The transition metal copper (Cu+) is an essential trace element for all biota. Its redox properties bestow Cu with capabilities that are simultaneously essential and potentially damaging to the cell. Free Cu is virtually absent in the cell. In mammalians liver is the major captor, distributor and excreter of Cu. Humans eliminate 95% of the Cu+ ingested with diet. The excretion of Cu into the bile is an attribute exclusive of the hepatocyte and bile is the major route of Cu elimination and the most important mechanism in Cu homoeostasis in mammals. The correlation between the release of ATP7B retained in the trans-Golgi network (TGN) and the role of ATP7B in excretion of Cu into the bile is firmly established. Yet, the pathway of ATP7B transport is poorly understood and its site of action is the subject of a hot debate. Our studies of Cu+-mediated ATP7B traffic in CAN 10 hepatoma cells showed that after its release from the TGN, ATP7B is basolateral sorted, inserted in the basolateral plasma membrane and transported by transcytosis to the bile canaliculus (BC). Insertion of ATP7B into the membrane of the BC is essential for excreting excess of cellular Cu+ into the medium. Contradicting recent reports, our studies find no evidence of ATP7B association with lysosomes and do not support the recent model of Cu+ excretion mediated by lysosome exocytosis. In recent months we have started a systematic study of the mutations that disrupt ATP7B traffic and cause Wilson disease and cuprotoxicosis with a genetic background of wild ATP7B. In a separate study we investigate the role of ESyt proteins in membrane dynamics and glucose and lipid metabolism in the adipocyte. New inroads in understanding the functioning of Esyt3, a protein associated with the endoplasmic reticulum (ER) that is believed to play a key role in anchoring the ER to the plasma membrane, include: the mapping of the Ca++ and phospholipid binding to the BM y C2-1,C2-2 y C2-3 domains; the characterization of its physical interaction with gelsolin; its role in lipid droplet biogenesis.
Cu+- induced relocation of the Cu+ transporter ATP7B from the trans-Golgi network to the bile canaliculus in CAN 10 hepatoma cells. Cells treated with Cu+ as indicated in the panels were studied for ATP7B location. Note the early transit of ATP7B through the cell basolateral domain (area delineated by the white dotted lines and the far end of the β catenin labelled plasma membrane) and the localization of ATP7B in the bile canaliculi, sealed by the ZO-1 positive tight junctions, after extensive treatment with Cu+.
|Last name||Name||Laboratory||Ext.*||Professional category|
|Pulido Vega||Diego||407||4436||dpulido(at)cbm.csic.es||E.Científicos Titulares de Organismos Públicos de Investigación|
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