RESUMO
BRCA1 expression is highly regulated to prevent genomic instability and tumorigenesis. Dysregulation of BRCA1 expression correlates closely with sporadic basal-like breast cancer and ovarian cancer. The most significant characteristic of BRCA1 regulation is periodic expression fluctuation throughout the cell cycle, which is important for the orderly progression of different DNA repair pathways throughout the various cell cycle phases and for further genomic stability. However, the underlying mechanism driving this phenomenon is poorly understood. Here, we demonstrate that RBM10-mediated RNA alternative splicing coupled to nonsense-mediated mRNA decay (AS-NMD), rather than transcription, determines the periodic fluctuations in G1/S-phase BRCA1 expression. Furthermore, AS-NMD broadly regulates the expression of period genes, such as DNA replication-related genes, in an uneconomical but more rapid manner. In summary, we identified an unexpected posttranscriptional mechanism distinct from canonical processes that mediates the rapid regulation of BRCA1 as well as other period gene expression during the G1/S-phase transition and provided insights into potential targets for cancer therapy.
Assuntos
Neoplasias da Mama , Degradação do RNAm Mediada por Códon sem Sentido , Humanos , Feminino , Processamento Alternativo , Splicing de RNA , Neoplasias da Mama/genética , Instabilidade Genômica , Proteína BRCA1/genética , Proteínas de Ligação a RNA/genéticaRESUMO
MRE11 nuclease forms a trimeric complex (MRN) with RAD50 and NBS1 and plays a central role in preventing genomic instability. When DNA double-strand breaks (DSBs) occur, MRN is quickly recruited to the damage site and initiates DNA end resection; accordingly, MRE11 must be tightly regulated to avoid inefficient repair or nonspecific resection. Here, we show that MRE11 and RAD50 form a complex (MRC) with C1QBP, which stabilizes MRE11/RAD50, while inhibiting MRE11 nuclease activity by preventing its binding to DNA or chromatin. Upon DNA damage, ATM phosphorylates MRE11-S676/S678 to quickly dissociate the MRC complex. Either excess or insufficient C1QBP impedes the recruitment of MRE11 to DSBs and impairs the DNA damage response. C1QBP is highly expressed in breast cancer and positively correlates with MRE11 expression, and the inhibition of C1QBP enhances tumor regression with chemotherapy. By influencing MRE11 at multiple levels, C1QBP is, thus, an important player in the DNA damage response.
Assuntos
Hidrolases Anidrido Ácido/metabolismo , Proteínas de Transporte/metabolismo , Proteínas de Ciclo Celular/metabolismo , Proteínas de Ligação a DNA/metabolismo , Recombinação Homóloga , Proteína Homóloga a MRE11/metabolismo , Proteínas Mitocondriais/metabolismo , Complexos Multiproteicos/metabolismo , Proteínas Nucleares/metabolismo , Hidrolases Anidrido Ácido/genética , Animais , Proteínas de Transporte/genética , Proteínas de Ciclo Celular/genética , Proteínas de Ligação a DNA/genética , Células HEK293 , Células HeLa , Humanos , Proteína Homóloga a MRE11/genética , Proteínas Mitocondriais/genética , Complexos Multiproteicos/genética , Proteínas Nucleares/genética , Estabilidade Proteica , Células Sf9 , SpodopteraRESUMO
P53-binding protein 1 (53BP1) plays critical roles in DNA double strand break (DSB) repair by promoting non-homologous end joining (NHEJ), and loss of 53BP1 abolishes PARPi sensitivity in BRCA1-deficient cells by restoring homologous recombination (HR). 53BP1 is one of the proteins initially recruited to sites of DSBs via recognition of H4K20me2 through the Tudor-UDR domain and H2AK15ub through the UDR motif. Although extensive studies have been conducted, it remains unclear how the post-translational modification of 53BP1 affects DSB repair pathway choice. Here, we identified 53BP1 as an acetylated protein and determined that acetylation of 53BP1 inhibit NHEJ and promote HR by negatively regulating 53BP1 recruitment to DSBs. Mechanistically, CBP-mediated acetylation of K1626/1628 in the UDR motif disrupted the interaction between 53BP1 and nucleosomes, subsequently blocking the recruitment of 53BP1 and its downstream factors PTIP and RIF1 to DSBs. Hyperacetylation of 53BP1, similar to depletion of 53BP1, restored PARPi resistance in BRCA1-deficient cells. Interestingly, 53BP1 acetylation was tightly regulated by HDAC2 to maintain balance between the HR and NHEJ pathways. Together, our results demonstrate that the acetylation status of 53BP1 plays a key role in its recruitment to DSBs and reveal how specific 53BP1 modification modulates the choice of DNA repair pathway.
Assuntos
Quebras de DNA de Cadeia Dupla , Reparo do DNA por Junção de Extremidades , DNA/metabolismo , Proteína 1 de Ligação à Proteína Supressora de Tumor p53/metabolismo , Acetilação , Sequência de Aminoácidos , DNA/química , DNA/genética , Proteínas de Ligação a DNA/química , Proteínas de Ligação a DNA/genética , Proteínas de Ligação a DNA/metabolismo , Células HEK293 , Células HeLa , Humanos , Nucleossomos/química , Nucleossomos/metabolismo , Ligação Proteica , Processamento de Proteína Pós-Traducional , Homologia de Sequência de Aminoácidos , Domínio Tudor , Proteína 1 de Ligação à Proteína Supressora de Tumor p53/química , Proteína 1 de Ligação à Proteína Supressora de Tumor p53/genéticaRESUMO
The RPA complex can integrate multiple stress signals into diverse responses by activating distinct DNA repair pathways. However, it remains unclear how RPA1 elects to activate a specific repair pathway during different types of DNA damage. Here, we report that PCAF/GCN5-mediated K163 acetylation of RPA1 is crucial for nucleotide excision repair (NER) but is dispensable for other DNA repair pathways. Mechanistically, we demonstrate that the acetylation of RPA1 is critical for the steady accumulation of XPA at damaged DNA sites and preferentially activates the NER pathway. DNA-PK phosphorylates and activates PCAF upon UV damage and consequently promotes the acetylation of RPA1. Moreover, the acetylation of RPA1 is tightly regulated by HDAC6 and SIRT1. Together, our results demonstrate that the K163 acetylation of RPA1 plays a key role in the repair of UV-induced DNA damage and reveal how the specific RPA1 modification modulates the choice of distinct DNA repair pathways.