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This Article Full Text Full Text (PDF) All Versions of this Article: 294/5/F1101    most recent 00413.2007v1 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 HighWire Google Scholar Articles by Taranta, A. Articles by Emma, F. PubMed PubMed Citation Articles by Taranta, A. Articles by Emma, F.

Identification and subcellular localization of a new cystinosin isoform

¹Department of Nephrology and Urology, Division of Nephrology, and ²Department of Laboratory Medicine, Bambino Gesù Children's Hospital and Research Institute, Rome, Italy; and ³Department of Pediatrics, Pediatric Nephrology, Radboud University Medical Center, Nijmegen, The Netherlands

Submitted 6 September 2007 ; accepted in final form 4 March 2008

Nephropathic cystinosis is a lysosomal disorder caused by functional defects of cystinosin, which mediates cystine efflux into the cytosol. The protein sequence contains at least two signals that target the protein to the lysosomal compartment, one of which is located at the carboxy terminal tail (GYDQL). We have isolated from a human kidney cDNA library a cystinosin isoform, which is generated by an alternative splicing of exon 12 that removes the GYDQL motif. Based on its last three amino acids, we have termed this protein cystinosin-LKG. Contrary to the lysosomal cystinosin isoform, expression experiments performed by transient transfection of green fluorescent protein fusion plasmids in HK2 cells showed that cystinosin-LKG is expressed in the plasma membrane, in lysosomes, and in other cytosolic structures. This subcellular localization of the protein was confirmed by transmission electron microscopy. In addition, immunogold labeling was observed in the endoplasmic reticulum and in the Golgi apparatus. Expression of the protein in renal tubular structures was also directly demonstrated by immunostaining of normal human kidney sections. The plasma membrane localization of cystinosin-LKG was directly tested by [³⁵S]cystine flux experiments in COS-1 cells. In the presence of a proton gradient, a marked enhancement of intracellular cystine transport was observed in cells overexpressing this isoform. These data indicate that the expression of the gene products encoded by the CTNS gene is not restricted to the lysosomal compartment. These finding may help elucidate the mechanisms of cell dysfunction in this disorder.

genetic disease; nephropathic cystinosis; cystine transport

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