title: Intracellular Ca(2+) regulates the cellular iron uptake in K562 cells.
abstract: Fluorescence quenching was used to study the kinetics of the transferrin receptor (TfR)-mediated iron uptake in the calcein-loaded K562 cells. It was found that elevation of intracellular free Ca(2+) ([Ca(2+)](i)) by thapsigargin (TG) speeds up the initial rate of iron uptake and increases the overall capacity of the cells in taking up iron. Depletion of intracellular Ca(2+) or complete chelation of extracellular Ca(2+) results in complete inhibition of the iron uptake in cells. To gain insight into molecular mechanism, IANBD-labeled transferrin (Tf) and microscopic fluorescence imaging were used to observe the endocytosis and recycling of the Tf-TfR complex in single live cells. The study showed that the preincubation of cells with TG or phorbol myristate acetate (PMA), the direct activator of protein kinase C (PKC), accelerated the endocytosis and recycling of the complex in a dose-dependent manner. W-7, the calmodulin antagonist, and GF109203X, a selected cell-permeant inhibitor of PKC, can reverse the acceleration. Analysis of actin polymerization in controlled, [Ca(2+)](i)-elevated and W-7-treated cells revealed that the actin polymerization is enhanced as [Ca(2+)](i) is raised, but reduced by W-7. The results suggest that the regulation of actin polymerization by intracellular Ca(2+) may play a central role in Ca(2+)-dependent iron uptake.
authors.affiliation: Institute of Biophysics, Chinese Academy of Sciences, 15 Datun Road, Chaoyang District, Beijing 100101, China.
authors.forename: Weimin
authors.initials: W
authors.lastname: Ci
authors.forename: Wenyu
authors.initials: W
authors.lastname: Li
authors.forename: Ya
authors.initials: Y
authors.lastname: Ke
authors.forename: Zhong-Ming
authors.initials: ZM
authors.lastname: Qian
authors.forename: Xun
authors.initials: X
authors.lastname: Shen
mesh_terms: D000199:Actins / Q000096:biosynthesis / Q000187:drug effects; D002118:Calcium / Q000378:metabolism*; D020013:Calcium Signaling / Q000187:drug effects / Q000502:physiology*; D002614:Chelating Agents / Q000494:pharmacology; D004705:Endocytosis / Q000187:drug effects / Q000502:physiology*; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005057:Eukaryotic Cells / Q000187:drug effects / Q000378:metabolism*; D005452:Fluoresceins; D006801:Humans; D007424:Intracellular Fluid / Q000187:drug effects / Q000378:metabolism*; D007501:Iron / Q000378:metabolism*; D010069:Oxadiazoles; D011108:Polymers / Q000378:metabolism; D011493:Protein Kinase C / Q000187:drug effects / Q000378:metabolism; D011990:Receptors, Transferrin / Q000187:drug effects / Q000378:metabolism*; D014168:Transferrin / Q000378:metabolism; D014407:Tumor Cells, Cultured; D015854:Up-Regulation / Q000187:drug effects / Q000502:physiology
chemical_list: D000199:Actins; D002614:Chelating Agents; D004791:Enzyme Inhibitors; D005452:Fluoresceins; D010069:Oxadiazoles; D011108:Polymers; D011990:Receptors, Transferrin; D014168:Transferrin; C035573:4-(N-(iodoacetoxy)ethyl-N-methyl)amino-7-nitrobenz-2-oxa-1,3-diazole; D007501:Iron; D011493:Protein Kinase C; D002118:Calcium; C007740:fluorexon