miR-21 Gene expression triggered by AP-1 is sustained through a double-negative feedback mechanism

J Mol Biol. 2008 May 2;378(3):492-504. doi: 10.1016/j.jmb.2008.03.015. Epub 2008 Mar 15.


miR-21 has been reported to be highly expressed in various cancers and to be inducible in a human promyelocytic cell line, HL-60, after phorbol 12-myristate 13-acetate (PMA) treatment. To examine molecular mechanisms involved in miR-21 expression, we analyzed the structure of the miR-21 gene by determining its promoter and primary transcripts. We show that activation protein 1 (AP-1) activates the miR-21 transcription in conjugation with the SWI/SNF complex, after PMA stimulation, through the conserved AP-1 and PU.1 binding sites in the promoter identified here. The previous findings of enhanced miR-21 expression in several cancers may therefore reflect the elevated AP-1 activity in these carcinomas. A single precursor RNA containing miR-21 was transcribed just downstream from the TATA box in this promoter, which is located in an intron of a coding gene, TMEM49. More important, expression of this overlapping gene is completely PMA-independent and all its transcripts are polyadenylated before reaching the miR-21 hairpin embedding region, indicating that miRNAs could have their own promoter even if overlapped with other genes. By available algorithms that predict miRNA target using a conservation of sequence complementary to the miRNA seed sequence, we next predicted and confirmed that the NFIB mRNA is a target of miR-21. NFIB protein usually binds the miR-21 promoter in HL-60 cells as a negative regulator and is swept off from the miR-21 promoter during PMA-induced macrophage differentiation of HL-60. The translational repression of NFIB mRNA by miR-21 accelerates clearance of NFIB in parallel with the simultaneous miR-21-independent transcriptional repression of NFIB after PMA stimulation. Since exogenous miR-21 expression moderately induced endogenous miR-21, an evolutionarily conserved double-negative feedback regulation would be operating as a mechanism to sustain miR-21 expression.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Base Sequence
  • Binding Sites
  • Chromosomal Proteins, Non-Histone / metabolism
  • Gene Expression Regulation*
  • HL-60 Cells
  • Humans
  • Macrophages / metabolism
  • MicroRNAs / genetics*
  • Molecular Sequence Data
  • NFI Transcription Factors / genetics
  • NFI Transcription Factors / metabolism
  • Promoter Regions, Genetic
  • RNA, Messenger / metabolism
  • Tetradecanoylphorbol Acetate / pharmacology
  • Transcription Factor AP-1 / metabolism*
  • Transcription Factors / metabolism


  • Chromosomal Proteins, Non-Histone
  • MIRN21 microRNA, human
  • MicroRNAs
  • NFI Transcription Factors
  • NFIB protein, human
  • RNA, Messenger
  • SWI-SNF-B chromatin-remodeling complex
  • Transcription Factor AP-1
  • Transcription Factors
  • Tetradecanoylphorbol Acetate