Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound   Target Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound

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Query: EC:2.7.11.1 (protein kinase)
81,284 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Effect of (2'-5')oligoadenylate (2-5A) on cellular and viral protein and RNA syntheses was investigated with two mouse cell lines, L929 and Lz (a subclone of L929). The oligonucleotide was introduced into the cells either by using calcium phosphate coprecipitation technique or by microinjection method. In L929 cells protein and viral RNA syntheses were severely inhibited by 2-5A, whereas in Lz cells, both were only slightly inhibited. The activities of 2-5A synthetase and double-stranded (ds)RNA-dependent protein kinase were enhanced by interferon (IFN) treatment roughly to the same extent and there was no significant difference in the level of 2'-5' phosphodiesterase activity either. On the other hand, 2-5A-dependent RNase (RNase L) activity in Lz cells was low, being about 10-20% of that of L929 cells. It was increased twofold after IFN treatment, but protein synthesis of Lz cells was not as sensitive to 2-5A as that of L929 cells even after IFN treatment. L929 and Lz cells were sensitive to the antiviral effect of mouse IFN against vesicular stomatitis virus (VSV) and Mengovirus. In contrast, however, Lz cells were relatively insensitive to the antiviral effect of IFN on vaccinia virus, whereas L929 cells were sensitive.
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PMID:Comparative studies on (2'-5')oligoadenylate-related enzyme systems and the antiviral effect of interferon in two mouse cell lines which differ in (2'-5')oligoadenylate sensitivity of their protein synthesizing system. 241 28

From the NIH 3T3 clone 1 line which is normally unprotected by interferon (IFN) against lytic virus infection we have selected subclones which show high sensitivity to IFN. The selection procedure was based on encephalomyocarditis virus (EMCV) as selection agent. In the IFN-sensitive subclones thus obtained EMCV replication was inhibited by IFN to a similar degree as observed in L929 cells. Like in the original NIH 3T3 clone 1 line, however, replication of vesicular stomatitis virus (VSV) and cell multiplication were only marginally affected by IFN. We measured the levels of known IFN-induced enzymes (2-5A-synthetase, dsRNA protein kinase and 2-5A-dependent RNase) in a number of subclones and found no consistent differences to the original population. Thus, the newly acquired IFN-dependent protection against EMCV may be mediated by a different antiviral mechanism.
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PMID:Studies on interferon-sensitive cells derived from the interferon-resistant NIH 3T3 clone 1 line. 242 4

The results of the present study permit the explanation of one of the mechanisms of the interconnection between the regulatory systems of cAMP and 2-5A. cAMP-dependent regulation of 2'-PDE was found to involve phosphorylation of the specific protein inhibitor. Originally, a similar way of regulation of the enzyme activity was discovered for protein phosphatase I. This enzyme has a specific protein inhibitor type 1, which is phosphorylated by cAMP-dependent protein kinase and is activated by phosphorylation (18). It is interesting that the molecular weights of 2'-PDE protein inhibitor and of the inhibitor type 1 of protein phosphatase I are essentially the same. There is also a certain similarity between the above described mechanism and phosphorylation of the regulatory subunit of cAMP-dependent protein kinase type 2. The regulatory subunit can also act as a protein inhibitor of the enzyme and change its properties as a result of phosphorylation (19). The results obtained permit as well a more detailed explanation for cAMP-dependent inhibition of cell proliferation. Evidently, cAMP elevation causes activation of cAMP-dependent phosphorylation which, in turn, leads to the induction of 2-5A synthetase and inhibition of 2'-PDE. As a result of variations in the activities of these enzymes, the level of 2-5A rises. The latter brings about the changes characteristic of the resting state. They involve activation of RNase L and the succeeding acceleration of RNA hydrolysis, inhibition of protein synthesis and cell proliferation. The resting state is characterized by a rapid turnover of macromolecules due to their intensive degradation (20). The above described scheme suggested that the rapid turnover of RNA during inhibition of cell proliferation can be partially accounted for by activation of 2-5A-dependent RNase L. Thus, it can be thought that at least one of the mechanisms of the antiproliferative effect of cAMP-dependent phosphorylation of proteins involves cAMP-dependent elevation of intracellular 2-5A. Evidently, a number of properties of the resting cells are determined by the elevated content of 2-5A. Finally, it should be noted that the interconnection between the systems of cAMP and 2-5A is a multiple process. We have earlier demonstrated (12) that 2-5A activates cAMP phosphodiesterase in NIH 3T3 cell homogenates. These data suggest that the mutual regulation of cAMP and 2-5A levels involves the negative feedback mechanism (Fig. 8).
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PMID:Regulation of 2-5 A phosphodiesterase activity by cAMP-dependent phosphorylation: mechanism and biological role. 300 Jan 46

The cytocidal activity of human immune interferon (IFN-gamma) in combination with the synthetic double-stranded RNA, poly(I).poly(C), was investigated in human colon carcinoma cell line HT-29. Three days of treatment with IFN-gamma (10 to 25 units/ml) resulted in 30 to 40% reduction in colony formation, whereas poly(I).poly(C) (25 to 100 micrograms/ml) reduced cell viability by 10 to 20% of control. The lethal effect of the combination of IFN-gamma and poly(I).poly(C) was synergistic wherein 70 to 90% reduction in colony formation was observed. Measurements of DNA, RNA, and protein synthesis after IFN-gamma and poly(I).poly(C) treatment showed a dose-dependent reduction in all three parameters. Recombinant IFN-gamma in combination with poly(I).poly(C) exhibited a similar effect. Studies evaluating the molecular mechanism of IFN-gamma and poly(I).poly(C) toxicity indicate a lack of involvement of the double-stranded RNA-dependent (2',5')oligoadenylate-RNase L and protein kinase pathways; however, the effect appears to be related to the inhibition of ribosomal RNA transcription in this cell line.
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PMID:Synergistic effect of human immune interferon and double-stranded RNA against human colon carcinoma cells in vitro. 392 Dec 46

Extracts from interferon-treated, not virus-infected Ehrlich ascites tumor cells differ in various biochemical characteristics from extracts of control cells. We studied three enzymes whose level is enhanced in cells upon treatment with IF and which are causing some of the differences. (2'-5')(A)n synthetase, an enzyme converting ATP into a series of (2'-5') linked oligoadenylates ((2'-5')(An)) in the presence of dsRNA was purified to homogeneity and characterized. The second enzyme, RNase L, a latent endonuclease, which can be activated by (2'-5')(A)n to cleave single-stranded RNAs, was purified several hundredfold. The activation of this enzyme is reversible and is lost upon removal of (2'-5')(A)n. The activation is not accompanied by a large change in shape of conformation of the enzyme. The third enzyme is a protein kinase which if activated by dsRNA can phosphorylate the peptide chain initiation factor eIF-2 and a protein designated P1 of 67,000 daltons. This enzyme was purified several thousandfold. The most highly purified preparation consists of three proteins with P1 as the most abundant component.
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PMID:Double-stranded RNA and the enzymology of interferon action. 616 95

Interferon exhibits pleotropic effects on homologous cells. Interferons may be used clinically for both antiviral and antitumor therapy. A better understanding of how interferon achieves its hormonal effects should be useful in developing more judicious and specific applications of these natural substances in therapy. Interferon induces increased activity of two enzymes, 2'5'-oligoadenylate synthetase and a protein kinase, that depend on double-stranded RNA for activation. 2'5' A polymerizes ATP into a novel 2'5'-linked oligonucleotide, which in turn can activate a latent cellular nuclease (RNase L) which degrades mRNA. The second dsRNA-dependent enzyme, a protein kinase, phosphorylates a protein of approximately 67,000 daltons as well as the small subunit of eukaryotic initiation factor (eIF-2). The phosphorylation of eIF-2 results in the inhibition of protein synthesis. The extent of sensitivity to exogenous interferon could be influenced by several factors, including the number of cell surface receptors for interferon and the rate and efficiency at which ligand binding and "processing" is achieved. Prostaglandins, cyclic nucleotides, and oxygen-free radicals could participate in modulation of interferon action at this level. Interferon induces specific changes in the composition of membrane lipids. These changes included loss of unsaturated fatty acids from phospholipids, significant increases in levels of unesterified fatty acids, and moderate increases in concentrations of triglycerides and cholesterol esters. The changes were absent in cells treated with interferon in the presence of inhibitors of fatty acid cyclooxygenase or superoxide dismutase. Whether or not interferon-associated lipid changes directly participate in interferon action is not yet clear. Apparent diversity in its mechanistic approach to virus inhibition may be the key to the success of interferon as a wide-spectrum antiviral agent. Heterogeneity in molecular species of interferon may signify its molecular evolutionary adaptations to specific needs and the eventual development of a "fool-proof" system that we now perceive as the "interferon-system." The observed pleotropic effects may be due to linkage to a broader cellular machinery that operates to identify and effectively handle "foreign" substances.
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PMID:Interferon-induced biochemical changes in cell membranes: possible role of cellular enzyme superoxide dismutase. 619 67

The vaccinia virus (VV) E3L gene, which encodes a potent inhibitor of the interferon (IFN)-induced, double-stranded RNA (dsRNA)-dependent protein kinase, PKR, is thought to be involved in the IFN-resistant phenotype of VV. The E3L gene products, p25 and p20, act as inhibitors of PKR, presumably by binding and sequestering activator dsRNA from the kinase. In this study we demonstrate that VV with the E3L gene specifically deleted (vP1080) was sensitive to the antiviral effects of IFN and debilitated in its ability to rescue vesicular stomatitis virus from the antiviral effects of IFN. Infection of L929 cells with E3L-minus virus led to rRNA degradation typical of activation of the 2'-5'-oligoadenylate synthetase/RNase L system, and extracts of infected cells lacked the PKR-inhibitory activity characteristic of wild-type VV. The reovirus S4 gene, which encodes a dsRNA-binding protein (sigma 3) that can also inhibit PKR activation by binding and sequestering activator dsRNA, was inserted into vP1080. The resultant virus (vP1112) was partially resistant to the antiviral effects of IFN in comparison with vP1080. Further studies demonstrated that transient expression of the reovirus sigma 3 protein rescued E3L-minus VV replication in HeLa cells. In these studies, rescue by sigma 3 mutants correlated with their ability to bind dsRNA. Finally, vP112 was also able to rescue the replication of the IFN-sensitive virus vesicular stomatitis virus in a manner similar to that of wild-type VV. Together, these results suggest that the reovirus S4 gene can replace the VV E3L gene with respect to interference with the IFN-induced antiviral activity.
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PMID:Reversal of the interferon-sensitive phenotype of a vaccinia virus lacking E3L by expression of the reovirus S4 gene. 752 85

The interferons are a family of secreted, multifunctional proteins which are components of the defenses of vertebrates against viral, bacterial, and parasitic infections and certain tumors. They exert their various activities by inducing the synthesis of a large variety of proteins. There are direct and indirect indications that several of these proteins may have tumor-suppressor activities. The interferon-inducible proteins implicated include: (i) a double-stranded RNA-activatable protein kinase that can phosphorylate and thereby inactivate the eukaryotic peptide chain initiation factor eIF-2; (ii) the interferon regulatory factors IRF-1 and IRF-2, which can modulate the expression of the interferons and of some interferon-inducible proteins; and (iii) RNase L, a latent endoribonuclease which can be activated by (2'-5')oligoadenylates, the products of a family of enzymes which are also interferon-inducible. It is note-worthy that some of the proteins encoded by tumor virus oncogenes (e.g., E1A from adenovirus, EBNA-2 from Epstein-Barr virus, and terminal protein from hepatitis B virus) impair the induction of at least some proteins by interferons.
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PMID:Tumor-suppressor genes: news about the interferon connection. 768 56

The sequence of RNase L has been re-examined by computer analysis. We propose a molecular architecture of RNase L, with an unusual combination, in one protein chain, of 9 ankyrin-like repeats, a functional active protein kinase and a C-terminal catalytic RNase similar to the yeast protein, IRE1. The protein kinase may be involved in a new signal transduction pathway which remains to be discovered.
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PMID:A hybrid protein kinase-RNase in an interferon-induced pathway? 769 13

2-5A antisense (2-5A-AS) molecules are chimeric oligonucleotides that cause 2-5A-dependent RNase (RNase L) to catalyze the selective cleavage of RNA in human cells. These composite nucleic acids consist of a 5'-monophosphorylated, 2',5'-linked oligoadenylate known as 2-5A (an activator of RNase L) covalently attached to antisense 3',5'-oligodeoxyribonucleotides. Here, we characterize the targeted cleavage of the double-stranded RNA-dependent protein kinase (PKR) mRNA by purified, recombinant human RNase L. A 2-5A-AS chimera, which contains complementary sequence to PKR mRNA, and unmodified 2-5A, which causes general RNA decay, were about 20- and 40-fold more active, respectively, than 2-5A-AS chimeras in which the DNA domains are not complementary to sequences in PKR mRNA. Directed cleavage was efficient because each 2-5A-AS chimera targeted many RNA molecules. Moreover, RNase L caused the catalytic cleavage of the RNA target (kcat of approximately 7 s-1). The precise sites of PKR mRNA cleavage caused by 2-5A-AS were mapped, using a primer extension assay, to phosphodiester bonds adjacent to the 3' terminus of the chimera binding site (5' on the RNA target) as well as within the chimera's oligonucleotide binding site itself. The selectivity of this approach is shown to be provided by the antisense arm of the chimera, which places the RNA target in close proximity to the RNase.
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PMID:Catalytic cleavage of an RNA target by 2-5A antisense and RNase L. 779 90


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