Expression of CX3CR1 associates with cellular migration, metastasis, and prognosis in human clear cell renal cell carcinoma.

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.