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Biomedical subjects

F Focher

Publications and source records attributed to F Focher.

At least 55 records · Page 3Linked to original sources
PubMed1991

Specific inhibition of human DNA ligase adenylation by a distamycin derivative possessing antitumor activity.

The antiviral distamycin A and its phenyl mustard derivative FCE24517 possessing antitumor activity were tested for their ability to inhibit macromolecular synthesis in three human and one murine cell line. While distamycin A was poorly active in these systems, FCE24517 inhibited DNA synthesis efficiently, RNA synthesis to a lower extent and had little effect on protein synthesis. These findings suggest that the in vivo activity of FCE24517 derives from the specific inhibition of DNA synthesis. When the two drugs were tested on several enzymes involved in human DNA metabolism a strikingly similar pattern of inhibition appeared, with distamycin A being the more potent. Both drugs showed: A), no inhibitory activity against thymidine kinase and DNA primase; B), low activity against DNA topoisomerases I and II and the 3'-5' exonuclease associated with the DNA polymerase epsilon; C), high activity against DNA polymerases alpha and epsilon, uracil-DNA glycosylase and the joining activity of the replicative DNA ligase; D), the highest inhibitory activity against the AMP-dependent DNA relaxing activity of DNA ligase. The strong in vitro inhibition of several DNA enzymatic activities, including DNA ligase, do not match with the in vivo activities of the two drugs. However a unique difference was observed: only FCE24517 inhibited the DNA-independent reaction of adenylation of human DNA ligase while the adenylation reaction of T4 and E. coli DNA ligase was unaffected by either drug. It is still unclear whether these properties are relevant for modulating the killing activity of FCE24517 against proliferating cells both in culture and in vivo. Nevertheless FCE24517 is the first known molecule capable of interacting directly and specifically with human DNA ligase.

Adenosine Monophosphate↗
PubMed1990

The specific binding of nuclear protein(s) to the cAMP responsive element (CRE) sequence (TGACGTCA) is reduced by the misincorporation of U and increased by the deamination of C.

Point mutations in the cAMP-responsive element (CRE) of the rat somatostatin gene promoter/enhancer sequence (TGACGTCA) were used as a model for assessing the effect of uracil, deriving either from misincorporation during DNA synthesis (T----U) or cytosine deamination (C----U), on the binding of sequence/specific regulatory proteins. The results show that the T----U conversion in both strands of the CRE palindromic sequence reduces its affinity for the CRE binding factor(s), suggesting the crucial role of the methyl group contributed by T for the correct recognition of the sequence. On the other hand, deamination of C in the CpG central dinucleotide (CpG----UpG) causes an increase of binding affinity which is further enhanced by the contemporary deamination in both strands. Then, both uracil misincorporation and cytosine deamination alter the binding to CRE sequence in vitro, suggesting that uracil, if not removed by uracil DNA-glycosylase, could be dangerous for cellular functions.

Animals↗
PubMed1990

Effect of divalent and monovalent cations on calf thymus PCNA-independent DNA polymerase delta and its 3'----5' exonuclease.

Recent data suggest that DNA polymerases alpha and delta might have a coordinate functional role at the replication fork. In this communication we show that Mg2+ is likely the natural metal activator for both enzymes. Mn2+, a known mutagenic agent, is a competitive inhibitor of Mg2+ for DNA polymerase delta and acompetitive for DNA polymerase alpha. The 3'----5' exonuclease activity associated with DNA polymerase delta is not affected upon addition of Mn2+. Be2+, another mutagenic agent, on the other hand, has an inhibitory effect on the 3'----5' exonuclease, but not on the DNA polymerase delta. The data presented might explain the mutagenic and carcinogenic potential of these two divalent cations.

Animals↗
PubMed1990

Activity profiles of enzymes that control the uracil incorporation into DNA during neuronal development.

We have shown that DNA polymerase beta, the only nuclear DNA polymerase present in adult neurons, cannot discriminate between dTTP and dUTP, having the same Km for both substrates. This fact suggests that during reparative DNA synthesis, in adult neurons, dUMP residues can be incorporated into DNA. Since uracil DNA-glycosylase functions to prevent the mutagenic effects of uracil in DNA coming as a product of deamination of cytosine residues or as a result of dUMP incorporation by DNA polymerase, we have studied the perinatal activity of uracil DNA-glycosylase and of 2 enzymes (nucleoside diphosphokinase and dUTPase) involved in dUTP metabolism. Our data indicate that during neuronal development there is a rapid decrease in uracil DNA-glycosylase which could impair the removal of uracil present in DNA in adult neurons. However, misincorporation of dUMP into DNA might be kept to a low frequency by the action of dUTPase present at all developmental stages.

Animals↗
PubMed1990

Structure-activity relationships of N2-substituted guanines as inhibitors of HSV1 and HSV2 thymidine kinases.

A series of N2-phenylguanines was synthesized and tested for inhibition of the thymidine kinases encoded by Herpes simplex viruses type 1 and type 2. Compounds with hydrophobic, electron-attracting groups in the meta position of the phenyl ring such as m-trifluoromethyl (m-CF3PG, IC50 = 0.1 microM) were the most potent inhibitors of both enzymes. Many derivatives were significantly more potent against the type 2 thymidine kinase, and can effectively discriminate between the two enzymes. Among other N2-substituted guanines, alkyl and benzyl derivatives were moderately potent inhibitors, and the type 2 enzyme was again more sensitive than the type 1 enzyme. None of the compounds inhibited the thymidine kinase isolated from the host HeLa cell line, suggesting that members of this class of compounds may be useful nonsubstrate, antiviral compounds for latent herpesvirus infections.

Chemical Phenomena↗
PubMed1990

Misincorporation of uracil into DNA as possible contributor to neuronal aging and abiotrophy.

Neuronal aging and abiotrophy may be related to the abnormal presence of uracil in DNA. Evidence which could support this hypothesis exists: 1) DNA polymerase beta, the only nuclear DNA polymerase present in adult neurons which is able to repair damaged DNA, incorporates dUTP or dTTP with the same efficiency. This suggests that in adult neurons the incorporation of dUTP into DNA is solely dependent on the relative intracellular concentration of dUTP; 2) uracil into DNA also arises from cytosine deamination; 3) at birth, when neurons stop proliferating, uracil DNA-glycosylase, the enzyme responsible of the removal of uracil from DNA, nearly disappears; 4) a significant replacement of thymine by uracil in DNA could produce genetic instability which in turn could affect the recognition of DNA sequences by enzymes and/or by regulatory DNA binding proteins. Thus enzymatic defects which might alter the intracellular dUTP pool, in different neuronal systems, could account for the multiplicity of the clinical manifestations of aging and neurodegenerative disorders. The increase of the age-specific rate of abiotrophic diseases may be due to accumulation with time of uracil containing DNA.

Cell Survival↗
PubMed1989

Calf thymus DNA polymerase delta independent of proliferating cell nuclear antigen (PCNA).

DNA polymerase delta from calf thymus was purified under conditions that minimized proteolysis to a specific activity of 27,000 units/mg. The four step isolation procedure included phosphocellulose, hydroxyapatite, heparin-Sepharose and FPLC-MonoS. This enzyme consists of four polypeptides with Mr of 140, 125, 48 and 40 kilodaltons. Velocity gradient sedimentation in glycerol removed the 48 kDa polypeptide while the other three sedimented with the DNA polymerase activity. The biochemical properties of the three subunit enzyme and the copurification of 3'----5' exonuclease activity were typical for a bona fide DNA polymerase delta. Tryptic peptide analysis showed that the 140 kDa polypeptide was different from the catalytic 180 kDa polypeptide of calf thymus DNA polymerase alpha. Both high Mr polypeptides (140 and 125 kDa) were catalytically active as analysed in an activity gel. Four templates were used by DNA polymerase delta with different preferences, namely poly(dA)/oligo(dT)12-18 much much greater than activated DNA greater than poly(dA-dT) greater than primed single-stranded M13DNA. Calf thymus proliferating cell nuclear antigen (PCNA) could not stimulated this DNA polymerase delta in any step of the isolation procedure. If tested on poly(dA)/oligo(dT)12-18 (base ratio 10:1), PCNA had no stimulatory effect on DNA polymerase delta when tested with low enzyme DNA ratio nor did it change the kinetic behaviour of the enzyme. DNA polymerase delta itself did not contain PCNA. The enzyme had an intrinsic processivity of several thousand bases, when tested either on the homopolymer poly(dA)/oligo(dT)12-18 (base ratio 64:1) or on primed single-stranded M13DNA. Contrary to DNA polymerase alpha, no pausing sites were seen with DNA polymerase delta. Under optimal in vitro replication conditions the enzyme could convert primed single-stranded circular M13 DNA of 7,200 bases to its double-stranded form in less than 10 min. This supports that a PCNA independent DNA polymerase delta exists in calf thymus in addition to a PCNA dependent enzyme (Lee, M.Y.W.T. et al. (1984) Biochemistry 23, 1906-1913).

Animals↗
PubMed1989

A double-loop model for the replication of eukaryotic DNA.

Coordinated DNA synthesis of both strands at the replication fork by a fixed 'replisome' may cause dynamic and topological problems. Based upon known properties of DNA helicase, DNA primase and DNA topoisomerases, and on novel properties of DNA polymerases and DNA ligase, we propose a 'double-loop' model for the replication of eukaryotic DNA that could minimize such problems.

Animals↗
PubMed1989

Nucleoside analogs as non-substrate inhibitors of herpes simplex viruses thymidine kinase.

We have examined the capacity of a series of 6-substituted pyrimidine and 2-substituted purine derivatives to inhibit mammalian thymidine kinase and the thymidine kinases encoded by type 1 and type 2 herpes simplex viruses. Several N2-substituted guanine and deoxy guanosine derivatives displayed selective inhibitory activity against the HSV-1 and HSV-2 thymidine kinases by competing with the phosphorylation of thymidine, suggesting a possible novel pharmacological approach to herpes viruses infections.

Cells, Cultured↗
PubMed1988

Replication of single-stranded porcine circovirus DNA by DNA polymerases alpha and delta.

Porcine circovirus is the only mammalian DNA virus so far known to contain a single-stranded circular genome (Tischer et al. (1982) Nature 295, 64-66). Replication of its small viral DNA (1.76 kb) appears to be dependent on cellular enzymes expressed during S-phase of the cell cycle (Tischer et al. (1987) Arch. Virol. 96, 39-57). In this paper we have exploited the porcine circovirus genome to probe for in vitro initiation and elongation of DNA replication by different preparations of calf thymus DNA polymerase alpha and delta as well as by a partially purified preparation from pig thymus. The results indicated that three different purification fractions of calf thymus DNA polymerase alpha and one from pig thymus initiate DNA synthesis at several sites on the porcine circovirus DNA. It appears that the sites at which DNA primase synthesizes primers are not entirely random. Subsequent DNA elongation by a highly purified DNA polymerase alpha holoenzyme which had been isolated by the criterion of replicating single-stranded M13 DNA (Ottiger et al. (1987) Nucleic Acids Res. 15, 4789-4807) is very efficient. Complete conversion to the double-stranded form is obtained in less than 1 min. When the DNA synthesis by DNA polymerase alpha is blocked with the DNA polymerase alpha specific monoclonal antibody SJK 132-20 after initiation by DNA primase, DNA polymerase delta can efficiently replicate from the primers. This in vitro DNA replication system may be used in analogy to the bacteriophage systems in E. coli to study initiation and elongation of DNA replication.

Animals↗
PubMed1988

Calf thymus DNA polymerase delta: purification, biochemical and functional properties of the enzyme after its separation from DNA polymerase alpha, a DNA dependent ATPase and proliferating cell nuclear antigen.

We have established a novel procedure to purify calf thymus DNA polymerase delta from cytoplasmic extracts. The enzyme has typical properties of DNA polymerase delta including a 3' - greater than 5' exonuclease activity and efficiently replicates natural occurring genomes such as primed single-stranded M13 DNA and single-stranded porcine circovirus DNA, this last one thanks to an associated or contaminating primase activity. A processivity of at least a thousand bases was evident and this in the apparent absence of proliferating cell nuclear antigen. The enzyme was purified through a procedure that allows the simultaneous isolation of DNA polymerase delta, DNA polymerase alpha-primase and a DNA dependent ATPase. All these enzymes coeluted from a phosphocellulose column. After chromatography on hydroxylapatite DNA polymerase delta separated from the coeluting DNA polymerase alpha and DNA dependent ATPase. Separation of the latter two was achieved on heparin-Sepharose. DNA polymerase delta was further purified by heparin-Sepharose and fast protein liquid chromatography. Purified DNA polymerase delta was resistant to the DNA polymerase alpha inhibitors BuPdGTP and BuAdATP and did not react with DNA polymerase alpha monoclonal and polyclonal antibodies. Based on this isolation protocol we can start to test biochemically the hypothesis whether DNA polymerase delta and DNA polymerase alpha might act coordinately at the replication fork as leading and lagging strand replicases, respectively.

Adenosine Triphosphatases↗
PubMed1988

Do DNA polymerases delta and alpha act coordinately as leading and lagging strand replicases?

The activity ratio of DNA polymerases delta and alpha in calf thymus was found to be invariably 1:1, irrespective of extraction procedure (8 types) and subcellular localization (cytoplasm, nucleus and microsomes). This was established by separation of the two forms by hydroxyapatite chromatography and by their response to specific inhibitors and monoclonal antibodies. This finding supports the dimeric DNA polymerase model [(1980) J. Biol. Chem. 255, 4290-4303], which proposes that DNA polymerases delta and alpha act coordinately as leading and lagging strand enzymes, respectively, at the replication fork.

Adenosine Triphosphate↗
PubMed1988

N2-phenyldeoxyguanosine: a novel selective inhibitor of herpes simplex thymidine kinase.

A series of N2-substituted guanine derivatives was screened against mammalian thymidine kinase and the thymidine kinase encoded by type I herpes simplex virus to examine their capacity to selectivity inhibit the viral enzyme. Several bases, nucleosides, and nucleotides displayed selective activity. The mechanism of action of the most potent derivative, N2-phenyl-2'-deoxyguanosine (PhdG) was studied in detail. PhdG (a) inhibited the viral enzyme competitively with respect to the substrates thymidine and deoxycytidine, (b) was completely resistant to phosphorylation, (c) displayed limited toxicity for the HeLa cell lines employed as hosts for viral infection, and (d) selectively inhibited viral thymidine kinase function in intact cultured cells. The results indicate that the PhdG drug prototype has potential as a selective anti-herpes agent and as a novel molecular probe of the structure and function of herpes simplex thymidine kinase.

Antiviral Agents↗
PubMed1987

Alteration of DNA tertiary structure by physical and chemical carcinogens: involvement in DNA repair processes.

Parameters defining the topological state of DNA seem extremely important for describing the reactive state of the same DNA molecules. We have shown that physical and chemical DNA modifying agents alter the tertiary structure of DNA molecules. Variations in the tertiary structure of DNA were studied by one dimensional electrophoresis on an agarose gel of partially relaxed plasmid DNA topoisomers, a technique allowing the measurement of alterations in the degree of supercoiling equivalent to fractions of superhelical turns. Unwinding angles of -10.1 degrees or -8.7 degrees per pyrimidine or thymine dimer respectively, of -12 degrees per apurinic site, and of -3.4 degrees per methylated purine were obtained by titrating the number of damaged sites necessary to reduce the number of superhelical turns by one in each topoisomer. On the contrary, enzymatic methylation of the C-5 position of cytosine (a modified base present in prokaryotic and eukaryotic DNAs) did not alter the DNA tertiary structure. We have also shown that local alterations in DNA structure caused by UV-irradiation inhibit bacterial DNA topoisomerase I and DNA methylase, and that the topological state of DNA substrate influences the mode of methylation of Hpa II DNA methylase. These findings suggest that the natural topological state of DNA substrate (linear, relaxed, or covalently closed duplex DNA with varying degrees of supercoiling) influences the mode of action of enzymes possibly involved in DNA repair processes, while DNA structural alterations caused by DNA modifying agents might influence DNA repair processes in two ways: either by driving the interaction between repair enzymes and the modified sites of DNA, or by inhibiting or changing the mode of action of enzymes normally acting on unmodified DNA.

Animals↗