Control of eIF2 alpha kinases by tyrosine phosphorylation : implications for gene translation and anti-viral signaling

Control of mRNA translation is one of the major regulatory events in eukaryotic gene expression. Recent research has established the existence of a protein kinase family in mammalian cells, whose members phosphorylate the alpha (alpha) subunit of the eukaryotic initiation factor eIF2 (eIF2alpha) at serine 51 and regulate mRNA translation under various stress conditions. The interferon (IFN)-inducible double-stranded (ds) RNA-activated protein kinase PKR is the prototype of this family. Stress conditions activate PKR by autophosphorylation which leads to inhibition of global protein (including viral protein) synthesis and the apoptosis of infected cells. PKR has been well-characterized as a serine/threonine kinase. However, the tyrosine kinase property of PKR and its functional activity remains undetermined. This study demonstrates that human PKR possesses tyrosine kinase activity and undergoes autophosphorylation at tyrosine (Tyr) residues 101, 162 and 293 in vitro and in vivo. Phosphorylation at these tyrosine residues enhances dsRNA binding-efficiency as well as the dimerization of PKR, which in turn favours the full-scale kinase activation and its substrate phosphorylation. Biologically, tyrosine phosphorylated PKR mediates the anti-viral and cellular anti-proliferation activity of the enzyme through its ability to regulate protein synthesis. In addition, the IFNs modulate PKR at both the transcriptional and posttranslational level. Specifically, tyrosine phosphorylation of PKR is inducible in response to stimulations with IFNs. The Janus kinases (Jaks), a group of cytoplasmic tyrosine kinases, are the upstream enzymes which phosphorylate PKR at Tyr101 and Tyr293 in vitro and in vivo. Moreover, induction of PKR tyrosine phosphorylation by IFNs presents a critical missing link between IFN signaling and the translational machinery which contributes to the early effect of IFNs in inhibiting viral protein synthesis. Such a prompt reaction might allow cells to induce IFN responsive-genes and further fortify the antiviral state of the host

Glucagon regulates hepatic lipid metabolism via cAMP and Insig-2 signaling: implication for the pathogenesis of hypertriglyceridemia and hepatic steatosis

Insulin induced gene-2 (Insig-2) is an ER-resident protein that inhibits the activation of sterol regulatory element-binding proteins (SREBPs). However, cellular factors that regulate Insig-2 expression have not yet been identified. Here we reported that cyclic AMP-responsive element-binding protein H (CREBH) positively regulates mRNA and protein expression of a liver specific isoform of Insig-2, Insig-2a, which in turn hinders SREBP-1c activation and inhibits hepatic de novo lipogenesis. CREBH binds to the evolutionally conserved CRE-BP binding elements located in the enhancer region of Insig-2a and upregulates its mRNA and protein expression. Metabolic hormone glucagon and nutritional fasting activated CREBH, which upregulated expression of Insig-2a in hepatocytes and inhibited SREBP-1c activation. In contrast, genetic depletion of CREBH decreased Insig-2a expression, leading to the activation of SREBP-1c and its downstream lipogenic target enzymes. Compromising CREBH-Insig-2 signaling by siRNA interference against Insig-2 also disrupted the inhibitory effect of this signaling pathway on hepatic de novo triglyceride synthesis. These actions resulted in the accumulation of lipid droplets in hepatocytes and systemic hyperlipidemia. Our study identified CREBH as the first cellular protein that regulates Insig-2a expression. Glucagon activated the CREBH-Insig-2a signaling pathway to inhibit hepatic de novo lipogenesis and prevent the onset of hepatic steatosis and hypertriglyceridemia

\u3ci\u3eAkkermansia muciniphila\u3c/i\u3e and its membrane protein ameliorates intestinal inflammatory stress and promotes epithelial wound healing via CREBH and miR‑143/145

Background The intestinal epithelial barrier is the interface for interaction between gut microbiota and host metabolic systems. Akkermansia muciniphila (A. muciniphila) is a key player in the colonic microbiota that resides in the mucus layer, whose abundance is selectively decreased in the faecal microbiota of inflammatory bowel disease (IBD) patients. This study aims to investigate the regulatory mechanism among A. muciniphila, a transcription factor cAMPresponsive element-binding protein H (CREBH), and microRNA-143/145 (miR-143/145) in intestinal inflammatory stress, gut barrier integrity and epithelial regeneration. Methods A novel mouse model with increased colonization of A muciniphila in the intestine of CREBH knockout mice, an epithelial wound healing assay and several molecular biological techniques were applied in this study. Results were analysed using a homoscedastic 2-tailed t-test. Results Increased colonization of A. muciniphila in mouse gut enhanced expression of intestinal CREBH, which was associated with the mitigation of intestinal endoplasmic reticulum (ER) stress, gut barrier leakage and blood endotoxemia induced by dextran sulfate sodium (DSS). Genetic depletion of CREBH (CREBH-KO) significantly inhibited the expression of tight junction proteins that are associated with gut barrier integrity, including Claudin5 and Claudin8, but upregulated Claudin2, a tight junction protein that enhances gut permeability, resulting in intestinal hyperpermeability and inflammation. Upregulation of CREBH by A. muciniphila further coupled with miR-143/145 promoted intestinal epithelial cell (IEC) regeneration and wound repair via insulin-like growth factor (IGF) and IGFBP5 signalling. Moreover, the gene expressing an outer membrane protein of A. muciniphila, Amuc_1100, was cloned into a mammalian cell-expression vector and successfully expressed in porcine and human IECs. Expression of Amuc_1100 in IECs could recapitulate the health beneficial effect of A. muciniphila on the gut by activating CREBH, inhibiting ER stress and enhancing the expression of genes involved in gut barrier integrity and IEC’s regeneration. Conclusions This study uncovers a novel mechanism that links A. muciniphila and its membrane protein with host CREBH, IGF signalling and miRNAs in mitigating intestinal inflammatory stress–gut barrier permeability and promoting intestinal wound healing. This novel finding may lend support to the development of therapeutic approaches for IBD by manipulating the interaction between host genes, gut bacteria and its bioactive components

Searching and Tagging: Two Sides of the Same Coin?

This paper presents the duality hypothesis of search and tagging, two important behaviors of web users. The hypothesis states that if a user views a document D in the search results for query Q, the user would tend to assign document $D$ a tag identical to or similar to Q; similarly, if a user tags a document D with a tag T, the user would tend to view document D if it is in the search results obtained using T as a query. We formalize this hypothesis with a unified probabilistic model for search and tagging, and show that empirical results of several tasks on search log and tag data sets, including ad hoc search, query suggestion, and query trend analysis, all support this duality hypothesis. Since the availability of search log is limited due to the privacy concern, our study opens up a highly promising direction of using tag data to approximate or supplement search log data for studying user behavior and improving search engine accuracy

Phytochemicals in fenugreek seed prevent high fat diet induced metabolic inflammation and NAFLD via the mediation of Akkermansia muciniphila

Introduction: Fenugreek (Trigonella foenum-graecum) is an annual legume that has been used as a spice throughout the world to enhance the sensory quality of foods. A number of health-beneficial bioactive compounds (i.e. trigonelline and diosgenin) have been identified in the seed of fenugreek. These compounds exert multiple health beneficial effects, including anti-obesity and anti-type 2 diabetes. The objective of our study is to determine the underlying mechanism of whole grain of fenugreek seed and purified bioactive compounds, trigonelline and diosgenin, in ameliorating high fat diet (HFD) induced metabolic inflammation and non-alcoholic fatty liver disease (NAFLD).Materials and Methods: Two groups of C57B6 mice were fed a HFD containing either a vehicle control or 2% of fenugreek seed for 7 weeks. Caloric intake and body weight were monitored weekly during the feeding trial. Glucose tolerance test was conducted to determine the insulin sensitivity. Q-RT-PCR, immunoblotting analysis and histological analysis were used to determine the expression of genes involved in metabolic inflammation and lipid metabolism.Results and Discussion: While caloric intake and body weight were comparable between control and fenugreek treated groups during the feeding trial, fenugreek seed containing diet significantly reduced circulation level of inflammatory cytokine TNFa. In the liver, fenugreek suppressed the gene expression of inflammatory cytokines, such as IL-1b and IL-6, and ameliorated hepatic ER stress. The improvement of metabolic inflammation was associated with less activation of genes involved in hepatic de novo lipid synthesis (i.e. FASN and ACC) and enhanced fatty b-oxidation which resulted in significant amelioration of HFD-induced hepatic steatosis, hyperlipidemia and insulin resistance. Analysis the populations of gut microbiota further revealed that the population of Akkermansia muciniphila, a gut bacterial strain that is involved in body weight regulation and insulin sensitivity, was significantly increased by fenugreek seed containing diet. In vitro, treating McA-RH7777, a rat hepatoma cell line, with purified phytochemicals of fenugreek seeds, trigonelline and diosgenin, inhibited hepatic de novo lipogenesis, attenuated ER stress induced by a saturated fatty acid, palmitic acid. These actions improved insulin sensitivity in McA-RH7777 cells by enhancing the functional activity of insulin signaling molecules, such as insulin receptor and AKT.Conclusion: Our study unveils a novel mechanism of the bioactive compounds, trigonelline and diosgenin, in fenugreek seed that ameliorate metabolic inflammation and hepatic steatosis via the mediation of gut bacteria. This finding may lend support for developing phytochemicals in fenugreek seed as prebiotic supplement for the prevention and treatment of hyperlipidemia and insulin resistance.<br/