Transcriptomic profiling of MCF7 and ZR-75-1 parental and RB1 knockout cells treated with palbociclib

In hormone receptor-positive (HR+) breast cancer, CDK4/6 inhibitors activate Rb by preventing its phosphorylation, forming a key component of current endocrine therapy regimens. How pharmacologically activated Rb remodels chromatin and influences transcription beyond cell cycle arrest remains poorly understood.

Here we show that CDK4/6 inhibition induces redistribution of hypo-phosphorylated Rb to promoters and enhancers. While Rb predictably binds to cell cycle gene promoters to repress transcription, at other sites it unexpectedly promotes expression of oestrogen-responsive genes by integrating into oestrogen receptor (ER)-rich transcriptional hubs. CDK4/6 inhibition enhances ER target gene expression in breast cancer cells, patient-derived xenografts, and clinical HR+ breast cancer samples in an Rb-dependent manner.