C-X-C Motif Ligand 1 (CXCL1) from melanoma cells down-regulates the invasion of their metastatic melanoma cells

The surgical resection of a primary melanoma is sometimes followed by the immediate development of distant metastases, suggesting that the primary melanoma might control the metastatic process. We hypothesized that a paracrine factor(s) from primary melanoma cells might regulate the progression of metastasizing melanoma cells. Here we attempted to identify the factor(s) from primary melanoma cells that regulate the invasion ability of metastatic melanoma cells. We used two mouse melanoma cell lines, B16 and B16/BL6, that latter of which is a subline of B16 melanoma and shows high metastatic potential to lung. We investigated the interaction between the parent B16 cells and daughter B16/BL6 cells by invasion assay, cell morphology, cytokine array, RT-PCR, and gelatin-zymography. The conditioned medium (CM) from B16 significantly (p=0.02) inhibited the invasion ability of B16/BL6 cells. The morphology of the B16/BL6 cells was changed from bipolar shape to a multipolar shape following the addition of the CM from B16. The B16 cells produced high levels of C-X-C motif ligand 1 (CXCL1), CXCL10, and M-CSF compared to the B16/BL6 cells. CXCL1 significantly (p=0.01) decreased the invasion ability of B16/BL6 cells, but CXCL10 and M-CSF did not. The invasion-inhibitory activity of the CM from B16 was significantly (p=0.046) suppressed following the addition of a neutralizing anti-CXCL1 antibody. The CM of B16 and CXCL1 increased the E-cadherin mRNA level and decreased MMP2 activity of B16/BL6 cells. These findings suggested that primary melanoma cells might down-regulate the invasion activity of metastatic melanoma cells through CXCL1 signaling.