MTUS2-AS1 suppression promotes DDX5 protein degradation to enhance the sensitivity of PARP inhibitors in BRCA-wild triple negative breast cancer.

Triple-negative breast cancer (TNBC) primarily relies on traditional adjuvant chemotherapy and radiotherapy, which have significant side effects and are prone to drug resistance. Poly ADP-ribose polymerase inhibitor (PARPi) has been approved for TNBC patients with BRCA mutation, but some BRCA wild-type patients with homologous recombination deficiencies are also sensitive to PARPi. Therefore, it is important to identify potential molecules that influence PARPi sensitivity in BRCA wild-type TNBC and to explore their specific mechanisms. Through CRISPR-cas9 loss-of-function screening, the lncRNA MTUS2-AS1 was identified to be significantly correlated with PARPi sensitivity in BRCA wild-type TNBC cells. In vitro and in vivo experiments were performed to investigate its function and underlying mechanism. We found that MTUS2-AS1 knockdown suppressed DNA damage repair and enhanced the anticancer effects of PARPi in BRCA-wild TNBC cells. Mechanistically, MTUS2-AS1 upregulates DDX5 protein expression by maintaining its stability, thereby promoting R-loop resolution, and suppressing DNA damage. Knocking down MTUS2-AS1 accelerated DDX5 protein degradation, reduced DDX5 protein expression, inhibitd R-loop resolution, promoted DNA damage, and ultimately enhanced the PARPi sensitivity in TNBC cells. Our study provided new insights into exploring the key molecules and mechanisms influencing the sensitivity of PARPi treatment and had great significance for screening benefit population and expanding the indications of PARPi treatment.