Increased cell surface expression of the
Thomsen-Friedenreich antigen (TF antigen, Galbeta1-3GalNAcalpha-) is a common feature in malignant and pre-malignant epithelia. Our previous studies have shown that dietary TF-binding
lectins from peanut (Arachis hypogea) and edible mushroom (Agaricus bisporus) produce marked but different effects on human intestinal epithelial cell proliferation. This study investigates the proliferative effects of the other two known dietary TF-binding
lectins:
jacalin (Artocarpus integrifolia, JAC) and amaranth
lectin (Amaranthus caudatus, ACA). JAC produced dose-dependent and non-cytotoxic inhibition of proliferation in HT29 human
colon cancer cells with maximal effects of 46 +/- 4% at 20 microg/ml, whereas ACA produced dose-dependent stimulation of proliferation with maximal effects of 22 +/- 3% at 20 microg/ml when assessed both by incorporation of [3H]
thymidine into
DNA and by cell counting. The
lectin-mediated effects were inhibitable by the presence of appropriate Galbeta1-3GalNAc-expressing
glycoproteins but differences existed between JAC and ACA in their patterns of inhibition by such substances.
Ligand binding equilibrium studies using iodinated
lectins revealed different Kd of the two
lectins for HT29 cell
surface glycoproteins.
Lectin blots of cell membrane extracts showed different binding patterns in all the four TF-binding
lectins. These results provide further evidence that dietary TF-binding
lectins can have marked effects on the proliferation of human malignant gastro-intestinal epithelial cells and hence may play a role in
intestinal cancer development, and also show that the
biological effects of dietary
lectins cannot be predicted solely from their
carbohydrate binding properties.