Abstract
Human concentrative nucleoside transporter 3 (hCNT3) is a broad-selectivity, high-affinity protein implicated in the uptake of most nucleoside-derived anticancer and antiviral drugs. Regulated trafficking of hCNT3 has been recently postulated as a suitable way to improve nucleoside-based therapies. Moreover, the recent identification of a putative novel hCNT3-type transporter lacking the first 69 amino acids and retained at the endoplasmic reticulum anticipated that the N terminus of hCNT3 contains critical motifs implicated in trafficking. In the current study, we have addressed this issue by using deletions and site-directed mutagenesis and plasma membrane expression and nucleoside uptake kinetic analysis. Data reveal that 1) a segment between amino acids 50 and 62 contains plasma membrane-sorting determinants in nonpolarized cells; 2) in particular, the Val57-Thr58-Val59 tripeptide seems to be the core of the export signal, whereas acidic motifs upstream and downstream of it seem to be important for the kinetics of the process; and 3) in polarized epithelia, the β-turn-forming motif 17VGFQ20 is necessary for proper apical expression of the protein.
Footnotes
↵ The online version of this article (available at http://molpharm.aspetjournals.org) contains supplemental material.
This research was supported in part by Centro de Investigación Biomédica en Red (an initiative of Instituto de Salud Carlos III); Generalitat de Catalunya [Grant 2009SGR624]; and the Ministerio de Ciencia e Innovación [Grant BFU2006-07556/BFI], SAF2008–00577].
Article, publication date, and citation information can be found at http://molpharm.aspetjournals.org.
doi:10.1124/mol.110.065920.
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ABBREVIATIONS:
- CLL
- chronic lymphocytic leukemia
- hCNT3
- human concentrative nucleoside transporter 3
- MDCK
- Madin-Darby canine kidney cells
- ER
- endoplasmic reticulum
- GFP
- green fluorescent protein.
- Received April 27, 2010.
- Accepted July 19, 2010.
- Copyright © 2010 The American Society for Pharmacology and Experimental Therapeutics
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