Purification of terminal deoxynucleotidyltransferase by oligonucleotide affinity chromatography

Triatoma infestans apyrases belong to the 5'-nucleotidase family

Apyrases are nucleoside triphosphate-diphosphohydrolases (EC 3.6.1.5) present in a variety of organisms. The apyrase activity found in the saliva of hematophagous insects is correlated with the prevention of ADP-induced platelet aggregation of the host during blood sucking. Purification of apyrase activity from the saliva of the triatomine bug Triatoma infestans was achieved by affinity chromatography on oligo(dT)-cellulose and gel filtration chromatography. The isolated fraction includes five N-glycosylated polypeptides of 88, 82, 79, 68 and 67 kDa apparent molecular masses. The isolated apyrase mixture completely inhibited aggregation of human blood platelets. Labeling with the ATP substrate analogue 5'-p-fluorosulfonylbenzoyladenosine showed that the five species have ATP-binding characteristic of functional apyrases. Furthermore, tandem mass spectroscopy peptide sequencing showed that the five species share sequence similarities with the apyrase from Aedes aegypti and with 5'-nucleotidases from other species. The complete cDNA of the 79-kDa enzyme was cloned, and its sequence confirmed that it encodes for an apyrase belonging to the 5'-nucleotidase family. The gene multiplication leading to the unusual salivary apyrase diversity in T. infestans could represent an important mechanism amplifying the enzyme expression during the insect evolution to hematophagy, in addition to an escape from the host immune response, thus enhancing acquisition of a meal by this triatomine vector of Chagas' disease.

Differential inhibitory effects of various flavonoids on the activities of reverse transcriptase and cellular DNA and RNA polymerases

Four flavonoids, 5,6,7-trihydroxyflavone (baicalein), 3,3',4',5,7-pentahydroxyflavone (quercetin), 3,3',4',5,6,7-hexahydroxyflavone (quercetagetin) and 3,3',4',5,5',7-hexahydroxyflavone (myricetin), were found to be potent inhibitors of reverse transcriptases from Rauscher murine leukemia virus (RLV) and human immunodeficiency virus (HIV). Under the reaction conditions employed, any one of these flavonoids almost completely inhibited the activity of RLV reverse transcriptase at a concentration of 1 microgram/ml. HIV reverse transcriptase was inhibited by 100%, 100%, 90% and 70% in the presence of 2 micrograms/ml quercetin, myricetin, quercetagetin and baicalein, respectively. The mode of inhibition of these flavonoids was competitive (RLV reverse transcriptase) or partially competitive (HIV reverse transcriptase) with respect to the template.primer complex, (rA)n.(dT), and noncompetitive with respect to the triphosphate substrate, dTTP. The Ki values for RLV reverse transcriptase were found to be 0.37 microM and 0.08 microM for baicalein and quercetin, respectively and those for HIV reverse transcriptase were 2.52 microM, 0.52 microM, 0.46 microM and 0.08 microM for baicalein, quercetin, quercetagetin and myricetin, respectively. Comparative studies with other flavonoids (hydroxyflavones, dihydroxyflavones and polyhydroxyflavones and flavanones) carried out to clarify the structure/activity relationships, revealed that the presence of both the unsaturated double bond between positions 2 and 3 of the flavonoid pyrone ring, and the three hydroxyl groups introduced on positions 5, 6 and 7, (i.e. baicalein) were a prerequisite for the inhibition of reverse transcriptase activity. Removal of the 6-hydroxyl group of baicalein required the introduction of three additional hydroxyl groups at positions 3, 3' and 4' (quercetin), to afford a compound still capable of inhibiting the reverse transcriptase activity. Quercetagetin which contains the structures of both baicalein and quercetin, and myricetin which has the structure of quercetin with an additional hydroxyl group on the 5' position also proved strong inhibitors of reverse transcriptase activity. The inhibition by baicalein of reverse transcriptase is highly specific, whereas quercetin and quercetagetin were also strong inhibitors of DNA polymerase beta and DNA polymerase I, respectively. Myricetin was also a potent inhibitor of both DNA polymerase alpha and DNA polymerase I.

Inhibitory effects of various 2',3'-dideoxynucleoside 5'-triphosphates on the utilization of 2'-deoxynucleoside 5'-triphosphates by terminal deoxynucleotidyltransferase from calf thymus

Inhibitory effects of four 2',3'-dideoxynucleoside 5'-triphosphates (i.e., those of 2',3'-dideoxyadenosine, 2',3'-dideoxycytidine, 2',3'-dideoxyguanosine and 2',3'-dideoxythymidine, ddATP, ddCTP, ddGTP and ddTTP, respectively) on the utilization of 2'-deoxynucleoside 5'-triphosphates (dNTPs) by terminal deoxynucleotidyltransferase (TdT) from calf thymus were examined in comparison with those of ribonucleoside triphosphates. All four dideoxy compounds strongly inhibited the dNTP utilization by TdT. The inhibitions by these dideoxy compounds were stronger with (dA) than with heat denatured DNA as the primer. Inhibition of TdT by any of these compounds was due to competition with the natural substrate dNTP for the same substrate binding site of the enzyme. Ki values for these dideoxynucleoside triphosphates (ddNTPs) were much lower than the Km values for the corresponding dNTPs indicating a higher affinity of TdT for ddNTP than for dNTP. Among the Ki values determined with (dA) as the primer, those for ddATP (1.3 microM), ddGTP (1.3 microM) and ddCTP (2.8 microM) were lower than that for ddTTP (17.5 microM). With heat-denatured DNA, the Ki for ddATP (2.9 microM) was smaller than those for the other dideoxynucleotides (7.3-35 microM). Also, both the Km for dATP and the Ki for ATP were the lowest among those of the respective deoxynucleotide substrates and ribonucleotide inhibitors. These results indicate that TdT has a stronger affinity for the adenine base of all of the ribo-, deoxyribo-, and dideoxyribo-nucleoside triphosphates than for the other bases of these nucleotides.

Differential inhibition by an antitumoral drug 10-[gamma-diethylaminopropylamino]-6-methyl-5H-pyrido[3',4': 4,5]pyrrolo [2,3-G]isoquinoline (BD-40), a pyrido-pyrrolo-isoquinoline derivative, of in vitro DNA synthesis catalyzed by various DNA polymerases

The effects of BD-40, a pyrido-pyrrolo-isoquinoline analogue of ellipticines, and its 2-acetylated derivative (BD-84) and in vitro DNA synthesis catalyzed by purified preparations of various DNA polymerases were examined. The major conclusions are: (1) Both BD-40 and BD-84 strongly inhibit the DNA synthesis by DNA polymerase or reverse transcriptase with poly(rA).oligo(dT) as the template.primer. (2) Both compounds moderately inhibit the DNA synthesis by DNA polymerase alpha or E. coli DNA polymerase I with activated DNA. However, the DNA synthesis by DNA polymerase beta is resistant to inhibition by BD-40 and slightly sensitive to that by BD-84. (3) BD-84 is more inhibitory than BD-40 in DNA syntheses by various DNA polymerases except in those by DNA polymerase alpha and terminal deoxyneuclotidyltransferase to which both compounds are similarly inhibitory. (4) Kinetic analyses revealed that the observed inhibitions are due to competition between the drug or the drug-bound template.primer and the free template.primer for the same binding site of the enzyme.

Differential inhibitory effects of some catechin derivatives on the activities of human immunodeficiency virus reverse transcriptase and cellular deoxyribonucleic and ribonucleic acid polymerases

The two components of Camellia sinensis (tea plant) [i.e., (-)-epicatechin gallate and (-)-epigallocatechin gallate] were found to differentially inhibit the activities of reverse transcriptase and cellular DNA and RNA polymerases. Under the assay conditions optimized for each enzyme species, the strongest inhibition by these compounds was observed with reverse transcriptase. The concentrations of (-)-epicatechin gallate and (-)-epigallocatechin gallate required for 50% inhibition of the activity of human immunodeficiency virus (HIV) reverse transcriptase were in the range of 0.01-0.02 microgram/mL. On the other hand, neither (-)-epicatechin, (-)-epigallocatechin, nor gallic acid, the constituents of (-)-epicatechin gallate and (-)-epigallocatechin gallate, was inhibitory to the activity of HIV reverse transcriptase at concentrations up to 1 microgram/mL. The mode of inhibition of reverse transcriptase and other DNA polymerases by these compounds was competitive with respect to the template-primer, whereas the mode of inhibition of RNA polymerase was competitive with respect to the nucleotide substrate. The Ki values of HIV reverse transcriptase for (-)-epicatechin gallate and (-)-epigallocatechin gallate were determined to be 7.2 and 2.8 nM, respectively, which are smaller by 1-2 orders of magnitude than the Ki's of other DNA and RNA polymerases for these compounds.

Differential inhibition of various deoxyribonucleic acid polymerases by Evans blue and aurintricarboxylic acid

The inhibitory effects of two anionic compounds, Evans blue and aurintricarboxylic acid (ATA), on various kinds of polynucleotide-synthesizing enzymes were examined. Under the assay conditions, optimized for each enzyme species, both these compounds strongly inhibited the activities of the purified human DNA polymerases alpha, beta, gamma, and DNA primase as well as those of DNA polymerase I and RNA polymerase from Escherichia coli and Rauscher leukemia virus reverse transcriptase. ATA was particularly effective in inhibiting retroviral reverse transcriptase and cellular DNA polymerase alpha. Evans blue, which is a structural analogue of suramin, exerted its inhibitory action largely by competing with the template.primer for the same binding site of the enzyme. On the other hand, ATA inhibited most, if not all, of these enzyme activities noncompetitively with respect to either the template.primers or nucleoside 5'-triphosphate substrates. The inhibition constants for ATA were, in general, smaller than those for Evans blue.

Differential inhibition of various mammalian DNA polymerase activities by ammonium 21-tungsto-9-antimoniate (HPA23)

The 21-tungsto-9-antimoniate ammonium salt (HPA23), known as an antiviral agent, has been shown to be a potent inhibitor of both human and murine DNA polymerase alpha and murine DNA polymerase gamma. HPA23 inhibited the activity of DNA polymerase alpha in noncompetitive fashion with respect to either deoxynucleotide substrate or nucleic acid template.primer. The Ki of murine DNA polymerase alpha for HPA23 was determined to be 24 nM. The activity of mouse DNA polymerase gamma also was strongly inhibited by HPA23 (Ki, 20 nM), and the mode of inhibition was competitive with respect to the template.primer, (rA)n.(dT)12-18, and noncompetitive to substrate, dTTP. DNA polymerase beta and terminal deoxynucleotidyltransferase, however, were relatively resistant to inhibition by HPA23. The observed inhibitions by HPA23 seem to be closely related to the polyanionic property of this drug.

Differential inhibition of various deoxyribonucleic and ribonucleic acid polymerases by suramin

The inhibitory effects of hexasodium sym-bis(m-aminobenzoyl-m-amino-p-methylbenzoyl-1-naphthylamino-4,6, 8-trisulfonate)carbamide (trivial name: suramin) on the activities of various deoxyribonucleic acid (DNA) and ribonucleic acid (RNA) polymerases from mammalian cells, bacteria and retrovirus were examined and compared with each other. Among the various DNA and RNA polymerases tested, the activities of DNA primase, DNA polymerase alpha, reverse transcriptase and Escherichia coli RNA polymerase were strongly inhibited by suramin, while the activities of other enzymes including DNA polymerases beta and gamma, terminal deoxynucleotidyl-transferase and DNA polymerase I were relatively resistant to inhibition by this drug. The inhibition by suramin of DNA polymerase alpha from KB cells and Rauscher murine leukemia virus (RLV) reverse transcriptase was due to competition with the respective template primer (activated DNA for alpha polymerase and (rA)n.(dT)12-18 for reverse transcriptase) for the template.primer-binding site of the enzyme, while the inhibition of DNA primase and E.coli RNA polymerase was due to competition with the ribonucleoside triphosphate substrate. The inhibition constants (Ki) of suramin were determined to be 2.6 microM, 0.35 microM, 0.54 microM and 0.70 microM for DNA primase, DNA polymerase alpha, RLV reverse transcriptase and E. coli RNA polymerase respectively. The observed inhibitions of these polynucleotide-synthesizing enzymes by suramin seem to explain, at least in part, an as yet unknown mechanism of trypanocidal action of this drug.

Disappearance of terminal deoxynucleotidyltransferase in human malignant T-lymphoblasts treated with a human alpha interferon preparation

Human T-lymphoblastoid cell lines RPMI 8402, MOLT-3, and CCRF-CEM were treated with interferon (IFN) to determine if the treatment would result in the disappearance of cellular terminaldeoxynucleotidyltransferase (TdT), a possible differentiation marker for T-lymphocytes. Incubation of RPMI 8402 cells in the presence of IFN preparation caused a decrease in the number of TdT-positive cells and in TdT activity of the cell extract. The inhibition of cell multiplication was dose dependent. The anticellular effect of IFN preparation was cytostatic, not cytocidal. The IFN preparation modified neither the TdT content nor proliferation of MOLT-3 and CCRF-CEM cell lines. The effects of IFN preparation thus varied with the cell line.

Induction of human malignant T-lymphoblastic cell lines MOLT-3 and jurkat by 12-O-tetradecanoylphorbol-13-acetate: biochemical, physical, and morphological characterization

The process of induction of human malignant T-lymphoblastic cell line MOLT-3 by the phorbol ester 12-O-tetradecanoylphorbol-13-acetate (TPA) was examined. It was found that the induction process by TPA, which included increase in cells with receptors to sheep red blood cells (E--rosette positive--E+) and decrease in the levels of the marker enzyme terminal deoxynucleotidyl transferase (TdT) was not affected by the presence of DNA synthesis inhibitor arabinofuranosylcytosine (Ara-C). The exposure time to TPA required to elicit these changes was found to be short, in the order of 1 hour or less. The kinetics of the increased in E+ cells, decrease in the levels of TdT in these cells, or decrease in the ability to proliferate as measured by colony formation were similar with exposure to TPA for 1, 6, 24, or 96 hours. We have examined the effect of antitumor promoter compounds on their ability to block induction of MOLT-3 cells by TPA. Results indicated that none of these compounds, dexamethasone, antipain, retinoic acid, and L-1-tosylamide-2-phenylethylchloromethyl ketone (TPCK), was effective in reducing the number of E+ cells induced by TPA. Examination of three other leukemic T-cell lines indicated that, in addition to MOLT-3, the leukemic T-cell line Jurkat also responded to TPA, whereas two other leukemic T-cells lines CCRF-CEM and CCRF-HSB-2 did not. Certain physical and morphological changes were also observed after stimulation of MOLT-3 cells and Jurkat cells by TPA. We found that, following the addition of TPA, the cell volumes of MOLT-3 cells decreased from an average of 1150 micrometers3 to about 500 micrometers3, whereas those of Jurkat were reduced to about 700 micrometers3 from 1100 micrometers3. Electron microscopic studies of these lymphoblasts also revealed that after treatment with TPA the induced cells were generally smaller in size with increase in the density of the nuclear materials and condensation of the chromatin structures.