Conventional tumor markers for non-invasive diagnosis of gastric cancer (GC) exhibit insufficient sensitivity and specificity to facilitate detection of early gastric cancer (EGC). We aimed to identify EGC-specific exosomal lncRNA biomarkers that are highly sensitive and stable for the non-invasive diagnosis of EGC. Hence, in the present study, exosomes from the plasma of five healthy individuals and ten stage I GC patients and from culture media of four human primary stomach epithelial cells and four gastric cancer cells (GCCs) were isolated. Exosomal RNA profiling was performed using RNA sequencing to identify EGC-specific exosomal lncRNAs. A total of 79 and 285 exosomal RNAs were expressed at significantly higher levels in stage I GC patients and GCCs, respectively, than that in normal controls. Through combinational analysis of the RNA sequencing results, we found two EGC-specific exosomal lncRNAs, lncUEGC1 and lncUEGC2, which were further confirmed to be remarkably up-regulated in exosomes derived from EGC patients and GCCs. Furthermore, stability testing demonstrates that almost all the plasma lncUEGC1 was encapsulated within exosomes and thus protected from RNase degradation. The diagnostic accuracy of exosomal lncUEGC1 was evaluated, and lncUEGC1 exhibited AUC values of 0.8760 and 0.8406 in discriminating EGC patients from healthy individuals and those with premalignant chronic atrophic gastritis, respectively, which was higher than the diagnostic accuracy of carcinoembryonic antigen. Consequently, exosomal lncUEGC1 may be promising in the development of highly sensitive, stable, and non-invasive biomarkers for EGC diagnosis.Electronic supplementary materialThe online version of this article (10.1186/s12943-018-0834-9) contains supplementary material, which is available to authorized users.

SummaryWnt signalling through b-catenin and the lymphoid-enhancing factor 1/T-cell factor (LEF1/TCF) family of transcription factors maintains stem cell properties in both normal and malignant tissues; however, the underlying molecular pathway involved in this process has not been completely defined. Using a microRNA microarray screening assay, we identified let-7 miRNAs as downstream targets of the Wnt-b-catenin pathway. Expression studies indicated that the Wnt-b-catenin pathway suppresses mature let-7 miRNAs but not the primary transcripts, which suggests a post-transcriptional regulation of repression. Furthermore, we identified Lin28, a negative let-7 biogenesis regulator, as a novel direct downstream target of the Wnt-b-catenin pathway. Loss of function of Lin28 impairs Wnt-bcatenin-pathway-mediated let-7 inhibition and breast cancer stem cell expansion; enforced expression of let-7 blocks the Wnt-b-catenin pathway-stimulated breast cancer stem cell phenotype. Finally, we demonstrated that the Wnt-b-catenin pathway induces Lin28 upregulation and let-7 downregulation in both cancer samples and mouse tumour models. Moreover, the delivery of a modified lin28 siRNA or a let-7a agomir into the premalignant mammary tissues of MMTV-wnt-1 mice resulted in a complete rescue of the stem cell phenotype driven by the Wnt-b-catenin pathway. These findings highlight a pivotal role for Lin28/let-7 in Wnt-b-catenin-pathwaymediated cellular phenotypes. Thus, the Wnt-b-catenin pathway, Lin28 and let-7 miRNAs, three of the most crucial stem cell regulators, connect in one signal cascade.

Resent studies have identified Pygopus as a core component of the ␤-catenin/T-cell factor (TCF)/ lymphoid-enhancing factor 1 (LEF) transcriptional activation complex required for the expression of canonical Wg/Wnt target genes in Drosophila. However, the biochemical involvement of mammalian Pygopus proteins in ␤-catenin/TCF/LEF gene activation remains controversial. In this study, we perform a series of molecular/biochemical experiments to demonstrate that Pygo2 associates with histone-modifying enzymatic complexes, specifically the MLL2 histone methyltransferase (HMT) and STAGA histone acetyltransferase (HAT) complexes, to facilitate their interaction with ␤-catenin and to augment Wnt1-induced, TCF/LEF-dependent transcriptional activation in breast cancer cells. We identify a critical domain in Pygo2 encompassing the first 47 amino acids that mediates its HMT/HAT interaction. We further demonstrate the importance of this domain in Pygo2's ability to transcriptionally activate both artificial and endogenous Wnt target genes and to expand breast cancer stem-like cells in culture. This work now links mechanistically Pygo2's role in histone modification to its enhancement of the Wntdependent transcriptional program and cancer stem-like cell expansion.Epigenetic regulation underlies tissue development, homeostasis, and tumorigenesis and includes the modification of the chromatin in transcriptional activation or repression. The basic repeating unit of the chromatin is the nucleosome consisting of 146 bp of DNA wrapped around a histone octamer containing two copies of each of the histones H2A, H2B, H3, and H4. Methylation and acetylation of lysine (K) residues on histone H3 and H4 tails confer either activating or silencing effects on transcription. Dimethylation (me2) and trimethylation (me3) of H3K4 and acetylation (Ac) of H3K9/K14 are associated with transcriptional activation while H3K9 and H3K27 methylation is associated with transcriptional repression (49). Histone methylation is catalyzed by histone methyltransferases (HMTs) and reversed by histone demethylases, whereas the steady-state acetylation levels of histone proteins are achieved by the actions of histone acetyltransferases (HATs) and histone deacetylases (HDACs) (11, 42).In Saccharomyces cerevisiae, a multisubunit complex containing the Drosophila trithorax-related protein Set1 has been shown to be responsible for mono-, di-, and trimethylation of histone H3K4 (7). In humans, multiple Set1-like HMT complexes with H3K4 HMT activities have been identified (12). Each of these complexes contains the SET domain-containing homologs of yeast Set1, including human Set1 (hSet1), MLL1 (mixed-lineage leukemia 1, also known as MLL, HRX, ALL1, or KMT2A), MLL2 (mixed-lineage leukemia 2, also known as HRX2 or KMT2B), MLL3 (mixed-lineage leukemia 3, also known as HALR or KMT2C), and MLL4 (mixed-lineage leukemia 4, also known as ALR or KMT2D) (2,16,22,30,37,46), which carry the enzymatic activity for the associated complexes. RbBP5, WDR5, and Ash2L, which are homologs ...

SummaryWnt-b-catenin signaling participates in the epithelial-mesenchymal transition (EMT) in a variety of cancers; however, its involvement in hepatocellular carcinoma (HCC) and downstream molecular events is largely undefined. HNF4a is the most prominent and specific factor maintaining the differentiation of hepatic lineage cells and a potential EMT regulator in HCC cells. However, the molecular mechanisms by which HNF4a maintains the differentiated liver epithelium and inhibits EMT have not been completely defined. In this study, we systematically explored the relationship between Wnt-b-catenin signaling and HNF4a in the EMT process of HCC cells. Our results indicated that HNF4a expression was negatively regulated during Wnt-b-catenin signaling-induced EMT through Snail and Slug in HCC cells. In contrast, HNF4a was found to directly associate with TCF4 to compete with b-catenin but facilitate transcription corepressor activities, thus inhibiting expression of EMT-related Wnt-b-catenin targets. Moreover, HNF4a may control the switch between the transcriptional and adhesion functions of b-catenin. Overexpression of HNF4a was found to completely compromise the Wnt-b-catenin-signaling-induced EMT phenotype. Finally, we determined the regulation pattern between Wnt-b-catenin signaling and HNF4a in rat tumor models. Our studies have identified a double-negative feedback mechanism controlling Wnt-b-catenin signaling and HNF4a expression in vitro and in vivo, which sheds new light on the regulation of EMT in HCC. The modulation of these molecular processes may be a method of inhibiting HCC invasion by blocking Wnt-b-catenin signaling or restoring HNF4a expression to prevent EMT.