Abstract
We have shown that degradation of asialo-orosomucoid (ASOR) in isolated rat hepatocytes occurs by two different intracellular pathways [Clarke, Oka and Weigel (1987) J. Biol. Chem. 262, 17384-17392] mediated by two subpopulations of cell surface galactosyl (Gal) receptors, designated State 1 or State 2 receptors. In the present study, several inhibitors were tested for their effects on ligand degradation by the State 1 or State 2 pathway. Leupeptin, monensin and chloroquine completely inhibited degradation of 125I-labelled ASOR in both pathways. Dose-response studies showed, however, that the State 2 pathway was more sensitive to leupeptin or monensin than the State 1 pathway. No differences were observed with chloroquine. For example, the onset of the inhibition in the State 2 and State 1 pathways occurred at about 0.05 and 0.3 μM-leupeptin respectively, a 6-fold difference. At 3.5 μM-monensin, 125I-ASOR degradation in the State 2 pathway was completely blocked, whereas degradation in the State 1 pathway was essentially unaffected. Colchicine was observed to give the largest differential sensitivity between the two pathways. The State 2 degradation pathway was about 30-fold more sensitive to colchicine than the State 1 pathway. Lumicolchicine had no affect. The onset of inhibition of the rate of 125I-ASOR degradation in the State 2 and State 1 pathways occurred at ~ 0.1 and 3.0 μM-colchicine respectively. At very high concentrations (> 0.1 mM), the State 1 pathway could be completely inhibited. We conclude that intracellular 125I-ASOR processing or delivery to degradative compartments in both the State 1 and State 2 Gal receptor pathways requires low pH. Ligand delivery to the degradative compartment does not require microtubules in the State 1 pathway, consistent with the very rapid onset of degradation in this pathway. The State 2 degradation pathway does require microtubules.
Original language | English (US) |
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Pages (from-to) | 277-284 |
Number of pages | 8 |
Journal | Biochemical Journal |
Volume | 262 |
Issue number | 1 |
DOIs | |
State | Published - 1989 |