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PubMedDate not supplied

A comparison of the effects of repeated administration of cyclophosphamide, cytosine arabinoside or their combination on smooth and skeletal muscle.

The pharmacological effects of repeated administration of 2 mg Kg-1 cytosine arabinoside, 40 mg Kg-1 cyclophosphamide or their combination, all given once weekly for 5 weeks, have been investigated in chicks. Cyclophosphamide did not affect responses to noradrenergic nerve stimulation or phenylephrine, depressed responses of the expansor secundariorum muscle to acetylcholine but sensitised the muscle to direct stimulation. Cytosine arabinoside depressed noradrenergic transmission and enhanced responses of the expansor muscle to phenylephrine and acetylcholine. The combination of both drugs enhanced responses to noradrenergic nerve stimulation due to increased alpha-adrenergic receptor mediated contraction and direct muscle sensitisation. Cyclophosphamide, cytosine arabinoside or their combination produced a non-specific depression of the upper oesophagus and ileum. The exception was the marked increase in response of the ileum from the combination group to agonist drugs, indicating synergism. The non-specific skeletal muscle depressant actions of cyclophosphamide and the combination groups were more pronounced than that of the cytosine arabinoside group.

Animals↗
PubMed1990

Randomized multicenter trial of cytosine arabinoside with mitoxantrone or daunorubicin in previously untreated adult patients with acute nonlymphocytic leukemia (ANLL). Lederle Cooperative Group.

This phase III, randomized trial in previously untreated adults with ANLL compared mitoxantrone plus cytosine arabinoside with the CALGB "7 + 3" daunorubicin-based regimen. Two hundred evaluable patients (98 treated with the mitoxantrone-based regimen and 102 with the daunorubicin-based regimen) were included in the analysis of efficacy. The median age of the patients was 60 years. The induction regimen comprised cytosine arabinoside 100 mg/m2 by infusion daily for 7 days and mitoxantrone 12 mg/m2 or daunorubicin 45 mg/m2 daily for days 1-3. If needed, a second induction course was administered: cytosine arabinoside for 5 days and mitoxantrone or daunorubicin for 2 days. Postremission therapy consisted of two consolidation courses, identical to the second induction course. Sixty-three percent (62 of 98) of patients treated with mitoxantrone achieved complete remission (CR), compared to 53% (54 of 102) treated with daunorubicin. The median time to CR was 35 days in patients treated with mitoxantrone and 43 days for those treated with daunorubicin. Eighty-nine percent (55 of 62) of patients treated with mitoxantrone who entered complete remission achieved CR following one induction course, compared to 68% (37 of 54) of patients treated with daunorubicin who entered CR. The median duration of CR was 240 days in patients treated with mitoxantrone and 198 days in those treated with daunorubicin; the median length of survival was 328 days in patients who received mitoxantrone and 247 days in those who received daunorubicin. The toxicity profiles in patients treated with either of the two regimens were comparable in incidence and in severity. Patients treated with mitoxantrone required fewer median platelet units and were treated with fewer median days of intravenous antibiotics, compared to those who received daunorubicin. Mitoxantrone in combination with cytosine arabinoside is effective in previously untreated ANLL. complete remissions occur more frequently after a single induction course of the mitoxantrone-based regimen, compared to the standard Cancer and Acute Leukemia Group B regimen. This should be explored in further trials.

Adult↗
PubMed1987

[Value of high-dose cytosine-arabinoside in the treatment of resistant acute leukemia].

Sixty-one patients with refractory or relapsed or secondary acute leukemia were treated with high-dose cytosine arabinoside (2-3 g/sq m in intravenous infusion every 12 hr to a 12-36 g/sq m total dose). m-Amsa or another antileukemic drug was given with cytosine arabinoside to 20 patients. Complete remission was achieved in 12 of 27 patients with acute myeloid leukemia, 5 of 8 patients with chemotherapy-induced leukemia, 3 of 7 patients with hematologic disorders in blastic crisis and 5 of 17 acute lymphoblastic leukemia patients. A similar response rate (6/16) was obtained when m-Amsa was given with cytosine-arabinoside. The median duration of remission was short (4 months in acute myeloid leukemia). Bone marrow transplantation was performed in 10 patients during the remission time. This regimen has acceptable toxicity; severe neurologic or hepatic disorders occurred in 18% of patients. These data suggest that high-dose cytosine arabinoside is an effective alternative in the treatment of resistant acute leukemia.

Acute Disease↗
PubMed1994

A phase III trial of high-dose cytosine arabinoside with or without etoposide in relapsed and refractory acute myelogenous leukemia. A Southeastern Cancer Study Group trial.

A phase III clinical trial was developed to test whether the addition of etoposide to a high-dose cytosine arabinoside regimen would improve the remission rate, duration of remission, and survival in relapsed and refractory patients with acute myelogenous leukemia. One hundred and thirty-one patients stratified by age, performance status, percentage of marrow blasts, platelet count, bilirubin and presence or absence of clinical infection, refractory or relapsed (+/- 9 months) were randomized to receive high-dose cytosine arabinoside, 3 g/m2 every 12 h for 6 days with or without three doses of etoposide, 100 mg/m2 days 7-9. Of 67 patients randomized to cytosine arabinoside alone, 31% obtained a complete remission with a median remission duration of 11.9 months. Of 66 patients randomized to the combination regimen, 38% obtained a complete remission with a median duration of 25 months. None of these differences were statistically significant. Significantly (p = 0.036) longer survival was seen in patients on the combination regimen under the age of 50. There was no difference in overall survival. Six and 8%, respectively, of patients were free of disease at 5 years. The addition of etoposide to a high-dose cytosine arabinoside regimen had at best a marginal effect at the expense of some increase in toxicity.

Adult↗
PubMed1990

The amino acid sequence of the CCGG recognizing DNA methyltransferase M.BsuFI: implications for the analysis of sequence recognition by cytosine DNA methyltransferases.

The Bacillus subtilis FI DNA methyltransferase (M.BsuFI) modifies the outer cytosine of the DNA sequence CCGG, causing resistance against R.BsuFI and R.MspI restriction. The M.BsuFI gene was cloned and expressed in B.subtilis and Escherichia coli. As derived from the nucleotide sequence, the M.BsuFI protein has 409 amino acids, corresponding to a molecular mass of 46,918 daltons. Including these data we have compared the nucleotide and amino acid sequences of different CCGG recognizing enzymes. These analyses showed that M.BsuFI is highly related to two other CCGG specific methyltransferases, M.MspI and M.HpaII, which were isolated from Gram-negative bacteria. Between M.BsuFI and M.MspI the sequence similarity is particularly significant in a region, which has been postulated to contain the target recognition domains (TRDs) of cytosine-specific DNA methyltransferases. Apparently M.BsuFI and M.MspI, derived from phylogenetic distant organisms, use highly conserved structural elements for the recognition of the CCGG target sequence. In contrast the very same region of M.HpaII is quite different from those of M.BsuFI and M.MspI. We attribute this difference to the different targeting of methylation within the sequence CCGG, where M.HpaII methylates the inner, M.BsuFI/M.MspI the outer cytosine. Also the CCGG recognizing TRD of the multispecific B.subtilis phage SPR Mtase is distinct from that of the host enzyme, possibly indicating different requirements for TRDs operative in mono- and multispecific enzymes.

Amino Acid Sequence↗
PubMed1986

Cytosine-specific DNA modification interferes with plasmid establishment in Escherichia coli K12: involvement of rglB.

Several chimeric pBR322/328 derivatives containing genes for cytosine-specific DNA methyltransferases (Mtases) can be transformed into the Escherichia coli K12/E. coli B hybrid strains HB101 and RR1 but not into other commonly used E. coli K12 strains. In vitro methylation of cytosine residues in pBR328 and other unrelated plasmids also reduces their potential to transform such methylation sensitive strains, albeit to a lesser degree than observed with plasmids containing Mtase genes. The extent of reduced transformability depends on the target specificity of the enzyme used for in vitro modification. The role of a host function in the discrimination against methylated plasmids was verified by the isolation of K12 mutants which tolerate cytosine methylated DNA. The mutations map in the vicinity of the serB locus. This and other data indicate that the host rglB function is involved in the discrimination against modified DNA.

Cytosine↗
PubMed1995

The crystal structure of HaeIII methyltransferase convalently complexed to DNA: an extrahelical cytosine and rearranged base pairing.

Many organisms expand the information content of their genome through enzymatic methylation of cytosine residues. Here we report the 2.8 A crystal structure of a bacterial DNA (cytosine-5)-methyltransferase (DCMtase), M. HaeIII, bound covalently to DNA. In this complex, the substrate cytosine is extruded from the DNA helix and inserted into the active site of the enzyme, as has been observed for another DCMtase, M. HhaI. The DNA is bound in a cleft between the two domains of the protein and is distorted from the characteristic B-form conformation at its recognition sequence. A comparison of structures shows a variation in the mode of DNA recognition: M. HaeIII differs from M. HhaI in that the remaining bases in its recognition sequence undergo an extensive rearrangement in their pairing. In this process, the bases are unstacked, and a gap 8 A long opens in the DNA.

Amino Acid Sequence↗
PubMed1999

Stable transformation of Toxoplasma gondii based on a pyrimethamine resistant trifunctional dihydrofolate reductase-cytosine deaminase-thymidylate synthase gene that confers sensitivity to 5-fluorocytosine.

To improve genetic models available for the analysis of apicomplexan protozoan parasites, bacterial sequences encoding the 427 amino acid cytosine deaminase (CD) gene were fused, in-frame, to an engineered linker domain of the high level pyrimethamine resistant form of the parasite bifunctional dihydrofolate reductase-thymidylate synthase (DHFR-TS) gene. Toxoplasma gondii was transformed with the plasmid containing the fused pyrimethamine resistant dihydrofolate reductase-cytosine deaminase-thymidylate synthase (DHFRm2m3-CD-TS) gene and parasites were selected in a high level of pyrimethamine. Transfected parasites that acquired resistance to pyrimethamine were cloned and evaluated for expression of the CD genetic marker. CD transgenic parasites acquired a high sensitivity to 5-fluorocytosine due to the intraparasitic conversion of this non-toxic prodrug to the cytotoxic compound 5-fluorouracil. Exogenously supplied cytosine or uracil rescued the growth of CD transgenic T. gondii parasites that were cultured in the presence of cytotoxic concentrations of 5-fluorouracil or 5-fluorocytosine. Bacterial CD fused to the pyrimethamine resistant DHFR-TS marker provides a novel genetic tool for new positive and negative genetic selection strategies in several protozoan parasites. An advantage of the CD genetic marker is that it is derived from a bacterial gene and can therefore be used in nearly any parasite genetic background for negative selection. This novel system should facilitate new approaches for the development of improved model genetic systems for the biological investigation of apicomplexan parasites.

Animals↗
PubMed2006

The binding of nuclear factors to the as-1 element in the CaMV 35S promoter is affected by cytosine methylation in vitro.

Transcriptional gene silencing (TGS) is often associated with an increased level of cytosine methylation in the affected promoters. The effect of methylation of the cauliflower mosaic virus (CaMV) 35S promoter sequence on its binding to factors present in the nuclei was analyzed by electrophoretic mobility shift assays using extracts of petunia flowers. Specific DNA-protein interactions were detected in the region of the CaMV 35S promoter that contains the as-1 element and the region between - 345 and - 208. The binding of protein factor(s) to the as-1 element was influenced by cytosine methylation, whereas the binding to the region between - 345 and - 208 was unaffected. The results suggest that cytosine methylation of the as-1 element potentially affects the activity of the CaMV 35S promoter.

Binding Sites↗
PubMed1995

Studies on the influence of cytosine methylation on DNA recombination and end-joining in mammalian cells.

To test the influence of cytosine methylation on homologous recombination and the rejoining of DNA double strand breaks in mammalian cells, we developed a sensitive and quantitative assay system using extrachromosomal substrates. First, methylation was introduced into substrates in vitro with the prokaryotic SssI methylase, which specifically methylates the C-5 position of cytosine bases within CpG dinucleotides, mimicking the mammalian DNA methyltransferase. Next, methylated substrates were incubated in mammalian cells for a sufficient length of time to recombine or rejoin prior to substrate recovery. Results from bacterial transformation of the substrates and from direct Southern analysis demonstrate that cytosine methylation has no detectable effect on either DNA end-joining or homologous recombination. Thus, the components of the protein machinery involved in these complex processes are unaffected by the major DNA modification in mammalian cells. These results leave open the possibility that methylation may modulate the accessibility of these components to chromosomal DNA by altering local chromatin structure.

Animals↗
PubMed2002

An in vitro screening method for DNA cytosine-C5-methylase inhibitor.

A specific inhibitor of DNA cytosine C5-methylases would be useful for studying genomic imprinting, X-chromosome inactivation, carcinogenesis, and regulation of tissue-specific gene expression, for these physiological phenomena appears to be regulated through DNA methylation in promoter sequences. This paper reports a novel convenient in vitro assay method for screening DNA cytosine C5-methylase inhibitor. Our method uses a commercially available Hae III methylase (cytosine C5 methylase), its corresponding Hae III endonuclease, and lambda DNA as their substrate.

Adenosine↗
PubMed1993

Sequence-specific and mechanism-based crosslinking of Dcm DNA cytosine-C5 methyltransferase of E. coli K-12 to synthetic oligonucleotides containing 5-fluoro-2'-deoxycytidine.

The product of the dcm gene is the only DNA cytosine-C5 methyltransferase of Escherichia coli K-12; it catalyses transfer of a methyl group from S-adenosyl methionine (SAM) to the C-5 position of the inner cytosine residue of the cognate sequence CCA/TGG. Sequence-specific, covalent crosslinking of the enzyme to synthetic oligonucleotides containing 5-fluoro-2'-deoxycytidine is demonstrated. This reaction is abolished if serine replaces the cysteine at residue #177 of the enzyme. These results lend strong support to a catalytic mechanism in which an enzyme sulfhydryl group undergoes Michael addition to the C5-C6 double bond, thus activating position C-5 of the substrate DNA cytosine residue for electrophilic attack by the methyl donor SAM. The enzyme is capable of self-methylation in a DNA-independent reaction requiring SAM and the presence of cysteine at position #177.

Base Sequence↗
PubMed1997

Cloning of the BssHII restriction-modification system in Escherichia coli : BssHII methyltransferase contains circularly permuted cytosine-5 methyltransferase motifs.

BssHII restriction endonuclease cleaves 5'-GCGCGC-3' on double-stranded DNA between the first and second bases to generate a four base 5'overhang. BssHII restriction endonuclease was purified from the native Bacillus stearothermophilus H3 cells and its N-terminal amino acid sequence was determined. Degenerate PCR primers were used to amplify the first 20 codons of the BssHII restriction endonuclease gene. The BssHII restriction endonuclease gene (bssHIIR) and the cognate BssHII methyltransferase gene (bssHIIM) were cloned in Escherichia coli by amplification of Bacillus stearothermophilus genomic DNA using PCR and inverse PCR. BssHII methyltransferase (M.BssHII) contains all 10 conserved cytosine-5 methyltransferase motifs, but motifs IX and X precede motifs I-VIII. Thus, the conserved motifs of M. BssHII are circularly permuted relative to the motif organizations of other cytosine-5 methyltransferases. M.BssHII and the non-cognate multi-specific phiBssHII methyltransferase, M.phiBss HII [Schumann,J. et al . (1995) Gene, 157, 103-104] share 34% identity in amino acid sequences from motifs I-VIII, and 40% identity in motifs IX-X. A conserved arginine is located upstream of a TV dipeptide in the N-terminus of M.BssHII that may be responsible for the recognition of the guanine 5' of the target cytosine. The BssHII restriction endonuclease gene was expressed in E.coli via a T7 expression vector.

Amino Acid Sequence↗
PubMed2005

Targeting of the activation-induced cytosine deaminase is strongly influenced by the sequence and structure of the targeted DNA.

Activation-induced deaminase (AID) initiates immunoglobulin somatic hypermutation (SHM). Since in vitro AID was shown to deaminate cytosines on single-stranded DNA or the nontranscribed strand, it remained a puzzle how in vivo AID targets both DNA strands equally. Here we investigate the roles of transcription and DNA sequence in cytosine deamination. Strikingly different results are found with different substrates. Depending on the target sequence, the transcribed DNA strand is targeted as well as or better than the nontranscribed strand. The preferential targeting is not related to the frequency of AID hot spots. Comparison of cytosine deamination by AID and bisulfite shows different targeting patterns suggesting that AID may locally unwind the DNA. We conclude that somatic hypermutation on both DNA strands is the natural outcome of AID action on a transcribed gene; furthermore, the DNA sequence or structure and topology play major roles in targeting AID in vitro and in vivo. On the other hand, the lack of mutations in the first approximately 100 nucleotides and beyond about 1 to 2 kb from the promoter of immunoglobulin genes during SHM must be due to special conditions of transcription and chromatin in vivo.

Ampicillin Resistance↗
PubMed1991

Enzymatic methylation of cytosine in DNA is prevented by adjacent O6-methylguanine residues.

The effect of O6-alkylation of guanine residues on the enzymic methylation of cytosine has been studied using synthetic oligonucleotides in which all guanines in cytosine-guanine sequences at potentially methylatable sites are replaced by O6-methylguanine. In contrast with the unmodified forms, which showed high acceptance activity for methyl-3H-labeled groups from S-adenosyl-L-[methyl-3H]methionine in the presence of DNA methylase, the modified oligonucleotides were not substrates for the enzyme either in the single-stranded or annealed forms. In view of the importance of cytosine methylation in the down-regulation of certain genes, the potential to affect gene expression by this mechanism may be a contributory factor in the toxic and carcinogenic effects of chemical methylating agents.

Base Sequence↗
PubMed1994

Increased binding of Sp1 to the gamma-globin gene promoter upon site-specific cytosine methylation.

We have studied the effect of site-specific cytosine methylation on the binding of nuclear proteins to the gamma-globin promoter region from -71 to -34. This sequence was recently shown to contain a stage selector element responsible for increased transcription from the gamma compared to the beta promoter when both are linked to Locus Control Region enhancer sequences. We observed that Sp1 binding to this sequence is increased upon site-specific cytosine methylation, such that only methylation of the cytosine in the -50 CpG dinucleotide effects Sp1 binding. Methylation of the distal C of the Hpall site has no effect. The possible functional role of Sp1 as a repressor of gamma-globin synthesis is discussed.

Animals↗
PubMed2006

Characterization of BlsM, a nucleotide hydrolase involved in cytosine production for the biosynthesis of blasticidin S.

Biosynthesis of the antifungal agent blasticidin S in Streptomyces griseochromogenes requires the formation of free cytosine. The blsM gene in the blasticidin S gene cluster is predicted to encode a protein that has sequence homology with several nucleoside transferases. In vitro analysis of recombinant BlsM revealed that the enzyme functions as a nucleotide hydrolase and catalyzes the formation of free cytosine by using cytidine 5'-monophosphate (CMP) as the preferred substrate. Cytosine production was significantly lower with CDP, CTP, and dCMP as alternate substrates. BlsM was also observed to have low-level cytidine deaminase activity, converting cytidine and deoxycytidine to uridine and deoxyuridine, respectively. Point mutations were introduced in blsM at putative catalytic residues to generate three mutant enzymes, BlsM Ser98Asp, Glu104Ala, and Glu104Asp. All three mutants lost CMP hydrolysis activity, but the Ser98Asp mutant showed a modest increase in cytidine deaminase activity.

Amino Acid Sequence↗
PubMed1994

Propylene oxide mutagenesis at template cytosine residues.

Propylene oxide (PO) is a widely used industrial reagent which is mutagenic and carcinogenic. We have recently shown that a variety of aliphatic epoxides, including propylene oxide, can react with DNA to form hydroxyalkyl adducts at N-3 of cytosine which rapidly undergo hydrolytic deamination to produce uracil adducts. These 3-hydroxyalkyl uracil adducts are stable in DNA and are postulated to be an important class of potentially mutagenic lesions. Mutagenesis at cytosine residues due to PO modification of single-stranded M13mp2/C141 DNA was studied by transfection of modified DNA into SOS and non-SOS induced E. coli host cells. Mutations of the proline (CCC) codon at C141 which result in reversion of the lacZ phenotype (blue plaques) were scored. It was found that PO treatment of single-stranded DNA results in dose-dependent mutagenesis that is highly SOS dependent. The spectrum of base-substitution mutations found at this site differed when PO-modified DNA was transfected into E. coli with different DNA repair backgrounds. These results indicate that propylene oxide induced DNA adducts at template cytosine residues are mutagenic in E. coli and that this mutagenesis is greatly increased by SOS processing. They also show that these lesions may be repaired by one or more mechanisms.

Bacteriophage M13↗