Department of Chemistry and Biochemistry, School of Advanced Science and Engineering, Waseda University, 3-4-1 Ohkubo, Shinjuku-ku, Tokyo, 169-8555, Japan.
Graduate Program in Biophysics and Biochemistry, Graduate School of Science, The University of Tokyo, Yayoi, Tokyo, 113-0032, Japan.
Sci Rep. 2020 Sep 24;10(1):15653. doi: 10.1038/s41598-020-71955-2.
During mitosis, spatiotemporal regulation of phosphorylation at the kinetochore is essential for accurate chromosome alignment and proper chromosome segregation. Aurora B kinase phosphorylates kinetochore substrates to correct improper kinetochore-microtubule (KT-MT) attachments, whereas tension across the centromeres inactivates Aurora B kinase, and PP2A phosphatase dephosphorylates the kinetochore proteins to stabilize the attachments. However, the molecular entity of the tension sensing mechanism remains elusive. In a previous report, we showed that centromeric SET/TAF1 on Sgo2 up-regulates Aurora B kinase activity via PP2A inhibition in prometaphase. Here we show that Aurora B and Bub1 at the centromere/kinetochore regulate both kinase activities one another in an inter-kinetochore distance-dependent manner, indicating a positive feedback loop. We further show that the centromeric pool of SET on Sgo2 depends on Bub1 kinase activity, and the centromeric localization of SET decreases in a distance-dependent manner, thereby inactivating Aurora B in metaphase. Consistently, ectopic targeting of SET to the kinetochores during metaphase hyperactivates Aurora B via PP2A inhibition, and thereby rescues the feedback loop. Thus, we propose that SET, Aurora B and Bub1 form a distance-dependent positive feedback loop, which spatiotemporally may act as a tension sensor at centromeres.
在有丝分裂过程中，动粒处磷酸化的时空调节对于准确的染色体排列和正确的染色体分离至关重要。极光激酶 B 磷酸化动粒底物以纠正不正确的动粒-微管（KT-MT）连接，而着丝粒处的张力使极光激酶 B 失活，PP2A 磷酸酶去磷酸化动粒蛋白以稳定连接。然而，张力感应机制的分子实体仍然难以捉摸。在之前的一份报告中，我们表明 Sgo2 上的着丝粒 SET/TAF1 通过 PP2A 抑制在上中期上调极光激酶 B 的激酶活性。在这里，我们表明着丝粒/动粒处的极光激酶 B 和 Bub1 以动粒间距离依赖的方式相互调节彼此的激酶活性，表明存在正反馈环。我们进一步表明，Sgo2 上 SET 的着丝粒池依赖于 Bub1 激酶活性，SET 的着丝粒定位以距离依赖的方式减少，从而在中期使 Aurora B 失活。一致地，中期将 SET 异位靶向到动粒会通过 PP2A 抑制过度激活 Aurora B，并由此挽救反馈环。因此，我们提出 SET、极光激酶 B 和 Bub1 形成一个距离依赖性的正反馈环，它可能作为着丝粒处的张力传感器在时空上发挥作用。
