Yu Xiaokui, He Li, Cao Peng, Yu Qiang
Department of Pharmacology, Shanghai Institute of Materia Medica, Chinese Academy of Sciences, Shanghai, China.
Laboratory of Cellular and Molecular Biology, Jiangsu Province Academy of Traditional Chinese Medicine, Nanjing, China.
PLoS One. 2015 May 26;10(5):e0128406. doi: 10.1371/journal.pone.0128406. eCollection 2015.
Activated STAT3 plays an important role in oncogenesis by stimulating cell proliferation and resisting apoptosis. STAT3 therefore is an attractive target for cancer therapy. We have screened a traditional Chinese herb medicine compound library and found Eriocalyxin B (EB), a diterpenoid from Isodon eriocalyx, as a specific inhibitor of STAT3. EB selectively inhibited constitutive as well as IL-6-induced phosphorylation of STAT3 and induced apoptosis of STAT3-dependent tumor cells. EB did not affect the upstream protein tyrosine kinases or the phosphatase (PTPase) of STAT3, but rather interacted directly with STAT3. The effects of EB could be abolished by DTT or GSH, suggesting a thiol-mediated covalent linkage between EB and STAT3. Site mutagenesis of cysteine in and near the SH2 domain of STAT3 identified Cys712 to be the critical amino acid for the EB-induced inactivation of STAT3. Furthermore, LC/MS/MS analyses demonstrated that an α, β-unsaturated carbonyl of EB covalently interacted with the Cys712 of STAT3. Computational modeling analyses also supported a direct interaction between EB and the Cys712 of STAT3. These data strongly suggest that EB directly targets STAT3 through a covalent linkage to inhibit the phosphorylation and activation of STAT3 and induces apoptosis of STAT3-dependent tumor cells.
活化的信号转导和转录激活因子3（STAT3）通过刺激细胞增殖和抵抗凋亡在肿瘤发生中起重要作用。因此，STAT3是癌症治疗的一个有吸引力的靶点。我们筛选了一个中药复方文库，发现毛萼乙素（EB），一种来自毛萼香茶菜的二萜类化合物，是STAT3的特异性抑制剂。EB选择性地抑制STAT3的组成型以及白细胞介素-6诱导的磷酸化，并诱导依赖STAT3的肿瘤细胞凋亡。EB不影响STAT3的上游蛋白酪氨酸激酶或磷酸酶（PTPase），而是直接与STAT3相互作用。DTT或GSH可消除EB的作用，提示EB与STAT3之间存在硫醇介导的共价连接。对STAT3的SH2结构域及其附近的半胱氨酸进行位点诱变，确定Cys712是EB诱导STAT3失活的关键氨基酸。此外，液相色谱/串联质谱分析表明，EB的α，β-不饱和羰基与STAT3的Cys712共价相互作用。计算模型分析也支持EB与STAT3的Cys712之间的直接相互作用。这些数据强烈表明，EB通过共价连接直接靶向STAT3，以抑制STAT3的磷酸化和激活，并诱导依赖STAT3的肿瘤细胞凋亡。
