Possible role of galectin‐9 in cell aggregation and apoptosis of human melanoma cell lines and its clinical significance

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Abstract
Galectin‐9 expression was examined in 6 human melanoma cell lines. Among them, MM‐BP proliferated with colony formation, but MM‐RU failed. RT‐PCR analysis revealed evident expression of galectin‐9 mRNA in MM‐BP but not in MM‐RU. MM‐BP expressed galectin‐9 protein both on the surface and in the cytoplasm, whereas MM‐RU expressed it only weakly in the cytoplasm. Exogenous galectin‐9 induced in vitro both cell aggregation and apoptosis of MM‐RU proliferating without colony formation. Association of galectin‐9 expression in melanoma cells with prognosis of the patients bearing melanocytic tumors was further examined. Galectin‐9 protein was strongly and homogeneously expressed in melanocytic nevi, but down‐regulated in melanoma cells especially in metastatic lesions. High galectin‐9 expression was inversely correlated with the progression of this disease, suggesting that high galectin‐9 expression in primary melanoma lesions links to a better prognosis.