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J. Biol. Chem., Vol. 278, Issue 44, 42920-42926, October 31, 2003

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Identification of a Mechanism by Which Lens Epithelial Cells Limit Accumulation of Overexpressed Ferritin H-chain^*

Malgorzata Goralska, Benjamin L. Holley, and M. Christine McGahan

From the Department of Molecular Biomedical Sciences, North Carolina State University, Raleigh, North Carolina 27606

The primary cultures of canine lens epithelial cells were transiently transfected with cDNAs for dog ferritin H- or L-chains in order to study differential expression of these chains. By using chain-specific antibodies, we determined that at 48 h after transfection overexpression of L-chain was much higher (9-fold over control) than that of H-chain (1.7-fold). We discovered that differentially transfected cells secrete overexpressed chains as homopolymeric ferritin into the media. Forty-eight hours after transfection accumulation of H-ferritin in the media was much higher (3-fold) than that of L-ferritin. This resulted in lowering of the concentration of H-chain in the cytosol. Co-transfection of cells with both H- and L-chain cDNAs increased the intracellular levels of H-chain and eliminated secretion of H-ferritin to the media. We concluded that lens epithelial cells differentially regulate concentration of both ferritin chains in the cytosol. The overexpressed L-chain accumulated in the cytosol as predominantly homopolymeric L-ferritin. This is in contrast to H-chain, which is removed to the media unless there is an L-chain available to form heteropolymeric ferritin. These data indicate that the inability of cells to more strictly control cytosolic levels of L-chain may augment its accumulation in lenses of humans with hereditary hyperferritinemia cataract syndrome, which is caused by overexpression of L-chain due to mutation in the regulatory element in the untranslated region of the mRNA of the chain.

Received for publication, June 3, 2003 , and in revised form, July 30, 2003.

^* This work was supported by National Institutes of Health Grant EY-04900. Part of this work was presented in abstract form at the XIV International Congress of Eye Research, Oct. 6–9, 2002, Geneva, Switzerland. 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.

To whom correspondence should be addressed: Dept. of Molecular Biomedical Sciences, North Carolina State University, 4700 Hillsborough St., Raleigh, NC 27606. Tel.: 919-515-4487; Fax: 919-515-3044; E-mail: margaret_goralska{at}ncsu.edu.

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