Transcription Factor C/EBPbeta Isoform Ratio Regulates Osteoclastogenesis Through MafB

EMBO J. 2009 Jun 17;28(12):1769-81. doi: 10.1038/emboj.2009.127. Epub 2009 May 14.

Abstract

Disequilibrium between bone-forming osteoblasts and bone-resorbing osteoclasts is central to many bone diseases. Here, we show that dysregulated expression of translationally controlled isoforms of CCAAT/enhancer-binding protein beta (C/EBPbeta) differentially affect bone mass. Alternative translation initiation that is controlled by the mammalian target of rapamycin (mTOR) pathway generates long transactivating (LAP(*), LAP) and a short repressive (LIP) isoforms from a single C/EBPbeta transcript. Rapamycin, an inhibitor of mTOR signalling increases the ratio of LAP over LIP and inhibits osteoclastogenesis in wild type (WT) but not in C/EBPbeta null (c/ebpbeta(-/-)) or in LIP knock-in (L/L) osteoclast precursors. C/EBPbeta mutant mouse strains exhibit increased bone resorption and attenuated expression of MafB, a negative regulator of osteoclastogenesis. Ectopic expression of LAP and LIP in monocytes differentially affect the MafB promoter activity, MafB gene expression and dramatically affect osteoclastogenesis. These data show that mTOR regulates osteoclast formation by modulating the C/EBPbeta isoform ratio, which in turn affects osteoclastogenesis by regulating MafB expression.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Bone and Bones / cytology
  • Bone and Bones / metabolism
  • CCAAT-Enhancer-Binding Protein-beta / metabolism*
  • Cell Differentiation*
  • Gene Knock-In Techniques
  • MafB Transcription Factor / metabolism*
  • Mice
  • Mice, Mutant Strains
  • Models, Biological
  • Mutation / genetics
  • Organ Size
  • Osteoblasts / cytology
  • Osteoblasts / metabolism
  • Osteoclasts / cytology*
  • Osteoclasts / metabolism
  • Protein Isoforms / metabolism
  • Protein Kinases / metabolism
  • TOR Serine-Threonine Kinases

Substances

  • CCAAT-Enhancer-Binding Protein-beta
  • MafB Transcription Factor
  • Mafb protein, mouse
  • Protein Isoforms
  • Protein Kinases
  • TOR Serine-Threonine Kinases
  • mTOR protein, mouse