Regulation of rheumatoid synoviocyte proliferation by endogenous p53 induction

Clin Exp Immunol. 2001 Nov;126(2):334-8. doi: 10.1046/j.1365-2249.2001.01677.x.


The p53 tumour suppressor protein protects cells from tumorigenic alterations by inducing either cell growth arrest or apoptosis. In the present study, we investigated the role of endogenous p53 expressed in rheumatoid arthritis synovial fibroblasts which show transformed-appearing phenotypes. Type B synovial cells (fibroblast-like synovial cells) were exposed to a proteasome inhibitor, carbobenzoxyl-leucinyl-leucinyl-leucinal (MG-132). During this process, the expressions of p53 and p21 were examined by Western blot. Cell cycle analysis of the synovial cells was determined by DNA staining using propidium iodide (PI). Inhibition of proteasome resulted in the accumulation of p53 which was followed by an increase in the amount of a cyclin-dependent kinase (CDK)-inhibitor, p21. As a consequence, the retinoblastoma gene product, Rb, remained in the hypophosphorylated state, thus preventing PDGF-stimulated synovial cells from progressing into S-phase. This study shows that endogenous p53, which is inducible in rheumatoid synovial cells, is functionally active based on the findings that its expression blocks the G1/S transition by inhibiting the CDK-mediated phosphorylation of Rb via p21 induction. Thus the induction of p53 using proteasome inhibitor may provide a new approach in the treatment of RA.

MeSH terms

  • Arthritis, Rheumatoid / pathology*
  • Arthritis, Rheumatoid / physiopathology*
  • Cell Cycle / drug effects
  • Cell Cycle / physiology
  • Cell Division / drug effects
  • Cell Division / physiology
  • Cells, Cultured
  • Cyclin-Dependent Kinase Inhibitor p21
  • Cyclins / biosynthesis
  • Cysteine Endopeptidases / metabolism
  • Cysteine Proteinase Inhibitors / pharmacology
  • Humans
  • Leupeptins / pharmacology
  • Multienzyme Complexes / antagonists & inhibitors
  • Multienzyme Complexes / metabolism
  • Phosphorylation
  • Platelet-Derived Growth Factor / pharmacology
  • Proteasome Endopeptidase Complex
  • Retinoblastoma Protein / metabolism
  • Synovial Membrane / pathology*
  • Tumor Suppressor Protein p53 / biosynthesis*
  • Tumor Suppressor Protein p53 / physiology


  • CDKN1A protein, human
  • Cyclin-Dependent Kinase Inhibitor p21
  • Cyclins
  • Cysteine Proteinase Inhibitors
  • Leupeptins
  • Multienzyme Complexes
  • Platelet-Derived Growth Factor
  • Retinoblastoma Protein
  • Tumor Suppressor Protein p53
  • Cysteine Endopeptidases
  • Proteasome Endopeptidase Complex
  • benzyloxycarbonylleucyl-leucyl-leucine aldehyde