The Ceruloplasmin Homolog Hephaestin and the Control of Intestinal Iron Absorption Gregory J. Anderson, 1 David M. Frazer, 1 Andrew T. McKie, 2 and Christopher D. Vulpe 3 Submitted 10/3/02 (Communicated by E. Beutler, M.D., 10/14/02) ABSTRACT: Hephaestin is the gene affected in the sex-linked anemic (sla) mouse. These animals have a defect in the export of iron from intestinal enterocytes into the circulation and this implicates hephaestin in the basolateral transfer step of iron absorption. Hephaestin is homologous to the plasma copper-containing protein ceruloplasmin, and all residues involved in copper binding and disulfide bond formation in ceruloplasmin are conserved in hephaestin. Unlike ceruloplasmin, hephaestin is an integral membrane protein with a single trans-membrane domain. It is highly expressed throughout the small intestine, to a lesser extent in the colon, and at low levels in several other tissues. Surprisingly, most hephaestin appears to be located intracellularly in a perinuclear distribu- tion. Like ceruloplasmin, hephaestin has a ferroxidase activity which is predicted to underlie its biological function. In addition, its expression is stimulated under iron deficient conditions. Analysis of the sla mouse has supported our model for the regulation of intestinal iron absorption whereby changes in systemic iron requirements alter the levels of basolateral transport components with subsequent regulation of brush border transport. © 2002 Elsevier Science (USA) Key Words: hephaestin, iron, iron absorption, intestine, ceruloplasmin, Ireg1, DMT1, Dcytb, ferroportin. INTRODUCTION The history of investigations into iron trans- port has been heavily focused on how cells take up iron, so much so that the role of cellular iron release in maintaining body iron homeostasis is often underappreciated. Most body cells are able to divest themselves of iron and this becomes readily apparent in the clinical setting during phlebotomy therapy for the iron overload disease hemochromatosis, where iron is efficiently mobi- lized from tissues for new hemoglobin synthesis to replace that removed during treatment. Further- more, several cell types are specially adapted for iron export. These include the intestinal epithelial cell, macrophages and placental trophoblast cells. Recent developments in identifying molecules in- volved in iron transport across membranes com- bined with older physiological studies have greatly enhanced our capacity to understand this important physiological process and have high- lighted the essential role of copper-containing proteins in cellular iron efflux. Dietary iron enters the body by traversing the epithelial cells of the proximal small intestine (1). These cells must not only take up iron from the intestinal lumen across the brush border, they must also export it across the basolateral mem- brane and into the circulation. Newly absorbed iron is bound by plasma transferrin for distribu- tion to cells throughout the body. While all body cells require iron for various essential cellular processes, immature erythroid cells have a partic- ularly high iron requirement for the synthesis of hemoglobin, and consequently approximately 80% of iron traffic is through the red cell com- Correspondence and reprint requests to: Greg Anderson, Iron Metabolism Laboratory, Queensland Institute of Medical Research, PO Royal Brisbane Hospital, Brisbane, Queensland 4029, Australia. Fax: +61-7-3362-0191. E-mail: gregA@qimr.edu.au. 1 Iron Metabolism Laboratory, Queensland Institute of Medical Research, PO Royal Brisbane Hospital, Brisbane, Queensland 4029, Australia. 2 Division of Life Sciences, King’s College, London SE19NN United Kingdom. 3 Department of Nutritional Sciences, University of California, Berkeley, CA, 94720. Anderson et al. Blood Cells, Molecules, and Diseases (2002) 29(3) Nov/Dec: 367–375 doi:10.1006/bcmd.2002.0576 1079-9796/02 $35.00 © 2002 Elsevier Science (USA) All rights reserved. 367