Cycling B-CLL cells are highly susceptible to inhibition of the proteasome: involvement of p27, early D-type cyclins, Bax, and caspase-dependent and -independent pathways

Exp Hematol. 2003 Mar;31(3):218-25. doi: 10.1016/s0301-472x(02)01076-7.


Objective: Although peripheral blood B-CLL cells are arrested in G0 phase of the cell cycle, a proliferating pool of cells in proliferation centers might be involved in disease progression. We have previously described an in vitro model of this proliferating pool of cells using B-CLL cells stimulated with immunostimulatory oligonucleotides (CpG-ODN) and interleukin-2. Lactacystin is a specific inhibitor of the proteasome and is a potent apoptosis inductor in resting peripheral B-CLL cells. In the present study, we investigated the effect of proteasome inhibition in proliferating B-CLL cells.

Methods: The effect of proteasome inhibition was analyzed using thymidine incorporation, annexin V assays, and TUNEL staining. Immunoblots were performed to evaluate expression of proteins involved in cell cycle and apoptosis regulation.

Results: Lactacystin blocked cell cycle progression in activated B-CLL cells and inhibited degradation of p27. Upregulation of cyclin D2 and D3 in activated B-CLL cells was inhibited while the expression of cdk2, cdk4, and cyclin E remained unchanged. Activated B-CLL cells were more susceptible to apoptosis induction as compared to resting B-CLL cells. Apoptosis induction was accompanied by cleavage of Bax, procaspase 8, procaspase 9, and procaspase 3. However, a broad-spectrum caspase inhibitor (z-VAD.fmk) only partially inhibited cell death although DNA degradation was completely inhibited.

Conclusion: Proteasome inhibition is highly effective in proliferating B-CLL cells and induces apoptosis using a caspase-dependent and -independent pathway.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Acetylcysteine / analogs & derivatives*
  • Acetylcysteine / pharmacology
  • Apoptosis / drug effects
  • Caspases / drug effects
  • Caspases / metabolism
  • Cell Cycle Proteins / drug effects*
  • Cell Cycle*
  • Cell Division / drug effects
  • Cyclin-Dependent Kinase Inhibitor p27
  • Cyclins / drug effects
  • Cysteine Endopeptidases
  • Cysteine Proteinase Inhibitors / pharmacology*
  • Dose-Response Relationship, Drug
  • Humans
  • Leukemia, Lymphocytic, Chronic, B-Cell / pathology*
  • Multienzyme Complexes / antagonists & inhibitors*
  • Proteasome Endopeptidase Complex
  • Proto-Oncogene Proteins / drug effects
  • Proto-Oncogene Proteins / metabolism
  • Proto-Oncogene Proteins c-bcl-2*
  • Tumor Suppressor Proteins / drug effects
  • bcl-2-Associated X Protein


  • BAX protein, human
  • Cell Cycle Proteins
  • Cyclins
  • Cysteine Proteinase Inhibitors
  • Multienzyme Complexes
  • Proto-Oncogene Proteins
  • Proto-Oncogene Proteins c-bcl-2
  • Tumor Suppressor Proteins
  • bcl-2-Associated X Protein
  • lactacystin
  • Cyclin-Dependent Kinase Inhibitor p27
  • Caspases
  • Cysteine Endopeptidases
  • Proteasome Endopeptidase Complex
  • Acetylcysteine