ABSTRACT
There is clear evidence that ionizing radiation (IR) causes leukemia. For many types of leukemia, the preleukemic fusion genes (PFG), as consequences of DNA damage and chromosomal translocations, occur in hematopoietic stem and progenitor cells (HSPC) in utero and could be detected in umbilical cord blood (UCB) of newborns. However, relatively limited information is available about radiation-induced apoptosis, DNA damage and PFG formation in human HSPC. In this study we revealed that CD34+ HSPC compared to lymphocytes: (i) are extremely radio-resistant showing delayed time kinetics of apoptosis, (ii) accumulate lower level of endogenous DNA damage/early apoptotic γH2AX pan-stained cells, (iii) have higher level of radiation-induced 53BP1 and γH2AX/53BP1 co-localized DNA double stranded breaks, and (iv) after low dose of IR may form very low level of BCR-ABL PFG. Within CD34+ HSPC we identified CD34+CD38+ progenitor cells as a highly apoptosis-resistant population, while CD34+CD38- hematopoietic stem/multipotent progenitor cells (HSC/MPP) as a population very sensitive to radiation-induced apoptosis. Our study provides critical insights into how human HSPC respond to IR in the context of DNA damage, apoptosis and PFG.
Subject(s)
DNA Breaks, Double-Stranded/radiation effects , Fetal Blood/radiation effects , Gene Fusion/radiation effects , Hematopoietic Stem Cells/radiation effects , Leukemia/genetics , Antigens, CD34/metabolism , Apoptosis/radiation effects , DNA Repair/genetics , Fusion Proteins, bcr-abl/genetics , Fusion Proteins, bcr-abl/radiation effects , Gene Fusion/genetics , Histones/genetics , Histones/metabolism , Humans , Infant, Newborn , Lymphocytes/radiation effects , Preleukemia/genetics , Radiation, Ionizing , Tumor Suppressor p53-Binding Protein 1/genetics , Tumor Suppressor p53-Binding Protein 1/metabolismABSTRACT
OBJECTIVE: To investigate the material foundation of the fusion of bcr and abl genes, and to explore the pathogenesis of chronic myeloid leukemia. METHODS: By FISH combined with laser confocal scanning microscopy, the three-dimension (3D) distribution of bcr and abl genes in the interphase nuclei of normal and irradiated IM-9 cells was studied in each cell cycle phases. RESULTS: abl and bcr genes distributed non-randomly in the interphase nuclei of IM-9 cells. abl gene preferably located at the outer layer and bcr near the core of the nucleus. The two genes were drawn near each other most in G(0) phase. The relative distance between the homologous genes was greater at proliferation phase than at quiescence phase. After irradiation, the relative distances from the two genes to the core and between the two genes were shortened, with the shortest distance between the two genes in S phase. CONCLUSION: Irradiation could change the 3D-distribution of abl and bcr genes in the interphase nuclei of IM-9 cell and accelerate them to draw near each other.
Subject(s)
Cell Nucleus/radiation effects , Fusion Proteins, bcr-abl/radiation effects , Genes, abl/radiation effects , Proto-Oncogene Proteins c-bcr/radiation effects , Cell Nucleus/genetics , Cell Nucleus/ultrastructure , Cells, Cultured , Female , Fusion Proteins, bcr-abl/genetics , Gene Fusion/radiation effects , Genes, abl/genetics , Humans , In Situ Hybridization, Fluorescence , Interphase/genetics , Interphase/radiation effects , Lymphocytes/ultrastructure , Microscopy, Confocal , Proto-Oncogene Proteins c-bcr/geneticsABSTRACT
The results of molecular investigations of blood mononuclears from 120 clean-up workers after 7-9 years of Chernobyl accident with the total exposure radiation doses ranging from 5 to 76 cGr are presented. Structural polymorphism of the leukemia associated bcr and ribosomal RNA (rRNA) genes were studied using Southern blot hybridization. Allelic polymorphism of bcr gene with characteristic for leukemia allele distribution was detected in 16.6%. Rearrangements of rRNA genes were observed in 13% of Chernobyl accident clean-up workers.
Subject(s)
Genome, Human , Leukocytes, Mononuclear/radiation effects , Power Plants , Radioactive Hazard Release , Alleles , DNA/blood , DNA/radiation effects , Dose-Response Relationship, Radiation , Fusion Proteins, bcr-abl/genetics , Fusion Proteins, bcr-abl/radiation effects , Humans , Leukemia, Myelogenous, Chronic, BCR-ABL Positive/genetics , Leukocytes, Mononuclear/ultrastructure , Microscopy, Electron , Polymorphism, Genetic/radiation effects , RNA, Ribosomal/genetics , RNA, Ribosomal/radiation effects , Time Factors , UkraineABSTRACT
Philadelphia chromosome (Ph)-positive leukaemia cells express the chimeric bcr/abl oncoprotein, whose deregulated protein tyrosine kinase (PTK) activity antagonizes the induction of apoptosis by DNA damaging agents. Treatment of Ph-positive K562, TOM 1 and KCL-22 cells with etoposide for 2d induced cytosolic vacuolation, but not nuclear condensation or DNA fragmentation. The bcr/abl kinase-selective inhibitor herbimycin A increased the induction of nuclear apoptosis by etoposide or gamma-radiation. The concentration of herbimycin required to synergize with etoposide was similar to that required to decrease the level of tyrosine phosphorylated proteins or of the protein tyrosine kinase activity of anti-abl immune complexes in K562 cells. The ability of herbimycin A to sensitize K562, TOM 1 or KCL-22 cells to apoptosis induction correlated with its ability to decrease the cellular content of phosphotyrosyl proteins in these Philadelphia-positive lines. Enhancement of nuclear apoptosis by herbimycin was not attributable to downregulation of the bcl-2 or bcl-XL anti-apoptotic proteins. In contrast, herbimycin protected Philadelphia-negative HL60 cells from apoptosis induction by etoposide and did not affect killing of NC37 and CEM cells. The data suggest that the induction of apoptosis is blocked in cells expressing the bcr/abl oncoprotein and that herbimycin A increases induction of programmed cell death following DNA damage. Selective PTK inhibitors may therefore be of value in securing the genetic death of Ph-positive leukaemia cells.
