application) Iron is essential for normal metabolic functions and disturbances of iron homeostasis can have significant clinical consequences. The amount of iron in the body is controlled at the point of absorption in the small intestine, yet the mechanism by which iron traverses the intestinal epithelium is poorly understood. In this application we aim to study in detail the mechanism of iron movement out of the epithelial cells and into the body by investigating the biology of two recently cloned genes. One of these, hephaestin, is known to play a role in iron export from the epithelium, while the other, ireg1, is proposed to play an important role in this process. We hypothesize that hephaestin and ireg1 interact to form a complex which transports iron across the basolateral membrane of intestinal enterocytes and delivers it to apotransferrin. This hypothesis will be tested by addressing several key questions: (1) Do hephaestin and ireg1 co-localise and physically interact in epithelia] cells? (2) Is this interaction sufficient to mediate iron movement across cellular membranes? (3) Can this complex directly or indirectly deliver iron to apotransferrin? and (4) How is the iron transport mediated by these proteins regulated? These issues will be addressed by conducting parallel studies using both intestinal tissue and cell lines overexpressing hephaestin and ireg1 and by studying iron transport in animal models. Immunomicroscopy, co-precipitation and the yeast two-hybrid system will be used to search for interactions between the two proteins. The role of hephaestin and ireg1 in iron transport will be studied by developing iron efflux assays in mammalian and yeast cells, and by the targeted disruption of the ireg1 gene in mice and the analysis of its phenotype. To determine whether the hephaestin/ireg1 complex delivers iron to apotransferrin, we will search for direct interactions between the proteins and will investigate the ability of apotransferrin to facilitate iron release from intestinal tissue and in a reconstituted iron efflux system. The iron-dependent regulation of ireg1 and hephaestin will be studied in cellular and animal models and a detailed analysis of the regulatory system will be carried out. In all studies, site directed mutagenesis will be used to dissect interactions at the molecular level. The iron efflux or transfer step of intestinal iron absorption has proved difficult to study in the past yet it is likely to be the rate-limiting for absorption under certain circumstances. However, the identification of hephaestin and ireg1 provides an unprecedented opportunity to investigate this process at the molecular level and to evaluate its role in human disorders of iron metabolism such as hereditary hemochromatosis and provides potential therapeutic targets.

Agency
National Institute of Health (NIH)
Institute
National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK)
Type
Research Project (R01)
Project #
5R01DK057800-03
Application #
6517766
Study Section
Special Emphasis Panel (ZDK1-GRB-1 (J2))
Program Officer
May, Michael K
Project Start
2000-06-01
Project End
2005-05-31
Budget Start
2002-06-01
Budget End
2003-05-31
Support Year
3
Fiscal Year
2002
Total Cost
$212,547
Indirect Cost
Name
University of California Berkeley
Department
Nutrition
Type
Schools of Earth Sciences/Natur
DUNS #
094878337
City
Berkeley
State
CA
Country
United States
Zip Code
94704
Lee, Seung-Min; Attieh, Zouhair K; Son, Hee Sook et al. (2012) Iron repletion relocalizes hephaestin to a proximal basolateral compartment in polarized MDCK and Caco2 cells. Biochem Biophys Res Commun 421:449-55
Tao, Yong-guang; Xu, Yong; Xu, H Eric et al. (2008) Mutations of glucocorticoid receptor differentially affect AF2 domain activity in a steroid-selective manner to alter the potency and efficacy of gene induction and repression. Biochemistry 47:7648-62
Simons Jr, S Stoney (2008) What goes on behind closed doors: physiological versus pharmacological steroid hormone actions. Bioessays 30:744-56
Chen, Huijun; Huang, Gang; Su, Trent et al. (2006) Decreased hephaestin activity in the intestine of copper-deficient mice causes systemic iron deficiency. J Nutr 136:1236-41
Frazer, David M; Anderson, Gregory J (2005) Iron imports. I. Intestinal iron absorption and its regulation. Am J Physiol Gastrointest Liver Physiol 289:G631-5
Kuo, Y M; Su, T; Chen, H et al. (2004) Mislocalisation of hephaestin, a multicopper ferroxidase involved in basolateral intestinal iron transport, in the sex linked anaemia mouse. Gut 53:201-6
Chen, Huijun; Attieh, Zouhair K; Su, Trent et al. (2004) Hephaestin is a ferroxidase that maintains partial activity in sex-linked anemia mice. Blood 103:3933-9
Frazer, David M; Wilkins, Sarah J; Millard, Kirstin N et al. (2004) Increased hepcidin expression and hypoferraemia associated with an acute phase response are not affected by inactivation of HFE. Br J Haematol 126:434-6
Frazer, D M; Inglis, H R; Wilkins, S J et al. (2004) Delayed hepcidin response explains the lag period in iron absorption following a stimulus to increase erythropoiesis. Gut 53:1509-15
Frazer, D M; Wilkins, S J; Becker, E M et al. (2003) A rapid decrease in the expression of DMT1 and Dcytb but not Ireg1 or hephaestin explains the mucosal block phenomenon of iron absorption. Gut 52:340-6

Showing the most recent 10 out of 15 publications