Functional Expression and Subcellular Localization of the Taurine Transporter TauT in Murine Neural Precursors

Abstract

Taurine addition to cultured embryonic neural precursor cells (NPC) significantly increased cell proliferation [Hernández-Benítez et al., 2010]. The medium used for NPC growing and proliferation is a fetal serum-free medium, and therefore, NPC become taurine depleted. Addition of taurine to the cultured medium fully replenished the cell taurine pool, suggesting the functional expression of a taurine transporter (TauT) in these cells. In the present study, TauT in NPC was functionally characterized and its protein expression and the subcellular distribution of immunoreactivity were determined. ³H-taurine uptake in NPC could be separated into a non-saturable component and a Na⁺/Cl^–-dependent, saturable component. The saturable component showed an apparent 2:1:1 Na⁺/Cl^–/taurine stoichiometry, a V_max of 0.39 ± 0.04 nmol/mg protein/min, and a K_m of 21.7 ± 2.6 µM. TauT in NPC was strongly inhibited by hypotaurine and β-alanine (92 and 79%, respectively) and reduced (71%) by γ-aminobutyric acid. TauT protein is expressed in NPC as a single band of about 70 kDa. Essentially all (98.8%) of the neurosphere-forming cells were positive to TauT immunoreactivity. Immunolocalization visualized by confocal microscopy localized TauT predominantly at the cell membrane. TauT was also found at the cytosol and only occasionally at the nuclear membrane. This study represents the first characterization of TauT in NPC.