Inhibition of poly(ADP-ribose) polymerase down-regulates BRCA1 and RAD51 in a pathway mediated by E2F4 and p130.
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.
Hegan
Denise Campisi
DC
Departments of Therapeutic Radiology, Yale University School of Medicine, New Haven, CT 06520, USA.
Lu
Yuhong
Y
Stachelek
Gregory C
GC
Crosby
Meredith E
ME
Bindra
Ranjit S
RS
Glazer
Peter M
PM
D045744:Cell Line, Tumor; D003110:Colonic Neoplasms / Q000235:genetics* / Q000378:metabolism*; D050719:Crk-Associated Substrate Protein / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D004260:DNA Repair / Q000187:drug effects / Q000502:physiology; D015536:Down-Regulation / Q000187:drug effects; D050704:E2F4 Transcription Factor / Q000378:metabolism*; D004791:Enzyme Inhibitors / Q000494:pharmacology; D019398:Genes, BRCA1 / Q000187:drug effects; D006801:Humans; D010616:Phenanthrenes / Q000494:pharmacology; D000071137:Poly (ADP-Ribose) Polymerase-1; D000067856:Poly(ADP-ribose) Polymerase Inhibitors; D011065:Poly(ADP-ribose) Polymerases / Q000378:metabolism; D011401:Promoter Regions, Genetic; D034741:RNA, Small Interfering / Q000235:genetics; D051135:Rad51 Recombinase / Q000235:genetics*; D011838:Radiation-Sensitizing Agents / Q000494:pharmacology
C493841:BCAR1 protein, human; D050719:Crk-Associated Substrate Protein; D050704:E2F4 Transcription Factor; C493762:E2F4 protein, human; D004791:Enzyme Inhibitors; D010616:Phenanthrenes; D000067856:Poly(ADP-ribose) Polymerase Inhibitors; D034741:RNA, Small Interfering; D011838:Radiation-Sensitizing Agents; C040601:phenanthridone; C499320:PARP1 protein, human; D000071137:Poly (ADP-Ribose) Polymerase-1; D011065:Poly(ADP-ribose) Polymerases; C495153:RAD51 protein, human; D051135:Rad51 Recombinase