Reduced DICER1 elicits an interferon response in endometrial cancer cells

PD-L1 expression is mediated by microRNA processing, Wnt/β-catenin signaling, and chemotherapy in Wilms tumor

Inhibition of immune checkpoint proteins is effective in adult cancers but has shown limited efficacy in pediatric cancers. While factors regulating expression of immune checkpoint proteins such as PD-L1 are well-documented in adult cancers, their regulation is poorly understood in pediatric cancers. Here, we show that PD-L1 is upregulated in distinct subsets of Wilms tumor, the most common pediatric kidney cancer. Specifically, chemotherapy-exposed Wilms tumor specimens exhibited higher levels of PD-L1 expression, and common chemotherapeutics upregulated PD-L1 in childhood cancer cell lines in vitro. Furthermore, mutations in CTNNB1 and DROSHA, the two most commonly mutated genes in Wilms tumor, correlated with higher PD-L1. Activation of Wnt/β-catenin signaling and knockdown of DROSHA or DICER1 both increase PD-L1 in vitro. Lastly, in adult cancers, DICER1 alterations are associated with immune gene expression signatures and improved survival in response to immune checkpoint inhibitors. Together, our results identify clinical and biological properties regulating PD-L1 in Wilms tumor that may inform precision therapy approaches in pediatric immuno-oncology.

Current advances in antiviral RNA interference in mammals

Mammals have potent innate immune systems that work together to fight against a variety of distinct viruses. In addition to interferon (IFN) response, which has been intensively studied, antiviral RNA interference (RNAi) is gradually being studied. However, previous studies indicated low Dicer activity on double-stranded RNA (dsRNA) substrates in vitro and that IFN response masks or inhibits antiviral RNAi in mammals. Therefore, whether or not the RNAi is functional for antiviral response in mammalian somatic cells is still an ongoing area of research. In this review, we will present the current advances in antiviral RNAi in mammals and focus on three fundamental questions critical to the intense debate about whether RNAi can function as an innate antiviral immunity in mammals.

Mouse B2 SINE elements function as IFN-inducible enhancers

Regulatory networks underlying innate immunity continually face selective pressures to adapt to new and evolving pathogens. Transposable elements (TEs) can affect immune gene expression as a source of inducible regulatory elements, but the significance of these elements in facilitating evolutionary diversification of innate immunity remains largely unexplored. Here, we investigated the mouse epigenomic response to type II interferon (IFN) signaling and discovered that elements from a subfamily of B2 SINE (B2_Mm2) contain STAT1 binding sites and function as IFN-inducible enhancers. CRISPR deletion experiments in mouse cells demonstrated that a B2_Mm2 element has been co-opted as an enhancer driving IFN-inducible expression of Dicer1. The rodent-specific B2 SINE family is highly abundant in the mouse genome and elements have been previously characterized to exhibit promoter, insulator, and non-coding RNA activity. Our work establishes a new role for B2 elements as inducible enhancer elements that influence mouse immunity, and exemplifies how lineage-specific TEs can facilitate evolutionary turnover and divergence of innate immune regulatory networks.

Dicer represses the interferon response and the double-stranded RNA-activated protein kinase pathway in mouse embryonic stem cells

Recent studies have demonstrated that embryonic stem cells (ESCs) are deficient in expressing type I interferons (IFN), the cytokines that play key roles in antiviral responses. However, the underlying molecular mechanisms and biological implications of this finding are poorly understood. In this study, we developed a synthetic RNA-based assay that can simultaneously assess multiple forms of antiviral responses. Dicer is an enzyme essential for RNA interference (RNAi), which is used as a major antiviral mechanism in invertebrates. RNAi activity is detected in wild-type ESCs but is abolished in Dicer knockout ESCs (D-/-ESCs) as expected. Surprisingly, D-/-ESCs have gained the ability to express IFN, which is otherwise deficient in wild-type ESCs. Furthermore, D-/-ESCs have constitutively active double-stranded RNA (dsRNA)-activated protein kinase (PKR), an enzyme that is also involved in antiviral response. D-/-ESCs show increased sensitivity to the cytotoxicity resulting from RNA transfection. The effects of dsRNA can be partly replicated with a synthetic B2RNA corresponding to the retrotransposon B2 short interspersed nuclear element. B2RNA has secondary structure features of dsRNA and accumulates in D-/-ESCs, suggesting that B2RNA could be a cellular RNA that activates PKR and contributes to the decreased cell proliferation and viability of D-/-ESCs. Treatment of D-/-ESCs with a PKR inhibitor and IFNβ-neutralizing antibodies increased cell proliferation rate and cell viability. Based on these findings, we propose that, in ESCs, Dicer acts as a repressor of antiviral responses and plays a key role in the maintenance of proliferation, viability, and pluripotency of ESCs.

Crosstalk Between Mammalian Antiviral Pathways

As part of their innate immune response against viral infections, mammals activate the expression of type I interferons to prevent viral replication and dissemination. An antiviral RNAi-based response can be also activated in mammals, suggesting that several mechanisms can co-occur in the same cell and that these pathways must interact to enable the best antiviral response. Here, we will review how the classical type I interferon response and the recently described antiviral RNAi pathways interact in mammalian cells. Specifically, we will uncover how the small RNA biogenesis pathway, composed by the nucleases Drosha and Dicer can act as direct antiviral factors, and how the type-I interferon response regulates the function of these. We will also describe how the factors involved in small RNA biogenesis and specific small RNAs impact the activation of the type I interferon response and antiviral activity. With this, we aim to expose the complex and intricate network of interactions between the different antiviral pathways in mammals.

DICER1: A Key Player in Rheumatoid Arthritis, at the Crossroads of Cellular Stress, Innate Immunity, and Chronic Inflammation in Aging

Loss-of-function or knockout mouse models have established a fundamental role for the RNAse III enzyme DICER1 in development and tissue morphogenesis and/or homeostasis. These functions are currently assumed to result mainly from the DICER1-dependent biogenesis of microRNAs which exhibit important gene expression regulatory properties. However, non-canonical DICER1 functions have recently emerged. These include interaction with the DNA damage response (DDR) pathway and the processing of cytotoxic non-coding RNAs, suggesting that DICER1 might also participate in the regulation of major cellular processes through miRNA-independent mechanisms. Recent findings indicated that reduced Dicer1 expression, which correlates with worsened symptoms in mouse models of joint inflammation, is also noted in fibroblast-like synoviocytes (FLS) harvested from rheumatoid arthritis (RA) patients, as opposed to FLS cultured from biopsies of osteoarthritic patients. In addition, low DICER1 levels are associated with the establishment of cellular stress and its associated responses, such as cellular senescence. Senescent and/or stressed cells are associated with an inflammatory secretome (cytokines and chemokines), as well as with "find-me" and "eat-me" signals which will attract and activate the innate immune compartment (NK cells, macrophages, and neutrophils) to be eliminated. Failure of this immunosurveillance mechanism and improper restauration of homeostasis could lead to the establishment of a systemic and chronic inflammatory state. In this review, we suggest that reduced DICER1 expression contributes to a vicious cycle during which accumulating inflammation and premature senescence, combined to inadequate innate immunity responses, creates the appropriate conditions for the initiation and/or progression of autoimmune-autoinflammatory diseases, such as RA.

Inhibition of PI3K-AKT-mTOR pathway sensitizes endometrial cancer cell lines to PARP inhibitors

BACKGROUND

Phosphatase and Tensin homolog (PTEN) is a tumor suppressor gene. Loss of its function is the most frequent genetic alteration in endometrioid endometrial cancers (70-80%) and high grade tumors (90%). We assessed the sensitivity of endometrial cancer cell lines to PARP inhibitors (olaparib and BMN-673) and a PI3K inhibitor (BKM-120), alone or in combination, in the context of their PTEN mutation status. We also highlighted a direct pathway linking PTEN to DNA repair.

METHODS

Using endometrial cancer cellular models with known PTEN status, we evaluated their homologous recombination (HR) functionality by RAD51 foci formation assay. The 50% Inhibitory concentration (IC50) of PI3K and PARP inhibitors in these cells was assessed, and western blotting was performed to determine the expression of proteins involved in the PI3K/mTOR pathway. Moreover, we explored the interaction between RAD51 and PI3K/mTOR by immunofluorescence. Next, the combination effect of PI3K and PARP inhibitors on cell proliferation was evaluated by a clonogenic assay.

RESULTS

Cells with mutated PTEN showed over-activation of the PI3K/mTOR pathway. These cells were more sensitive to PARP inhibition compared to PTEN wild-type cells. In addition, PI3K inhibitor treatment reduced RAD51 foci formation in PTEN mutated cells, and sensitized these cells to PARP inhibitor.

CONCLUSION

Targeting both PARP and PI3K might lead to improved personalized therapeutic approaches in endometrial cancer patients with PTEN mutations. Understanding the complex interaction of PTEN mutations with DNA repair in endometrial cancer will help to better select patients that are likely to respond to some of the new and costly targeted therapies.

Dicer1 dysfunction promotes stemness and aggression in endometrial carcinoma

Endometrial carcinoma is one of the most common gynecological malignancies, but the molecular events involved in the development and progression of endometrial carcinoma remain unclear. Dicer1 and cancer stem cells play important roles in cell motility and survival. This study investigated the role of the let-7 family and Dicer1 in the stemness of endometrial carcinoma cells. We profiled Dicer1 expression in clinical samples and explored its relationship with stem cell-associated markers and clinical parameters. We showed that Dicer1 dysfunction leads to the enrichment of tumor stemness features and tumor aggression both in vitro and in vivo. We also identified the mechanism related to this potential tumor-predisposing phenotype: loss of Dicer1 induced abnormal expression of the let-7 family, which comprises well-known tumor suppressors, thus regulating stemness in endometrial carcinoma cells.

Effects of Sodium Butyrate Treatment on Histone Modifications and the Expression of Genes Related to Epigenetic Regulatory Mechanisms and Immune Response in European Sea Bass (Dicentrarchus Labrax) Fed a Plant-Based Diet

Bacteria that inhabit the epithelium of the animals' digestive tract provide the essential biochemical pathways for fermenting otherwise indigestible dietary fibers, leading to the production of short-chain fatty acids (SCFAs). Of the major SCFAs, butyrate has received particular attention due to its numerous positive effects on the health of the intestinal tract and peripheral tissues. The mechanisms of action of this four-carbon chain organic acid are different; many of these are related to its potent regulatory effect on gene expression since butyrate is a histone deacetylase inhibitor that play a predominant role in the epigenetic regulation of gene expression and cell function. In the present work, we investigated in the European sea bass (Dicentrarchus labrax) the effects of butyrate used as a feed additive on fish epigenetics as well as its regulatory role in mucosal protection and immune homeostasis through impact on gene expression. Seven target genes related to inflammatory response and reinforcement of the epithelial defense barrier [tnfα (tumor necrosis factor alpha) il1β, (interleukin 1beta), il-6, il-8, il-10, and muc2 (mucin 2)] and five target genes related to epigenetic modifications [dicer1(double-stranded RNA-specific endoribonuclease), ehmt2 (euchromatic histone-lysine-N-methyltransferase 2), pcgf2 (polycomb group ring finger 2), hdac11 (histone deacetylase-11), and jarid2a (jumonji)] were analyzed in fish intestine and liver. We also investigated the effect of dietary butyrate supplementation on histone acetylation, by performing an immunoblotting analysis on liver core histone extracts. Results of the eight-week-long feeding trial showed no significant differences in weight gain or SGR (specific growth rate) of sea bass that received 0.2% sodium butyrate supplementation in the diet in comparison to control fish that received a diet without Na-butyrate. Dietary butyrate led to a twofold increase in the acetylation level of histone H4 at lysine 8, but showed no effect on the histone H3 at Lys9. Moreover, two different isoforms of histone H3 that might correspond to the H3.1 and H3.2 isoforms previously found in terrestrial animals were separated on the immunoblots. The expression of four (il1 β, il8, irf1, and tnfα) out of seven analyzed genes related to mucosal protection and inflammatory response was significantly different between the two analyzed tissues but only il10 showed differences in expression due to the interaction between tissue and butyrate treatment. In addition, butyrate caused significant changes in vivo in the expression of genes related to epigenetic regulatory mechanisms such as hdac11, ehmt2, and dicer1. Statistical analysis by two-way ANOVA for these genes showed not only significant differences due to the butyrate treatment, but also due to the interaction between tissue and treatment.

Inhibiting DNA Methylation Causes an Interferon Response in Cancer via dsRNA Including Endogenous Retroviruses

We show that DNA methyltransferase inhibitors (DNMTis) upregulate immune signaling in cancer through the viral defense pathway. In ovarian cancer (OC), DNMTis trigger cytosolic sensing of double-stranded RNA (dsRNA) causing a type I interferon response and apoptosis. Knocking down dsRNA sensors TLR3 and MAVS reduces this response 2-fold and blocking interferon beta or its receptor abrogates it. Upregulation of hypermethylated endogenous retrovirus (ERV) genes accompanies the response and ERV overexpression activates the response. Basal levels of ERV and viral defense gene expression significantly correlate in primary OC and the latter signature separates primary samples for multiple tumor types from The Cancer Genome Atlas into low versus high expression groups. In melanoma patients treated with an immune checkpoint therapy, high viral defense signature expression in tumors significantly associates with durable clinical response and DNMTi treatment sensitizes to anti-CTLA4 therapy in a pre-clinical melanoma model.

The role of microRNAs in the pathogenesis of endometrial cancer: a systematic review

INTRODUCTION

Epigenetics seem to play a primary role in the current research on the pathogenesis of different types of endometrial cancer. Data so far indicate that microRNAs regulate different pathways that could lead to carcinogenesis when not functioning properly. The aim of this review is to summarize current knowledge on microRNAs that have been associated with endometrial cancer development.

MATERIAL AND METHODS

From July 2014 to August 2014, we conducted a comprehensive research utilizing major online search engines (Pubmed, Crossref, Google Scholar). The main keywords used in our search were endometrial cancer/carcinoma; microRNA; epigenetics; novel biomarkers; pathogenesis.

RESULTS

Overall, we identified 155 studies, although only 77 were eligible for this review. Different miRNAs were identified to contribute either promoting the carcinogenesis in the endometrium or inhibiting different steps of endometrial cancer development. Tumour growth, cell proliferation, apoptosis and invasion metastasis have been identified as the main processes where miRNAs seem to be implicated.

CONCLUSIONS

microRNAs are effective regulators of gene expression that has a significant role in the pathogenesis of endometrial cancer. Research concerning possible therapeutic implications has been promising, although there is still a significant distance to be covered between research observations and clinical results. Extensive preclinical and translational research is still required to improve the efficacy and minimize unwanted effects of miRNAs-based therapy.

Immune regulation by low doses of the DNA methyltransferase inhibitor 5-azacitidine in common human epithelial cancers

Epigenetic therapy is emerging as a potential therapy for solid tumors. To investigate its mechanism of action, we performed integrative expression and methylation analysis of 63 cancer cell lines (breast, colorectal, and ovarian) after treatment with the DNA methyltransferase inhibitor 5-azacitidine (AZA). Gene Set Enrichment Analysis demonstrated significant enrichment for immunomodulatory pathways in all three cancers (14.4-31.3%) including interferon signaling, antigen processing and presentation, and cytokines/chemokines. Strong upregulation of cancer testis antigens was also observed. An AZA IMmune gene set (AIMs) derived from the union of these immunomodulatory pathway genes classified primary tumors from all three types, into "high" and "low" AIM gene expression subsets in tumor expression data from both TCGA and GEO. Samples from selected patient biopsies showed upregulation of AIM genes after treatment with epigenetic therapy. These results point to a broad immune stimulatory role for DNA demethylating drugs in multiple cancers.

ARF and p53 coordinate tumor suppression of an oncogenic IFN-β-STAT1-ISG15 signaling axis

The ARF and p53 tumor suppressors are thought to act in a linear pathway to prevent cellular transformation in response to various oncogenic signals. Here, we show that loss of p53 leads to an increase in ARF protein levels, which function to limit the proliferation and tumorigenicity of p53-deficient cells by inhibiting an IFN-β-STAT1-ISG15 signaling axis. Human triple-negative breast cancer (TNBC) tumor samples with coinactivation of p53 and ARF exhibit high expression of both STAT1 and ISG15, and TNBC cell lines are sensitive to STAT1 depletion. We propose that loss of p53 function and subsequent ARF induction creates a selective pressure to inactivate ARF and propose that tumors harboring coinactivation of ARF and p53 would benefit from therapies targeted against STAT1 and ISG15 activation.

MicroRNAs: The Missing Link in the Biology of Graft-Versus-Host Disease?

Graft-versus-host disease (GVHD) is still the major complication of allogeneic hematopoietic stem cell transplantation. Despite extensive studies in understanding the pathophysiology of GVHD, its pathogenesis remains unclear. Recently, important functions of microRNAs have been demonstrated in various autoimmune diseases and cancers such as psoriasis and lymphoma. This review highlights the need to investigate the role of microRNAs in GVHD and hypothesizes that microRNAs may be one of the missing links in our understanding of GVHD, with the potential for novel therapeutics.

Glycogen synthase kinase 3β inhibition as a therapeutic approach in the treatment of endometrial cancer

Alternative strategies beyond current chemotherapy and radiation therapy regimens are needed in the treatment of advanced stage and recurrent endometrial cancers. There is considerable promise for biologic agents targeting the extracellular signal-regulated kinase (ERK) pathway for treatment of these cancers. Many downstream substrates of the ERK signaling pathway, such as glycogen synthase kinase 3β (GSK3β), and their roles in endometrial carcinogenesis have not yet been investigated. In this study, we tested the importance of GSK3β inhibition in endometrial cancer cell lines and in vivo models. Inhibition of GSK3β by either lithium chloride (LiCl) or specific GSK3β inhibitor VIII showed cytostatic and cytotoxic effects on multiple endometrial cancer cell lines, with little effect on the immortalized normal endometrial cell line. Flow cytometry and immunofluorescence revealed a G2/M cell cycle arrest in both type I (AN3CA, KLE, and RL952) and type II (ARK1) endometrial cancer cell lines. In addition, LiCl pre-treatment sensitized AN3CA cells to the chemotherapy agent paclitaxel. Administration of LiCl to AN3CA tumor-bearing mice resulted in partial or complete regression of some tumors. Thus, GSK3β activity is associated with endometrial cancer tumorigenesis and its pharmacologic inhibition reduces cell proliferation and tumor growth.