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Molecular and Cellular Biology, January 2009, p. 129-139, Vol. 29, No. 1
0270-7306/09/$08.00+0     doi:10.1128/MCB.00963-08
Copyright © 2009, American Society for Microbiology. All Rights Reserved.

Novel Proteolytic Processing of the Ectodomain of the Zinc Transporter ZIP4 (SLC39A4) during Zinc Deficiency Is Inhibited by Acrodermatitis Enteropathica Mutations {triangledown}

Taiho Kambe{dagger} and Glen K. Andrews*

Department of Biochemistry and Molecular Biology, University of Kansas Medical Center, Kansas City, Kansas 66160-7421

Received 18 June 2008/ Returned for modification 18 July 2008/ Accepted 14 October 2008

The zinc transporter ZIP4 (SLC39A4) is mutated in humans with the rare, autosomal recessive genetic disease acrodermatitis enteropathica. In mice, this gene is essential during early embryonic development. ZIP4 is dynamically regulated by multiple posttranscriptional mechanisms, and studies of mouse ZIP4 reported herein reveal that the ectodomain, the extracellular amino-terminal half of the protein, is proteolytically removed during prolonged zinc deficiency while the remaining eight-transmembrane carboxyl-terminal half of the protein is accumulated on the plasma membrane as an abundant form of ZIP4. This novel ZIP4 processing occurs in vivo in the intestine and visceral endoderm, in mouse Hepa cells that express the endogenous Slc39a4 gene and in transfected MDCK and CaCo2 cells, but not HEK293 cells. In transfected MDCK and CaCo2 cells, the ectodomain accumulated and remained associated with membranes when zinc was deficient. ZIP4 cleavage was attenuated by inhibitors of endocytosis, which suggests that the processed protein is recycled back to the plasma membrane and that the ectodomain may be internalized. Ectodomain cleavage is inhibited by acrodermatitis enteropathica mutations near a predicted metalloproteinase cleavage site which is also essential for proper ectodomain cleavage, and overexpression of processed ZIP4 or ZIP4 with ectodomain truncations rendered the mouse Mt1 gene hypersensitive to zinc. These finding suggest that the processing of ZIP4 may represent a significant regulatory mechanism controlling its function.

* Corresponding author. Mailing address: Department of Biochemistry and Molecular Biology, Mail Stop 3030, University of Kansas Medical Center, 39th and Rainbow Blvd., Kansas City, KS 66160-7421. Phone: (913) 588-6935. Fax: (913) 588-3920. E-mail: gandrews{at}kumc.edu

{triangledown} Published ahead of print on 20 October 2008.

{dagger} Permanent address: Division of Integrated Life Science, Graduate School of Biostudies, Kyoto University, Kyoto 606-8502, Japan.

Molecular and Cellular Biology, January 2009, p. 129-139, Vol. 29, No. 1
0270-7306/09/$08.00+0     doi:10.1128/MCB.00963-08
Copyright © 2009, American Society for Microbiology. All Rights Reserved.





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