CHARACTERIZATION OF TAURINE TRANSPORT IN HUMAN GLIOMA GL15 CELL-LINE - REGULATION BY PROTEIN-KINASE-C

Data describing characteristics of taurine transport system in human b rain cells are not currently available. We have used GL15 cells, a cel l line of human brain origin that keeps some properties of normal glia l cells, to investigate these characteristics. The human glioma cell l ine GL15 was found to take up taurine. The uptake was strictly sodium- dependent. Replacement of NaCl with choline chloride almost totally ab olished the uptake. There was also an anion requirement for the uptake system, and Cl- was the most potent among several monovalent anions t ested. The uptake process was specific for beta-amino acids such as ta urine, hypotaurine and p-alanine. The kinetics of uptake were studied. Apparently, a single transport system with a K-m of 8.95 +/- 0.26 mu M was responsible for the uptake. A maximal velocity of 1.32 +/- 0.03 nmol/mg of protein/10 min was found. Stoichiometric analysis revealed that two Na+ and one Cl- ions were involved in the translocation of on e taurine molecule. Phorbol 12-myristate 13-acetate (PMA), a potent st imulator of protein kinase C (PKC), inhibited taurine uptake. Maximal inhibition was obtained at 50 nM after 1 hr of treatment. This effect was prevented by pretreatment of the cells with chelerythrine, a poten t and selective inhibitor of PKC. The transport of beta-alanine was in hibited to a comparative extent. The mechanism of this inhibition was not investigated, but it was found that this inhibitory effect was not prevented by cycloheximide, actinomycin D, colchicine or cytochalasin D, indicating that neither protein synthesis, nor microfilament funct ion were involved. The effect of PMA was associated with an impairment of kinetic constants. It is concluded that human GL15 cells have a ta urine transporter similar to that expressed in rodent glial cells, and that the activation of PKC can modulate the activity of this transpor ter.