Cell cycle-regulated phosphorylation of the human SIX1 homeodomain protein
Cell cycle-regulated phosphorylation of the human SIX1 homeodomain protein
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DOI：
10.1074/jbc.m002446200
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发表时间：
2000-07-21
影响因子：
4.8
通讯作者：
Seldin, DC
中科院分区：
文献类型：
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作者：
Ford, HL;Landesman-Bollag, E;Seldin, DC
人SIX1（HSIX1）是Six类同源结构域蛋白的成员，涉及肌肉、眼睛、头部和大脑的发育。为了进一步了解HSIX1在细胞周期和癌症中的作用，我们开发了一种HSIX1特异性抗体，以研究细胞周期各个阶段的蛋白质表达。我们先前的工作表明，随着细胞退出S期，HSIX1 mRNA表达增加，并且HSIX1的过表达可以减弱DNA损伤诱导的G₂细胞周期检查点。在44%的原发性乳腺癌和90%的转移性病变中观察到HSIX1 mRNA的过表达。现在我们证明HSIX1是一种核磷蛋白，在MCF7细胞和非洲爪蟾提取物中，在有丝分裂时会高度磷酸化。在有丝分裂中观察到的磷酸化模式与在体外使用酪蛋白激酶II（CK2）处理重组HSIX1所观察到的模式相似。芹菜素，一种选择性的CK2抑制剂，可减少HSIX1在间期和有丝分裂期的磷酸化。用芹菜素处理MCF7细胞会导致在G₂/M边界处呈剂量依赖性的阻滞，这表明CK2和HSIX1一样，参与G₂/M转换。在体外被CK2高度磷酸化的HSIX1失去了结合醛缩酶A启动子（pM）的MEF3位点的能力，并且在有丝分裂期间观察到与pM的结合减少。因为CK2和HSIX1都与癌症和细胞周期控制有关，我们提出，其活性受CK2调节的HSIX1是CK2在G₂/M检查点控制中的一个相关靶点，并且这两种分子参与同一条通路，该通路的失调会导致癌症。
Human SIX1 (HSIX1) is a member of the Six class of homeodomain proteins implicated in muscle, eye, head, and brain development. To further understand the role of HSIX1 in the cell cycle and cancer, we developed an HSIX1-specific antibody to study protein expression at various stages of the cell cycle. Our previous work demonstrated that HSIX1 mRNA expression increases as cells exit S phase and that overexpression of HSIX1 can attenuate a DNA damage-induced G(2) cell cycle checkpoint. Overexpression of HSIX1 mRNA was observed in 44% of primary breast cancers and 90% of metastatic lesions. Now wt? demonstrate that HSIX1 is a nuclear phosphoprotein that becomes hyperphosphorylated at mitosis in both MCF7 cells and in Xenopus extracts. The pattern of phosphorylation observed in mitosis is similar to that seen by treating recombinant HSIX1 with casein kinase II (CK2) in vitro, Apigenin, a selective CK2 inhibitor, diminishes interphase and mitotic phosphorylation of HSIX1. Treatment of MCF7 cells with apigenin leads to a dose-dependent arrest at the G(2)/M boundary, implicating CK2, like HSIX1, in the G(2)/M transition. HSIX1 hyperphosphorylated in vitro by CK2 loses its ability to bind the MEF3 sites of the aldolase A promoter (pM), and decreased binding to pM is observed during mitosis, Because CK2 and HSIX1 have both been implicated in cancer and in cell cycle control, we propose that HSIX1, whose activity is regulated by CK2, is a relevant target of CK2 in G(2)/M checkpoint control and that both molecules participate in the same pathway whose dysregulation leads to cancer.