Lee Sang Min, Bae Jae Ho, Kim Mi Ju, Lee Hyun Sun, Lee Min Ki, Chung Byung Seon, Kim Dong Wan, Kang Chi Dug, Kim Sun Hee
Department of Biochemistry, Research Center for Ischemic Tissue Regeneration, College of Medicine, Pusan National University, Pusan 602-739, South Korea.
J Pharmacol Exp Ther. 2007 Sep;322(3):1084-92. doi: 10.1124/jpet.107.124461. Epub 2007 Jun 14.
Bcr-Abl-independent signaling pathways are known to be involved in imatinib resistance in some patients with chronic myelogenous leukemia (CML). In this study, to find new targets for imatinib-resistant CML displaying loss of Bcr-Abl kinase target dependence, we isolated imatinib-resistant variants, K562/R1, K562/R2, and K562/R3, which showed profound declines of Bcr-Abl levels and its tyrosine kinase activity, from K562 cells. Importantly, the imatinib resistance mechanism in these variants also included aberrant acetylation of nonhistone proteins such as p53, Ku70, and Hsp90 that was due to upregulation of histone deacetylases (HDACs) and down-regulation of histone acetyltransferase (HAT). In comparison with K562 cells, the imatinib-resistant variants showed up-regulation of HDAC1, -2, and -3 (class I HDACs) and class III SIRT1 and down-regulation of CBP/p300 and PCAF with HAT activity, and thereby p53 and cytoplasmic Ku70 were aberrantly acetylated. In addition, these were associated with down-regulation of Bax and up-regulation of Bcl-2. In contrast, the class II HDAC6 level was significantly decreased, and this was accompanied by an increase of Hsp90 acetylation in the imatinib-resistant variants, which was closely associated with loss of Bcr-Abl. These results indicate that alteration of the normal balance of HATs and HDACs leads to deregulated acetylation of Hsp90, p53, and Ku70 and thereby leads to imatinib resistance, suggesting the importance of the acetylation status of apoptosis-related nonhistone proteins in Bcr-Abl-independent imatinib resistance. We also revealed that imatinib-resistant K562 cells were more sensitive to suberoylanilide hydroxamic acid, an HDAC inhibitor, than K562 cells. These findings may have implications for HDAC as a molecular target in imatinib-resistant leukemia cells.
已知在一些慢性粒细胞白血病（CML）患者中，Bcr-Abl非依赖性信号通路与伊马替尼耐药有关。在本研究中，为了找到对伊马替尼耐药且显示出Bcr-Abl激酶靶点依赖性丧失的CML的新靶点，我们从K562细胞中分离出伊马替尼耐药变体K562/R1、K562/R2和K562/R3，这些变体显示Bcr-Abl水平及其酪氨酸激酶活性显著下降。重要的是，这些变体中的伊马替尼耐药机制还包括非组蛋白如p53、Ku70和Hsp90的异常乙酰化，这是由于组蛋白去乙酰化酶（HDAC）上调和组蛋白乙酰转移酶（HAT）下调所致。与K562细胞相比，伊马替尼耐药变体显示HDAC1、-2和-3（I类HDAC）以及III类SIRT1上调，具有HAT活性的CBP/p300和PCAF下调，从而导致p53和细胞质Ku70异常乙酰化。此外，这些与Bax下调和Bcl-2上调有关。相反，II类HDAC6水平显著降低，这伴随着伊马替尼耐药变体中Hsp90乙酰化增加，这与Bcr-Abl缺失密切相关。这些结果表明，HAT和HDAC的正常平衡改变导致Hsp90、p53和Ku70的乙酰化失调，从而导致伊马替尼耐药，提示凋亡相关非组蛋白的乙酰化状态在Bcr-Abl非依赖性伊马替尼耐药中的重要性。我们还发现，伊马替尼耐药的K562细胞比K562细胞对HDAC抑制剂辛二酰苯胺异羟肟酸更敏感。这些发现可能意味着HDAC作为伊马替尼耐药白血病细胞的分子靶点。
