Plasma membrane and intracellular pools of transferrin receptors decline during in vitro cultivation of U937 cells

Abstract

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.

Improvement in Peptide Detection for Proteomics Analyses Using NanoLC−MS and High-Field Asymmetry Waveform Ion Mobility Mass Spectrometry

“…Previous reports have indicated this protein to be downregulated in macrophage following cell differentiation . It is noteworthy that CD71 is expressed at levels less than 50 000 copies/cell as reported from Scatchard analyses c shows the extracted in chromatogram for peptide ion m / z 684.4, which exhibit a 3.5-fold higher abundance in the macrophage compared to the monocyte cell extract.…”

“…39 It is noteworthy that CD71 is expressed at levels less than 50 000 copies/cell as reported from Scatchard analyses. 40 Figure 9c shows the extracted in chromatogram for peptide ion m/z 684.4, which exhibit a 3.5-fold higher abundance in the macrophage compared to the monocyte cell extract. This peptide was identified as LLTSFLPAQLLR and was unambiguously assigned to CD98, a galectin-binding receptor present in both monocytes and macrophages.…”

Low levels of poliovirus replication in primary human monocytes: possible interactions with lymphocytes

“…Washed blood cells were divided into two samples (106 cells each) and each sample was stained in three sequential staining and rinsing steps [8,39]. One sampte was used for a negative control (using isotype matched mAbs) and the other was the experimental.…”

Possible role of membrane gamma-glutamyltransferase activity in the facilitation of transferrin-dependent and -independent iron uptake by cancer cells.

“…After 24 h, cells were incubated in RPMI containing BSA 0.1%, at 37°C for 45 min, in order to allow the detachment of bovine Tf contained in FCS [37]. After changing the medium with fresh RPMI/BSA 0.1%, 4 μl/ml of the 55 Fe-Tf solution were added to cell cultures and the incubations were prolonged at 37°C for 2.5 h. Control samples were mantained at 4°C, i.e.…”