title: Dynamics of toxin and lectin receptors on a lymphoma cell line and its toxin-resistant variant using ferritin-conjugated, 125I-labeled ligand.
abstract: The dynamics of the toxin Ricinus communis agglutinin II (RCAII or ricin) on cells of a murine lymphoma line (BW5147) and a toxin-resistant variant line (BW5147RicR.3) that is 200 times more resistant than the parent to direct RCAII cytotoxicity were examined using ferritin-conjugated, affinity purified, 125I-labeled RCAII (ferritin-125I-RCAII). Ferritin-125I-RCAII was indistinguishable from native RCAII in quantitative binding and cytotoxicity experiments. When RCAII-sensitive BW5147 and -resistant BW5147RicR.3 cells were labeled with ferritin-125I-RCAII at various toxin concentrations (1--10 microgram/ml), no differences in toxin binding were observed. These same cells were examined by electron microscopy. At low ferritin-125I-RCAII concentrations (1-3 microgram/ml RCAII) where only the parental BW5147 cells were significantly more sensitive to RCAII, toxin receptors were internalized by ferritin-125I-RCAII-induced endocytosis. In parallel experiments, ferritin-125I-RCAII that bound to the resistant BW5147RicR.3 cells remained relatively dispersed or clustered, and there was little evidence of transport into cells via endocytosis. At higher ferritin-125I-RCAII concentrations (greater than 7 microgram/ml RCAII) where both parental and resistant variant cells are sensitive to the cytotoxic effects of RCAII, more ferritin-conjugated toxin was bound, and subsequent endocytosis occurred to a similar degree in both cell types. Endocytosis of ferritin-conjugated concanavalin A was indistinguishable on RCAII-sensitive parental and resistant variant cells at all concentrations tested. The results suggest that a specific defect on the selected BW5147RicR.3 cells prevents RCAII entry into these cells a low toxin concentrations, rendering them more resistant to the cytotoxic effects of RCAII.
mesh_terms: D000818:Animals; D002460:Cell Line; D003208:Concanavalin A / Q000378:metabolism*; D004351:Drug Resistance; D004705:Endocytosis; D005293:Ferritins; D014644:Genetic Variation; D007457:Iodine Radioisotopes; D008223:Lymphoma; D051379:Mice; D009374:Neoplasms, Experimental; D011952:Receptors, Concanavalin A / Q000378:metabolism*; D011955:Receptors, Drug / Q000378:metabolism*; D012276:Ricin / Q000378:metabolism* / Q000633:toxicity
chemical_list: D007457:Iodine Radioisotopes; D011952:Receptors, Concanavalin A; D011955:Receptors, Drug; D003208:Concanavalin A; D005293:Ferritins; D012276:Ricin