Dynamic Bcl-xL (S49) and (S62) Phosphorylation/Dephosphorylation during Mitosis Prevents Chromosome Instability and Aneuploidy in Normal Human Diploid Fibroblasts

PLoS One. 2016 Jul 11;11(7):e0159091. doi: 10.1371/journal.pone.0159091. eCollection 2016.


Bcl-xL proteins undergo dynamic phosphorylation/dephosphorylation on Ser49 and Ser62 residues during mitosis. The expression of Bcl-xL(S49A), (S62A) and dual (S49/62A) phosphorylation mutants in tumor cells lead to severe mitotic defects associated with multipolar spindle, chromosome lagging and bridging, and micro-, bi- and multi-nucleated cells. Because the above observations were made in tumor cells which already display genomic instability, we now address the question: will similar effects occur in normal human diploid cells? We studied normal human diploid BJ foreskin fibroblast cells expressing Bcl-xL (wild type), (S49A), (S49D), (S62A), (S62D) and the dual-site (S49/62A) and (S49/62D) mutants. Cells expressing S49 and/or S62 phosphorylation mutants showed reduced kinetics of cell population doubling. These effects on cell population doubling kinetics correlated with early outbreak of senescence with no impact on the cell death rate. Senescent cells displayed typical senescence-associated phenotypes including high-level of senescence-associated β-galactosidase activity, interleukin-6 (IL-6) secretion, tumor suppressor p53 and cyclin-dependent kinase inhibitor p21Waf1/Cip1 activation as well as γH2A.X-associated nuclear chromatin foci. Fluorescence in situ hybridization analysis and Giemsa-banded karyotypes revealed that the expression of Bcl-xL phosphorylation mutants in normal diploid BJ cells provoked chromosome instability and aneuploidy. These findings suggest that dynamic Bcl-xL(S49) and (S62) phosphorylation/dephosphorylation cycles are important in the maintenance of chromosome integrity during mitosis in normal cells. They could impact future strategies aiming to develop and identify compounds that could target not only the anti-apoptotic domain of Bcl-xL protein, but also its mitotic domain for cancer therapy.

MeSH terms

  • Aneuploidy*
  • Cell Line
  • Chromosomal Instability*
  • Diploidy*
  • Fibroblasts / cytology
  • Fibroblasts / metabolism*
  • Gene Expression Regulation
  • Humans
  • Mitosis*
  • Mutation*
  • Phosphorylation
  • bcl-X Protein / genetics
  • bcl-X Protein / metabolism*


  • bcl-X Protein

Grants and funding

This work was funded by Grant MOP-97913 from the Canadian Institutes of Health Research and Grant 328207 from the Natural Sciences and Engineering Research Council of Canada to RB, and a grant from the Cancer Research Network of Fonds de recherche du Québec- Santé to JH. PSB received scholarships from the Faculté des études supérieures (Université de Montréal, Canada) and the Fondation de l'Institut du cancer de Montréal (Canada).