Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:2.7.11.1 (protein kinase)
 81,284 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Successful host defense against viral infections relies on early production of type I interferon (IFN) and subsequent activation of a cellular cytotoxic response. The acute IFN and inflammatory response against virus infections is mediated by cellular pattern-recognition receptors (PRRs) that recognize specific molecular structures on viral particles or products of viral replication. Toll-like receptors (TLRs) constitute a class of membrane-bound PRRs capable of detecting microbial infections. While TLR2 and TLR4, which were first identified to recognize Gram-positive and Gram-negative bacteria, respectively, sense specific viral proteins on the cell surface, TLRs 3, 7, 8, and 9 serve as receptors for viral nucleic acids in endosomic compartments. In addition to TLRs, cells express cytoplasmic PRRs such as the RNA helicase retinoic acid inducible gene I and the kinase double-stranded RNA-activated protein kinase R, both of which sense dsRNA, a characteristic signature of viral replication, and initiate a protective cellular response. Here we review the recent progress in our understanding of PRRs and viral infections and discuss the molecular and cellular responses evoked by virus-activated PRRs. Finally, we look into what is currently known about the role of PRRs in viral infections in vivo.
 ...
PMID:Reading the viral signature by Toll-like receptors and other pattern recognition receptors. 1563 78

The ability to distinguish foreign nucleic acids from abundant self nucleic acids is essential to protect the host from invading pathogens. Several innate immune surveillance systems have evolved to detect nucleic acids and trigger cellular responses to eliminate foreign invaders. For RNA recognition, these include double stranded (ds)RNA-dependent protein kinase, Toll-like receptor (TLR)3, TLR7, TLR8, retinoic acid-inducible gene (RIG)-I and melanoma differentiation-associated gene 5. In the case of the nucleic-acid-sensing TLRs, endosomal localization is thought to be crucial for providing self versus non-self discrimination. For RNA-sensing in the cytoplasm, RIG-I was recently shown to detect and directly bind to the 5'-end of certain viral RNA genomes, specifically, to a 5'-triphosphate group. Such 5'-triphosphates are generally removed from, or masked on, host RNA species, thereby remaining silent to innate immunity and providing a structural basis for the distinction between self and non-self RNA. The mechanisms by which MDA5 senses RNA are unclear at present but seem to involve the sensing of dsRNA structures.
 ...
PMID:RIG-I: tri-ing to discriminate between self and non-self RNA. 1730 33

The cytoplasmic CARD-containing DExD/H box RNA helicases RIG-I and MDA5 act as sensors of viral infections through recognition of viral double-stranded (ds) RNAs. They both associate with the mitochondrial adaptor IPS-1 (also referred to as MAVS, VISA, and CARDIF) through homotypic CARD-CARD interactions. IPS-1, in turn, triggers signaling pathways, including activation of the protein kinases TBK1 and IKKepsilon, responsible for the phosphorylation of IRF3, a key transcription factor involved in interferon (IFN) synthesis, one essential element of the innate immune response. RIG-I remains in an autoinhibited state in the absence of dsRNA, through an internal repressor domain (RD) that binds within both its CARD and its RNA helicase domains and therefore acts in cis to control its multimerization and interaction with IPS-1. Ectopic expression of the RD prevents signaling and increases cell permissiveness to viruses, including hepatitis C virus. LGP2, which is another DExD/H RNA helicase of the RIG-I and MDA5 family and which is devoid of CARD domain, negatively controls IFN induction at different levels: by sequestering dsRNA, by blocking RIG-I's multimerization in trans through a domain analogous to the RIG-I RD, and by competing with the protein kinase IKKepsilon for a common interaction site on IPS-1. The ability of RIG-I and LGP2 to exert such a feedback control at the earliest steps of IFN synthesis allows the cells to exert a tight regulation of the induction of the innate immune response.
 ...
PMID:Regulation of interferon production by RIG-I and LGP2: a lesson in self-control. 1747 9

Virus-infection of mammalian cells causes transcriptional induction of many cellular genes, collectively called as "viral stress-inducible genes." The proteins encoded by these genes are essential to maintain cell-virus homeostasis, which is required for both virus replication and host survival. Many viral products, including RNA, DNA, and proteins, can induce these genes by using distinct, but partially overlapping, signaling pathways. Type I interferons, direct products of virus infection, can also induce many of these genes, thus providing a positive feedback loop. Double-stranded RNA, a common by-product of virus replication, can induce them by multiple signaling pathways initiated by Toll-like receptor 3 or RIG-I/Mda-5. Several viral stress-inducible proteins inhibit protein synthesis. Proteins of the P56 family bind to the translation initiation factor, eIF-3, and block translation initiation. PKR, a protein kinase, phosphorylates a different initiation factor, eIF-2, and inhibits translation initiation. However, unlike P56, PKR needs to be first activated by dsRNA or PACT, another cellular protein. Another family of enzymes, the 2'-5' oligoadenylate synthetases, synthesizes 2'-5' linked oligoadenylates [2-5(A)] in the presence of dsRNA; 2-5(A) activates the latent ribonuclease, RNase L, which degrades mRNA. Many viruses have evolved mechanisms to evade these genes by blocking their induction or actions; often more than one strategy is used by the same virus to achieve this goal. Thus, in an infected cell, equilibrium is reached between the virus and the cell with regards to the viral stress-inducible genes.
 ...
PMID:Viral stress-inducible genes. 1776 7

The immediate response to viral infection relies on pattern-recognition receptors (PRRs), most prominently the Toll-like receptors (TLRs) and the RNA helicases RIG-I and MDA5, as well as double stranded RNA-dependent protein kinase (PKR) and the DNA receptor, DAI. These PRRs recognize pathogen-associated molecular patterns (PAMPs) such as viral proteins and nucleic acids. The engagement of these receptors then initiates intracellular signaling cascades which ultimately cause the activation of transcription factors and the expression of type I interferons and pro-inflammatory cytokines. This innate response establishes an anti-viral state in the infected cell and its neighbours and alerts immune cells to the danger. In order to establish a productive infection, viruses need to overcome this initial anti-viral response. Evasion of innate immune defences is achieved by means of viral proteins that inhibit the signaling cascades emanating from the PRRs. The same innate signal transduction pathways have been implicated in conditions of sterile inflammation, such as rheumatoid arthritis and multiple sclerosis, and in autoimmunity. Because viral proteins target crucial host proteins involved in these pathways, they can point the way to key drug targets. Further, the viral proteins themselves or derivatives of them may be of use therapeutically to curtail inflammation and autoimmunity.
 ...
PMID:The interplay between viruses and innate immune signaling: recent insights and therapeutic opportunities. 1786 52

Keratinocytes play a key role in innate immune responses of the skin to bacterial and viral pathogens. Viral double-stranded RNA and its synthetic analogue polyriboinosinic-polyribocytidylic acid (poly-IC) are recognized via multiple pathways involving the receptors Toll-like receptor 3 (TLR3), protein kinase R (PKR), and the recently described cytosolic RNA helicases retinoic acid-inducible gene-I (RIG-I) and melanoma differentiation-associated gene 5 (MDA5). We show that preincubation of human keratinocytes with IFN-alpha enhances the proinflammatory responses to poly-IC. Kinetic studies suggest that this is mediated via upregulation of the receptors TLR3, PKR, RIG-I, and MDA5. Interestingly, expression of RIG-I, MDA5, and PKR was significantly increased in lesional skin from patients with psoriasis, a chronic inflammatory skin disease that is characterized by high IFN-alpha levels. These results suggest that psoriatic keratinocytes show increased sensitivity to viral RNA intermediates, thereby leading to excessive proinflammatory responses and maintenance of the inflammatory skin phenotype. Here, we provide early evidence that point toward a role for the recently described cytosolic innate RNA receptors in non-viral chronic inflammatory diseases.
 ...
PMID:IFN-alpha enhances poly-IC responses in human keratinocytes by inducing expression of cytosolic innate RNA receptors: relevance for psoriasis. 1792 88

Production of type I IFN is the key response to viral infection. Since the discovery of type I IFNs in 1957, long double-stranded RNA formed during replication of many viruses was thought to be responsible for type I IFN induction, and for decades double-stranded RNA-activated protein kinase (PKR) was thought to be the receptor. Recently, this picture has dramatically changed. It now became evident that not PKR but two members of the Toll-like receptor (TLR) family, TLR7 and TLR9, and two cytosolic helicases, RIG-I and MDA-5, are responsible for the majority of type I IFNs induced upon recognition of viral nucleic acids. In this review, we focus on the molecular mechanisms by which those innate immune receptors detect viral infection. Based on the recent progress in the field, we now know that TLR7, TLR9, and RIG-I do not require long double-stranded RNA for type I IFN induction.
 ...
PMID:Beyond double-stranded RNA-type I IFN induction by 3pRNA and other viral nucleic acids. 1796 50

Molecular patterns in pathogenic RNAs can be recognized by the innate immune system, and a component of this response is the interferon-induced enzyme RNA-activated protein kinase (PKR). The major activators of PKR have been proposed to be long double-stranded RNAs. We report that RNAs with very limited secondary structures activate PKR in a 5'-triphosphate-dependent fashion in vitro and in vivo. Activation of PKR by 5'-triphosphate RNA is independent of RIG-I and is enhanced by treatment with type 1 interferon (IFN-alpha). Surveillance of molecular features at the 5' end of transcripts by PKR presents a means of allowing pathogenic RNA to be distinguished from self-RNA. The evidence presented here suggests that this form of RNA-based discrimination may be a critical step in mounting an early immune response.
 ...
PMID:5'-triphosphate-dependent activation of PKR by RNAs with short stem-loops. 1804 89

Emerging evidence suggests an important role for human epidermal keratinocytes in innate immune mechanisms against bacterial and viral skin infections. The proinflammatory effect of viral infections can be mimicked by double-stranded RNA (dsRNA). Herein, we demonstrate that keratinocytes express all known dsRNA sensing receptors at a constitutive and inducible level, and that they use several downstream signaling pathways leading to a broad pattern of gene expression, not only proinflammatory and immune response genes under the control of NF-kappaB, but also genes under transcriptional control of IRF3. As a consequence, dsRNA, a stimulus for TLR3, protein kinase R (PKR), and the RNA helicases retinoic acid-inducible gene I (RIG-I) and MDA5, induces a status of antiviral defense in keratinocytes. Using inhibitors for the various dsRNA signaling pathways and specific small interfering RNA for TLR3, RIG-I, and MDA5, we demonstrated that in human keratinocytes, TLR3 seems to be necessary for NF-kappaB but not for IRF3 activation, whereas RIG-I and MDA5 are crucial for IRF3 activation. PKR is essential for the dsRNA response in both signaling pathways and thus represents the central antiviral receptor for dsRNA stimulation. Moreover, human keratinocytes up-regulate TLR7, the receptor for single-stranded RNA, in response to stimulation with dsRNA, which renders keratinocytes functionally responsive to the TLR7 agonist gardiquimod, a member of the imidazoquinoline antiviral immune response modifier family. Thus, in addition to building a physical barrier against infectious pathogens, keratinocytes are specially equipped with a full antiviral defense program that enables them to efficiently target viral infections of the skin.
 ...
PMID:Double-stranded RNA induces an antiviral defense status in epidermal keratinocytes through TLR3-, PKR-, and MDA5/RIG-I-mediated differential signaling. 1868 60

Interferon inducible protein kinase PKR is a component of innate immunity and mediates antiviral actions by recognizing pathogen associated molecular patterns (PAMPs). A well-known activator of PKR is long dsRNA, which can be produced during viral replication. Our recent results indicate that PKR can also be activated by short stem-loop RNA in a 5'-triphosphate-dependent fashion. A 5'-triphosphate is present primarily in foreign RNAs such as viral and bacterial transcripts, while a non-activating 5'-cap or 5'-monophosphate is present in most cellular RNAs. Additional studies indicate that internal RNA modifications and non-Watson-Crick motifs also repress PKR activation, and do so in an RNA structure-specific fashion. Interestingly, self-RNAs have more nucleoside modifications than non-self RNAs. Internal and 5'-end RNA modifications have repressive effects on other innate immune sensors as well, including TLR3, TLR7, TLR8, and RIG-I, suggesting that nucleoside modifications suppress innate immunity on a wide scale.
 ...
PMID:A brilliant disguise for self RNA: 5'-end and internal modifications of primary transcripts suppress elements of innate immunity. 1876 34


1 2 3 4 5 6 7 Next >>