Chromosome segregation errors: a double-edged sword - TI Pharma

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Figure 2. Selective inhibition of Mps1 results in inhibition of mitotic checkpoint signaling
A) Graphs depict the percentage of mitotic cells after treatment of RPE-1 (top), U2OS (middle) and Hela (bottom) cell lines with
250ng/ml nocodazole and indicated concentrations of compound-5 for 12 hours. Percentage of mitotic cells was determined as the
number of MPM2 positive nuclei. Average of 3 independent experiments is shown + SD. B) Hela lysates immuno-blotted for Mps1,
Securin and Cyclin B-1 after indicated treatments for 18 hours. C) Graph depicts the mitotic index after compound-5 treatment
relative to the mitotic index of control treated (0nM compound-5) cells of each individual cell line. Mitotic index was determined as
in (A) Average of 3 independent experiments is shown + SD.
mitotic checkpoint signaling and the alignment of chromosomes at the spindle equator (reviewed in
167 ).
To examine the effect of compound-5 on the fidelity of chromosome segregation in the absence of
microtubule targeting drugs, anaphase progression was followed by time-lapse microscopy (Fig.3A).
The percentage of RPE-1, U2OS and Hela cells that displayed either mild or severe chromosome
segregation defects in anaphase increased from 5%, 10% and 20% in control cells respectively to
100%, 100% and 98% upon treatment with 100 nM of compound-5 (Fig.3A). In line with these effects
on chromosome segregation, U2OS cells also displayed chromosome alignment defects (80% versus
30% in control cells) already when treated with 30nM compound-5 in the presence of the proteasome
inhibitor MG132 (Fig.3B). This effect was rescued by expressing the Mps1 gate-keeper mutant in U2OS
cells, again confirming the Mps1 specific inhibition (Fig.3B).
Mps1 inhibition selectively kills tumor cells
Partially depleting Mps1 specifically sensitizes tumor cells to the microtubule stabilizing drug taxol 299 .
To determine whether we could confirm those effects by partial inhibition, rather than depletion of