GEOapplication/xmlftp://ftp.ncbi.nlm.nih.gov/geo/series/GSE328nnn/GSE328796/primaryOK200GenomicsHomo sapiensGenome binding/occupancy profiling by high throughput sequencinghttps://www.ncbi.nlm.nih.gov/geo/query/acc.cgi?acc=GSE328796GEOGSEfalseTargeting Cyclin K-CDK12 Synergizes with ATR Inhibition by Limiting RPA Chromatin Loading in Triple-Negative Breast Cancer [ChIP-seq]Cyclin K-CDK12 inhibition has emerged as a promising therapeutic strategy to induce homologous recombination deficiency (HRD). However, clinical and genomic studies have not clearly linked CDK12 inactivation to HRD. Here, we demonstrate that cyclin K-CDK12 depletion drives a replication stress (RS)-associated vulnerability through RPA regulation. A DNA damage response-focused CRISPR screen identified DNA replication factors and ATR activators as top sensitizers to cyclin K degradation. Consistently, cyclin K-CDK12 depletion synergized with ATR inhibition in triple-negative breast cancer (TNBC) models. Cyclin K degradation reduces RPA chromatin loading and impairs ATR activation, compromising cellular tolerance to RS and increasing susceptibility to ATR inhibition. We show that CDK12-mediated phosphorylation of CDC5L is required for RPA chromatin loading and mediates resistance to combined cyclin K and ATR depletion. Our findings identify cyclin K-CDK12 as a critical regulator of RPA dynamics and support its inhibition as rational therapy for RS-high tumors, including TNBC.2026/04/27GSE328796GSM9689860GSM9689861GSM9689857GSM9689856GSM9689859GSM968985824676328796Homo sapiens