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This Article Full Text Full Text (PDF) Supplemental Videos All Versions of this Article: 296/4/C663    most recent 00396.2008v1 Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via Google Scholar Google Scholar Articles by Subramanian, V. S. Articles by Said, H. M. Search for Related Content PubMed PubMed Citation Articles by Subramanian, V. S. Articles by Said, H. M.

MEMBRANE TRANSPORTERS, ION CHANNELS, AND PUMPS

Membrane targeting and intracellular trafficking of the human sodium-dependent multivitamin transporter in polarized epithelial cells

¹Department of Medicine and ²Department of Physiology and Biophysics, University of California, Irvine; and ³Department of Veterans Affairs Medical Center, Long Beach, California; ⁴Department of Pharmacology, University of Minnesota Medical School, Minneapolis, Minnesota; and ⁵Department of Internal Medicine, University of New Mexico, Albuquerque, New Mexico

Submitted 4 August 2008 ; accepted in final form 6 February 2009

The human sodium-dependent multivitamin transporter (hSMVT) mediates sodium-dependent uptake of biotin in renal and intestinal epithelia. To date, however, there is nothing known about the structure-function relationship or targeting sequences in the hSMVT polypeptide that control its polarized expression within epithelia. Here, we focused on the role of the COOH-terminal tail of hSMVT in the targeting and functionality of this transporter. A full-length hSMVT-green fluorescent protein (GFP) fusion protein was functional and expressed at the apical membrane in renal and intestinal cell lines. Microtubule disrupting agents disrupted the mobility of trafficking vesicles and impaired cell surface delivery of hSMVT, which was also prevented in cells treated with dynamitin (p50), brefeldin, or monensin. Progressive truncation of the COOH-terminal tail impaired the functionality and targeting of the transporter. First, biotin transport decreased by approximately 20–30% on deletion of up to 15 COOH-terminal amino acids of hSMVT, a decrease mimicked solely by deletion of the terminal PDZ motif (TSL). Second, deletions into the COOH-terminal tail (between residues 584-612, containing a region of predicted high surface accessibility) resulted in a further drop in hSMVT transport (to 40% of wild-type). Third, apical targeting was lost on deletion of a helical-prone region between amino acids 570-584. We conclude that the COOH tail of hSMVT contains several determinants important for polarized targeting and biotin transport.

biotin; epithelial polarity; vitamin; microtubule