Gene Summary

Gene:CX3CR1; C-X3-C motif chemokine receptor 1
Aliases: V28, CCRL1, GPR13, CMKDR1, GPRV28, CMKBRL1
Summary:Fractalkine is a transmembrane protein and chemokine involved in the adhesion and migration of leukocytes. The protein encoded by this gene is a receptor for fractalkine. The encoded protein also is a coreceptor for HIV-1, and some variations in this gene lead to increased susceptibility to HIV-1 infection and rapid progression to AIDS. Four transcript variants encoding two different isoforms have been found for this gene. [provided by RefSeq, Jan 2010]
Databases:OMIM, HGNC, Ensembl, GeneCard, Gene
Protein:CX3C chemokine receptor 1
Source:NCBIAccessed: 01 September, 2019


What does this gene/protein do?
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Pathways:What pathways are this gene/protein implicaed in?
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Cancer Overview

Research Indicators

Publications Per Year (1994-2019)
Graph generated 02 September 2019 using data from PubMed using criteria.

Literature Analysis

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Tag cloud generated 01 September, 2019 using data from PubMed, MeSH and CancerIndex

Latest Publications: CX3CR1 (cancer-related)

Zhuang Q, Cheng K, Ming Y
CX3CL1/CX3CR1 Axis, as the Therapeutic Potential in Renal Diseases: Friend or Foe?
Curr Gene Ther. 2017; 17(6):442-452 [PubMed] Free Access to Full Article Related Publications
The fractalkine receptor chemokine (C-X3-C motif) receptor 1 (CX3CR1) and its highly selective ligand CX3CL1 mediate chemotaxis and adhesion of immune cells, which are involved in the pathogenesis and progression of numerous inflammatory disorders and malignancies. The CX3CL1/CX3CR1 axis has recently drawn attention as a potential therapeutic target because it is involved in the ontogeny, homeostatic migration, or colonization of renal phagocytes. We performed a Medline/PubMed search to detect recently published studies that explored the relationship between the CX3CL1/CX3CR1 axis and renal diseases and disorders, including diabetic nephropathy, renal allograft rejection, infectious renal diseases, IgA nephropathy, fibrotic kidney disease, lupus nephritis and glomerulonephritis, acute kidney injury and renal carcinoma. Most studies demonstrated its role in promoting renal pathopoiesis; however, several recent studies showed that the CX3CL1/CX3CR1 axis could also reduce renal pathopoiesis. Thus, the CX3CL1/CX3CR1 axis is now considered to be a double-edged sword that could provide novel perspectives into the pathogenesis and treatment of renal diseases and disorders.

Huang L, Ma B, Ma J, Wang F
Fractalkine/CX3CR1 axis modulated the development of pancreatic ductal adenocarcinoma via JAK/STAT signaling pathway.
Biochem Biophys Res Commun. 2017; 493(4):1510-1517 [PubMed] Related Publications
Pancreatic ductal adenocarcinoma (PDAC) is a fatal malignancy with an estimated 5 year survival rate of approximately 5% of all stages combined. High potential of PDAC metastasis is a leading cause for high mortality and poor prognosis. The majority of patients present with distant metastasis at diagnosis. Fractalkine (FKN) is recognized as a chemokine and a specific ligand of CX3CR1. It has been reported that FKN/CX3CR1 system was upregulated in many types of solid tumors. However, role of FKN/CX3CR1 in PDAC development remains unclear. In the current investigation, we found that FKN and CX3CR1 expression was significantly increased in PDAC tissues, especially in the metastatic samples, and was highly-correlated with severity of PDAC. Ectopic expression of FKN promoted the proliferation and migration of PDAC, while knockdown of CX3CR1 reversed the function of FKN. In addition, PDAC cells with FKN-deficiency showed impaired proliferation and migration activity. The underlying mechanism is that FKN/CX3CR1 activated JAK/STAT signaling, which in turn regulated cell growth. Consistently, in vivo tumorigenesis assay validated the regulatory role of FKN/CX3CR1 in PDAC growth. Our investigation helped understanding the pathogenesis of PDAC occurrence, and demonstrated critical role of FKN/CX3CR1 in PDAC development.

Jung K, Heishi T, Khan OF, et al.
Ly6Clo monocytes drive immunosuppression and confer resistance to anti-VEGFR2 cancer therapy.
J Clin Invest. 2017; 127(8):3039-3051 [PubMed] Free Access to Full Article Related Publications
Current anti-VEGF therapies for colorectal cancer (CRC) provide limited survival benefit, as tumors rapidly develop resistance to these agents. Here, we have uncovered an immunosuppressive role for nonclassical Ly6Clo monocytes that mediates resistance to anti-VEGFR2 treatment. We found that the chemokine CX3CL1 was upregulated in both human and murine tumors following VEGF signaling blockade, resulting in recruitment of CX3CR1+Ly6Clo monocytes into the tumor. We also found that treatment with VEGFA reduced expression of CX3CL1 in endothelial cells in vitro. Intravital microscopy revealed that CX3CR1 is critical for Ly6Clo monocyte transmigration across the endothelium in murine CRC tumors. Moreover, Ly6Clo monocytes recruit Ly6G+ neutrophils via CXCL5 and produce IL-10, which inhibits adaptive immunity. Preventing Ly6Clo monocyte or Ly6G+ neutrophil infiltration into tumors enhanced inhibition of tumor growth with anti-VEGFR2 therapy. Furthermore, a gene therapy using a nanoparticle formulated with an siRNA against CX3CL1 reduced Ly6Clo monocyte recruitment and improved outcome of anti-VEGFR2 therapy in mouse CRCs. Our study unveils an immunosuppressive function of Ly6Clo monocytes that, to our knowledge, has yet to be reported in any context. We also reveal molecular mechanisms underlying antiangiogenic treatment resistance, suggesting potential immunomodulatory strategies to enhance the long-term clinical outcome of anti-VEGF therapies.

Kallemeijn MJ, de Ridder D, Schilperoord-Vermeulen J, et al.
Dysregulated signaling, proliferation and apoptosis impact on the pathogenesis of TCRγδ+ T cell large granular lymphocyte leukemia.
PLoS One. 2017; 12(4):e0175670 [PubMed] Free Access to Full Article Related Publications
TCRγδ+ T-LGL leukemia is a rare form of chronic mature T cell disorders in elderly, which is generally characterized by a persistently enlarged CD3+CD57+TCRγδ+ large granular lymphocyte population in the peripheral blood with a monoclonal phenotype. Clinically, the disease is heterogeneous, most patients being largely asymptomatic, although neutropenia, fatigue and B symptoms and underlying diseases such as autoimmune diseases or malignancies are also often observed. The etiology of TCRγδ+ T-LGL proliferations is largely unknown. Here, we aimed to investigate underlying molecular mechanisms of these rare proliferations by performing gene expression profiling of TCRγδ+ T-LGL versus normal TCRγδ+ T cell subsets. From our initial microarray dataset we observed that TCRγδ+ T-LGL leukemia forms a separate group when compared with different healthy control TCRγδ+ T cell subsets, correlating best with the healthy TemRA subset. The lowest correlation was seen with the naive subset. Based on specific comparison between healthy control cells and TCRγδ+ T-LGL leukemia cells we observed up-regulation of survival, proliferation and hematopoietic system related genes, with a remarkable down-regulation of apoptotic pathway genes. RQ-PCR validation of important genes representative for the dataset, including apoptosis (XIAP, CASP1, BCLAF1 and CFLAR), proliferation/development (ID3) and inflammation (CD28, CCR7, CX3CR1 and IFNG) processes largely confirmed the dysregulation in proliferation and apoptosis. Based on these expression data we conclude that TCRγδ+ T-LGL leukemia is likely the result of an underlying aberrant molecular mechanisms leading to increased proliferation and reduced apoptosis.

Chen Z, Feng X, Herting CJ, et al.
Cellular and Molecular Identity of Tumor-Associated Macrophages in Glioblastoma.
Cancer Res. 2017; 77(9):2266-2278 [PubMed] Free Access to Full Article Related Publications
In glioblastoma (GBM), tumor-associated macrophages (TAM) represent up to one half of the cells of the tumor mass, including both infiltrating macrophages and resident brain microglia. In an effort to delineate the temporal and spatial dynamics of TAM composition during gliomagenesis, we used genetically engineered and GL261-induced mouse models in combination with CX3CR1

Amit M, Na'ara S, Leider-Trejo L, et al.
Upregulation of RET induces perineurial invasion of pancreatic adenocarcinoma.
Oncogene. 2017; 36(23):3232-3239 [PubMed] Related Publications
Tumor spread along nerves, a phenomenon known as perineurial invasion, is common in various cancers including pancreatic ductal adenocarcinoma (PDAC). Neural invasion is associated with poor outcome, yet its mechanism remains unclear. Using the transgenic Pdx-1-Cre/KrasG12D /p53R172H (KPC) mouse model, we investigated the mechanism of neural invasion in PDAC. To detect tissue-specific factors that influence neural invasion by cancer cells, we characterized the perineurial microenvironment using a series of bone marrow transplantation (BMT) experiments in transgenic mice expressing single mutations in the Cx3cr1, GDNF and CCR2 genes. Immunolabeling of tumors in KPC mice of different ages and analysis of human cancer specimens revealed that RET expression is upregulated during PDAC tumorigenesis. BMT experiments revealed that BM-derived macrophages expressing the RET ligand GDNF are highly abundant around nerves invaded by cancer. Inhibition of perineurial macrophage recruitment, using the CSF-1R antagonist GW2580 or BMT from CCR2-deficient donors, reduced perineurial invasion. Deletion of GDNF expression by perineurial macrophages, or inhibition of RET with shRNA or a small-molecule inhibitor, reduced perineurial invasion in KPC mice with PDAC. Taken together, our findings show that RET is upregulated during pancreas tumorigenesis and its activation induces cancer perineurial invasion. Trafficking of BM-derived macrophages to the perineurial microenvironment and secretion of GDNF are essential for pancreatic cancer neural spread.

Mays AC, Feng X, Browne JD, Sullivan CA
Chemokine and Chemokine Receptor Profiles in Metastatic Salivary Adenoid Cystic Carcinoma.
Anticancer Res. 2016; 36(8):4013-8 [PubMed] Related Publications
AIM: To characterize the chemokine pattern in metastatic salivary adenoid cystic carcinoma (SACC).
MATERIALS AND METHODS: Real-time polymerase chain reaction (RT-PCR) was used to compare chemokine and chemokine receptor gene expression in two SACC cell lines: SACC-83 and SACC-LM (lung metastasis). Chemokines and receptor genes were then screened and their expression pattern characterized in human tissue samples of non-recurrent SACC and recurrent SACC with perineural invasion.
RESULTS: Expression of chemokine receptors C5AR1, CCR1, CCR3, CCR6, CCR7, CCR9, CCR10, CXCR4, CXCR6, CXCR7, CCRL1 and CCRL2 were higher in SACC-83 compared to SACC-LM. CCRL1, CCBP2, CMKLR1, XCR1 and CXCR2 and 6 chemokine genes (CCL13, CCL27, CXCL14, CMTM1, CMTM2, CKLF) were more highly expressed in tissues of patients without tumor recurrence/perineural invasion compared to those with tumor recurrence. CCRL1 (receptor), CCL27, CMTM1, CMTM2, and CKLF (chemokine) genes were more highly expressed in SACC-83 and human tissues of patients without tumor recurrence/perineural invasion.
CONCLUSION: CCRL1, CCL27, CMTM1, CMTM2 and CKLF may play important roles in the development of tumor metastases in SACC.

Maiga A, Lemieux S, Pabst C, et al.
Transcriptome analysis of G protein-coupled receptors in distinct genetic subgroups of acute myeloid leukemia: identification of potential disease-specific targets.
Blood Cancer J. 2016; 6(6):e431 [PubMed] Free Access to Full Article Related Publications
Acute myeloid leukemia (AML) is associated with poor clinical outcome and the development of more effective therapies is urgently needed. G protein-coupled receptors (GPCRs) represent attractive therapeutic targets, accounting for approximately 30% of all targets of marketed drugs. Using next-generation sequencing, we studied the expression of 772 GPCRs in 148 genetically diverse AML specimens, normal blood and bone marrow cell populations as well as cord blood-derived CD34-positive cells. Among these receptors, 30 are overexpressed and 19 are downregulated in AML samples compared with normal CD34-positive cells. Upregulated GPCRs are enriched in chemokine (CCR1, CXCR4, CCR2, CX3CR1, CCR7 and CCRL2), adhesion (CD97, EMR1, EMR2 and GPR114) and purine (including P2RY2 and P2RY13) receptor subfamilies. The downregulated receptors include adhesion GPCRs, such as LPHN1, GPR125, GPR56, CELSR3 and GPR126, protease-activated receptors (F2R and F2RL1) and the Frizzled family receptors SMO and FZD6. Interestingly, specific deregulation was observed in genetically distinct subgroups of AML, thereby identifying different potential therapeutic targets in these frequent AML subgroups.

Shen F, Zhang Y, Jernigan DL, et al.
Novel Small-Molecule CX3CR1 Antagonist Impairs Metastatic Seeding and Colonization of Breast Cancer Cells.
Mol Cancer Res. 2016; 14(6):518-27 [PubMed] Free Access to Full Article Related Publications
UNLABELLED: Recent evidence indicates that cancer cells, even in the absence of a primary tumor, recirculate from established secondary lesions to further seed and colonize skeleton and soft tissues, thus expanding metastatic dissemination and precipitating the clinical progression to terminal disease. Recently, we reported that breast cancer cells utilize the chemokine receptor CX3CR1 to exit the blood circulation and lodge to the skeleton of experimental animals. Now, we show that CX3CR1 is overexpressed in human breast tumors and skeletal metastases. To assess the clinical potential of targeting CX3CR1 in breast cancer, a functional role of CX3CR1 in metastatic seeding and progression was first validated using a neutralizing antibody for this receptor and transcriptional suppression by CRISPR interference (CRISPRi). Successively, we synthesized and characterized JMS-17-2, a potent and selective small-molecule antagonist of CX3CR1, which was used in preclinical animal models of seeding and established metastasis. Importantly, counteracting CX3CR1 activation impairs the lodging of circulating tumor cells to the skeleton and soft-tissue organs and also negatively affects further growth of established metastases. Furthermore, nine genes were identified that were similarly altered by JMS-17-2 and CRISPRi and could sustain CX3CR1 prometastatic activity. In conclusion, these data support the drug development of CX3CR1 antagonists, and promoting their clinical use will provide novel and effective tools to prevent or contain the progression of metastatic disease in breast cancer patients.
IMPLICATIONS: This work conclusively validates the instrumental role of CX3CR1 in the seeding of circulating cancer cells and is expected to pave the way for pairing novel inhibitors of this receptor with current standards of care for the treatment of breast cancer patients. Mol Cancer Res; 14(6); 518-27. ©2016 AACR.

Meireles M, Marques C, Norberto S, et al.
Anthocyanin effects on microglia M1/M2 phenotype: Consequence on neuronal fractalkine expression.
Behav Brain Res. 2016; 305:223-8 [PubMed] Related Publications
Microglia mediate multiple aspects of neuroinflammation, including cytotoxicity, repair, regeneration, and immunosuppression due to their ability to acquire diverse activation states, or phenotypes. Modulation of microglial phenotype or microglia-neuron crosstalk can be an appealing neurotherapeutic strategy. Anthocyanins are a class of flavonoids found e.g., in berries that has been attracting interest due to its neuroprotective potential. However, there are no data clarifying the impact of anthocyanins on microglial phenotype or on microglia-neuron crosstalk (CX3CR1/CX3CL1). N9 microglia cell line was treated with 1μM cyanidin (Cy), cyanidin-3-glucose (Cy3glc) and a methylated form of cyanidin-3-glucose (Met-Cy3glc) in basal conditions and with LPS/IL-4 stimulation. SH-SY5Y cell line was treated with the conditioned medium of microglia and with the anthocyanins alone. At basal conditions, microglia treatment with anthocyanins for 24h induced a less pro-inflammatory profile. Decreased TNF-α mRNA expression was induced either by Cy and Met-Cy3glc. LPS markedly increase IL-6 mRNA expression, which was lowered by Cy3glc. IL-1β LPS-induced expression was reverted by Cy. Cy increased CX3CL1 mRNA expression in SH-SY5Y comparing either with control or LPS. Anthocyanins and metabolites were not able to shift microglia to an M2 strict phenotype however they did interact with microglia biology. There was an attenuation of M1 phenotype and increase of neuronal expression of CX3CL1 mRNA. Understanding how flavonoids modulate microglia-neuron crosstalk can open new directions for future nutritional interventions.

Seifert M, Garbe M, Friedrich B, et al.
Comparative transcriptomics reveals similarities and differences between astrocytoma grades.
BMC Cancer. 2015; 15:952 [PubMed] Free Access to Full Article Related Publications
BACKGROUND: Astrocytomas are the most common primary brain tumors distinguished into four histological grades. Molecular analyses of individual astrocytoma grades have revealed detailed insights into genetic, transcriptomic and epigenetic alterations. This provides an excellent basis to identify similarities and differences between astrocytoma grades.
METHODS: We utilized public omics data of all four astrocytoma grades focusing on pilocytic astrocytomas (PA I), diffuse astrocytomas (AS II), anaplastic astrocytomas (AS III) and glioblastomas (GBM IV) to identify similarities and differences using well-established bioinformatics and systems biology approaches. We further validated the expression and localization of Ang2 involved in angiogenesis using immunohistochemistry.
RESULTS: Our analyses show similarities and differences between astrocytoma grades at the level of individual genes, signaling pathways and regulatory networks. We identified many differentially expressed genes that were either exclusively observed in a specific astrocytoma grade or commonly affected in specific subsets of astrocytoma grades in comparison to normal brain. Further, the number of differentially expressed genes generally increased with the astrocytoma grade with one major exception. The cytokine receptor pathway showed nearly the same number of differentially expressed genes in PA I and GBM IV and was further characterized by a significant overlap of commonly altered genes and an exclusive enrichment of overexpressed cancer genes in GBM IV. Additional analyses revealed a strong exclusive overexpression of CX3CL1 (fractalkine) and its receptor CX3CR1 in PA I possibly contributing to the absence of invasive growth. We further found that PA I was significantly associated with the mesenchymal subtype typically observed for very aggressive GBM IV. Expression of endothelial and mesenchymal markers (ANGPT2, CHI3L1) indicated a stronger contribution of the micro-environment to the manifestation of the mesenchymal subtype than the tumor biology itself. We further inferred a transcriptional regulatory network associated with specific expression differences distinguishing PA I from AS II, AS III and GBM IV. Major central transcriptional regulators were involved in brain development, cell cycle control, proliferation, apoptosis, chromatin remodeling or DNA methylation. Many of these regulators showed directly underlying DNA methylation changes in PA I or gene copy number mutations in AS II, AS III and GBM IV.
CONCLUSIONS: This computational study characterizes similarities and differences between all four astrocytoma grades confirming known and revealing novel insights into astrocytoma biology. Our findings represent a valuable resource for future computational and experimental studies.

Erreni M, Siddiqui I, Marelli G, et al.
The Fractalkine-Receptor Axis Improves Human Colorectal Cancer Prognosis by Limiting Tumor Metastatic Dissemination.
J Immunol. 2016; 196(2):902-14 [PubMed] Related Publications
Human colorectal cancer (CRC) is a frequent neoplasia in Western countries, and its metastatic progression is a major cause of cancer-related death. In search of specific molecules upregulated in CRC, with possible clinical relevance, we performed a differential gene-profiling analysis in surgery-derived CRC samples and adjacent uninvolved intestinal mucosa. The chemokine CX3CL1 and its specific receptor CX3CR1 were significantly upregulated in tumors. Higher expression of CX3CL1 and CX3CR1 was confirmed by immunohistochemistry in 100 CRC tumor samples (stages I-III). Unexpectedly, high immune scores of CX3CL1 did not correlate with the density of tumor-infiltrating CD3(+) T cells or CD68(+) macrophages. Coexpression of ligand and receptor by tumor cells (axis-positive tumors) significantly associated with longer disease-free (p = 0.01) and disease-specific survival (p = 0.001). Conversely, axis-negative tumors (with low expression of both ligand and receptor) had increased risk of tumor relapse (p = 0.02), and increased likelihood of metachronous metastasis (p = 0.001), including after stage adjustment (p = 0.006). Transduction of CX3CL1 and CX3CR1 in CRC tumor cell lines induced cell aggregation that strongly inhibited in vitro migration in chemotaxis assays. In a mouse model of spleen-liver metastases, cancer dissemination to liver was dramatically reduced in CX3CL1-CX3CR1-expressing tumors, and ligand-receptor interaction was confirmed in cancer cells in vivo by fluorescence resonance energy transfer analysis. In conclusion, tumoral expression of the CX3CL1-CX3CR1 chemokine axis functions as a retention factor, increasing homotypic cell adhesion and limiting tumor spreading to metastatic sites. Lack or low levels of expression of CX3CL1-CX3CR1 by tumor cells identifies a group of CRC patients at increased risk of metastatic progression.

Gurler H, Macias V, Kajdacsy-Balla AA, Barbolina MV
Examination of the Fractalkine and Fractalkine Receptor Expression in Fallopian Adenocarcinoma Reveals Differences When Compared to Ovarian Carcinoma.
Biomolecules. 2015; 5(4):3438-47 [PubMed] Free Access to Full Article Related Publications
Fallopian adenocarcinoma is a rare malignancy arising in the epithelium of the fallopian tube. Fallopian tube epithelium has been proposed as a tissue origin for high-grade serous ovarian carcinoma, the deadliest gynecologic malignancy. Given the commonalities in dissemination and treatment of these malignancies, we contemplated the possibility of similar patterns of gene expression underlying their progression. To reveal potential similarities or differences in the gene expression of fallopian adenocarcinoma and high-grade serous ovarian carcinoma, we tested expression of the fractalkine receptor (CX3CR1) and its ligand, fractalkine (CX3CL1), in the specimens of normal and pathologic fallopian tube using immunohistochemistry. Our data show that CX3CR1 is expressed in the normal, cancer adjacent normal, inflammatory, and malignant fallopian epithelium. CX3CL1 was expressed only by the normal and cancer adjacent normal fallopian tube epithelium; its expression was largely lost in the inflammatory and malignant fallopian epithelium. In opposite, both CX3CR1 and CX3CL1 are expressed in high-grade serous ovarian carcinoma. These findings are consistent with an idea that fallopian adenocarcinoma and high-grade serous ovarian carcinoma, although currently thought to arise from the same organ, may not share similar molecular characteristics.

Nielsen KR, Steffensen R, Bendtsen MD, et al.
Inherited Inflammatory Response Genes Are Associated with B-Cell Non-Hodgkin's Lymphoma Risk and Survival.
PLoS One. 2015; 10(10):e0139329 [PubMed] Free Access to Full Article Related Publications
BACKGROUND: Malignant B-cell clones are affected by both acquired genetic alterations and by inherited genetic variations changing the inflammatory tumour microenvironment.
METHODS: We investigated 50 inflammatory response gene polymorphisms in 355 B-cell non-Hodgkin's lymphoma (B-NHL) samples encompassing 216 diffuse large B cell lymphoma (DLBCL) and 139 follicular lymphoma (FL) and 307 controls. The effect of single genes and haplotypes were investigated and gene-expression analysis was applied for selected genes. Since interaction between risk genes can have a large impact on phenotype, two-way gene-gene interaction analysis was included.
RESULTS: We found inherited SNPs in genes critical for inflammatory pathways; TLR9, IL4, TAP2, IL2RA, FCGR2A, TNFA, IL10RB, GALNT12, IL12A and IL1B were significantly associated with disease risk and SELE, IL1RN, TNFA, TAP2, MBL2, IL5, CX3CR1, CHI3L1 and IL12A were, associated with overall survival (OS) in specific diagnostic entities of B-NHL. We discovered noteworthy interactions between DLBCL risk alleles on IL10 and IL4RA and FL risk alleles on IL4RA and IL4. In relation to OS, a highly significant interaction was observed in DLBCL for IL4RA (rs1805010) * IL10 (rs1800890) (HR = 0.11 (0.02-0.50)). Finally, we explored the expression of risk genes from the gene-gene interaction analysis in normal B-cell subtypes showing a different expression of IL4RA, IL10, IL10RB genes supporting a pathogenetic effect of these interactions in the germinal center.
CONCLUSIONS: The present findings support the importance of inflammatory genes in B-cell lymphomas. We found association between polymorphic sites in inflammatory response genes and risk as well as outcome in B-NHL and suggest an effect of gene-gene interactions during the stepwise oncogenesis.

Feng X, Szulzewsky F, Yerevanian A, et al.
Loss of CX3CR1 increases accumulation of inflammatory monocytes and promotes gliomagenesis.
Oncotarget. 2015; 6(17):15077-94 [PubMed] Free Access to Full Article Related Publications
The most abundant populations of non-neoplastic cells in the glioblastoma (GBM) microenvironment are resident microglia, macrophages and infiltrating monocytes from the blood circulation. The mechanisms by which monocytes infiltrate into GBM, their fate following infiltration, and their role in GBM growth are not known. Here we tested the hypothesis that loss of the fractalkine receptor CX3CR1 in microglia and monocytes would affect gliomagenesis. Deletion of Cx3cr1 from the microenvironment resulted in increased tumor incidence and shorter survival times in glioma-bearing mice. Loss of Cx3cr1 did not affect accumulation of microglia/macrophages in peri-tumoral areas, but instead indirectly promoted the trafficking of CD11b+CD45hiCX3CR1lowLy-6ChiLy-6G-F4/80-/low circulating inflammatory monocytes into the CNS, resulting in their increased accumulation in the perivascular area. Cx3cr1-deficient microglia/macrophages and monocytes demonstrated upregulation of IL1β expression that was inversely proportional to Cx3cr1 gene dosage. The Proneural subgroup of the TCGA GBM patient dataset with high IL1β expression showed shorter survival compared to patients with low IL1β. IL1β promoted tumor growth and increased the cancer stem cell phenotype in murine and human Proneural glioma stem cells (GSCs). IL1β activated the p38 MAPK signaling pathway and expression of monocyte chemoattractant protein (MCP-1/CCL2) by tumor cells. Loss of Cx3cr1 in microglia in a monocyte-free environment had no impact on tumor growth and did not alter microglial migration. These data suggest that enhancing signaling to CX3CR1 or inhibiting IL1β signaling in intra-tumoral macrophages can be considered as potential strategies to decrease the tumor-promoting effects of monocytes in Proneural GBM.

Wada A, Ito A, Iitsuka H, et al.
Role of chemokine CX3CL1 in progression of multiple myeloma via CX3CR1 in bone microenvironments.
Oncol Rep. 2015; 33(6):2935-9 [PubMed] Related Publications
Several chemokines/chemokine receptors such as CXCL12, CCL3, CXCR4 and CCR1 attract multiple myelomas to specific microenvironments. In the present study, we investigated whether the CX3CL1/CX3CR1 axis is involved in the interaction of the multiple myeloma cells with their microenvironment. The expression of CX3CR1 (also known as fractalkine) was detected in three of the seven human myeloma cell lines. CX3CL1-induced phosphorylation of Akt and ERK1/2 was detected in the CX3CR1-positive cell lines, but not in the CX3CR1-negative cell lines. In addition, CX3CL1-induced cell adhesion to fibronectin and vascular cell adhesion molecule-1 (VCAM-1) in the human myeloma RPMI-8226 cell line. We also investigated whether a relationship existed between myeloma cells and osteoclasts that may function via the CX3CL1/CX3CR1 axis. Conditioned medium from CX3CL1-stimulated RPMI-8226 cells drastically increased the osteoclast differentiation. Collectively, the results from the present study support the concept of the CX3CL1-mediated activation of the progression of the multiple myeloma via CX3CR1. Thus, CX3CR1 may represent a potential therapeutic target for the treatment of multiple myeloma in a bone microenvironment.

Zhao W, Xu Y, Xu J, et al.
Subsets of myeloid-derived suppressor cells in hepatocellular carcinoma express chemokines and chemokine receptors differentially.
Int Immunopharmacol. 2015; 26(2):314-21 [PubMed] Related Publications
Tumors induce the recruitment and expansion of myeloid-derived suppressor cells (MDSCs), a heterogeneous population of cells that can be further sub-divided into polymorphonuclear Ly6G(+) PMN-MDSCs and monocytic Ly6G(-) Mo-MDSCs. To identify chemokines and chemokine-related genes that are differentially expressed within the tumor microenvironment in these two MDSC subsets, we established an orthotopic hepatocellular carcinoma model in immunocompetent mice. Splenic PMN-MDSCs and Mo-MDSCs were isolated to >95% homogeneity by flow cytometry. Using a real-time PCR array, we investigated the expression of 84 genes encoding chemokines and cytokines, chemokine receptors, and related signaling molecules involved with chemotaxis. Clustering analysis suggested that a core set of chemokine-related genes is expressed in both PMN-MDSC and Mo-MDSC populations, but that the expression profile is broader for Mo-MDSCs. Furthermore, 11 genes are more highly expressed in PMN-MDSCs and 12 genes are more highly expressed in Mo-MDSCs. Among these, PMN-MDSCs express Cxcr1, Cxcr2 and Il1b at 33.03- to 109.76-fold higher levels than in Mo-MDSCs, and Mo-MDSCs express eight genes (Ccr2, Ccr5, Cmklr1, Cx3cr1, Ccr3, Ccl9, Cmtm3 and Cxcl16) at 30.2 to 515.5-fold higher levels than in PMN-MDSCs. These results suggest that the profile of chemokines and chemokine-related genes is more expansive for Mo-MDSCs than for PMN-MDSCs. The differential expression of chemokines and chemokine-associated genes may regulate the presence and activity of PMN-MDSCs and Mo-MDSCs in the tumor microenvironment.

Blonska M, Zhu Y, Chuang HH, et al.
Jun-regulated genes promote interaction of diffuse large B-cell lymphoma with the microenvironment.
Blood. 2015; 125(6):981-91 [PubMed] Free Access to Full Article Related Publications
Diffuse large B-cell lymphoma (DLBCL) is an aggressive disease with a high proliferation rate. However, the molecular and genetic features that drive the aggressive clinical behavior of DLBCL are not fully defined. Here, we have demonstrated that activated Jun signaling is a frequent event in DLBCL that promotes dissemination of malignant cells. Downregulation of Jun dramatically reduces lymphoma cell adhesion to extracellular matrix proteins, subcutaneous tumor size in nude mice, and invasive behavior, including bone marrow infiltration and interaction with bone marrow stromal cells. Furthermore, using a combination of RNA interference and gene expression profiling, we identified Jun target genes that are associated with disseminated lymphoma. Among them, ITGAV, FoxC1, and CX3CR1 are significantly enriched in patients with 2 or more extranodal sites. Our results point to activated Jun signaling as a major driver of the aggressive phenotype of DLBCL.

Wei LM, Cao S, Yu WD, et al.
Overexpression of CX3CR1 is associated with cellular metastasis, proliferation and survival in gastric cancer.
Oncol Rep. 2015; 33(2):615-24 [PubMed] Related Publications
The CX3CR1/CX3CL1 axis is involved in the metastasis and prognosis of many types of cancer; however, whether CX3CR1 is expressed in gastric cancer cells and whether it participates in gastric cancer metastasis remain unknown. We investigated the expression of CX3CR1 in gastric cancer tissues and non‑neoplastic gastric tissues in vivo and in gastric cancer cell lines and a gastric epithelial cell line in vitro, and then the functional roles of CX3CR1 in cellular metastasis, proliferation and survival were explored. We observed that CX3CR1 was highly expressed in gastric cancer tissues in vivo and was related to lymph node metastasis, higher clinical TNM stage and larger tumor size. In vitro, CX3CR1 overexpression promoted gastric cancer cell migration, invasion, proliferation and survival. Additionally, different from several chemokine receptors, CX3CR1 was also expressed in non-neoplastic gastric tissues and in gastric epithelial cells and played a functional role in vitro. Notably, gastric cancer tissues expressed higher CX3CR1 compared with that in the non-neoplastic gastric tissues in vivo, while in vitro, CX3CR1 expresssion in the gastric cancer cell lines was equivalent or significantly lower than that in the gastric epithelial cell line, which suggests that the high expression of CX3CR1 in gastric cancer in vivo might be induced, not constitutive. Altogether, our findings suggest that on the one hand overexpression of CX3CR1 promoted gastric cancer metastasis, proliferation and survival; on the other hand, appropriate expression of CX3CR1 in normal gastric tissues may play a physiological role in tissue remodeling after injury and/or epithelial renewal. Additionally, the tumor microenvironment may play an important role in the high expression of CX3CR1 in gastric cancer cells.

Shi JY, Yang LX, Wang ZC, et al.
CC chemokine receptor-like 1 functions as a tumour suppressor by impairing CCR7-related chemotaxis in hepatocellular carcinoma.
J Pathol. 2015; 235(4):546-58 [PubMed] Related Publications
Atypical chemokine receptors (ACRs) have been discovered to participate in the regulation of tumour behaviour. Here we report a tumour-suppressive role of a novel ACR member, CC chemokine receptor like 1 (CCRL1), in human hepatocellular carcinoma (HCC). Both mRNA and protein expressions of CCRL1 correlated with the malignant phenotype of HCC cells and were significantly down-regulated in tumour tissue compared with paired normal liver tissue. In both the initial and validation cohorts (n = 240 and n = 384, respectively), CCRL1 deficiency was associated with advanced tumour stage and was an independent index for worse survival and increased recurrence. Furthermore, knock-down or forced expression of CCRL1 revealed that CCRL1 suppressed the proliferation and invasion of HCC cells in vitro and reduced tumour growth and lung metastasis in vivo, with depressed levels of CCL19 and CCL21. By sequestrating CCL19 and CCL21, CCRL1 reduced their binding to CCR7 and consequently mitigated the detrimental impact of CCR7, including Akt-GSK3β pathway activation and nuclear accumulation of β-catenin in tumour cells. Clinically, the prognostic value of the CCR7 expression in HCC depended on the expression level of CCRL1, suggesting that CCRL1 may serve as an upstream switch for the CCR7 signalling cascade. Together, our findings suggest that CCRL1 impairs chemotactic events associated with CCR7 in the progression and metastasis of HCC. Our results also show a potential interplay between typical and atypical chemokine receptors in human cancer. Copyright © 2014 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

Gutknecht MF, Bouton AH
Functional significance of mononuclear phagocyte populations generated through adult hematopoiesis.
J Leukoc Biol. 2014; 96(6):969-80 [PubMed] Free Access to Full Article Related Publications
Tissue homeostasis requires a complete repertoire of functional macrophages in peripheral tissues. Recent evidence indicates that many resident tissue macrophages are seeded during embryonic development and persist through adulthood as a consequence of localized proliferation. Mononuclear phagocytes are also produced during adult hematopoiesis; these cells are then recruited to sites throughout the body, where they function in tissue repair and remodeling, resolution of inflammation, maintenance of homeostasis, and disease progression. The focus of this review is on mononuclear phagocytes that comprise the nonresident monocyte/macrophage populations in the body. Key features of monocyte differentiation are presented, focusing primarily on the developmental hierarchy that is established through this process, the markers used to identify discrete cell populations, and novel, functional attributes of these cells. These features are then explored in the context of the tumor microenvironment, where mononuclear phagocytes exhibit extensive plasticity in phenotype and function.

Hattermann K, Sebens S, Helm O, et al.
Chemokine expression profile of freshly isolated human glioblastoma-associated macrophages/microglia.
Oncol Rep. 2014; 32(1):270-6 [PubMed] Related Publications
Several studies have substantiated the hypothesis that tumor progression is not only driven by the tumor cells themselves but also by their interaction with intrinsic and surrounding stromal cells. Tumor-associated macrophages and microglial cells (TAMs) represent one major stromal cell component of glioblastomas. Additionally, in many gliomas, chemokines are highly expressed and some chemokines were already linked to settlement of TAMs in tumors. However, although chemoattraction mechanisms mediated by chemokines and their receptors are well documented, information on their expression and role in TAMs, particularly in patients, is limited. Therefore, we investigated the transcription of the chemokine-receptor combinations CXCL12-CXCR4-CXCR7, CXCL16-CXCR6 and CX3CL1-CX3CR1 in freshly isolated TAMs from 20 human glioblastomas in relation to in vitro polarized M1- and M2-macrophages. We demonstrated that TAMs express both M1- and M2-markers. Compared to in vitro polarized macrophages, the M1-marker interleukin (IL)-6 was similarly expressed, whereas IL-1β and tumor necrosis factor (TNF)-α were found at lower levels. The M2-marker IL-10 was comparably expressed, while CD163 and transforming growth factor (TGF)-β were detected with one tenth lower intensities in TAMs. All investigated chemokines/receptors were transcribed at moderate to high levels in TAMs as well as in vitro polarized macrophages. However, CX3CR1 was markedly higher and CXCR7 was somewhat higher expressed in TAMs, whereas M2-macrophages were characterized by the highest CXCL12 and a moderate CX3CL1 expression. Collectively, TAMs share properties of M1- and M2-macrophages and show a considerably higher expression of the chemokine receptors CXCR7 and CX3CR1.

Lv CY, Zhou T, Chen W, et al.
Preliminary study correlating CX3CL1/CX3CR1 expression with gastric carcinoma and gastric carcinoma perineural invasion.
World J Gastroenterol. 2014; 20(15):4428-32 [PubMed] Free Access to Full Article Related Publications
AIM: To study the relationship between the CX3CL1 chemokine, its receptor CX3CR1, and gastric carcinoma/gastric carcinoma perineural invasion (PNI).
METHODS: Thirty cases of gastric carcinoma were surgically resected (radical resection or palliative resection) between February 2012 and July 2012. Tumour and tumour-adjacent tissues were evaluated for the presence of CX3CL1 (ELISA) and CX3CR1 (immunohistochemistry and Western blotting) in an effort to analyse the relationship between CX3CL1/CX3CR1 and gastric carcinoma/gastric carcinoma PNI.
RESULTS: Of these 30 cases, 14 were PNI-positive (46.7%). No significant differences in CX3CL and CX3CR1 expression in tumour-adjacent tissues were found between the PNI positive and negative groups. Expression levels of CX3CL and CX3CR1 in tumour tissues were significantly higher than those in adjacent tissues (P < 0.01), and were significantly higher in tumour tissues from the PNI-positive group compared to the PNI-negative group (P < 0.01).
CONCLUSION: CX3CL1/CX3CR1 expression may be associated with the occurrence and development of gastric carcinoma as well as gastric carcinoma PNI.

Ren H, Zhao T, Sun J, et al.
The CX3CL1/CX3CR1 reprograms glucose metabolism through HIF-1 pathway in pancreatic adenocarcinoma.
J Cell Biochem. 2013; 114(11):2603-11 [PubMed] Related Publications
One of the hallmarks of cancer is revised glucose metabolism that promotes cell survival and proliferation. In pancreatic cancer, the regulatory mechanism of glucose metabolism remains to be elucidated. In this study, we found that CX3CR1 is expressed in pancreatic cancer cells lines. Exogenous or transfected CX3CL1 increased glucose uptake and lactate secretion. CX3CL1 stimulated HIF-1 expression through PI3K/Akt and MAPK pathways. Furthermore, knockdown of HIF-1 blocked CX3CL1-modified glucose metabolism in pancreatic adenocarcinoma cells. In conclusion, the CX3CL1/CX3CR1 reprograms glucose metabolism through HIF-1 pathway in pancreatic cancer cells.

Hattermann K, Li G, Hugo HH, et al.
Expression of the chemokines CXCL12 and CX3CL1 and their receptors in human nerve sheath tumors.
Histol Histopathol. 2013; 28(10):1337-49 [PubMed] Related Publications
Peripheral nerve sheath tumors are in most cases slowly growing neoplasms that can be adequately cured by surgical resection. However, facing the risk of a neurosurgical intervention and the trend of multiple relapses of nerve sheath tumors the development of additional therapy strategies seems to be favourable, and therefore substantiated knowledge of molecular and cellular mechanisms in nerve sheath tumors should be achieved. Here, we firstly describe the expression of the chemokines CXCL12 (SDF-1) and CX3CL1 (fractalkine) and their respective receptors CXCR4, CXCR7 and CX3CR1 in different entities of human nerve sheath tumors and normal control tissues. Both ligands and their receptors are expressed in high to moderate levels on mRNA and protein level in benign and malignant nerve sheath tumors. While CXCL12 was mainly found in schwannoma cells (S100⁺) in situ, its receptor CXCR4 is also partly found on CD11b-positive macrophages / microglia and its alternative receptor CXCR7 is also expressed by endothelial cells and macrophages. CX3CL1 is expressed by parts of the schwannoma and endothelial cells, whereas its receptor CX3CR1 is expressed by nearly all tumor cells and macrophages, but not by endothelial cells. Taken together, we could show the presence of CXCL12 and CX3CL1 and their respective receptors in benign and malignant human nerve sheath tumors. Further investigations may show their functional role in health and disease.

Courivaud C, Bamoulid J, Loupy A, et al.
Influence of fractalkine receptor gene polymorphisms V249I-T280M on cancer occurrence after renal transplantation.
Transplantation. 2013; 95(5):728-32 [PubMed] Related Publications
BACKGROUND: Fractalkine (CX3CL1) and its receptor (CX3CR1) are involved in antitumor immunity. Two common single nucleotide polymorphisms of the CX3CR1 gene, V249I and T280M, have been associated with reduced fractalkine signaling characterized by decreased adhesive function, signaling, and chemotaxis of leukocytes. We hypothesized that a renal transplant recipient (RTR) carrying the homozygous I249M280 genotype could experience more cancer due to lower CX3CL1-dependent antitumorigenic effects.
METHODS: We studied the association between these polymorphisms and cancer incidence in two independent cohorts of RTR, including a total of 622 patients.
RESULTS: The median follow-up was 8.7 and 7.9 years for the first and second cohorts, respectively. Analysis of 622 patients identified 20 (3.2%) I249M280 homozygous patients, 321 (51.6%) V249T280 homozygous patients, and 281 (45.2%) heterozygous patients. I249M280 homozygotes have an independent increased risk of cancer (hazard ratio [95% confidence interval], 3.3 [1.04-10.52], P=0.043 for cohort 1 and 9.2 [1.67-50.91], P=0.011 for cohort 2) compared with other patients. Age and male gender were also risk factors for cancer occurrence.
CONCLUSIONS: CX3CR1 gene polymorphism is associated with a higher rate of cancer in RTRs. Such findings may be used to influence immunosuppressive strategies and optimize patient management.

Zhao T, Gao S, Wang X, et al.
Hypoxia-inducible factor-1α regulates chemotactic migration of pancreatic ductal adenocarcinoma cells through directly transactivating the CX3CR1 gene.
PLoS One. 2012; 7(8):e43399 [PubMed] Free Access to Full Article Related Publications
CX3CR1 is an important chemokine receptor and regulates the chemotactic migration of pancreatic ductal adenocarcinoma (PDAC) cells. Up to now, its regulatory mechanism remains largely undefined. Here, we report that hypoxia upregulates the expression of CX3CR1 in pancreatic cancer cells. When hypoxia-inducible factor (HIF)-1α expression was knocked down in vitro and in vivo, the expression of CX3CR1 was significantly decreased. Chromatin immunoprecipitation assay demonstrated that HIF-1α bound to the hypoxia-response element (HRE; 5'-A/GCGTG-3') of CX3CR1 promoter under normoxia, and this binding was significantly enhanced under hypoxia. Overexpression of HIF-1α significantly upregulated the expression of luciferase reporter gene under the control of the CX3CR1 promoter in pancreatic cancer cells. Importantly, we demonstrated that HIF-1α may regulate cancer cell migration through CX3CR1. The HIF-1α/CX3CR1 pathway might represent a valuable therapeutic target to prevent invasion and distant metastasis in PDAC.

Xiao LJ, Chen YY, Lin P, et al.
Hypoxia increases CX3CR1 expression via HIF-1 and NF‑κB in androgen-independent prostate cancer cells.
Int J Oncol. 2012; 41(5):1827-36 [PubMed] Related Publications
The unique CX3C chemokine CX3CL1 and its cognate receptor CX3CR1 have been implicated in organ-specific metastasis of various types of tumors. Hypoxia, a common phenomenon in solid tumors, is associated with a malignant cancer phenotype. Previous studies have proved that hypoxia facilitates cancer cell metastasis through upregulation of specific chemokine receptors. We hypothesized that hypoxia could upregulate CX3CR1 expression and lead to an increased chemotactic response to CX3CL1 in prostate cancer cells. In the present study, we found that CX3CR1 expression was significantly increased in androgen-independent prostate cancer cells, including DU145, PC-3 and PC-3M, following exposure to hypoxia. This upregulation of CX3CR1 corresponded to a significant increase in migration and invasion of prostate cancer cells under hypoxic conditions, which was attenuated after knocking down CX3CR1 expression. In addition, we examined the possible role of HIF-1 and NF-κB in the process of hypoxia-induced CX3CR1 expression and hypoxia-mediated metastasis. Attenuation of HIF-1 and NF-κB transcriptional activity by siRNAs or pharmacological inhibitors, abrogated hypoxia-induced upregulation of CX3CR1, and also prevented the migration and invasion of DU145 cells under a hypoxic environment. In summary, our study demonstrated that HIF-1 and NF-κB are essential for hypoxia-regulated CX3CR1 expression, which is associated with increased migratory and invasive potential of prostate cancer cells. CX3CR1 signaling is a potential therapeutic target in the adjuvant treatment of prostate cancer.

Kim M, Rooper L, Xie J, et al.
Fractalkine receptor CX(3)CR1 is expressed in epithelial ovarian carcinoma cells and required for motility and adhesion to peritoneal mesothelial cells.
Mol Cancer Res. 2012; 10(1):11-24 [PubMed] Free Access to Full Article Related Publications
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.

Eckl J, Buchner A, Prinz PU, et al.
Transcript signature predicts tissue NK cell content and defines renal cell carcinoma subgroups independent of TNM staging.
J Mol Med (Berl). 2012; 90(1):55-66 [PubMed] Related Publications
Clear cell renal cell carcinoma (ccRCC) is an aggressive and difficult to manage cancer. Immunotherapy has the potential to induce long-lasting regression in a small group of patients. However, severe side effects limit broad application which highlights the need for a marker to distinguish responder from nonresponder. TNMG staging, referring to tumor size, lymph node involvement, presence of metastasis, and grade of tumor differentiation, represents an important prognostic system but is not useful for predicting responders to immunotherapy. NK cells are potent antitumor effector cells, and a role as prognostic marker in some solid tumors has been suggested. As NK cells are responsive to various immune modifiers, they may be important mediators of patient response to immunotherapies, in particular those including IL-2. We report that the NK cell percentage within RCC-infiltrating lymphocytes, as determined by flow cytometry, allows ccRCC subgrouping in NK(high)/NK(low) tissues independent of TNMG classification. Quantitative reverse transcriptase polymerase chain reaction using whole-tissue RNA identified four markers (NKp46, perforin, CX(3)CL1, and CX(3)CR1) whose transcript levels reproduced the NK(high)/NK(low) tissue distinction identified by flow cytometry with high selectivity and specificity. Combined in a multiplex profile and analyzed using neural network, the accuracy of predicting the NK(high)/NK(low) groups was 87.8%, surpassing that of each single marker. The tissue transcript signature, based on a robust high-throughput methodology, is easily amenable to archive material and clinical translation. This now allows the analysis of large patient cohorts to substantiate a role of NK cells in cancer progression or response to immunotherapy.

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