Effect of monensin on receptor recycling during continuous endocytosis of asialoorosomucoid.
The binding of asialoglycoproteins to their liver cell receptor results in internalization of the ligand-receptor complex. These complexes rapidly appear in intracellular compartments termed endosomes whose acidification results in ligand-receptor dissociation. Ligand and receptor subsequently segregate: ligand is transported to lysosomes and is degraded while receptor recycles to the cell surface. The proton ionophore monensin prevents acidification of endosomes and reversibly inhibits this acid-dependent dissociation of ligand from receptor. The present study determined the effect of monensin treatment of short-term cultured rat hepatocytes on cell-surface-receptor content, determined both by their binding activity and immunologically, following continuous endocytosis of asialoorosomucoid. Inclusion of 5 microM monensin in the incubation medium reduced the number of immunologically detectable cell-surface receptors by 20% in the absence of ligand. During continuous endocytosis of asialoorosomucoid, inclusion of monensin resulted in a 30-40% reduction of cell-surface receptor detectable either by ligand binding or immunologically. These results suggest that the reduced liver-cell-surface content of receptor in monensin is due to intracellular trapping of ligand-receptor complexes. The reduction of surface receptor during monensin incubation in the absence of ligand suggests that "constitutive recycling" of plasma membrane components also requires intracellular acidification.
Kaiser
J
J
Liver Research Center, Albert Einstein College of Medicine, Bronx, New York 10461.
Stockert
R J
RJ
Wolkoff
A W
AW
D000818:Animals; D037263:Asialoglycoprotein Receptor; D001212:Asialoglycoproteins; D002478:Cells, Cultured; D004705:Endocytosis / Q000187:drug effects*; D008099:Liver / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D008985:Monensin / Q000494:pharmacology*; D009961:Orosomucoid / Q000031:analogs & derivatives* / Q000378:metabolism; D051381:Rats; D011971:Receptors, Immunologic / Q000187:drug effects* / Q000378:metabolism
D037263:Asialoglycoprotein Receptor; D001212:Asialoglycoproteins; D009961:Orosomucoid; D011971:Receptors, Immunologic; C017030:asialoorosomucoid; D008985:Monensin