Regulation of granulocyte and monocyte differentiation by CCAAT/enhancer binding protein alpha.
CCAAT/enhancer binding protein alpha (C/EBPalpha)-ER induces 32Dcl3 neutrophilic differentiation and inhibits 32DPKCdelta maturation to macrophages in response to phorbol ester. In 32Dcl3 cells, C/EBPalpha-ER rapidly induces the PU.1 and C/EBPalpha RNAs even in the presence of cycloheximide, suggesting that these are direct C/EBPalpha genetic targets. C/EBPalpha strongly binds and modestly activates the murine PU.1 promoter via an evolutionarily conserved binding site. C/EBPalpha-ER variants incapable of binding DNA still slow G1 progression but do not induce differentiation. N-terminally truncated C/EBPalpha variants, including the p30 isoform expressed in a subset of AMLs, also retain the ability to slow 32D cl3 proliferation, whereas the C/EBPalpha(BRM2)-ER variant does not slow G1 progression, has a reduced capacity to induce early granulocytic markers, and does not induce terminal maturation. In 32DPKCdelta cells, C/EBPalpha-ER strongly inhibits endogenous or exogenous JunB induction, dependent upon the outer surface of the C/EBPalpha basic region, but does not inhibit c-Jun, PU.1, or C/EBPbeta expression. Exogenous JunB restores AP-1 DNA binding but does not overcome inhibition of monopoiesis by C/EBPalpha-ER. In summary, we propose that while C/EBPalpha is required for development of immature granulocyte-monocyte progenitors, C/EBPalpha subsequently inhibits monopoiesis, via inhibition of JunB express and via additional activities, and induces granulopoiesis, via induction of PU.1, C/EBPepsilon, and cell cycle arrest.
Friedman
Alan D
AD
Department of Pediatric Oncology, Johns Hopkins University, 1650 Orleans Street, Baltimore, MD 21231, USA. afriedm2@jhem.jhmi.edu
Keefer
Jeffrey R
JR
Kummalue
Tanawan
T
Liu
Huaitian
H
Wang
Qian-fei
QF
Cleaves
Rebecca
R
D000818:Animals; D022763:CCAAT-Enhancer-Binding Protein-alpha / Q000378:metabolism*; D002454:Cell Differentiation; D006098:Granulocytes / Q000166:cytology* / Q000378:metabolism*; D006801:Humans; D009000:Monocytes / Q000166:cytology* / Q000378:metabolism*; D011518:Proto-Oncogene Proteins / Q000235:genetics; D016755:Proto-Oncogene Proteins c-jun / Q000235:genetics; D016188:Receptors, Granulocyte Colony-Stimulating Factor / Q000235:genetics; D015534:Trans-Activators / Q000235:genetics; D000099232:Proto-Oncogene Protein Spi-1
D022763:CCAAT-Enhancer-Binding Protein-alpha; D011518:Proto-Oncogene Proteins; D016755:Proto-Oncogene Proteins c-jun; D016188:Receptors, Granulocyte Colony-Stimulating Factor; D015534:Trans-Activators; D000099232:Proto-Oncogene Protein Spi-1