RESUMO
Replication stress results from obstacles to replication fork progression, including ongoing transcription, which can cause transcription-replication conflicts. Oncogenic signaling can promote global increases in transcription activity, also termed hypertranscription. Despite the widely accepted importance of oncogene-induced hypertranscription, its study remains neglected compared with other causes of replication stress and genomic instability in cancer. A growing number of recent studies are reporting that oncogenes, such as RAS, and targeted cancer treatments, such as bromodomain and extraterminal motif (BET) bromodomain inhibitors, increase global transcription, leading to R-loop accumulation, transcription-replication conflicts, and the activation of replication stress responses. Here we discuss our mechanistic understanding of hypertranscription-induced replication stress and the resulting cellular responses, in the context of oncogenes and targeted cancer therapies.
Assuntos
Replicação do DNA , Neoplasias , Dano ao DNA , Instabilidade Genômica , Humanos , Neoplasias/genética , Oncogenes , Estruturas R-LoopRESUMO
Stalled replication forks can be restarted and repaired by RAD51-mediated homologous recombination (HR), but HR can also perform post-replicative repair after bypass of the obstacle. Bulky DNA adducts are important replication-blocking lesions, but it is unknown whether they activate HR at stalled forks or behind ongoing forks. Using mainly BPDE-DNA adducts as model lesions, we show that HR induced by bulky adducts in mammalian cells predominantly occurs at post-replicative gaps formed by the DNA/RNA primase PrimPol. RAD51 recruitment under these conditions does not result from fork stalling, but rather occurs at gaps formed by PrimPol re-priming and resection by MRE11 and EXO1. In contrast, RAD51 loading at double-strand breaks does not require PrimPol. At bulky adducts, PrimPol promotes sister chromatid exchange and genetic recombination. Our data support that HR at bulky adducts in mammalian cells involves post-replicative gap repair and define a role for PrimPol in HR-mediated DNA damage tolerance.
Assuntos
Adutos de DNA/genética , DNA Primase/metabolismo , DNA Polimerase Dirigida por DNA/metabolismo , Recombinação Homóloga/fisiologia , Enzimas Multifuncionais/metabolismo , 4-Nitroquinolina-1-Óxido/toxicidade , 7,8-Di-Hidro-7,8-Di-Hidroxibenzo(a)pireno 9,10-óxido/metabolismo , Benzo(a)Antracenos/administração & dosagem , Benzo(a)Antracenos/toxicidade , Linhagem Celular , Adutos de DNA/metabolismo , DNA Primase/genética , DNA de Cadeia Simples , DNA Polimerase Dirigida por DNA/genética , Humanos , Enzimas Multifuncionais/genética , Quinolonas/toxicidade , Rad51 Recombinase/genética , Rad51 Recombinase/metabolismo , Imagem Individual de Molécula , Troca de Cromátide IrmãRESUMO
BET bromodomain proteins are required for oncogenic transcription activities, and BET inhibitors have been rapidly advanced into clinical trials. Understanding the effects of BET inhibition on processes such as DNA replication will be important for future clinical applications. Here, we show that BET inhibition, and specifically inhibition of BRD4, causes replication stress through a rapid overall increase in RNA synthesis. We provide evidence that BET inhibition acts by releasing P-TEFb from its inhibitor HEXIM1, promoting interference between transcription and replication. Unusually, these transcription-replication conflicts do not activate the ATM/ATR-dependent DNA damage response but recruit the homologous recombination factor RAD51. Both HEXIM1 and RAD51 promote BET inhibitor-induced fork slowing but also prevent a DNA damage response. Our data suggest that BET inhibitors slow replication through concerted action of transcription and recombination machineries and shed light on the importance of replication stress in the action of this class of experimental cancer drugs.
