Mao Yinghui, Abrieu Ariane, Cleveland Don W
Ludwig Institute for Cancer Research, University of California, San Diego, 9500 Gilman Drive, La Jolla, CA 92093, USA.
Cell. 2003 Jul 11;114(1):87-98. doi: 10.1016/s0092-8674(03)00475-6.
The mitotic checkpoint prevents advance to anaphase prior to successful attachment of every centromere/kinetochore to mitotic spindle microtubules. Using purified components and Xenopus egg extracts, the kinetochore-associated microtubule motor CENP-E is now shown to be the activator of the essential checkpoint kinase BubR1. Since kinase activity and the checkpoint are silenced following CENP-E-dependent microtubule attachment in extracts or binding of CENP-E antibodies that do not disrupt CENP-E association with BubR1, CENP-E mediates silencing of BubR1 signaling. Checkpoint signaling requires the normal level of BubR1 containing a functional Mad3 domain implicated in Cdc20 binding, but only a small fraction need be kinase competent. This supports bifunctional roles for BubR1 in the checkpoint: an enzymatic one requiring CENP-E-dependent activation of its kinase activity at kinetochores and a stoichiometric one as a direct inhibitor of Cdc20.
有丝分裂检查点可防止在每个着丝粒/动粒成功附着到有丝分裂纺锤体微管之前进入后期。利用纯化的成分和非洲爪蟾卵提取物，现已表明与动粒相关的微管马达蛋白CENP-E是关键检查点激酶BubR1的激活剂。由于在提取物中依赖CENP-E的微管附着或不破坏CENP-E与BubR1结合的CENP-E抗体结合后，激酶活性和检查点会沉默，因此CENP-E介导BubR1信号的沉默。检查点信号传导需要正常水平的含有与Cdc20结合相关的功能性Mad3结构域的BubR1，但只有一小部分需要具备激酶活性。这支持了BubR1在检查点中的双功能作用：一种酶促作用，需要CENP-E依赖的动粒处其激酶活性的激活；另一种化学计量作用，作为Cdc20的直接抑制剂。
