title: Characterization of transferrin receptor-dependent GaC-Tf-FeN transport in human leukemic HL60 cells.
abstract: BACKGROUND
  Understanding the uptake of GaC-Tf-FeN by cells will provide key insights into studies on transferrin-mediated drug delivery.
  
  
  METHODS
  The mechanism of GaC-Tf-FeN transporting into and out of HL60 cells has been investigated by comparing transports between GaC-Tf-FeN and apoTf by means of 125I-labeled transferrin.
  
  
  RESULTS
  An association constant for GaC-Tf-FeN was 2 times that for apoTf. GaC-Tf-FeN and apoTf of cell surface-bound displayed similar kinetics during the uptake, but the release rates of internalized GaC-Tf-FeN and apoTf from cells were different which showed characteristic disparate. The release continued to occur during the incubation of GaC-Tf-FeN in the presence of nonradioactive apoTf. Neither NaN3 nor NH4Cl could completely block internalization of GaC-Tf-FeN, but they prevented the release of GaC-Tf-FeN from the cells. Excess cold unlabeled apoTf could overcome the block in the release due to NH4Cl but not NaN3. The binding and internalization of GaC-Tf-FeN could be competitively inhibited by nonradioactive apoTf. It implies that both bind to the same receptor on the membrane and the localization of GaC-Tf-FeN resembles that of apoTf inside cells. Pretreated cells with pronase abolished the binding of GaC-Tf-FeN significantly.
  
  
  CONCLUSIONS
  On the basis of these findings, we proposed the "transferrin receptor" for the mechanism of GaC-Tf-FeN transport by HL60 cells.
authors.affiliation: Key Laboratory of Chemical Biology and Molecular Engineering of Ministry of Education, Institute of Molecular Science, Shanxi University, Taiyuan, Shanxi 030006, China.
authors.forename: Ying-Qi
authors.initials: YQ
authors.lastname: Li
authors.forename: Bin
authors.initials: B
authors.lastname: Liu
authors.forename: Chun-Gui
authors.initials: CG
authors.lastname: Zhao
authors.forename: Wei
authors.initials: W
authors.lastname: Zhang
authors.forename: Bin-Sheng
authors.initials: BS
authors.lastname: Yang
mesh_terms: D000643:Ammonium Chloride / Q000494:pharmacology; D001059:Apoproteins / Q000378:metabolism / Q000493:pharmacokinetics* / Q000494:pharmacology; D001667:Binding, Competitive / Q000187:drug effects; D001692:Biological Transport / Q000187:drug effects; D004305:Dose-Response Relationship, Drug; D005708:Gallium / Q000737:chemistry; D018922:HL-60 Cells; D006801:Humans; D007457:Iodine Radioisotopes; D007501:Iron / Q000737:chemistry; D007700:Kinetics; D015473:Leukemia, Promyelocytic, Acute / Q000378:metabolism / Q000473:pathology; D011402:Pronase / Q000494:pharmacology; D011485:Protein Binding / Q000187:drug effects; D011990:Receptors, Transferrin / Q000502:physiology*; D019810:Sodium Azide / Q000494:pharmacology; D014168:Transferrin / Q000737:chemistry / Q000378:metabolism / Q000493:pharmacokinetics* / Q000494:pharmacology
chemical_list: D001059:Apoproteins; D007457:Iodine Radioisotopes; D011990:Receptors, Transferrin; D014168:Transferrin; C028284:apotransferrin; D000643:Ammonium Chloride; D019810:Sodium Azide; D005708:Gallium; D007501:Iron; D011402:Pronase