Small-molecule kinase inhibitors provide insight into Mps1 cell cycle function

Abstract

Mps1, a dual-specificity kinase, is required for the proper functioning of the spindle assembly checkpoint and the maintenance of chromosomal stability. As Mps1 function has been implicated in numerous phases of the cell cycle, it is expected the development of a potent, selective small molecule inhibitor of Mps1 would greatly facilitate dissection of Mps1-related biology. We describe the cellular effects and Mps1 co-crystal structures of novel, selective small molecule inhibitors of Mps1. Consistent with RNAi studies, chemical inhibition of Mps1 leads to defects in Mad1 and Mad2 establishment at unattached kinetochores, decreased Aurora B kinase activity, premature mitotic exit, and gross aneuploidy, without any evidence of centrosome duplication defects. However, in U2OS cells possessing extra centrosomes, an abnormality found in some cancers, Mps1 inhibition increases the frequency of multipolar mitoses. Lastly, Mps1 inhibitor treatment resulted in a decrease in cancer cell viability.

Characterization of novel MPS1 inhibitors with preclinical anticancer activity

“…Even in the absence of SAC activators, both classes of MPS1 inhibitors markedly increased the rate of chromosome misalignments resulting from erroneous MT-KT attachments and promoted a premature anaphase entry (i.e., before the formation of a correct equatorial metaphase plate). These results are in line with previous findings obtained with other MPS1-specific inhibitors, [8][9][10]12,15,47 upon MPS1 depletion 16,24 or following the conditional knockout of TTK, 11 confirming the central implication of this mitotic kinase in SAC function and chromosome congression. Upon exposure to MPS1 inhibitors, colorectal carcinoma cells displayed severely abnormal anaphases, and, as they progressed in mitosis, they underwent two alternative catastrophic fates: (i) they divided in a bipolar (often asymmetrical) manner, generating two aneuploid cells that most often died in the following interphase, or (ii) they failed to complete cytokinesis and hence became hyperploid.…”

“…10,16 Consistent with these observations, both the inhibition/depletion and the overexpression of MPS1 abrogate SAC functions, leading to aneuploidy/polyploidy and eventually cell death. 9,16,[22][23][24] MPS1 appears to play additional, more controversial, roles in mitosis or interphase. For instance, MPS1 not only may influence mitotic exit and cytokinesis 25 but also seems to promote the assembly of a cytosolic anaphase-promoting complex/cyclosome inhibitory complex during interphase to define the overall timing of the M phase.…”

“…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.…”

Killing cells by targeting mitosis

“…45,46,48,51 In contrast to other cell cycle checkpoints, the SAC is essential for cell survival, and targeting this mitotic checkpoint could constitute 59,60 Interestingly, compared with non-transformed cells, cancer cell lines are more sensitive to undergo cell death in response to checkpoint abrogation. 52,61 Whether this is a consequence of the abnormal number of chromosomes commonly found in tumor cells (Box 1) is not well established. It has been proposed that, as a consequence of the extra chromosomes, tumor cells may require more time to properly align chromosomes at metaphase.…”

Studying Kinetochore Kinases

“…22 If a large number of live microscopy experiments are performed then keep the microscope unit at 37°C permanently. This will prevent downtime without affecting the quality of the fixed analysis.…”