engleski

ΔNp73α compromises G2/M checkpoint inducing genomic instability in response to DNA damage

Deregulation of the cell cycle progression is a common feature of tumor cells and one of the driving forces in tumorigenesis, mostly by leading to unscheduled proliferation and genomic instability. The canonical p53 protein (p53α) and its relative p73 are shown to have various roles in cell cycle regulation in stress conditions, especially as a part of DNA damage response signaling pathways. ΔNp73α, a potentially oncogenic isoform of p73 is often overexpressed in different human tumors and tumor cell lines in correlation with increased chemo- and radioresistance and worse prognosis. To understand better molecular mechanisms underlying the tumor-associated action of ΔNp73α, we investigated the effects of ΔNp73α ectopic expression on cycle progression of normal and tumor cells after DNA damage. Normal human fibroblasts (NHF) and U2OS human osteosarcoma cells infected with retroviral vectors harboring ΔNp73α were treated with different doses of γ-irradiation or topoisomerase II inhibitor ICRF-193 that specifically causes arrest in G2/M checkpoint. Cell cycle distribution was determined by FACS analysis measuring the DNA content after propidium iodide staining. The expression of several proteins involved in the control of cell cycle and DNA damage response was analysed by Western blot and immunofluorescence. U2OS cells overexpressing ΔNp73α showed higher percentage of tetraploid and polyploid cells after γ-irradiation in comparison to control cells, especially at longer time periods post- treatment. This was accompanied by lower p21, and higher cyclin B1 and A expression. This phenotype was even more pronounced upon treatment with ICRF-193. By contrast, the effect of ΔNp73α on DNA damage response in NHF was more modest, limited to certain increase of polyploidy. Our results show that ΔNp73α perturbs G2/M checkpoint control by abrogating cell cycle arrest after DNA damage leading to increased genomic instability. This could be one of the possible mechanisms of exerting its oncogenic role.

ΔNp73α; cell cycle control; DNA damage; G2/M checkpoint; p21

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