Analysis of the checkpoint genes controlling induction of chromosome aberrations by radiation.

为了分析控制辐射诱导的染色体畸变和染色体不稳定的基因，我们分离了酵母有丝分裂检查点基因的几个哺乳动物同源物，并使用人类肿瘤细胞系和癌组织检测了它们的生化特性。最近，我们分离了一个编码新蛋白丝氨酸/苏氨酸蛋白激酶AIM-1的大鼠基因，其是有丝分裂期间胞质分裂开始的关键调节剂。在这项研究中，我们克隆了两个人类激酶基因参与有丝分裂，人类基因的功能同系物大鼠AIM-1和丝氨酸/苏氨酸激酶15，STK 15，这也被称为Aik和极光2。在具有多核细胞的人肿瘤细胞系中，发现AIM-1过表达，并且在人二倍体成纤维细胞中外源诱导野生型AIM-1的过表达引起多核性和非整倍性。因此，AIM-1被认为在有丝分裂进程的调节中起重要作用。有趣的是，AIM-1和STK 15在人结直肠肿瘤中均过表达，但只有AIM-1的表达水平随着肿瘤恶性程度的增加而增加，提示AIM-1的表达可能参与肿瘤的进展。最近的研究表明，Ipl 1/aurora蛋白激酶家族具有组蛋白H3丝氨酸10位点特异性磷酸化活性。我们使用针对磷酸化组蛋白H3的抗体检测了各种人类癌细胞系中组蛋白H3磷酸化的水平，然后发现在有丝分裂期间组蛋白H3被过度磷酸化，并且在显示AIM-1过表达的非整倍体癌细胞系中磷酸化组蛋白H3的量比正常人类二倍体成纤维细胞中高得多。这些数据表明，AIM-1是一个有丝分裂阻滞点的调节剂，组蛋白H3的过度磷酸化导致AIM-1过表达癌细胞的染色体不稳定性。

To analyze the genes controlling radiation-induced chromosome aberration and chromosomal instability which is commonly found in human cancer cells, we have isolated several mammalian homologues of the yeast mitotic checkpoint genes and examined their biochemical properties using human tumor cell lines and cancerous tissues.Recently, we isolated a rat gene encoding a novel protein serine/threonine protein kinase, AIM-1, which is a key regulator of the onset of cytokinesis during mitosis. In this study, we cloned two human kinase genes involved in mitosis, the human genes for a functional homologue of rat AIM-1 and for serine/threoine kinase 15, STK15 which is also known as Aik and aurora2. In human tumor cell lines with multinuclear cells, AIM-1 was found to be overexpressed, and the exogenously induced overexpression of wild-type AIM-1 in human diploid fibroblasts caused multinuclearity and aneuploidy. Thus, AIM-1 is considered to play an important role in the regulation of mitotic progression. Interestingly, the AIM-1 and STK15 were overexpressed in human colorectal tumors, but only the expression levels of AIM-1 were increased with their grades of malignancy, indicating that AIM-1 expression may be involved in tumor progression.Recent studies indicated that Ipl1/aurora family of protein kinase had an activity of site-specific phosphorylation of histone H3 at serine 10. We examined the levels of histone H3 phosphorylation in various human cancer cell lines using an antibody against phosphorylated histone H3, and then found that hitone H3 was hyperphosphorylated during mitosis and the amount of phophorylated histone H3 was much higher in aneuploid cancer cell lines displaying an overexpression of AIM-1 than in normal human diploid fibroblasts. These data indicate that AIM-1 is a regulator of mitotic chickpoints and that hyperphosphorylation of histone H3 causes chromosomal instability in AIM-1-overexpressing cancer cells.