Direct transcriptional regulation of Bim by FoxO3a mediates STI571-induced apoptosis in Bcr-Abl-expressing cells
Direct transcriptional regulation of Bim by FoxO3a mediates STI571-induced apoptosis in Bcr-Abl-expressing cells
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DOI：
10.1038/sj.onc.1208421
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发表时间：
2005-03-31
期刊：
影响因子：
8
通讯作者：
Lam, EWF
中科院分区：
文献类型：
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作者：
Essafi, A;de Mattos, SF;Lam, EWF
本研究以人BV173和小鼠BaF3/bcr-Abl表达细胞为模型系统，研究STI571和FOXO3a调控Bim表达和细胞凋亡的分子机制。FOXO3a位于Ber-Abl信号的下游，在Bcr-Abl阳性的BV173和BaF3/BCR-Abl细胞中被结构性磷酸化。STI571抑制BCR-Abl激酶可导致FOXO3a激活，诱导Bim表达和细胞凋亡。利用报告基因分析，我们证明STI571和FOXO3a通过位于启动子内的FoxO结合位点(FHRE)激活Bim转录。DNA下拉和染色质免疫沉淀分析证实了这一点。我们发现FOXO3a的有条件激活导致Bim表达和细胞凋亡的诱导。相反，在表达bcr-Abl的细胞中沉默FOXO3a会取消STI571介导的BIM诱导和凋亡。综上所述，这些结果清楚地证实了FOXO3a是ST1571诱导细胞凋亡的关键调控因子，并表明Bim是FOXO3a的直接转录靶点，介导了STI571诱导的细胞凋亡。因此，STI571诱导FOXO3a活性的积累，而FOXO3a活性又直接与启动子中的FHRE结合，从而激活Bim表达和细胞凋亡。
In this study, we have used the human BV173 and the mouse BaF3/Bcr-Abl-expressing cell lines as model systems to investigate the molecular mechanisms whereby STI571 and FoxO3a regulate Bim expression and apoptosis. FoxO3a lies downstream of Ber-Abl signalling and is constitutively phosphorylated in the Bcr-Abl-positive BV173 and BaF3/Bcr-Abl cells. Inhibition of Bcr-Abl kinase by STI571 results in FoxO3a activation, induction of Bim expression and apoptosis. Using reporter gene assays, we demonstrate that STI571 and FoxO3a activate Bim transcription through a FoxO-binding site (FHRE) located within the promoter. This was verified by DNA pull-down and chromatin immunoprecipitation analyses. We find that conditional activation of FoxO3a leads to induction of Bim expression and apoptosis. Conversely, silencing of FoxO3a in Bcr-Abl-expressing cells abolishes STI571-mediated Bim induction and apoptosis. Together, the results presented clearly confirm FoxO3a as a key regulator of apoptosis induced by ST1571, and show that Bim is a direct transcriptional target of FoxO3a that mediates the STI571-induced apoptosis. Thus, STI571 induces an accumulation of FoxO3a activity which in turn binds directly to an FHRE in the promoter to activate Bim expression and apoptosis.