Increased activity of poly(ADP-ribose)-polymerase in PML-depleted cells - novel perspectives for cancer therapy

Abstract

Aim. To investigate the relationship between PML expression and poly(ADP-ribose)-polymerase (PARP) activity in physiological conditions and at genotoxic stress induced by chemotherapy and ionizing radiation. Methods. The study was conducted on BJ fibroblasts cultured in DMEM/199 medium supplemented with fetal bovine serum, L-glutamine and antibiotics. PML down-regulation was achieved by short interfering ribonucleic acid transfection. To induce deoxyribonucleic acid (DNA) damage in BJ fibroblasts, doxorubicin and hydroxyurea or ionizing radiation were used. PARP activity, formation of DNA double-strand breaks and DNA damage response were examined by Western blotting and immunofluorescence microscopy. Results. PML knockdown was accomplished with an increased PARP activity, confirmed by an increased expression of poly-ADP-ribose (PAR) polymers. At PML knockdown ant DNA damage caused by chemotherapy and ionizing radiation, there is a significant increase in PAR polymers expression as well as increase in the number of cells containing PAR foci. Conclusion. Increased activity of poly(ADP-ribose)-polymerase at PML knockdown and DNA damaging conditions indicates the compensatory response due to insufficiency of the homologous recombination mechanisms. The phenomenon found widens the spectrum of malignancies that might be potentially sensitive to the therapy with poly(ADP-ribose)-polymerase inhibitors.