Effects of cytokines on synthesis and function of the hepatic asialoglycoprotein receptor

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Abstract
In this study we have investigated whether cytokines, critical mediators of the immune response, might have a direct effect on the expression and/or function of the human hepatic asialoglycoprotein receptor (ASGPR). Binding and uptake of asialoglycoproteins by the human hepatoma cell line, HepG2, and by freshly isolated rat hepatocytes were inhibited by 50% after 3–6 hours and completely abolished following a 24 hour exposure to tumor necrosis factor (TNF) α, interferon (INF) α or γ, or interleukin‐2 (IL‐2). The loss of ASGPR binding activity mediated by IL‐2 was reversible up to 4 hours of exposure and accompanied by the selective phosphorylatior, of the cell‐surface receptor. Steady‐state levels of total cellular ASGPR protein remained unchanged over the first 6 hours of IL‐2 incubation but declined in a dose dependent manner thereafter. This down regulation of ASGPR expression was due to reduced synthesis as a result of reduced receptor transcript levels. No loss was detected, however, of cell surface‐associated receptor protein even after 24 hours of IL‐2 incubation, suggesting that cytokine induced phosphorvlation constitutes a mechanism to regulate receptor activity.