Chromosome instability in tumor cells due to defects in Aurora B mediated error correction at kinetochores

We characterized a panel of cancer cells and found that they exhibited chromosome instability (CIN) that was associated with high frequencies of aberrant kinetochore:microtubule attachments. Failure to resolve these defective attachments before anaphase onset can lead to missegregation of chromosomes. Aurora B kinase is concentrated at the inner centromere where it contributes to multiple kinetochore functions, one of which is in error-correction. Analysis of several CIN cell lines showed that many aspects of Aurora B kinase functions were normal. Furthermore, the amount and activity of Aurora B kinase was not reduced at the kinetochores of CIN cells that were examined. However, phosphorylation of a centromeric biosensor for Aurora B in OVCAR10, MCF7 and U2OS cells was consistently reduced relative to non CIN cells. This suggested a localized problem with Aurora B’s ability to phosphorylate substrates important for error correction. This possibility was supported by our ability to improve error correction and reduce the frequency of lagging chromosome in CIN cells by directing endogenous Aurora B to the region of centromere that was tested by the biosensor. Our studies suggest that the kinetochores of CIN cells have a defect that limits accessibility of Aurora B to substrates that are important for error-correction.本研究对一组肿瘤细胞系进行了表征，发现这些细胞均存在染色体不稳定性（chromosome instability, CIN），该特征与异常动粒-微管附着的高发生率相关。若在有丝分裂后期起始前未能纠正这些异常附着，可导致染色体错分离。极光B激酶（Aurora B kinase）富集于内着丝粒区域，参与调控多项动粒相关功能，其中一项为错误校正过程。对多株CIN细胞系的分析显示，极光B激酶的多数功能均表现正常。此外，在所检测的CIN细胞的动粒处，极光B激酶的表达量与催化活性均未出现降低。然而，相较于非CIN细胞，OVCAR10、MCF7及U2OS细胞中针对极光B激酶的着丝粒生物传感器的磷酸化水平始终呈下降趋势。这提示极光B激酶对错误校正相关底物的磷酸化能力存在局部缺陷。我们通过将内源性极光B激酶靶向至生物传感器所检测的着丝粒区域，成功改善了CIN细胞的错误校正能力并降低了滞后染色体的发生率，这一结果进一步支持了上述推测。本研究表明，CIN细胞的动粒存在一处缺陷，该缺陷会限制极光B激酶与错误校正相关底物的可及性。