Identification of an erythroid active element in the transferrin receptor gene

Hemoglobin synthesis consumes most of the iron that is taken up by cells fr om plasma transferrin, and this process requires very high expression of tr ansferrin receptors (TfR) at the membranes of erythroid cells. Studies in o ur and other laboratories indicate that a dramatic increase in TfR levels d uring erythroid differentiation occurs at the transcriptional level. In thi s study, we investigated the transcriptional regulation of the TfR in terms of its promoter activity and DNA-protein binding in murine erythroleukemia cells. Reporter gene assays revealed that the TfR promoter activity was st imulated 6-8-fold in murine erythroleukemia cells induced to differentiate into hemoglobin-synthesizing cells by either Me2SO or N,N'-hexamethylene-bi s-acetamide, A minimal region (-118 to +14) was required for the differenti ation-induced promoter activity. Mutation of either an Ets-binding site or an activator protein-1/cyclic AMP-response element-like motif within this r egion, but not disruption of the adjacent GC-rich/specificity protein-1 seq uence, inhibited the inducible promoter activity. Electrophoresis mobility shift assays suggest that the cyclic AMP-response element-binding proteins/ activating transcription factor-like factors and Ets-like factors bind cons titutively to this bipartite element. Upon induction of differentiation, a shift in the pattern of the cyclic AMP-response element-binding protein/act ivating transcription factor-like binding factors was observed. Our data in dicate that the TfR gene promoter contains an erythroid active element that stimulates the receptor gene transcription upon induction of hemoglobin sy nthesis.