Chronic Ethanol Administration Decreases the Ligand Binding Properties and the Cellular Content of the Mannose 6-Phosphatelinsulin-Like Growth Gactor II Receptor in Rat Hepatocytes

Authors

• James Haorah, ?Liver Study Unit, Research Service (151), The Veterans Affairs (VA) Medical Center, 4101 Woolworth Avenue, Omaha, NE 68105, USA
• Daniel L. McVicker, ?Liver Study Unit, Research Service (151), The Veterans Affairs (VA) Medical Center, 4101 Woolworth Avenue, Omaha, NE 68105, USA
• James C. Byrd, University qf Nebraska College qf Medicine, Omaha, NE 68105, USA
• Richard G. MacDonald, University qf Nebraska College qf Medicine, Omaha, NE 68105, USA
• Terrence M. Donohue, Jr., ?Liver Study Unit, Research Service (151), The Veterans Affairs (VA) Medical Center, 4101 Woolworth Avenue, Omaha, NE 68105, USA

Date of this Version

2002

Comments

Published in Biochemical Pharmacology 63 (2002) 1229-1 239.

Abstract

We have shown previously that chronic ethanol administration impairs the maturation of lysosomal enzymes in rat hepatocytes. The mannose 6-phosphate/insulin-like growth factor I1 receptor (M6PLGF-IIR) is a protein that facilitates the transport of lysosomal enzymes into the lysosome. Therefore, we examined whether ethanol consumption altered the ligand binding properties and the cellular content of M6P/IGF-IIR. Rats were pair-fed liquid diets containing either ethanol (36% of calories) or isocaloric maltose-dextrin for either 1 week or 5-7 weeks. Hepatocytes prepared from these animals were examined for receptor-ligand binding and receptor content. One week of ethanol feeding had no significant effect on ligand [radioiodinated pentamannose phosphate conjugated to bovine serum albumin (¹²⁵I - PMP-BSA)] binding to hepatocytes, but cells from rats fed ethanol for 5-7 weeks bound less ¹²⁵I-PMP-BSA than pair-fed controls. Scatchard plot analysis revealed that the number of ¹²⁵I -PMP-BSA binding sites in hepatocytes from ethanol-fed rats was 49% lower than that of controls. ¹²⁵I-PMP-BSA binding by perivenular (PV) and periportal (PP) hepatocytes from ethanol-fed rats was, respectively, 40 and 48% lower than their controls, but there was no significant difference between these two types of hepatocytes. Ligand blot analysis using ¹²⁵I -insulin-like growth factor II (¹²⁵I –IGF-II) also showed that the receptor in lysates of hepatocytes from ethanol-fed rats bound 26-27% less ligand than controls. Similarly, immunoblot analysis of cell lysates from ethanol-fed rats revealed 62% lower levels of immunoreactive M6P/IGF-IIR than controls. Feeding rats a low carbohydrate-ethanol diet did not exacerbate the reduction in M6P/IGF-IIR-ligand binding nor did it reduce the levels of immunoreactive receptor. Our findings indicate that chronic ethanol consumption lowers M6P/IGF-IIR activity and content in hepatocytes. This reduction may account, in part, for the impaired processing and delivery of acid hydrolases to lysosomes previously observed in ethanol-fed rats.