Cell cycle disturbances and mitotic catastrophes in HeLa Hep2 cells following 2.5 to 10 Gy of ionizing radiation.
OBJECTIVE
Experimental radioimmunotherapy delivering absorbed doses of 2.5 to 10 Gy has been shown to cause growth retardation of tumors. The purpose of this study was to elucidate the sequential molecular and cellular events occurring in HeLa Hep2 cells exposed to such doses.


METHODS
Dose-response curves, activation of cell cycle checkpoints, and mitotic behavior were investigated in HeLa Hep2 cells following 2.5- to 10-Gy irradiation by carrying out 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assays, Western blots, fluorescence-activated cell sorting analysis, and immunofluorescence stainings. Terminal deoxyribonucleotidyl transferase-mediated dUTP nick end labeling staining was used to detect apoptosis.


RESULTS
A G2-M arrest was shown by fluorescence-activated cell sorting analysis. p53 and p21 were found to be up-regulated but were not immediately related to the arrest. The G2-M arrest was transient and the cells reentered the cell cycle still containing unrepaired cellular damage. This premature entry caused an increase of anaphase bridges, lagging chromosomal material, and multipolar mitotic spindles as visualized by propidium iodide staining and immunofluorescence staining with alpha-tubulin and gamma-tubulin antibodies. Furthermore, a dose-dependent significant increase in centrosome numbers from 12.6+/-6.6% to 67+/-5.3% was identified as well as a dose-dependent increase of polyploid cells from 2.8+/-1.3% to 17.6+/-2.1% with the highest absorbed dose of 10 Gy. These disturbances caused the cells to progress into mitotic catastrophe and a fraction of these dying cells showed apoptotic features as displayed by terminal deoxyribonucleotidyl transferase-mediated dUTP nick end labeling staining 5 to 7 days after irradiation.


CONCLUSIONS
An absorbed dose of 2.5 to 10 Gy was shown to force HeLa Hep2 cells into mitotic catastrophe and delayed apoptosis. These might be important cell death mechanisms involved in tumor growth retardation following radioimmunotherapy of solid tumors.
Eriksson
David
D
Department of Immunology, Umeå university, Umeå, Sweden.
Löfroth
Per-Olov
PO
Johansson
Lennart
L
Riklund
Katrine Ahlström
KA
Stigbrand
Torgny
T
D017209:Apoptosis / Q000528:radiation effects; D015153:Blotting, Western; D002455:Cell Division / Q000502:physiology / Q000528:radiation effects*; D003037:Cobalt Radioisotopes; D050759:Cyclin-Dependent Kinase Inhibitor p21 / Q000378:metabolism; D004307:Dose-Response Relationship, Radiation; D005434:Flow Cytometry; D016195:G2 Phase / Q000502:physiology / Q000528:radiation effects*; D005720:Gamma Rays; D006367:HeLa Cells / Q000528:radiation effects; D006801:Humans; D020287:In Situ Nick-End Labeling; D008938:Mitosis / Q000528:radiation effects*; D016159:Tumor Suppressor Protein p53 / Q000378:metabolism
C493956:CDKN1A protein, human; D003037:Cobalt Radioisotopes; D050759:Cyclin-Dependent Kinase Inhibitor p21; D016159:Tumor Suppressor Protein p53