Receptor-mediated endocytosis of thrombin-antithrombin III complex by the human monocytoid cell line U937.
Receptor-mediated endocytosis of thrombin-antithrombin III (TAT) complex was characterized with the monocytoid cell line U937. At 4 degrees C, U937 cells bound TAT but not antithrombin III in a rapid, specific, saturable, and reversible manner. [125I]TAT binding to U937 cells was not inhibited by antithrombin III and hardly by thrombin, but 75% inhibited by a 50 molar excess of the unlabeled TAT. There were about 79,000 binding sites/cell (Kd = 68 nM). The TAT receptor on U937 cells may be distinct from the serpin-enzyme complex (SEC) receptor, since a synthetic peptide corresponding to the recognition sequence of SEC receptor did not compete with TAT binding to the cells. Receptor-bound TAT was internalized into the cells after switching the temperature from 4 to 37 degrees C and thereafter degraded in lysosomes.
Takeya
H
H
Department of Molecular Biology on Genetic Disease, Mie University School of Medicine, Japan.
Hamada
T
T
Kume
M
M
Suzuki
K
K
D000595:Amino Acid Sequence; D000990:Antithrombin III / Q000378:metabolism*; D002460:Cell Line; D004705:Endocytosis; D006801:Humans; D066298:In Vitro Techniques; D046911:Macromolecular Substances; D008969:Molecular Sequence Data; D009000:Monocytes / Q000378:metabolism; D011956:Receptors, Cell Surface / Q000378:metabolism*; D013696:Temperature; D013917:Thrombin / Q000378:metabolism*; D014407:Tumor Cells, Cultured
D046911:Macromolecular Substances; D011956:Receptors, Cell Surface; D000990:Antithrombin III; D013917:Thrombin