The Interaction of CircESR1 and HNRNPAB Regulates Cell Cycle Transition of Breast Cancer Cell.

The mechanisms by which circRNAs regulate estrogen receptor (ER)-positive breast progression and therapeutic resistance remain poorly defined. By screening circRNAs involved in ER signaling, circESR1 was identified as a novel circRNA exhibiting high specificity of expression in ER+ breast cancer. CircESR1 interacted with HNRNPAB, which was transcriptionally activated by ER/SP1 signaling. HNRNPAB promoted the back-splicing and expression of circESR1 by binding to the Alu elements of cognate pre-mRNA; and circESR1 transcripts increased the stability and expression of HNRNPAB, ensuring an efficient positive feedback loop as reflected in antiestrogen-resistant breast cancer cells. Furthermore, HNRNPAB interacted and stabilized CDK1 and CDK6 mRNA, which was facilitated by its asymmetrical binding of circESR1, to promote cell cycle progression. Patients whose cancer exhibited high levels of circESR1 and/or HNRNPAB exhibited advanced prognostic stage and poor survival. Combined use of circESR1 ASO and CDK4/6 inhibitors were shown to be an effective therapeutic approach overcoming antiestrogen resistance in breast cancer xenograft models. Hence, these findings elucidated a novel signaling complex centered around circESR1 and HNRNPAB in ER+ breast cancer, and suggested that circESR1 might represent a potential therapeutic target for this disease.