CCAAT/Enhancer-binding Protein α (C/EBPα) Is Important for Osteoclast Differentiation and Activity

J Biol Chem. 2016 Jul 29;291(31):16390-403. doi: 10.1074/jbc.M115.674598. Epub 2016 Apr 20.

Abstract

CCAAT/enhancer-binding protein (C/EBPα) can appoint mouse bone marrow (MBM) cells to the osteoclast (OC) lineage for osteoclastogenesis. However, whether C/EBPα is also involved in OC differentiation and activity is unknown. Here we demonstrated that C/EBPα overexpression in MBM cells can promote OC differentiation and strongly induce the expression of the OC genes encoding the nuclear factor of activated T-cells, c1 (NFATc1), cathepsin K (Cstk), and tartrate-resistant acid phosphatase 5 (TRAP) with receptor activator of NF-κB ligand-evoked OC lineage priming. Furthermore, while investigating the specific stage of OC differentiation that is regulated by C/EBPα, our gene overexpression studies revealed that, although C/EBPα plays a stronger role in the early stage of OC differentiation, it is also involved in the later stage. Accordingly, C/EBPα knockdown drastically inhibits osteoclastogenesis and markedly abrogates the expression of NFATc1, Cstk, and TRAP during OC differentiation. Consistently, C/EBPα silencing revealed that, although lack of C/EBPα affects all stages of OC differentiation, it has more impact on the early stage. Importantly, we showed that ectopic expression of rat C/EBPα restores osteoclastogenesis in C/EBPα-depleted MBM cells. Furthermore, our subsequent functional assays showed that C/EBPα exhibits a dispensable role on actin ring formation by mature OCs but is critically involved in bone resorption by stimulating extracellular acidification and regulating cell survival. We revealed that C/EBPα is important for receptor activator of NF-κB ligand-induced Akt activation, which is crucial for OC survival. Collectively, these results indicate that C/EBPα functions throughout osteoclastogenesis as well as in OC function. This study provides additional understanding of the roles of C/EBPα in OC biology.

Keywords: Akt PKB; CCAAT-enhancer-binding protein (C/EBP); bone; differentiation; osteoclast; transcription factor.

Publication types

  • Research Support, N.I.H., Extramural

MeSH terms

  • Animals
  • Bone Marrow Cells / metabolism*
  • Bone Resorption*
  • CCAAT-Enhancer-Binding Proteins / genetics
  • CCAAT-Enhancer-Binding Proteins / metabolism*
  • Cell Differentiation*
  • Gene Knockdown Techniques
  • Mice
  • NFATC Transcription Factors / genetics
  • NFATC Transcription Factors / metabolism
  • Osteoclasts / metabolism*
  • RANK Ligand / genetics
  • RANK Ligand / metabolism
  • Rats
  • Tartrate-Resistant Acid Phosphatase / genetics
  • Tartrate-Resistant Acid Phosphatase / metabolism

Substances

  • CCAAT-Enhancer-Binding Proteins
  • CEBPA protein, mouse
  • NFATC Transcription Factors
  • Nfatc1 protein, mouse
  • RANK Ligand
  • Tnfsf11 protein, mouse
  • Acp5 protein, mouse
  • Tartrate-Resistant Acid Phosphatase