DNA Lesions Induced by Replication Stress Trigger Mitotic Aberration and Tetraploidy Development

Abstract

During tumorigenesis, cells acquire immortality in association with the development of genomic instability. However, it is still elusive how genomic instability spontaneously generates during the process of tumorigenesis. Here, we show that precancerous DNA lesions induced by oncogene acceleration, which induce situations identical to the initial stages of cancer development, trigger tetraploidy/aneuploidy generation in association with mitotic aberration. Although oncogene acceleration primarily induces DNA replication stress and the resulting lesions in the S phase, these lesions are carried over into the M phase and cause cytokinesis failure and genomic instability. Unlike directly induced DNA double-strand breaks, DNA replication stress-associated lesions are cryptogenic and pass through cell-cycle checkpoints due to limited and ineffective activation of checkpoint factors. Furthermore, since damaged M-phase cells still progress in mitotic steps, these cells result in chromosomal mis-segregation, cytokinesis failure and the resulting tetraploidy generation. Thus, our results reveal a process of genomic instability generation triggered by precancerous DNA replication stress.

The Arf/p53 Protein Module, Which Induces Apoptosis, Down-regulates Histone H2AX to Allow Normal Cells to Survive in the Presence of Anti-cancer Drugs

“…Unlike Immortalized Cells, Normal Cells Survive in the Presence of CPT by Down-regulating H2AX-MEFs become immortal because of genomic instability (19) and mutations in the Arf/p53 protein module (either Arf or p53) (21), processes similar to those that occur during cancer development (22). Therefore, to test our hypothesis that cellular transformation results in changes in drug sensitivity, we examined the response of MEFs to CPT both before and after immortalization.…”

“…Although it is still unclear how the downregulation of H2AX is controlled by the Arf/p53 protein mod- ule (30), the process only occurs in normal cells under the regulation of both Arf and p53 (14), which prevents transformation (19,31). The results of this study show that normal cells down-regulate H2AX and enter a quiescent state in response to CPT, which is identical to the growth arrest observed when cells proliferate normally and clearly differently from CPT-resistant BT474 cancer cells (see supplemental Fig.…”

“…H2AX overexpression experiments were performed as described previously (17,18). FACS analysis and double thymidine block were performed as described previously (19). The SA ␤-galactosidase assay was performed as described previously (14).…”

DNA damage and breast cancer

“…During this time chromosomal abnormalities can accumulate in the DNA synthesis phase of the cell cycle (S phase) and carry over to mitosis (M phase). The result can trigger tetraploidy, aneuploidy or chromosomal breakage at fragile sites on chromosomes [31] . The DNA replication stress model suggests that genomic instability is activated by hyper-proliferation induced by "oncogenes" or genes which when over-expressed induce high levels of proliferation [32] .…”

“…Spontaneous recombination in response to DNA damage occurs due to lesions that do not block the replication fork, but instead leave potential recombinogenic substrates such as single-stranded gaps in DNA sequences [28,29,51,52] . Double strand breaks are caused by environmental carcinogen exposure (such as exposure to certain benzene-derived products) [54][55][56] and replication stress [31,32] . This type of DNA damage is repaired through (1) HR recombination (as described above) or (2) non-homologous end-joining (NHEJ).…”