To investigate the effect of BRCA1 gene silencing on the repair of DNA double-strand breaks (DSBs) induced by lead acetate in human lymphoblastoid TK6 cells.

A stable BRCA1-silenced TK6 cell model was established using lentivirus-mediated shRNA technology. Cells were divided into four groups: normal group (untreated control group), control group (empty vector control group), shRNA-NC group (negative control lentivirus group), and shRNA-BRCA1 group (BRCA1 knockdown group). All exposed groups were treated with 480 μmol/L lead acetate for 24 h. Silencing efficiency was confirmed by qPCR and Western blot. DNA damage was assessed by immunofluorescence staining for γ-H2AX foci. Cell cycle and apoptosis were analyzed by flow cytometry. The expression of key proteins in the homologous recombination (HR) and non-homologous end joining (NHEJ) repair pathways and DNA damage response (DDR) signaling molecules was detected by Western blot.

The BRCA1 silencing model was successfully constructed, with significantly lower levels of BRCA1 mRNA and protein in the shRNA-BRCA1 group compared to the control and shRNA-NC groups (P<0.05). Under lead exposure, the shRNA-BRCA1 group showed a significantly higher positive rate of γ-H2AX (26.94±2.93)%, a higher proportion of G1 phase cells (65.31±1.13)%, and a higher apoptosis rate (52.84±1.21)% compared to all other groups (P<0.05), while the proportion of S phase cells (8.59±0.45)% was further reduced. Protein analysis revealed that, compared to the control and shRNA-NC groups, the expression of the HR key protein Rad51 was decreased (0.52±0.10) in the shRNA-BRCA1 group, while the expression levels of the NHEJ pathway protein 53BP1 (9.73±0.87) and the DDR signaling molecules ATM (6.10±0.48), ATR (6.25±0.92), CHK1 (2.35±0.46), and DNA-PKcs (3.85±0.93) were significantly increased (P<0.05).

BRCA1 silencing inhibits homologous recombination repair, exacerbates lead-induced DNA double-strand breaks, arrests the G1/S phase progression, and intensifies apoptosis. The mechanism may be related to the activation of the ATM/ATR-CHK1 pathway and compensatory upregulation of the NHEJ repair pathway.