Role of C/EBP homologous protein (CHOP-10) in the programmed activation of CCAAT/enhancer-binding protein-β during adipogenesis

Role of C/EBP homologous protein (CHOP-10) in the programmed activation of CCAAT/enhancer-binding protein-β during adipogenesis

Qi-Qun Tang* and
M. Daniel Lane

Department of Biological Chemistry, The Johns Hopkins University School of Medicine, Baltimore, MD 21209

Contributed by M. Daniel Lane

Abstract

Hormone induction of growth-arrested preadipocytes triggers mitotic clonal expansion followed by expression of CCAAT/enhancer-binding protein (C/EBP)α and differentiation into adipocytes. The order of these events is critical because C/EBPα is antimitotic and its expression prematurely would block the mitotic clonal expansion required for differentiation. C/EBPβ, a transcriptional activator of the C/EBPα gene, is expressed early in the differentiation program, but lacks DNA-binding activity and fails to localize to centromeres until preadipocytes traverse the G₁-S checkpoint of mitotic clonal expansion. Evidence is presented that dominant-negative CHOP-10 expressed by growth-arrested preadipocytes transiently sequesters C/EBPβ by heterodimerization. As preadipocytes reach S phase, CHOP-10 is down-regulated, apparently releasing C/EBPβ from inhibitory constraint and allowing transactivation of the C/EBPα gene. In support of these findings, up-regulation of CHOP-10 with the protease inhibitor N-acetyl-Leu-Leu-norleucinal prevents activation of C/EBPβ, expression of C/EBPα, and adipogenesis.

Footnotes

↵ * To whom reprint requests should be addressed. E-mail: qqtang{at}welchlink.welch.jhu.edu.
Article published online before print: Proc. Natl. Acad. Sci. USA, 10.1073/pnas.220425597.
Article and publication date are at www.pnas.org/cgi/doi/10.1073/pnas.220425597
Abbreviations:

ALLN,

N-acetyl-Leu-Leu-norleucinal;

C/EBP,

CCAAT/enhancer-binding protein;

EMSA,

electrophoretic mobility-shift analysis