p53 binding to target sites is dynamically regulated before and after ionizing radiation-mediated DNA damage.
Although radiation therapy has been an important modality for cancer treatment, the molecular mechanisms underlying the overall genomic response of mammalian cells to radiation are not well characterized. The success of radiation therapy using ionizing radiation relies upon the regulation of both the cell cycle and apoptosis, as conferred by the activation of DNA damage-responsive genes. To better understand the key players involved in this response, expression-profiling experiments were performed using custom-made cDNA microarrays. In MOLT-4 lymphoma tumor cells, the induction of target gene products following irradiation supports a major role for p53 as a transcriptional activator, but also invokes questions regarding conditional transcription regulation following irradiation. Using chromatin immunoprecipitation (ChIP), p53 binding to chromatin was examined following irradiation using primers that are specific for p53 binding sites in target genes. PCR analysis indicates dynamic target gene binding. Thus, at 8 hours following radiation treatment, the p21 and puma promoter sites were characterized by relative increases in chromatin precipitation, while the bax promoter site was not. Because the binding of p53 to these sites only changed modestly following radiation, other studies were conducted to characterize the presence of constitutive binding to putative p53 DNA binding sites in several other genes.
Department of Cancer Biology, Lerner Research Institute, The Cleveland Clinic Foundation, Cleveland, Ohio 44195, USA.
Meredith E
ME
Crosby
Marcela
M
Oancea
Alex
A
Almasan
D051017:Apoptosis Regulatory Proteins; D001665:Binding Sites / Q000235:genetics; D045744:Cell Line, Tumor; D002843:Chromatin / Q000378:metabolism*; D004249:DNA Damage; D017931:DNA Primers; D016373:DNA, Antisense / Q000737:chemistry; D004273:DNA, Neoplasm / Q000378:metabolism* / Q000528:radiation effects; D005786:Gene Expression Regulation / Q000528:radiation effects; D006801:Humans; D015458:Leukemia, T-Cell / Q000235:genetics / Q000378:metabolism*; D020411:Oligonucleotide Array Sequence Analysis; D016133:Polymerase Chain Reaction; D011518:Proto-Oncogene Proteins / Q000378:metabolism / Q000528:radiation effects; D011839:Radiation, Ionizing; D016159:Tumor Suppressor Protein p53 / Q000378:metabolism* / Q000528:radiation effects
D051017:Apoptosis Regulatory Proteins; C438378:BBC3 protein, human; D002843:Chromatin; D017931:DNA Primers; D016373:DNA, Antisense; D004273:DNA, Neoplasm; D011518:Proto-Oncogene Proteins; D016159:Tumor Suppressor Protein p53