1524

CX3CR1

chemokine (C-X3-C motif) receptor 1;CX3CR1;chemokine (C-X3-C motif) receptor 1

C-X3-C CKR-1|CMK-BRL-1|CMK-BRL1|CX3C chemokine receptor 1|G protein-coupled receptor 13|G-protein coupled receptor 13|beta chemokine receptor-like 1|chemokine (C-C) receptor-like 1|chemokine (C-X3-C) receptor 1|fractalkine receptor

3p21.3

protein-coding

OBJECTIVES: The identification of critical proteins regulating cancer cell metastasis, in clear cell renal cell carcinoma (CCRCC), is important for prediction of prognosis, prevention of metastasis, and treatment of this lethal malignancy. In the present study, we evaluated the role of CX3CR1 in cellular adhesion, migration, and metastasis in CCRCC. We further investigated the downstream molecular signaling mechanism of fractalkine (FKN)-CX3CR1-induced migration and metastasis. MATERIALS AND METHODS: The expression and localization of CX3CR1 in RCC cell lines were assessed by immunofluorescence analysis. The migration of cancer cells was examined by wound healing and transwell migration assay. The expression level of CX3CR1 and FKN in 78 CCRCC individual samples, 16 normal kidney cortex tissue samples, and 16 cases of metastatic lesions of CCRCC were evaluated using immunohistochemical analysis on tissue microarray. The signal pathway of functional FKN was analyzed by the use of the western-blotting method and inhibitory migration assay. RESULTS: CX3CR1 was expressed in human RCC cell lines, and only membrane positive cells were responsible for FKN-induced cell migration. Extracellular signal-related kinases (ERK1/2) and phosphatidyl-inositide 3 kinase/Akt (PI3K/Akt) were each activated upon soluble FKN stimulation in a time-dependent manner, whereas blockades of MEK, PI3K, and G proteins prevented FKN-mediated cellular migration. Furthermore, CCRCC tissue microarray immunohistochemistry data revealed a clear association of strong CX3CR1 expression with tumor metastasis and poor prognosis. CONCLUSIONS: CX3CR1 expression is associated with the process of cellular migration in vitro and tumor metastasis of CCRCC in vivo. Both clinical and molecular cellular evidence suggest that CX3CR1 is a potential marker and therapeutic target for CCRCC prognostic prediction and treatment.

BACKGROUND: Macrophages, the key component of the tumor microenvironment, are differentiated mononuclear phagocyte lineage cells that are characterized by specific phenotypic characteristics that have been implicated in tumor growth, angiogenesis, and invasion. CX3CR1, the chemoattractant cytokine CX3CL1 receptor, plays an important role in modulating inflammatory responses, including monocyte homeostasis and macrophage phenotype and function. However, the role of CX3CR1 in the regulation of the tumor inflammatory microenvironment is not fully understood. METHODS: Using in vivo hepatic metastasis model, human colon carcinoma specimens, immunohistochemical staining, TUNEL staining, flow cytometry analysis, Western blotting assay and co-culture in three-dimensional peptide gel, we determined the effects of CX3CR1 on angiogenic macrophage survival and tumor metastasis. RESULTS: In this study, we found that CX3CR1 was expressed in human colon carcinomas in a histologic grade- and stage-dependent manner, and CX3CR1 upregulation in TAMs was correlated with poor prognosis. Furthermore, we showed that in a microenvironment lacking CX3CR1, the liver metastasis of colon cancer cells was significantly inhibited. The underlying mechanism is associated with decrease accumulation of angiogenic macrophages that can be partly attributed to increased apoptosis in the tumor microenvironment, thus leading to impaired tumor angiogenesis in the liver and suppressed tumor metastasis. CONCLUSIONS: Our results suggest a role of CX3CR1 in angiogenic macrophage survival in the tumor microenvironment contributing to tumor metastasis.

metastatic diffusion is a major adverse prognostic determinant in lung cancer, that is ultimately responsible for significant morbidity, organ failure and death. Chemokine signaling pathways are known to guide site-specific metastatic spread in solid tumours. However, little is known about the contribution of CX3CR1 in the systemic dissemination of lung cancer. Syngeneic primary lung cancer/metastasis tissue microarray slides were constructed using 98 post-mortem specimens taken from patients with untreated lung cancer and immunostained for CX3CR1. Clinicopathological correlation between CX3CR1 expression and patient demographics, tumour histology, stage and pattern of metastatic spread was performed using chi2 test. CX3CR1 immunopositivity was significantly higher in non-small cell lung cancer (NSCLC) compared to small cell (SCLC) primary (p<0.001) and secondary tumours (p<0.001), with >75% of the metastatic sites staining positively in NSCLC. CX3CR1 positivity was significantly associated with stage and number of metastatic sites (p=0.03). At patients' death CX3CR1-negative lung adenocarcinomas were more likely to have spread to the brain and the liver (p=0.01). CX3CR1 is upregulated in NSCLC metastatic disease and its expression in primary lung tumours relates inversely to organotropic spread of cancer cells to the brain and the liver.

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.