Homologous recombination (HR) is crucial for maintaining genomic integrity and is tightly regulated, yet the role of ubiquitin-dependent degradation in HR proteins remains poorly understood. Through high-throughput screening for compounds that modulate the DNA replication stress response, we identify ML367 and its derivative, UNI418. Kinase profiling and detail molecular analyses reveal that UNI418 inhibits PIKfyve and PIP5K1C, reducing inositol hexaphosphate (IP6) levels and triggering Cul4A-dependent degradation of RAD51, CtIP, and CHK1. Further analysis identifies WDR5 as a DCAF protein that facilitates Cul4A-mediated proteolysis of RAD51 and CHK1. Functionally, UNI418 suppresses HR, enhances tumor sensitivity to PARP inhibitors (PARPis), and re-sensitizes PARPi-resistant tumor cells in both in vitro and in vivo xenograft models. These findings reveal a Cul4A-WDR5-dependent proteolysis pathway regulating HR protein stability via phosphatidyl inositol signaling. This mechanism offers a promising therapeutic strategy for overcoming PARPi resistance and improving combinatorial cancer treatment strategies. Homologous recombination (HR) safeguards genome stability, but the regulation of HR proteins remains unclear. Here, the authors show that the compound UNI418 inhibits lipid kinases PIKfyve and PIP5K1C, reducing IP6 levels and triggering Cul4A–WDR5 dependent degradation of HR proteins, thereby suppressing HR and overcoming PARP inhibitor resistance.
Lee et al. (Sat,) studied this question.