title: Tumor-promoting, phorbol ester-induced phosphorylation of cell-surface transferrin receptors in human erythroleukemia cells.
abstract: When human erythroleukemia cells (K562) were exposed to phorbol-12-myristate 13-acetate (PMA), phosphorylation of transferrin receptors was enhanced 5-fold with 10(-7) M PMA and 7-fold with 10(-6) M PMA, but not with 4 alpha-phorbol (5 X 10(-7) M). Stimulation took place in serine residues in the cytoplasmic domain of the receptor. Although phosphorylation in the control cells took place in both cell-surface and intracellular receptors, phosphorylation in PMA-treated cells increased only in the cell-surface receptors, not in the intracellular receptors. The number of receptors on the cell surface increased slightly with the increase in phosphorylation at the cell surface, in the PMA-treated cells. No difference in transferrin binding was found for the control and PMA-treated cells. These results indicate that enhanced phosphorylation of the transferrin receptor takes place on the cell surface only and that it presumably is mediated by protein kinase C.
authors.forename: H
authors.initials: H
authors.lastname: Kohno
authors.forename: S
authors.initials: S
authors.lastname: Taketani
authors.forename: R
authors.initials: R
authors.lastname: Tokunaga
mesh_terms: D000818:Animals; D000911:Antibodies, Monoclonal / Q000276:immunology; D002460:Cell Line; D002462:Cell Membrane / Q000378:metabolism; D004591:Electrophoresis, Polyacrylamide Gel; D006801:Humans; D004915:Leukemia, Erythroblastic, Acute / Q000378:metabolism*; D051379:Mice; D010704:Phorbols / Q000494:pharmacology*; D010766:Phosphorylation; D011956:Receptors, Cell Surface / Q000032:analysis / Q000187:drug effects*; D011990:Receptors, Transferrin; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology*; D014168:Transferrin / Q000378:metabolism*
chemical_list: D000911:Antibodies, Monoclonal; D010704:Phorbols; D011956:Receptors, Cell Surface; D011990:Receptors, Transferrin; D014168:Transferrin; D013755:Tetradecanoylphorbol Acetate