Acquired melanocyte stimulating hormone-inducible chemotaxis following macrophage fusion with Cloudman S91 melanoma cells.

Fusion of Cloudman S91 melanoma cells with macrophages results in hybrids with increased metastatic potential. Here, we report that such hybrids acquire new pathways for motility. Compared to parental melanoma cells and low metastatic hybrids, the metastatic hybrids showed far stronger responses to 3T3- and lung fibroblast-conditioned media, primary lung slices, fibronectin (FN), and a Mr 120,000 FN fragment and, unlike parental cells, were further stimulated by pretreatment with melanocyte-stimulating hormone/1-methyl-3-isobutylxanthine. Hybrid migration was due primarily to chemotaxis, with chemokinesis being a minor component. Thus, the metastatic hybrids acquired melanocyte-stimulating hormone-inducible motility, perhaps reflecting the FN fragment chemotaxis of macrophages. The results support a long-standing hypothesis that metastasis is initiated following hybridization between tumor-invading phagocytes and cells of the primary tumor.