SLC5A7

SLC5A7 (CHT1/hCHT) is a Na+-dependent high-affinity choline transporter that mediates the choline reuptake step supplying acetylcholine synthesis (PMID:17005849, PMID:25073461). Expressed in Xenopus oocytes it carries out Na+- and Cl−-dependent choline transport and a hemicholinium-3 (HC-3)-sensitive choline-induced current, with Cl− acting in a regulatory rather than co-transported role; external protons titrate residues supporting choline binding to reduce transport and HC-3 binding with a pKa near 7.4 (PMID:17005849). The protein adopts a 13-transmembrane topology in the SLC5 (Na+/glucose co-transporter) family (PMID:25073461), and cryo-EM of the closely related bacterial ortholog sfCHT establishes a conserved LeuT-fold inward-facing translocation mechanism with Na+ coordination and a cytosolic choline-release pathway recapitulated by CHT1 mutagenesis (PMID:42213839). Transporter availability is set largely by regulated surface trafficking: CHT1 undergoes rapid clathrin-mediated endocytosis dependent on a C-terminal dileucine-like motif, with an intracellular endosomal and synaptic-vesicle reserve pool, such that disrupting the motif (L530A/V531A) enhances surface expression and current (PMID:16524384, PMID:17005849). Surface levels are downregulated by Par-4 binding, which reduces membrane incorporation without changing choline affinity (PMID:15090548), and by Nedd4-2-mediated ubiquitination (PMID:22361880), while insulin acting through PI3-kinase/Akt acutely increases surface CHT and choline uptake (PMID:26161852). Beyond cholinergic neurons, CHT1 is also expressed and functionally active in non-neuronal tissues including ciliated tracheal epithelium and vascular cells (PMID:12654636, PMID:14623932). A coding SNP causing an Ile-to-Val substitution in the third transmembrane segment reduces uptake activity to 50–60% of wild-type (PMID:25073461).

1. 2003 Medium

   Established that CHT1 function is not restricted to neurons by demonstrating active, HC-3-sensitive high-affinity choline uptake in non-neuronal epithelial and vascular cells, broadening its physiological scope to peripheral ACh synthesis.

   Evidence RT-PCR, immunohistochemistry, electron microscopy, and [3H]-choline uptake in tracheal epithelium and aortic segments/vascular cells

   PMID:12654636 PMID:14623932

   Open questions at the time

   • Functional consequence of non-neuronal ACh synthesis not defined
   • Trafficking regulation in these cells not addressed
2. 2004 Medium

   Identified Par-4 as a physical partner that negatively regulates CHT1 by limiting its plasma-membrane incorporation, providing an early mechanism for setting surface transporter density.

   Evidence Reciprocal Co-IP with domain mapping, cell-surface biotinylation, and kinetic choline uptake in transfected IMR-32 neural cells

   PMID:15090548

   Open questions at the time

   • Single lab
   • Physiological context of Par-4 regulation in vivo unclear
   • Mechanism by which Par-4 blocks membrane incorporation undefined
3. 2006 High

   Defined the core transport biophysics and the endocytic basis for a reserve pool, showing Na+/Cl−-dependent choline transport, proton inactivation, and a dileucine-dependent clathrin endocytosis pathway with a surface-enhancing trafficking mutant.

   Evidence Voltage-clamp electrophysiology, choline uptake and pH titration in Xenopus oocytes; subcellular fractionation, immunolocalization, and dileucine-motif mutagenesis (review synthesis)

   PMID:16524384 PMID:17005849

   Open questions at the time

   • Stoichiometry of Na+ coupling not fully resolved
   • Endogenous trigger for endocytic cycling not defined
4. 2006 Medium

   Linked CHT1 dysfunction to a presenilin-1 mutation, showing the M146V allele impairs CHT1 ligand-binding affinity rather than its surface expression.

   Evidence Choline uptake kinetics, HC-3 binding, and biotinylation in primary cortical neurons from PS-1 M146V knock-in mice

   PMID:17196556

   Open questions at the time

   • Molecular mechanism by which PS-1 alters CHT1 affinity unknown
   • Not extended to human disease tissue
5. 2007 Medium

   Showed nitrosative/oxidative stress (peroxynitrite) suppresses choline uptake by accelerating CHT1 internalization, identifying redox stress as an acute regulator of surface transporter.

   Evidence Choline uptake kinetics, biotinylation, HC-3 binding, and internalization assays in cells expressing FLAG-tagged rat CHT

   PMID:17971421

   Open questions at the time

   • Molecular target of peroxynitrite on CHT not identified
   • Single lab
6. 2012 Medium

   Identified Nedd4-2 as an E3 ligase that ubiquitinates CHT1 and downregulates its surface level, placing CHT1 turnover under ubiquitin control.

   Evidence Reciprocal Co-IP, Nedd4-2 siRNA knockdown, and choline uptake/surface quantification in HEK293 cells

   PMID:22361880

   Open questions at the time

   • Ubiquitination site on CHT1 not mapped
   • Single lab, heterologous cells
7. 2014 Medium

   Defined CHT1 topology as a 13-TM SLC5-family transporter and showed a third-TM Ile-to-Val SNP reduces uptake to 50–60%, linking sequence variation to transport capacity.

   Evidence Functional uptake assay of SNP variant, hydropathy/topology analysis, sequence homology

   PMID:25073461

   Open questions at the time

   • Population-level phenotypic consequence of SNP not established
   • Structural basis of the SNP effect not resolved at the time
8. 2015 Medium

   Established insulin–PI3K/Akt signaling as an acute regulator of CHT1 surface trafficking and demonstrated that chronic insulin (insulin resistance) blunts this control.

   Evidence Choline uptake, phospho-Akt Western blots, PI3K inhibition, and TIRF live-cell imaging of CHT trafficking in differentiated SH-SY5Y cells

   PMID:26161852

   Open questions at the time

   • Direct molecular link between Akt and CHT trafficking machinery undefined
   • Single lab
9. 2017 Medium

   Connected β-amyloid to cholinergic deficit by showing Aβ reduces surface CHT1 and routes it to lysosomal degradation, with N-terminal Aβ antibody rescue.

   Evidence Uptake assays, biotinylation, endosome/lysosome localization, bafilomycin A1 and neutralizing antibody experiments in SH-SY5Y cells

   PMID:29163036

   Open questions at the time

   • Receptor mediating Aβ effect on CHT1 not identified
   • Bafilomycin rescued surface but not activity, leaving an additional inhibitory mechanism unexplained
10. 2016 Low

    Suggested transcriptional/translational upregulation of CHT1 by CXCL12 via Akt, coupling chemokine signaling to cholinergic capacity.

    Evidence Western blot, RT-PCR, ACh ELISA, ChAT activity, and pharmacological Akt inhibition in PC12 cells and primary rat neurons

    PMID:27941337

    Open questions at the time

    • Pharmacological inhibition only, no direct CHT1 activity measurement
    • Single lab
    • Direct transcriptional mechanism not established
11. 2026 High

    Resolved the structural mechanism of choline translocation by cryo-EM of a bacterial ortholog, establishing a conserved LeuT-fold inward-facing pathway validated by CHT1 mutagenesis.

    Evidence Cryo-EM of Na+/choline-bound sfCHT, computational analysis, and transport assays of sfCHT and CHT1 site-directed variants

    PMID:42213839

    Open questions at the time

    • No experimental structure of human CHT1 itself
    • Outward-facing and intermediate states not captured

• How the multiple surface-regulatory inputs (Par-4, Nedd4-2 ubiquitination, PI3K/Akt, redox stress, Aβ) are integrated at the endocytic/recycling machinery to set CHT1 density at active terminals remains unresolved.
• No unified model linking signaling inputs to the dileucine/clathrin endocytic apparatus
• No human CHT1 structure to map regulatory residues
• In vivo relevance of individual regulators largely untested