Recycling of the asialoglycoprotein receptor and the effect of lysosomotropic amines in hepatoma cells.

Abstract

Receptor-mediated uptake and degradation of 125I-asialoorosomucoid (ASOR) in human hepatoma HepG2 cells is inhibited by the lysosomotropic amines chloroquine and primaquine. In the absence of added ligand at 37.degree. C, these amines induce a rapid (t1/2 [half-time] 5.5-6 min) and reversible loss of cell surface 125I-ASOR binding sites as well as a rapid decrease in 125I-ASOR uptake and degradation. There is no effect of these amines on the binding of 125I-ASOR to the cell surface at 4.degree. C or on the rate of internalization of prebound 125I-ASOR. The loss of 125I-ASOR surface binding at 37.degree. C is not attributable to altered affinity of ligand-receptor binding. In the presence of added ligand at 37.degree. C, there is a more rapid (t1/2 2.5-3 min) loss of hepatoma cell surface receptors. The amines inhibit the rapid return of the internalized receptor to the cell surface. The nature of this loss of 125I-ASOR surface binding sites was examined by following the fate of receptor molecules after biosynthetic labeling and after cell surface iodination. At 37.degree. C, chloroquine and primaquine induce a loss of asialoglycoprotein receptor molecules from the hepatoma cell surface to an internal pool.