Sasaki M, Sugimoto K, Tamayose K, Ando M, Tanaka Y, Oshimi K
Department of Internal Medicine, Division of Hematology, Juntendo University School of Medicine, Tokyo, Japan.
Oncogene. 2006 Jun 22;25(26):3621-7. doi: 10.1038/sj.onc.1209404. Epub 2006 Jan 30.
Bub1 is a component of the mitotic spindle checkpoint apparatus. Abnormality of this apparatus is known to cause multinuclei formation, a hallmark of chromosomal instability (CIN). A549, aneuploid cell line, aberrantly passed through the mitotic phase and became multinuclei morphology in the presence of nocodazole. Time-lapse videomicroscopy showed unreported bizarre morphology, which we named 'mitotic lobulation' in A549 cells just before the exit from mitosis and multinuclei formation. External expression of wild-type Bub1-EGFP clearly suppressed the multinuclei formation by retaining A549 cells at the mitotic phase during 48 h of time-lapse observation. This suppressive effect on mitotic aberrancy should not be mere restoration of normal Bub1 function, because A549 cells express proper amount of Bub1, which distributed cytoplasm during interphase and concentrated at kinetochore in metaphase. Furthermore, external expression of wild-type Bub1-EGFP suppressed multinuclei formation induced by Tax both in A549 and HeLa cells. Tax is known to induce mitotic abnormality by binding and inactivating Mad1. These observations, therefore, suggest functional redundancy between Bub1 and other mitotic checkpoint protein(s) and a possibility of correction of mitotic aberrancy by external Bub1 expression.
Bub1是有丝分裂纺锤体检查点装置的一个组成部分。已知该装置异常会导致多核形成，这是染色体不稳定（CIN）的一个标志。非整倍体细胞系A549在存在诺考达唑的情况下异常通过有丝分裂期并变成多核形态。延时视频显微镜显示了未报道过的奇异形态，我们将其命名为A549细胞在有丝分裂退出和多核形成之前的“有丝分裂叶状化”。野生型Bub1-EGFP的外源表达通过在48小时的延时观察期间将A549细胞阻滞在有丝分裂期，明显抑制了多核形成。这种对有丝分裂异常的抑制作用不应仅仅是正常Bub1功能的恢复，因为A549细胞表达适量的Bub1，其在间期分布于细胞质中，在中期集中于动粒。此外，野生型Bub1-EGFP的外源表达在A549和HeLa细胞中均抑制了Tax诱导的多核形成。已知Tax通过结合并使Mad1失活来诱导有丝分裂异常。因此，这些观察结果提示Bub1与其他有丝分裂检查点蛋白之间存在功能冗余，以及通过外源表达Bub1来纠正有丝分裂异常的可能性。
