Abstract
The spindle assembly checkpoint (SAC) restrains anaphase progression to ensure all chromosomes attach properly to the spindle. Although SAC timing has been extensively investigated in mitosis, its mechanism of regulation in interphase is unclear. We report that PTEN functions as a crucial activator of SAC timing and protects chromosome segregation under both spindle poison treated and untreated conditions. We show that PTEN physically interacts with MAD1 and promotes its dimerization and localization in the nuclear pore. Consequently, PTEN is important for the formation of the mitotic checkpoint complex (MCC) in interphase. We propose PTEN/MAD1 signaling is essential for maintenance of SAC timing and chromosome integrity.
Highlights
The spindle assembly checkpoint (SAC) prevents chromosome separation until each chromosome is properly attached to the spindle
To determine whether this phenomenon is caused by SAC arrest dysfunction or by defects in other stages of the cell cycle, we tracked the proportional change of G2 and M phase cells after nocodazole treatment in WT and PTEN-/- HCT116 cells
The major components of the mitotic checkpoint complex (MCC) were evaluated with gel filtration chromatography analysis, and it was a surprise to find a large proportion of both MAD2 and BUBR1 reside in PTEN null cells as monomers (Figure 5C, right panel, lane 5-8 and lane 10-12), in sharp contrast to HCT116 cells where most of these components reside in protein complexes (Figure 5D, left panel, lane 2-4), The phosphorylation status of PTEN was monitored during this analysis, and we found that phosphorylated PTEN is mainly monomeric (Supplementary Figure 6)
Summary
The spindle assembly checkpoint (SAC) prevents chromosome separation until each chromosome is properly attached to the spindle. Current studies have concluded that the SAC is directly coupled to KT-MT attachments by its promotion of the mitotic checkpoint complex (MCC) during mitosis [3,4,5]. It must be emphasized that MAD1 contributes to SAC timing through shuttling nuclear transport [6, 7], and assembly of a pre-mitotic anaphase inhibitor in interphase [8]. MAD1 cycles between the nuclear pore complex (NPC) and the kinetochore MCC during the cell cycle, and its interphase localization at the NPC is required for generation of a sufficient SAC timing interval [9]. The underlying mechanism of interphase MAD1 modulation is unknown
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