The importance of abrogation of G2-phase arrest in combined effect of TRAIL and ionizing radiation.
BACKGROUND
In this work we studied the relationship between the enhanced expression of DR5 receptor and the effect of combination of TRAIL and ionizing radiation on cell cycle arrest and apoptosis induction in human leukemia cell line HL-60.


METHODS
DR5, APO2.7 and cell cycle were analyzed by flow cytometry. Proteins Bid and Mcl-1 were analyzed by Western-blotting. For clonogenic survival, colony assay on methylcellulose was used.


RESULTS
Ionizing radiation caused significantly enhanced positivity of DR5 receptors 24 h after irradiation with high doses (6 and 8 Gy). An increase of DR5 receptor positivity after a dose of 2 Gy was not statistically significant and application of TRAIL 48 h after irradiation did not increase the apoptosis induction. However, a decrease of radiation-induced G(2) phase arrest and an increase of apoptosis were observed when TRAIL was applied 16 h before irradiation with the dose of 2 Gy. Incubation with 6 microg/l TRAIL for 16 h reduced D(0) value from 2.9 Gy to 1.5 Gy. The induction of apoptosis by TRAIL was accompanied by Bid cleavage and a decrease of antiapoptotic Mcl-1 16 h after incubation with TRAIL.


CONCLUSIONS
TRAIL in concentration of 6 microg/l applied 16 h before irradiation by the dose of 1.5 Gy caused the death of 63% of clonogenic tumor cells, similarly as the dose of 2.9 Gy alone, which is in good correlation with the enhanced apoptosis induction.
Rezácová
Martina
M
Institute of Medical Biochemistry, Faculty of Medicine Hradec Králové, Charles University Prague, Hradec Králové, Czech Republic. rezacovam@lfhk.cuni.cz
Vávrová
Jirina
J
Vokurková
Doris
D
Tichý
Ales
A
Knízek
Jirí
J
Psutka
Jan
J
D051017:Apoptosis Regulatory Proteins / Q000494:pharmacology*; D002453:Cell Cycle / Q000187:drug effects / Q000528:radiation effects; D004307:Dose-Response Relationship, Radiation; D016195:G2 Phase / Q000187:drug effects / Q000502:physiology* / Q000528:radiation effects*; D005720:Gamma Rays; D018922:HL-60 Cells; D006801:Humans; D008562:Membrane Glycoproteins / Q000494:pharmacology*; D053220:Receptors, TNF-Related Apoptosis-Inducing Ligand; D018124:Receptors, Tumor Necrosis Factor / Q000502:physiology / Q000528:radiation effects; D053221:TNF-Related Apoptosis-Inducing Ligand; D014409:Tumor Necrosis Factor-alpha / Q000494:pharmacology*
D051017:Apoptosis Regulatory Proteins; D008562:Membrane Glycoproteins; D053220:Receptors, TNF-Related Apoptosis-Inducing Ligand; D018124:Receptors, Tumor Necrosis Factor; D053221:TNF-Related Apoptosis-Inducing Ligand; C505639:TNFRSF10B protein, human; C505653:TNFSF10 protein, human; D014409:Tumor Necrosis Factor-alpha