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J. Biol. Chem., Vol. 280, Issue 43, 36221-36227, October 28, 2005

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Menkes Copper ATPase (Atp7a) Is a Novel Metal-responsive Gene in Rat Duodenum, and Immunoreactive Protein Is Present on Brush-border and Basolateral Membrane Domains^*

From the Departments of Pediatrics and Nutritional Sciences, Steele Children's Research Center, University of Arizona Health Sciences Center, Tucson, Arizona 85724

We previously noted strong induction of genes related to intestinal copper homeostasis (Menkes Copper ATPase (Atp7a) and metallothionein) in the duodenal epithelium of iron-deficient rats across several stages of postnatal development (Collins, J. F., Franck, C. A., Kowdley, K. V., and Ghishan, F. K. (2005) Am. J. Physiol., 288, G964–G971). We now report significant copper loading in the livers and intestines of iron-deficient rats. These findings are consistent with the hypothesis that there is increased intestinal copper transport during iron deficiency. We additionally found that hepatic Atp7b gene expression does not change with iron deficiency, suggesting that liver copper excretion is not altered. We have developed polyclonal antibodies against rat ATP7A, and we demonstrate the specificity of the immunogenic reaction. We show that the ATP7A protein is present on apical domains of duodenal enterocytes in control rats and on brush-border and basolateral membrane domains in iron-deprived rats. This localization is surprising, as previous in vitro studies have suggested that ATP7A traffics between the trans-Golgi network and the basolateral membrane. We further demonstrate that ATP7A protein levels are dramatically increased in brush-border and basolateral membrane vesicles isolated from iron-deficient rats. Other experiments show that iron refeeding partially corrects the hematological abnormalities seen in iron-deficient rats but that it does not ameliorate ATP7A protein induction, suggesting that Atp7a does not respond to intracellular iron levels. We conclude that ATP7A is involved in copper loading observed during iron deficiency and that increased intestinal copper transport is of physiological relevance, as copper plays important roles in overall body iron homeostasis.

Received for publication, June 21, 2005 , and in revised form, August 3, 2005.

^* This work was supported by National Institutes of Health Grant 5 R21 DK068349. The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.

¹ Both authors contributed equally to this work.

² To whom correspondence should be addressed: State University of New York at Buffalo, Dept. of Exercise and Nutrition Sciences, 15 Farber Hall, Buffalo, NY 14214-8001. Tel.: 716-829-3680 (ext. 230); Fax: 716-829-3700; E-mail: jfc8{at}buffalo.edu.

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