Effects of retinoids and phorbol esters on the sensitivity of different cell lines to the polypeptide toxins modeccin, abrin, ricin and diphtheria toxin

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Abstract
The effects of retinoic acid and 12-O-tetradecanoylphorbol-13-acetate [TPA] on the sensitivities of a number of cell lines to the toxins modeccin, abrin, ricin and diphtheria toxin were studied. Retinoic acid and some other retinoids protected a number of the cell lines against the toxins. HeLa [human cervical carcinoma] cells that were protected bound much more retinoic acid than L [mouse neoplastic fibroblast] cells that were not protected. The tumor promoter [TPA] increased the sensitivity of cells to abrin, ricin and modeccin in the absence and in the presence of retinoic acid. Neither retinoic acid nor TPA affected the extent of binding and pinocytotic uptake of toxins by the cells. Apparently retinoic acid and TPA interfere with the entry of the toxins through the cell membrane.