p53 Activation in Chronic Radiation-Treated Breast Cancer Cells

Regulation of MDM2/p14ARF

Liqun Xia, Aimee Paik, Jian-Jian Li

Research output: Contribution to journalArticle

26 Citations (Scopus)

Abstract

Mammalian cells chronically exposed to ionizing radiation (IR) induce stress response with a tolerance to the subsequent cytotoxicity of IR. Although p53 is well documented in IR response, the signaling network causing p53 activation in chronic IR remains to be identified. Using breast carcinoma MCF+FIR cells that showed a transient radioresistance after exposure chronically to fractionated IR (FIR), the present study shows that the basal DNA binding and transcriptional activity of p53 was elevated by FIR. p53-controlled luciferase activity was strikingly induced (∼7.9-fold) with little enhancement of p53/DNA binding activity (∼1.3-fold). The phosphorylated p53 (Thr 55) was increased in the cytoplasm and nucleus of MCF+FIR but not in the sham-FIR control cells. On the contrary, the sham-FIR control MCF-7 cells showed a low p53 luciferase transcription (∼3-fold) but a striking enhancement of p53/DNA binding (12-fold) after 5 Gy of IR. To determine the signaling elements regulating p53 activity, DNA microarray of MCF+FIR using sham-FIR MCF-7 cells as a reference demonstrated that the mRNA of p21, MDM2, and p14ARF was up-regulated. Time course Western blot analysis, however, showed no difference in p21 induction. In contrast, MDM2 that was absent in control cells and was predominantly induced by IR was not induced in MCF+FIR cells. In agreement with MDM2 inhibition, MDM2-inhibitory protein p14ARF was increased in MCF+FIR cells. In summary, these results demonstrate that up-regulation of p14ARF paralleled with MDM2 inhibition contributes to p53 accumulation in the nucleus and causes a high responsiveness of p53 in chronic IR-treated breast cancer cells.

Original languageEnglish (US)
Pages (from-to)221-228
Number of pages8
JournalCancer Research
Volume64
Issue number1
DOIs
StatePublished - Jan 1 2004
Externally publishedYes

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Tumor Suppressor Protein p14ARF
Ionizing Radiation
Radiation
Breast Neoplasms
MCF-7 Cells
Luciferases
DNA
Radiation Dosage
Oligonucleotide Array Sequence Analysis
Cytoplasm
Up-Regulation
Western Blotting
Messenger RNA

ASJC Scopus subject areas

  • Cancer Research
  • Oncology

Cite this

p53 Activation in Chronic Radiation-Treated Breast Cancer Cells : Regulation of MDM2/p14ARF. / Xia, Liqun; Paik, Aimee; Li, Jian-Jian.

In: Cancer Research, Vol. 64, No. 1, 01.01.2004, p. 221-228.

Research output: Contribution to journalArticle

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abstract = "Mammalian cells chronically exposed to ionizing radiation (IR) induce stress response with a tolerance to the subsequent cytotoxicity of IR. Although p53 is well documented in IR response, the signaling network causing p53 activation in chronic IR remains to be identified. Using breast carcinoma MCF+FIR cells that showed a transient radioresistance after exposure chronically to fractionated IR (FIR), the present study shows that the basal DNA binding and transcriptional activity of p53 was elevated by FIR. p53-controlled luciferase activity was strikingly induced (∼7.9-fold) with little enhancement of p53/DNA binding activity (∼1.3-fold). The phosphorylated p53 (Thr 55) was increased in the cytoplasm and nucleus of MCF+FIR but not in the sham-FIR control cells. On the contrary, the sham-FIR control MCF-7 cells showed a low p53 luciferase transcription (∼3-fold) but a striking enhancement of p53/DNA binding (12-fold) after 5 Gy of IR. To determine the signaling elements regulating p53 activity, DNA microarray of MCF+FIR using sham-FIR MCF-7 cells as a reference demonstrated that the mRNA of p21, MDM2, and p14ARF was up-regulated. Time course Western blot analysis, however, showed no difference in p21 induction. In contrast, MDM2 that was absent in control cells and was predominantly induced by IR was not induced in MCF+FIR cells. In agreement with MDM2 inhibition, MDM2-inhibitory protein p14ARF was increased in MCF+FIR cells. In summary, these results demonstrate that up-regulation of p14ARF paralleled with MDM2 inhibition contributes to p53 accumulation in the nucleus and causes a high responsiveness of p53 in chronic IR-treated breast cancer cells.",
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