Differential expression of chemokine receptors on uveal melanoma cells and their metastases

PURPOSE. To determine the expression of the chemokine receptors CXCR4 and CCR7 on human uveal melanoma cells and their metastases and the effect of liver-borne factors on the chemotactic responses of uveal melanoma cells. METHODS. Four human uveal melanoma cell lines and three cell lines of uveal melanoma metastases were examined by RT-PCR and flow cytometry for their constitutive expression of CXCR4 and CCR7. The effect of the liver and liver-borne factors on the expression of CXCR4 and CCR7 was determined after intracameral, intrasplenic, and subcutaneous transplantation of uveal melanoma cells in nude mice. Chemotactic responses of melanoma cells to liver-borne factors were determined by in vitro chemotaxis assays using protein extracts of hepatocytes and striated muscle tissue. RESULTS. All the primary uveal melanoma cell lines expressed CXCR4 and CCR7 message and protein, whereas the metastases cell lines expressed little or no chemokine receptor. Extracts of human liver cells stimulated chemotaxis of uveal melanoma cells, which could be inhibited by anti-CXCR4 antibody. Liver-borne factors also induced the downregulation of CXCR4 and CCR7 on uveal melanoma cells. Uveal melanoma cells maintained their high expression of CXCR4 and CCR7 after intracameral transplantation. However, CXCR4 and CCR7 expression was sharply reduced in liver metastases arising from intraocular melanomas. CONCLUSIONS. CXCR4 and CCR7 provide directional migration of uveal melanoma cells toward the liver, the most common site for the formation of uveal melanoma metastases. However, soluble factors elaborated by hepatocytes induce the downregulation of CXCR4 and CCR7 on metastatic uveal melanoma cells.