engleski

The role of ΔNp73α in response to genotoxic stress in normal and tumor human cells

p73 gene encodes numerous protein isoforms divided into two groups according to alternative promoter usage: tumor-suppressive TAp73 isoforms whose functions partly overlap with those of wild-type p53, and potentially oncogenic ΔNp73 isoforms which inhibit wild-type p53, p63 and p73. Since ΔNp73 isoforms are often overexpressed in human tumors showing enhanced chemoresistance, they are considered as potential markers of worse prognosis. Our investigation is focused on the impact of ΔNp73α overexpression on cell cycle regulation and response to different DNA damaging agents (ICRF-193, bleomycin, γ-irradiation) in normal and tumor human cells. ΔNp73α was overexpressed in wild-type human dermal fibroblasts (HDF-WT), HDF expressing human papilloma virus HPV16-E6 oncoprotein (HDF-E6), and U2OS human osteosarcoma cell line by retroviral infection. Our video-microscopy experiments showed that in HDF-WT ΔNp73α overexpression abrogates G2 cell cycle arrest after treatment with topoisomerase II inhibitor ICRF-193. In agreement with this, we found lower p21 expression in cells with ΔNp73α compared to control ones upon ICRF-193 treatment. To explore potential role of ΔNp73α at the G2/M checkpoint, HDF-WT and HDF-E6 were synchronized at G1/S boundary and exposed to γ- irradiation (12 Gy) after release, but FACS analysis showed no significant difference between cells expressing ΔNp73α and control. FACS analysis of γ-irradiated (3 and 5 Gy) HDF-WT and U2OS cells revealed higher percentage of polyploidy in cells overexpressing ΔNp73α. Further analysis of cell cycle progression and specific DNA damage signaling pathways will help to elucidate the role of ΔNp73α in the process of oncogenesis.

p73; cell cycle; DNA damage

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