Association of PDZ-containing protein PDZD11 with the human sodium-dependent multivitamin transporter.

Intestinal absorption of biotin is mediated via the sodium-dependent multivitamin transporter (SMVT). Studies from our laboratory and others have characterized different aspects of the human SMVT (hSMVT), but nothing is currently known about protein(s) that may interact with hSMVT and affect its physiology/biology. In this study, a PDZ-containing protein PDZD11 was identified as an interacting partner with hSMVT using yeast two-hybrid screen of a human intestinal cDNA library. The interaction between hSMVT and PDZD11 was confirmed by in vitro GST-pull-down assay and in vivo in a mammalian cell environment by a two-hybrid luciferase and coimmunoprecipitation assays. Furthermore, confocal imaging of live human intestinal epithelial HuTu-80 cells expressing hSMVT-GFP and DsRed-PDZD11 demonstrated colocalization of these two proteins. We also examined the functional consequence of the interaction between hSMVT and PDZD11 in HuTu-80 cells and observed significant induction in [(3)H]biotin uptake upon coexpression of hSMVT and PDZD11. In contrast, knocking down of PDZD11 with gene-specific small interfering RNA led to a significant decrease in biotin uptake; biotinylation assay showed this to be associated with a marked decrease in level of expression of hSMVT at the cell membrane. By truncation approach, we also demonstrated that the PDZ binding domain that is located in the COOH-terminal tail of hSMVT polypeptide is involved in the interaction with PDZD11. These results demonstrate for the first time that PDZD11 is an interacting partner with hSMVT in intestinal epithelial cells and that this interaction affects hSMVT function and cell biology.

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