Transferrin (TF), the major iron-binding protein in plasma of vertebrates, plays a vital and central role in iron metabolism. It is a growth factor required for proliferating normal and malignant cells. By virtue of its high affinity for iron, TF limits the availability of the metal to microbial invaders, and thus forms an important part of the bacteriostatic activity of plasma. The liver is the major site of TF synthesis. Research in our laboratory during the past two years has demonstrated the synthesis of TF by the T4 """"""""inducer"""""""" subset of T lymphocytes and identified a heretofore unknown autocrine role of transferrin required for lymphocyte proliferation. TF synthesis has also been detected in bone-forming cells. The TF promoter is one of the relatively strong eukaryotic promoters studied. The most important factors which influence TF synthesis are iron storage levels and steroid hormones. With the isolation and characterization of human TF genomic DNA, we have located conserved sequences identical or homologous to regulatory elements for heavy metals and steroid receptors in the 5' region of TF gene. A sequence proposed to be required for T lymphocyte- specific gene expression was also identified in the TF promoter region. The human TF gene is therefore a promising model for the study of gene regulation. In this proposed study, molecular mechanisms involved in the transferrin gene regulation will be analyzed. The nature and the origin of a 62 kD TF protein specifically produced by T cells will be characterized. The procedures to be employed in this study to investigate the molecular events that regulate TF biosynthesis in response to iron deficiency and estrogen induction include in vitro mutagenesis, minigene transfection, Southwestern blotting and genomic footprinting. TF expression in vivo will be analyzed in transgenic mice. Results from the study described here will provide a molecular basis for the regulation of a gene required for cell proliferation.
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