Plasma membrane and intracellular pools of transferrin receptors decline during in vitro cultivation of U937 cells.
Transferrin receptor expression in the monocyte-like cell line U937 was investigated during in vitro cultivation. U937 cells expressed a single class of high affinity surface transferrin receptors (KD approximately 4 nM), with apparent subunit Mr of 90-95,000 Da as determined by SDS-reducing PAGE. [125I]-transferrin binding studies on detergent-solubilized cells revealed that half to two-thirds of the total functional binding sites were located intracellularly. Radioligand binding, immunofluorescence and flow cytometry studies were performed on intact, detergent-solubilized, or saponin-permeabilized cells, using either transferrin or the anti-transferrin receptor monoclonal antibody OKT9 IgG. These studies demonstrated that functional and antigenic transferrin receptor levels were maximal on cells 24 h after subculture at low density and declined during the culture period. Scatchard analysis of radioligand binding data suggested that the decline in functional transferrin binding sites resulted from a decline in the number of available receptors. These results demonstrate that in U937 cells there is a density-dependent regulation of transferrin receptor expression, resulting in a loss of functional and antigenic receptors from both plasma membrane and intracellular locations.
Salcedo
T W
TW
Department of Pathology, State University of New York, Stony Brook 11794-8691.
Fleit
H B
HB
D002455:Cell Division; D002460:Cell Line; D002462:Cell Membrane / Q000378:metabolism*; D005434:Flow Cytometry; D005455:Fluorescent Antibody Technique; D006801:Humans; D007457:Iodine Radioisotopes; D007700:Kinetics; D016403:Lymphoma, Large B-Cell, Diffuse; D011869:Radioligand Assay; D011990:Receptors, Transferrin / Q000378:metabolism*; D014168:Transferrin / Q000378:metabolism
D007457:Iodine Radioisotopes; D011990:Receptors, Transferrin; D014168:Transferrin