CCAAT/enhancer-binding protein beta promotes osteoblast differentiation by enhancing Runx2 activity with ATF4.
Although CCAAT/enhancer-binding protein beta (C/EBPbeta) is involved in osteocalcin gene expression in osteoblast in vitro, the physiological importance of and molecular mechanisms governing C/EBPbeta in bone formation remain to be elucidated. In particular, it remains unclear whether C/EBPbeta acts as a homodimer or a heterodimer with other proteins during osteoblast differentiation. Here, deletion of the C/EBPbeta gene from mice resulted in delayed bone formation with concurrent suppression of chondrocyte maturation and osteoblast differentiation. The expression of type X collagen as well as chondrocyte hypertrophy were suppressed in mutant bone, providing new insight into the possible roles of C/EBPbeta in chondrocyte maturation. In osteoblasts, luciferase reporter, gel shift, DNAP, and ChIP assays demonstrated that C/EBPbeta heterodimerized with activating transcription factor 4 (ATF4), another basic leucine zipper transcription factor crucial for osteoblast maturation. This complex interacted and transactivated osteocalcin-specific element 1 (OSE1) of the osteocalcin promoter. C/EBPbeta also enhanced the synergistic effect of ATF4 and Runx2 on osteocalcin promoter transactivation by enhancing their interaction. Thus, our results provide evidence that C/EBPbeta is a crucial cofactor in the promotion of osteoblast maturation by Runx2 and ATF4.
Department of Biochemistry, The Cancer Institute of the Japanese Foundation for Cancer Research, Tokyo 135-8550, Japan.
Hiroyuki
H
Tominaga
Shingo
S
Maeda
Makoto
M
Hayashi
Shu
S
Takeda
Shizuo
S
Akira
Setsuro
S
Komiya
Takashi
T
Nakamura
Haruhiko
H
Akiyama
Takeshi
T
Imamura
D051701:Activating Transcription Factor 4 / Q000235:genetics / Q000378:metabolism*; D000818:Animals; D001483:Base Sequence; D015415:Biomarkers / Q000378:metabolism; D001842:Bone and Bones / Q000166:cytology / Q000196:embryology / Q000378:metabolism; D022782:CCAAT-Enhancer-Binding Protein-beta / Q000235:genetics / Q000378:metabolism*; D002454:Cell Differentiation / Q000502:physiology*; D002478:Cells, Cultured; D019902:Chondrocytes / Q000166:cytology / Q000502:physiology; D050659:Core Binding Factor Alpha 1 Subunit / Q000235:genetics / Q000378:metabolism*; D018507:Gene Expression Regulation, Developmental; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D010006:Osteoblasts / Q000166:cytology / Q000502:physiology*; D015675:Osteocalcin / Q000235:genetics / Q000378:metabolism; D011401:Promoter Regions, Genetic
D015415:Biomarkers; D022782:CCAAT-Enhancer-Binding Protein-beta; D050659:Core Binding Factor Alpha 1 Subunit; C493716:Runx2 protein, mouse; D015675:Osteocalcin; D051701:Activating Transcription Factor 4