Growth inhibition by CDK-cyclin and PCNA binding domains of p21 occurs by distinct mechanisms and is regulated by ubiquitin-proteasome pathway

Oncogene. 1999 Jul 29;18(30):4313-25. doi: 10.1038/sj.onc.1202686.


The CDK inhibitor, p21WAF1/Cip1 blocks cell cycle progression. In vitro, the N-terminus of p21 binds and inhibits CDK-cyclin kinase activity, whereas the C-terminus binds and inhibits PCNA (proliferating cell nuclear antigen) function. PCNA is essential for processivity of both DNA polymerase delta and epsilon. We have performed a detailed analysis of growth inhibition by the N- and C-terminal regions of p21, and determined whether the N- and C-terminal regions mediate this effect by different mechanisms. Expression of either the N- or the C-terminal region of p21 inhibits DNA synthesis and cell growth, but not as efficiently as full length p21. The effectiveness of the two p21 domains is dependent on their stability which is determined by the ubiquitin-proteasome pathway. The stabilization of the N- and C-terminal region of p21 increases their effectiveness as inhibitors of DNA synthesis to levels comparable to full length p21. Inhibition of DNA synthesis by the N-terminal region of p21 involves suppression of E2F activity. In contrast, inhibition by the C-terminal region of p21 is not accompanied by suppression of E2F activity, but is mediated via PCNA binding. The C-terminal region of p21 therefore inhibits cell growth by a mechanism distinct from that of the N-terminal region containing the CDK-cyclin inhibitory domain.

Publication types

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

MeSH terms

  • 3T3 Cells
  • Acetylcysteine / analogs & derivatives
  • Acetylcysteine / pharmacology
  • Animals
  • CDC2-CDC28 Kinases*
  • Cyclin-Dependent Kinase 2
  • Cyclin-Dependent Kinase Inhibitor p21
  • Cyclin-Dependent Kinases / immunology
  • Cyclin-Dependent Kinases / metabolism*
  • Cyclins / genetics*
  • Cyclins / immunology
  • Cyclins / metabolism
  • Cycloheximide / pharmacology
  • Cysteine Endopeptidases / metabolism
  • Cysteine Proteinase Inhibitors / pharmacology
  • Gene Deletion
  • Gene Expression Regulation, Neoplastic
  • Growth Inhibitors*
  • Hemagglutinins / immunology
  • Humans
  • Leupeptins / pharmacology
  • Mice
  • Models, Genetic
  • Multienzyme Complexes / metabolism
  • Mutagenesis
  • Osteosarcoma / metabolism
  • Proliferating Cell Nuclear Antigen / metabolism*
  • Proteasome Endopeptidase Complex
  • Protein Synthesis Inhibitors / pharmacology
  • Protein-Serine-Threonine Kinases / immunology
  • Time Factors
  • Transfection
  • Tumor Cells, Cultured
  • Ubiquitins / metabolism*


  • CDKN1A protein, human
  • Cdkn1a protein, mouse
  • Cyclin-Dependent Kinase Inhibitor p21
  • Cyclins
  • Cysteine Proteinase Inhibitors
  • Growth Inhibitors
  • Hemagglutinins
  • Leupeptins
  • Multienzyme Complexes
  • Proliferating Cell Nuclear Antigen
  • Protein Synthesis Inhibitors
  • Ubiquitins
  • acetylleucyl-leucyl-norleucinal
  • lactacystin
  • Cycloheximide
  • Protein-Serine-Threonine Kinases
  • CDC2-CDC28 Kinases
  • CDK2 protein, human
  • Cdk2 protein, mouse
  • Cyclin-Dependent Kinase 2
  • Cyclin-Dependent Kinases
  • Cysteine Endopeptidases
  • Proteasome Endopeptidase Complex
  • Acetylcysteine