Human SLFN5 is a transcriptional co-repressor of STAT1-mediated interferon responses and promotes the malignant phenotype in glioblastoma

The role of interferon beta in neurological diseases and its potential therapeutic relevance

Interferon beta (IFNβ) is a member of the type-1 interferon family and has various immunomodulatory functions in neuropathological conditions. Although the level of IFNβ is low under healthy conditions, it is increased during inflammatory processes to protect the central nervous system (CNS). In particular, microglia and astrocytes are the main sources of IFNβ upon inflammatory insult in the CNS. The protective effects of IFNβ are well characterized in reducing the progression of multiple sclerosis (MS); however, little is understood about its effects in other neurological/neurodegenerative diseases. In this review, different types of IFNs and their signaling pathways will be described. Then we will focus on the potential role and therapeutic effect of IFNβ in several CNS-related diseases such as Alzheimer's disease, Parkinson's disease, Huntington's disease, amyotrophic lateral sclerosis, stroke, spinal cord injury, prion disease and spinocerebellar ataxia 7.

Feasibility of Using a Type I IFN-Based Non-Animal Approach to Predict Vaccine Efficacy and Safety Profiles

Animal-based tests are used for the control of vaccine quality. However, because highly purified and safe vaccines are now available, alternative approaches that can replace or reduce animal use for the assessment of vaccine outcomes must be established. In vitro tests for vaccine quality control exist and have already been implemented. However, these tests are specifically designed for some next-generation vaccines, and this makes them not readily available for testing other vaccines. Therefore, universal non-animal tests are still needed. Specific signatures of the innate immune response could represent a promising approach to predict the outcome of vaccines by non-animal methods. Type I interferons (IFNs) have multiple immunomodulatory activities, which are exerted through effectors called interferon stimulated genes (ISGs), and are one of the most important immune signatures that might provide potential candidate molecular biomarkers for this purpose. This paper will mainly examine if this idea might be feasible by analyzing all relevant published studies that have provided type I IFN-related biomarkers for evaluating the safety and efficacy profiles of vaccines using an advanced transcriptomic approach as an alternative to the animal methods. Results revealed that such an approach could potentially provide biomarkers predictive of vaccine outcomes after addressing some limitations.

Schlafens: Emerging Therapeutic Targets

The interferon (IFN) family of immunomodulatory cytokines has been a focus of cancer research for over 50 years with direct and indirect implications in cancer therapy due to their properties to inhibit malignant cell proliferation and modulate immune responses. Among the transcriptional targets of the IFNs is a family of genes referred to as Schlafens. The products of these genes, Schlafen proteins, exert important roles in modulating cellular proliferation, differentiation, immune responses, viral replication, and chemosensitivity of malignant cells. Studies have demonstrated that abnormal expression of various Schlafens contributes to the pathophysiology of various cancers. Schlafens are now emerging as promising biomarkers and potentially attractive targets for drug development in cancer research. Here, we highlight research suggesting the use of Schlafens as cancer biomarkers and the rationale for the development of specific drugs targeting Schlafen proteins.

Signaling by Type I Interferons in Immune Cells: Disease Consequences

This review addresses interferon (IFN) signaling in immune cells and the tumor microenvironment (TME) and examines how this affects cancer progression. The data reveal that IFNs exert dual roles in cancers, dependent on the TME, exhibiting both anti-tumor activity and promoting cancer progression. We discuss the abnormal IFN signaling induced by cancerous cells that alters immune responses to permit their survival and proliferation.

Knockdown of Slfn5 alleviates lipopolysaccharide-induced pneumonia by regulating Janus kinase/signal transduction and activator of transcription pathway

Background

In recent years, the incidence of pneumonia has been increasing, which is the main cause of death and morbidity of children and the elderly in the world. Slfn5 is implicated in multiple cancers, and Slfn5 promotes epithelial-mesenchymal transition and metastasis in lung cancer. However, the influences of Slfn5 in pneumonia have not yet been completely cleared. Herein, we aimed to explore the underlying effects and regulatory mechanisms of Slfn5 in lipopolysaccharide (LPS)-induced pneumonia in mice and A549 cells.

Methods

Mice were intratracheally administered 5 mg/kg LPS to construct pneumonia model. In vitro, A549 cells were treated with 10 µg/mL LPS to construct cellular pneumonia model. Slfn5 expression was detected using immunohistochemistry and western blotting. Haematoxylin and eosin staining, TUNEL (terminal deoxynucleotidyl transferasemediated deoxyuridine triphosphate‑biotin nick end‑labelling), and western blotting were performed to assess pathological injury and inflammation. MTT [3(4,5‑dimethyl‑2‑thiazolyl)‑2,5‑diphenyl‑2‑H‑tetrazolium bromide], flow cytometry, and enzyme-linked immunosorbent assay analysis were performed to analyze cell viability, apoptosis, and inflammation. Gene set enrichment analysis was performed to explore the mechanism of Slfn5 in pneumonia.

Results

Slfn5 expression was upregulated in LPS-induced pneumonia in mice and A549 cells. In mice, knockdown of Slfn5 weakened LPS-induced lung injury and inflammation and decreased the expression of p-JAK2, p-JAK3, and p-STAT3. In LPS-stimulated A549 cells, downregulation of Slfn5 expression increased and Slfn5 overexpression decreased cell viability. Downregulation of Slfn5 expression decreased and Slfn5 overexpression increased cell apoptosis, inflammation and the expression of p-JAK2, p-JAK3, and p-STAT3. AG490, an inhibitor of the JAK/STAT pathway, reversed the damaging effects of Slfn5 overexpression.

Conclusions

In the LPS-induced pneumonia model, Slfn5 knockdown alleviated LPS-induced lung injury by regulating the JAK/STAT pathway.

Progress in investigating the relationship between Schlafen5 genes and malignant tumors

The Schlafen5(SLFN5)gene belongs to the third group of the Schlafen protein family. As a tumor suppressor gene, SLFN5 plays a pivotal role in inhibiting tumor growth, orchestrating cell cycle regulation, and modulating the extent of cancer cell infiltration and metastasis in various malignancies. However, the high expression of SLFN 5 in some tumors was positively correlated with lymph node metastasis, tumor stage, and tumor grade. This article endeavors to elucidate the reciprocal relationship between the SLFN5 gene and malignant tumors, thereby enhancing our comprehension of the intricate mechanisms underlying the SLFN5 gene and its implications for the progression, invasive potential, and metastatic behavior of malignant tumors. At the same time, this paper summarizes the basis of SLFN 5 as a new biomarker of tumor diagnosis and prognosis, and provides new ideas for the target treatment of tumor.

Insights into Gene Regulation under Temozolomide-Promoted Cellular Dormancy and Its Connection to Stemness in Human Glioblastoma

The aggressive features of glioblastoma (GBM) are associated with dormancy. Our previous transcriptome analysis revealed that several genes were regulated during temozolomide (TMZ)-promoted dormancy in GBM. Focusing on genes involved in cancer progression, Chemokine (C-C motif) Receptor-Like (CCRL)1, Schlafen (SLFN)13, Sloan-Kettering Institute (SKI), Cdk5 and Abl Enzyme Substrate (Cables)1, and Dachsous Cadherin-Related (DCHS)1 were selected for further validation. All showed clear expression and individual regulatory patterns under TMZ-promoted dormancy in human GBM cell lines, patient-derived primary cultures, glioma stem-like cells (GSCs), and human GBM ex vivo samples. All genes exhibited complex co-staining patterns with different stemness markers and with each other, as examined by immunofluorescence staining and underscored by correlation analyses. Neurosphere formation assays revealed higher numbers of spheres during TMZ treatment, and gene set enrichment analysis of transcriptome data revealed significant regulation of several GO terms, including stemness-associated ones, indicating an association between stemness and dormancy with the involvement of SKI. Consistently, inhibition of SKI during TMZ treatment resulted in higher cytotoxicity, proliferation inhibition, and lower neurosphere formation capacity compared to TMZ alone. Overall, our study suggests the involvement of CCRL1, SLFN13, SKI, Cables1, and DCHS1 in TMZ-promoted dormancy and demonstrates their link to stemness, with SKI being particularly important.

The Wheel of p53 Helps to Drive the Immune System

The p53 tumor suppressor protein is best known as an inhibitor of the cell cycle and an inducer of apoptosis. Unexpectedly, these functions of p53 are not required for its tumor suppressive activity in animal models. High-throughput transcriptomic investigations as well as individual studies have demonstrated that p53 stimulates expression of many genes involved in immunity. Probably to interfere with its immunostimulatory role, many viruses code for proteins that inactivate p53. Judging by the activities of immunity-related p53-regulated genes it can be concluded that p53 is involved in detection of danger signals, inflammasome formation and activation, antigen presentation, activation of natural killer cells and other effectors of immunity, stimulation of interferon production, direct inhibition of virus replication, secretion of extracellular signaling molecules, production of antibacterial proteins, negative feedback loops in immunity-related signaling pathways, and immunologic tolerance. Many of these p53 functions have barely been studied and require further, more detailed investigations. Some of them appear to be cell-type specific. The results of transcriptomic studies have generated many new hypotheses on the mechanisms utilized by p53 to impact on the immune system. In the future, these mechanisms may be harnessed to fight cancer and infectious diseases.

SLFN5-mediated chromatin dynamics sculpt higher-order DNA repair topology

Repair of DNA double-strand breaks (DSBs) elicits three-dimensional (3D) chromatin topological changes. A recent finding reveals that 53BP1 assembles into a 3D chromatin topology pattern around DSBs. How this formation of a higher-order structure is configured and regulated remains enigmatic. Here, we report that SLFN5 is a critical factor for 53BP1 topological arrangement at DSBs. Using super-resolution imaging, we find that SLFN5 binds to 53BP1 chromatin domains to assemble a higher-order microdomain architecture by driving damaged chromatin dynamics at both DSBs and deprotected telomeres. Mechanistically, we propose that 53BP1 topology is shaped by two processes: (1) chromatin mobility driven by the SLFN5-LINC-microtubule axis and (2) the assembly of 53BP1 oligomers mediated by SLFN5. In mammals, SLFN5 deficiency disrupts the DSB repair topology and impairs non-homologous end joining, telomere fusions, class switch recombination, and sensitivity to poly (ADP-ribose) polymerase inhibitor. We establish a molecular mechanism that shapes higher-order chromatin topologies to safeguard genomic stability.

SLFN5 promotes reversible epithelial and mesenchymal transformation in ovarian cancer

Ovarian cancer is a disease with increasing incidence worldwide, and there is an urgent need for chemotherapy and biological targeted therapy. Epithelial-mesenchymal transformation (EMT) is an important initiation stage for tumor cells to acquire the ability to invade and metastasize. A growing number of findings suggest that human Schlafen family member 5(SLFN5) plays a key role in malignancy. However, the role of SLFN5 in ovarian cancer cells has not been fully elucidated. Samples were collected from patients with ovarian cancer diagnosed in Hangzhou First People's Hospital, and the expression of SLFN5 was detected by fluorescence quantitative PCR. The relationship between SLFN5 expression and the progression and malignancy of ovarian cancer was analyzed by using the expression profile data from the Cancer Genome Atlas (TCGA) database. The mRNA expression levels of SLFN5 related upstream and downstream signaling pathways were studied by fluorescence quantitative PCR. Silencing SLFN5 was performed by siRNA transfection. The expression of SLFN5 and transfer-related proteins was examined by Western blot. Transwell and wound healing experiments investigated the migration and invasion ability of ovarian cancer cells. TCGA database analysis results showed that in the population with high SLFN5 expression, compared with the group with low SLFN5 expression, OS was worse (P = 0.011). SLFN5 silencing had a significant inhibitory effect on EMT and invasion movement of ovarian cancer cells. RT-PCR method was used to detect the mRNA changes of SLFN5 in ovarian cancer tissue and adjacent tissue. It was found that the expression of SLFN5 in ovarian cancer tissue was increased, with a significant difference (P < 0.05). Together, these results suggest that SLFN5 may play a synergistic role in tumorigenesis and development of ovarian cancer cells, providing a potential target for future drug development for the treatment of ovarian cancer.

tRNA-like Transcripts from the NEAT1-MALAT1 Genomic Region Critically Influence Human Innate Immunity and Macrophage Functions

The evolutionary conserved NEAT1-MALAT1 gene cluster generates large noncoding transcripts remaining nuclear, while tRNA-like transcripts (mascRNA, menRNA) enzymatically generated from these precursors translocate to the cytosol. Whereas functions have been assigned to the nuclear transcripts, data on biological functions of the small cytosolic transcripts are sparse. We previously found NEAT1^-/- and MALAT1^-/- mice to display massive atherosclerosis and vascular inflammation. Here, employing selective targeted disruption of menRNA or mascRNA, we investigate the tRNA-like molecules as critical components of innate immunity. CRISPR-generated human ΔmascRNA and ΔmenRNA monocytes/macrophages display defective innate immune sensing, loss of cytokine control, imbalance of growth/angiogenic factor expression impacting upon angiogenesis, and altered cell-cell interaction systems. Antiviral response, foam cell formation/oxLDL uptake, and M1/M2 polarization are defective in ΔmascRNA/ΔmenRNA macrophages, defining first biological functions of menRNA and describing new functions of mascRNA. menRNA and mascRNA represent novel components of innate immunity arising from the noncoding genome. They appear as prototypes of a new class of noncoding RNAs distinct from others (miRNAs, siRNAs) by biosynthetic pathway and intracellular kinetics. Their NEAT1-MALAT1 region of origin appears as archetype of a functionally highly integrated RNA processing system.

SLFN11 Negatively Regulates Noncanonical NFκB Signaling to Promote Glioblastoma Progression

Glioblastoma (GBM) is an aggressive and incurable brain tumor in nearly all instances, whose disease progression is driven in part by the glioma stem cell (GSC) subpopulation. Here, we explored the effects of Schlafen family member 11 (SLFN11) in the molecular, cellular, and tumor biology of GBM. CRISPR/Cas9-mediated knockout of SLFN11 inhibited GBM cell proliferation and neurosphere growth and was associated with reduced expression of progenitor/stem cell marker genes, such as NES, SOX2, and CD44. Loss of SLFN11 stimulated expression of NFκB target genes, consistent with a negative regulatory role for SLFN11 on the NFκB pathway. Furthermore, our studies identify p21 as a direct transcriptional target of NFκB2 in GBM whose expression was stimulated by loss of SLFN11. Genetic disruption of SLFN11 blocked GBM growth and significantly extended survival in an orthotopic patient-derived xenograft model. Together, our results identify SLFN11 as a novel component of signaling pathways that contribute to GBM and GSC with implications for future diagnostic and therapeutic strategies.

Significance:

We identify a negative regulatory role for SLFN11 in noncanonical NFκB signaling that results in suppression of the cell-cycle inhibitor p21. We provide evidence that SLFN11 contributes to regulation of stem cell markers in GBM, promoting the malignant phenotype. In addition, SLFN11 targeting triggers p21 expression and antitumor responses. Our studies define a highly novel function for SLFN11 and identify it as a potential therapeutic target for GBM.

SIRT5 is a proviral factor that interacts with SARS-CoV-2 Nsp14 protein

SARS-CoV-2 non-structural protein Nsp14 is a highly conserved enzyme necessary for viral replication. Nsp14 forms a stable complex with non-structural protein Nsp10 and exhibits exoribonuclease and N7-methyltransferase activities. Protein-interactome studies identified human sirtuin 5 (SIRT5) as a putative binding partner of Nsp14. SIRT5 is an NAD-dependent protein deacylase critical for cellular metabolism that removes succinyl and malonyl groups from lysine residues. Here we investigated the nature of this interaction and the role of SIRT5 during SARS-CoV-2 infection. We showed that SIRT5 interacts with Nsp14, but not with Nsp10, suggesting that SIRT5 and Nsp10 are parts of separate complexes. We found that SIRT5 catalytic domain is necessary for the interaction with Nsp14, but that Nsp14 does not appear to be directly deacylated by SIRT5. Furthermore, knock-out of SIRT5 or treatment with specific SIRT5 inhibitors reduced SARS-CoV-2 viral levels in cell-culture experiments. SIRT5 knock-out cells expressed higher basal levels of innate immunity markers and mounted a stronger antiviral response, independently of the Mitochondrial Antiviral Signaling Protein MAVS. Our results indicate that SIRT5 is a proviral factor necessary for efficient viral replication, which opens novel avenues for therapeutic interventions.

Schlafen family is a prognostic biomarker and corresponds with immune infiltration in gastric cancer

The Schlafen (SLFN) gene family plays an important role in immune cell differentiation and immune regulation. Previous studies have found that the increased SLFN5 expression in patients with intestinal metaplasia correlates with gastric cancer (GC) progression. However, no investigation has been conducted on the SLFN family in GC. Therefore, we systematically explore the expression and prognostic value of SLFN family members in patients with GC, elucidating their possible biological function and its correlation with tumor immune cells infiltration. TCGA database results indicated that the SLFN5, SLFN11, SLFN12, SLFN12L, and SLFN13 expression was significantly higher in GC. The UALCAN and KM plotter databases indicated that enhanced the SLFN family expression was associated with lymph node metastasis, tumor stage, and tumor grade and predicted an adverse prognosis. cBioportal database revealed that the SLFN family had a high frequency of genetic alterations in GC (about 12%), including mutations and amplification. The GeneMANIA and STRING databases identified 20 interacting genes and 16 interacting proteins that act as potential targets of the SLFN family. SLFN5, SLFN11, SLFN12, SLFN12L, and SLFN14 may be implicated in the immunological response, according to Gene Set Enrichment Analysis (GSEA) and Kyoto Encyclopedia of Genes and Genomes (KEGG). Additionally, Timer and TISIDB databases indicate that SLFN5, SLFN11, SLFN12, SLFN12L, and SLFN14 are involved in the immune response. Furthermore, Timer, TCGA, and TISIDB databases suggested that the SLFN5, SLFN11, SLFN12, SLFN12L, and SLFN14 expression in GC is highly linked with immune cell infiltration levels, immune checkpoint, and the many immune cell marker sets expression. We isolated three samples of peripheral blood mononuclear cell (PBMC) and activated T cells; the results showed the expression of SLFN family members decreased significantly when T cell active. In conclusion, the SLFN family of proteins may act as a prognostic indicator of GC and is associated with immune cell infiltration and immune checkpoint expression in GC. Additionally, it may be involved in tumor immune evasion by regulating T cell activation.

The Long Noncoding RNA MEG3 Retains Epithelial-Mesenchymal Transition by Sponging miR-146b-5p to Regulate SLFN5 Expression in Breast Cancer Cells

More and more studies have shown that long noncoding RNAs (lncRNAs) play essential roles in malignant tumors. The lncRNA MEG3 serves as a crucial molecule in breast cancer development, but the specific molecular mechanism needs to be further explored. We previously reported that Schlafen family member 5 (SLFN5) inhibits breast cancer malignant development by regulating epithelial-mesenchymal transition (EMT), invasion, and proliferation/apoptosis. Herein, we demonstrated that MEG3 was downregulated in pan-cancers and correlated with SLFN5 expression positively in breast cancer by bioinformatics analysis of TCGA and UCSC Xena data. Intervention with MEG3 positively affected SLFN5 expression in breast cancer cells. MEG3 repressed EMT and migration/invasion, similar to our previously reported functions of SLFN5 in breast cancer. Through bioinformatics analysis of starBase and LncBase data, 12 miRNAs were found to regulate both SLFN5 and MEG3, in which miR-146b-5p was confirmed to be regulated by MEG3 using MEG3 siRNA and overexpression method. MiR-146b-5p could bind to both SLFN5 3′UTR and MEG3, and inhibit their expression in a competing endogenous RNA mechanism, assayed by luciferase reporter and RNA pull down methods. Therefore, we conclude that MEG3 positively modulates SLFN5 expression by sponging miR-146b-5p and inhibits breast cancer development.

Regulation of IFNα-induced expression of the short ACE2 isoform by ULK1

The novel coronavirus, severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has been shown to hijack angiotensin converting enzyme 2 (ACE2) for entry into mammalian cells. A short isoform of ACE2, termed deltaACE2 (dACE2), has recently been identified. In contrast to ACE2, the short dACE2 isoform lacks the ability to bind the spike protein of SARS-CoV-2. Several studies have proposed that expression of ACE2 and/or dACE2 is induced by interferons (IFNs). Here, we report that drug-targeted inhibition or silencing of Unc51-like kinase 1 (ULK1) results in repression of type I IFN-induced expression of the dACE2 isoform. Notably, dACE2 is expressed in various squamous tumors. In efforts to identify pharmacological agents that target this pathway, we found that fisetin, a natural flavonoid, is an ULK1 inhibitor that decreases type I IFN-induced dACE2 expression. Taken together, our results establish a requirement for ULK1 in the regulation of type I IFN-induced transcription of dACE2 and raise the possibility of clinical translational applications of fisetin as a novel ULK1 inhibitor.

Schlafen 5 suppresses human immunodeficiency virus type 1 transcription by commandeering cellular epigenetic machinery

Schlafen-5 (SLFN5) is an interferon-induced protein of the Schlafen family, which are involved in immune responses and oncogenesis. To date, little is known regarding its anti-HIV-1 function. Here, the authors report that overexpression of SLFN5 inhibits HIV-1 replication and reduces viral mRNA levels, whereas depletion of endogenous SLFN5 promotes HIV-1 replication. Moreover, they show that SLFN5 markedly decreases the transcriptional activity of HIV-1 long terminal repeat (LTR) via binding to two sequences in the U5-R region, which consequently represses the recruitment of RNA polymerase II to the transcription initiation site. Mutagenesis studies show the importance of nuclear localization and the N-terminal 1-570 amino acids fragment in the inhibition of HIV-1. Further mechanistic studies demonstrate that SLFN5 interacts with components of the PRC2 complex, G9a and Histone H3, thereby promoting H3K27me2 and H3K27me3 modification leading to silencing HIV-1 transcription. In concert with this, they find that SLFN5 blocks the activation of latent HIV-1. Altogether, their findings demonstrate that SLFN5 is a transcriptional repressor of HIV-1 through epigenetic modulation and a potential determinant of HIV-1 latency.

Structural, molecular, and functional insights into Schlafen proteins

Schlafen (SLFN) genes belong to a vertebrate gene family encoding proteins with high sequence homology. However, each SLFN is functionally divergent and differentially expressed in various tissues and species, showing a wide range of expression in cancer and normal cells. SLFNs are involved in various cellular and tissue-specific processes, including DNA replication, proliferation, immune and interferon responses, viral infections, and sensitivity to DNA-targeted anticancer agents. The fundamental molecular characteristics of SLFNs and their structures are beginning to be elucidated. Here, we review recent structural insights into the N-terminal, middle and C-terminal domains (N-, M-, and C-domains, respectively) of human SLFNs and discuss the current understanding of their biological roles. We review the distinct molecular activities of SLFN11, SLFN5, and SLFN12 and the relevance of SLFN11 as a predictive biomarker in oncology.

The diverse roles that Schlafen family proteins play in cell proliferation, immune modulation, and other biological processes make them promising targets for treating and tracking diseases, especially cancer. Ukhyun Jo and Yves Pommier from the National Cancer Institute in Bethesda, USA, review the molecular characteristics and structural features of Schlafen proteins. These proteins take their name from the German word for “sleep”, as the first described Schlafen proteins caused cells to stop dividing, although later reports found that related members of the same protein family serve myriad cellular functions, including in the regulation of DNA replication. A better understanding of Schlafen proteins could open up new avenues in cancer management, for instance, diagnostics that monitor activity levels of one such protein, SLFN11, could help oncologists predict how well patients might respond to anti-cancer therapies.

Competition for Dominance Within Replicating Quasispecies During Prolonged SARS-CoV-2 Infection in an Immunocompromised Host

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) variants of concern (VOCs) emerge for their capability to better adapt to the human host aimed and enhance human-to-human transmission. Mutations in spike largely contributed to adaptation. Viral persistence is a prerequisite for intra-host virus evolution, and this likely occurred in immunocompromised patients who allow intra-host long-term viral replication. The underlying mechanism leading to the emergence of variants during viral persistence in the immunocompromised host is still unknown. Here, we show the existence of an ensemble of minor mutants in the early biological samples obtained from an immunocompromised patient and their dynamic interplay with the master mutant during a persistent and productive long-term infection. In particular, after 222 days of active viral replication, the original master mutant, named MB61⁰, was replaced by a minor quasispecies (MB61²²²) expressing two critical mutations in spike, namely Q493K and N501T. Isolation of the two viruses allowed us to show that MB61²²² entry into target cells occurred mainly by the fusion at the plasma membrane (PM), whereas endocytosis characterized the entry mechanism used by MB61⁰. Interestingly, coinfection of two human cell lines of different origin with the SARS-CoV-2 isolates highlighted the early and dramatic predominance of MB61²²² over MB61⁰ replication. This finding may be explained by a faster replicative activity of MB61²²² as compared to MB61⁰ as well as by the capability of MB61²²² to induce peculiar viral RNA-sensing mechanisms leading to an increased production of interferons (IFNs) and, in particular, of IFN-induced transmembrane protein 1 (IFITM1) and IFITM2. Indeed, it has been recently shown that IFITM2 is able to restrict SARS-CoV-2 entry occurring by endocytosis. In this regard, MB61²²² may escape the antiviral activity of IFITMs by using the PM fusion pathway for entry into the target cell, whereas MB61⁰ cannot escape this host antiviral response during MB61²²² coinfection, since it has endocytosis as the main pathway of entry. Altogether, our data support the evidence of quasispecies fighting for host dominance by taking benefit from the cell machinery to restrict the productive infection of competitors in the viral ensemble. This finding may explain, at least in part, the extraordinary rapid worldwide turnover of VOCs that use the PM fusion pathway to enter into target cells over the original pandemic strain.

Schlafens Can Put Viruses to Sleep

The Schlafen gene family encodes for proteins involved in various biological tasks, including cell proliferation, differentiation, and T cell development. Schlafens were initially discovered in mice, and have been studied in the context of cancer biology, as well as their role in protecting cells during viral infection. This protein family provides antiviral barriers via direct and indirect effects on virus infection. Schlafens can inhibit the replication of viruses with both RNA and DNA genomes. In this review, we summarize the cellular functions and the emerging relationship between Schlafens and innate immunity. We also discuss the functions and distinctions of this emerging family of proteins as host restriction factors against viral infection. Further research into Schlafen protein function will provide insight into their mechanisms that contribute to intrinsic and innate host immunity.

Structural and biochemical characterization of human Schlafen 5

The Schlafen family belongs to the interferon-stimulated genes and its members are involved in cell cycle regulation, T cell quiescence, inhibition of viral replication, DNA-repair and tRNA processing. Here, we present the cryo-EM structure of full-length human Schlafen 5 (SLFN5) and the high-resolution crystal structure of the highly conserved N-terminal core domain. We show that the core domain does not resemble an ATPase-like fold and neither binds nor hydrolyzes ATP. SLFN5 binds tRNA as well as single- and double-stranded DNA, suggesting a potential role in transcriptional regulation. Unlike rat Slfn13 or human SLFN11, human SLFN5 did not cleave tRNA. Based on the structure, we identified two residues in proximity to the zinc finger motif that decreased DNA binding when mutated. These results indicate that Schlafen proteins have divergent enzymatic functions and provide a structural platform for future biochemical and genetic studies.

SIRT5 is a proviral factor that interacts with SARS-CoV-2 Nsp14 protein

SARS-CoV-2 non-structural protein Nsp14 is a highly conserved enzyme necessary for viral replication. Nsp14 forms a stable complex with non-structural protein Nsp10 and exhibits exoribonuclease and N7-methyltransferase activities. Protein-interactome studies identified human sirtuin 5 (SIRT5) as a putative binding partner of Nsp14. SIRT5 is an NAD-dependent protein deacylase critical for cellular metabolism that removes succinyl and malonyl groups from lysine residues. Here we investigated the nature of this interaction and the role of SIRT5 during SARS-CoV-2 infection. We showed that SIRT5 stably interacts with Nsp14, but not with Nsp10, suggesting that SIRT5 and Nsp10 are parts of separate complexes. We found that SIRT5 catalytic domain is necessary for the interaction with Nsp14, but that Nsp14 does not appear to be directly deacylated by SIRT5. Furthermore, knock-out of SIRT5 or treatment with specific SIRT5 inhibitors reduced SARS-CoV-2 viral levels in cell-culture experiments. SIRT5 knock-out cells expressed higher basal levels of innate immunity markers and mounted a stronger antiviral response. Our results indicate that SIRT5 is a proviral factor necessary for efficient viral replication, which opens novel avenues for therapeutic interventions.

Heterogeneous microenvironmental stiffness regulates pro-metastatic functions of breast cancer cells

Besides molecular and phenotypic variations observed in cancer cells, intratumoral heterogeneity also occurs in the tumor microenvironment. Correlative stiffness maps of different intratumor locations in breast tumor biopsies show that stiffness increases from core to periphery. However, how different local ECM stiffness regulates key functions of cancer cells in tumor progression remains unclear. Although increased tissue stiffness is an established driver of breast cancer progression, conclusions from 2D cultures do not correspond with newer data from cancer cells in 3D environments. Many past studies of breast cancer in 3D culture fail to recapitulate the stiffness of a real breast tumor or the various local stiffnesses present in a tumor microenvironment. In this study, we developed a series of collagen/alginate hybrid hydrogels with adjustable stiffness to match the core, middle, and peripheral zones of a breast tumor. We used this hydrogel system to investigate effects of different local stiffness on morphology, proliferation, and migration of breast cancer cells. RNA sequencing of cells in hydrogels with different stiffness revealed changes in multiple cellular processes underlying cancer progression, including angiogenesis and metabolism. We discovered that tumor cells in a soft environment enriched YAP1 and AP1 signaling related genes, whereas tumor cells in a stiff environment became more pro-angiogenic by upregulating fibronectin 1 (FN1) and matrix metalloproteinase 9 (MMP9) expression. This systematic study defines how the range of environmental stiffnesses present in a breast tumor regulates cancer cells, providing new insights into tumorigenesis and disease progression at the tumor-stroma interface. STATEMENT OF SIGNIFICANCE: Applied a well-defined hybrid hydrogel system to mimic the tumor microenvironment with heterogeneous local stiffness. Breast cancer cells tended to proliferate in soft core environment while migrate in stiff peripheral environment. Breast cancer cells shift from glycolysis to OXPHOS and fatty acid metabolism responding to stiff matrix microenvironment. The transcriptomic profile of breast cancer cells altered due to microenvironmental stiffness changes.

The Yin and Yang of Type I IFNs in Cancer Promotion and Immune Activation

Type I Interferons (IFNs) are key regulators of natural and therapy-induced host defense against viral infection and cancer. Several years of remarkable progress in the field of oncoimmunology have revealed the dual nature of these cytokines. Hence, Type I IFNs may trigger anti-tumoral responses, while leading immune dysfunction and disease progression. This dichotomy relies on the duration and intensity of the transduced signaling, the nature of the unleashed IFN stimulated genes, and the subset of responding cells. Here, we discuss the role of Type I IFNs in the evolving relationship between the host immune system and cancer, as we offer a view of the therapeutic strategies that exploit and require an intact Type I IFN signaling, and the role of these cytokines in inducing adaptive resistance. A deep understanding of the complex, yet highly regulated, network of Type I IFN triggered molecular pathways will help find a timely and immune"logical" way to exploit these cytokines for anticancer therapy.

Schlafens: Emerging Proteins in Cancer Cell Biology

Schlafens (SLFN) are a family of genes widely expressed in mammals, including humans and rodents. These intriguing proteins play different roles in regulating cell proliferation, cell differentiation, immune cell growth and maturation, and inhibiting viral replication. The emerging evidence is implicating Schlafens in cancer biology and chemosensitivity. Although Schlafens share common domains and a high degree of homology, different Schlafens act differently. In particular, they show specific and occasionally opposing effects in some cancer types. This review will briefly summarize the history, structure, and non-malignant biological functions of Schlafens. The roles of human and mouse Schlafens in different cancer types will then be outlined. Finally, we will discuss the implication of Schlafens in the anti-tumor effect of interferons and the use of Schlafens as predictors of chemosensitivity.

SLFN5 Regulates LAT1-Mediated mTOR Activation in Castration-Resistant Prostate Cancer

Androgen deprivation therapy (ADT) is the standard of care for treatment of nonresectable prostate cancer. Despite high treatment efficiency, most patients ultimately develop lethal castration-resistant prostate cancer (CRPC). In this study, we performed a comparative proteomic analysis of three in vivo, androgen receptor (AR)-responsive orthograft models of matched hormone-naïve prostate cancer and CRPC. Differential proteomic analysis revealed that distinct molecular mechanisms, including amino acid (AA) and fatty acid metabolism, are involved in the response to ADT in the different models. Despite this heterogeneity, Schlafen family member 5 (SLFN5) was identified as an AR-regulated protein in CRPC. SLFN5 expression was high in CRPC tumors and correlated with poor patient outcome. In vivo, SLFN5 depletion strongly impaired tumor growth in castrated conditions. Mechanistically, SLFN5 interacted with ATF4 and regulated the expression of LAT1, an essential AA transporter. Consequently, SLFN5 depletion in CRPC cells decreased intracellular levels of essential AA and impaired mTORC1 signaling in a LAT1-dependent manner. These results confirm that these orthograft models recapitulate the high degree of heterogeneity observed in patients with CRPC and further highlight SLFN5 as a clinically relevant target for CRPC. SIGNIFICANCE: This study identifies SLFN5 as a novel regulator of the LAT1 amino acid transporter and an essential contributor to mTORC1 activity in castration-resistant prostate cancer.

Schlafen 5 as a novel therapeutic target in pancreatic ductal adenocarcinoma

We provide evidence that a member of the human Schlafen (SLFN) family of proteins, SLFN5, is overexpressed in human pancreatic ductal adenocarcinoma (PDAC). Targeted deletion of SLFN5 results in decreased PDAC cell proliferation and suppresses PDAC tumorigenesis in in vivo PDAC models. Importantly, high expression levels of SLFN5 correlate with worse outcomes in PDAC patients, implicating SLFN5 in the pathophysiology of PDAC that leads to poor outcomes. Our studies establish novel regulatory effects of SLFN5 on cell cycle progression through binding/blocking of the transcriptional repressor E2F7, promoting transcription of key genes that stimulate S phase progression. Together, our studies suggest an essential role for SLFN5 in PDAC and support the potential for developing new therapeutic approaches for the treatment of pancreatic cancer through SLFN5 targeting.

Human Schlafen 5 Inhibits Proliferation and Promotes Apoptosis in Lung Adenocarcinoma via the PTEN/PI3K/AKT/mTOR Pathway

BACKGROUND

Human Schlafen 5 (SLFN5) is reported to inhibit or promote the proliferation of several specific types of cancer cells by our lab and other researchers. We are curious about its implications in lung adenocarcinoma (LUAC), a malignant tumor with a high incidence rate and high mortality.

METHOD

Lentiviral stable transfections of SLFN5-specific shRNA for knockdown and SLFN5 full-length coding sequence for overexpression were performed in LUAC cell for proliferation analysis in vitro and in vivo in nude mice. Clinical LUAC samples were collected for immunohistochemical analysis of SLFN5 protein levels.

RESULTS

We found that knockdown of endogenous SLFN5 upregulates cancer cell proliferation while inhibiting apoptosis. Besides, SLFN5 inhibition on proliferation was also observed in a nude mouse xenograft model. In contrast, overexpression of exogenous SLFN5 inhibited cell proliferation in vitro and in vivo and promoted apoptosis. As to the signaling pathway, we found phosphatase and tensin homolog on chromosome 10 (PTEN) was positively regulated by SLFN5, while its downstream signaling pathway AKT/mammalian target of rapamycin (mTOR) was inhibited. Moreover, compared with adjacent normal tissues, SLFN5 protein levels were markedly decreased in lung adenocarcinoma tissues. In conclusion, these suggest that human SLFN5 plays inhibitory roles in LUAC progression through the PTEN/PI3K/AKT/mTOR pathway, providing a potential target for developing drugs for lung cancer therapy in the future.

Type I and II Interferons in the Anti-Tumor Immune Response

The interferons (IFNs) are essential components of the immune response against infections and malignancies. IFNs are potent promoters of the anti-tumor response, but there is also evidence that feedback mechanisms regulated by IFNs negatively control immune responses to avoid hyper-activation and limit inflammation. This balance of responses plays an important role in cancer surveillance, immunoediting and response to anticancer therapeutic approaches. Here we review the roles of both type I and type II IFNs on the control of the immune response against malignancies in the context of effects on both malignant cells and cells of the immune system in the tumor microenvironment.

Comparative proteomics identifies Schlafen 5 (SLFN5) as a herpes simplex virus restriction factor that suppresses viral transcription

Intrinsic antiviral host factors confer cellular defence by limiting virus replication and are often counteracted by viral countermeasures. We reasoned that host factors that inhibit viral gene expression could be identified by determining proteins bound to viral DNA (vDNA) in the absence of key viral antagonists. Herpes simplex virus 1 (HSV-1) expresses E3 ubiquitin-protein ligase ICP0 (ICP0), which functions as an E3 ubiquitin ligase required to promote infection. Cellular substrates of ICP0 have been discovered as host barriers to infection but the mechanisms for inhibition of viral gene expression are not fully understood. To identify restriction factors antagonized by ICP0, we compared proteomes associated with vDNA during HSV-1 infection with wild-type virus and a mutant lacking functional ICP0 (ΔICP0). We identified the cellular protein Schlafen family member 5 (SLFN5) as an ICP0 target that binds vDNA during HSV-1 ΔICP0 infection. We demonstrated that ICP0 mediates ubiquitination of SLFN5, which leads to its proteasomal degradation. In the absence of ICP0, SLFN5 binds vDNA to repress HSV-1 transcription by limiting accessibility of RNA polymerase II to viral promoters. These results highlight how comparative proteomics of proteins associated with viral genomes can identify host restriction factors and reveal that viral countermeasures can overcome SLFN antiviral activity.

Type I Interferon (IFN)-Regulated Activation of Canonical and Non-Canonical Signaling Pathways

For several decades there has been accumulating evidence implicating type I interferons (IFNs) as key elements of the immune response. Therapeutic approaches incorporating different recombinant type I IFN proteins have been successfully employed to treat a diverse group of diseases with significant and positive outcomes. The biological activities of type I IFNs are consequences of signaling events occurring in the cytoplasm and nucleus of cells. Biochemical events involving JAK/STAT proteins that control transcriptional activation of IFN-stimulated genes (ISGs) were the first to be identified and are referred to as "canonical" signaling. Subsequent identification of JAK/STAT-independent signaling pathways, critical for ISG transcription and/or mRNA translation, are denoted as "non-canonical" or "non-classical" pathways. In this review, we summarize these signaling cascades and discuss recent developments in the field, specifically as they relate to the biological and clinical implications of engagement of both canonical and non-canonical pathways.

miR-525-5p Modulates Proliferation and Epithelial-Mesenchymal Transition of Glioma by Targeting Stat-1

Background

Glioma is the most aggressive human brain tumor. Recent studies revealed that microRNAs play vital roles in glioma. However, the function of microRNA-525-5p (miR-525-5p) in glioma remains unclear.

Methods

qRT-PCR and Western blotting were used to evaluate mRNA and protein levels in glioma tissues and cells. Colony formation, CCK-8, and Edu assays evaluated the growth of glioma cells. Wound-healing, transwell, and 3D invasion assays examined the migration and invasion activities of glioma cells. Luciferase reporter assays assessed the regulatory relationship interaction between miR-525-5p and Stat-1. A mouse xenograft model was used to examine the effect of miR-525-5p on glioma in vivo.

Results

miR-525-5p expression was downregulated in glioma tissues and cells. Overexpressing miR-525-5p decreased the growth of glioma cells and reduced the migration, invasion, and epithelial–mesenchymal transition of glioma cells. Bioinformatics analysis identified Stat-1 as a potential target of miR-525-5p, and dual luciferase reporter assays revealed that miR-525-5p negatively regulates Stat-1. Decreased Stat-1 led to the inhibition of FOXM1, affecting NF-κB signaling activity. Overexpressing miR-525-5p reduced tumor development in vivo.

Conclusion

miR-525-5p negatively regulates cell proliferation, migration, invasion, and epithelial–mesenchymal transition in glioma, and Stat 1 is a target of miR-525-5p. miR-525-5p may be a potential target for glioma treatment.

SLFN5 influences proliferation and apoptosis by upregulating PTEN transcription via ZEB1 and inhibits the purine metabolic pathway in breast cancer

Human Schlafen-5 (SLFN5) is aberrantly involved in tumorigenesis in several types of cancer. However, its implications in breast cancer (BRCA) are unknown. Herein, we demonstrated that SLFN5 expression is negatively associated with the tumour growth of human BRCA using GEO database analysis and clinical sample immunostaining. Lentiviral overexpression of SLFN5 in BRCA cell lines suppressed tumourigenicity in nude mice. Knockdown and overexpression of SLFN5 in BRCA cell lines proved that SLFN5 can inhibit cell proliferation and colony formation and promote apoptosis by upregulating the transcription of a known cancer suppressor gene (the phosphatase and tensin homologue on chromosome 10, PTEN), resulting in molecular changes in the downstream AKT pathway and in proliferation/apoptosis. Lentiviral knockdown and overexpression of ZEB1 blocked the changes in the PTEN and AKT pathways and in the colony formation ability caused by SLFN5 knockdown and overexpression, respectively. Luciferase reporter assays demonstrated that ZEB1 can inhibit the PTEN promoter activity in MCF7 cells by binding to a motif in the PTEN promoter. Metabonomics analysis showed that SLFN5 influences many metabolic pathways and especially decreases purine metabolites, including inosine, xanthine, and hypoxanthine. In conclusion, our findings suggest that SLFN5 may be an important protective factor against BRCA, as it regulates PTEN transcription, the AKT pathway, and proliferation/apoptosis via ZEB1 mediation and inhibits the purine metabolic pathway. Thus, SLFN5 may be a potential therapeutic target for BRCA.

Single cell heterogeneity in influenza A virus gene expression shapes the innate antiviral response to infection

Viral infection outcomes are governed by the complex and dynamic interplay between the infecting virus population and the host response. It is increasingly clear that both viral and host cell populations are highly heterogeneous, but little is known about how this heterogeneity influences infection dynamics or viral pathogenicity. To dissect the interactions between influenza A virus (IAV) and host cell heterogeneity, we examined the combined host and viral transcriptomes of thousands of individual cells, each infected with a single IAV virion. We observed complex patterns of viral gene expression and the existence of multiple distinct host transcriptional responses to infection at the single cell level. We show that human H1N1 and H3N2 strains differ significantly in patterns of both viral and host anti-viral gene transcriptional heterogeneity at the single cell level. Our analyses also reveal that semi-infectious particles that fail to express the viral NS can play a dominant role in triggering the innate anti-viral response to infection. Altogether, these data reveal how patterns of viral population heterogeneity can serve as a major determinant of antiviral gene activation.

A multi-omics analysis reveals the unfolded protein response regulon and stress-induced resistance to folate-based antimetabolites

Stress response pathways are critical for cellular homeostasis, promoting survival through adaptive changes in gene expression and metabolism. They play key roles in numerous diseases and are implicated in cancer progression and chemoresistance. However, the underlying mechanisms are only poorly understood. We have employed a multi-omics approach to monitor changes to gene expression after induction of a stress response pathway, the unfolded protein response (UPR), probing in parallel the transcriptome, the proteome, and changes to translation. Stringent filtering reveals the induction of 267 genes, many of which have not previously been implicated in stress response pathways. We experimentally demonstrate that UPR‐mediated translational control induces the expression of enzymes involved in a pathway that diverts intermediate metabolites from glycolysis to fuel mitochondrial one‐carbon metabolism. Concomitantly, the cells become resistant to the folate-based antimetabolites Methotrexate and Pemetrexed, establishing a direct link between UPR‐driven changes to gene expression and resistance to pharmacological treatment.

The unfolded protein response (UPR) is a stress response pathway implicated in numerous diseases and chemotherapy resistance. Here, the authors define the UPR regulon with a multi-omics strategy, uncovering changes to mitochondrial one-carbon metabolism and concomitant resistance to folate-based therapeutics.

Human Schlafen 5 regulates reversible epithelial and mesenchymal transitions in breast cancer by suppression of ZEB1 transcription

BACKGROUND

Human Schlafen 5 (SLFN5) has been reported to inhibit or promote cell invasion in tumours depending on their origin. However, its role in breast cancer (BRCA) is undetermined.

METHODS

Differential expression analyses using The Cancer Genome Atlas (TCGA) data, clinical samples and cell lines were performed. Lentiviral knockdown and overexpression experiments were performed to detect changes in cell morphology, molecular markers and invasion. Chromatin immunoprecipitation-sequencing (ChIP-Seq) and luciferase reporter assays were performed to detect the SLFN5-binding motif.

RESULTS

TCGA, clinical samples and cell lines showed that SLFN5 expression was negatively correlated with BRCA metastasis. SLFN5 knockdown induced epithelial-mesenchymal transition (EMT) and enhanced invasion in BRCA cell lines. However, overexpression triggered mesenchymal-epithelial transition (MET). SLFN5 inhibited the expression of ZEB1 but not ZEB2, SNAI1, SNAI2, TWIST1 or TWIST2. Knockdown and overexpression of ZEB1 indicated that it was a mediator of the SLFN5-governed phenotype and invasion changes. Moreover, SLFN5 inhibited ZEB1 transcription by directly binding to the SLFN5-binding motif on the ZEB1 promoter, but a SLFN5 C-terminal deletion mutant did not.

CONCLUSION

SLFN5 regulates reversible epithelial and mesenchymal transitions, and inhibits BRCA metastasis by suppression of ZEB1 transcription, suggesting that SLFN5 could be a potential target for BRCA therapy.

Fibronectin has multifunctional roles in posterior capsular opacification (PCO)

Fibrotic posterior capsular opacification (PCO), one of the major complications of cataract surgery, occurs when lens epithelial cells (LCs) left behind post cataract surgery (PCS) undergo epithelial to mesenchymal transition, migrate into the optical axis and produce opaque scar tissue. LCs left behind PCS robustly produce fibronectin, although its roles in fibrotic PCO are not known. In order to determine the function of fibronectin in PCO pathogenesis, we created mice lacking the fibronectin gene (FN conditional knock out -FNcKO) from the lens. While animals from this line have normal lenses, upon lens fiber cell removal which models cataract surgery, FNcKO LCs exhibit a greatly attenuated fibrotic response from 3 days PCS onward as assessed by a reduction in surgery-induced cell proliferation, and fibrotic extracellular matrix (ECM) production and deposition. This is correlated with less upregulation of Transforming Growth Factor β (TGFβ) and integrin signaling in FNcKO LCs PCS concomitant with sustained Bone Morphogenetic Protein (BMP) signaling and elevation of the epithelial cell marker E cadherin. Although the initial fibrotic response of FNcKO LCs was qualitatively normal at 48 h PCS as measured by the upregulation of fibrotic marker protein αSMA, RNA sequencing revealed that the fibrotic response was already quantitatively attenuated at this time, as measured by the upregulation of mRNAs encoding molecules that control, and are controlled by, TGFβ signaling, including many known markers of fibrosis. Most notably, gremlin-1, a known regulator of TGFβ superfamily signaling, was upregulated sharply in WT LCs PCS, while this response was attenuated in FNcKO LCs. As exogenous administration of either active TGFβ1 or gremlin-1 to FNcKO lens capsular bags rescued the attenuated fibrotic response of fibronectin null LCs PCS including the loss of SMAD2/3 phosphorylation, this suggests that fibronectin plays multifunctional roles in fibrotic PCO development.

Using regulatory variants to detect gene-gene interactions identifies networks of genes linked to cell immortalisation

The extent to which the impact of regulatory genetic variants may depend on other factors, such as the expression levels of upstream transcription factors, remains poorly understood. Here we report a framework in which regulatory variants are first aggregated into sets, and using these as estimates of the total cis-genetic effects on a gene we model their non-additive interactions with the expression of other genes in the genome. Using 1220 lymphoblastoid cell lines across platforms and independent datasets we identify 74 genes where the impact of their regulatory variant-set is linked to the expression levels of networks of distal genes. We show that these networks are predominantly associated with tumourigenesis pathways, through which immortalised cells are able to rapidly proliferate. We consequently present an approach to define gene interaction networks underlying important cellular pathways such as cell immortalisation.

Silenced ZNF154 Is Associated with Longer Survival in Resectable Pancreatic Cancer

Pancreatic cancer has become the third leading cause of cancer-related death in the Western world despite advances in therapy of other cancerous lesions. Late diagnosis due to a lack of symptoms during early disease allows metastatic spread of the tumor. Most patients are considered incurable because of metastasized disease. On a cellular level, pancreatic cancer proves to be rather resistant to chemotherapy. Hence, early detection and new therapeutic targets might improve outcomes. The detection of DNA promoter hypermethylation has been described as a method to identify putative genes of interest in cancer entities. These genes might serve as either biomarkers or might lead to a better understanding of the molecular mechanisms involved. We checked tumor specimens from 80 patients who had undergone pancreatic resection for promoter hypermethylation of the zinc finger protein ZNF154. Then, we further characterized the effects of ZNF154 on cell viability and gene expression by in vitro experiments. We found a significant association between ZNF154 hypermethylation and better survival in patients with resectable pancreatic cancer. Moreover, we suspect that the cell growth suppressor SLFN5 might be linked to a silenced ZNF154 in pancreatic cancer.

Overexpression of SLFN5 induced the epithelial-mesenchymal transition in human lung cancer cell line A549 through β-catenin/Snail/E-cadherin pathway

Lung cancer is a disease with increasing morbidity worldwide in recent years. Approaches such as chemotherapy and biological targeting for its treatment are urgently needed. Epithelial-mesenchymal transition (EMT) is an important initiation stage for tumor cells to acquire invasive and metastatic abilities. Increasing findings have shown that human schlafen family member 5 (SLFN5) plays a key role in malignant tumors. However, the role of SLFN5 in lung cancer cells is not completely elucidated yet. In this study, overexpression or knockdown of SLFN5 gene were induced by lentiviral transfection in human lung cancer cell line A549, then the EMT of A549 was detected by green fluorescent protein labeling method, the migrative and invasive abilities were evaluated via transwell and wound-healing tests in vitro and chick chorioallantoic membrane inoculation in vivo, and the possible mechanism was studied by quantitative real-time PCR and Western blotting. Our results demonstrated that overexpression of SLFN5 promoted the morphology transformation of A549 from epithelial to mesenchymal, as well as migration and invasion. However, knockdown of SLFN5 resulted in the opposite results. Moreover, with the development of EMT after SLFN5 was overexpressed, A549 exhibited enhanced translocation of β-catenin from membrane to cytoplasm or nucleus, with higher level of EMT-related transcription factor Snail, and lower expression of adhesin E-cadherin. Together these results suggest that SLFN5 may act as a synergist in lung cancer cell tumorigenesis and progression, providing a potential target for developing drugs for lung cancer therapy in future.

Long noncoding RNA HAS2-AS1 promotes tumor progression in glioblastoma via functioning as a competing endogenous RNA

Glioblastoma multiforme (GBM) is a refractory tumor with poor prognosis and requires more effective treatment regimens. It has been confirmed that long noncoding RNAs (lncRNAs) substantially regulate various human disease including GBM. However, the biological roles and its underlying molecular mechanisms still need to be further investigated. In this study, the biological function and potential molecular mechanism of lncHAS2-AS1 in GBM were explored. It was discovered that HAS2-AS1 was elevated in glioma tissues and correlated with the prognosis of patients with glioma. Reduction of HAS2-AS1 suppressed the migration and invasion in vitro and in vivo. The transcription factor STAT1 could raise HAS2-AS1 by binding to its promoter region. Besides, HAS2-AS1 could adjust PRPS1 via sponging miR-608 in a direct manner. On the whole, the results of this study evidence that HAS2-AS1 is an oncogene and a potential therapeutic target for GBM.

Deciphering the three-domain architecture in schlafens and the structures and roles of human schlafen12 and serpinB12 in transcriptional regulation

Schlafen proteins are important in cell differentiation and defense against viruses, and yet this family of vertebrate proteins is just beginning to be understood at the molecular level. Here, the three-dimensional architecture and molecular interfaces of human schlafen12 (hSLFN12), which promotes intestinal stem cell differentiation, are analyzed by sequence conservation and structural modeling in light of the functions of its homologs and binding partners. Our analysis shows that the schlafen or divergent AAA ATPase domain described in the N-terminal region of schlafens in databases and the literature is a misannotation. This N-terminal region is conclusively an AlbA_2 DNA/RNA binding domain, forming the conserved core of schlafens and their sequence homologs from bacteria through mammals. Group III schlafens additionally contain a AAA NTPase domain in their C-terminal helicase region. In hSLFN12, we have uncovered a domain matching rho GTPases, which directly follows the AlbA_2 domain in all group II-III schlafens. Potential roles for the GTPase-like domain include antiviral activity and cytoskeletal interactions that contribute to nucleocytoplasmic shuttling and cell polarization during differentiation. Based on features conserved with rSlfn13, the AlbA_2 region in hSLFN12 is likely to bind RNA, possibly as a ribonuclease. We hypothesize that RNA binding by hSLFN12 contributes to an RNA-induced transcriptional silencing/E3 ligase complex, given the functions of hSLFN12's partners, SUV39H1, JMJD6, and PDLIM7. hSLFN12's partner hSerpinB12 may contribute to heterochromatin formation, based on its homology to MENT, or directly regulate transcription via its binding to RNA polymerase II. The analysis presented here provides clear architectural and transcriptional regulation hypotheses to guide experimental design for hSLFN12 and the thousands of schlafens that share its motifs.

Interferon signaling in cancer. Non-canonical pathways and control of intracellular immune checkpoints

The interferons (IFNs) are cytokines with important antineoplastic and immune modulatory effects. These cytokines have been conserved through evolution as important elements of the immune surveillance against cancer. Despite this, defining their precise and specific roles in the generation of antitumor responses remains challenging. Emerging evidence suggests the existence of previously unknown roles for IFNs in the control of the immune response against cancer that may redefine our understanding on how these cytokines function. Beyond the engagement of classical JAK-STAT signaling pathways that promote transcription and expression of gene products, the IFNs engage multiple other signaling cascades to generate products that mediate biological responses and outcomes. There is recent emerging evidence indicating that IFNs control the expression of both traditional immune checkpoints like the PD-L1/PD1 axis, but also less well understood "intracellular" immune checkpoints whose targeting may define new approaches for the treatment of malignancies.

SLFN5 suppresses cancer cell migration and invasion by inhibiting MT1-MMP expression via AKT/GSK-3β/β-catenin pathway

Human SLFN5 inhibits invasions of IFNα-sensitive renal clear-cell carcinoma and melanoma cells. However, whether this inhibition is confined to these IFNα-sensitive cancers is unclear. Here we show that SLFN5 expressions on both mRNA and protein levels are significantly higher in non/low-invasive cancer cell lines (breast cancer cell line MCF7, colorectal cancer cell line HCT116 and lung cancer cell line A549) than in highly-invasive cancer cell lines (fibrosarcoma cell line HT1080 and renal clear cell cancer cell line 786-0). SLFN5 knockdown in non/low-invasive cancer cell lines enhanced MT1-MMP expression and increased migration and invasion in vitro, and in vivo. Furthermore, SLFN5 overexpression in HT1080 and 786-0 inhibited MT1-MMP expression and repressed migration and invasion. MT1-MMP is instrumental in SLFN5-controlled inhibition of cancer cell migration and invasion, as shown by MT1-MMP-knockdown and -overexpression analyses. SLFN5 knockdown activated AKT/GSK-3β/β-catenin pathway by promotion AKT phosphorylation and subsequent GSK-3β phosphorylation, further β-catenin translocation into nucleus as un-phosphorylated protein at Ser33, 37 and 45 and Thr41 sites. This is the first study to report that SLFN5 inhibits cancer migration and invasiveness in several common cancer cell lines by repressing MT1-MMP expression via the AKT/GSK-3β/β-catenin signalling pathway, suggesting that SLFN5 plays wide inhibitory roles in various cancers.

Slfn2 Regulates Type I Interferon Responses by Modulating the NF-κB Pathway

Although members of the Slfn family have been implicated in the regulation of type I interferon (IFN) responses, the mechanisms by which they mediate their effects remain unknown. In the present study, we provide evidence that targeted disruption of the Slfn2 gene leads to increased transcription of IFN-stimulated genes (ISGs) and enhanced type I IFN-mediated antiviral responses. We demonstrate that Slfn2 interacts with protein phosphatase 6 regulatory subunit 1 (PPP6R1), leading to reduced type I IFN-induced activation of nuclear factor kappa B (NF-κB) signaling, resulting in reduced expression of ISGs. Altogether, these data suggest a novel mechanism by which Slfn2 controls ISG expression and provide evidence for a critical role for Slfn2 in the regulation of IFN-mediated biological responses.

Microglia have a more extensive and divergent response to interferon-α compared with astrocytes

Type I interferons (IFN-I) are crucial for effective antimicrobial defense in the central nervous system (CNS) but also can cause severe neurological disease (termed cerebral interferonopathy) as exemplified by Aicardi-Goutières Syndrome. In the CNS, microglia and astrocytes have essential roles in host responses to infection and injury, with both cell types responding to IFN-I. While the IFN-I signaling pathways are the same in astrocytes and microglia, the extent to which the IFN-I responses of these cells differ, if at all, is unknown. Here we determined the global transcriptional responses of astrocytes and microglia to the IFN-I, IFN-α. We found that under basal conditions, each cell type has a unique gene expression pattern reflective of its developmental origin and biological function. Following stimulation with IFN-α, astrocytes and microglia also displayed a common core response that was characterized by the increased expression of genes required for pathogen detection and elimination. Compared with astrocytes, microglia had a more extensive and diverse response to IFN-α with significantly more genes with expression upregulated (282 vs. 141) and downregulated (81 vs. 3). Further validation was documented for selected IFN-I-regulated genes in a murine model of cerebral interferonopathy. In all, the findings highlight not only overlapping but importantly divergent responses to IFN-I by astrocytes versus microglia. This suggests specialized roles for these cells in host defense and in the development of cerebral interferonopathy.

Meeting summary: 2nd Aegean Conference on Cytokine Signaling in Cancer

Cytokines and chemokines are intricately connected to cancer initiation, progression and metastasis as well as to innate and adaptive host defense mechanisms against transformed cells. The Aegean Conference on Cytokine Signaling in Cancer (ACCSC) aims to bring together researchers in this highly targeted area of cancer research in a lovely and relaxing Greek-Mediterranean backdrop to discuss latest developments. Being small in size with about one hundred participants, this conference fosters scientific and social interactions among established and emerging scientists in clinical and basic research in diverse fields of oncology, biochemistry, biophysics, genetics and immunology. The 2nd ACCSC held at Heraklion on the Greek island of Crete was organized by Serge Fuchs (University of Pennsylvania), Mathias Muller (University of Veterinary Medicine Vienna), Leonidas Platanias (Northwestern University, Chicago) and Belinda Parker (La Trobe University, Melbourne) between May 30 and June 04, 2017, was a great success in every single aspect of a high level scientific meeting. Signaling within cancer cells as well as in stromal and immune cells is the common thread of this conference series. An outline of the research topics discussed at this conference is presented here to emphasize its high quality and to stimulate interest among cytokine researchers to participate in future ACCSC meetings.