Enhancement by retinoic acid of the sensitivity of different tumor cell lines to the sialic acid-specific toxin of Entamoeba histolytica.

Treatment of several tumor cell lines, including the murine melanomas B16 and S91 and the human sarcoma Hs791 and Hs705, with retinoic acid resulted in an increased sialylation of specific cell surface membrane sialoglycoproteins. This treatment also augmented the sensitivity of these cells to the cytopathic effects of a sialic acid-specific toxin from Entamoeba histolytica. In contrast, a similar treatment with retinoic acid of a retinoic acid-resistant mutant clone S91-C154, which does not increase sialylation of cell surface glycoproteins, failed to alter the susceptibility of the cells to the E. histolytica toxin. These results imply that cell surface sialoglycoproteins serve as receptors for the amoebic toxin.