TY - JOUR
T1 - Ethanol consumption decreases the synthesis of the mannose 6-phosphate/insulin-like growth factor II receptor but does not decrease its messenger RNA
AU - Haorah, James
AU - MacDonald, Richard G.
AU - Stoner, Julie A.
AU - Donohue, Terrence M.
PY - 2003/2/15
Y1 - 2003/2/15
N2 - The mannose 6-phosphate/insulin-like growth factor II receptor (M6P/IGF-IIR) is a protein that facilitates the transport of acid hydrolases into the lysosome. We have shown that chronic ethanol consumption lowers the M6P/IGF-IIR content in rat hepatocytes. Here, we determined the steady-state level of mRNA encoding M6P/IGF-IIR, as well as the rate of receptor synthesis, to ascertain whether the ethanol-elicited reduction in receptor protein content is related to changes in either or both of these parameters. Rats were pair-fed the normal carbohydrate (NC) or low carbohydrate high-fat (LC) liquid diets containing either ethanol or isocaloric maltose-dextrin for 7-8 weeks. RNA was isolated from hepatocytes and from whole livers of these animals and subjected to reverse transcription-polymerase chain reaction (RT-PCR) to determine the mRNA levels encoding M6P/IGF-IIR. Hepatocytes isolated from these animals were also radiolabeled with Pro-mix L-[35S] in vitro cell labeling mix to measure incorporation into total cellular protein and the immunoprecipitated M6P/IGF-IIR protein. The steady-state levels of M6P/IGF-IIR mRNA in both hepatocytes and whole livers from ethanol-fed rats were the same as those from their respective controls regardless of whether they were fed the NC or the LC diets. Hepatocytes from ethanol-fed rats showed a 36% lower rate of total protein synthesis and an even greater reduction (70%) in receptor synthesis. When the relative rate of receptor synthesis was calculated, hepatocytes from ethanol-fed rats had a 53% lower relative rate of receptor synthesis compared with controls. Autoradiographic analysis of the immunoprecipitated receptor protein from ethanol-fed rats also indicated a 79% decline in the total M6P/IGF-IIR protein synthetic rate compared with pair-fed controls. We conclude that the ethanol-elicited reduction of M6P/IGF-IIR content was, in part, related to a concomitant reduction of receptor protein synthesis but not to a decline in its mRNA level. Thus, the ethanol-elicited decline in receptor protein synthesis may be due to defective M6P/IGF-IIR mRNA translation.
AB - The mannose 6-phosphate/insulin-like growth factor II receptor (M6P/IGF-IIR) is a protein that facilitates the transport of acid hydrolases into the lysosome. We have shown that chronic ethanol consumption lowers the M6P/IGF-IIR content in rat hepatocytes. Here, we determined the steady-state level of mRNA encoding M6P/IGF-IIR, as well as the rate of receptor synthesis, to ascertain whether the ethanol-elicited reduction in receptor protein content is related to changes in either or both of these parameters. Rats were pair-fed the normal carbohydrate (NC) or low carbohydrate high-fat (LC) liquid diets containing either ethanol or isocaloric maltose-dextrin for 7-8 weeks. RNA was isolated from hepatocytes and from whole livers of these animals and subjected to reverse transcription-polymerase chain reaction (RT-PCR) to determine the mRNA levels encoding M6P/IGF-IIR. Hepatocytes isolated from these animals were also radiolabeled with Pro-mix L-[35S] in vitro cell labeling mix to measure incorporation into total cellular protein and the immunoprecipitated M6P/IGF-IIR protein. The steady-state levels of M6P/IGF-IIR mRNA in both hepatocytes and whole livers from ethanol-fed rats were the same as those from their respective controls regardless of whether they were fed the NC or the LC diets. Hepatocytes from ethanol-fed rats showed a 36% lower rate of total protein synthesis and an even greater reduction (70%) in receptor synthesis. When the relative rate of receptor synthesis was calculated, hepatocytes from ethanol-fed rats had a 53% lower relative rate of receptor synthesis compared with controls. Autoradiographic analysis of the immunoprecipitated receptor protein from ethanol-fed rats also indicated a 79% decline in the total M6P/IGF-IIR protein synthetic rate compared with pair-fed controls. We conclude that the ethanol-elicited reduction of M6P/IGF-IIR content was, in part, related to a concomitant reduction of receptor protein synthesis but not to a decline in its mRNA level. Thus, the ethanol-elicited decline in receptor protein synthesis may be due to defective M6P/IGF-IIR mRNA translation.
KW - Liver
KW - Low carbohydrate diet
KW - Messenger RNA
KW - RT-PCR
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UR - http://www.scopus.com/inward/citedby.url?scp=0037441387&partnerID=8YFLogxK
U2 - 10.1016/S0006-2952(02)01605-2
DO - 10.1016/S0006-2952(02)01605-2
M3 - Article
C2 - 12566093
AN - SCOPUS:0037441387
VL - 65
SP - 637
EP - 648
JO - Biochemical Pharmacology
JF - Biochemical Pharmacology
SN - 0006-2952
IS - 4
ER -