Abnormal Cytokinesis after X-Irradiation in Tumor Cells that Override the G2 DNA Damage Checkpoint

Abstract

X-irradiation-induced DNA damage perturbs the G 1 , S, and G 2 phases of the cell cycle. The behavior of cells after they have experienced a DNA damage checkpoint delay is poorly characterized. We therefore examined the fates of irradiated tumor cells that have overcome a prolonged G 2 checkpoint delay. Most irradiated cells progressed through mitosis without significant delay, but failed to complete cytokinesis as they remained tethered to each other at the midbody. We observed that the movement of centrioles at the time of cytokinesis was impaired in the irradiated, bridged cells. We attribute the perturbation of centriole dynamics to the presence of chromatin bridges that spanned the daughter cells. The bridged cells exhibited different fates that included death, fusion that formed multinucleated cells, or another round of mitosis with no noticeable cell cycle delays. The presence of ;H2AX foci in the bridge as well as in the separated nuclei indicated that cells were proliferating despite the presence of DNA damage. It seems that DNA damage checkpoints were not reactivated in cells that overrode a prolonged G 2 delay. Cells deficient in ATM, H2AX, XRCC3, or ligase 4 exhibited a higher frequency of radiation-induced bridges than controls, suggesting that the DNA bridges resulted from inadequate DNA repair. These data show a previously unappreciated cytologic hallmark of DNA damage in dividing cells. Chromatin bridges that interfere with cytokinesis are likely to contribute to the replication failure and clonogenic death of cells exposed to irradiation. [Cancer Res 2008;68(10):3724-32]

Cytokinesis failure occurs in Fanconi anemia pathway–deficient murine and human bone marrow hematopoietic cells

“…Nevertheless, the origin of these DNA bridges is still unclear; they may result from various defects, including persistent DNA double-strand breaks (36). Interestingly, X-irradiation, a common cause of double-strand breaks, has been reported to induce chromatin bridges and trigger binucleation (37). It is therefore tempting to speculate that unrepaired DNA double-strand breaks resulting from collapsed replication forks may be the source of elevated chromatin bridges in FA pathway-deficient cells.…”

The NF90/NF45 Complex Participates in DNA Break Repair via Nonhomologous End Joining

“…Stained cells were mounted in Vectashield (Vector Laboratories) or mounting medium (Sigma). Images were taken with a Zeiss LSM510 (confocal: 40ϫ objective), Zeiss Axiovert 200 M (63ϫ objective), or Nikon Eclipse E800 (10,20, and 65ϫ objective) microscope with the Axio Vision 4.6.3 or NIS elements BR3.0 software program.…”

“…Such failure of proper mitotic progression is associated with disruption of genomic integrity. Multinucleated cells have been observed following DNA damage caused by X-irradiation of HeLa cells (14,20,57) or after depletion of proteins that play a part in chromosome segregation and DNA repair (6,11,13,26,27,57), including DNA-PK (9,11,27,57). Repair of DSBs, essential for the maintenance of genome integrity, can occur through homologous recombination or nonhomologous end joining (NHEJ).…”

Biological Effects Induced by Ultraviolet Radiation in Human Fibroblasts

“…Other authors, however, have found more antioxidant molecules in fibroblasts than in keratinocytes. Yohn et al (1991), using cells from different donors, found increased GSH-Px, SOD and catalase in fibroblasts compared to keratinocytes, and in keratinocytes compared to melanocytes (Huang et al, 2008).…”