miR-29b represses intestinal mucosal growth by inhibiting translation of cyclin-dependent kinase 2

Expression Patterns of miR-29b and miR-148a in Colostrum of Awassi Sheep With Higher Immunoglobulin G Levels

This study aimed to investigate the compositional parameters and expression patterns of miR-29b and miR-148a in sheep colostrum containing low and high levels of Immunoglobulin G (IgG). Blood and colostrum samples were collected within the first 6 h following birth from 24 pregnant Awassi sheep. On the basis of the determined colostrum IgG levels, low (Low IgG [LIGG], 44.83 ± 4.97 mg/mL) and high (High IgG [HIGG], 80.71 ± 3.31 mg/mL) groups were formed. In addition to measuring colostrum compositional parameters, expressions of miR-29b and miR-148a were determined in plasma and colostrum. Although somatic cell score (SCS), pH and electrical conductivity (EC) were higher, fat-free dry matter (FFDM), protein, lactose and freezing point were lower in HIGG group. Compared to LIGG, miR-29b was downregulated approximately 5-fold in the HIGG, whereas miR-148a was downregulated more than 3-fold in colostrum. There were negative correlations between colostrum miR-148a and colostrum IgG, SCS and pH. Colostrum IgG was positively correlated with pH and freezing point and negatively correlated with FFDM, protein and lactose. Area under the curve (AUC) values of SCS, pH, FFDM, protein, lactose, freezing point, EC and miR-148a (colostrum) were significant. Sensitivity and specificity of pH were 100% and 66.7%, of SCS were 81.8% and 66.7% and of miR-148a (Colostrum) were 75% and 75% in HIGG and LIGG. According to the results, miR-29b might be an important molecular target for lamb development, whereas miR-148a could be a potential biomarker for colostrum quality. Moreover, the study showed that SCS and pH might be useful diagnostic parameters for IgG status because of higher sensitivity rates and AUC values.

Posttranscriptional Regulation of Intestinal Mucosal Growth and Adaptation by Noncoding RNAs in Critical Surgical Disorders

The human intestinal epithelium has an impressive ability to respond to insults and its homeostasis is maintained by well-regulated mechanisms under various pathophysiological conditions. Nonetheless, acute injury and inhibited regeneration of the intestinal epithelium occur commonly in critically ill surgical patients, leading to the translocation of luminal toxic substances and bacteria to the bloodstream. Effective therapies for the preservation of intestinal epithelial integrity and for the prevention of mucosal hemorrhage and gut barrier dysfunction are limited, primarily because of a poor understanding of the mechanisms underlying mucosal disruption. Noncoding RNAs (ncRNAs), which include microRNAs (miRNAs), long ncRNAs (lncRNAs), circular RNAs (circRNAs), and small vault RNAs (vtRNAs), modulate a wide array of biological functions and have been identified as orchestrators of intestinal epithelial homeostasis. Here, we feature the roles of many important ncRNAs in controlling intestinal mucosal growth, barrier function, and repair after injury-particularly in the context of postoperative recovery from bowel surgery. We review recent literature surrounding the relationships between lncRNAs, microRNAs, and RNA-binding proteins and how their interactions impact cell survival, proliferation, migration, and cell-to-cell interactions in the intestinal epithelium. With advancing knowledge of ncRNA biology and growing recognition of the importance of ncRNAs in maintaining the intestinal epithelial integrity, ncRNAs provide novel therapeutic targets for treatments to preserve the gut epithelium in individuals suffering from critical surgical disorders.

Small non-coding RNAs and pancreatic ductal adenocarcinoma: Linking diagnosis, pathogenesis, drug resistance, and therapeutic potential

This review comprehensively investigates the intricate interplay between small non-coding RNAs (sncRNAs) and pancreatic ductal adenocarcinoma (PDAC), a devastating malignancy with limited therapeutic options. Our analysis reveals the pivotal roles of sncRNAs in various facets of PDAC biology, spanning diagnosis, pathogenesis, drug resistance, and therapeutic strategies. sncRNAs have emerged as promising biomarkers for PDAC, demonstrating distinct expression profiles in diseased tissues. sncRNA differential expression patterns, often detectable in bodily fluids, hold potential for early and minimally invasive diagnostic approaches. Furthermore, sncRNAs exhibit intricate involvement in PDAC pathogenesis, regulating critical cellular processes such as proliferation, apoptosis, and metastasis. Additionally, mechanistic insights into sncRNA-mediated pathogenic pathways illuminate novel therapeutic targets and interventions. A significant focus of this review is dedicated to unraveling sncRNA mechanisms underlying drug resistance in PDAC. Understanding these mechanisms at the molecular level is imperative for devising strategies to overcome drug resistance. Exploring the therapeutic landscape, we discuss the potential of sncRNAs as therapeutic agents themselves as their ability to modulate gene expression with high specificity renders them attractive candidates for targeted therapy. In summary, this review integrates current knowledge on sncRNAs in PDAC, offering a holistic perspective on their diagnostic, pathogenic, and therapeutic relevance. By elucidating the roles of sncRNAs in PDAC biology, this review provides valuable insights for the development of novel diagnostic tools and targeted therapeutic approaches, crucial for improving the prognosis of PDAC patients.

Interaction between microRNA-195 and HuR regulates Paneth cell function in the intestinal epithelium by altering SOX9 translation

Paneth cells at the bottom of small intestinal crypts secrete antimicrobial peptides, enzymes, and growth factors and contribute to pathogen clearance and maintenance of the stem cell niche. Loss of Paneth cells and their dysfunction occur commonly in various pathologies, but the mechanism underlying the control of Paneth cell function remains largely unknown. Here, we identified microRNA-195 (miR-195) as a repressor of Paneth cell development and activity by altering SOX9 translation via interaction with RNA-binding protein HuR. Tissue-specific transgenic expression of miR-195 (miR195-Tg) in the intestinal epithelium decreased the levels of mucosal SOX9 and reduced the numbers of lysozyme-positive (Paneth) cells in mice. Ectopically expressed SOX9 in the intestinal organoids derived from miR-195-Tg mice restored Paneth cell development ex vivo. miR-195 did not bind to Sox9 mRNA but it directly interacted with HuR and prevented HuR binding to Sox9 mRNA, thus inhibiting SOX9 translation. Intestinal mucosa from mice that harbored both Sox9 transgene and ablation of the HuR locus exhibited lower levels of SOX9 protein and Paneth cell numbers than those observed in miR-195-Tg mice. Inhibition of miR-195 activity by its specific antagomir improved Paneth cell function in HuR-deficient intestinal organoids. These results indicate that interaction of miR-195 with HuR regulates Paneth cell function by altering SOX9 translation in the small intestinal epithelium.NEW & NOTEWORTHY Our results indicate that intestinal epithelial tissue-specific transgenic miR-195 expression decreases the levels of SOX9 expression, along with reduced numbers of Paneth cells. Ectopically expressed SOX9 in the intestinal organoids derived from miR-195-Tg mice restores Paneth cell development ex vivo. miR-195 inhibits SOX9 translation by preventing binding of HuR to Sox9 mRNA. These findings suggest that interaction between miR-195 and HuR controls Paneth cell function via SOX9 in the intestinal epithelium.

miRNA Expression Analysis of IPEC-J2 Cells Damaged by Soybean 7S Globulin Reveals ssc-miR-221-5p as the Factor Alleviating Cell Damage

The most significant and sensitive antigen protein that causes diarrhea in weaned pigs is soybean 7S globulin. Therefore, identifying the primary target for minimizing intestinal damage brought on by soybean 7S globulin is crucial. MicroRNA (miRNA) is closely related to intestinal epithelium's homeostasis and integrity. However, the change of miRNAs' expression and the function of miRNAs in Soybean 7S globulin injured-IPEC-J2 cells are still unclear. In this study, the miRNAs' expression profile in soybean 7S globulin-treated IPEC-J2 cells was investigated. Fifteen miRNAs were expressed differently. The differentially expressed miRNA target genes are mainly concentrated in signal release, cell connectivity, transcriptional inhibition, and Hedgehog signaling pathway. Notably, we noticed that the most significantly decreased miRNA was ssc-miR-221-5p after soybean 7S globulin treatment. Therefore, we conducted a preliminary study on the mechanisms of ssc-miR-221-5p in soybean 7S globulin-injured IPEC-J2 cells. Our research indicated that ssc-miR-221-5p may inhibit ROS production to alleviate soybean 7S globulin-induced apoptosis and inflammation in IPEC-J2 cells, thus protecting the cellular mechanical barrier, increasing cell proliferation, and improving cell viability. This study provides a theoretical basis for the prevention and control of diarrhea of weaned piglets.

Aberrant miR-29 is a predictive feature of severe phenotypes in pediatric Crohn's disease

Crohn's disease (CD) is a chronic inflammatory gut disorder. Molecular mechanisms underlying the clinical heterogeneity of CD remain poorly understood. MicroRNAs (miRNAs) are important regulators of gut physiology, and several have been implicated in the pathogenesis of adult CD. However, there is a dearth of large-scale miRNA studies for pediatric CD. We hypothesized that specific miRNAs uniquely mark pediatric CD. We performed small RNA-Seq of patient-matched colon and ileum biopsies from treatment-naive pediatric patients with CD (n = 169) and a control cohort (n = 108). Comprehensive miRNA analysis revealed 58 miRNAs altered in pediatric CD. Notably, multinomial logistic regression analysis revealed that index levels of ileal miR-29 are strongly predictive of severe inflammation and stricturing. Transcriptomic analyses of transgenic mice overexpressing miR-29 show a significant reduction of the tight junction protein gene Pmp22 and classic Paneth cell markers. The dramatic loss of Paneth cells was confirmed by histologic assays. Moreover, we found that pediatric patients with CD with elevated miR-29 exhibit significantly lower Paneth cell counts, increased inflammation scores, and reduced levels of PMP22. These findings strongly indicate that miR-29 upregulation is a distinguishing feature of pediatric CD, highly predictive of severe phenotypes, and associated with inflammation and Paneth cell loss.

Gut Microbiota-MicroRNA Interactions in Intestinal Homeostasis and Cancer Development

Pre-clinical models and clinical studies highlight the significant impact of the host-microbiota relationship on cancer development and treatment, supporting the emerging trend for a microbiota-based approach in clinical oncology. Importantly, the presence of polymorphic microbes is considered one of the hallmarks of cancer. The epigenetic regulation of gene expression by microRNAs affects crucial biological processes, including proliferation, differentiation, metabolism, and cell death. Recent evidence has documented the existence of bidirectional gut microbiota-microRNA interactions that play a critical role in intestinal homeostasis. Importantly, alterations in microRNA-modulated gene expression are known to be associated with inflammatory responses and dysbiosis in gastrointestinal disorders. In this review, we summarize the current findings about miRNA expression in the intestine and focus on specific gut microbiota-miRNA interactions linked to intestinal homeostasis, the immune system, and cancer development. We discuss the potential clinical utility of fecal miRNA profiling as a diagnostic and prognostic tool in colorectal cancer, and demonstrate how the emerging trend of gut microbiota modulation, together with the use of personalized microRNA therapeutics, might bring improvements in outcomes for patients with gastrointestinal cancer in the era of precision medicine.

Long noncoding RNA uc.230/CUG-binding protein 1 axis sustains intestinal epithelial homeostasis and response to tissue injury

Intestinal epithelial integrity is commonly disrupted in patients with critical disorders, but the exact underlying mechanisms are unclear. Long noncoding RNAs transcribed from ultraconserved regions (T-UCRs) control different cell functions and are involved in pathologies. Here, we investigated the role of T-UCRs in intestinal epithelial homeostasis and identified T-UCR uc.230 as a major regulator of epithelial renewal, apoptosis, and barrier function. Compared with controls, intestinal mucosal tissues from patients with ulcerative colitis and from mice with colitis or fasted for 48 hours had increased levels of uc.230. Silencing uc.230 inhibited the growth of intestinal epithelial cells (IECs) and organoids and caused epithelial barrier dysfunction. Silencing uc.230 also increased IEC vulnerability to apoptosis, whereas increasing uc.230 levels protected IECs against cell death. In mice with colitis, reduced uc.230 levels enhanced mucosal inflammatory injury and delayed recovery. Mechanistic studies revealed that uc.230 increased CUG-binding protein 1 (CUGBP1) by acting as a natural decoy RNA for miR-503, which interacts with Cugbp1 mRNA and represses its translation. These findings indicate that uc.230 sustains intestinal mucosal homeostasis by promoting epithelial renewal and barrier function and that it protects IECs against apoptosis by serving as a natural sponge for miR-503, thereby preserving CUGBP1 expression.

MiR-29b-3p Inhibits the Inflammation Injury in Human Umbilical Vein Endothelial Cells by Regulating SEC23A

This study aims to investigate the effects of miR-29b-3p on the inflammation injury of human umbilical vein endothelial cells (HUVECs) induced by lipopolysaccharide (LPS) and explore the underlying mechanisms. The effects of different concentrations of LPS (0, 1, 5 and 10 μg/mL) on inflammation injury in HUVECs are detected by ELISA, CCK-8, EdU, flow cytometry and western blot analyses to determine the optimal stimulus concentration. After stimulating HUVECs with 10 μg/mL LPS, the expression levels of miR-29b-3p are detected, and the effects of miR-29b-3p on inflammation injury are detected by ELISA, CCK-8, EdU, flow cytometry and western blot analyses. Bioinformatic analysis, luciferase reporter assay and confirmatory experiments are applied to identify the target gene bound with miR-29b-3p. Rescue experiments have verified the roles of miR-29b-3p and the target gene in inflammation injury. We found that pro-inflammatory factor was increased, apoptosis was promoted, and cell proliferation was inhibited after the treatment of LPS in HUVECs. Overexpression of miR-29b-3p inhibited LPS-induced inflammatory response and apoptosis while promoting proliferation in HUVECs. Besides, bioinformatics analysis indicated that SEC23A was the target gene of miR-29b-3p and the confirmatory experiments showed that SEC23A was negatively correlated with miR-29b-3p and positively correlated with LPS concentration. Rescue experiments revealed that overexpression of SEC23A partially enhanced the inflammation injury effects in LPS-induced HUVECs with overexpression of miR-29b-3p. Hence, miR-29b-3p repressed inflammatory response, cell apoptosis and promoted cell proliferation in LPS-induced HUVECs by targeting SEC23A, providing a potential target for treating sepsis.

Circular RNA CircHIPK3 Promotes Homeostasis of the Intestinal Epithelium by Reducing MicroRNA 29b Function

BACKGROUND & AIMS

Circular RNAs (circRNAs) are a class of endogenous noncoding RNAs that form covalently closed circles. Although circRNAs influence many biological processes, little is known about their role in intestinal epithelium homeostasis. We surveyed circRNAs required to maintain intestinal epithelial integrity and identified circular homeodomain-interacting protein kinase 3 (circHIPK3) as a major regulator of intestinal epithelial repair after acute injury.

METHODS

Intestinal mucosal tissues were collected from mice exposed to cecal ligation and puncture for 48 hours and patients with inflammatory bowel diseases and sepsis. We isolated primary enterocytes from the small intestine of mice and derived intestinal organoids. The levels of circHIPK3 were silenced in intestinal epithelial cells (IECs) by transfection with small interfering RNAs targeting the circularization junction of circHIPK3 or elevated using a plasmid vector that overexpressed circHIPK3. Intestinal epithelial repair was examined in an in vitro injury model by removing part of the monolayer. The association of circHIPK3 with microRNA 29b (miR-29b) was determined by biotinylated RNA pull-down assays.

RESULTS

Genome-wide profile analyses identified ∼300 circRNAs, including circHIPK3, differentially expressed in the intestinal mucosa of mice after cecal ligation and puncture relative to sham mice. Intestinal mucosa from patients with inflammatory bowel diseases and sepsis had reduced levels of circHIPK3. Increasing the levels of circHIPK3 enhanced intestinal epithelium repair after wounding, whereas circHIPK3 silencing repressed epithelial recovery. CircHIPK3 silencing also inhibited growth of IECs and intestinal organoids, and circHIPK3 overexpression promoted intestinal epithelium renewal in mice. Mechanistic studies revealed that circHIPK3 directly bound to miR-29b and inhibited miR-29 activity, thus increasing expression of Rac1, Cdc42, and cyclin B1 in IECs after wounding.

CONCLUSIONS

In studies of mice, IECs, and human tissues, our results indicate that circHIPK3 improves repair of the intestinal epithelium at least in part by reducing miR-29b availability.

The RNA-binding protein HuR regulates intestinal epithelial restitution by modulating Caveolin-1 gene expression

The integrity of the intestinal mucosal barrier protects hosts against pathological conditions. Early mucosal restitution after wounding refers to epithelial cell migration into a defect. The RNA-binding protein HuR plays an important role in the posttranscriptional regulation of gene expression and is involved in many aspects of cellular physiology. In the present study, we investigated the role of HuR in the regulation of cell migration through the posttranscriptional regulation of Caveolin-1 (Cav-1). Online software was used to identify Cav-1 mRNA as a potential target of HuR. The interaction of HuR with Cav-1 mRNA was investigated via ribonucleoprotein immunoprecipitation (RNP IP) assays and biotin pulldown analysis. HuR was found to bind specifically to the Cav-1 3'-UTR rather than the coding region or 5'-UTR. Transfection of cells with siHuR decreased both HuR protein levels and Cav-1 protein levels; conversely, ectopic overexpression of HuR via infection of cells with an adenoviral vector containing HuR cDNA (AdHuR) increased Cav-1 protein levels without disturbing Cav-1 mRNA levels. Thus, HuR enhanced Cav-1 expression in vitro by stimulating Cav-1 translation. Intestinal epithelium-specific HuR knockout in mice decreased Cav-1 protein levels without changing Cav-1 mRNA levels, consistent with the in vitro results. Decreasing the levels of HuR via siHuR transfection inhibited early epithelial repair, but this effect was reversed by ectopic overexpression of GFP-tagged Cav-1. These results indicate that posttranscriptional regulation of Cav-1 gene expression by HuR plays a critical role in the regulation of rapid epithelial repair after wounding.

MicroRNA-195 regulates Tuft cell function in the intestinal epithelium by altering translation of DCLK1

Intestinal Tuft cells sense luminal contents to influence the mucosal immune response against eukaryotic infection. Paneth cells secrete antimicrobial proteins as part of the mucosal protective barrier. Defects in Tuft and Paneth cells occur commonly in various gut mucosal disorders. MicroRNA-195 (miR-195) regulates the stability and translation of target mRNAs and is involved in many aspects of cell processes and pathologies. Here, we reported the posttranscriptional mechanisms by which miR-195 regulates Tuft and Paneth cell function in the small intestinal epithelium. Mucosal tissues from intestinal epithelial tissue-specific miR-195 transgenic (miR195-Tg) mice had reduced numbers of double cortin-like kinase 1 (DCLK1)-positive (Tuft) and lysozyme-positive (Paneth) cells, compared with tissues from control mice, but there were no effects on Goblet cells and enterocytes. Intestinal organoids expressing higher miR-195 levels from miR195-Tg mice also exhibited fewer Tuft and Paneth cells. Transgenic expression of miR-195 in mice failed to alter growth of the small intestinal mucosa but increased vulnerability of the gut barrier in response to lipopolysaccharide (LPS). Studies aimed at investigating the mechanism underlying regulation of Tuft cells revealed that miR-195 directly interacted with the Dclk1 mRNA via its 3'-untranslated region and inhibited DCLK1 translation. Interestingly, the RNA-binding protein HuR competed with miR-195 for binding Dclk1 mRNA and increased DCLK1 expression. These results indicate that miR-195 suppresses the function of Tuft and Paneth cells in the small intestinal epithelium and further demonstrate that increased miR-195 disrupts Tuft cell function by inhibiting DCLK1 translation via interaction with HuR.

RNA-binding proteins and long noncoding RNAs in intestinal epithelial autophagy and barrier function

The intestinal autophagy and barrier function are crucial for maintaining the epithelium homeostasis and tightly regulated through well-controlled mechanisms. RNA-binding proteins (RBPs) and long noncoding RNAs (lncRNAs) modulate gene expression at the posttranscription level and are intimately involved in different physiological processes and diverse human diseases. In this review, we first highlight the roles of several RBPs and lncRNAs in the regulation of intestinal epithelial autophagy and barrier function, particularly focusing on the emerging evidence of RBPs and lncRNAs in the control of mRNA stability and translation. We additionally discuss recent findings that the interactions between RBPs and lncRNAs alter the fate of their target transcripts and thus influence gut epithelium host defense in response to stressful environments. These exciting advances in understanding the posttranscriptional control of the epithelial autophagy and barrier function by RBPs and lncRNAs provide a strong rationale for developing new effective therapeutics based on targeting RBPs and/or lncRNAs to preserve the intestinal epithelial integrity in patients with critical illnesses.

LncRNA TUG1 regulates the balance of HuR and miR-29b-3p and inhibits intestinal epithelial cell apoptosis in a mouse model of ulcerative colitis

This study aimed to investigate the role of long non-coding RNA (lncRNA) taurine up-regulated 1 (TUG1) in the development of ulcerative colitis (UC) and to explore the underlying mechanisms. A murine model of UC was induced by dextran sodium sulfate (DSS) exposure. The colonic epithelial YAMC cells were treated with TNF-α to simulate the inflammatory environment of intestinal epithelial cells (IECs). RNA pull-down and RIP assays were performed to analyze the interaction between TUG1 and HuR. Luciferase activity assay was conducted to evaluate the interaction between TUG1 and miR-29b-3p. Cell proliferation was evaluated by MTT assay. Cell apoptosis was assessed by flow cytometry and western blot analysis of apoptosis-related proteins. TUG1 overexpression promoted cell proliferation and inhibited cell apoptosis in the TNF-α-stimulated YAMC cells. The mechanistic analysis showed that TUG1 positively regulated the HuR/c-myc axis via its interaction with HuR, leading to upregulation of c-myc expression; meanwhile, TUG1 negatively regulated the miR-29b-3p/CDK2 signaling via binding to miR-29b-3p, leading to derepression of CDK2 expression. Further animal experiments showed that TUG1 overexpression attenuated UC progression in the DSS-induced UC in mice. Collectively, TUG1 inhibits IEC apoptosis and UC progression by regulating the balance of HuR and miR-29b-3p.

Exploration of Long Non-coding RNAs and Circular RNAs in Porcine Milk Exosomes

RNA in milk exosomes can be absorbed in the mammalian intestinal tract and function in gene expression regulations. Our previous work demonstrated that porcine milk exosomes (PME) contain large amounts of miRNAs and mRNAs. Increasing evidence suggests that long non-coding RNAs (lncRNAs) and circular RNAs (circRNAs) are of particular interest, given their key role in diverse biological processes of animals. However, the expression profiles and the potential functions of lncRNAs and circRNAs in PME are still unknown. In the present study, we isolated PME by ultracentrifugation and performed a comprehensive analysis of lncRNA and circRNA in PME by using RNA sequencing. As a result, 2,466 novel lncRNAs, 809 annotated lncRNAs, and 61 circRNAs were identified in PME. The lncRNAs shared similar characteristics with other mammals in terms of length, exon number, and open reading frames. However, lncRNAs showed a higher level compared with mRNAs. Eight lncRNAs and five circRNAs in PME were selected for PCR identification. A functional enrichment analysis on the target genes of lncRNAs indicated that these genes were involved in cellular macromolecule metabolic, RNA metabolic, and immune processes. The circRNAs host genes were enriched in nucleic acid binding and adherence junction. We also evaluated the potential interaction targets between miRNAs and PME lncRNAs or circRNAs, and the results showed that the PME lncRNAs and the circRNAs have a high density of miRNA target sites. The top 20 highly expressed lncRNAs were found to interact with the proliferation-related miRNAs, and the circRNAs potentially targeted many miRNAs that are associated with the intestinal barrier. This study is the first to provide a resource for lncRNA and circRNA research of porcine milk. Moreover, the potential interaction between lncRNA/circRNA and miRNA is revealed. The present study expands our knowledge of non-coding RNAs in milk, and additional research is necessary to confirm their exactly physiological functions.

RNA-binding protein HuR regulates translation of vitamin D receptor modulating rapid epithelial restitution after wounding

Homeostasis of the intestinal epithelium is tightly regulated by numerous extracellular and intracellular factors including vitamin D and the vitamin D receptor (VDR). VDR is highly expressed in the intestinal epithelium and is implicated in many aspects of gut mucosal pathophysiology, but the exact mechanism that controls VDR expression remains largely unknown. The RNA-binding protein human antigen R (HuR) regulates the stability and translation of target mRNAs and thus modulates various cellular processes and functions. Here we report a novel role of HuR in the posttranscriptional control of VDR expression in the intestinal epithelium. The levels of VDR in the intestinal mucosa decreased significantly in mice with ablated HuR, compared with control mice. HuR silencing in cultured intestinal epithelial cells (IECs) also reduced VDR levels, whereas HuR overexpression increased VDR abundance; neither intervention changed cellular Vdr mRNA content. Mechanistically, HuR bound to Vdr mRNA via its 3'-untranslated region (UTR) and enhanced VDR translation in IECs. Moreover, VDR silencing not only inhibited IEC migration over the wounded area in control cells but also prevented the increased migration in cells overexpressing HuR, although it did not alter IEC proliferation in vitro and growth of intestinal organoids ex vivo. The human intestinal mucosa from patients with inflammatory bowel diseases exhibited decreased levels of both HuR and VDR. These results indicate that HuR enhances VDR translation by directly interacting with its mRNA via 3'-UTR and that induced VDR by HuR is crucial for rapid intestinal epithelial restitution after wounding.

Interaction between HuR and circPABPN1 Modulates Autophagy in the Intestinal Epithelium by Altering ATG16L1 Translation

Intestinal epithelial autophagy is crucial for host defense against invasive pathogens, and defects in this process occur frequently in patients with inflammatory bowel disease (IBD) and other mucosal disorders, but the exact mechanism that activates autophagy is poorly defined. Here, we investigated the role of RNA-binding protein HuR (human antigen R) in the posttranscriptional control of autophagy-related genes (ATGs) in the intestinal epithelium. We found that targeted deletion of HuR in intestinal epithelial cells (IECs) specifically decreased the levels of ATG16L1 in the intestinal mucosa. Intestinal mucosa from patients with IBD exhibited reduced levels of both HuR and ATG16L1. HuR directly interacted with Atg16l1 mRNA via its 3' untranslated region and enhanced ATG16L1 translation, without affecting Atg16l1 mRNA stability. Circular RNA circPABPN1 blocked HuR binding to Atg16l1 mRNA and lowered ATG16L1 production. HuR silencing in cultured IECs also prevented rapamycin-induced autophagy, which was abolished by overexpressing ATG16L1. These findings indicate that HuR regulates autophagy by modulating ATG16L1 translation via interaction with circPABPN1 in the intestinal epithelium.

RNA-Binding Protein HuR Regulates Paneth Cell Function by Altering Membrane Localization of TLR2 via Post-transcriptional Control of CNPY3

BACKGROUND & AIMS

Paneth cells secrete antimicrobial proteins including lysozyme via secretory autophagy as part of the mucosal protective response. The ELAV like RNA-binding protein 1 (ELAVL1, also called HuR) regulates stability and translation of messenger RNAs (mRNAs) and many aspects of mucosal physiology. We studied the posttranscriptional mechanisms by which HuR regulates Paneth cell function.

METHODS

Intestinal mucosal tissues were collected from mice with intestinal epithelium (IE)-specific disruption of HuR (IE-HuR^-/-), HuR^fl/fl-Cre^- mice (controls), and patients with inflammatory bowel diseases and analyzed by histology and immunohistochemistry. Paneth cell functions were determined by lysozyme-immunostaining assays. We isolated primary enterocytes from IE-HuR^-/- and control mice and derived intestinal organoids. HuR and the chaperone CNPY3 were overexpressed from transgenes in intestinal epithelial cells (IECs) or knocked down with small interfering RNAs. We performed RNA pulldown assays to investigate interactions between HuR and its target mRNAs.

RESULTS

Intestinal tissues from IE-HuR^-/- mice had reduced numbers of Paneth cells, and Paneth cells had fewer lysozyme granules per cell, compared with tissues from control mice, but there were no effects on Goblet cells or enterocytes. Intestinal mucosa from patients with inflammatory bowel diseases had reduced levels of HuR and fewer Paneth cells. IE-HuR^-/- mice did not have the apical distribution of TLR2 in the intestinal mucosa as observed in control mice. IECs from IE-HuR^-/- mice expressed lower levels of CNPY3. Intestinal organoids from IE-HuR^-/- mice were smaller and contained fewer buds compared with those generated from controls, and had fewer lysozyme-positive cells. In IECs, knockdown of HuR decreased levels of the autophagy proteins LC3-I and LC3-II, compared with control cells, and prevented rapamycin-induced autophagy. We found HuR to interact directly with the Cnpy3 mRNA coding region and increase levels of CNPY3 by increasing the stability and translation of Cnpy3 mRNA. CNPY3 bound TLR2, and cells with knockdown of CNPY3 or HuR lost membrane localization of TLR2, but increased cytoplasmic levels of TLR2.

CONCLUSIONS

In studies of mice, IECs, and human tissues, we found HuR to increase expression of CNPY3 at the posttranscriptional level. CNPY3 is required for membrane localization of TLR2 and Paneth cell function.

RNA-Binding Protein HuR Regulates Rac1 Nucleocytoplasmic Shuttling Through Nucleophosmin in the Intestinal Epithelium

BACKGROUND & AIMS

The mammalian intestinal epithelium is a rapidly self-renewing tissue in the body, and its homeostasis is tightly regulated via well-controlled mechanisms. The RNA-binding protein HuR is essential for maintaining gut epithelial integrity, and targeted deletion of HuR in intestinal epithelial cells (IECs) disrupts mucosal regeneration and delays repair after injury. Here, we defined the role of HuR in regulating subcellular distribution of small guanosine triphosphatase Rac1 and investigated the implication of nucleophosmin (NPM) as a molecular chaperone in this process.

METHODS

Studies were conducted in intestinal epithelial tissue-specific HuR knockout (IE-HuR^-/-) mice and cultured IEC-6 cells, derived from rat small intestinal crypts. Functions of HuR and NPM in vitro were investigated via their gene silencing and overexpression.

RESULTS

The abundance of cytoplasmic Rac1 in the small intestinal mucosa increased significantly in IE-HuR^-/- mice, although HuR deletion did not alter total Rac1 levels. HuR silencing in cultured IECs also increased the cytoplasmic Rac1 levels, without an effect on whole-cell Rac1 content. In addition, HuR deficiency in the intestinal epithelium decreased the levels of NPM in IE-HuR^-/- mice and cultured IECs. NPM physically interacted with Rac1 and formed the NPM/Rac1 complex. NPM silencing decreased the NPM/Rac1 association and inhibited nuclear accumulation of Rac1, along with an increase in cytoplasmic abundances of Rac1. In contrast, ectopically expressed NPM enhanced Rac1 nuclear translocation and restored Rac1 subcellular localization to near normal in HuR-deficient cells.

CONCLUSIONS

These results indicate that HuR regulates Rac1 nucleocytoplasmic shuttling in the intestinal epithelium by altering NPM expression.

Long noncoding RNAs in intestinal epithelium homeostasis

The epithelium of the mammalian intestinal mucosa is a rapidly self-renewing tissue in the body, and its homeostasis is preserved through well-controlled mechanisms. Long noncoding RNAs (lncRNAs) regulate a variety of biological functions and are intimately involved in the pathogenesis of diverse human diseases. Here we highlight the roles of several lncRNAs expressed in the intestinal epithelium, including uc.173, SPRY4-IT1, H19, and Gata6, in maintaining the integrity of the intestinal epithelium, focusing on the emerging evidence of lncRNAs in the regulation of intestinal mucosal regeneration and epithelial barrier function. We also discuss recent results that the interactions between lncRNAs with microRNAs and the RNA-binding protein HuR influence epithelial homeostasis. With rapidly advancing knowledge of lncRNAs, there is also growing recognition that lncRNAs in the intestinal epithelium might be promising therapeutic targets in our efforts to protect the integrity of the intestinal epithelium in response to stressful environments.

Genetic and molecular origins of colorectal Cancer among the Iranians: an update

BACKGROUND

Colorectal cancer (CRC) is one the leading causes of cancer related deaths among Iranians. Despite the various progresses in new therapeutic methods, it has still a low rate of survival. This high ratio of mortality is mainly related to the late diagnosis, in which the patients refer for treatment in advanced stages of tumor. MAIN BODY: colorectal cancer progression is largely associated with molecular and genetic bases. Although Iran has a high ratio of CRC mortality, there is not an efficient genetic panel for detection and prognosis. Therefore, it is critical to introduce new diagnostic markers with ability to detect in early stages.

CONCLUSION

Present review summarizes all of the genetic and epigenetic factors which are reported in CRC until now among the Iranian patients to pave the way of incorporation of new ethnic specific markers into the clinical practice and development of new targeted therapeutic methods.

Regulation of Intestinal Epithelial Barrier Function by Long Noncoding RNA uc.173 through Interaction with MicroRNA 29b

The mammalian intestinal epithelium establishes a selectively permeable barrier that supports nutrient absorption and prevents intrusion by noxious luminal substances and microbiota. The effectiveness and integrity of the barrier function are tightly regulated via well-controlled mechanisms. Long noncoding RNAs transcribed from ultraconserved regions (T-UCRs) control diverse cellular processes, but their roles in the regulation of gut permeability remain largely unknown. Here we report that the T-UCR uc.173 enhances intestinal epithelial barrier function by antagonizing microRNA 29b (miR-29b). Decreasing the levels of uc.173 by gene silencing led to dysfunction of the intestinal epithelial barrier in cultured cells and increased the vulnerability of the gut barrier to septic stress in mice. uc.173 specifically stimulated translation of the tight junction (TJ) claudin-1 (CLDN1) by associating with miR-29b rather than by binding directly to CLDN1 mRNA. uc.173 acted as a natural decoy RNA for miR-29b, which interacts with CLDN1 mRNA via the 3' untranslated region and represses its translation. Ectopically expressed uc.173 abolished the association of miR-29b with CLDN1 mRNA and restored claudin-1 expression to normal levels in cells overexpressing miR-29b, thus rescuing the barrier function. These results highlight a novel function of uc.173 in controlling gut permeability and define a mechanism by which uc.173 stimulates claudin-1 translation, by decreasing the availability of miR-29b to CLDN1 mRNA.

Notch1 primes CD4 T cells for T helper type I differentiation through its early effects on miR-29

The transmembrane receptor, Notch1 plays an important role during the differentiation of CD4 T cells into T helper (Th) subsets in the presence of appropriate cytokines, including differentiation into Th1 cells. MicroRNAs have also been shown to be important regulators of immune responses, including negatively regulating cytokine production by Th1 cells. The miR-29 family of microRNAs can act to inhibit tbx21 and ifng transcription, two important pro-inflammatory genes that are abundantly expressed in Th1 cells. Here we show that Notch1 may prime CD4 T cells to be responsive to Th1-polarizing cues through its early repressive effects on the miR-29 family of microRNAs. Using a combination of cell lines and primary cells, we demonstrate that Notch1 can repress miR-29a, miR-29b, and miR-29c transcription through a mechanism that is independent of NF-κB. We further show that this repression is mediated by canonical Notch signaling and requires active Mastermind like (MAML) 1, but this process is superseded by positive regulation of miR-29 in response to IFNγ at later stages of CD4 T cell activation and differentiation. Collectively, our data suggest an additional mechanism by which Notch1 signaling may fine-tune Th1 cell differentiation.

Regulation of Cell Cycle Regulatory Proteins by MicroRNAs in Uterine Leiomyoma

The objective of this study was to determine whether miR-93, miR-29c, and miR-200c, which we previously reported to be downregulated in leiomyomas, target cell cycle regulatory proteins that influence cell proliferation. Based on TargetScan algorithm 3 cell cycle regulatory proteins namely, E2F transcription factor 1 (E2F1), Cyclin D1 (CCND1) and CDK2 which were predicted to be targets of these miRNAs were  further analyzed. In 30 hysterectomy specimens, we found the expression of E2F1 and CCND1 messenger RNA (mRNA) was increased in leiomyoma as compared to matched myometrium, with no significant changes in CDK2 mRNA levels. There was a significant increase in the abundance of all 3 proteins in leiomyoma in comparison with matched myometrium. Using luciferase reporter assay, we demonstrated E2F1 and CCND1 are targets of miR-93 and CDK2 is a target of miR-29c and miR-200c. We confirmed these findings through transfection studies in which transfection of primary leiomyoma cells with miR-93 resulted in a significant decrease in the expression of E2F1 and CCND1 mRNA and protein levels, whereas knockdown of miR-93 had the opposite effect. Similarly, overexpression of miR-29c and miR-200c in leiomyoma cells inhibited the expression of CDK2 protein and mRNA, whereas knockdown of this microRNAs (miRNA) had the opposite effect. Transfection of miR-29c, miR-200c, and miR-93 in primary leiomyoma cells resulted in a time-dependent inhibition of cell proliferation and cell motility. These results collectively indicate that the 3 miRNAs known to be downregulated in fibroid tumors are critical in regulation of cell proliferation because of their effects on 3 key cell cycle regulatory proteins, which are overexpressed in uterine leiomyomas.

Long Noncoding RNA uc.173 Promotes Renewal of the Intestinal Mucosa by Inducing Degradation of MicroRNA 195

BACKGROUND AND AIMS

The mammalian intestinal epithelium self-renews rapidly and homeostasis is preserved via tightly controlled mechanisms. Long noncoding RNAs transcribed from ultraconserved regions (T-UCRs) control different cell functions, but little is known about their role in maintaining the integrity of the intestinal epithelium. We searched for T-UCRs that regulate growth of the intestinal mucosa and investigated the mechanism by which T-UCR uc.173 regulates epithelial renewal.

METHODS

C57BL/6J mice were deprived of food for 48 hours in fasting experiments. Some mice were given intraperitoneal injections of a plasmid encoding LNA-anti-uc.173, to knock down endogenous uc.173. For studies using organoids, primary enterocytes were isolated from the intestine and transfected with the uc.173 transgene to increase uc.173 levels. Intestinal epithelial cells (Caco-2 and IEC-6 lines) were transfected with LNA-anti-uc.173 or uc.173 transgene. We quantified intestinal epithelial renewal based on BrdU incorporation, villus height and crypt depth, and cell number. The association of uc.173 with microRNA 195 (miRNA195) was determined by RNA pull-down assays.

RESULTS

Genome-wide profile analyses identified 21 T-UCRs, including uc.173, that were differentially expressed between intestinal mucosa of fasted vs non-fasted mice. Increasing levels of uc.173 by expression of a transgene increased growth of intestinal epithelial cells and organoids. Decreasing uc.173 levels by LNA-anti-uc.173 in mice reduced renewal of the intestinal epithelium. We found that uc.173 interacted directly with the primary transcript of miRNA195, leading to miRNA195 degradation.

CONCLUSIONS

In analyses of intestinal epithelial cells and mice, we identified uc.173 noncoding RNA that regulates growth of the intestinal mucosa and stimulates intestinal epithelial renewal by reducing levels of miRNA195.

Telmisartan inhibits hepatocellular carcinoma cell proliferation in vitro by inducing cell cycle arrest

Hepatocellular carcinoma (HCC) is the most common primary malignancy of the liver and the third leading cause of cancer-related death. Telmisartan, a widely used antihypertensive drug, is an angiotensin II type 1 (AT1) receptor blocker (ARB) that might inhibit cancer cell proliferation, but the mechanisms through which telmisartan affects various cancers remain unknown. The aim of the present study was to evaluate the effects of telmisartan on human HCC and to assess the expression of microRNAs (miRNAs). We studied the effects of telmisartan on HCC cells using the HLF, HLE, HepG2, HuH-7 and PLC/PRF/5 cell lines. In our experiments, telmisartan inhibited the proliferation of HLF, HLE and HepG2 cells, which represent poorly differentiated types of HCC cells. However, HuH-7 and PLC/PRF/5 cells, which represent well-differentiated types of HCC cells, were not sensitive to telmisartan. Telmisartan induced G₀/G₁ cell cycle arrest of HLF cells by inhibiting the G₀-to-G₁ cell cycle transition. This blockade was accompanied by a marked decrease in the levels of cyclin D1, cyclin E and other cell cycle-related proteins. Notably, the activity of the AMP-activated protein kinase (AMPK) pathway was increased, and the mammalian target of rapamycin (mTOR) pathway was inhibited by telmisartan treatment. Additionally, telmisartan increased the level of caspase-cleaved cytokeratin 18 (cCK18), partially contributed to the induction of apoptosis in HLF cells and reduced the phosphorylation of ErbB3 in HLF cells. Furthermore, miRNA expression was markedly altered by telmisartan in vitro. In conclusion, telmisartan inhibits human HCC cell proliferation by inducing cell cycle arrest.

Cooperative Repression of Insulin-Like Growth Factor Type 2 Receptor Translation by MicroRNA 195 and RNA-Binding Protein CUGBP1

Insulin-like growth factor type 2 (IGF2) receptor (IGF2R) recognizes mannose 6-phosphate-containing molecules and IGF2 and plays an important role in many pathophysiological processes, including gut mucosal adaptation. However, the mechanisms that control cellular IGF2R abundance are poorly known. MicroRNAs (miRNAs) and RNA-binding proteins (RBPs) critically regulate gene expression programs in mammalian cells by modulating the stability and translation of target mRNAs. Here we report that miRNA 195 (miR-195) and RBP CUG-binding protein 1 (CUGBP1) jointly regulate IGF2R expression at the posttranscriptional level in intestinal epithelial cells. Both miR-195 and CUGBP1 interacted with the 3' untranslated region (3'-UTR) of Igf2r mRNA, and the association of CUGBP1 with Igf2r mRNA enhanced miR-195 binding to Igf2r mRNA. Ectopically expressed CUGBP1 and miR-195 repressed IGF2R translation cooperatively without altering the stability of Igf2r mRNA. Importantly, the miR-195- and CUGBP1-repressed levels of cellular IGF2R led to a disruption in the structure of the trans-Golgi network. These findings indicate that IGF2R expression is controlled posttranscriptionally by two factors that associate with Igf2r mRNA and suggest that miR-195 and CUGBP1 dampen IGF signaling by inhibiting IGF2R translation.

HuR Enhances Early Restitution of the Intestinal Epithelium by Increasing Cdc42 Translation

The mammalian intestinal mucosa exhibits a spectrum of responses after acute injury and repairs itself rapidly to restore the epithelial integrity. The RNA-binding protein HuR regulates the stability and translation of target mRNAs and is involved in many aspects of gut epithelium homeostasis, but its exact role in the regulation of mucosal repair after injury remains unknown. We show here that HuR is essential for early intestinal epithelial restitution by increasing the expression of cell division control protein 42 (Cdc42) at the posttranscriptional level. HuR bound to the Cdc42 mRNA via its 3' untranslated region, and this association specifically enhanced Cdc42 translation without an effect on the Cdc42 mRNA level. Intestinal epithelium-specific HuR knockout not only decreased Cdc42 levels in mucosal tissues, but it also inhibited repair of damaged mucosa induced by mesenteric ischemia/reperfusion in the small intestine and by dextran sulfate sodium in the colon. Furthermore, Cdc42 silencing prevented HuR-mediated stimulation of cell migration over the wounded area by altering the subcellular distribution of F-actin. These results indicate that HuR promotes early intestinal mucosal repair after injury by increasing Cdc42 translation and demonstrate the importance of HuR deficiency in the pathogenesis of delayed mucosal healing in certain pathological conditions.

Tranilast Inhibits Genes Functionally Involved in Cell Proliferation, Fibrosis, and Epigenetic Regulation and Epigenetically Induces miR-29c Expression in Leiomyoma Cells

Tranilast (N-3,4-dimethoxycinnamoyl anthranilic acid) is an antiallergic agent with inhibitory effects on cell proliferation and extracellular matrix production. Here we assess the effect of tranilast on the expression of miR-29c and genes functionally involved in cell proliferation, fibrosis, and epigenetic regulation in isolated leiomyoma smooth muscle cells (LSMC). Tranilast significantly inhibited the rate of LSMC proliferation, which was associated with downregulation of cell cycle progression genes cyclin D1 (CCND1) and cyclin-dependent kinase 2 (CDK2) expression at messenger RNA and protein levels ( P < .05). Tranilast also suppressed the expression of collagen type I (COL1), collagen type III alpha 1 chain (COL3A1), the profibrotic cytokine, transforming growth factor β-3 (TGF-β3), DNA (cytosine-5)-methyltransferase 1 (DNMT1), and enhancer of zeste homolog 2 (EZH2), which regulate epigenetic status of gene promoters ( P < .05). Tranilast also significantly induced the expression of cellular and secreted miR-29c through downregulation of methylation status of miR-29c promoter ( P < .05). In addition, tranilast suppressed the activity of luciferase reporter containing 3'UTR of COL3A1 and CDK2, which are downstream targets of miR-29c ( P < .05). Knockdown of miR-29c expression attenuated the inhibitory effects of tranilast on COL3A1 and CDK2 protein expression ( P < .05). Collectively, these findings suggest that tranilast could have therapeutic potential as an inhibitory agent for leiomyoma growth and its associated symptoms.

Regulation of cyclin D1 by arsenic and microRNA inhibits adipogenesis

Low-dose chronic exposure to arsenic in drinking water represents a global public health concern with established risks for metabolic and cardiovascular disease, as well as cancer. While the linkage between arsenic and disease is strong, further understanding of the molecular mechanisms of its pathogenicity is required. Previous reports demonstrated the ability of arsenic to interfere with adipogenesis, which may mediate its effects in promoting metabolic disease. We hypothesized that microRNA are important regulators of most if not all mesenchymal stem cell processes that are dysregulated by arsenic exposure to impair lipogenesis. Arsenic increased the expression of miR-29b in white adipose tissue, as well as human mesenchymal stem cells (hMSCs) isolated from adipose tissue. Exposing hMSCs to arsenic increased abundance of miR-29b and cyclin D1 to promote proliferation over differentiation. Paradoxically, inhibition of miR-29b enhanced the inhibitory effect of arsenic on differentiation. This paradox was attributed to a requirement for miR-29 in regulating cyclin D1 expression as stable inhibition of miR-29b eliminated the cyclic pattern of cyclin D1 expression. Temporal regulation of cyclin D1 is critical for adipogenic differentiation, and the data suggest a paradigm where arsenic disruption of miR-29b regulatory pathways impairs adipogenic differentiation and ultimately adipose metabolic homeostasis.

Posttranscriptional regulation of intestinal epithelial integrity by noncoding RNAs

Maintenance of the gut epithelial integrity under stressful environments requires epithelial cells to rapidly elicit changes in gene expression patterns to regulate their survival, adapt to stress, and keep epithelial homeostasis. Disruption of the intestinal epithelial integrity occurs commonly in patients with various critical illnesses, leading to the translocation of luminal toxic substances and bacteria to the blood stream. Recently, noncoding RNAs (ncRNAs) have emerged as a novel class of master regulators of gene expression and are fundamentally involved in many aspects of gut mucosal regeneration, protection, and epithelial barrier function. Here, we highlight the roles of several intestinal epithelial tissue-specific microRNAs, including miR-222, miR-29b, miR-503, and miR-195, and long ncRNAs such as H19 and SPRY4-IT1 in the regulation of cell proliferation, apoptosis, migration, and cell-to-cell interactions and also further analyze the mechanisms through which ncRNAs and their interactions with RNA-binding proteins modulate the stability and translation of target mRNAs. WIREs RNA 2017, 8:e1399. doi: 10.1002/wrna.1399 For further resources related to this article, please visit the WIREs website.

Posttranscriptional regulation of 14-3-3ζ by RNA-binding protein HuR modulating intestinal epithelial restitution after wounding

The 14‐3‐3ζ is a member of the family of 14‐3‐3 proteins and participates in many aspects of cellular processes, but its regulation and involvement in gut mucosal homeostasis remain unknown. Here, we report that 14‐3‐3ζ expression is tightly regulated at the posttranscription level by RNA‐binding protein HuR and plays an important role in early intestinal epithelial restitution after wounding. The 14‐3‐3ζ was highly expressed in the mucosa of gastrointestinal tract and in cultured intestinal epithelial cells (IECs). The 3′ untranslated region (UTR) of the 14‐3‐3ζ mRNA was bound to HuR, and this association enhanced 14‐3‐3ζ translation without effect on its mRNA content. Conditional target deletion of HuR in IECs decreased the level of 14‐3‐3ζ protein in the intestinal mucosa. Silencing 14‐3‐3ζ by transfection with specific siRNA targeting the 14‐3‐3ζ mRNA suppressed intestinal epithelial restitution as indicated by a decrease in IEC migration after wounding, whereas ectopic overexpression of the wild‐type 14‐3‐3ζ promoted cell migration. These results indicate that HuR induces 14‐3‐3ζ translation via interaction with its 3′ UTR and that 14‐3‐3ζ is necessary for stimulation of IEC migration after wounding.

Novel miR-5582-5p functions as a tumor suppressor by inducing apoptosis and cell cycle arrest in cancer cells through direct targeting of GAB1, SHC1, and CDK2

MicroRNAs (miRNAs) play pivotal roles in tumorigenesis as either tumor suppressors or oncogenes. In the present study, we discovered and demonstrated the tumor suppressive function of a novel miRNA miR-5582-5p. miR-5582-5p induced apoptosis and cell cycle arrest in cancer cells, but not in normal cells. GAB1, SHC1, and CDK2 were identified as direct targets of miR-5582-5p. Knockdown of GAB1/SHC1 or CDK2 phenocopied the apoptotic or cell cycle arrest-inducing function of miR-5582-5p, respectively. The expression of miR-5582-5p was lower in tumor tissues than in adjacent normal tissues of colorectal cancer patients, while the expression of the target proteins exhibited patterns opposite to that of miR-5582-5p. Intratumoral injection of a miR-5582-5p mimic or induced expression of miR-5582-5p in tumor cells suppressed tumor growth in HCT116 xenografts. Collectively, our results suggest a novel tumor suppressive function for miR-5582-5p and its potential applicability for tumor control.

Post-transcriptional regulation of Wnt co-receptor LRP6 and RNA-binding protein HuR by miR-29b in intestinal epithelial cells

MicroRNAs (miRNAs) control gene expression by binding to their target mRNAs for degradation and/or translation repression and are implicated in many aspects of cellular physiology. Our previous study shows that miR-29b acts as a biological repressor of intestinal mucosal growth, but its exact downstream targets remain largely unknown. In the present study, we found that mRNAs, encoding Wnt co-receptor LRP6 (low-density lipoprotein-receptor-related protein 6) and RNA-binding protein (RBP) HuR, are novel targets of miR-29b in intestinal epithelial cells (IECs) and that expression of LRP6 and HuR is tightly regulated by miR-29b at the post-transcriptional level. miR-29b interacted with both Lrp6 and HuR mRNAs via their 3′-UTRs and inhibited LRP6 and HuR expression by destabilizing Lrp6 and HuR mRNAs and repressing their translation. Studies using heterologous reporter constructs revealed a greater repressive effect of miR-29b through a single binding site in the Lrp6 or HuR 3′-UTR, whereas deletion mutation of this site prevented miR-29b-induced repression of LRP6 and HuR expression. Repression of HuR by miR-29b in turn also contributed to miR-29b-induced LRP6 inhibition, since ectopic overexpression of HuR in cells overexpressing miR-29b restored LRP6 expression to near normal levels. Taken together, our results suggest that miR-29b inhibits expression of LRP6 and HuR post-transcriptionally, thus playing a role in the regulation of IEC proliferation and intestinal epithelial homoeostasis.

H19 Long Noncoding RNA Regulates Intestinal Epithelial Barrier Function via MicroRNA 675 by Interacting with RNA-Binding Protein HuR

The disruption of the intestinal epithelial barrier function occurs commonly in various pathologies, but the exact mechanisms responsible are unclear. The H19 long noncoding RNA (lncRNA) regulates the expression of different genes and has been implicated in human genetic disorders and cancer. Here, we report that H19 plays an important role in controlling the intestinal epithelial barrier function by serving as a precursor for microRNA 675 (miR-675). H19 overexpression increased the cellular abundance of miR-675, which in turn destabilized and repressed the translation of mRNAs encoding tight junction protein ZO-1 and adherens junction E-cadherin, resulting in the dysfunction of the epithelial barrier. Increasing the level of the RNA-binding protein HuR in cells overexpressing H19 prevented the stimulation of miR-675 processing from H19, promoted ZO-1 and E-cadherin expression, and restored the epithelial barrier function to a nearly normal level. In contrast, the targeted deletion of HuR in intestinal epithelial cells enhanced miR-675 production in the mucosa and delayed the recovery of the gut barrier function after exposure to mesenteric ischemia/reperfusion. These results indicate that H19 interacts with HuR and regulates the intestinal epithelial barrier function via the H19-encoded miR-675 by altering ZO-1 and E-cadherin expression posttranscriptionally.

Long noncoding RNA SPRY4-IT1 regulates intestinal epithelial barrier function by modulating the expression levels of tight junction proteins

Epithelial cells line the intestinal mucosa and form an important barrier to a wide array of noxious substances in the lumen. Disruption of the barrier integrity occurs commonly in various pathologies. Long noncoding RNAs (lncRNAs) control diverse biological processes, but little is known about the role of lncRNAs in regulation of the gut permeability. Here we show that the lncRNA SPRY4-IT1 regulates the intestinal epithelial barrier function by altering expression of tight junction (TJ) proteins. SPRY4-IT1 silencing led to dysfunction of the epithelial barrier in cultured cells by decreasing the stability of mRNAs encoding TJ proteins claudin-1, claudin-3, occludin, and JAM-1 and repressing their translation. In contrast, increasing the levels of SPRY4-IT1 in the intestinal mucosa protected the gut barrier in mice exposed to septic stress by increasing the abundance of TJ proteins. SPRY4-IT1 directly interacted with TJ mRNAs, and this process was enhanced through the association with the RNA-binding protein HuR. Of interest, the intestinal mucosa from patients with increased gut permeability exhibited a decrease in the levels of SPRY4-IT1. These findings highlight a novel role for SPRY4-IT1 in controlling the intestinal epithelial barrier and define a mechanism by which SPRY4-IT1 modulates TJ expression by altering the stability and translation of TJ mRNAs.

CUGBP1 and HuR regulate E-cadherin translation by altering recruitment of E-cadherin mRNA to processing bodies and modulate epithelial barrier function

The effectiveness and stability of epithelial barrier depend on apical junctional complexes, which consist of tight junctions (TJs) and adherens junctions (AJs). E-cadherin is the primary component of AJs, and it is essential for maintenance of cell-to-cell interactions and regulates the epithelial barrier. However, the exact mechanism underlying E-cadherin expression, particularly at the posttranscriptional level, remains largely unknown. RNA-binding proteins CUG-binding protein 1 (CUGBP1) and HU antigen R (HuR) are highly expressed in the intestinal epithelial tissues and modulate the stability and translation of target mRNAs. Here, we present evidence that CUGBP1 and HuR interact directly with the 3'-untranslated region of E-cadherin mRNA and regulate E-cadherin translation. CUGBP1 overexpression in Caco-2 cells inhibited E-cadherin translation by increasing the recruitment of E-cadherin mRNA to processing bodies (PBs), thus resulting in an increase in paracellular permeability. Overexpression of HuR exhibited an opposite effect on E-cadherin expression by preventing the translocation of E-cadherin mRNA to PBs and therefore prevented CUGBP1-induced repression of E-cadherin expression. Elevation of HuR also abolished the CUGBP1-induced epithelial barrier dysfunction. These findings indicate that CUGBP1 and HuR negate each other's effects in regulating E-cadherin translation by altering the recruitment of E-cadherin mRNA to PBs and play an important role in the regulation of intestinal barrier integrity under various pathophysiological conditions.

Circulating levels of the miRNAs, miR-194, and miR-29b, as clinically useful biomarkers for colorectal cancer

The microRNAs (miRNAs), miR-194 and miR-29b, have been shown to downregulate in colorectal cancer (CRC) and may identify and classify CRC patients as compared with those in control subjects. In the current study, we aimed to explore whether the serum levels of the miRNAs could be potential biomarkers for diagnosis and prognosis of CRC. A quantitative reverse-transcription polymerase chain reaction (qRT-PCR) assay was utilized to determine and compare serum levels of miR-194 and miR-29b in 55 patients with CRC and 55 control subjects. The correlations between levels of the miRNAs and clinicopathological stages of cancer were analyzed in patients. Receiver operating characteristic (ROC) curve and survival analyses were carried out, respectively, to determine diagnostic and prognostic values of the miRNAs. Serum levels of miR-194 and miR-29b were found to be significantly lower in CRC patients than those in control subjects (P < 0.0001). Moreover, serum levels of the miRNAs in patients were inversely correlated with the advanced TNM stages (P = 0.01). ROC curve and survival analyses revealed that reduced levels of the miRNAs could serve as diagnostic and prognostic biomarkers for patients with CRC (P = 0.0001). Serum levels of miR-194 and miR-29b may serve as potential biomarkers for diagnosis and prognosis of CRC.

miR-195 plays a role in steroid resistance of ulcerative colitis by targeting Smad7

An imbalance in pro- and anti-inflammation is an important mechanism of steroid resistance in UC (ulcerative colitis), and miRNAs may participate in this process. The present study aimed to explore whether miRNAs play a role in the steroid resistance of UC by regulating gene expression of the inflammation signal pathway. SS (steroid-sensitive) patients, SR (steroid-resistant) patients and healthy individuals were recruited. In vivo miRNA profiles of serum samples showed that miR-195 was decreased significantly in the SR group compared with the SS group (P<0.05). This result was confirmed by qPCR (quantitative real-time PCR) and miRNA ISH (in situ hybridization) in serum and colon tissue samples. Online software was used to identify Smad7 mRNA as a potential target of miR-195. The direct interaction of miR-195 and Smad7 mRNA was investigated using a biotinylated miR-195 pull-down assay. Overexpression of a miR-195 precursor lowered cellular levels of Smad7 protein; conversely, antagonism of miR-195 enhanced Smad7 translation without disturbing Smad7 mRNA levels. A luciferase reporter assay revealed a repressive effect of miR-195 via a single Smad7 3'-UTR target site, and point mutation of this site prevented miR-195-induced repression of Smad7 translation. Furthermore, increased levels of miR-195 led to a decrease in c-Jun and p65 expression. In contrast, transfection with anti-miR-195 led to increased levels of c-Jun and p65 protein. The decrease in miR-195 led to an increase in Smad7 expression and corresponding up-regulation of p65 and the AP-1 (activator protein 1) pathway, which might explain the mechanism of steroid resistance in UC patients.

Transgenic Expression of miR-222 Disrupts Intestinal Epithelial Regeneration by Targeting Multiple Genes Including Frizzled-7

Defects in intestinal epithelial integrity occur commonly in various pathologies. miR-222 is implicated in many aspects of cellular function and plays an important role in several diseases, but its exact biological function in the intestinal epithelium is underexplored. We generated mice with intestinal epithelial tissue-specific overexpression of miR-222 to investigate the function of miR-222 in intestinal physiology and diseases in vivo. Transgenic expression of miR-222 inhibited mucosal growth and increased susceptibility to apoptosis in the small intestine, thus leading to mucosal atrophy. The miR-222-elevated intestinal epithelium was vulnerable to pathological stress, since local overexpression of miR-222 not only delayed mucosal repair after ischemia/reperfusion-induced injury, but also exacerbated gut barrier dysfunction induced by exposure to cecal ligation and puncture. miR-222 overexpression also decreased expression of the Wnt receptor Frizzled-7 (FZD7), cyclin-dependent kinase 4 and tight junctions in the mucosal tissue. Mechanistically, we identified the Fzd7 messenger ribonucleic acid (mRNA) as a novel target of miR-222 and found that [miR-222/Fzd7 mRNA] association repressed Fzd7 mRNA translation. These results implicate miR-222 as a negative regulator of normal intestinal epithelial regeneration and protection by downregulating expression of multiple genes including the Fzd7. Our findings also suggest a novel role of increased miR-222 in the pathogenesis of mucosal growth inhibition, delayed healing and barrier dysfunction.

Competition between RNA-binding proteins CELF1 and HuR modulates MYC translation and intestinal epithelium renewal

The mammalian intestinal epithelium is one of the most rapidly self-renewing tissues in the body, and its integrity is preserved through strict regulation. The RNA-binding protein (RBP) ELAV-like family member 1 (CELF1), also referred to as CUG-binding protein 1 (CUGBP1), regulates the stability and translation of target mRNAs and is implicated in many aspects of cellular physiology. We show that CELF1 competes with the RBP HuR to modulate MYC translation and regulates intestinal epithelial homeostasis. Growth inhibition of the small intestinal mucosa by fasting in mice was associated with increased CELF1/Myc mRNA association and decreased MYC expression. At the molecular level, CELF1 was found to bind the 3'-untranslated region (UTR) of Myc mRNA and repressed MYC translation without affecting total Myc mRNA levels. HuR interacted with the same Myc 3'-UTR element, and increasing the levels of HuR decreased CELF1 binding to Myc mRNA. In contrast, increasing the concentrations of CELF1 inhibited formation of the [HuR/Myc mRNA] complex. Depletion of cellular polyamines also increased CELF1 and enhanced CELF1 association with Myc mRNA, thus suppressing MYC translation. Moreover, ectopic CELF1 overexpression caused G1-phase growth arrest, whereas CELF1 silencing promoted cell proliferation. These results indicate that CELF1 represses MYC translation by decreasing Myc mRNA association with HuR and provide new insight into the molecular functions of RBPs in the regulation of intestinal mucosal growth.

JunD enhances miR-29b levels transcriptionally and posttranscriptionally to inhibit proliferation of intestinal epithelial cells

Through its actions as component of the activating protein-1 (AP-1) transcription factor, JunD potently represses cell proliferation. Here we report a novel function of JunD in the regulation of microRNA expression in intestinal epithelial cells (IECs). Ectopically expressed JunD specifically increased the expression of primary and mature forms of miR-29b, whereas JunD silencing inhibited miR-29b expression. JunD directly interacted with the miR-29b1 promoter via AP-1-binding sites, whereas mutation of AP-1 sites from the miR-29b1 promoter prevented JunD-mediated transcriptional activation of the miR-29b1 gene. JunD also enhanced formation of the Drosha microprocessor complex, thus further promoting miR-29b biogenesis. Cellular polyamines were found to regulate miR-29b expression by altering JunD abundance, since the increase in miR-29b expression levels in polyamine-deficient cells was abolished by JunD silencing. In addition, miR-29b silencing prevented JunD-induced repression of IEC proliferation. Our findings indicate that JunD activates miR-29b by enhancing its transcription and processing, which contribute to the inhibitory effect of JunD on IEC growth and maintenance of gut epithelium homeostasis.

Modulation by miR-29b of intestinal epithelium homoeostasis through the repression of menin translation

Menin regulates distinct cellular functions by regulating gene transcription through its interaction with partner transcription factors, but the exact mechanisms that control menin levels remain largely unknown. In the present study we report that Men1 mRNA, encoding menin, is a novel target of miR-29b and that miR-29b/Men1 mRNA association regulates menin expression post-transcriptionally in rat intestinal epithelial cells (IECs). Overexpression of a miR-29b precursor lowered the levels of Men1 mRNA modestly, but reduced new synthesis of menin robustly; conversely, antagonism of miR-29b enhanced menin protein synthesis and steady-state levels. The repressive effect of miR-29b on menin expression was mediated through a single binding site in the coding region of Men1 mRNA, because point mutation of this site prevented miR-29b-induced repression of menin translation. Increasing cellular polyamines due to overexpression of ornithine decarboxylase (ODC) enhanced menin translation by reducing miR-29b, whereas polyamine depletion by inhibiting ODC increased it, thus suppressing menin expression. Moreover, an increase in menin abundance in an miR-29b-silenced population of IECs led to increased sensitivity to apoptosis, which was prevented by silencing menin. These findings indicate that miR-29b represses translation of Men1 mRNA, in turn affecting intestinal epithelial homoeostasis by altering IEC apoptosis.

The intestinal epithelial cell cycle: uncovering its 'cryptic' nature

PURPOSE OF REVIEW

To discuss the recent landmark findings that have increased our understanding not only of the role of the epithelial cell cycle in the homeostasis of the small intestine, but also its relevance to inflammation and cancer.

RECENT FINDINGS

Recent data have unveiled novel information on protein interactions directly involved in the cell cycle as well as in the pathways that transduce external environmental signals to the cell cycle. A growing body of the recent evidence confirms the importance of food as well as hormonal regulation in the gut on cell cycle. Information on the contribution of the epithelial microenvironment, including the microbiota, has grown substantially in the recent years as well as on the gene-environment interactions and the multiple epigenetic mechanisms involved in regulating cell-cycle proteins and signalling. Finally, further studies investigating the dysregulation of the cell cycle during inflammation and proliferation have increased our understanding of the pathophysiology of chronic inflammatory diseases and cancer.

SUMMARY

This review highlights some of the most recent advances that further emphasize the importance of the cell cycle in the small intestine during homeostasis as well as in inflammation and cancer.

The P-loop region of Schlafen 3 acts within the cytosol to induce differentiation of human Caco-2 intestinal epithelial cells

Schlafen 3 (Slfn3) mediates rodent enterocyte differentiation in vitro and in vivo, required for intestinal function. Little is known about Schlafen protein structure-function relationships. To define the Slfn3 domain that promotes differentiation, we studied villin and sucrase isomaltase (SI) promoter activity in Slfn3-null human Caco-2BBE cells transfected with full-length rat Slfn3 DNA or truncated constructs. Confocal microscopy and Western blots showed that Slfn3 is predominantly cytosolic. Villin promoter activity, increased by wild type Slfn3, was further enhanced by adding a nuclear exclusion sequence, suggesting that Slfn3 does not affect transcription by direct nuclear action. We therefore sought to dissect the region in Slfn3 stimulating promoter activity. Since examination of the Slfn3 N-terminal region revealed sequences similar to both an aminopeptidase (App) and a divergent P-loop resembling those in NTPases, we initially divided Slfn3 into an N-terminal domain containing the App and P-loop regions, and a C-terminal region. Only the N-terminal construct stimulated promoter activity. Further truncation indicated that both the App and the smaller P-loop constructs enhanced promoter activity similarly to the N-terminal sequence. Point mutations within the N-terminal region (R128L, altering a critical active site residue in the App domain, and L212D, conserved in Schlafens but variable in P-loop proteins) did not affect activity. These results show that Slfn3 acts in the cytosol to trigger a secondary signal cascade that elicits differentiation marker expression and narrows the active domain to the third of the Slfn3 sequence homologous to P-loop NTPases, a first step in understanding its mechanism of action.

Caveolin-1 enhances rapid mucosal restitution by activating TRPC1-mediated Ca2+ signaling

Early rapid mucosal restitution occurs as a consequence of epithelial cell migration to reseal superficial wounds, a process independent of cell proliferation. Our previous studies revealed that the canonical transient receptor potential-1 (TRPC1) functions as a store-operated Ca(2+) channel (SOCs) in intestinal epithelial cells (IECs) and regulates epithelial restitution after wounding, but the exact mechanism underlying TRPC1 activation remains elusive. Caveolin-1 (Cav1) is a major component protein that is associated with caveolar lipid rafts in the plasma membrane and was recently identified as a regulator of store-operated Ca(2+) entry (SOCE). Here, we showed that Cav1 plays an important role in the regulation of mucosal restitution by activating TRPC1-mediated Ca(2+) signaling. Target deletion of Cav1 delayed gastric mucosal repair after exposure to hypertonic NaCl in mice, although it did not affect total levels of TRPC1 protein. In cultured IECs, Cav1 directly interacted with TRPC1 and formed Cav1/TRPC1 complex as measured by immunoprecipitation assays. Cav1 silencing in stable TRPC1-transfected cells by transfection with siCav1 reduced SOCE without effect on the level of resting [Ca(2+)]cyt. Inhibition of Cav1 expression by siCav1 and subsequent decrease in Ca(2+) influx repressed epithelial restitution, as indicated by a decrease in cell migration over the wounded area, whereas stable ectopic overexpression of Cav1 increased Cav1/TRPC1 complex, induced SOCE, and enhanced cell migration after wounding. These results indicate that Cav1 physically interacts with and activates TRPC1, thus stimulating TRPC1-mediated Ca(2+) signaling and rapid mucosal restitution after injury.