Inhibition of poly(ADP-ribose) polymerase down-regulates BRCA1 and RAD51 in a pathway mediated by E2F4 and p130

• Published in: Proceedings of the National Academy of Sciences - PNAS Vol. 107; no. 5; pp. 2201 - 2206
• Main Authors: Hegan, Denise Campisi, Lu, Yuhong, Stachelek, Gregory C, Crosby, Meredith E, Bindra, Ranjit S, Glazer, Peter M
• Format: Journal Article
• Language: English
• Published: United States National Academy of Sciences 02.02.2010; National Acad Sciences
• Subjects: Adenosine diphosphate; Antibodies; Biological Sciences; Breast cancer; Cancer therapies; Cell Line, Tumor; Cell lines; Cells; Clinical trials; Colonic Neoplasms - genetics; Colonic Neoplasms - metabolism; Crk-Associated Substrate Protein - antagonists & inhibitors; Crk-Associated Substrate Protein - genetics; Crk-Associated Substrate Protein - metabolism; Cytotoxicity; Deoxyribonucleic acid; DNA; DNA damage; DNA repair; DNA Repair - drug effects; DNA Repair - physiology; Down regulation; Down-Regulation - drug effects; E2F4 Transcription Factor - metabolism; Enzyme Inhibitors - pharmacology; gene expression regulation; Genes, BRCA1 - drug effects; HEK293 cells; Humans; Hypoxia; Inhibitors; Ionizing radiation; NAD ADP-ribosyltransferase; neoplasm cells; neoplasms; Phenanthrenes - pharmacology; Poly (ADP-Ribose) Polymerase-1; Poly(ADP-ribose) Polymerase Inhibitors; Poly(ADP-ribose) Polymerases - metabolism; Promoter Regions, Genetic; Rad51 Recombinase - genetics; Radiation tolerance; Radiation-Sensitizing Agents - pharmacology; Ribonucleic acid; RNA; RNA, Small Interfering - genetics; Small interfering RNA; therapeutics; tumor suppressor proteins
• ISSN: 0027-8424; 1091-6490; 1091-6490
• DOI: 10.1073/pnas.0904783107

Inhibitors of poly(ADP-ribose) polymerase (PARP) are in clinical trials for cancer therapy, on the basis of the role of PARP in recruitment of base excision repair (BER) factors to sites of DNA damage. Here we show that PARP inhibition to block BER is toxic to hypoxic cancer cells, in which homology-dependent repair (HDR) is known to be down-regulated. However, we also report the unexpected finding that disruption of PARP, itself, either via chemical PARP inhibitors or siRNAs targeted to PARP-1, can inhibit HDR by suppressing expression of BRCA1 and RAD51, key factors in HDR of DNA breaks. Mechanistically, PARP inhibition was found to cause increased occupancy of the BRCA1 and RAD51 promoters by repressive E2F4/p130 complexes, a pathway prevented by expression of HPV E7, which disrupts p130 activity, or by siRNAs to knock down p130 expression. Functionally, disruption of p130 by E7 expression or by siRNA knockdown also reverses the cytotoxicity and radiosensitivity associated with PARP inhibition, suggesting that the down-regulation of BRCA1 and RAD51 is central to these effects. Direct measurement of HDR using a GFP-based assay demonstrates reduced HDR in cells treated with PARP inhibitors. This work identifies a mechanism by which PARP regulates DNA repair and suggests new strategies for combination cancer therapies.