miR-21 Gene expression triggered by AP-1 is sustained through a double-negative feedback mechanism.
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.
Fujita
Shuji
S
Division of Host-Parasite Interaction, Department of Microbiology and Immunology, Institute of Medical Science, University of Tokyo, 4-6-1 Shirokanedai, Minato-ku, Tokyo 108-8639, Japan.
Ito
Taiji
T
Mizutani
Taketoshi
T
Minoguchi
Shigeru
S
Yamamichi
Nobutake
N
Sakurai
Kouhei
K
Iba
Hideo
H
D001483:Base Sequence; D001665:Binding Sites; D002868:Chromosomal Proteins, Non-Histone / Q000378:metabolism; D005786:Gene Expression Regulation; D018922:HL-60 Cells; D006801:Humans; D008264:Macrophages / Q000378:metabolism; D035683:MicroRNAs / Q000235:genetics*; D008969:Molecular Sequence Data; D051839:NFI Transcription Factors / Q000235:genetics / Q000378:metabolism; D011401:Promoter Regions, Genetic; D012333:RNA, Messenger / Q000378:metabolism; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology; D018808:Transcription Factor AP-1 / Q000378:metabolism*; D014157:Transcription Factors / Q000378:metabolism
D002868:Chromosomal Proteins, Non-Histone; C524940:MIRN21 microRNA, human; D035683:MicroRNAs; D051839:NFI Transcription Factors; C110754:NFIB protein, human; D012333:RNA, Messenger; C445179:SWI-SNF-B chromatin-remodeling complex; D018808:Transcription Factor AP-1; D014157:Transcription Factors; D013755:Tetradecanoylphorbol Acetate