Expression of TfR2 mRNA in MEL cells during erythrocytic differentiation and in response to iron status.

(A) Expression of TfR2 mRNA during differentiation of MEL cells. MEL cells were cultured in the presence of 2% DMSO, 75 μM hemin, 2% DMSO + 75 μM hemin, or 2% DMSO + 10⁻⁷ M dexamethasone (Dex) for 5 days. Upper panel shows the hemoglobin concentration in the cell lysates. Hemoglobin concentration was determined by the benzidine method and shown as a percentage of total cellular lysate. Lower panel shows the results of Northern blot analysis. Approximately 20 μg total RNA was loaded in each lane. The membrane was sequentially hybridized with³²P-labeled murine TfR1, TfR2 (3′-part, 1.4 kb), and murine GAPDH cDNA probes. (B) Effects of cellular iron status on expression of murine Tf receptors in MEL cells. MEL cells were cultured with various concentrations of Fe₂(NO₃)₃ or DFO for 2 days, and Northern blot analysis was performed. The membrane was sequentially hybridized with ³²P-labeled murine TfR1, TfR2, and GAPDH cDNA probes. (A-B) Relative expression levels of TfRs are calculated by an image analyzer, standardized by the values of GAPDH, and shown as bar graphs (■, TfR1;, TfR2).