FOXO3a induces differentiation of Bcr-Abl- transformed cells through transcriptional down-regulation of Id1
FOXO3a induces differentiation of Bcr-Abl- transformed cells through transcriptional down-regulation of Id1
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DOI：
10.1074/jbc.m606669200
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发表时间：
2007-01-26
影响因子：
4.8
通讯作者：
Coffer, Paul J.
中科院分区：
文献类型：
--
作者：
Birkenkamp, Kim U.;Essafi, Abdelkader;Coffer, Paul J.
白血病转化通常需要激活蛋白激酶B（PKB/c-Akt），其特征为增殖增加、凋亡减少和分化阻滞。PKB磷酸化并灭活FOXO叉头转录因子亚家族的成员。研究表明，PKB的过度活化通过主动抑制FOXO介导的特定基因的调节来维持白血病表型。我们已经发现转录抑制因子Id 1（DNA结合抑制因子1）的表达被FOXO 3a激活所废除。抑制PKB激活或生长因子剥夺也导致Id 1启动子活性，Id 1 mRNA和蛋白质表达的强烈下调。Id 1在Bcr-Abl转化的K562细胞中高度表达，与高PKB活化和FOXO 3a磷酸化相关。化学抑制剂STI 571抑制Bcr-Abl导致FOXO 3a激活和Id 1表达下调。通过进行染色质免疫沉淀试验和启动子突变分析，我们证明，FOXO 3a作为一个转录抑制因子直接绑定到Id 1启动子。STI 571治疗，或组成型活性FOXO 3a的表达，导致K562细胞的红系分化，这是抑制异位表达的Id 1。总之，我们的数据有力地表明，高表达的Id 1，通过PKB介导的抑制FOXO 3a，是维持白血病表型的关键。
Leukemic transformation often requires activation of protein kinase B (PKB/c-Akt) and is characterized by increased proliferation, decreased apoptosis, and a differentiation block. PKB phosphorylates and inactivates members of the FOXO subfamily of Forkhead transcription factors. It has been suggested that hyperactivation of PKB maintains the leukemic phenotype through actively repressing FOXO-mediated regulation of specific genes. We have found expression of the transcriptional repressor Id1 (inhibitor of DNA binding 1) to be abrogated by FOXO3a activation. Inhibition of PKB activation or growth factor deprivation also resulted in strong down-regulation of Id1 promoter activity, Id1 mRNA, and protein expression. Id1 is highly expressed in Bcr-Abl-transformed K562 cells, correlating with high PKB activation and FOXO3a phosphorylation. Inhibition of Bcr-Abl by the chemical inhibitor STI571 resulted in activation of FOXO3a and down-regulation of Id1 expression. By performing chromatin immunoprecipitation assays and promoter-mutation analysis, we demonstrate that FOXO3a acts as a transcriptional repressor by directly binding to the Id1 promoter. STI571 treatment, or expression of constitutively active FOXO3a, resulted in erythroid differentiation of K562 cells, which was inhibited by ectopic expression of Id1. Taken together our data strongly suggest that high expression of Id1, through PKB-mediated inhibition of FOXO3a, is critical for maintenance of the leukemic phenotype.