Expression of haptoglobin receptors in human hepatoma cells.
The uptake of radio-labeled hemoglobin-haptoglobin complex (Hb-Hp) by human hepatoma PLC/PRF/5 and HepG2 cells was investigated in an attempt to characterize the uptake process and intracellular transport. Human hepatoma cells took up Hb-Hp in a receptor-mediated manner. Scatchard analysis of binding revealed that PLC/PRF/5 and HepG2 cells exhibited about 21,000 and 63,000 haptoglobin receptors/cell, with a dissociation constant (Kd) of 8.0 and 17 nM, respectively. Human hepatocytes in primary culture also expressed about 84,000 receptors/cells, with a Kd of 7.4 nM. The hemoglobin-haptoglobin complex was internalized and subsequently the internalized Hb-Hp was slowly degraded in the cells. Preincubation of the cells with Hb-Hp resulted in a decrease in binding of the radioactive Hb-Hp to the cell surface, and was accompanied with an accumulation of intracellular receptors. The uptake of Hb-Hp by the cells was not inhibited by 100 microM chloroquine or by 10 mM methylamine, but was inhibited by 50 microM monodansylcadaverine. Hemoglobin-heme taken up by the cells induced microsomal heme oxygenase. Thus, human hepatoma PLC/PRF/5 and HepG2 cells can take up Hb-Hp by haptoglobin receptor-mediated endocytosis and Hb-Hp probably causes translocation of the haptoglobin receptors from the cell surface to the cell interior where they can be degraded. The internalized heme-moiety of hemoglobin can regulate the expression of heme oxygenase.
Department of Hygiene, Kansai Medical University, Osaka, Japan.
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Okuda
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Tokunaga
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Taketani
D001692:Biological Transport; D002103:Cadaverine / Q000031:analogs & derivatives / Q000494:pharmacology; D006528:Carcinoma, Hepatocellular / Q000378:metabolism*; D002478:Cells, Cultured; D002738:Chloroquine / Q000494:pharmacology; D004705:Endocytosis; D004790:Enzyme Induction; D006242:Haptoglobins / Q000378:metabolism*; D006419:Heme Oxygenase (Decyclizing) / Q000378:metabolism; D006454:Hemoglobins / Q000378:metabolism*; D006801:Humans; D015151:Immunoblotting; D007700:Kinetics; D008099:Liver / Q000166:cytology / Q000378:metabolism; D008113:Liver Neoplasms / Q000378:metabolism*; D008744:Methylamines / Q000494:pharmacology; D008862:Microsomes, Liver / Q000201:enzymology; D011956:Receptors, Cell Surface / Q000378:metabolism*; D011503:Transglutaminases / Q000037:antagonists & inhibitors; D014407:Tumor Cells, Cultured
D006242:Haptoglobins; D006454:Hemoglobins; D008744:Methylamines; D011956:Receptors, Cell Surface; C035492:haptoglobin-hemoglobin complex; D002738:Chloroquine; C027451:methylamine; D006419:Heme Oxygenase (Decyclizing); D011503:Transglutaminases; C008542:monodansylcadaverine; D002103:Cadaverine