Division of Medicinal Chemistry, College of Pharmacy, The Ohio State University, Columbus, OH 43210, USA.
Hepatology. 2011 Jan;53(1):148-59. doi: 10.1002/hep.23964.
Histone deacetylase (HDAC) inhibitors exhibit a unique ability to degrade topoisomerase (topo)IIα in hepatocellular carcinoma (HCC) cells, which contrasts with the effect of topoII-targeted drugs on topoIIβ degradation. This selective degradation might foster novel strategies for HCC treatment in light of the correlation of topoIIα overexpression with the aggressive tumor phenotype and chemoresistance. Here we report a novel pathway by which HDAC inhibitors mediate topoIIα proteolysis in HCC cells. Our data indicate that HDAC inhibitors transcriptionally activated casein kinase (CK)2α expression through increased association of acetylated histone H3 with the CK2α gene promoter. In turn, CK2 facilitated the binding of topoIIα to COP9 signalosome subunit (Csn)5 by way of topoIIα phosphorylation. Furthermore, we identified Fbw7, a Csn5-interacting F-box protein, as the E3 ligase that targeted topoIIα for degradation. Moreover, knockdown of CK2α, Csn5, or Fbw7 reversed HDAC inhibitor-induced topoIIα degradation. Mutational analysis indicates that the (1361) SPKLSNKE(1368) motif plays a crucial role in regulating topoIIα protein stability. This motif contains the consensus recognition sites for CK2 (SXXE), glycogen synthase kinase (GSK)3β (SXXXS), and Fbw7 (SPXXS). This study also reports the novel finding that topoIIα may be a target of GSK3β phosphorylation. Evidence suggests that CK2 serves as a priming kinase, through phosphorylation at Ser1365, for GSK3β-mediated phosphorylation at Ser1361. This double phosphorylation facilitated the recruitment of Fbw7 to the phospho-degron (1361) pSPKLpS(1365) of topoIIα, leading to its ubiquitin-dependent degradation.
This study shows a novel pathway by which HDAC inhibitors facilitate the selective degradation of topoIIα, which underlies the complexity of the functional role of HDAC in regulating tumorigenesis and aggressive phenotype in HCC cells.
组蛋白去乙酰化酶（HDAC）抑制剂在肝细胞癌（HCC）细胞中表现出独特的降解拓扑异构酶（topo）IIα的能力，这与拓扑异构酶 II 靶向药物对 topoIIβ 降解的作用形成对比。鉴于 topoIIα 过表达与侵袭性肿瘤表型和化疗耐药性的相关性，这种选择性降解可能为 HCC 治疗提供新的策略。在这里，我们报告了 HDAC 抑制剂在 HCC 细胞中介导 topoIIα 蛋白水解的新途径。我们的数据表明，HDAC 抑制剂通过增加乙酰化组蛋白 H3 与 CK2α 基因启动子的结合，转录激活了酪蛋白激酶（CK）2α 的表达。反过来，CK2 通过 topoIIα 磷酸化促进了 topoIIα 与 COP9 信号体亚基（Csn）5 的结合。此外，我们鉴定了 Fbw7，一种与 Csn5 相互作用的 F 框蛋白，作为靶向 topoIIα 进行降解的 E3 连接酶。此外，CK2α、Csn5 或 Fbw7 的敲低逆转了 HDAC 抑制剂诱导的 topoIIα 降解。突变分析表明，（1361）SPKLSNKE（1368）基序在调节 topoIIα 蛋白稳定性方面起着至关重要的作用。该基序包含 CK2（SXXE）、糖原合成酶激酶（GSK）3β（SXXXS）和 Fbw7（SPXXS）的共识识别位点。本研究还报告了新的发现，即 topoIIα 可能是 GSK3β 磷酸化的靶标。有证据表明，CK2 通过磷酸化 Ser1365 作为启动激酶，为 GSK3β 介导的 Ser1361 磷酸化提供条件。这种双重磷酸化促进了 Fbw7 募集到 topoIIα 的磷酸化降解基序（1361）pSPKLpS（1365），导致其依赖泛素的降解。
本研究表明了一种新途径，即 HDAC 抑制剂促进 topoIIα 的选择性降解，这是 HDAC 调节 HCC 细胞中肿瘤发生和侵袭性表型的复杂功能作用的基础。
