Sil phosphorylation in a Pin1 binding domain affects the duration of the spindle checkpoint.

SIL is an immediate-early gene that is essential for embryonic development and is implicated in T-cell leukemia-associated translocations. We now show that the Sil protein is hyperphosphorylated during mitosis or in cells blocked at prometaphase by microtubule inhibitors. Cell cycle-dependent phosphorylation of Sil is required for its interaction with Pin1, ...
a regulator of mitosis. Point mutation of the seven (S/T)P sites between amino acids 567 and 760 reduces mitotic phosphorylation of Sil, Pin1 binding, and spindle checkpoint duration. When a phosphorylation site mutant Sil is stably expressed, the duration of the spindle checkpoint is shortened in cells challenged with taxol or nocodazole, and the cells revert to a G2-like state. This event is associated with the downregulation of the kinase activity of the Cdc2/cyclin B1 complex and the dephosphorylation of the threonine 161 on the Cdc2 subunit. Sil downregulation by plasmid-mediated RNA interference limited the ability of cells to activate the spindle checkpoint and correlated with a reduction of Cdc2/cyclin B1 activity and phosphorylation on T161 on the Cdc2 subunit. These data suggest that a critical region of Sil is required to mediate the presentation of Cdc2 activity during spindle checkpoint arrest.
Mesh Terms:
Binding Sites, Cell Cycle, DNA, HeLa Cells, Humans, Intracellular Signaling Peptides and Proteins, Mitosis, NIMA-Interacting Peptidylprolyl Isomerase, Oncogene Proteins, Fusion, Peptidylprolyl Isomerase, Phosphorylation, Protein Binding, Protein Structure, Tertiary, RNA Interference, Spindle Apparatus, Time Factors
Mol Cell Biol
Date: Aug. 01, 2005
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