miR-21 gene expression triggered by AP-1 is sustained through a double-negative feedback mechanism
miR-21 gene expression triggered by AP-1 is sustained through a double-negative feedback mechanism
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DOI：
10.1016/j.jmb.2008.03.015
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发表时间：
2008-05-02
影响因子：
5.6
通讯作者：
Iba, Hlideo
中科院分区：
文献类型：
--
作者：
Fujita, Shuji;Ito, Taiji;Iba, Hlideo
据报道，miR-21在各种癌症中高表达，并在人类早幼粒细胞HL-60细胞系中经12-肉豆蔻酸13-醋酸佛波酯（PMA）处理后可诱导表达。为了研究参与miR-21表达的分子机制，我们通过确定其启动子和初级转录本分析了miR-21基因的结构。我们发现，激活蛋白1 （AP-1）在PMA刺激后，通过在这里鉴定的启动子中保守的AP-1和PU.1结合位点，激活miR-21与SWI/SNF复合物结合的转录。因此，先前在几种癌症中miR-21表达增强的发现可能反映了这些癌症中AP-1活性的升高。包含miR-21的单个前体RNA在该启动子的TATA盒下游转录，该启动子位于编码基因TMEM49的内含子中。更重要的是，该重叠基因的表达完全不依赖于pma，其所有转录本在到达miR-21发夹嵌入区之前都被聚腺苷化，这表明miRNAs即使与其他基因重叠也可能有自己的启动子。通过使用与miRNA种子序列互补的序列保守性来预测miRNA靶标的现有算法，我们接下来预测并证实了NFIB mRNA是miR-21的靶标。NFIB蛋白通常作为负调节因子结合HL-60细胞中的miR-21启动子，并在pma诱导的HL-60巨噬细胞分化过程中从miR-21启动子中被清除。miR-21对NFIB mRNA的翻译抑制加速了NFIB的清除，同时在PMA刺激后，miR-21独立的NFIB转录抑制同时发生。由于外源性miR-21表达适度诱导内源性miR-21，一种进化保守的双负反馈调节可能是维持miR-21表达的机制。(C) 2008 Elsevier Ltd版权所有。
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 miR21-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. (C) 2008 Elsevier Ltd. All rights reserved.