Salcedo T W, Fleit H B
Department of Pathology, State University of New York, Stony Brook 11794-8691.
Cell Prolif. 1991 Jul;24(4):383-401. doi: 10.1111/j.1365-2184.1991.tb01167.x.
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.
在体外培养过程中，研究了单核细胞样细胞系U937中转铁蛋白受体的表达情况。U937细胞表达一类单一的高亲和力表面转铁蛋白受体（解离常数约为4 nM），通过SDS还原PAGE测定，其亚基的表观分子量为90 - 95,000 Da。对去污剂溶解的细胞进行的[125I] - 转铁蛋白结合研究表明，总功能结合位点的一半至三分之二位于细胞内。使用转铁蛋白或抗转铁蛋白受体单克隆抗体OKT9 IgG，对完整细胞、去污剂溶解的细胞或皂角苷通透的细胞进行了放射性配体结合、免疫荧光和流式细胞术研究。这些研究表明，在低密度传代培养24小时后的细胞上，功能性和抗原性转铁蛋白受体水平最高，并在培养期间下降。对放射性配体结合数据的Scatchard分析表明，功能性转铁蛋白结合位点的减少是由于可用受体数量的下降所致。这些结果表明，在U937细胞中，转铁蛋白受体的表达存在密度依赖性调节，导致质膜和细胞内位置的功能性和抗原性受体均丧失。
