Iron is taken into proliferating eukaryotic cells via a high affinity receptor for the serum iron-carrying protein transferrin. The transferrin receptor is an integral membrane glycoprotein for which synthesis, degradation, and dynamics are highly regulated. Iron availability modulates the expression of the transferrin receptor in a number of cell types including K562 cells, a human erythroleukemia line. The rate of receptor biosynthesis has been found to be decreased when iron is provided to cells and to be increased when iron is provided to cells and to be increased when intracellular iron is chelated. The cellular distribution of the receptor and its rate of degradation have been shown to be affected by exposure of K562 cells to a monoclonal antibody recognizing the human tansferrin receptor. Using a cDNA probe for the receptor, clones have been isolated from a human genomic library constructed in lambda bacteriophage. One such genomic clone (termed LambdaTR4) has been characterized as representing the 5' portion of the human transferrin receptor gene including the promoter region, exon 1, and a portion of intron 1. A variety of chimeric constructs have been produced in which regions of LambdaTR4 are linked to the bacterial gene for chloramphenicol acetyl transferase (CAT). By transfecting these CAT constructs into CAT-recipient cells, two regions of LambdaTR4 have been implicated as being important in gene expression.
