Differences in mutant p53 protein stability and functional activity in teniposide-sensitive and -resistant human leukemic CEM cells

Oncogene. 2000 Oct 12;19(43):5010-9. doi: 10.1038/sj.onc.1203865.


We examined p53 protein stability and DNA damage-induced p53-dependent responses in a human leukemic CEM cell line and two teniposide-resistant sublines, CEM/VM-1 and CEM/VM-1-5 ( approximately 40 and 400-fold resistant to teniposide, respectively). Although all cell lines contain the same p53 mutations at codons 175 (Arg-->His) and 248 (Arg-->Gln), the constitutive levels of p53 were progressively increased with the resistance of the cells to teniposide. By pulse-chase experiments, we found that the half-lives of mutant p53 protein were approximately 12, 17, and >30 h in CEM, CEM/VM-1, and CEM/VM-1-5 cells, respectively. The prolonged half-lives of p53 in these cells is consistent with the fact that the protein harbors the indicated mutations. Of note, however, is the fact that the increased p53 protein half-lives in the two drug-resistant cell lines corresponds to a proportional decrease in MDM2 protein levels but an increase in p53-MDM2 binding interactions. This suggests that MDM2-mediated p53 degradation may be altered in our leukemic cell lines. The DNA damage-induced p53 response is fully functional in the drug-sensitive CEM cells containing a mutant p53, but this pathway is attenuated in the drug-resistant cells. Specifically, while the mutant p53 was phosphorylated at serine-15 in response to ionizing radiation in all these cell lines, mutant p53 induction in response to teniposide or ionizing radiation and induction of the p53-target genes, p21 and GADD45 only occurred in the drug-sensitive CEM cells. As assessed by MTT cytotoxicity assay, CEM cells were also significantly more sensitive to ionizing radiation, compared to the drug-resistant cell lines, and this correlated with p53 induction. Collectively, these results suggest that changes in constitutive mutant p53 protein levels, p53-MDM2 binding interactions, and altered regulation of the DNA damage-inducible p53-dependent pathway may play a role in drug- and radiation-responsiveness in these cells.

Publication types

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

MeSH terms

  • Antineoplastic Agents / pharmacology*
  • Cyclin-Dependent Kinase Inhibitor p21
  • Cyclins / biosynthesis
  • Cyclins / genetics
  • DNA Damage / genetics*
  • DNA, Neoplasm / drug effects
  • DNA, Neoplasm / metabolism
  • Drug Resistance, Neoplasm
  • Humans
  • Intracellular Signaling Peptides and Proteins
  • Leukemia / drug therapy
  • Leukemia / genetics
  • Leukemia / metabolism
  • Nuclear Proteins*
  • Nucleic Acid Synthesis Inhibitors / pharmacology
  • Phosphorylation / radiation effects
  • Protein Binding
  • Protein Biosynthesis
  • Proteins / genetics
  • Proto-Oncogene Proteins / biosynthesis
  • Proto-Oncogene Proteins / genetics
  • Proto-Oncogene Proteins / metabolism
  • Proto-Oncogene Proteins c-bcl-2 / biosynthesis
  • Proto-Oncogene Proteins c-bcl-2 / genetics
  • Proto-Oncogene Proteins c-mdm2
  • Teniposide / pharmacology*
  • Transcriptional Activation / drug effects
  • Tumor Cells, Cultured / drug effects
  • Tumor Cells, Cultured / radiation effects
  • Tumor Suppressor Protein p53 / biosynthesis
  • Tumor Suppressor Protein p53 / genetics
  • Tumor Suppressor Protein p53 / physiology*
  • bcl-2-Associated X Protein


  • Antineoplastic Agents
  • CDKN1A protein, human
  • Cyclin-Dependent Kinase Inhibitor p21
  • Cyclins
  • DNA, Neoplasm
  • GADD45 protein
  • Intracellular Signaling Peptides and Proteins
  • Nuclear Proteins
  • Nucleic Acid Synthesis Inhibitors
  • Proteins
  • Proto-Oncogene Proteins
  • Proto-Oncogene Proteins c-bcl-2
  • Tumor Suppressor Protein p53
  • bcl-2-Associated X Protein
  • Teniposide
  • MDM2 protein, human
  • Proto-Oncogene Proteins c-mdm2