title: Cell surface ceramide controls translocation of transferrin receptor to clathrin-coated pits.
abstract: Transferrin receptor mediates internalization of transferrin with bound ferric ions through the clathrin-dependent pathway. We found that binding of transferrin to the receptor induced rapid generation of cell surface ceramide which correlated with activation of acid, but not neutral, sphingomyelinase. At the onset of transferrin internalization both ceramide level and acid sphingomyelinase activity returned to their basic levels. Down-regulation of acid sphingomyelinase in cells with imipramine or silencing of the enzyme expression with siRNA stimulated transferrin internalization and inhibited its recycling. In these conditions colocalization of transferrin with clathrin was markedly reduced. Simultaneously, K(+) depletion of cells which interfered with the assembly of clathrin-coated pits inhibited the uptake of transferrin much less efficiently than it did in control conditions. The down-regulation of acid sphingomyelinase activity led to the translocation of transferrin receptor to the raft fraction of the plasma membrane upon transferrin binding. The data suggest that lack of cell surface ceramide, generated in physiological conditions by acid sphingomyelinase during transferrin binding, enables internalization of transferrin/transferrin receptor complex by clathrin-independent pathway.
authors.affiliation: Laboratory of Molecular Cell Biology, Zoology Department, Assiut University, Assiut, Egypt. eltayeb702002@yahoo.com
authors.forename: Abo Bakr
authors.initials: AB
authors.lastname: Abdel Shakor
authors.forename: Mona Mohamed
authors.initials: MM
authors.lastname: Atia
authors.forename: Katarzyna
authors.initials: K
authors.lastname: Kwiatkowska
authors.forename: Andrzej
authors.initials: A
authors.lastname: Sobota
mesh_terms: D002518:Ceramides / Q000378:metabolism*; D002966:Clathrin / Q000378:metabolism*; D003034:Coated Pits, Cell-Membrane / Q000378:metabolism*; D015536:Down-Regulation; D006801:Humans; D007477:Ions / Q000737:chemistry; D019169:Jurkat Cells; D011188:Potassium / Q000378:metabolism; D011485:Protein Binding; D021381:Protein Transport; D034622:RNA Interference; D034741:RNA, Small Interfering / Q000378:metabolism; D011990:Receptors, Transferrin / Q000378:metabolism*; D013108:Sphingomyelin Phosphodiesterase / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism; D014168:Transferrin / Q000378:metabolism
chemical_list: D002518:Ceramides; D002966:Clathrin; D007477:Ions; D034741:RNA, Small Interfering; D011990:Receptors, Transferrin; D014168:Transferrin; C112980:acid sphingomyelinase-1; D013108:Sphingomyelin Phosphodiesterase; D011188:Potassium