Regulation of C/EBPbeta mRNA expression and C/EBPbeta promoter activity by protein kinases A and C in a myelomonocytic cell line (HD11).
OBJECTIVE
The transcription factor CCAAT/enhancer- binding protein (C/EBP) beta is involved in inflammatory responses in immune cells, including myelomonocytic cells. In this study, signal transduction pathways regulating C/EBPbeta expression were investigated.


METHODS
The expression of C/EBPbeta mRNA in cells treated with various activators and inhibitors of PKA and PKC was analyzed by Northern blot hybridization. C/EBPbeta promoter activity was investigated by transient transfection assays with C/EBPbeta promoter CAT constructs.


RESULTS
Phorbol 12-myristate 13-acetate (PMA), forskolin and 3-isobutyl-1-methyl-xanthine (IBMX), an inhibitor of cAMP and cGMP phosphodiesterases, but not cGMP, when added to chicken myelomonocytic HD11 cells, markedly stimulated the C/EBPbeta mRNA expression. However, transfection experiments using HD11 cells showed that CAT constructs controlled by the 5' flanking sequence from -704 to +24 of chicken C/EBPbeta gene were activated by PMA, but not by forskolin. In contrast to forskolin, IBMX was able to activate the C/EBPbeta promoter CAT constructs. Further transient transfection experiments using other cell lines demonstrated that the chicken C/EBPbeta promoter was responsive to forskolin in mouse fibroblasts NIH3T3, but not in human hepatoma HepG2 cells. Increase in C/EBPbeta mRNA stability in HD11 cells was induced by forskolin and PMA.


CONCLUSIONS
The results indicate that the C/EBPbeta gene is regulated transcriptionally as well as post-transcriptionally in response to forskolin and PMA, and the forskolin responsiveness of the C/EBPbeta promoter seems to depend on cellular cAMP turnover.
Goethe
R
R
Institute for Microbiology, Department of Infectious Diseases, University of Veterinary Medicine, Bischofsholer Damm 15, 30173 Hannover, Germany.
Basler
T
T
Phi-van
L
L
D015056:1-Methyl-3-isobutylxanthine / Q000378:metabolism; D000818:Animals; D001483:Base Sequence; D022782:CCAAT-Enhancer-Binding Protein-beta / Q000235:genetics / Q000378:metabolism; D002460:Cell Line; D002645:Chickens; D005576:Colforsin / Q000378:metabolism; D017868:Cyclic AMP-Dependent Protein Kinases / Q000378:metabolism*; D005786:Gene Expression Regulation; D006801:Humans; D051379:Mice; D008969:Molecular Sequence Data; D009000:Monocytes / Q000166:cytology*; D010726:Phosphodiesterase Inhibitors / Q000378:metabolism; D011401:Promoter Regions, Genetic; D011493:Protein Kinase C / Q000378:metabolism*; D020871:RNA Stability; D012333:RNA, Messenger / Q000378:metabolism*; D016415:Sequence Alignment; D015398:Signal Transduction / Q000502:physiology; D013755:Tetradecanoylphorbol Acetate / Q000378:metabolism
D022782:CCAAT-Enhancer-Binding Protein-beta; D010726:Phosphodiesterase Inhibitors; D012333:RNA, Messenger; D005576:Colforsin; D017868:Cyclic AMP-Dependent Protein Kinases; D011493:Protein Kinase C; D013755:Tetradecanoylphorbol Acetate; D015056:1-Methyl-3-isobutylxanthine