DNA-dependent protein kinase inhibitor (OK-1035) suppresses p21 expression in HCT116 cells containing wild-type p53 induced by adriamycin

Biochem Biophys Res Commun. 1996 Apr 16;221(2):207-12. doi: 10.1006/bbrc.1996.0575.


The tumor growth suppressor p21 has been shown to be induced by wild-type p53 (wt-p53) and to be a potent inhibitor of cyclin-dependent kinases and PCNA/DNA polymerase delta. Although wt-p53 is reported to be phosphorylated by several protein kinases, the function and significance of the phosphorylation of wt-p53 are not yet fully understood. Using OK-1035, a selective inhibitor of DNA-dependent protein kinase (DNA-PK), we demonstrated the importance of the phosphorylation of wt-p53 by DNA-PK in the DNA damage-mediated expression of the p21 gene. Treatment of HCT116, a human colon carcinoma cell line, with adriamycin induced the expression of wt-p53 and p21. By addition of OK-1035 to this culture, the induction of p21 protein was significantly decreased in a dose-dependent manner, whereas wt-p53 induction was not affected. Northern blot analysis revealed that suppression of p21 protein expression by OK-1035 resulted from reduction in the level of p21 mRNA. OK-1035 did not directly affect the binding ability of wt-p53 to its consensus DNA sequence. Our observations support the idea that wt-p53 induces the transcriptional activation of the p21 gene only after it is phosphorylated by DNA-PK.

MeSH terms

  • Amino Acid Sequence
  • Base Sequence
  • Consensus Sequence
  • DNA / drug effects
  • DNA Damage
  • DNA-Activated Protein Kinase
  • DNA-Binding Proteins*
  • Doxorubicin / pharmacology*
  • Gene Expression Regulation / drug effects*
  • Humans
  • Hydrazones / pharmacology*
  • Molecular Sequence Data
  • Nuclear Proteins
  • Oncogene Protein p21(ras) / genetics*
  • Promoter Regions, Genetic
  • Protein-Serine-Threonine Kinases / antagonists & inhibitors*
  • Pyridones / pharmacology*
  • Tumor Cells, Cultured
  • Tumor Suppressor Protein p53 / genetics*


  • 3-cyano-5-(4-pyridyl)-6-hydrazonomethyl-2-pyridone
  • DNA-Binding Proteins
  • Hydrazones
  • Nuclear Proteins
  • Pyridones
  • Tumor Suppressor Protein p53
  • Doxorubicin
  • DNA
  • DNA-Activated Protein Kinase
  • PRKDC protein, human
  • Protein-Serine-Threonine Kinases
  • Oncogene Protein p21(ras)