Hephaestin: A Copper Protein Involved in Iron Metabolism

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DESCRIPTION (provided by applicant): Iron deficiency adversely affects over one-third of the world's population. Conversely, iron overload disease hemochromatosis is one of the commonest genetic defects in man. In order to maintain a balance between deficiency and toxicity, multiple regulatory systems exist to optimize iron levels in the human body. The absorption of iron by the intestine is central to this regulation because no physiologic means exists to excrete excess iron. Our long-term goal is to understand how changes the body communicates its iron needs to the intestine and how the intestine controls iron absorption into the body. We previously identified, hephaestin, which oxidizes iron from ferrous to ferric iron and is required for moving iron from gut cells into the body. We are studying its function and role in intestinal iron transport and whole body iron homeostasis. Remarkable changes occur in response to iron deficiency, the expression of iron transport proteins increase and some proteins including hephaestin move from intracellular locations to the cell surface to facilitate iron transport. In systemic iron deficiency, the intestinal enterocyte is poised for maximal absorption but is also capable of buffering the uptake of iron in case of potentially toxic dietary levels. In this study, we will ask three questions. 1) How is hephaestin regulated in response to local and systemic iron status? We will independently manipulate dietary and systemic iron status in mice to define the dietary versus systemic effects on hephaestin and other iron transport proteins. We will use cell culture studies to define the regulatory mechanisms. 2) What regulates the movement of hephaestin? We will define the dietary conditions for movement and the rate at which it occurs. We will use a cell culture system to identify the parts of hephaestin that are necessary for movement. We will try to identify the proteins that play a role in the movement of hephaestin. Finally, we will ask 3) how iron oxidation by hephaestin facilitates iron transport ? Hephaestin could be directly required in order to release iron from the iron transporter or alternatively it could create a gradient of ferrous iron which would drive the transport of iron. Iron transport assays using a buffer system that allows us to very tightly control the amount of ferrous and ferric iron will allow us to distinguish between these possibilities.