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

Mol Cell Biol. 2005 Aug;25(15):6660-72. doi: 10.1128/MCB.25.15.6660-6672.2005.


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.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Binding Sites
  • Cell Cycle / physiology*
  • DNA / metabolism
  • HeLa Cells
  • Humans
  • Intracellular Signaling Peptides and Proteins
  • Mitosis / physiology
  • NIMA-Interacting Peptidylprolyl Isomerase
  • Oncogene Proteins, Fusion / metabolism*
  • Peptidylprolyl Isomerase / deficiency
  • Peptidylprolyl Isomerase / genetics
  • Peptidylprolyl Isomerase / metabolism*
  • Peptidylprolyl Isomerase / physiology
  • Phosphorylation
  • Protein Binding
  • Protein Structure, Tertiary
  • RNA Interference
  • Spindle Apparatus / metabolism*
  • Time Factors


  • Intracellular Signaling Peptides and Proteins
  • NIMA-Interacting Peptidylprolyl Isomerase
  • Oncogene Proteins, Fusion
  • STIL protein, human
  • DNA
  • PIN1 protein, human
  • Peptidylprolyl Isomerase