BRCA1 recruitment to damaged DNA sites is dependent on CDK9

Abstract

Double strand break lesions, the most toxic type of DNA damage, are repaired primarily through 2 distinct pathways: homology-directed recombination (HR) and non-homologous end-joining (NHEJ). BRCA1 and 53BP1, 2 proteins containing the BRCT modular domain, play an important role in DNA damage response (DDR) by orchestrating the decision between HR and NHEJ, but the precise mechanisms regarding both pathways are not entirely understood. Previously, our group identified a putative interaction between BRCA1 and BARD1 (BRCA1-associated RING domain 1) and the cyclin-dependent kinase (CDK9). CDK9 is a component of the positive transcription elongation complex and has been implicated in genome integrity maintenance associated with the replication stress response. Here we show that CDK9 interacts with endogenous BRCA1 and BARD1 mediated by their RING finger and BRCT domains, and describe CDK9 ionizing radiation-induced foci (IRIF) formation and its co-localization with BRCA1 in DNA damage sites. Cells lacking CDK9 are characterized by an altered g¡H2AX foci dynamics after DNA damage, a reduced efficiency in HR but not in NHEJ repair, failure to form BRCA1 and RAD51 IRIF and increased sensitivity to genotoxic agents. These data indicate that CDK9 is a player in the DDR and is consistent with its participation in HR pathway by modulating BRCA1 response.

CTDP1 regulates breast cancer survival and DNA repair through BRCT-specific interactions with FANCI

“…BRCA1 C-terminal (BRCT) domains are restricted to a specialized group of only 23 proteins that are predominantly associated with DNA damage response (DDR) pathways 1–3 . The BRCT domain serves as a scaffold for organizing multi-protein complexes that orchestrate the decision between homologous recombination (HR) and non-homologous end joining (NHEJ) through the recruitment of specific repair proteins to sites of DNA damage 4–7 . In the human proteome, CTDP1 is the only phosphatase that also encodes a BRCT domain 1 , suggesting it could play a unique role by regulating the phosphorylation-mediated signaling involved in the DDR.…”

CDK9 Expression Shows Role as a Potential Prognostic Biomarker in Breast Cancer Patients Who Fail to Achieve Pathologic Complete Response after Neoadjuvant Chemotherapy

“…Furthermore, its loss results in spontaneous replication stress and genetic instability [ 10 ]. CDK9 also promotes DNA double-strand break (DSB) repair by homologous recombination (HR) by facilitating recruitment of the BRCA1 breast tumor suppressor protein to DNA damage sites [ 6 ] and associates with Ku70, which is involved in DSB repair by non-homologous end joining (NHEJ) [ 5 ]. CDK9's role in promoting genome integrity is regulated at least in part through deacetylation by the SIRT2 sirtuin deacetylase and breast tumor suppressor protein, which promotes its kinase activity [ 11 ] and in turn phosphorylates UBE2A and directs H2Bub1 and PCNA ubiquitinylation [ 12 ].…”

Targeting CDK9 for the Treatment of Glioblastoma

“…High expression of BRCA1 has been shown to correlate with lower overall survival in glioblastoma patients [ 61 ], underscoring the need to investigate treatments that can dysregulate BRCA1 signaling. Importantly, CDK9 has been shown to modulate the recruitment of BRCA1 to DSBs and plays an important role in the BRCA1-mediated homologous recombination (HR) DNA repair process ( Figure 2 E) [ 62 ]. Cell survival assays performed in wild-type BRCA1 mammary gland carcinoma cells, for example, demonstrated that knockdown of CDK9 impaired recruitment of BRCA1 to DSBs and sensitized cells to radiation [ 62 ].…”