Department of Molecular Biology, Umeå University, Umeå, Sweden.
Exp Cell Res. 2010 Jul 15;316(12):2017-26. doi: 10.1016/j.yexcr.2010.04.008. Epub 2010 Apr 25.
Op18/stathmin (Op18) is a microtubule-destabilizing protein that is phosphorylation-inactivated during mitosis and its normal function is to govern tubulin subunit partitioning during interphase. Human tumors frequently overexpress Op18 and a tumor-associated Q18-->E mutation has been identified that confers hyperactivity, destabilizes spindle microtubules, and causes mitotic aberrancies, polyploidization, and chromosome loss in K562 leukemia cells. Here we determined whether wild-type and mutant Op18 have the potential to cause chromosomal instability by some means other than interference with spindle assembly, and thereby bypassing the spindle assembly checkpoint. Our approach was based on Op18 derivatives with distinct temporal order of activity during mitosis, conferred either by differential phosphorylation inactivation or by anaphase-specific degradation through fusion with the destruction box of cyclin B1. We present evidence that excessive Op18 activity generates chromosomal instability through interference occurring subsequent to the metaphase-to-anaphase transition, which reduces the fidelity of chromosome segregation to spindle poles during anaphase. Similar to uncorrected merotelic attachment, this mechanism evades detection by the spindle assembly checkpoint and thus provides an additional route to chromosomal instability.
Op18/stathmin（Op18）是一种微管解聚蛋白，在有丝分裂期间被磷酸化失活，其正常功能是在有丝分裂间期控制微管亚基的分配。人类肿瘤经常过度表达 Op18，并且已经鉴定出一种与肿瘤相关的 Q18-->E 突变，该突变赋予了 Op18 过度活性、微管解聚、导致有丝分裂异常、多倍体形成和 K562 白血病细胞中的染色体丢失。在这里，我们确定野生型和突变型 Op18 是否有可能通过干扰纺锤体组装以外的其他方式导致染色体不稳定，从而绕过纺锤体组装检查点。我们的方法基于在有丝分裂期间具有不同活性时间顺序的 Op18 衍生物，通过与细胞周期蛋白 B1 的破坏盒融合，通过差异磷酸化失活或后期特异性降解来赋予活性。我们提出的证据表明，过多的 Op18 活性通过发生在中期到后期过渡之后的干扰来产生染色体不稳定性，这会降低后期向纺锤体极的染色体分离的保真度。与未校正的桥联连接类似，该机制逃避了纺锤体组装检查点的检测，因此为染色体不稳定性提供了另一种途径。
