Identification of an Erythroid Active Element in the Transferrin Receptor Gene

Hemoglobin synthesis consumes most of the iron that is taken up by cells from plasma transferrin, and this process requires very high expression of transferrin receptors (TfR) at the membranes of erythroid cells. Studies in our and other laboratories indicate that a dramatic increase in TfR levels during erythroid differentiation occurs at the transcriptional level. In this 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 stimulated 6 -8-fold in murine erythroleukemia cells induced to differentiate into hemoglobinsynthesizing cells by either Me 2 SO or N,N-hexamethylene-bis-acetamide. A minimal region (118 to 14) was required for the differentiation-induced promoter activity. Mutation of either an Ets-binding site or an activator protein-1/cyclic AMP-response element-like motif within this region, but not disruption of the adjacent GC-rich/specificity protein-1 sequence, inhibited the inducible promoter activity. Electrophoresis mobility shift assays suggest that the cyclic AMP-response element-binding proteins/activating transcription factorlike factors and Ets-like factors bind constitutively to this bipartite element. Upon induction of differentiation, a shift in the pattern of the cyclic AMP-response element-binding protein/activating transcription factor-like binding factors was observed. Our data indicate that the TfR gene promoter contains an erythroid active element that stimulates the receptor gene transcription upon induction of hemoglobin synthesis.