Cell biology of the human thiamine transporter-1 (hTHTR1) - Intracellular trafficking and membrane targeting mechanisms

Department of Neurobiology and Behavior, University of California, Irvine 92697, USA.
Journal of Biological Chemistry (Impact Factor: 4.57). 03/2003; 278(6):3976-84. DOI: 10.1074/jbc.M210717200
Source: PubMed


The human thiamine transporter hTHTR1 is involved in the cellular accumulation of thiamine (vitamin B1) in many tissues. Thiamine deficiency disorders, such as thiamine-responsive megaloblastic anemia (TRMA), which is associated with specific mutations within hTHTR1, likely impairs the functionality and/or intracellular targeting of hTHTR1. Unfortunately, nothing is known about the mechanisms that control the intracellular trafficking or membrane targeting of hTHTR1. To identify molecular determinants involved in hTHTR1 targeting, we generated a series of hTHTR1 truncations fused with the green fluorescent protein and imaged the targeting and trafficking dynamics of each construct in living duodenal epithelial cells. Whereas the full-length fusion protein was functionally expressed at the plasma membrane, analysis of the truncated mutants demonstrated an essential role for both NH(2)-terminal sequence and the integrity of the backbone polypeptide for cell surface expression. Most notably, truncation of hTHTR1 within a region where several TRMA truncations are clustered resulted in intracellular retention of the mutant protein. Finally, confocal imaging of the dynamics of intracellular hTHTR1 vesicles revealed a critical role for microtubules, but not microfilaments, in hTHTR1 trafficking. Taken together, these results correlate hTHTR1 structure with cellular expression profile and reveal a critical dependence on hTHTR1 backbone integrity and microtubule-based trafficking processes for functional expression of hTHTR1.

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Available from: Hamid M. Said
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    • "After the intravenous administration of 50 mg of TH hydrochloride the plasma half-time is about 96 minutes. Thus, for correcting TH deficiency the administration of parenteral TH in many smaller doses rather than in an equivalent single dose seems justified (Donnino; Boulware, Subramanian et al. 2003). The blood brain barrier (BBB) allows the passage of free TH and THMP through both active and passive mechanisms. "

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    • "Recently, microtubule cytoskeleton networks have been implicated in the subcellular movements of some proteins including glucose transporter isoform (GLUT4) or thiamine transporter (THTR1) (Liu et al. 2003; Subramanian et al. 2003). It is likely that LTA is another molecule that uses the microtubule cytoskeleton network for translocation, and galectin-2 mediates LTA trafficking through binding to microtubules, although the precise role of galectin-2 in this trafficking machinery complex has yet to be elucidated (Fig. 6). "
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