The nuclear receptor ER? engages AGO2 in regulation of gene transcription, RNA splicing and RISC loading

Background: The RNA-binding protein Argonaute 2 (AGO2) is a key effector of RNA-silencing pathways It exerts a pivotal role in microRNA maturation and activity and can modulate chromatin remodeling, transcriptional gene regulation and RNA splicing. Estrogen receptor beta (ER?) is endowed with oncosuppressive activities, antagonizing hormone-induced carcinogenesis and inhibiting growth and oncogenic functions in luminal-like breast cancers (BCs), where its expression correlates with a better prognosis of the disease. Results: Applying interaction proteomics coupled to mass spectrometry to characterize nuclear factors cooperating with ER? in gene regulation, we identify AGO2 as a novel partner of ER? in human BC cells. ER?-AGO2 association was confirmed in vitro and in vivo in both the nucleus and cytoplasm and is shown to be RNA-mediated. ChIP-Seq demonstrates AGO2 association with a large number of ER? binding sites, and total and nascent RNA-Seq in ER?+vs ER?-cells, and before and after AGO2 knock-down in ER?+cells, reveals a widespread involvement of this factor in ER?-mediated regulation of gene transcription rate and RNA splicing. Moreover, isolation and sequencing by RIP-Seq of ER?-associated long and small RNAs in the cytoplasm suggests involvement of the nuclear receptor in RISC loading, indicating that it may also be able to directly control mRNA translation efficiency and stability. Conclusions: These results demonstrate that AGO2 can act as a pleiotropic functional partner of ER?, indicating that both factors are endowed with multiple roles in the control of key cellular functions.