DOCTER: a genetically encoded switchable protein module for ERα-mediated transcriptional regulation.

The inhibition of estrogen receptor (ER)-mediated genomic signaling in ER-positive cancer cells has long been a primary focus of therapeutic strategies. Here, we introduce a switchable competitive inhibition system for ERα-mediated transcriptional regulation, termed DOCTER (Drug-induced On-Off Competitor for Transcription mediated by ERα). DOCTER integrates the Tet-On induced Cre-loxP recombination system to enable precise, reversible on/off switching. We demonstrate that DOCTER effectively inhibits ERα-mediated transcriptional regulation in breast cancer cells, modulating both exogenous and endogenous gene expression, and remains effective in cells harboring ERα ligand-binding domain (LBD) mutations. Upon drug induction, DOCTER exhibits controllable and reversible inhibition. To visualize these dynamic switching events in real time, we developed a multi-color fluorescent reporting system that enables monitoring of complete DOCTER switch-off within 24 hours. Our study provides a novel approach for time-specific transcriptional regulation and offers broad potential for applications in genetic research and therapeutic development.