Cyclin K condensates bridge CDK12 to phosphorylate and drive oncogenic YAP activation in hepatocellular carcinoma

Targeting transcriptional condensates is an emerging paradigm for cancer therapy. A key player is the transcriptional coactivator YAP (Yes-associated protein), which drives tumor-specific programs that fuel tumor progression and therapeutic resistance. Cyclin K, partnered with cyclin-dependent kinases (CDKs) CDK12/CDK13, is essential for transcription elongation, but its role in specific oncogenic programs was unclear. Here, we identify Cyclin K as an essential vulnerability across multiple cancer types. The CDK12/Cyclin K complex binds YAP via Cyclin K and forms a regulatory condensate to bridge YAP phosphorylation by CDK12. Such a phosphorylation at threonine-398 impedes YAP inhibition by its canonical LATS kinases, stabilizes YAP, and enables its further condensation with TEAD4 to stimulate YAP oncogenic activity. Coexpression of CDK12/Cyclin K and YAP predicts sensitivity to Cyclin K inhibitors in hepatocellular carcinoma cells and patient-derived xenografts. Thus, we define CDK12/Cyclin K as a critical regulator of YAP-driven transcriptional addiction and a biomarker for patient stratification who mostly benefit from therapies targeting the CDK12/Cyclin K–YAP axis.