squamous cell carcinoma (OSCC) has a tendency to migrate and metastasize. WNT1-inducible signaling pathway protein 1 (WISP-1) is a cysteine-rich protein that belongs to the Cyr61, CTGF, Nov (CCN) family of matrix cellular proteins. The effect of WISP-1 on human OSCC cells, however, is unknown. Here, we showed that WISP-1 increased cell migration and intercellular adhesion molecule-1 (ICAM-1) expression in OSCC cells. Pretreatment of cells with integrin αvβ3 monoclonal antibody (mAb) significantly abolished WISP-1–induced cell migration and ICAM-1 expression. On the other hand, WISP-1–mediated cell motility and ICAM-1 upregulation were attenuated by ASK1, JNK, and p38 inhibitor. Furthermore, WISP-1 also enhanced activator protein 1 (AP-1) activation, and the integrin αvβ3 mAb, and ASK1, JNK, and p38 inhibitors reduced WISP-1–mediated AP-1 activation. Moreover, WISP-1 and ICAM-1 expression correlated with the tumor stage of patients with OSCC. Our results indicate that WISP-1 enhances the migration of OSCC cells by increasing ICAM-1 expression through the αvβ3 integrin receptor and the ASK1, JNK/p38, and AP-1 signal transduction pathways.     

Naa10p and IKKα interaction regulates EMT in oral squamous cell carcinoma via TGF-β1/Smad pathway

Epithelial-mesenchymal transition (EMT) has been contributed to increase migration and invasion of cancer cells. However, the correlate of Naa10p and IKKα with EMT in oral squamous cell carcinoma (OSCC) is not yet fully understood. In our present study, we found N-α-acetyltransferase 10 protein (Naa10p) and IκB kinase α (IKKα) were abnormally abundant in oral squamous cell carcinoma (OSCC). Bioinformatic results indicate that the expression of Naa10p and IKKα is correlated with TGF-β1/Smad and EMT-related molecules. The Transwell migration, invasion, qRT-PCR and Western blot assay indicated that Naa10p repressed OSCC cell migration, invasion and EMT, whereas IKKα promoted TGF-β1–mediated OSCC cell migration, invasion and EMT. Mechanistically, Naa10p inhibited IKKα activation of Smad3 through the interaction with IKKα directly in OSCC cells after TGF-β1 stimulation. Notably, knockdown of Naa10p reversed the IKKα-induced change in the migration, invasion and EMT-related molecules in OSCC cells after TGF-β1 stimulation. These findings suggest that Naa10p interacted with IKKα mediates EMT in OSCC cells through TGF-β1/Smad, a novel pathway for preventing OSCC.     

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.     

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.     

CX3CR1 is required for airway inflammation by promoting T helper cell survival and maintenance in inflamed lung

Allergic asthma is a T helper type 2 (T(H)2)-dominated disease of the lung. In people with asthma, a fraction of CD4(+) T cells express the CX3CL1 receptor, CX3CR1, and CX3CL1 expression is increased in airway smooth muscle, lung endothelium and epithelium upon allergen challenge. Here we found that untreated CX3CR1-deficient mice or wild-type (WT) mice treated with CX3CR1-blocking reagents show reduced lung disease upon allergen sensitization and challenge. Transfer of WT CD4(+) T cells into CX3CR1-deficient mice restored the cardinal features of asthma, and CX3CR1-blocking reagents prevented airway inflammation in CX3CR1-deficient recipients injected with WT T(H)2 cells. We found that CX3CR1 signaling promoted T(H)2 survival in the inflamed lungs, and injection of B cell leukemia/lymphoma-2 protein (BCl-2)-transduced CX3CR1-deficient T(H)2 cells into CX3CR1-deficient mice restored asthma. CX3CR1-induced survival was also observed for T(H)1 cells upon airway inflammation but not under homeostatic conditions or upon peripheral inflammation. Therefore, CX3CR1 and CX3CL1 may represent attractive therapeutic targets in asthma.     

The anti-atherosclerotic effect of tanshinone IIA is associated with the inhibition of TNF-α-induced VCAM-1, ICAM-1 and CX3CL1 expression

Tanshinone IIA is one of the major diterpenes in Salvia miltiorrhiza. The inhibitory effect of Tanshinone IIA on atherosclerosis has been reported, but the underlying mechanism is not fully understood. The present study aimed to study the anti-atherosclerosis effect of Tanshinone IIA on the adhesion of monocytes to vascular endothelial cells and related mechanism. Results showed that Tanshinone IIA, at the concentrations without cytotoxic effect, dose-dependently inhibited the adhesion of THP-1 monocytes to the TNF-α-stimulated human vascular endothelial cells. The expressions of cell adhesion molecules including VCAM-1, ICAM-1 and E-selectin were induced by TNF-α in HUVECs at both the mRNA and protein levels. The mRNA and protein expressions of VCAM-1 and ICAM-1, but not E-selectin, were both significantly suppressed by Tanshinone IIA in a dose dependent manner. In addition, the TNF-α-induced mRNA expression of fractalkine/CX3CL1 and the level of soluble fractalkine were both reduced by Tanshinone IIA. We also found that Tanshinone IIA significantly inhibited TNF-α-induced nuclear translocation of NF-κB which was resulted from the inhibitory effect of Tanshinone IIA on the TNF-α-activated phosphorylation of IKKα, IKKβ, IκB and NF-κB. As one of the major components of Salvia miltiorrhiza, Tanshinone IIA alone exerted more potent effect on inhibiting the adhesion of monocytes to vascular endothelial cells when compared with Salvia miltiorrhiza. All together, these results demonstrate a novel underlying mechanism for the anti-inflammatory effect of Tanshinone IIA by modulating TNF-α-induced expression of VCAM-1, ICAM-1 and fractalkine through inhibition of TNF-α-induced activation of IKK/NF-κB signaling pathway in human vascular endothelial cells.     

CCN6 enhances ICAM-1 expression and cell motility in human chondrosarcoma cells

Chondrosarcoma is a type of highly malignant tumor with a potent capacity to invade locally and cause distant metastasis. Chondrosarcoma shows a predilection for metastasis to the lungs. CCN6 is a cysteine-rich protein that belongs to the CCN (Cyr61, CTGF, and Nov) family of matricellular proteins. However, the effects of CCN6 on human chondrosarcoma cells are largely unknown. In this study, we found that CCN6 increased the migration and the expression of intercellular adhesion molecule-1 (ICAM-1) in human chondrosarcoma cells. αvβ3 and αvβ5 integrin monoclonal antibody and mitogen-activated protein kinase (MEK) inhibitors (PD98059 and U0126) inhibited the CCN6-induced increase of the migration and ICAM-1 up-regulation of chondrosarcoma cells. CCN6 stimulation increased the phosphorylation of focal adhesion kinase (FAK), MEK, and extracellular signal-regulated kinase (ERK). In addition, activator protein-1 (AP-1) inhibitors suppressed the cell migration and ICAM-1 expression enhanced by CCN6. Moreover, CCN6 increased AP-1 luciferase activity and binding of c-Jun to the AP-1 element on the ICAM-1 promoter. Taken together, our results indicate that CCN6 enhances the migration of chondrosarcoma cells by increasing ICAM-1 expression through the αvβ3 and αvβ5 integrin receptor, FAK, MEK, ERK, c-Jun, and AP-1 signal transduction pathway.     

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。     

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.     

Activity of adenosine receptors type 1 Is required for CX3CL1-mediated neuroprotection and neuromodulation in hippocampal neurons

The chemokine fractalkine (CX(3)CL1) is constitutively expressed by central neurons, regulating microglial responses including chemotaxis, activation, and toxicity. Through the activation of its own specific receptor, CX(3)CR1, CX(3)CL1 exerts both neuroprotection against glutamate (Glu) toxicity and neuromodulation of the glutamatergic synaptic transmission in hippocampal neurons. Using cultured hippocampal neuronal cell preparations, obtained from CX(3)CR1(-/-) (CX(3)CR1(GFP/GFP)) mice, we report that these same effects are mimicked by exposing neurons to a medium conditioned with CX(3)CL1-treated mouse microglial cell line BV2 (BV2-st medium). Furthermore, CX(3)CL1-induced neuroprotection from Glu toxicity is mediated through the adenosine receptor 1 (AR(1)), being blocked by neuronal cell preparations treatment with 1,3-dipropyl-8-cyclopentylxanthine (DPCPX), a specific inhibitor of AR(1), and mimicked by both adenosine and the specific AR(1) agonist 2-chloro-N(6)-cyclopentyladenosine. Similarly, experiments from whole-cell patch-clamped hippocampal neurons in culture, obtained from CX(3)CR1(+/+) mice, show that CX(3)CL1-induced depression of alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid- (AMPA-) type Glu receptor-mediated current (AMPA-current), is associated with AR(1) activity being blocked by DPCPX and mimicked by adenosine. Furthermore, BV2-st medium induced a similar AMPA-current depression in CX(3)CR1(GFP/GFP) hippocampal neurons and this depression was again blocked by DPCPX. We also report that CX(3)CL1 induced a significant release of adenosine from microglial BV2 cells, as measured by HPLC analysis. We demonstrate that (i) CX(3)CL1, along with AR(1), are critical players for counteracting Glu-mediated neurotoxicity in the brain and (ii) AR(1) mediates neuromodulatory action of CX(3)CL1 on hippocampal neurons.     

CX3CL1 promotes tumour cell by inducing tyrosine phosphorylation of cortactin in lung cancer

It has been reported that chemokine CX₃CL1 can regulate various tumours by binding to its unique receptor CX₃CR1. However, the effect of CX₃CL1-CX₃CR1 on the lung adenocarcinoma and lung squamous cell carcinoma is still unclear. Here, we showed that CX₃CL1 can further invasion and migration of lung adenocarcinoma A549 and lung squamous cell carcinoma H520. In addition, Western blot and immunofluorescence test indicated CX₃CL1 up-regulated the phosphorylation level of cortactin, which is a marker of cell pseudopodium. Meanwhile, the phosphorylation levels of c-Src and c-Abl, which are closely related to the regulation of cortactin phosphorylation, are elevated. Nevertheless, the src/abl inhibitor bosutinib and mutations of cortactin phosphorylation site could inhibit the promotion effect of CX₃CL1 on invasion and migration of A549 and H520. Moreover, these results of MTT, Hoechst staining and Western blot suggested that CX₃CL1 had no effect on the proliferation and apoptosis of A549 and H520 in vitro. The effects of CX₃CL1 were also verified by the subcutaneous tumour formation in nude mice, which showed that it could promote proliferation and invasion of A549 in vivo. In summary, our results indicated that CX₃CL1 furthered invasion and migration in lung cancer cells partly via activating cortactin, and CX₃CL1 may be a potential molecule in regulating the migration and invasion of lung cancer.     

Fractalkine receptor CX(3)CR1 is expressed in epithelial ovarian carcinoma cells and required for motility and adhesion to peritoneal mesothelial cells

Epithelial ovarian carcinoma (EOC) is a deadly disease, and little is known about the mechanisms underlying its metastatic progression. Using human specimens and established cell lines, we determined that the G-protein-coupled seven-transmembrane fractalkine receptor (CX(3)CR1) is expressed in primary and metastatic ovarian carcinoma cells. Ovarian carcinoma cells robustly migrated toward CX(3)CL1, a specific ligand of CX(3)CR1, in a CX(3)CR1-dependent manner. Silencing of CX(3)CR1 reduced migration toward human ovarian carcinoma ascites fluid by approximately 70%. Importantly, adhesion of ovarian carcinoma cells to human peritoneal mesothelial cells was dependent on CX(3)CL1/CX(3)CR1 signaling. In addition, CX(3)CL1 was able to induce cellular proliferation. Together, our data suggest that the fractalkine network may function as a major contributor to the progression of EOC, and further attention to its role in the metastasis of this deadly malignancy is warranted.     

Prostaglandin E2/EP1 Signaling Pathway Enhances Intercellular Adhesion Molecule 1 (ICAM-1) Expression and Cell Motility in Oral Cancer Cells

Oral squamous cell carcinoma has a striking tendency to migrate and metastasize. Cyclooxygenase (COX)-2, the inducible isoform of prostaglandin (PG) synthase, has been implicated in tumor metastasis. However, the effects of COX-2 on human oral cancer cells are largely unknown. We found that overexpression of COX-2 or exogenous PGE₂ increased migration and intercellular adhesion molecule 1 (ICAM)-1 expression in human oral cancer cells. Using pharmacological inhibitors, activators, and genetic inhibition of EP receptors, we discovered that the EP1 receptor, but not other PGE receptors, is involved in PGE₂-mediated cell migration and ICAM-1 expression. PGE₂-mediated migration and ICAM-1 up-regulation were attenuated by inhibitors of protein kinase C (PKC)δ, and c-Src. Activation of the PKCδ, c-Src, and AP-1 signaling pathway occurred after PGE₂ treatment. PGE₂-induced expression of ICAM-1 and migration activity were inhibited by a specific inhibitor, siRNA, and mutants of PKCδ, c-Src, and AP-1. In addition, migration-prone sublines demonstrated that cells with increased migration ability had higher expression of COX-2 and ICAM-1. Taken together, these results indicate that the PGE₂ and EP1 interaction enhanced migration of oral cancer cells through an increase in ICAM-1 production.     

The chemokines, CX3CL1, CCL14, and CCL4, promote human trophoblast migration at the feto-maternal interface

Human embryo implantation is a complex process involving blastocyst attachment to the endometrial epithelium and subsequent trophoblast invasion of the decidua. Chemokines, critical regulators of leukocyte migration, are abundant in endometrial epithelial and decidual cells at this time. We hypothesized that endometrial chemokines stimulate trophoblast invasion. Chemokine receptors CX3CR1 and CCR1 were immunolocalized in human first-trimester implantation sites, specifically to endovascular extravillous trophoblasts, but not to the invading interstitial EVTs (iEVTs), with weak staining also on syncytium. CCR3 was localized to invading iEVTs and to microvilli on the syncytial surface. Expression of CX3CL1 (fractalkine), CCL7 (MCP-3), and their receptors (CX3CR1, CCR1, CCR2, CCR3, and CCR5) mRNA was examined in cellular components of the maternal-embryonic interface by RT-PCR. Both chemokines were abundant in entire endometrium and placenta, endometrial cells (primary cultures and HES, a human endometrial epithelial cell line) and trophoblast cell lines (JEG-3, ACIM-88, and ACIM-32). Chemokine receptor mRNA was expressed by placenta and trophoblast cell lines: CCR1 by all trophoblast cell types, whereas CCR2, CCR3, and CX3CR1 were more variable. CX3CR1, CCR1, CCR2, and CCR5 were also expressed by endometrial cells. Migration assays used the trophoblast cell line most closely resembling extravillous cytotrophoblast (AC1M-88). Trophoblast migration occurred in response to CX3CL1, CCL14, and CCL4, but not CCL7. Endometrial cell-conditioned media also stimulated trophoblast migration; this was attenuated by neutralizing antibodies to CX3CL1 and CCL4. Thus, chemokines are expressed by maternal and embryonic cells during implantation, whereas corresponding receptors are on trophoblast cells. Promotion of trophoblast migration by chemokines and endometrial cell conditioned medium indicates an important involvement of chemokines in maternal-fetal communication.     

Functional adhesiveness of the CX3CL1 chemokine requires its aggregation. Role of the transmembrane domain

In its native form, the chemokine CX3CL1 is a firmly adhesive molecule promoting leukocyte adhesion and migration and hence involved, along with its unique receptor CX3CR1, in various inflammatory processes. Here we investigated the role of molecular aggregation in the CX3CL1 adhesiveness. Assays of bioluminescence resonance energy transfer (BRET) and homogeneous time-resolved fluorescence (HTRF) in transfected cell lines and in primary cells showed specific signals indicative of CX3CL1 clustering. Truncation experiments showed that the transmembrane domain played a central role in this aggregation. A chimera with mutations of the 12 central transmembrane domain residues had significantly reduced BRET signals and characteristics of a non-clustering molecule. This mutant was weakly adhesive according to flow and dual pipette adhesion assays and was less glycosylated than CX3CL1, although, as we demonstrated, loss of glycosylation did not affect the CX3CL1 adhesive potency. We postulate that cell surfaces express CX3CL1 as a constitutive oligomer and that this oligomerization is essential for its adhesive potency. Inhibition of CX3CL1 self-assembly could limit the recruitment of CX3CR1-positive cells and may be a new pathway for anti-inflammatory therapies.