Chromosomal instability by inefficient Mps1 auto-activation due to a weakened mitotic checkpoint and lagging chromosomes.
BACKGROUND
Chromosomal instability (CIN), a feature widely shared by cells from solid tumors, is caused by occasional chromosome missegregations during cell division. Two of the causes of CIN are weakened mitotic checkpoint signaling and persistent merotelic attachments that result in lagging chromosomes during anaphase.


RESULTS
Here we identify an autophosphorylation event on Mps1 that is required to prevent these two causes of CIN. Mps1 is phosphorylated in mitotic cells on at least 7 residues, 4 of which by autophosphorylation. One of these, T676, resides in the activation loop of the kinase domain and a mutant that cannot be phosphorylated on T676 is less active than wild-type Mps1 but is not kinase-dead. Strikingly, cells in which endogenous Mps1 was replaced with this mutant are viable but missegregate chromosomes frequently. Anaphase is initiated in the presence of misaligned and lagging chromosomes, indicative of a weakened checkpoint and persistent merotelic attachments, respectively.


CONCLUSIONS
We propose that full activity of Mps1 is essential for maintaining chromosomal stability by allowing resolution of merotelic attachments and to ensure that single kinetochores achieve the strength of checkpoint signaling sufficient to prevent premature anaphase onset and chromosomal instability. To our knowledge, phosphorylation of T676 on Mps1 is the first post-translational modification in human cells of which the absence causes checkpoint weakening and CIN without affecting cell viability.
Department of Physiological Chemistry and Cancer Genomics Centre, UMC Utrecht, Utrecht, The Netherlands.
Nannette
N
Jelluma
Arjan B
AB
Brenkman
Ian
I
McLeod
John R
JR
Yates
Don W
DW
Cleveland
René H
RH
Medema
Geert J P L
GJ
Kops
D018797:Cell Cycle Proteins / Q000502:physiology*; D002460:Cell Line; D043171:Chromosomal Instability; D002877:Chromosomes, Human; D005434:Flow Cytometry; D005455:Fluorescent Antibody Technique; D006801:Humans; D008938:Mitosis / Q000502:physiology*; D010766:Phosphorylation; D017346:Protein Serine-Threonine Kinases / Q000502:physiology*; D011505:Protein-Tyrosine Kinases
D018797:Cell Cycle Proteins; D011505:Protein-Tyrosine Kinases; D017346:Protein Serine-Threonine Kinases; C075840:TTK protein, human