Apotransferrin is internalized and distributed in the same way as holotransferrin in K562 cells.
Transferrin (Tf), a naturally existing protein, has received considerable attention in the area of drug targeting since it is biodegradable, non-toxic, and non-immunogenic. The efficient cellular uptake of Tf shows it has potential in the delivery of anti-cancer drugs, proteins, and therapeutic genes into proliferating malignant cells that overexpress transferrin receptor (TfR). In human serum, about 30% of Tf exists in the iron-saturated form (Fe(2)-Tf) and the remainder exists as apotransferrin (apo-Tf). Understanding the uptake of apo-Tf by cells will provide key insights into studies on Tf-mediated drug delivery. In the present study, we investigated visually the transport of apo-Tf into K562 cells and its intracellular localization by laser-scanning confocal microscopy (LSCM) and flow cytometry analysis (FCA). It was found that, like Fe(2)-Tf, apo-Tf can be taken up into the cells. The process is time- and temperature-dependent, competitively inhibited by Fe(2)-Tf, and significantly abolished by pronase pretreatment. Visual evidence showed that the transport of apo-Tf into K562 cells is a TfR-mediated process. Furthermore, the investigations using optical-slicing technique demonstrated that the distribution of apo-Tf is similar to that of Fe(2)-Tf, both appearing in the perinuclear region in ball-in-bowl shape.
School of Pharmaceutical Science and Joint Laboratory of Perking University & The Hong Kong Polytechnic University, Perking University, Beijing, People's Republic of China.
Du
D
Xiu-Lian
Wang
W
Kui
Ke
K
Ya
Yuan
Y
Lan
Li
L
Rong-Chang
Chang
C
Yan Zhong
Ho
H
Kwok Ping
Qian
Q
Zhong Ming
D001059:Apoproteins / Q000493:pharmacokinetics*; D001692:Biological Transport / Q000187:drug effects / Q000502:physiology; D016503:Drug Delivery Systems; D016650:Fluorescein-5-isothiocyanate; D005456:Fluorescent Dyes; D006801:Humans; D020014:K562 Cells; D018613:Microscopy, Confocal; D011402:Pronase / Q000494:pharmacology; D013696:Temperature; D013997:Time Factors; D014168:Transferrin / Q000493:pharmacokinetics*
D001059:Apoproteins; D005456:Fluorescent Dyes; D014168:Transferrin; C028284:apotransferrin; C110714:holotransferrin; D011402:Pronase; D016650:Fluorescein-5-isothiocyanate