MOLECULAR BIOLOGY AND GENETICS DEPARTMENTAL SEMINAR
“Loss of the Mastl Kinase Weakens the Spindle Assembly Checkpoint*”
Assist. Prof. Kasım Diril, iBG-İzmir, Dokuz Eylül University
Mastl is an essential mitotic kinase that inhibits the phosphatase activity directed toward mitotic Cdk1 substrates. To analyze the consequences of Mastl loss in vivo, we have created a conditional knockout mouse model. Although Mastl deficient MEFs could enter mitosis, they progressed through mitosis without completing cytokinesis despite the presence of misaligned chromosomes, resulting in chromosome segregation defects. Furthermore, we found Mastl kinase was required for robust spindle assembly checkpoint (SAC) maintenance since the duration of mitotic arrest caused by microtubule poisons in Mastl KO MEFs is shortened, which correlates with premature disappearance of the essential SAC protein Mad1 at the kinetochores. Notably, Mastl KO MEFs displayed reduced phosphorylation of a number of proteins in mitosis, which included the essential SAC kinase MPS1. We further found that Mastl is required for phosphorylation of MPS1 at multiple sites as well as robust MPS1 kinase activity in mitosis. In contrast, treatment of Mastl deficient cells with the phosphatase inhibitor okadaic acid rescued the defects in MPS1 kinase activity, mislocalization of MPS1 and Mad1 at the kinetochore, and premature SAC silencing. Moreover, in vitro dephosphorylation assays showed that Mastl promotes persistent MPS1 phosphorylation by inhibiting PP2A/B55-mediated MPS1 dephosphorylation rather than affecting Cdk1 kinase activity. These results suggest a key regulatory function of the Mastl kinase in preventing premature SAC silencing.
*Diril et al. 2016, PLOS Genetics
Date-Time : Wednesday, December 14 at 15:40
Place : SBZ-14
Host : Serkan Göktuna