Y-box binding protein-1 down-regulates expression of carbamoyl phosphate synthetase-I by suppressing CCAAT enhancer-binding protein-alpha function in mice.
OBJECTIVE
Carbamoyl phosphate synthetase-I (CPS1) is a key enzyme in the urea cycle and patients with defects in the function or expression of CPS1 suffer from hyperammonemia. CPS1 is expressed in the liver at neonatal and adult stages in a CCAAT enhancer-binding protein-alpha (C/EBPalpha)-dependent manner. Despite expression of C/EBPalpha, CPS1 is not expressed in fetal liver, indicating an additional factor is involved in the regulation of CPS1 expression. The aim of this study was to elucidate the mechanism of CPS1 expression.


METHODS
Microarray was performed to find Y-box binding protein-1 (YB-1) that was expressed in mouse fetal liver. The role of YB-1 in CPS1 expression was investigated by overexpression of YB-1 in mouse fetal liver culture and luciferase reporter assays using the CPS1 promoter. Chromatin immunoprecipitation assay was used to examine recruitment of YB-1 to the CPS1 promoter in vivo.


RESULTS
Expression of YB-1 and CPS1 was inversely correlated in vivo, and YB-1 inhibited CPS1 expression and ammonia clearance in fetal liver culture. Although YB-1 was not expressed in adult liver, acute liver injury up-regulated YB-1 and down-regulated CPS1, accompanying an increase of the serum ammonia level. YB-1 inhibited C/EBPalpha-induced transcription from the CPS1 promoter via the Y-box near the C/EBPalpha-binding site. Chromatin immunoprecipitation assays demonstrated that YB-1 was recruited to the CPS1 promoter in fetal and injured adult liver, but not in normal adult liver.


CONCLUSIONS
YB-1 is a key regulator of ammonia detoxification by negatively regulating CPS1 expression via suppression of C/EBPalpha function.
Chen
Yen-Rong
YR
Institute of Molecular and Cellular Biosciences, The University of Tokyo, Japan.
Sekine
Keisuke
K
Nakamura
Koji
K
Yanai
Hiroyuki
H
Tanaka
Minoru
M
Miyajima
Atsushi
A
D000367:Age Factors; D000641:Ammonia / Q000378:metabolism; D000818:Animals; D000831:Animals, Newborn; D001483:Base Sequence; D022762:CCAAT-Enhancer-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D002222:Carbamoyl-Phosphate Synthase (Ammonia) / Q000235:genetics / Q000378:metabolism*; D002478:Cells, Cultured; D056486:Chemical and Drug Induced Liver Injury / Q000201:enzymology; D004195:Disease Models, Animal; D015536:Down-Regulation; D020869:Gene Expression Profiling / Q000379:methods; D018507:Gene Expression Regulation, Developmental; D015971:Gene Expression Regulation, Enzymologic; D017930:Genes, Reporter; D005865:Gestational Age; D022781:Hepatocytes / Q000201:enzymology*; D006801:Humans; D008099:Liver / Q000196:embryology / Q000201:enzymology*; D051379:Mice; D008810:Mice, Inbred C57BL; D008969:Molecular Sequence Data; D020411:Oligonucleotide Array Sequence Analysis; D011401:Promoter Regions, Genetic; D011485:Protein Binding; D013997:Time Factors; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism*; D014158:Transcription, Genetic; D014161:Transduction, Genetic; D014508:Urea / Q000378:metabolism
D000641:Ammonia; D022762:CCAAT-Enhancer-Binding Proteins; D002222:Carbamoyl-Phosphate Synthase (Ammonia); D014157:Transcription Factors; D014508:Urea; C530718:CEBPA protein, mouse; C541744:Ybx1 protein, mouse