Ethanol inhibits asialoglycoprotein receptor synthesis but augments its mRNA expression in a human hepatoma cell line

Abstract

The effect of ethanol on the expression of asialoglycoprotein receptor protein and its mRNA was studied in a human hepatoma cell line, HepG2. The number of asialoglycoprotein receptors on the cell surface was decreased to 60% of the control level, without a loss in affinity, by incubating the cells with 100 mM ethanol. The decrease in cell surface asialoglycoprotein receptors was paralleled by a decrease in total receptor numbers, including intracellular and surface receptors. The internalization of asialoglycoprotein was also diminished, to 44% of that in control cells. The decreases in cell surface receptors and total receptor numbers were partially restored by 2 mM 4-methylpyrazole, suggesting that ethanol metabolites participated in the diminution of asialoglycoprotein receptor expression. However, the steady-state expression of asialoglycoprotein receptor mRNA was increased in ethanol-treated cells and further augmented by a longer ethanol exposure. These paradoxical results, i.e., the decrease of asialoglycoprotein receptor protein and the increase of its mRNA expression, suggest that the reduction in the asialoglycoprotein receptor protein is a post-transcriptional event and that a possible feedback regulatory mechanism may control asialoglycoprotein receptor gene transcription and/or impair the degradation of its mRNA.

Ethanol Induces Transforming Growth Factor‐α Expression in Hepatocytes, Leading to Stimulation of Collagen Synthesis by Hepatic Stellate Cells

“…Therefore, we speculated that alternative mechanisms might involve the direct release of one or more humoral factors from ethanol-injured hepatocytes that stimulate collagen synthesis in HSCs and liver fibroblasts. We previously disclosed that human hepatoblastoma HepG2 cells are highly potent in metabolizing ethanol in a similar manner as normal hepatocytes (Kato et al, 1998;Kohgo et al, 1994). We then found that a~6,000 Da polypeptide secreted from ethanolexposed HepG2 cells was capable of stimulating collagen synthesis in human fibroblast IMR-90 cells (Inui et al, 1996).…”

Suppressive effect of ethanol on the expression of hepatic asialoglycoprotein receptors augmented by interleukin-1β, interleukin-6, and tumor necrosis factor-α

“…In a previous study, we examined whether HepG2 cells had a metabolic pathway for ethanol as a normal hepatocyte function, and we showed that these cells had significantly high alcohol dehydrogenase (ADH) activity (similar to that in rat liver tissue), and this activity was similar to that in human liver in vivo. 16 In the present study, we incubated the HepG2 cells with 100 mM ethanol; as such a high blood level of ethanol has been found in patients with alcoholic liver disease, 24,25 this concentration seemed to be suitable for an in vitro experiment. This concentration had previously been used in an investigation of the effects of ethanol on human macrophage functions.…”

“…6,8 Most of these proteins are glycoproteins, which are catabolized exclusively by AGPRs in hepatic parenchymal cells. 16,20,22 The human hepatoma cell line, HepG2, used in this study shows numerous normal hepatocyte functions, such as the synthesis and secretion of serum glycoproteins, 14 and the ability to internalize and degrade asialoglycoproteins mediated by the AGPRs. 20 We therefore selected the HepG2 cell line as a model for studying the effects of cytokines on the expression of AGPRs in human hepatocytes.…”

“…To modulate AGPR synthesis, HepG2 cells were cultured for 7 days in the presence or absence of 100 mM ethanol in 12-well tissue culture plates (Flow Laboratories) as described previously. 16 In this open culture system, the ethanol concentration decreased by 25% after 48 h in the absence of the cells. Therefore, culture media were changed every 2 days to maintain an approximate concentration of 100 mM ethanol.…”

“…We have already reported that AGPR in HepG2 cells was decreased by ethanol in a dosedependent manner, and that the decrease in AGPR was partially inhibited by treatment with 4-methyl pyrazol, an aldehyde dehydrogenase inhibitor. 16 Accordingly, the ethanol-induced decrease in AGPR may possibly be explained by additional factors such as the direct toxicity of ethanol and the effect of a non-ADH pathway.…”