Mitotic centromere-associated kinesin (MCAK) plays an essential role in spindle formation and in correction of improper microtubule-kinetochore attachments. The localization and activity of MCAK at the centromere/kinetochore are controlled by Aurora B kinase. However, MCAK is also abundant in the cytosol and at centrosomes during mitosis, and its regulatory mechanism at these sites is unknown. We show here that cyclin-dependent kinase 1 (Cdk1) phosphorylates T537 in the core domain of MCAK and attenuates its microtubule-destabilizing activity
in vitro and
in vivo. Phosphorylation of MCAK by Cdk1 promotes the release of MCAK from centrosomes and is required for proper spindle formation. Interfering with the regulation of MCAK by Cdk1 causes dramatic defects in spindle formation and in chromosome positioning. This is the first study demonstrating that Cdk1 regulates the localization and activity of MCAK in mitosis by directly phosphorylating the catalytic core domain of MCAK.Chromosomes are properly attached to the mitotic spindles, and chromosome movement is tightly linked to the structure and dynamics of spindle microtubules during mitosis. Important regulators of microtubule dynamics are the kinesin-13 proteins (
37). This kinesin superfamily is defined by the localization of the conserved kinesin core motor domain in the middle of the polypeptide (
19). Kinesin-13 proteins induce microtubule depolymerization by disassembling tubulin subunits from the polymer end (
6). Among them,
mitotic
centromere-
associated
kinesin (MCAK) is the best-characterized member of the family. It depolymerizes microtubules
in vitro and
in vivo, regulates microtubule dynamics, and has been implicated in correcting misaligned chromosomes (
12,
14,
16,
24). In agreement with these observations, both overexpression and inhibition of MCAK result in a disruption of microtubule dynamics, leading further to improper spindle assembly and errors in chromosome alignment and segregation (
7,
11,
15,
22,
33). The importance of MCAK in ensuring the faithful segregation of chromosomes is consistent with the observation that MCAK is highly expressed in several types of cancer and thus is likely to be involved in causing aneuploidy (
25,
32).While MCAK is found both in the cytoplasm and at the centromeres throughout the cell cycle, it is highly enriched on centrosomes, the centromeres/kinetochores, and the spindle midzone during mitosis (
18,
21,
36,
38). In accordance with its localizations, MCAK affects many aspects throughout mitosis, from spindle assembly and maintenance (
3,
10,
36) to chromosome positioning and segregation (
14,
21,
35). Thus, the precise control of the localization and activity of MCAK is crucial for maintaining genetic integrity during mitosis. Regulation of MCAK on the centromeres/kinetochores by Aurora B kinase in mitosis has been intensively investigated (
1,
28,
29,
43). The data reveal that MCAK is phosphorylated on several serine/threonine residues by Aurora B, which inhibits the microtubule-destabilizing activity of MCAK and regulates its localization on chromosome arms/centromeres/kinetochores during mitosis (
1,
18,
28). Moreover, in concert with Aurora B, ICIS (
inner
centromere Kin
I stimulator), a protein targeting the inner centromeres in an MCAK-dependent manner, may regulate MCAK at the inner centromeres and prevent kinetochore-microtubule attachment errors in mitosis by stimulating the activity of MCAK (
27). Interestingly, hSgo2, a recently discovered inner centromere protein essential for centromere cohesion, has been reported to be important in localizing MCAK to the centromere and in spatially regulating its mitotic activity (
13). These data highlight that the activity and localization of MCAK on the centromeres/kinetochores during mitosis are tightly controlled by Aurora B and its cofactors. Remarkably, MCAK concentrates at spindle poles from prophase to telophase during mitosis (
18); however, only a few studies have been done to deal with that issue. Aurora A-depleted prometaphase cells delocalize MCAK from spindle poles but accumulate the microtubule-stabilizing protein ch-TOG at poles (
5), implying that Aurora A might influence the centrosomal localization of MCAK in mitosis. Aurora A is also found to be important for focusing microtubules at aster centers and for facilitating the transition from asters to bipolar spindles in
Xenopus egg extracts (
42). In addition, it has been revealed that Ca
2+/calmodulin-dependent protein kinase II gamma (CaMKII gamma) suppresses MCAK''s activity, which is essential for bipolar spindle formation in mitosis (
11). More work is required to gain insight into the regulatory mechanisms of MCAK at spindle poles during mitosis.Deregulated cyclin-dependent kinases (Cdks) are very often linked to genomic and chromosomal instability (
20). Cyclin B1, the regulatory subunit of Cdk1, is localized to unattached kinetochores and contributes to efficient microtubule attachment and proper chromosome alignment (
2,
4). We observed that knockdown of cyclin B1 induces defects in chromosome alignment and mitotic spindle formation (N.-N. Kreis, M.
Sanhaji, A. Krämer, K. Sommor, F. Rödel, K. Strebhardt, and J. Yuan, submitted for publication). Yet, how Cdk1/cyclin B1 carries out these functions is not very well understood. In this context, it is extremely interesting to investigate the relationship between the essential mitotic kinase Cdk1 and the microtubule depolymerase MCAK in human cells.
相似文献