Despite clear evidence that exosomal microRNAs (miRNAs) are able to modulate the cellular microenvironment and that exosomal RNA cargo selection is deregulated in pathological conditions, the mechanisms controlling specific RNA sorting into extracellular vesicles are still poorly understood. Here, we identified the RNA binding protein SYNCRIP (synaptotagmin-binding cytoplasmic RNA-interacting protein; also known as hnRNP-Q or NSAP1) as a component of the hepatocyte exosomal miRNA sorting machinery. SYNCRIP knockdown impairs sorting of miRNAs in exosomes. Furthermore, SYNCRIP directly binds to specific miRNAs enriched in exosomes sharing a common extra-seed sequence (hEXO motif). The hEXO motif has a role in the regulation of miRNA localization, since embedment of this motif into a poorly exported miRNA enhances its loading into exosomes. This evidence provides insights into the mechanisms of miRNA exosomal sorting process. Moreover, these findings open the way for the possible selective modification of the miRNAs exosomal cargo.

BackgroundEstrogen receptors alpha (ERα) and beta (ERβ) are transcription factors (TFs) that mediate estrogen signaling and define the hormone-responsive phenotype of breast cancer (BC). The two receptors can be found co-expressed and play specific, often opposite, roles, with ERβ being able to modulate the effects of ERα on gene transcription and cell proliferation. ERβ is frequently lost in BC, where its presence generally correlates with a better prognosis of the disease. The identification of the genomic targets of ERβ in hormone-responsive BC cells is thus a critical step to elucidate the roles of this receptor in estrogen signaling and tumor cell biology.ResultsExpression of full-length ERβ in hormone-responsive, ERα-positive MCF-7 cells resulted in a marked reduction in cell proliferation in response to estrogen and marked effects on the cell transcriptome. By ChIP-Seq we identified 9702 ERβ and 6024 ERα binding sites in estrogen-stimulated cells, comprising sites occupied by either ERβ, ERα or both ER subtypes. A search for TF binding matrices revealed that the majority of the binding sites identified comprise one or more Estrogen Response Element and the remaining show binding matrixes for other TFs known to mediate ER interaction with chromatin by tethering, including AP2, E2F and SP1. Of 921 genes differentially regulated by estrogen in ERβ+ vs ERβ- cells, 424 showed one or more ERβ site within 10 kb. These putative primary ERβ target genes control cell proliferation, death, differentiation, motility and adhesion, signal transduction and transcription, key cellular processes that might explain the biological and clinical phenotype of tumors expressing this ER subtype. ERβ binding in close proximity of several miRNA genes and in the mitochondrial genome, suggests the possible involvement of this receptor in small non-coding RNA biogenesis and mitochondrial genome functions.ConclusionsResults indicate that the vast majority of the genomic targets of ERβ can bind also ERα, suggesting that the overall action of ERβ on the genome of hormone-responsive BC cells depends mainly on the relative concentration of both ERs in the cell.

PIWI-interacting small non-coding RNAs (piRNAs) are genetic and epigenetic regulatory factors in germline cells, where they maintain genome stability, are involved in RNA silencing and regulate gene expression. We found that the piRNA biogenesis and effector pathway are present in human breast cancer (BC) cells and, analyzing smallRNA-Seq data generated from BC cell lines and tumor biopsies, we identified >100 BC piRNAs, including some very abundant and/or differentially expressed in mammary epithelial compared to BC cells, where this was influenced by estrogen or estrogen receptor β, and in cancer respect to normal breast tissues. A search for mRNAs targeted by the BC piRNome revealed that eight piRNAs showing a specific expression pattern in breast tumors target key cancer cell pathways. Evidence of an active piRNA pathway in BC suggests that these small non-coding RNAs do exert transcriptional and post-transcriptional gene regulatory actions also in cancer cells.

Pharmacological inhibition of DOT1L blocks estrogen receptor signaling in breast cancer.

Widespread genome hypo-methylation and promoter hyper-methylation of epithelium-specific genes are hallmarks of stable epithelial-to-mesenchymal transition (EMT), which in prostate cancer (PCa) correlates with castration resistance, cancer stem cells generation, chemoresistance and worst prognosis. Exploiting our consolidated 'ex-vivo' system, we show that cancer-associated fibroblasts (CAFs) released factors have pivotal roles in inducing genome methylation changes required for EMT and stemness in EMT-prone PCa cells. By global DNA methylation analysis and RNA-Seq, we provide compelling evidence that conditioned media from CAFs explanted from two unrelated patients with advanced PCa, stimulates concurrent DNA hypo- and hyper-methylation required for EMT and stemness in PC3 and DU145, but not in LN-CaP and its derivative C4-2B, PCa cells. CpG island (CGI) hyper-methylation associates with repression of genes required for epithelial maintenance and invasion antagonism, whereas activation of EMT markers and stemness genes correlate with CGI hypo-methylation. Remarkably, methylation variations and EMT-regulated transcripts almost completely reverse qualitatively and quantitatively during MET. Unsupervised clustering analysis of the PRAD TCGA data set with the differentially expressed (DE) and methylated EMT signature, identified a gene cluster of DE genes defined by a CAF+ and AR- phenotype and worst diagnosis. This gene cluster includes the relevant factors for EMT and stemness, which display DNA methylation variations in regulatory regions inversely correlated to their expression changes, thus strongly sustaining the ex-vivo data. DNMT3A-dependent methylation is essential for silencing epithelial maintenance and EMT counteracting genes, such as CDH1 and GRHL2, that is, the direct repressor of ZEB1, the key transcriptional factor for EMT and stemness. Accordingly, DNMT3A knock-down prevents EMT entry. These results shed light on the mechanisms of establishment and maintenance of coexisting DNA hypo- and hyper-methylation patterns during cancer progression, the generation of EMT and cell stemness in advanced PCa, and may pave the way to new therapeutic implications.

Estrogen effects on mammary epithelial and breast cancer (BC) cells are mediated by the nuclear receptors ERa and ERb, transcription factors that display functional antagonism with each other, with ERb acting as oncosuppressor and interfering with the effects of ERa on cell proliferation, tumor promotion and progression. Indeed, hormone-responsive, ERa þ BC cells often lack ERb, which when present associates with a less aggressive clinical phenotype of the disease. Recent evidences point to a significant role of microRNAs (miRNAs) in BC, where specific miRNA expression profiles associate with distinct clinical and biological phenotypes of the lesion. Considering the possibility that ERb might influence BC cell behavior via miRNAs, we compared miRNome expression in ERb þ vs ERbÀ hormone-responsive BC cells and found a widespread effect of this ER subtype on the expression pattern of these non-coding RNAs. More importantly, the expression pattern of 67 miRNAs, including 10 regulated by ERb in BC cells, clearly distinguishes ERb þ , node-negative, from ERbÀ, metastatic, mammary tumors. Molecular dissection of miRNA biogenesis revealed multiple mechanisms for direct regulation of this process by ERb þ in BC cell nuclei. In particular, ERb downregulates miR-30a by binding to two specific sites proximal to the gene and thereby inhibiting pri-miR synthesis. On the other hand, the receptor promotes miR-23b, -27b and 24-1 accumulation in the cell by binding in close proximity of the corresponding gene cluster and preventing in situ the inhibitory effects of ERa on pri-miR maturation by the p68/DDX5-Drosha microprocessor complex. These results indicate that cell autonomous regulation of miRNA expression is part of the mechanism of action of ERb in BC cells and could contribute to establishment or maintenance of a less aggressive tumor phenotype mediated by this nuclear receptor.

BackgroundThe 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 (ERβ) 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.ResultsApplying interaction proteomics coupled to mass spectrometry to characterize nuclear factors cooperating with ERβ in gene regulation, we identify AGO2 as a novel partner of ERβ in human BC cells. ERβ–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 ERβ binding sites, and total and nascent RNA-Seq in ERβ + vs ERβ − cells, and before and after AGO2 knock-down in ERβ + cells, reveals a widespread involvement of this factor in ERβ-mediated regulation of gene transcription rate and RNA splicing. Moreover, isolation and sequencing by RIP-Seq of ERβ-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.ConclusionsThese results demonstrate that AGO2 can act as a pleiotropic functional partner of ERβ, indicating that both factors are endowed with multiple roles in the control of key cellular functions.Electronic supplementary materialThe online version of this article (doi:10.1186/s13059-017-1321-0) contains supplementary material, which is available to authorized users.

Platelet activation triggers thrombus formation in physiological and pathological conditions, such as acute coronary syndromes. Current therapies still fail to prevent thrombotic events in numerous patients, indicating that the mechanisms modulating platelet response during activation need to be clarified. The evidence that platelets are capable of de novo protein synthesis in response to stimuli raised the issue of how megakaryocyte-derived mRNAs are regulated in these anucleate cell fragments. Proteogenomics was applied here to investigate this phenomeon in platelets activated in vitro with Collagen or Thrombin Receptor Activating Peptide. Combining proteomics and transcriptomics allowed in depth platelet proteome characterization, revealing a significant effect of either stimulus on proteome composition. In silico analysis revealed the presence of resident immature RNAs in resting platelets, characterized by retained introns, while unbiased proteogenomics correlated intron removal by RNA splicing with changes on proteome composition upon activation. This allowed identification of a set of transcripts undergoing maturation by intron removal during activation and resulting in accumulation of the corresponding peptides at exon-exon junctions. These results indicate that RNA splicing events occur in platelets during activation and that maturation of specific pre-mRNAs is part of the activation cascade, contributing to a dynamic fine-tuning of the transcriptome.