Study The Function Of MPS1 In Mitosis

Mitosis is the most important process of cell cycle and its purpose is to allocate equal genetic material to daughter cells.Defects in mitosis will generate aneuploidy daughter cells,which further promote chromosomal instability and tumorgenesis.The spindle assembly checkpoint(SAC)is a critical cell surveillance system that ensures the accuracy of chromosome segregation and suppresses aneuploidy.MPS1 is an essential protein kinase for the integrity of SAC function.Knock down or inhibit the kinase activity of MPS1 can cause the SAC malfunction,and cells exit mitosis quickly.Human MPS1 suffers comprehensive phosphorylation during mitosis.Nevertheless,the functions of many phosphorylation sites are unclear.In this study,we first demonstrated the negative correlation between MPS1 kinetochore localization and its kinase activity.Next,we systematically investigated the function of 8 autophosphorylation sites outside of catalytic domain.We found autophosphorylation negatively regulate the kinetochore localization of MPS1.We next explored whether these autophosphorylation sites are essential for faithful mitotic progression.Indeed,MPS1-8A mutant expression causes a short delay in metaphase.On the contrary,MPS1-8D expression leads significantly elevated frequency of lagging chromosome in anaphase,indicating impaired SAC function.We future demonstrated that decreased kinetochore recruitment of key SAC factors,BubRl and Mad2,in MPS1-8D expressing cells.Together,our data indicated the physiological dynamics of autophosphorylation is required for precise mitotic progression.MPS1 was reported to play a function in facilitating chromosome alignment.However,whether MPS1 does such function through promoting Aurora B activity is controversial.Here,we reexamined the function of MPS1 in chromosome alignment.Unexpectedly,we found that knocking down MPS1 induced very slight chromosome alignment defects.However,consistent with the publications,we observed severe chromosomal alignment defects in MPS1 specific small molecular inhibitor treated cells.The major difference between RNAi and MPS1 inhibitor is RNAi disrupt the kinetochore localization of MPS1,whereas inhibiting induces sharply elevated kinetochore localization of MPS1.We therefore presume sharp defective phenotype caused by MPS1 inhibitors was due to deregulation of MPS1 kinetochore localization.The elevated association of inactive MPS1 with kinetochore may prevent the establishment of proper microtubule attachment.In summary,my work uncovers the role of MPS1 autophosphorylation dynamics in the maintenance of faithful chromosome segregation during mitosis and offers a new explanation of MPS1 function in chromosome alignment.