Characterization of transferrin receptor-dependent GaC–Tf–FeN transport in human leukemic HL60 cells

BackgroundUnderstanding the uptake of GaC–Tf–FeN by cells will provide key insights into studies on transferrin-mediated drug delivery.MethodsThe 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.ResultsAn 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.ConclusionOn the basis of these findings, we proposed the “transferrin receptor” for the mechanism of GaC–Tf–FeN transport by HL60 cells.