Zhou Qun, Agoston Agoston T, Atadja Peter, Nelson William G, Davidson Nancy E
The Sidney Kimmel Comprehensive Cancer Center, Johns Hopkins University, 1650 Orleans Street, CRB Room 144, Baltimore, MD 21231, USA.
Mol Cancer Res. 2008 May;6(5):873-83. doi: 10.1158/1541-7786.MCR-07-0330.
Histone deacetylases (HDAC) play a critical role in chromatin modification and gene expression. Recent evidence indicates that HDACs can also regulate functions of nonhistone proteins by catalyzing the removal of acetylated lysine residues. Here, we show that the HDAC inhibitor LBH589 down-regulates DNA methyltransferase 1 (DNMT1) protein expression in the nucleus of human breast cancer cells. Cotreatment with the proteasomal inhibitor MG-132 abolishes the ability of LBH589 to reduce DNMT1, suggesting that the proteasomal pathway mediates DNMT1 degradation on HDAC inhibition. Deletion of the NH(2)-terminal 120 amino acids of DNMT1 diminishes LBH589-induced ubiquitination, indicating that this domain is essential for its proteasomal degradation. DNMT1 recruits the molecular chaperone heat shock protein 90 (Hsp90) to form a chaperone complex. Treatment with LBH589 induces hyperacetylation of Hsp90, thereby inhibiting the association of DNMT1 with Hsp90 and promoting ubiquitination of DNMT1. In addition, inactivation of HDAC1 activity by small interfering RNA and MS-275 is associated with Hsp90 acetylation in conjunction with reduction of DNMT1 protein expression. We conclude that the stability of DNMT1 is maintained in part through its association with Hsp90. Disruption of Hsp90 function by HDAC inhibition is a unique mechanism that mediates the ubiquitin-proteasome pathway for DNMT1 degradation. Our studies suggest a new role for HDAC1 and identify a novel mechanism of action for the HDAC inhibitors as down-regulators of DNMT1.
组蛋白去乙酰化酶（HDAC）在染色质修饰和基因表达中发挥关键作用。最近的证据表明，HDAC还可通过催化去除乙酰化赖氨酸残基来调节非组蛋白的功能。在此，我们表明HDAC抑制剂LBH589可下调人乳腺癌细胞核中DNA甲基转移酶1（DNMT1）的蛋白表达。与蛋白酶体抑制剂MG-132共同处理可消除LBH589降低DNMT1的能力，这表明蛋白酶体途径介导了HDAC抑制作用下DNMT1的降解。删除DNMT1的NH（2）末端120个氨基酸可减少LBH589诱导的泛素化，表明该结构域对其蛋白酶体降解至关重要。DNMT1招募分子伴侣热休克蛋白90（Hsp90）形成伴侣复合物。用LBH589处理可诱导Hsp90的高乙酰化，从而抑制DNMT1与Hsp90的结合并促进DNMT1的泛素化。此外，小干扰RNA和MS-275使HDAC1活性失活与Hsp90乙酰化以及DNMT1蛋白表达降低相关。我们得出结论，DNMT1的稳定性部分通过其与Hsp90的结合得以维持。HDAC抑制作用破坏Hsp90功能是介导DNMT1降解的泛素-蛋白酶体途径的独特机制。我们的研究揭示了HDAC1的新作用，并确定了HDAC抑制剂作为DNMT1下调剂的新作用机制。
