YAP/BRD4‐controlled ROR1 promotes tumor‐initiating cells and hyperproliferation in pancreatic cancer

Tumor‐initiating cells are major drivers of chemoresistance and attractive targets for cancer therapy, however, their identity in human pancreatic ductal adenocarcinoma (PDAC) and the key molecules underlying their traits remain poorly understood. Here, we show that a cellular subpopulation with partial epithelial‐mesenchymal transition (EMT)‐like signature marked by high expression of receptor tyrosine kinase‐like orphan receptor 1 (ROR1) is the origin of heterogeneous tumor cells in PDAC. We demonstrate that ROR1 depletion suppresses tumor growth, recurrence after chemotherapy, and metastasis. Mechanistically, ROR1 induces the expression of Aurora kinase B (AURKB) by activating E2F through c‐Myc to enhance PDAC proliferation. Furthermore, epigenomic analyses reveal that ROR1 is transcriptionally dependent on YAP/BRD4 binding at the enhancer region, and targeting this pathway reduces ROR1 expression and prevents PDAC growth. Collectively, our findings reveal a critical role for ROR1high cells as tumor‐initiating cells and the functional importance of ROR1 in PDAC progression, thereby highlighting its therapeutic targetability. Synopsis Cancer cell diversity and contribution of tumor‐initiating cells to pancreatic ductal adenocarcinoma (PDAC) progression remain poorly defined. In this work, single‐cell RNA sequencing and functional analyses uncovered targetable tumor‐initiating cells in PDAC. Heterogeneous tumor cells in PDAC arise from a subpopulation with partial EMT signature characterized by high expression of ROR1. Intratumoral ROR1 high cells are tumor‐initiating cells with increased tumorigenic capacity. ROR1 functionally promotes PDAC tumor growth, relapse after chemotherapy, and metastasis. ROR1 induces the expression of AURKB via activation of AKT/c‐Myc/E2F signaling, thereby enhancing PDAC proliferation. ROR1 transcription is dependent on the YAP/BRD4 axis. Graphical Abstract ROR1 marks an aggressive partial EMT cell cluster and enhances PDAC proliferation via c‐Myc/E2F/AURKB signaling.