Regulation of C/EBPbeta isoforms by MAPK pathways in HL60 cells induced to differentiate by 1,25-dihydroxyvitamin D3

Exp Cell Res. 2006 Jul 1;312(11):2054-65. doi: 10.1016/j.yexcr.2006.03.003. Epub 2006 Apr 19.


C/EBPbeta is known to be important for monocytic differentiation and macrophage function. Here, we found that expression of all three C/EBPbeta isoforms induced in HL60 cells by 1,25-dihydroxyvitamin D3 (1,25D) was upregulated in a sustained manner that correlates with the appearance of monocytic phenotype and with the G1 phase cell cycle arrest. In 1,25D-resistant HL60-40AF cells, isoforms beta-1 and beta-3 were expressed at levels comparable to 1,25D-sensitive HL60-G cells, but isoform beta-2 was difficult to detect. Treatment of sensitive HL60 cells with 1,25D resulted in predominantly nuclear localization of C/EBP isoforms beta-2 and beta-3, while a large proportion of C/EBPbeta-1 remained in the cytoplasm. Attenuation of the MEK-ERK MAPK pathway by the inhibitor PD98059 markedly reduced the expression, 1,25D-induced phosphorylation and nuclear localization of C/EBPbeta-2 and C/EBPbeta-3. Interestingly, only the lower molecular mass isoforms of C/EBPbeta phosphorylated on Thr235 were found in the nuclei, while C/EBPbeta-1 was constitutively phosphorylated and was detected principally in the cytoplasmic fraction. Although the role of C/EBPbeta isoforms in 1,25D-induced differentiation is complex, our results taken together strongly suggest that the phosphorylation of C/EBPbeta isoforms on Thr235 takes place mainly via the MEK-ERK pathway and that C/EBPbeta-2 is the principal transcription factor in this cell system.

Publication types

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

MeSH terms

  • CCAAT-Enhancer-Binding Protein-beta / physiology*
  • Calcitriol / pharmacology*
  • Cell Differentiation / drug effects
  • Cell Differentiation / physiology*
  • Cell Line, Tumor
  • Dose-Response Relationship, Drug
  • HL-60 Cells
  • Humans
  • Kinetics
  • MAP Kinase Signaling System / physiology*
  • Mitogen-Activated Protein Kinases / metabolism*
  • Phosphorylation
  • Protein Isoforms / physiology
  • Up-Regulation


  • CCAAT-Enhancer-Binding Protein-beta
  • Protein Isoforms
  • Mitogen-Activated Protein Kinases
  • Calcitriol