Phospho-Bcl-x(L)(Ser62) plays a key role at DNA damage-induced G(2) checkpoint

Cell Cycle. 2012 Jun 1;11(11):2159-69. doi: 10.4161/cc.20672. Epub 2012 Jun 1.


Accumulating evidence suggests that Bcl-xL, an anti-apoptotic member of the Bcl-2 family, also functions in cell cycle progression and cell cycle checkpoints. Analysis of a series of phosphorylation site mutants reveals that cells expressing Bcl-xL(Ser62Ala) mutant are less stable at the G 2 checkpoint and enter mitosis more rapidly than cells expressing wild-type Bcl-xL or Bcl-xL phosphorylation site mutants, including Thr41Ala, Ser43Ala, Thr47Ala, Ser56Ala and Thr115Ala. Analysis of the dynamic phosphorylation and location of phospho-Bcl-xL(Ser62) in unperturbed, synchronized cells and during DNA damage-induced G 2 arrest discloses that a pool of phospho-Bcl-xL(Ser62) accumulates into nucleolar structures in etoposide-exposed cells during G 2 arrest. In a series of in vitro kinase assays, pharmacological inhibitors and specific siRNAs experiments, we found that Polo kinase 1 and MAPK9/JNK2 are major protein kinases involved in Bcl-xL(Ser62) phosphorylation and accumulation into nucleolar structures during the G 2 checkpoint. In nucleoli, phospho-Bcl-xL(Ser62) binds to and co-localizes with Cdk1(cdc2), the key cyclin-dependent kinase required for entry into mitosis. These data indicate that during G 2 checkpoint, phospho-Bcl-xL(Ser62) stabilizes G 2 arrest by timely trapping of Cdk1(cdc2) in nucleolar structures to slow mitotic entry. It also highlights that DNA damage affects the dynamic composition of the nucleolus, which now emerges as a piece of the DNA damage response.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • CDC2 Protein Kinase / metabolism
  • Cell Cycle Proteins / antagonists & inhibitors
  • Cell Cycle Proteins / genetics
  • Cell Cycle Proteins / metabolism
  • DNA Damage*
  • Etoposide / pharmacology
  • G2 Phase Cell Cycle Checkpoints / drug effects
  • HeLa Cells
  • Humans
  • Mitogen-Activated Protein Kinase 9 / antagonists & inhibitors
  • Mitogen-Activated Protein Kinase 9 / genetics
  • Mitogen-Activated Protein Kinase 9 / metabolism
  • Phosphorylation
  • Protein Binding
  • Protein Serine-Threonine Kinases / antagonists & inhibitors
  • Protein Serine-Threonine Kinases / genetics
  • Protein Serine-Threonine Kinases / metabolism
  • Proto-Oncogene Proteins / antagonists & inhibitors
  • Proto-Oncogene Proteins / genetics
  • Proto-Oncogene Proteins / metabolism
  • RNA Interference
  • RNA, Small Interfering
  • bcl-X Protein / metabolism*


  • Cell Cycle Proteins
  • Proto-Oncogene Proteins
  • RNA, Small Interfering
  • bcl-X Protein
  • Etoposide
  • Mitogen-Activated Protein Kinase 9
  • Protein Serine-Threonine Kinases
  • polo-like kinase 1
  • CDC2 Protein Kinase