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:2.7.1.21 (thymidine kinase)
7,561 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Acyclovir [9-(2-hydroxyethoxymethyl)guanine] inhibits Epstein-Barr virus (EBV) replication in lymphoblastoid cells at concentrations nontoxic to cellular growth. The mode of action of the drug against EBV differs from the mechanism described in herpes simplex virus systems. Due to the absence of virus-specified thymidine kinase, the drug is poorly phosphorylated in EBV-infected cells. The extent of monophosphorylation is similar both in mock-infected and EBV-infected cells. Despite weak phosphorylation of the drug, the replication of linear EBV DNA is inhibited due to exquisite sensitivity of the viral DNA polymerase. Activation of acyclovir does not require phosphorylation by virus-specified thymidine kinase, inhibition of different herpes-group viruses depends on three variable factors: degree of phosphorylation, cellular metabolism of the drug, and degree of sensitivity of the viral polymerase. Interaction of acyclovir-triphosphate with EBV DNA polymerase is reversible. Cells infected with EBV and treated with acyclovir resume virus replication following removal of the drug even after long exposure. Acyclovir inhibits replication of linear genomes and stops production of virus, but has no effect on latent cellular infection. These results lead us to predict that acyclovir will suppress, but not cure, EBV infection.
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PMID:Perspectives on interactions of acyclovir with Epstein-Barr and other herpes viruses. 628 10

All cells that harbor the Epstein-Barr virus (EBV) genome contain a neoantigen in the nucleus (EBNA). By transfection we located a segment of the genome that encodes or induces an antigen serologically related to EBNA. The responsible genes are found in the 3.4-megaldalton BamHI fragment K of EBV DNA, specifically in the left 1.9 megadaltons represented by HindIII fragment I1. Mouse LTK- cells were cotransformed with recombinant plasmids, containing the herpes simplex virus thymidine kinase gene and either EcoRI fragment B or BamHI fragment of K of EBV DNA. The TK+ cells surviving in selective medium were cloned. About 50% of the clones expressed the neoantigen in every nucleus. These mouse cells were used as antigens in immunofluorescence tests. Antibody to the nuclear antigen was found in 30 human sera known to contain antibody to EBNA; it was not detected in 18 sera that did not have antibody to EBNA. Mouse cells expressing EBNA as the result of acquisition of cloned EBV DNA fragments should prove useful in the characterization of the structure of this antigen and as reagents for the diagnosis of EBV infections.
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PMID:Stable expression in mouse cells of nuclear neoantigen after transfer of a 3.4-megadalton cloned fragment of Epstein-Barr virus DNA. 629 Oct 59

1-beta-D-Arabinofuranosylthymine (araT) is a selective inhibitor of Epstein-Barr virus replication induced in both thymidine kinase (TK)-negative (TK-) and TK+ variants of the lymphoid cell line P3HR-I. This analog has no effect on the growth of noninduced cells (T. Ooka and A. Calender, Virology 104:219-223, 1980). The synthesis of early antigens is not affected by the analog, whereas that of late viral capsid antigens is completely inhibited, as demonstrated by the indirect immunofluorescence technique; kinetic reassociation experiments have also shown that araT strongly inhibits replication of viral DNA. Phosphorylation of the tritiated form of the analog ([3H]araT) was analyzed by thin-layer chromatography in cultures of control and induced cells, and the results demonstrated that only induced cells can convert the analog to the triphosphate form. These results indicate that the selective effect of araT in induced cells is probably related to a new virally induced TK activity. Preliminary characterization of this new activity has shown that it is able to phosphorylate the analog specifically, whereas cellular TKs cannot. araTTP, a final phosphorylation product of araT, is a potent inhibitor of Epstein-Barr virus-specific DNA polymerase, suggesting a possible inhibitory action of this product on Epstein-Barr virus replication.
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PMID:Effect of arabinofuranosylthymine on the replication of Epstein-Barr virus and relationship with a new induced thymidine kinase activity. 629 56

A guanosine analog, 9-[(1,3-dihydroxy-2-propoxy)methyl]guanine (DHPG), was found to inhibit herpes simplex virus type 1 (HSV-1), herpes simplex virus type 2, cytomegalovirus, and Epstein-Barr virus replication by greater than 50% at concentrations that do not inhibit cell growth in culture. The potency of the drug against all of these viruses is greater than that of 9-[(2-hydroxyethoxy)methyl]guanine (acyclovir). DHPG was active against HSV-1 growth during the early phase of virus replication and had no activity when added at a later time after infection. Its antiviral activity was irreversible. Thymidine partially neutralized its action. The anti-HSV-1 activity of DHPG was dependent on the induction and the properties of virus-induced thymidine kinase. Virus variants that induced altered virus thymidine kinase and became resistant to acyclovir were still as sensitive to DHPG as the parental virus. DHPG is active against five different HSV variants with induced altered DNA polymerase and resistance to acyclovir.
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PMID:Unique spectrum of activity of 9-[(1,3-dihydroxy-2-propoxy)methyl]-guanine against herpesviruses in vitro and its mode of action against herpes simplex virus type 1. 630 4

9-([2-Hydroxy-1-(hydroxymethyl)ethoxy]methyl)guanine (2'-nor-2'-deoxyguanosine; 2'NDG) selectively inhibits the replication of herpes group viruses. In cell culture studies 2'NDG was at least 10-fold more potent than acyclovir (ACV) in inhibition of human cytomegalovirus replication and Epstein-Barr virus-induced lymphocyte transformation and was about as effective as ACV in inhibition of herpes simplex viruses 1 and 2 and varicella zoster virus. Orally administered 2'NDG was 6- to 50-fold more efficacious than ACV in treating systemic or local HSV-1 infection or HSV-2 intravaginal infection in mice. The mode of action of 2'NDG appears to involve phosphorylation by herpes simplex virus thymidine kinase and subsequent phosphorylations by cellular kinases to produce 2'NDG triphosphate, which is a potent inhibitor of herpes virus DNA polymerase. Compared to ACV, 2'NDG was a more efficient substrate for HSV-1 thymidine kinase (Vmax/Km for 2'NDG 30-fold higher than that of ACV), whereas 2'NDG monophosphate is a more efficient substrate for GMP kinase (Vmax/Km for 2'NDG monophosphate 492-fold higher than that for ACV monophosphate). The combined effect is more rapid production of the inhibitory triphosphate from 2'NDG than from ACV.
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PMID:9-([2-hydroxy-1-(hydroxymethyl)ethoxy]methyl)guanine: a selective inhibitor of herpes group virus replication. 630 64

Acyclovir [9-(2-hydroxyethoxymethyl)guanine] (ACV), a potent antiviral compound, was phosphorylated to the same extent by extracts from untreated and iododeoxyuridine-treated Epstein-Barr virus-containing latent D98/HR-1 somatic hybrid cells. ATP was the preferred phosphate donor over other nucleoside triphosphates. The cytosol extract from D98/HR-1 cells effected optimum phosphorylation of thymidine at pH 8.0, whereas ACV was phosphorylated equally well over a wide pH range. Electrophoretic analysis of thymidine kinase-, deoxycytidine kinase-, and ACV-phosphorylating activities from both untreated and iododeoxyuridine-treated cell extracts displayed identical properties. A small part (5 to 10%) of the loaded ACV-phosphorylating activity seemed to migrate with the deoxycytidine kinase activity from cytosol. dTTP and dCTP, at relatively high concentrations, partially inhibited ACV-phosphorylating activity. The results suggest that Epstein-Barr virus does not code for its own thymidine kinase and that phosphorylation of ACV in Epstein-Barr virus-producing cells is carried out by multiple or as yet unidentified ATP-dependent nonspecific cellular phosphotransferases.
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PMID:Phosphorylation of acyclovir in vitro in activated Burkitt somatic cell hybrids. 631 70

Chemical treatment with a combination of 12-O-tetradecanoylphorbol-13-acetate and n-butyrate or superinfection with P3HR-1 virus effectively induced a novel thymidine kinase (TK) in Raji and NC37 TK-negative mutant cells. Sera from patients with nasopharyngeal carcinoma containing a high antibody titer against Epstein-Barr virus early antigen could inactivate this induced enzyme while sera from normal donors, even those containing a high titer of antibodies to virus capsid antigen, had no effect on the enzyme. Also, the induced enzyme was relatively insensitive to thymidine triphosphate inhibition.
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PMID:Characterization of Epstein-Barr virus-related thymidine kinase induced in nonproducer cells by superinfection or chemical treatment. 632 93

In a previous study the BamHI-K fragment of Epstein-Barr virus DNA was shown to induce a nuclear antigen, Epstein-Barr virus nuclear antigen (EBNA), when cotransfected with the herpes simplex virus thymidine kinase gene into mouse LTK- cells. We have now inserted the BamHI-K fragment and a BamHI/HindIII subfragment, I1f , into shuttle vectors containing the origin of replication of simian virus 40. These plasmids have been introduced into COS-1, which are monkey kidney cells transformed by an origin-defective simian virus 40 genome. This expression system permitted rapid characterization of antigens, mRNAs, and proteins related to EBNA. The same-sized EBNA protein (approximately 78,000) was made after transfection with BamHI-K (5.2 kilobase pairs [kbp]) or the I1f subfragment (2.9 kbp). A deletion of about 600 bp occurred when the I1f fragment was propagated on the pSV2 plasmid in Escherichia coli. The deleted fragment gave rise to a smaller protein (approximately 52,000). These data provide evidence that EBNA is encoded by the 2.9-kbp I1f and is not an induced cellular protein. Nuclear antigen and polypeptide expression occurred equally well when the Epstein-Barr virus DNA was cloned on PSV2 -gpt or pSVOd . The latter plasmid lacks sequences allowing for efficient early gene transcription as well as splicing and polyadenylation signals which are present in pSV2 . Preliminary mapping of the EBNA gene transcripts demonstrated that two mRNAs (2.9 and 2.4 kilobases [kb]) are homologous to the I1f fragment. Taken together, the data suggest that the 2.9-kbp I1f fragment contains the structural gene for EBNA synthesis. COS-1 cells will thus provide a valuable system in which to analyze functional domains of the EBNA gene.
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PMID:Expression in COS-1 cells of Epstein-Barr virus nuclear antigen from a complete gene and a deleted gene. 632 12

To understand the mechanism of regulation of bovine herpesvirus 4 (BHV-4) early gene expression by immediate-early (IE) gene products, we studied activation of expression of the BHV-4 early gene encoding thymidine kinase (TK). BHV-4 encodes two IE RNAs. IE RNA 2 encodes a protein with predicted amino acid sequence similarity to the Epstein-Barr virus (EBV) R transactivator. The BHV-4 TK promoter-regulatory region was specifically transactivated approximately 9-fold by the IE2 gene product in transient expression cotransfection assays. Deletion analysis localized the IE2 responsive element(s) within a 72 bp fragment 5' to the start of transcription. Multiple copies of this 72 bp fragment conferred IE2-responsiveness on an enhancerless simian virus 40 (SV40) promoter and mediated IE2 transactivation in either orientation. Gel retardation assays demonstrated a sequence-specific complex between the IE2 gene product and the 72 bp DNA fragment, and indicated that the IE2 gene product binds DNA as a dimer. Sequences contained in a 25 bp subfragment were sufficient for IE2-DNA complex formation. No nucleotide sequence similarity was noted between the TK IE2-binding fragment and the consensus binding site for the EBV R transactivator. A single amino acid change in the putative DNA-binding domain of the IE2 gene product abolished both complex formation in vitro and transactivation activity in vivo.
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PMID:Interaction of bovine herpesvirus 4 (BHV-4) immediate early 2 gene product with BHV-4 thymidine kinase promoter-regulatory region. 759 47

The growth transforming potential of Epstein-Barr virus (EBV) for Burkitt's lymphoma and nasopharyngeal carcinoma is now extended to other neoplasia, such as Hodgkin's disease, peripheral T-cell tumor and gastric cancer. We have generated an EBV recombinant with a selectable marker at the viral thymidine kinase locus. Recombinant EBV was successfully infected into a human T-cell line, MT-2. Following incubation in the selective medium, drug resistant MT-2 cell clones were isolated and proved to be infected with recombinant EBV. EBV-infected MT-2 cell clones expressed EBNA 1 and LMP 1 and very little of EBNA 2, showing the BamHI F promoter-driven latency II form of infection, which is seen in non-B-cell tumors. This is the first report of in vitro generation of latency II type EBV infection. The present system of persistent EBV infection in T cells should be a good model for investigating the pathogenic role of EBV in non-B-cell tumors.
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PMID:Persistent Epstein-Barr virus infection in a human T-cell line: unique program of latent virus expression. 764 89


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