Regulation of asialoglycoprotein receptor synthesis by inflammation-related cytokines in HepG2 cells

The asialoglycoprotein receptor (AGPR) is responsible for the catabolism of acute phase proteins. The effects of inflammation-related cytokines on the expression of AGPR were investigated in HepG2 cells derived from a human hepatoblastoma cell line. Binding studies, using a [125I]-labeled asialo-orosomucoid ligand, revealed that AGPR numbers on cell surfaces were increased by interleukin-1 (IL-1), interleukin-6 (IL-6), and tumor necrosis factor (TNF). In cells treated with IL-1, IL-6, or TNF, immunohistochemical staining with an anti-AGPR monoclonal antibody demonstrated augmented expression. Pulse labeling analysis, using [35S]-labeled methionine, showed newly synthesized AGPR in both the precursor and the mature forms. When IL-1, IL-6, and TNF were added to the culture medium, total synthesis of AGPR (sum of the mature and precursor forms) was increased. In addition, the relative proportion of the synthesized precursor form of AGPR was higher in cytokine-treated than in untreated cells, suggesting that these cytokines augment the synthesis of AGPR, particularly in the stage prior to glycosylation.