Mnk Kinases in Cytokine Signaling and Regulation of Cytokine Responses

Functional characterization of irf3 against viral hemorrhagic septicemia virus infection using a CRISPR/Cas9-mediated zebrafish knockout model

Interferon regulatory factors (IRFs) are transcription factors involved in immune responses, such as pathogen response regulation, immune cell growth, and differentiation. IRFs are necessary for the synthesis of type I interferons through a signaling cascade when pathogen recognition receptors identify viral DNA or RNA. We discovered that irf3 is expressed in the early embryonic stages and in all immune organs of adult zebrafish. We demonstrated the antiviral immune mechanism of Irf3 against viral hemorrhagic septicemia virus (VHSV) using CRISPR/Cas9-mediated knockout zebrafish (irf3-KO). In this study, we used a truncated Irf3 protein, encoded by irf3 with a 10 bp deletion, for further investigation. Upon VHSV injection, irf3-KO zebrafish showed dose-dependent high and early mortality compared with zebrafish with the wild-type Irf3 protein (WT), confirming the antiviral activity of Irf3. Based on the results of expression analysis of downstream genes upon VHSV challenge, we inferred that Irf3 deficiency substantially affects the expression of ifnphi1 and ifnphi2. However, after 5 days post infection (dpi), ifnphi3 expression was not significantly altered in irf3-KO compared to that in WT, and irf7 transcription showed a considerable increase in irf3-KO after 5 dpi, indicating irf7's control over ifnphi3 expression. The significantly reduced expression of isg15, viperin, mxa, and mxb at 3 dpi also supported the effect of Irf3 deficiency on the antiviral activity in the early stage of infection. The higher mortality in irf3-KO zebrafish than in WT might be due to an increased inflammation and tissue damage that occurs in irf3-KO because of delayed immune response. Our results suggest that Irf3 plays a role in antiviral immunity of zebrafish by modulating critical immune signaling molecules and regulating antiviral immune genes.

The role of MNK1-mTORC1 pathway in modulating macrophage responses to Vibrio vulnificus infection

Vibrio vulnificus (Vv) is known to cause life-threatening infections, particularly septicemia. These patients often exhibit elevated levels of pro-inflammatory cytokines. While it is established that mitogen-activated protein kinase (MAPK)-interacting kinase (MNK) contributes to the production of pro-inflammatory cytokines, the role of MNK in macrophages during Vv infection remains unclear. In this study, we investigate the impact of MNK on macrophages. We demonstrate that the inhibition of MNK in J774A.1 cells, when treated with lipopolysaccharide or Vv, resulted in decreased production of tumor necrosis factor alpha and interleukin-6, without affecting their transcription. Interestingly, treatment with MNK inhibitor CGP57380 led to enhanced phosphorylation of MNK1 but decreased phosphorylation of eIF4E. Moreover, MNK1 knockout cells exhibited an increased capacity for phagocytosis and clearance of Vv, with more acidic phagosomes than the parental cells. Notably, CGP57380 did not impact phagocytosis, bacterial clearance, or phagosome acidification in Vv-infected J774A.1 cells. Considering the reported association between MNK and mammalian target of rapamycin complex 1 (mTORC1) activation, we investigated the mTORC1 signaling in MNK1 knockout cells infected with Vv. Our results revealed that attenuation of the mTORC1 signaling in these cells and treatment with the mTORC1 inhibitor rapamycin significantly enhanced bacterial clearance in J774A.1 cells following Vv infection. In summary, our findings suggest that MNK promotes the Vv-induced cytokine production in J774A.1 cells without affecting their transcription levels. MNK1 appears to impair the phagocytosis, bacterial clearance, and phagosome acidification in Vv-infected J774A.1 cells through the MNK1-mTORC1 signaling pathway rather than the MNK1-eIF4E signaling pathway. Our findings highlight the importance of the MNK1-mTORC1 pathway in modulating macrophage responses to Vv infection.

IMPORTANCE

Mitogen-activated protein kinase (MAPK)-interacting kinase (MNK) plays a role in promoting the production of tumor necrosis factor alpha and interleukin-6 in macrophages during Vibrio vulnificus (Vv) infection. Inhibition or knockout of MNK1 in J774A.1 cells resulted in reduced cytokine production without affecting their transcription levels. MNK1 also impairs phagocytosis, bacterial clearance, and phagosome acidification in Vv-infected cells through the MNK1-mammalian target of rapamycin complex 1 (mTORC1) signaling pathway. The findings highlight the importance of the MNK1-mTORC1 pathway in modulating macrophage responses to Vv infection.

Cynomolgus macaques as a translational model of human immune responses to yellow fever 17D vaccination

The non-human primate (NHP) model (specifically rhesus and cynomolgus macaques) has facilitated our understanding of the pathogenic mechanisms of yellow fever (YF) disease and allowed the evaluation of the safety and efficacy of YF-17D vaccines. However, the accuracy of this model in mimicking vaccine-induced immunity in humans remains to be fully determined. We used a systems biology approach to compare hematological, biochemical, transcriptomic, and innate and antibody-mediated immune responses in cynomolgus macaques and human participants following YF-17D vaccination. Immune response progression in cynomolgus macaques followed a similar course as in adult humans but with a slightly earlier onset. Yellow fever virus neutralizing antibody responses occurred earlier in cynomolgus macaques [by Day 7[(D7)], but titers > 10 were reached in both species by D14 post-vaccination and were not significantly different by D28 [plaque reduction neutralization assay (PRNT)50 titers 3.6 Log vs 3.5 Log in cynomolgus macaques and human participants, respectively; P = 0.821]. Changes in neutrophils, NK cells, monocytes, and T- and B-cell frequencies were higher in cynomolgus macaques and persisted for 4 weeks versus less than 2 weeks in humans. Low levels of systemic inflammatory cytokines (IL-1RA, IL-8, MIP-1α, IP-10, MCP-1, or VEGF) were detected in either or both species but with no or only slight changes versus baseline. Similar changes in gene expression profiles were elicited in both species. These included enriched and up-regulated type I IFN-associated viral sensing, antiviral innate response, and dendritic cell activation pathways D3-D7 post-vaccination in both species. Hematological and blood biochemical parameters remained relatively unchanged versus baseline in both species. Low-level YF-17D viremia (RNAemia) was transiently detected in some cynomolgus macaques [28% (5/18)] but generally absent in humans [except one participant (5%; 1/20)].IMPORTANCECynomolgus macaques were confirmed as a valid surrogate model for replicating YF-17D vaccine-induced responses in humans and suggest a key role for type I IFN.

Molecular characterization, expression profile, and antiviral activity of redlip mullet (Liza haematocheila) viperin

Viperin is known to exhibit activity against RNA viral infection. Viral hemorrhagic septicemia virus (VHSV) is a negative-sense single-stranded RNA virus that causes severe loss in aquaculture species. Susceptible species include redlip mullets (Liza haematocheila), which has become an economically important euryhaline mugilid species in offshore aquaculture along the west coast of Korea. Although interferon-stimulated genes are suspected to act against VHSV, specific pathways or mechanisms of these antiviral actions in redlip mullets have not yet been established. In silico studies of the mullet viperin (Lhrsad2) revealed an S-adenosyl methionine binding conserved domain containing the ⁷⁷CNYKCGFC⁸⁴ sequence. In the tissue distribution, the highest levels of lhrsad2 expression were observed in the blood. When injected with poly(I:C), an approximately 17-fold upregulation (compared to the control) of viperin was detected in the blood after 24 h. Furthermore, non-viral immune stimuli, including Lactococcus garvieae (L. garvieae) and lipopolysaccharide (LPS), that were injected into redlip mullets were not found to induce considerable levels of viperin expression. Subcellular analysis revealed that Lhrsad2 localized to the endoplasmic reticulum (ER). To investigate Lhrsad2's antiviral effects against VHSV, cells overexpressing lhrsad2 were infected with VHSV, and then the viral titer and viral gene expression were analyzed. Both assays revealed the potential of Lhrsad2 to significantly reduce VHSV transcription and replication. In brief, the current study illustrates the remarkable ability of viperin to weaken VHSV in redlip mullet.

Lipid droplets diversity and functions in inflammation and immune response

INTRODUCTION

Lipid droplets (LDs) are dynamic and evolutionary conserved lipid-enriched organelles composed of a core of neutral lipids surrounded by a monolayer of phospholipids associated with a diverse array of proteins that are cell- and stimulus-regulated. Far beyond being simply a deposit of neutral lipids, accumulating evidence demonstrate that LDs act as spatial and temporal local for lipid and protein compartmentalization and signaling organization.

AREAS COVERED

This review focuses on the progress in our understanding of LD protein diversity and LD functions in the context of cell signaling and immune responses, highlighting the relationship between LD composition with the multiple roles of this organelle in immunometabolism, inflammation and host-response to infection.

EXPERT OPINION

LDs are essential platforms for various cellular processes, including metabolic regulation, cell signaling, and immune responses. The functions of LD in infection and inflammatory disease are associated with the dynamic and complexity of their proteome. Our contemporary view place LDs as critical regulators of different inflammatory and infectious diseases and key markers of leukocyte activation.

Viperin has species-specific roles in response to herpes simplex virus infection

Viperin is a gene with a broad spectrum of antiviral functions and various mechanisms of action. The role of viperin in herpes simplex virus type 1 (HSV-1) infection is unclear, with conflicting data in the literature that is derived from a single human cell type. We have addressed this gap by investigating viperin during HSV-1 infection in several cell types, spanning species and including immortalized, non-immortalized and primary cells. We demonstrate that viperin upregulation by HSV-1 infection is cell-type-specific, with mouse cells typically showing greater increases compared with those of human origin. Further, overexpression and knockout of mouse, but not human viperin significantly impedes and increases HSV-1 replication, respectively. In primary mouse fibroblasts, viperin upregulation by infection requires viral gene transcription and occurs in a predominantly IFN-independent manner. Further we identify the N-terminal domain of viperin as being required for the anti-HSV-1 activity. Interestingly, this is the region of viperin that differs most between mouse and human, which may explain the apparent species-specific activity against HSV-1. Finally, we show that HSV-1 virion host shutoff (vhs) protein is a key viral factor that antagonises viperin in mouse cells. We conclude that viperin can be upregulated by HSV-1 in mouse and human cells, and that mouse viperin has anti-HSV-1 activity.

The antiviral enzyme viperin inhibits cholesterol biosynthesis

Many enveloped viruses bud from cholesterol-rich lipid rafts on the cell membrane. Depleting cellular cholesterol impedes this process and results in viral particles with reduced viability. Viperin (Virus Inhibitory Protein, Endoplasmic Reticulum-associated, Interferon iNducible) is an endoplasmic reticulum membrane-associated enzyme that exerts broad-ranging antiviral effects, including inhibiting the budding of some enveloped viruses. However, the relationship between viperin expression and the retarded budding of virus particles from lipid rafts on the cell membrane is unclear. Here, we investigated the effect of viperin expression on cholesterol biosynthesis using transiently expressed genes in the human cell line human embryonic kidney 293T (HEK293T). We found that viperin expression reduces cholesterol levels by 20% to 30% in these cells. Following this observation, a proteomic screen of the viperin interactome identified several cholesterol biosynthetic enzymes among the top hits, including lanosterol synthase (LS) and squalene monooxygenase (SM), which are enzymes that catalyze key steps in establishing the sterol carbon skeleton. Coimmunoprecipitation experiments confirmed that viperin, LS, and SM form a complex at the endoplasmic reticulum membrane. While coexpression of viperin was found to significantly inhibit the specific activity of LS in HEK293T cell lysates, coexpression of viperin had no effect on the specific activity of SM, although did reduce SM protein levels by approximately 30%. Despite these inhibitory effects, the coexpression of neither LS nor SM was able to reverse the viperin-induced depletion of cellular cholesterol levels, possibly because viperin is highly expressed in transfected HEK293T cells. Our results establish a link between viperin expression and downregulation of cholesterol biosynthesis that helps explain viperin's antiviral effects against enveloped viruses.

Immunotherapies targeting stimulatory pathways and beyond

Co-stimulatory and co-inhibitory molecules play a critical role in T cell function. Tumor cells escape immune surveillance by promoting immunosuppression. Immunotherapy targeting inhibitory molecules like anti-CTLA-4 and anti-PD-1/PD-L1 were developed to overcome these immunosuppressive effects. These agents have demonstrated remarkable, durable responses in a small subset of patients. The other mechanisms for enhancing anti-tumor activities are to target the stimulatory pathways that are expressed on T cells or other immune cells. In this review, we summarize current phase I/II clinical trials evaluating novel immunotherapies targeting stimulatory pathways and outline their advantages, limitations, and future directions.

Whole-exome sequencing of de novo genetic variants in a Chinese family with a sporadic case of congenital nonsyndromic hearing loss

Background: We examined the genetic variants of a Chinese family with a 22-month-old infant with sporadic non-syndromic sensorineural hearing loss (NSHL). Methods: The whole-exome sequence data in the family, especially the de novo variants presented in the patient, were analyzed and the effect of the disease-causing genetic variants on the protein expression level and cellular localization were examined by cell-based functional assay. Results: The infant had no known NSHL-causing variants, except two compound heterozygous variants in connexin26 gene GJB2; one was the c.79G>A, c.341A>G haplotype from the asymptomatic mother who was benign, and the other was a de novo pathogenic c.262G>C (p.A88P). In vitro, GJB2 with c.262G>C was weakly expressed and displayed a punctate distribution in the cytoplasm and cytomembrane, while wild type GJB2 was robustly expressed in the cytomembrane. We deduced that the de novo pathogenic GJB2 c.262G>C exacerbated loss-of-function in the context of leaky variants c.79G>A, c.341A>G in the patient. Interestingly, further analysis of exome sequences revealed that the occurrence of de novo pathogenic variants in the infant was frequent. Among the total~47,000 variants, 143 were de novo in the patient, whereas among all 74 variants predicted to be pathogenic/likely pathogenic, 21 were heterozygous and two were homozygous de novo. The occurrence rate of de novo deleterious variants was much higher (31.1%, 23/74) than that in total (0.34%, 143/47,000). It is notable that most genes with de novo deleterious variants were environment-sensitive, such as GJB2, MNK1, MNK2, MUC4, RAD21 and DNA copy number variations. Conclusions: The full picture of genetic variants in the exome might help us to interpret the NSHL-causing variants. More research is needed into the causes of de novo deleterious variants and gene-environment interactions in congenital NSHL.

Whole-exome sequencing of de novo genetic variants in a Chinese family with a sporadic case of congenital nonsyndromic hearing loss

Background: We examined the genetic variants of a Chinese family with a 22-month-old infant with sporadic non-syndromic sensorineural hearing loss (NSHL). Methods: The whole-exome sequence data in the family, especially the de novo variants presented in the patient, were analyzed and the effect of the disease-causing genetic variants on the protein expression level and cellular localization were examined by cell-based functional assay. Results: The infant had no known NSHL-causing variants, except two compound heterozygous variants in connexin26 gene GJB2; one was the c.79G>A, c.341A>G haplotype from the asymptomatic mother which was benign, and the other was a de novo pathogenic c.262G>C (p.A88P). In vitro, GJB2 with c.262G>C was weakly expressed and displayed a punctate distribution in the cytoplasm and cytomembrane, while wild type GJB2 was robustly expressed in the cytomembrane. We deduced that the de novo pathogenic GJB2 c.262G>C exacerbated loss-of-function in the context of leaky variants c.79G>A, c.341A>G in the patient. Interestingly, further analysis of exome sequences revealed that the occurrence of de novo pathogenic variants in the infant was frequent. Among the total~47,000 variants, 143 were de novo in the patient, whereas among all 74 variants predicted to be pathogenic/likely pathogenic, 21 were heterozygous and two were homozygous de novo. The occurrence rate of de novo deleterious variants was much higher (31.1%, 23/74) than that in total (0.34%, 143/47,000). It is notable that most genes with de novo deleterious variants were environment-sensitive, such as GJB2, MNK1, MNK2, MUC4, RAD21 and DNA copy number variations. Conclusions: The full picture of genetic variants in the exome might help us to interpret the NSHL-causing variants. More research is needed into the causes of de novo deleterious variants and gene-environment interactions in congenital NSHL.

Dance with the Devil: Stress Granules and Signaling in Antiviral Responses

Cells have evolved highly specialized sentinels that detect viral infection and elicit an antiviral response. Among these, the stress-sensing protein kinase R, which is activated by double-stranded RNA, mediates suppression of the host translation machinery as a strategy to limit viral replication. Non-translating mRNAs rapidly condensate by phase separation into cytosolic stress granules, together with numerous RNA-binding proteins and components of signal transduction pathways. Growing evidence suggests that the integrated stress response, and stress granules in particular, contribute to antiviral defense. This review summarizes the current understanding of how stress and innate immune signaling act in concert to mount an effective response against virus infection, with a particular focus on the potential role of stress granules in the coordination of antiviral signaling cascades.

Comparative Transcriptomic Analysis of Rhinovirus and Influenza Virus Infection

Rhinovirus (RV) and influenza virus are the most frequently detected respiratory viruses among adult patients with community acquired pneumonia. Previous clinical studies have identified major differences in the clinical presentations and inflammatory or immune response during these infections. A systematic transcriptomic analysis directly comparing influenza and RV is lacking. Here, we sought to compare the transcriptomic response to these viral infections. Human airway epithelial Calu-3 cells were infected with contemporary clinical isolates of RV, influenza A virus (IAV), or influenza B virus (IBV). Host gene expression was determined using RNA-seq. Differentially expressed genes (DEGs) with respect to mock-infected cells were identified using the overlapping gene-set of four different statistical models. Transcriptomic analysis showed that RV-infected cells have a more blunted host response with fewer DEGs than IAV or IBV-infected cells. IFNL1 and CXCL10 were among the most upregulated DEGs during RV, IAV, and IBV infection. Other DEGs that were highly expressed for all 3 viruses were mainly genes related to type I or type III interferons (RSAD2, IDO1) and chemokines (CXCL11). Notably, ICAM5, a known receptor for enterovirus D68, was highly expressed during RV infection only. Gene Set Enrichment Analysis (GSEA) confirmed that pathways associated with interferon response, innate immunity, or regulation of inflammatory response, were most perturbed for all three viruses. Network analysis showed that steroid-related pathways were enriched. Taken together, our data using contemporary virus strains suggests that genes related to interferon and chemokine predominated the host response associated with RV, IAV, and IBV infection. Several highly expressed genes, especially ICAM5 which is preferentially-induced during RV infection, deserve further investigation.

Newcastle Disease virus infection activates PI3K/Akt/mTOR and p38 MAPK/Mnk1 pathways to benefit viral mRNA translation via interaction of the viral NP protein and host eIF4E

Newcastle disease virus (NDV), a member of the Paramyxoviridae family, can activate PKR/eIF2α signaling cascade to shutoff host and facilitate viral mRNA translation during infection, however, the mechanism remains unclear. In this study, we revealed that NDV infection up-regulated host cap-dependent translation machinery by activating PI3K/Akt/mTOR and p38 MAPK/Mnk1 pathways. In addition, NDV infection induced p38 MAPK/Mnk1 signaling participated 4E-BP1 hyperphosphorylation for efficient viral protein synthesis when mTOR signaling is inhibited. Furthermore, NDV NP protein was found to be important for selective cap-dependent translation of viral mRNAs through binding to eIF4E during NDV infection. Taken together, NDV infection activated multiple signaling pathways for selective viral protein synthesis in infected cells, via interaction between viral NP protein and host translation machinery. Our results may help to design novel targets for therapeutic intervention against NDV infection and to understand the NDV anti-oncolytic mechanism.

Viruses are obligate intracellular parasites and have no protein translation machinry of their own. Therefore, viruses remain exclusively dependent on host translation machinery to ensure viral protein synthesis and progeny virion production during infection. We previous reported that Newcastle disease virus (NDV) shutoff host and facilitate viral mRNA translation by activating PKR/eIF2α signaling cascade. Here, we demonstrated that NDV infection up-regulated host cap-dependent translation machinery by activating PI3K/Akt/mTOR and p38 MAPK/Mnk1 pathways. Furthermore, NDV NP protein was found to be important for selective cap-dependent translation of viral mRNAs. Our findings highlight a new strategy how virus used host translation machinery for selective viral protein synthesis.

Viperin Reveals Its True Function

Most cells respond to viral infections by activating innate immune pathways that lead to the induction of antiviral restriction factors. One such factor, viperin, was discovered almost two decades ago based on its induction during viral infection. Since then, viperin has been shown to possess activity against numerous viruses via multiple proposed mechanisms. Most recently, however, viperin was demonstrated to catalyze the conversion of cytidine triphosphate (CTP) to 3'-deoxy-3',4'-didehydro-CTP (ddhCTP), a previously unknown ribonucleotide. Incorporation of ddhCTP causes premature termination of RNA synthesis by the RNA-dependent RNA polymerase of some viruses. To date, production of ddhCTP by viperin represents the only activity of viperin that links its enzymatic activity directly to an antiviral mechanism in human cells. This review examines the multiple antiviral mechanisms and biological functions attributed to viperin.

The MNK1/2-eIF4E Axis as a Potential Therapeutic Target in Melanoma

: Melanoma is a type of skin cancer that originates in the pigment-producing cells of the body known as melanocytes. Most genetic aberrations in melanoma result in hyperactivation of the mitogen activated protein kinase (MAPK) and phosphoinositide 3-kinase (PI3K) pathways. We and others have shown that a specific protein synthesis pathway known as the MNK1/2-eIF4E axis is often dysregulated in cancer. The MNK1/2-eIF4E axis is a point of convergence for these signaling pathways that are commonly constitutively activated in melanoma. In this review we consider the functional implications of aberrant mRNA translation in melanoma and other malignancies. Moreover, we discuss the consequences of inhibiting the MNK1/2-eIF4E axis on the tumor and tumor-associated cells, and we provide important avenues for the utilization of this treatment modality in combination with other targeted and immune-based therapies. The past decade has seen the increased development of selective inhibitors to block the action of the MNK1/2-eIF4E pathway, which are predicted to be an effective therapy regardless of the melanoma subtype (e.g., cutaneous, acral, and mucosal).

Targeting viperin to the mitochondrion inhibits the thiolase activity of the trifunctional enzyme complex

Understanding the mechanisms by which viruses evade host cell immune defenses is important for developing improved antiviral therapies. In an unusual twist, human cytomegalovirus co-opts the antiviral radical SAM enzyme viperin (virus-inhibitory protein, endoplasmic reticulum-associated, interferon-inducible) to enhance viral infectivity. This process involves translocation of viperin to the mitochondrion, where it binds the β-subunit (HADHB) of the mitochondrial trifunctional enzyme complex that catalyzes thiolysis of β-ketoacyl-CoA esters as part of fatty acid β-oxidation. Here we investigated how the interaction between these two enzymes alters their activities and affects cellular ATP levels. Experiments with purified enzymes indicated that viperin inhibits the thiolase activity of HADHB, but, unexpectedly, HADHB activates viperin, leading to synthesis of the antiviral nucleotide 3'-deoxy-3',4'-didehydro-CTP. Measurements of enzyme activities in lysates prepared from transfected HEK293T cells expressing these enzymes mirrored the findings obtained with purified enzymes. Thus, localizing viperin to mitochondria decreased thiolase activity, and coexpression of HADHB significantly increased viperin activity. Furthermore, targeting viperin to mitochondria also increased the rate at which HADHB is retrotranslocated out of mitochondria and degraded, providing an additional mechanism by which viperin reduces HADHB activity. Targeting viperin to mitochondria decreased cellular ATP levels by more than 50%, consistent with the enzyme disrupting fatty acid catabolism. These results provide biochemical insight into the mechanism by which human cytomegalovirus subverts viperin; they also provide a biochemical rationale for viperin's recently discovered role in regulating thermogenesis in adipose tissues.

Expression, subcellular localization, and potential antiviral function of three interferon regulatory factors in the big-belly seahorse (Hippocampus abdominalis)

Interferon regulatory factors (IRFs) are among the most important transcription mediators and have multiple biological functions, such as antiviral and antimicrobial defense, cell differentiation, immune modulation, and apoptosis. Three IRF family members (HaIRF4-like, HaIRF6, and HaIRF8) of the big belly seahorse (Hippocampus abdominalis) were molecularly and functionally characterized at the sequence and transcriptional level. The coding sequences of HaIRF4-like, HaIRF6, and HaIRF8 were 1214, 1485, and 1266 bp in length, encoding proteins of size 46.21, 55.32, and 47.56 kDa, respectively. Potential viral transcription and replication was detected against VHSV infection using qPCR in HaIRFs-transfected FHM cells. IRFs significantly reduced viral gene expression at 24 h and 48 h post infection and the expression of interferon-stimulated genes (ISGs) was modulated at transcriptional level upon HaIRF overexpression in FHM cells. Subcellular HaIRF localization was observed using GFP-tagged expression vectors in FHM cells. HaIRF4-like and HaIRF8 were localized to the nucleus, whereas HaIRF6 was observed in the cytoplasm. All three IRFs were ubiquitously expressed in all analyzed tissues of the big belly seahorse. The mRNA expression of IRF4-like, IRF6, and IRF8 increased significantly post injection in the blood and gills following LPS, poly (I:C), and Streptococcus iniae challenge. These findings demonstrate that seahorse IRFs are involved in host defense mechanisms against immune stimulants and HaIRFs induce interferon and ISGs which trigger antiviral activity against viral infections in the host.

Differential methylation and expression of genes in the hypoxia-inducible factor 1 signaling pathway are associated with paclitaxel-induced peripheral neuropathy in breast cancer survivors and with preclinical models of chemotherapy-induced neuropathic pain

BACKGROUND

Paclitaxel is an important chemotherapeutic agent for the treatment of breast cancer. Paclitaxel-induced peripheral neuropathy (PIPN) is a major dose-limiting toxicity that can persist into survivorship. While not all survivors develop PIPN, for those who do, it has a substantial negative impact on their functional status and quality of life. No interventions are available to treat PIPN. In our previous studies, we identified that the HIF-1 signaling pathway (H1SP) was perturbed between breast cancer survivors with and without PIPN. Preclinical studies suggest that the H1SP is involved in the development of bortezomib-induced and diabetic peripheral neuropathy, and sciatic nerve injury. The purpose of this study was to identify H1SP genes that have both differential methylation and differential gene expression between breast cancer survivors with and without PIPN.

METHODS

A multi-staged integrated analysis was performed. In peripheral blood, methylation was assayed using microarray and gene expression was assayed using RNA-seq. Candidate genes in the H1SP having both differentially methylation and differential expression were identified between survivors who received paclitaxel and did (n = 25) and did not (n = 25) develop PIPN. Then, candidate genes were evaluated for differential methylation and differential expression in public data sets of preclinical models of PIPN and sciatic nerve injury.

RESULTS

Eight candidate genes were identified as both differential methylation and differential expression in survivors. Of the eight homologs identified, one was found to be differential expression in both PIPN and "normal" mice dorsal root ganglia; three were differential methylation in sciatic nerve injury versus sham rats in both pre-frontal cortex and T-cells; and two were differential methylation in sciatic nerve injury versus sham rats in the pre-frontal cortex.

CONCLUSIONS

This study is the first to evaluate for methylation in cancer survivors with chronic PIPN. The findings provide evidence that the expression of H1SP genes associated with chronic PIPN in cancer survivors may be regulated by epigenetic mechanisms and suggests genes for validation as potential therapeutic targets.

Cell Fate Control by Translation: mRNA Translation Initiation as a Therapeutic Target for Cancer Development and Stem Cell Fate Control

Translation of mRNA is an important process that controls cell behavior and gene regulation because proteins are the functional molecules that determine cell types and function. Cancer develops as a result of genetic mutations, which lead to the production of abnormal proteins and the dysregulation of translation, which in turn, leads to aberrant protein synthesis. In addition, the machinery that is involved in protein synthesis plays critical roles in stem cell fate determination. In the current review, recent advances in the understanding of translational control, especially translational initiation in cancer development and stem cell fate control, are described. Therapeutic targets of mRNA translation such as eIF4E, 4EBP, and eIF2, for cancer treatment or stem cell fate regulation are reviewed. Upstream signaling pathways that regulate and affect translation initiation were introduced. It is important to regulate the expression of protein for normal cell behavior and development. mRNA translation initiation is a key step to regulate protein synthesis, therefore, identifying and targeting molecules that are critical for protein synthesis is necessary and beneficial to develop cancer therapeutics and stem cells fate regulation.

MNK-eIF4E signalling is a highly conserved mechanism for sensory neuron axonal plasticity: evidence from Aplysia californica

Injury to sensory neurons causes an increase in the excitability of these cells leading to enhanced action potential generation and a lowering of spike threshold. This type of sensory neuron plasticity occurs across vertebrate and invertebrate species and has been linked to the development of both acute and persistent pain. Injury-induced plasticity in sensory neurons relies on localized changes in gene expression that occur at the level of mRNA translation. Many different translation regulation signalling events have been defined and these signalling events are thought to selectively target subsets of mRNAs. Recent evidence from mice suggests that the key signalling event for nociceptor plasticity is mitogen-activated protein kinase-interacting kinase (MNK) -mediated phosphorylation of eukaryotic translation initiation factor (eIF) 4E. To test the degree to which this is conserved in other species, we used a previously described sensory neuron plasticity model in Aplysia californica. We find, using a variety of pharmacological tools, that MNK signalling is crucial for axonal hyperexcitability in sensory neurons from Aplysia. We propose that MNK-eIF4E signalling is a core, evolutionarily conserved, signalling module that controls nociceptor plasticity. This finding has important implications for the therapeutic potential of this target, and it provides interesting clues about the evolutionary origins of mechanisms important for pain-related plasticity. This article is part of the Theo Murphy meeting issue 'Evolution of mechanisms and behaviour important for pain'.

Molecular characterization and expression analysis of rockfish (Sebastes schlegelii) viperin, and its ability to enervate RNA virus transcription and replication in vitro

Viperin, also known as RSAD2 (Radical S-adenosyl methionine domain containing 2), is an interferon-induced endoplasmic reticulum-associated antiviral protein. Previous studies have shown that viperin levels are elevated in the presence of viral RNA, but it has rarely been characterized in marine organisms. This study was designed to functionally characterize rockfish viperin (SsVip), to examine the effects of different immune stimulants on its expression, and to determine its subcellular localization. SsVip is a 349 amino acid protein with a predicted molecular mass of 40.24 kDa. It contains an S-adenosyl l-methionine binding conserved domain with a CNYKCGFC sequence. Unchallenged tissue expression analysis using quantitative real time PCR (qPCR) revealed SsVip expression to be the highest in the blood, followed by the spleen. When challenged with poly I:C, SsVip was upregulated by approximately 60-fold in the blood after 24 h, and approximately 50-fold in the spleen after 12 h. Notable upregulation was detected throughout the poly I:C challenge experiment in both tissues. Significant expression of SsVip was detected in the blood following Streptococcus iniae and lipopolysaccharide challenge, and viral hemorrhagic septicemia virus (VHSV) gene transcription was significantly downregulated during SsVip overexpression. Furthermore, cell viability assay and virus titer quantification with the presence of SsVip revealed a significant reduction in virus replication. As with previously identified viperin counterparts, SsVip was localized in the endoplasmic reticulum. Our findings show that SsVip is an antiviral protein crucial to innate immune defense.

Discovery of novel Mnk inhibitors using mutation-based induced-fit virtual high-throughput screening

Mnk kinases (Mnk1 and 2) are downstream effectors of Map kinase pathways and regulate phosphorylation of eukaryotic initiation factor 4E. Engagement of the Mnk pathway is critical in acute myeloid leukemia (AML) leukemogenesis and Mnk inhibitors have potent antileukemic properties in vitro and in vivo, suggesting that targeting Mnk kinases may provide a novel approach for treating AML. Here, we report the development and application of a mutation-based induced-fit in silico screen to identify novel Mnk inhibitors. The Mnk1 structure was modeled by temporarily mutating an amino acid that obstructs the ATP-binding site in the Mnk1 crystal structure while carrying out docking simulations of known inhibitors. The hit compounds display activity in Mnk biochemical and cellular assays, including acute myeloid leukemia progenitors. This approach will enable further rational structure-based drug design of new Mnk inhibitors and potentially novel ways of therapeutically targeting this kinase.

Fat, fight, and beyond: The multiple roles of lipid droplets in infections and inflammation

Increased accumulation of cytoplasmic lipid droplets (LDs) in host nonadipose cells is commonly observed in response to numerous infectious diseases, including bacterial, parasite, and fungal infections. LDs are lipid-enriched, dynamic organelles composed of a core of neutral lipids surrounded by a monolayer of phospholipids associated with a diverse array of proteins that are cell and stimulus regulated. Far beyond being simply a deposit of neutral lipids, LDs have come to be seen as an essential platform for various cellular processes, including metabolic regulation, cell signaling, and the immune response. LD participation in the immune response occurs as sites for compartmentalization of several immunometabolic signaling pathways, production of inflammatory lipid mediators, and regulation of antigen presentation. Infection-driven LD biogenesis is a complexly regulated process that involves innate immune receptors, transcriptional and posttranscriptional regulation, increased lipid uptake, and new lipid synthesis. Accumulating evidence demonstrates that intracellular pathogens are able to exploit LDs as an energy source, a replication site, and/or a mechanism of immune response evasion. Nevertheless, LDs can also act in favor of the host as part of the immune and inflammatory response to pathogens. Here, we review recent findings that explored the new roles of LDs in the context of host-pathogen interactions.

The Novel Mnk1/2 Degrader and Apoptosis Inducer VNLG-152 Potently Inhibits TNBC Tumor Growth and Metastasis

Currently, there are no effective therapies for patients with triple-negative breast cancer (TNBC), an aggressive and highly metastatic disease. Activation of eukaryotic initiation factor 4E (eIF4E) by mitogen-activated protein kinase (MAPK)-interacting kinases 1 and 2 (Mnk1/2) play a critical role in the development, progression and metastasis of TNBC. Herein, we undertook a comprehensive study to evaluate the activity of a first-in-class Mnk1/2 protein degraders, racemic VNLG-152R and its two enantiomers (VNLG-152E1 and VNLG-152E2) in in vitro and in vivo models of TNBC. These studies enabled us to identify racemic VNLG-152R as the most efficacious Mnk1/2 degrader, superior to its pure enantiomers. By targeting Mnk1/2 protein degradation (activity), VNLG-152R potently inhibited both Mnk-eIF4E and mTORC1 signaling pathways and strongly regulated downstream factors involved in cell cycle regulation, apoptosis, pro-inflammatory cytokines/chemokines secretion, epithelial-mesenchymal transition (EMT) and metastasis. Most importantly, orally bioavailable VNLG-152R exhibited remarkable antitumor (91 to 100% growth inhibition) and antimetastatic (~80% inhibition) activities against cell line and patient-derived TNBC xenograft models, with no apparent host toxicity. Collectively, these studies demonstrate that targeting Mnk-eIF4E/mTORC1 signaling with a potent Mnk1/2 degrader, VNLG-152R, is a novel therapeutic strategy that can be developed as monotherapy for the effective treatment of patients with primary/metastatic TNBC.

Molecular and transcriptional insights into viperin protein from Big-belly seahorse (Hippocampus abdominalis), and its potential antiviral role

Viperin is recognized as an antiviral protein that is stimulated by interferon, viral exposures, and other pathogenic molecules in vertebrate. In this study, a viperin homolog in the Big-belly seahorse (Hippocampus abdominalis; HaVip) was functionally characterized to determine its subcellular localization, expression pattern, and antiviral activity in vitro. The HaVip coding sequence encodes a 348 amino acid polypeptide with predicted molecular weight of 38.48 kDa. Sequence analysis revealed that HaVip comprises three main domains: the N-terminal amphipathic α-helix, a radical S-adenosyl-l-methionine (SAM) domain, and a conserved C-terminal domain. Transfected GFP-tagged HaVip protein was found to localize to the endoplasmic reticulum (ER). Overexpressed-HaVip in FHM cells was found to significantly reduce viral capsid gene expression in VHSV infection in vitro. Under normal physiological conditions, HaVip expression was ubiquitously detected in all 14 examined tissues of the seahorse, with the highest expression observed in the heart, followed by skin and blood. In vivo studies showed that HaVip was rapidly and predominantly upregulated in blood, kidney, and intestinal tissue upon poly (I:C) stimulus. LPS and Streptococus iniae challenges caused a significant increase in expression of HaVip in all the analyzed tissues. The obtained results suggest that HaVip is involved in the immune system of the seahorse, triggering antiviral and antibacterial responses, upon viral and bacterial pathogenic infections.

eIF4E phosphorylation regulates ongoing pain, independently of inflammation, and hyperalgesic priming in the mouse CFA model

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CFA-induced inflammation resolves more rapidly in mice lacking MNK-eIF4E signaling.

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Ongoing pain responses are reduced in mice lacking MNK-eIF4E signaling while inflammatory responses are unchanged.

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Hyperalgesic priming in CFA is absent in mice lacking MNK-eIF4E signaling.

Mitogen activated protein kinase-interacting kinase (MNK)-mediated phosphorylation of the mRNA cap binding protein eIF4E controls the translation of a subset of mRNAs that are involved in neuronal and immune plasticity. MNK-eIF4E signaling plays a crucial role in the response of nociceptors to injury and/or inflammatory mediators. This signaling pathway controls changes in excitability that drive acute pain sensitization as well as the translation of mRNAs, such as brain-derived neurotrophic factor (BDNF), that enhance plasticity between dorsal root ganglion (DRG) nociceptors and second order neurons in the spinal dorsal horn. However, since MNK-eIF4E signaling also regulates immune responses, we sought to assess whether decreased pain responses are coupled to decreased inflammatory responses in mice lacking MNK-eIF4E signaling. Our results show that while inflammation resolves more quickly in mice lacking MNK-eIF4E signaling, peak inflammatory responses measured with infrared imaging are not altered in the absence of this signaling pathway even though pain responses are significantly decreased. We also find that inflammation fails to produce hyperalgesic priming, a model for the transition to a chronic pain state, in mice lacking MNK-eIF4E signaling. We conclude that MNK-eIF4E signaling is a critical signaling pathway for the generation of nociceptive plasticity leading to acute pain responses to inflammation and the development of hyperalgesic priming.

Comparative transcriptome analysis of zebrafish (Danio rerio) brain and spleen infected with spring viremia of carp virus (SVCV)

Spring viremia of carp virus (SVCV) is the pathogen of spring viremia of carp (SVC) and often causes acute hemorrhagic symptoms in various kinds of cyprinids and induces serious environmental and economic losses. However, the molecular mechanisms of infection remain poorly understood, especially at the individual level. In this study, zebrafish was employed as the infection model to explore the pathogenesis of SVCV. 4 groups of zebrafish tissues were set and RNA sequencing (RNA-Seq) technology was employed to analyze the differentially expressed genes (DEGs) after SVCV-infection. A total of 360,971,498 clean reads were obtained from 12 samples, 382 DEGs in the brain and 926 DEGs in the spleen were identified. These DEGs were annotated into three ontologies after gene ontology (GO) enrichment analysis. The Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis showed that these DEGs were primarily related to Influenza A pathway and Herpes simplex infection pathway in brain and Tuberculosis and Toxoplasmosis pathways in spleen, and all of these pathways may be involved in response to pathogen invasion. At the same time, 3' and 5' alternative splicing (AS) events were significantly up-regulated in the spleen. The transcriptome analysis results demonstrated changes and tissue-specific influences caused by SVCV in vivo, which provided us with more information to understand the complex relationships between SVCV and its host.

Expression profiles of immune mediators in feline Coronavirus-infected cells and clinical samples of feline Coronavirus-positive cats

Background

There are two biotypes of feline coronavirus (FCoV): the self-limiting feline enteric coronavirus (FECV) and the feline infectious peritonitis virus (FIPV), which causes feline infectious peritonitis (FIP), a fatal disease associated with cats living in multi-cat environments. This study provides an insight on the various immune mediators detected in FCoV-positive cats which may be responsible for the development of FIP.

Results

In this study, using real-time PCR and multiplex bead-based immunoassay, the expression profiles of several immune mediators were examined in Crandell-Reese feline kidney (CRFK) cells infected with the feline coronavirus (FCoV) strain FIPV 79–1146 and in samples obtained from FCoV-positive cats. CRFK cells infected with FIPV 79–1146 showed an increase in the expression of interferon-related genes and pro-inflammatory cytokines such as MX1, viperin, CXCL10, CCL8, RANTES, KC, MCP1, and IL8. In addition, an increase in the expression of the above cytokines as well as GM-CSF and IFNγ was also detected in the PBMC, serum, and peritoneal effusions of FCoV-positive cats. Although the expression of MX1 and viperin genes was variable between cats, the expression of these two genes was relatively higher in cats having peritoneal effusion compared to cats without clinically obvious effusion. Higher viral load was also detected in the supernatant of peritoneal effusions compared to in the plasma of FCoV-positive cats. As expected, the secretion of IL1β, IL6 and TNFα was readily detected in the supernatant of peritoneal effusions of the FCoV-positive cats.

Conclusions

This study has identified various pro-inflammatory cytokines and interferon-related genes such as MX1, viperin, CXCL10, CCL8, RANTES, KC, MCP1, IL8, GM-CSF and IFNγ in FCoV-positive cats. With the exception of MX1 and viperin, no distinct pattern of immune mediators was observed that distinguished between FCoV-positive cats with and without peritoneal effusion. Further studies based on definitive diagnosis of FIP need to be performed to confirm the clinical importance of this study.

Methyl-Arginine Profile of Brain from Aged PINK1-KO+A53T-SNCA Mice Suggests Altered Mitochondrial Biogenesis

Hereditary Parkinson's disease can be triggered by an autosomal dominant overdose of alpha-Synuclein (SNCA) or the autosomal recessive deficiency of PINK1. We recently showed that the combination of PINK1-knockout with overexpression of A53T-SNCA in double mutant (DM) mice potentiates phenotypes and reduces survival. Now we studied brain hemispheres of DM mice at age of 18 months in a hypothesis-free approach, employing a quantitative label-free global proteomic mass spectrometry scan of posttranslational modifications focusing on methyl-arginine. The strongest effects were documented for the adhesion modulator CMAS, the mRNA decapping/deadenylation factor PATL1, and the synaptic plasticity mediator CRTC1/TORC1. In addition, an intriguing effect was observed for the splicing factor PSF/SFPQ, known to interact with the dopaminergic differentiation factor NURR1 as well as with DJ-1, the protein responsible for the autosomal recessive PARK7 variant of PD. CRTC1, PSF, and DJ-1 are modulators of PGC1alpha and of mitochondrial biogenesis. This pathway was further stressed by dysregulations of oxygen sensor EGLN3 and of nuclear TMPO. PSF and TMPO cooperate with dopaminergic differentiation factors LMX1B and NURR1. Further dysregulations concerned PRR18, TRIO, HNRNPA1, DMWD, WAVE1, ILDR2, DBNDD1, and NFM. Thus, we report selective novel endogenous stress responses in brain, which highlight early dysregulations of mitochondrial homeostasis and midbrain vulnerability.

Interferon γ (IFNγ) Signaling via Mechanistic Target of Rapamycin Complex 2 (mTORC2) and Regulatory Effects in the Generation of Type II Interferon Biological Responses

We provide evidence for a unique pathway engaged by the type II IFN receptor, involving mTORC2/AKT-mediated downstream regulation of mTORC1 and effectors. These events are required for formation of the eukaryotic translation initiation factor 4F complex (eIF4F) and initiation of mRNA translation of type II interferon-stimulated genes. Our studies establish that Rictor is essential for the generation of type II IFN-dependent antiviral and antiproliferative responses and that it controls the generation of type II IFN-suppressive effects on normal and malignant hematopoiesis. Together, our findings establish a central role for mTORC2 in IFNγ signaling and type II IFN responses.

Intestinal toxicity of the masked mycotoxin deoxynivalenol-3-β-D-glucoside

Natural food contaminants such as mycotoxins are an important problem for human health. Deoxynivalenol (DON) is one of the most common mycotoxins detected in cereals and grains. Its toxicological effects mainly concern the immune system and the gastrointestinal tract. This toxin is a potent ribotoxic stressor leading to MAP kinase activation and inflammatory response. DON frequently co-occurs with its glucosylated form, the masked mycotoxin deoxynivalenol-3-β-D-glucoside (D3G). The toxicity of this later compound remains unknown in mammals. This study aimed to assess the ability of D3G to elicit a ribotoxic stress and to induce intestinal toxicity. The toxicity of D3G and DON (0-10 µM) was studied in vitro, on the human intestinal Caco-2 cell line, and ex vivo, on porcine jejunal explants. First, an in silico analysis revealed that D3G, contrary to DON, was unable to bind to the A-site of the ribosome peptidyl transferase center, the main targets for DON toxicity. Accordingly, D3G did not activate JNK and P38 MAPKs in treated Caco-2 cells and did not alter viability and barrier function on cells, as measured by the trans-epithelial electrical resistance. Treatment of intestinal explants for 4 h with 10 µM DON induced morphological lesions and up-regulated the expression of pro-inflammatory cytokines as measured by qPCR and pan-genomic microarray analysis. By contrast, expression profile of D3G-treated explants was similar to that of controls, and these explants did not show histomorphology alteration. In conclusion, our data demonstrated that glucosylation of DON suppresses its ability to bind to the ribosome and decreases its intestinal toxicity.

Targeting the translation machinery in cancer

Dysregulation of mRNA translation is a frequent feature of neoplasia. Many oncogenes and tumour suppressors affect the translation machinery, making aberrant translation a widespread characteristic of tumour cells, independent of the genetic make-up of the cancer. Therefore, therapeutic agents that target components of the protein synthesis apparatus hold promise as novel anticancer drugs that can overcome intra-tumour heterogeneity. In this Review, we discuss the role of translation in cancer, with a particular focus on the eIF4F (eukaryotic translation initiation factor 4F) complex, and provide an overview of recent efforts aiming to 'translate' these results to the clinic.

Interferon receptor signaling in malignancy: a network of cellular pathways defining biological outcomes

IFNs are cytokines with important antiproliferative activity and exhibit key roles in immune surveillance against malignancies. Early work initiated over three decades ago led to the discovery of IFN receptor activated Jak-Stat pathways and provided important insights into mechanisms for transcriptional activation of IFN-stimulated genes (ISG) that mediate IFN biologic responses. Since then, additional evidence has established critical roles for other receptor-activated signaling pathways in the induction of IFN activities. These include MAPK pathways, mTOR cascades, and PKC pathways. In addition, specific miRNAs appear to play a significant role in the regulation of IFN signaling responses. This review focuses on the emerging evidence for a model in which IFNs share signaling elements and pathways with growth factors and tumorigenic signals but engage them in a distinctive manner to mediate antiproliferative and antiviral responses.

Mnk kinase pathway: Cellular functions and biological outcomes

The mitogen-activated protein kinase (MAPK) interacting protein kinases 1 and 2 (Mnk1 and Mnk2) play important roles in controlling signals involved in mRNA translation. In addition to the MAPKs (p38 or Erk), multiple studies suggest that the Mnk kinases can be regulated by other known kinases such as Pak2 and/or other unidentified kinases by phosphorylation of residues distinct from the sites phosphorylated by the MAPKs. Several studies have established multiple Mnk protein targets, including PSF, heterogenous nuclear ribonucleoprotein A1, Sprouty 2 and have lead to the identification of distinct biological functions and substrate specificity for the Mnk kinases. In this review we discuss the pathways regulating the Mnk kinases, their known substrates as well as the functional consequences of engagement of pathways controlled by Mnk kinases. These kinases play an important role in mRNA translation via their regulation of eukaryotic initiation factor 4E (eIF4E) and their functions have important implications in tumor biology as well as the regulation of drug resistance to anti-oncogenic therapies. Other studies have identified a role for the Mnk kinases in cap-independent mRNA translation, suggesting that the Mnk kinases can exert important functional effects independently of the phosphorylation of eIF4E. The role of Mnk kinases in inflammation and inflammation-induced malignancies is also discussed.

Regulation of interferon-dependent mRNA translation of target genes

Interferons (IFNs) are released by cells on exposure to various stimuli, including viruses, double-stranded RNA, and other cytokines and various polypeptides. These IFNs play important physiological and pathophysiological roles in humans. Many clinical studies have established activity for these cytokines in the treatment of several malignancies, viral syndromes, and autoimmune disorders. In this review, the regulatory effects of type I and II IFN receptors on the translation-initiation process mediated by mechanistic target of rapamycin (mTOR) and mitogen-activated protein kinase (MAPK) pathways and the known mechanisms of control of mRNA translation of IFN-stimulated genes are summarized and discussed.

Essential role for the Mnk pathway in the inhibitory effects of type I interferons on myeloproliferative neoplasm (MPN) precursors

The mechanisms of generation of the antineoplastic effects of interferons (IFNs) in malignant hematopoietic cells remain to be precisely defined. We examined the activation of type I IFN-dependent signaling pathways in malignant cells transformed by Jak2V617F, a critical pathogenic mutation in myeloproliferative neoplasms (MPNs). Our studies demonstrate that during engagement of the type I IFN receptor (IFNAR), there is activation of Jak-Stat pathways and also engagement of Mnk kinases. Activation of Mnk kinases is regulated by the Mek/Erk pathway and is required for the generation of IFN-induced growth inhibitory responses, but Mnk kinase activation does not modulate IFN-regulated Jak-Stat signals. We demonstrate that for type I IFNs to exert suppressive effects in malignant hematopoietic progenitors from patients with polycythemia vera, induction of Mnk kinase activity is required, as evidenced by studies involving pharmacological inhibition of Mnk or siRNA-mediated Mnk knockdown. Altogether, these findings provide evidence for key and essential roles of the Mnk kinase pathway in the generation of the antineoplastic effects of type I IFNs in Jak2V617F-dependent MPNs.

Emerging themes in radical SAM chemistry

Enzymes in the radical SAM (RS) superfamily catalyze a wide variety of reactions through unique radical chemistry. The characteristic markers of the superfamily include a [4Fe-4S] cluster coordinated to the protein via a cysteine triad motif, typically CX(3)CX(2)C, with the fourth iron coordinated by S-adenosylmethionine (SAM). The SAM serves as a precursor for a 5'-deoxyadenosyl radical, the central intermediate in nearly all RS enzymes studied to date. The SAM-bound [4Fe-4S] cluster is located within a partial or full triosephosphate isomerase (TIM) barrel where the radical chemistry occurs protected from the surroundings. In addition to the TIM barrel and a RS [4Fe-4S] cluster, many members of the superfamily contain additional domains and/or additional Fe-S clusters. Recently characterized superfamily members are providing new examples of the remarkable range of reactions that can be catalyzed, as well as new structural and mechanistic insights into these fascinating reactions.