Initial expression of phosphoenolpyruvate carboxykinase gene in fetal hepatocytes: role of transcription factors.
OBJECTIVE
Hepatic phosphoenolpyruvate carboxykinase (PEPCK; EC 4.1.1.32) gene is absent in fetal liver. However, this gene can be initially expressed in 20-day-old fetal hepatocyte primary cultures under specific hormonal stimulation. The role of transcriptional factors involved is also studied.


METHODS
Primary 20-day-old fetal hepatocytes have been cultured and Northern-blot and nuclear run-on transcription assays have been performed.


RESULTS
Fetal hepatocytes in culture initially expressed PEPCK gene by dibutyryl cAMP, in the presence of dexamethasone. Dibutyryl cAMP increased by 8-fold the rate of transcription of PEPCK gene at 30 min, and produced a 50-fold increase in its mRNA content at 3 h. This induction of PEPCK expression by cAMP occurred in the presence of sustained levels of CCAAT/enhancer binding protein (C/EBP) alpha-delta mRNAs, and was accompanied by an increase in the rate of transcription and mRNA content of C/EBP beta gene, and a decrease in the expression of c-myc, in the absence of c-fos expression. In addition, insulin or phorbol esters decreased by 50% the PEPCK rate of transcription and its mRNA accumulation induced by dibutyryl cAMP. This inhibitory effect of insulin or phorbol esters on PEPCK gene expression was accompanied by an increase in the rate of transcription and mRNA content of nuclear factors such as c-fos and c-myc, the expression of C/EBPs remaining essentially unmodified.
Molero
C
C
Departamento de Bioquia Molecular, Centro Mixto C.S.I.C.-U.C.M. Facultad de Farmacia, Universidad Complutense, Madrid, Spain.
Valverde
A M
AM
Teruel
T
T
Benito
M
M
Lorenzo
M
M
D000818:Animals; D015152:Blotting, Northern; D003994:Bucladesine / Q000494:pharmacology; D022762:CCAAT-Enhancer-Binding Proteins; D002273:Carcinogens / Q000494:pharmacology; D018929:Cell Culture Techniques; D004268:DNA-Binding Proteins / Q000494:pharmacology; D015971:Gene Expression Regulation, Enzymologic / Q000187:drug effects / Q000502:physiology*; D007004:Hypoglycemic Agents / Q000494:pharmacology; D007328:Insulin / Q000494:pharmacology; D008099:Liver / Q000166:cytology / Q000187:drug effects / Q000196:embryology / Q000201:enzymology*; D009687:Nuclear Proteins / Q000494:pharmacology; D010703:Phorbol Esters / Q000494:pharmacology; D010729:Phosphoenolpyruvate Carboxykinase (GTP) / Q000235:genetics* / Q000378:metabolism; D012333:RNA, Messenger / Q000032:analysis*; D051381:Rats; D017208:Rats, Wistar; D014157:Transcription Factors / Q000494:pharmacology*
D022762:CCAAT-Enhancer-Binding Proteins; D002273:Carcinogens; D004268:DNA-Binding Proteins; D007004:Hypoglycemic Agents; D007328:Insulin; D009687:Nuclear Proteins; D010703:Phorbol Esters; D012333:RNA, Messenger; D014157:Transcription Factors; D003994:Bucladesine; D010729:Phosphoenolpyruvate Carboxykinase (GTP)