CCAAT/enhancer binding protein epsilon: changes in function upon phosphorylation by p38 MAP kinase.
C/EBPepsilon, a member of the CCAAT/enhancer binding protein family, is a transcription factor important in neutrophil differentiation. We have determined that it is phosphorylated on multiple serine and threonine residues and can be a target for phosphorylation by a number of kinases. We identified a threonine at amino acid 75, part of a consensus mitogen-activated protein (MAP) kinase site within the transactivation domain of C/EBPepsilon, as being phosphorylated only by p38 MAP kinase. Phosphorylation of this residue resulted in enhanced transcriptional activity on a myeloid-specific promoter in in vitro transient transfection reporter assays. We also determined that phosphorylation at Thr75 yielded a protein that was more effective at binding its cognate DNA sequence compared with the wild-type nonphosphorylated C/EBPepsilon. Stable expression of C/EBPepsilonT75A in interleukin 3 (IL-3)-dependent 32Dcl3 did not result in the up-regulation of expression of secondary granule genes compared with wild-type C/EBPepsilon or C/EBPepsilonT75D. Therefore we suggest that C/EBPepsilon is a target for p38 MAP kinase activity.
Williamson
Elizabeth A
EA
Department of Medicine, Hematology/Oncology, Cedars-Sinai Medical Center, University of California-Los Angeles, USA. ewilliamson@salud.unm.edu
Williamson
Ian K
IK
Chumakov
Alexey M
AM
Friedman
Alan D
AD
Koeffler
H Phillip
HP
D022762:CCAAT-Enhancer-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D002460:Cell Line; D017868:Cyclic AMP-Dependent Protein Kinases / Q000378:metabolism; D004247:DNA / Q000378:metabolism; D005786:Gene Expression Regulation; D006801:Humans; D019950:Mitogen-Activated Protein Kinase 1 / Q000378:metabolism; D009154:Mutation / Q000235:genetics; D010766:Phosphorylation; D047428:Protein Kinase Inhibitors / Q000494:pharmacology; D013912:Threonine / Q000235:genetics / Q000378:metabolism; D048051:p38 Mitogen-Activated Protein Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism*
D022762:CCAAT-Enhancer-Binding Proteins; D047428:Protein Kinase Inhibitors; D013912:Threonine; D004247:DNA; D017868:Cyclic AMP-Dependent Protein Kinases; D019950:Mitogen-Activated Protein Kinase 1; D048051:p38 Mitogen-Activated Protein Kinases