Classical isoforms of PKC as regulators of CAT-1 transporter activity in pulmonary artery endothelial cells

We examined which isoforms of protein kinase C (PKC) may be involved in the regulation of cationic amino acid transporter-1 (CAT-1) transport activity in cultured pulmonary artery endothelial cells (PAEC). An activator of classical and novel isoforms of PKC, phorbol 12-myristate-13-acetate (PMA; 100 nM), inhibited CAT-1-mediated L-arginine transport in PAEC after a 1-h treatment and activated L-arginine uptake after an 18-h treatment of cells. These changes in L-arginine transport were not related to the changes in the expression of the CAT-1 transporter. The inhibitory effect of PMA on L-arginine transport was accompanied by a translocation of PKCα (a classical PKC isoform) from the cytosol to the membrane fraction, whereas the activating effect of PMA on L-arginine transport was accompanied by full depletion of the expression of PKCα in PAEC. A selective activator of Ca²⁺-dependent classical isoforms of PKC, thymeleatoxin (Thy; 100 nM; 1-h and 18-h treatments), induced the same changes in L-arginine uptake and PKCα translocation and depletion as PMA. The effects of PMA and Thy on L-arginine transport in PAEC were attenuated by a selective inhibitor of classical PKC isoforms Go 6976 (1 μM). Phosphatidylinositol-3,4,5-triphosphate-dipalmitoyl (PIP; 5 μM), which activates novel PKC isoforms, did not affect L-arginine transport in PAEC after 1-h and 18-h treatment of cells. PIP (5 μM; 1 h) induced the translocation of PKCε (a novel PKC isoform) from the cytosolic to the particulate fraction and did not affect the translocation of PKCα. These results demonstrate that classical isoforms of PKC are involved in the regulation of CAT-1 transport activity in PAEC. We suggest that translocation of PKCα to the plasma membrane induces phosphorylation of the CAT-1 transporter, which leads to inhibition of its transport activity in PAEC. In contrast, depletion of PKCα after long-term treatment with PMA or Thy promotes dephosphorylation of the CAT-1 transporter and activation of its activity.