title: Complete inhibition of transferrin recycling by monensin in K562 cells.
abstract: Monensin blocks human transferrin recycling in a dose-dependent and reversible manner in K562 cells, reaching 100% inhibition at a noncytocidal dose of 10(-5) M, whereas transferrin recycling is virtually unaffected by noncytocidal doses of chloroquine. The intracellular pathway of human transferrin in K562 cells, both in the presence and absence of 10(-5) M monensin, was localized by indirect immunofluorescence. Monensin blocks transferrin recycling by causing internalized ligand to accumulate in the perinuclear region of the cell. The effect of 10(-5) M monensin on human transferrin kinetics was quantitatively measured by radioimmunoassay and showed a positive correlation with immunofluorescent studies. Immunoelectron microscopic localization of human transferrin as it cycles through K562 cells reveals the appearance of perinuclear transferrin-positive multivesicular bodies within 3 min of internalization, with subsequent exocytic delivery of the ligand to the cell surface via transferrin-staining vesicles arising from these perinuclear structures within 5 min of internalization. Inhibition of ligand recycling with 10(-5) M monensin causes dilated transferrin-positive multivesicular bodies to accumulate within the cell with no evidence of recycling vesicles. A coordinated interaction between multivesicular bodies and the Golgi apparatus appears to be involved in the recycling of transferrin in K562 cells. Cell-surface-binding sites for transferrin were reduced by 50% with 10(-5) M monensin treatment; however, this effect was not attenuated by 80% protein synthesis inhibition with cycloheximide, supporting the idea that the transferrin receptor is also recycled through the Golgi.
mesh_terms: D002460:Cell Line; D002738:Chloroquine / Q000494:pharmacology; D005455:Fluorescent Antibody Technique; D005663:Furans / Q000494:pharmacology*; D006801:Humans; D007700:Kinetics; D015470:Leukemia, Myeloid, Acute; D008854:Microscopy, Electron; D008985:Monensin / Q000494:pharmacology*; D011956:Receptors, Cell Surface / Q000032:analysis / Q000378:metabolism*; D011990:Receptors, Transferrin; D014168:Transferrin / Q000037:antagonists & inhibitors*
chemical_list: D005663:Furans; D011956:Receptors, Cell Surface; D011990:Receptors, Transferrin; D014168:Transferrin; D002738:Chloroquine; D008985:Monensin