Phosphoregulation of Spc105 by Mps1 and PP1 Regulates Bub1 Localization to Kinetochores

Abstract

Summary Kinetochores are the macromolecular complexes that interact with microtubules to mediate chromosome segregation [1]. Accurate segregation requires that kinetochores make bioriented attachments to microtubules from opposite poles. Attachments between kinetochores and microtubules are monitored by the spindle checkpoint, a surveillance system that prevents anaphase until every pair of chromosomes makes proper bioriented attachments [2]. Checkpoint activity is correlated with the recruitment of checkpoint proteins to the kinetochore [1]. Mps1 is a conserved protein kinase that regulates segregation and the spindle checkpoint, but few of the targets that mediate its functions have been identified. Here, we show that Mps1 is the major kinase activity that co-purifies with budding yeast kinetochore particles and identify the conserved Spc105/KNL-1/Blinkin kinetochore protein as a substrate. Phosphorylation of conserved MELT motifs within Spc105 recruits the Bub1 protein to kinetochores and this is reversed by protein phosphatase I (PP1). Spc105 mutants lacking Mps1 phosphorylation sites are defective in the spindle checkpoint and exhibit growth defects. Together, these data identify Spc105 as a key target of the Mps1 kinase and show that the opposing activities of Mps1 and PP1 regulate the kinetochore localization of the Bub1 protein.

The Composition, Functions, and Regulation of the Budding Yeast Kinetochore

“…The Mps1 kinase is also essential for yeast kinetochore biorientation and its substrates have started to be identified (Shimogawa et al 2006;Maure et al 2007;Kemmler et al 2009;London et al 2012). Mps1 phosphorylates a number of sites in the Dam1 protein, and cells expressing a S218A S221A phosphomutant appear to biorient sister kinetochores and satisfy the checkpoint without making end-on microtubule attachments (Shimogawa et al 2006(Shimogawa et al , 2010.…”

“…First, the Mps1 kinase appears to be the most upstream signal and recruits downstream checkpoint components to kinetochores (Hardwick et al 1996;Heinrich et al 2012;London et al 2012;Shepperd et al 2012;Yamagishi et al 2012). Mps1 copurifies with Ndc80 and interacts with its N-terminal domain in vitro (Kemmler et al 2009), suggesting that Ndc80 may be the kinetochore receptor for Mps1.…”

Bimodal activation of BubR1 by Bub3 sustains mitotic checkpoint signaling

“…Recently, Bub3 has been shown to bind the phospho MELT motif on KNL-1 for kinetochore localization of Bub1 (budding uninhibited by benzimidazole 1), disruption of which caused a defective checkpoint (24)(25)(26)(27) with Bub1 binding to kinetochores apparently required for binding of other checkpoint proteins (28)(29)(30)(31)(32). A role for Bub3 in mitotic checkpoint silencing has also been proposed in fission yeast (33).…”

Characterization of novel MPS1 inhibitors with preclinical anticancer activity

“…6 Although the precise contribution of MPS1 to SAC functions remains elusive, 7 accumulating evidence suggests that MPS1 facilitates SAC activation by promoting the recruitment of SAC components to unoccupied KTs. [8][9][10][11][12][13][14][15] MPS1 has also been implicated in the so-called 'error correction mechanism', 16 a poorly characterized process that resolves the erroneous KT-MT attachments that frequently form in the early steps of mitosis. 17,18 According to current models, AURKB, one component of the chromosomal passenger complex (reviewed by Ruchaud et al 19 ), catalyzes this process by destabilizing incorrect attachments, hence generating free KTs that activate the SAC.…”