Two genetic loci participate in the regulation by iron of the gene for the human transferrin receptor.

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Abstract
Iron regulation of the human transferrin receptor gene was examined in murine cells transformed with chimeric constructs containng the human transferrin receptor gene''s promoter and either the structural gene for bacterial chloramphenicol acetyltransferase or the human transferrin receptor cDNA. The activity of the transferrin receptor gene''s promoter with the heterologous indicator gene was found to be $ 3-fold higher in cells treated with the iron chelator desferioxamine than in cells treated with the iron source, hemin. A higher degree of iron regulation was seen in the expression of the human transferrin receptor cDNA driven by its own promoter. The receptor cDNA under the control of the simian virus 40 early promoter was iron-regulated. Several human transferrin receptor transcripts differing in the 3'' end were produced in the murine cells regardless of the promoter used, with the shorter transcripts being relatively unregulated by iron. Deletion of cDNA corresponding to most of the 3'' untranslated portion of the mRNA for the receptor ablated the iron regulation. We conclude that at least two genetic elements exist for the regulation of the transferrin receptor gene by iron. One has its locus in the DNA upstream of the transferrin receptor gene transcription start site, and the other is dependent upon the integrity of the sequences in the 3'' end of the gene.