| Popis: |
1 The human cationic amino acid transporter hCAT-1 contains several consensus sequences for phosphorylation by protein kinase C (PKC). This study investigates the eAect of PKC activation on hCAT-1-mediated transport. 2 When expressed in Xenopus laevis oocytes, hCAT-1-mediated L-arginine transport was reduced to 44+3% after a 30 min treatment of the oocytes with 100 nM phorbol-12-myristate-13-acetate (PMA). 4a-phorbol-12,13-didecanoate (4a-PDD, 100 nM) had no eAect. 3 In EA.hy926 endothelial cells, maximal inhibition of hCAT-1-mediated L-arginine transport (to 3‐11% of control) was observed after treatment of the cells with 100 nM PMA for 4 h. A 20‐30 h exposure of the cells to 100 nM PMA led to the recovery of the L-arginine uptake rate that was now resistant to a second application of PMA. Phorbol-12,13-dibutyrate had similar eAects as PMA, whereas 4a-PDD had no eAect. One mM bisindolylmaleimide I reduced the PMA eAect significantly. 4 Interestingly, a 4 h treatment with 100 nM PMA increased the expression of hCAT-1 mRNA 3‐ 5 fold. hCAT-1 protein levels were unchanged for up to 4 h after PMA treatment and then increased slightly between 8‐28 h. 5 It is concluded that PMA downregulates the intrinsic activity of hCAT-1 by a pathway involving protein kinase C. British Journal of Pharmacology (2001) 132, 1193‐1200 |
Plný text