Lectin binding is known to be able to elicit signalling events relevant for various aspects of cell physiology. The influence of lectin binding on melanoma cells remains relatively unexplored. The aim of our study was to investigate the in vitro effects of five plant lectins, namely peanut (PNA), wheat germ (WGA), concanavalin A (Con-A), Griffonia simplicifolia (GSA-IA4) and Phaseolus vulgaris (PHA-L) agglutinins, on the cell proliferation of melanoma cell lines (SK-MEL-28, HT-144 and C32) cultured in media supplemented with either 10 or 1 fetal calf serum (FCS). Cell proliferation was assessed by means of the tetrazolium derivative reduction (MTT) assay. Four lectin concentrations were tested, namely 0.05, 0.5, 5 and 50 ug/ml, in four experimental settings, namely 1, 3, 5 and 7 days after the addition of each lectin to the culture media. Determination of the cell gain compartment (percentage of cells in the S and G2 phases of the cell cycle) was done by means of digital cell image analysis assessed on Feulgen-stained nuclei. Our results demonstrated that of the five lectins under study, four had a globally significant dose-dependent toxic effect on melanoma cell proliferation. The fifth lectin, PNA, had a significant stimulatory effect on the C32 cell line. Low doses of lectins may produce a transient increase in cell proliferation. Increasing the FCS from 1 to 10 in the culture media significantly antagonized lectin-induced toxicity in the three cell lines. The cell kinetics measurements showed that the inhibition of cell growth was merely due to cell death. The present data strongly suggest that some lectins might influence the proliferation of melanoma cells. In addition, because lectins are present in our diet and are able to pass into the systemic circulation, we speculate that lectins may exert an influence on melanoma growth under clinical conditions.
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