Sequential phosphorylation of CCAAT enhancer-binding protein beta by MAPK and glycogen synthase kinase 3beta is required for adipogenesis.
CCAAT enhancer-binding protein (C/EBP)beta, C/EBPalpha, and peroxisome proliferator activated receptor (PPAR)gamma act in a cascade where C/EBPbeta activates expression of C/EBPalpha and PPARgamma, which then function as pleiotropic activators of genes that produce the adipocyte phenotype. When growth-arrested 3T3-L1 preadipocytes are induced to differentiate, C/EBPbeta is rapidly expressed but still lacks DNA-binding activity. After a long (14-hour) lag, glycogen synthase kinase 3beta enters the nucleus, which correlates with hyperphosphorylation of C/EBPbeta and acquisition of DNA-binding activity. Concurrently, 3T3-L1 preadipocytes synchronously enter S phase and undergo mitotic clonal expansion, a prerequisite for terminal differentiation. Ex vivo and in vitro experiments with C/EBPbeta show that phosphorylation of Thr-188 by mitogen-activating protein kinase "primes" C/EBPbeta for subsequent phosphorylation on Ser-184 and Thr-179 by glycogen synthase kinase 3beta, acquisition of DNA-binding function, and transactivation of the C/EBPalpha and PPARgamma genes. The delayed transactivation of the C/EBPalpha and PPARgamma genes by C/EBPbeta appears necessary to allow mitotic clonal expansion, which would otherwise be prevented, because C/EBPalpha and PPARgamma are antimitotic.
Tang
Qi-Qun
QQ
Departments of Pediatrics (Division of Endocrinology), McKusick-Nathans Institute of Genetic Medicine, Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA. qtang1@jhem.jhmi.edu
Grønborg
Mads
M
Huang
Haiyan
H
Kim
Jae-Woo
JW
Otto
Tamara C
TC
Pandey
Akhilesh
A
Lane
M Daniel
MD
D041721:3T3-L1 Cells; D017667:Adipocytes / Q000166:cytology* / Q000378:metabolism; D000818:Animals; D022782:CCAAT-Enhancer-Binding Protein-beta / Q000378:metabolism*; D002454:Cell Differentiation / Q000502:physiology*; D002467:Cell Nucleus / Q000378:metabolism; D047369:Chromatin Immunoprecipitation; D002853:Chromatography, Liquid; D004591:Electrophoresis, Polyacrylamide Gel; D038362:Glycogen Synthase Kinase 3 / Q000378:metabolism*; D000071679:Glycogen Synthase Kinase 3 beta; D015151:Immunoblotting; D007525:Isoelectric Focusing; D013058:Mass Spectrometry; D051379:Mice; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism*; D047495:PPAR gamma / Q000378:metabolism; D010766:Phosphorylation; D015533:Transcriptional Activation / Q000502:physiology
D022782:CCAAT-Enhancer-Binding Protein-beta; D047495:PPAR gamma; D000071679:Glycogen Synthase Kinase 3 beta; C000605507:Gsk3b protein, mouse; D020928:Mitogen-Activated Protein Kinases; D038362:Glycogen Synthase Kinase 3