N-terminal region of CCAAT/enhancer-binding protein epsilon is critical for cell cycle arrest, apoptosis, and functional maturation during myeloid differentiation.
CCAAT/enhancer-binding protein epsilon (C/EBPepsilon) plays a critical role in terminal myeloid differentiation. Differentiation is an integrated process of cell cycle arrest, morphological change, functional maturation, and apoptosis. However, the molecular networks underlying these events in C/EBPepsilon-induced differentiation remain poorly understood. To reveal these mechanisms, we performed a detailed molecular analysis of C/EBPepsilon-induced differentiation using an inducible form of C/EBPepsilon. The activation of C/EBPepsilon induced growth arrest, morphological differentiation, the expression of CD11b and secondary granule proteins, and apoptosis in myeloid cell lines. Unlike C/EBPalpha, C/EBPepsilon dramatically up-regulated p27 with a concomitant down-regulation of cdk4/6 and cyclin D2/A/E. Moreover, the anti-apoptotic proteins Bcl-2 and Bcl-x were down-regulated, whereas pro-apoptotic protein Bax remained unchanged. Using a variety of mutants, we revealed that these events were all regulated by the N-terminal activation domain of C/EBPepsilon. Interestingly, some of the differentiation processes such as the induction of secondary granule protein genes were clearly inhibited by c-Myc; however, inhibition of apoptosis by Bcl-x did not affect the entire differentiation processes. These data indicate the N terminus of C/EBPepsilon to be solely responsible for most aspects of myeloid differentiation, and these events were differentially affected by c-Myc.
Nakajima
Hideaki
H
Center of Excellence, The Institute of Medical Science, The University of Tokyo, Tokyo 108-8639, Japan. hnakajim@ims.u-tokyo.ac.jp
Watanabe
Naohide
N
Shibata
Fumi
F
Kitamura
Toshio
T
Ikeda
Yasuo
Y
Handa
Makoto
M
D000818:Animals; D017209:Apoptosis; D022762:CCAAT-Enhancer-Binding Proteins / Q000378:metabolism*; D002453:Cell Cycle; D002454:Cell Differentiation; D053938:DNA Fragmentation; D015536:Down-Regulation; D051379:Mice; D009154:Mutation; D022423:Myeloid Cells / Q000166:cytology*; D017434:Protein Structure, Tertiary; D013329:Structure-Activity Relationship; D013629:Tamoxifen / Q000031:analogs & derivatives / Q000494:pharmacology; D013997:Time Factors; D015854:Up-Regulation
D022762:CCAAT-Enhancer-Binding Proteins; D013629:Tamoxifen; C070790:CEBPE protein, human; C016601:afimoxifene