ALT-EJ GENERA REARREGLOS CROMOSÓMICOS EN RESPUESTA A ETOPÓSIDO EN CÉLULAS HUMANAS CON LOS PRINCIPALES SISTEMAS DE REPARACIÓN DE RUPTURAS DE DOBLE CADENA COMPROMETIDOS

Abstract

The antitumor drug Etoposide (ETO) induces DNA double-strand breaks (DSB) and is associated with the development of secondary neoplasms in treated patients. DSB are repaired by two main mechanisms, homologous recombination (HR) and classical non-homologous end joining (c-NHEJ). When HR and c-NHEJ are defective, DSB are repaired by the PARP-1-dependent alternative end-joining (alt-EJ) pathway. The involvement of alt-EJ in the progression of DSB induced by ETO in the G2 phase of human cells was analyzed. HeLa cells deficient in HR (cohesin RAD21 inhibition, HeLa RAD21kd) and their nonsilencing control (HeLa NS) were established. Cells were treated with ETO in the presence of a chemical inhibitor of DNA-PKcs (DNA-PKi, c-NHEJ). In both cell lines, ETO-induced DSB (γH2AX+) in G2 phase were increased compared to their controls. The incorrect repair of DSB in DNA-PKcs- and RAD21-deficient cells caused a synergistic augment in chromatid exchanges and dicentric chromosomes in the first and second metaphase, respectively. In contrast, the frequency of dicentric chromosomes was reduced in PARP-1-deficient cells (HeLa PARP-1kd) following ETO treatment. In HeLa RAD21kd binucleated cells, DNA-PKi/ETO increased the percentage of cells with ≥20 γH2AX foci in the G1-postmitotic phase and of micronuclei at 96 h. A greater accumulation in G2/M was observed in HeLa NS treated with DNA-PKi/ ETO compared with HeLa RAD21kd at 8 h. The cell cycle restarted in HeLa NS at 16 h; however, the G2/M accumulation was maintained in HeLa RAD21kd. Chromosomal rearrangements obtained when DNAPKcs and RAD21 were absent and their decrease in HeLa PARP-1kd cells suggest that alt-EJ contributes to their formation.