MEMBRANE TRANSPORTERS, ION CHANNELS, AND PUMPS |
Activation of classical protein kinase C decreases transport via systems y+ and y+L
Alexander Rotmann,*
Alexandra Simon,*
Ursula Martiné,
Alice Habermeier, , and
Ellen I. Closs
Department of Pharmacology, Johannes Gutenberg University, Mainz, Germany
Received for publication 13 June 2006.
Accepted for publication 29 January 2007.
Abstract:
Activation of protein kinase C (PKC) downregulates the human cationic amino acid transporters hCAT-1 (SLC7A1) and hCAT-3 (SLC7A3) (Rotmann A, Strand D, Martiné U, Closs EI. J Biol Chem 279: 54185–54192, 2004; Rotmann A, Vekony N, Gassner D, Niegisch G, Strand D, Martine U, Closs EI. Biochem J 395: 117–123, 2006). However, others found that PKC increased arginine transport in various mammalian cell types, suggesting that the expression of different arginine transporters might be responsible for the opposite PKC effects. We thus investigated the consequence of PKC activation by phorbol-12-myristate-13-acetate (PMA) in various human cell lines expressing leucine-insensitive system y+ [hCAT-1, hCAT-2B (SLC7A2), or hCAT-3] as well as leucine-sensitive system y+L [y+LAT1 (SLC7A7) or y+LAT2 (SLC7A6)] arginine transporters. PMA reduced system y+ activity in all cell lines tested, independent of the hCAT isoform expressed, while mRNAs encoding the individual hCAT isoforms were either unchanged or increased. System y+L activity was also inhibited by PMA. The extent and onset of inhibition varied between cell lines; however, a PMA-induced increase in arginine transport was never observed. In addition, when expressed in Xenopus laevis oocytes, y+LAT1 and y+LAT2 activity was reduced by PMA, and this inhibition could be prevented by the PKC inhibitor bisindolylmaleimide I. In ECV304 cells, PMA-induced inhibition of systems y+ and y+L could be prevented by Gö6976, a specific inhibitor of conventional PKCs. Thymelea toxin, which activates preferentially classical PKC, had a similar inhibitory effect as PMA. In contrast, phosphatidylinositol-3,4,5-triphosphate-dipalmitoyl, an activator of atypical PKC, had no effect. These data demonstrate that systems y+ and y+L are both downregulated by classical PKC.
Key Words: human cationic amino acid transporter • system y+L amino acid transporter
Address for reprint requests and other correspondence: E. I. Closs, Dept. of Pharmacology, Johannes Gutenberg Univ., Obere Zahlbacher Str. 67, 55101 Mainz, Germany (e-mail: Closs{at}uni-mainz.de)
