Synergistic activation of the human choline acetyltransferase gene by c-Myb and C/EBPbeta.
To elucidate regulatory mechanisms at the transcriptional level of the human choline acetyltransferase gene (hChAT) we performed cotransfections assays in NG108-15 and SN56 cells using ChAT-CAT reporter plasmids with c-Myb and C/EBPbeta expression plasmids. The hChAT gene has several promoters, one of which (promoter P2 or M-type) is both c-Myb and C/EBPbeta inducible as 3-4-fold trans-activation was obtained in both cell lines when using either c-Myb or C/EBPbeta expression vectors alone. The simultaneous expression of c-Myb and C/EBPbeta in the absence or presence of NGFI-C (egr4) leads respectively to a 15-fold and 32-fold synergistic transcriptional activation of promoter P2. In the region upstream of exon M (P2) we identified a functional composite element including a c-Myb next to a C/EBP binding site. An oligonucleotide containing the composite element confers c-Myb and C/EBPbeta responsiveness to a heterologous promoter which is reduced after mutation of the c-Myb binding site. We also show that the coactivators CBP/p300 are required for c-Myb and C/EBPbeta trans-activation function and that RARalpha, RXRalpha and T3R have an inhibitory action on the synergistic transcriptional activity of c-Myb and C/EBPbeta and propose a model to explain the phenomena. Taken together, the results suggest that the synergistic effect of c-Myb and C/EBPbeta, previously observed in the hematopoietic system, functions equally in the neuronal system.
Robert
Isabelle
I
Laboratoire de Génétique Moléculaire des Eucaryotes, CNRS/INSERM U 184, Faculté de Médecine, 11 rue Humann, 67085 Strasbourg, France.
Sutter
Anne
A
Quirin-Stricker
Christiane
C
D000818:Animals; D001665:Binding Sites; D022762:CCAAT-Enhancer-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D002795:Choline O-Acetyltransferase / Q000235:genetics* / Q000378:metabolism; D017930:Genes, Reporter; D006801:Humans; D046911:Macromolecular Substances; D051379:Mice; D011401:Promoter Regions, Genetic; D011485:Protein Binding; D020598:Proto-Oncogene Proteins c-myb / Q000235:genetics / Q000378:metabolism*; D051381:Rats; D014158:Transcription, Genetic; D015533:Transcriptional Activation; D014407:Tumor Cells, Cultured
D022762:CCAAT-Enhancer-Binding Proteins; D046911:Macromolecular Substances; D020598:Proto-Oncogene Proteins c-myb; D002795:Choline O-Acetyltransferase