title: Activation of classical protein kinase C reduces the expression of human cationic amino acid transporter 3 (hCAT-3) in the plasma membrane.
abstract: We have previously shown that activation of PKC (protein kinase C) results in internalization of hCAT-1 [human CAT-1 (cationic amino acid transporter 1)] and a decrease in arginine transport [Rotmann, Strand, Martiné and Closs (2004) J. Biol. Chem. 279, 54185-54192]. However, others found increased transport rates for arginine in response to PKC activation, suggesting a differential effect of PKC on different CAT isoforms. Therefore we investigated the effect of PKC on hCAT-3, an isoform expressed in thymus, brain, ovary, uterus and mammary gland. In Xenopus laevis oocytes and human U373MG glioblastoma cells, hCAT-3-mediated L-arginine transport was significantly reduced upon treatment with compounds that activate classical PKC. In contrast, inactive phorbol esters and an activator of novel PKC isoforms had no effect. PKC inhibitors (including the PKCalpha-preferring Ro 31-8280) reduced the inhibitory effect of the PKC-activating compounds. Microscopic analyses revealed a PMA-induced reduction in the cell-surface expression of fusion proteins between hCAT-3 and enhanced green fluorescent protein expressed in X. laevis oocytes and glioblastoma cells. Western-blot analysis of biotinylated surface proteins demonstrated a PMA-induced decrease in hCAT-3 in the plasma membrane, but not in total protein lysates. Pretreatment with a PKC inhibitor also reduced this PMA effect. It is concluded that similar to hCAT-1, hCAT-3 activity is decreased by PKC via reduction of transporter molecules in the plasma membrane. Classical PKC isoforms seem to be responsible for this effect.
authors.affiliation: Department of Pharmacology, Johannes Gutenberg University, Obere Zahlbacher Strasse 67, 55101 Mainz, Germany.
authors.forename: Alexander
authors.initials: A
authors.lastname: Rotmann
authors.forename: Nicole
authors.initials: N
authors.lastname: Vékony
authors.forename: Davina
authors.initials: D
authors.lastname: Gassner
authors.forename: Günter
authors.initials: G
authors.lastname: Niegisch
authors.forename: Dennis
authors.initials: D
authors.lastname: Strand
authors.forename: Ursula
authors.initials: U
authors.lastname: Martiné
authors.forename: Ellen I
authors.initials: EI
authors.lastname: Closs
mesh_terms: D000818:Animals; D000918:Antibody Specificity; D001120:Arginine / Q000378:metabolism; D001692:Biological Transport / Q000187:drug effects; D027201:Cationic Amino Acid Transporter 1 / Q000378:metabolism*; D045744:Cell Line, Tumor; D002462:Cell Membrane / Q000378:metabolism*; D015536:Down-Regulation / Q000235:genetics; D004789:Enzyme Activation; D005909:Glioblastoma / Q000378:metabolism; D006801:Humans; D009865:Oocytes / Q000378:metabolism; D011493:Protein Kinase C / Q000378:metabolism*; D018243:Teratocarcinoma / Q000378:metabolism; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology; D014407:Tumor Cells, Cultured; D014981:Xenopus
chemical_list: D001120:Arginine; D027201:Cationic Amino Acid Transporter 1; D011493:Protein Kinase C; D013755:Tetradecanoylphorbol Acetate; C499482:SLC7A3 protein, human