Puccetti Elena, Obradovic Darja, Beissert Tim, Bianchini Andrea, Washburn Birgit, Chiaradonna Ferdinando, Boehrer Simone, Hoelzer Dieter, Ottmann Oliver Gerhard, Pelicci Pier Giuseppe, Nervi Clara, Ruthardt Martin
Med. Klinik III/Abtl. Hämatologie, Johann Wolfgang Goethe-Universität, 60590 Frankfurt, Germany.
Cancer Res. 2002 Dec 1;62(23):7050-8.
Acute myeloid leukemia (AML)-associated chromosomal translocations result in formation of chimeric transcription factors, such as PML/RARalpha, PLZF/RARalpha, and AML-1/ETO, of which the components are involved in regulation of transcription by chromatin modeling through histone acetylation/deacetylation. The leukemic differentiation block is attributed to deregulated transcription caused by these chimeric fusion proteins, which aberrantly recruit histone-deacetylase (HDAC) activity. One essential differentiation pathway blocked by the leukemic fusion proteins is the vitamin (Vit) D(3) signaling. Here we investigated the mechanisms by which the leukemic fusion proteins interfere with VitD(3)-induced differentiation. The VitD(3)-receptor (VDR) is, like the retinoid receptors RAR, retinoid X receptor, and the thyroid hormone receptor (TR), a ligand-inducible transcription factor. In the absence of ligand, the transcriptional activity of TR and RAR is silenced by recruitment of HDAC activity through binding to corepressors. In the presence of ligand, TR and RAR activate transcription by releasing HDAC activity and by recruiting histone-acetyltransferase activity. Here we report that VDR binds corepressors in a ligand-dependent manner and that inhibition of HDAC activity increases VitD(3) sensitivity of HL-60 cells. Nevertheless, the inhibition of HDAC activity is unable to overcome the block of VitD(3)-induced differentiation caused by PLZF/RARalpha expression. Here we demonstrate that the expression of the translocation products PML/RARalpha and PLZF/RARalpha impairs the localization of VDR in the nucleus by binding to VDR. Furthermore, the overexpression of VDR in U937 cells expressing AML-related translocation products completely abolishes the block of VitD(3)-induced differentiation. Taken together these data indicate that the AML-associated translocation products block differentiation not only by interfering with chromatin-modeling but also by sequestering factors involved in the differentiation signaling pathways, such as VDR in the VitD(3)-induced differentiation.
急性髓系白血病（AML）相关的染色体易位导致嵌合转录因子的形成，如早幼粒细胞白血病蛋白/维甲酸受体α（PML/RARα）、早幼粒细胞白血病锌指蛋白/维甲酸受体α（PLZF/RARα）和急性髓细胞白血病1/八聚体结合转录因子（AML-1/ETO），其组成成分通过组蛋白乙酰化/去乙酰化参与染色质重塑对转录的调控。白血病分化阻滞归因于这些嵌合融合蛋白导致的转录失调，这些蛋白异常募集组蛋白去乙酰化酶（HDAC）活性。白血病融合蛋白阻断的一条重要分化途径是维生素（Vit）D3信号通路。在此，我们研究了白血病融合蛋白干扰VitD3诱导分化的机制。维生素D3受体（VDR）与维甲酸受体RAR、维甲酸X受体以及甲状腺激素受体（TR）一样，是一种配体诱导型转录因子。在没有配体的情况下，TR和RAR的转录活性通过与共抑制因子结合募集HDAC活性而被沉默。在有配体的情况下，TR和RAR通过释放HDAC活性并募集组蛋白乙酰转移酶活性来激活转录。在此我们报告，VDR以配体依赖的方式结合共抑制因子，并且抑制HDAC活性可增加HL-60细胞对VitD3的敏感性。然而，抑制HDAC活性无法克服由PLZF/RARα表达导致的VitD3诱导分化的阻滞。在此我们证明，易位产物PML/RARα和PLZF/RARα的表达通过与VDR结合损害其在细胞核中的定位。此外，在表达AML相关易位产物的U937细胞中过表达VDR可完全消除VitD3诱导分化的阻滞。综上所述，这些数据表明，AML相关的易位产物不仅通过干扰染色质重塑，还通过隔离参与分化信号通路的因子（如VitD3诱导分化中的VDR）来阻断分化。
