Inhibition of Protein Kinase CK2 Affects Thymidylate Synthesis Cycle Enzyme Level and Distribution in Human Cancer Cells

Thymidylate synthase (TS), dihydrofolate reductase (DHFR), and serine hydroxymethyltransferase (SHMT) constitute the thymidylate synthesis cycle providing thymidylate for DNA synthesis and repair. Our previous studies indicated that TS and DHFR are the substrates of protein kinase CK2. This work has been aimed at the elucidation of the effect of CK2 activity on cell cycle progression, thymidylate synthesis enzyme expression and localization, and the role of CK2-mediated TS phosphorylation in in vitro di- and trimolecular complex formation. The results were obtained by means of western blot, confocal microscopy, flow cytometry, quantitative polymerase chain reaction (QPCR), quartz crystal microbalance with dissipation monitoring (QCM-D), and microthermophoresis (MST). Our research indicates that CK2 inhibition does not change the levels of the transcripts; however, it affects the protein levels of DHFR and TS in both tested cell lines, i.e., A549 and CCRF-CEM, and the level of SHMT1 in CCRF-CEM cells. Moreover, we show that CK2-mediated phosphorylation of TS enables the protein (pTS) interaction with SHMT1 and leads to the stability of the tri-complex containing SHMT1, DHFR, and pTS. Our results suggest an important regulatory role of CK2-mediated phosphorylation for inter- and intracellular protein level of enzymes involved in the thymidylate biosynthesis cycle.

Simultaneous Inhibition of Protein Kinase CK2 and Dihydrofolate Reductase Results in Synergistic Effect on Acute Lymphoblastic Leukemia Cells

BACKGROUND/AIM

Recently, we demonstrated the ability of inhibitors of protein kinase 2 (casein kinase II; CK2) to enhance the efficacy of 5-fluorouracil, a thymidylate synthase (TYMS)-directed drug for anticancer treatment. The present study aimed to investigate the antileukemic effect of simultaneous inhibition of dihydrofolate reductase (DHFR), another enzyme involved in the thymidylate biosynthesis cycle, and CK2 in CCRF-CEM acute lymphoblastic leukemia cells.

MATERIALS AND METHODS

The influence of combined treatment on apoptosis and cell-cycle progression, as well as the endocellular level of DHFR protein and inhibition of CK2 were determined using flow cytometry and western blot analysis, respectively. Real-time quantitative polymerase chain reaction was used to examine the influence of silmitasertib (CX-4945), a selective inhibitor of CK2 on the expression of DHFR and TYMS genes.

RESULTS

The synergistic effect was correlated with the increase of annexin V-binding cell fraction, caspase 3/7 activation and a significant reduce in the activity of CK2. An increase of DHFR protein level was observed in CCRF-CEM cells after CX-4945 treatment, with the mRNA level remaining relatively constant.

CONCLUSION

The obtained results demonstrate a possibility to improve methotrexate-based anti-leukemia therapy by simultaneous inhibition of CK2. The effect of CK2 inhibition on DHFR expression suggests the important regulatory role of CK2-mediated phosphorylation of DHFR inside cells.

ERCC1-deficient cells and mice are hypersensitive to lipid peroxidation

Lipid peroxidation (LPO) products are relatively stable and abundant metabolites, which accumulate in tissues of mammals with aging, being able to modify all cellular nucleophiles, creating protein and DNA adducts including crosslinks. Here, we used cells and mice deficient in the ERCC1-XPF endonuclease required for nucleotide excision repair and the repair of DNA interstrand crosslinks to ask if specifically LPO-induced DNA damage contributes to loss of cell and tissue homeostasis. Ercc1^-/- mouse embryonic fibroblasts were more sensitive than wild-type (WT) cells to the LPO products: 4-hydroxy-2-nonenal (HNE), crotonaldehyde and malondialdehyde. ERCC1-XPF hypomorphic mice were hypersensitive to CCl₄ and a diet rich in polyunsaturated fatty acids, two potent inducers of endogenous LPO. To gain insight into the mechanism of how LPO influences DNA repair-deficient cells, we measured the impact of the major endogenous LPO product, HNE, on WT and Ercc1^-/- cells. HNE inhibited proliferation, stimulated ROS and LPO formation, induced DNA base damage, strand breaks, error-prone translesion DNA synthesis and cellular senescence much more potently in Ercc1^-/- cells than in DNA repair-competent control cells. HNE also deregulated base excision repair and energy production pathways. Our observations that ERCC1-deficient cells and mice are hypersensitive to LPO implicates LPO-induced DNA damage in contributing to cellular demise and tissue degeneration, notably even when the source of LPO is dietary polyunsaturated fats.

8-Oxoguanine incision activity is impaired in lung tissues of NSCLC patients with the polymorphism of OGG1 and XRCC1 genes

Decreased repair of oxidative DNA damage is a risk factor for developing certain human malignancies. We have previously found that the capacity of 8-oxo-7,8-dihydroguanine repair was lower in leukocytes of NSCLC patients than in controls. To explain these observations, we searched for mutations and polymorphisms in the OGG1 gene among 88 NSCLC patients and 79 controls. One patient exhibited a heterozygous mutation in exon 1, which resulted in Arg46Gln substitution. Normal lung and tumor tissue carrying this mutation showed markedly lower 8-oxoG incision activity than the mean for all patients. The predominant polymorphism of OGG1 was Ser326Cys. A significant difference was observed in the frequencies of the OGG1 variants between populations of NSCLC patients and controls. The frequency of the Cys326 allele and the number of Cys326Cys homozygotes was higher among patients than controls. In individuals with either Ser326Cys or Cys326Cys genotype 8-oxoG incision rate was lower than in those with both Ser326 alleles, either in lung or leukocytes. Moreover, 8-oxodG level was higher in lung tissue and leukocytes of patients carrying two Cys326 alleles and in leukocytes of patients with the Ser326Cys genotype. We also screened for polymorphisms of the XRCC1 gene. Only heterozygotes of the XRCC1 variants Arg194Trp, Arg280His and Arg399Gln were found among patients and controls, with the frequency of Arg280His being significantly higher among patients. NSCLC patients with Arg280His or Arg399Gln polymorphism revealed lower 8-oxoG incision activity in their lung tissues, but not in leukocytes. We can conclude that the OGG1 Ser326Cys polymorphisms may have an impact on the efficiency of 8-oxoG incision in humans and the XRCC1 His280 and Gln399 may influence the OGG1 activity in tissues exposed to chronic oxidative/inflammatory stress. Higher frequency of the OGG1 Cys326 allele among NSCLC patients may partially explain the impairment of the 8-oxoG repair observed in their leukocytes.

Aberrant repair of etheno-DNA adducts in leukocytes and colon tissue of colon cancer patients

To assess the role of lipid peroxidation-induced DNA damage and repair in colon carcinogenesis, the excision rates and levels of 1,N(6)-etheno-2'-deoxyadenosine (epsilondA), 3,N(4)-etheno-2'-deoxycytidine (epsilondC), and 1,N(2)-etheno-2'-deoxyguanosine (1,N(2)-epsilondG) were analyzed in polymorphic blood leukocytes (PBL) and resected colon tissues of 54 colorectal carcinoma (CRC) patients and PBL of 56 healthy individuals. In PBL the excision rates of 1,N(6)-ethenoadenine (epsilonAde) and 3,N(4)-ethenocytosine (epsilonCyt), measured by the nicking of oligodeoxynucleotide duplexes with single lesions, and unexpectedly also the levels of epsilondA and 1,N(2)-epsilondG, measured by LC/MS/MS, were lower in CRC patients than in controls. In contrast the mRNA levels of repair enzymes, alkylpurine- and thymine-DNA glycosylases and abasic site endonuclease (APE1), were higher in PBL of CRC patients than in those of controls, as measured by QPCR. In the target colon tissues epsilonAde and epsilonCyt excision rates were higher, whereas the epsilondA and epsilondC levels in DNA, measured by (32)P-postlabeling, were lower in tumor than in adjacent colon tissue, although a higher mRNA level was observed only for APE1. This suggests that during the onset of carcinogenesis, etheno adduct repair in the colon seems to be under a complex transcriptional and posttranscriptional control, whereby deregulation may act as a driving force for malignancy.

Sequence-specific p53 gene damage by chloroacetaldehyde and its repair kinetics in Escherichia coli

Oxidative stress and certain environmental carcinogens, e.g. vinyl chloride and its metabolite chloroacetaldehyde (CAA), introduce promutagenic exocyclic adducts into DNA, among them 1,N(6)-ethenoadenine (epsilonA), 3,N(4)-ethenocytosine (epsilonC) and N(2),3-ethenoguanine (epsilonG). We studied sequence-specific interaction of the vinyl-chloride metabolite CAA with human p53 gene exons 5-8, using DNA Polymerase Fingerprint Analysis (DPFA), and identified sites of the highest sensitivity. CAA-induced DNA damage was more extensive in p53 regions which revealed secondary structure perturbations, and were localized in regions of mutation hot-spots. These perturbations inhibited DNA synthesis on undamaged template. We also studied the repair kinetics of CAA-induced DNA lesions in E. coli at nucleotide resolution level. A plasmid bearing full length cDNA of human p53 gene was modified in vitro with 360 mM CAA and transformed into E. coli DH5alpha strain, in which the adaptive response system had been induced by MMS treatment before the cells were made competent. Following transformation, plasmids were re-isolated from transformed cultures 35, 40, 50 min and 1-24 h after transformation, and further subjected to LM-PCR, using ANPG, MUG and Fpg glycosylases to identify the sites of DNA damage. In adaptive response-induced E. coli cells the majority of DNA lesions recognized by ANPG glycosylase were removed from plasmid DNA within 35 min, while MUG glycosylase excised base modifications only within 50 min, both in a sequence-dependent manner. In non-adapted cells resolution of plasmid topological forms was perturbed, suggesting inhibition of one or more bacterial topoisomerases by unrepaired epsilon-adducts. We also observed delayed consequences of DNA modification with CAA, manifesting as secondary DNA breaks, which appeared 3 h after transformation of damaged DNA into E. coli, and were repaired after 24 h.

Sequence-specific p53 gene damage by chloroacetaldehyde and its repair kinetics in Escherichia coli

Oxidative stress and certain environmental carcinogens, e.g. vinyl chloride and its metabolite chloroacetaldehyde (CAA), introduce promutagenic exocyclic adducts into DNA, among them 1,N(6)-ethenoadenine (epsilonA), 3,N(4)-ethenocytosine (epsilonC) and N(2),3-ethenoguanine (epsilonG). We studied sequence-specific interaction of the vinyl-chloride metabolite CAA with human p53 gene exons 5-8, using DNA Polymerase Fingerprint Analysis (DPFA), and identified sites of the highest sensitivity. CAA-induced DNA damage was more extensive in p53 regions which revealed secondary structure perturbations, and were localized in regions of mutation hot-spots. These perturbations inhibited DNA synthesis on undamaged template. We also studied the repair kinetics of CAA-induced DNA lesions in E. coli at nucleotide resolution level. A plasmid bearing full length cDNA of human p53 gene was modified in vitro with 360 mM CAA and transformed into E. coli DH5alpha strain, in which the adaptive response system had been induced by MMS treatment before the cells were made competent. Following transformation, plasmids were re-isolated from transformed cultures 35, 40, 50 min and 1-24 h after transformation, and further subjected to LM-PCR, using ANPG, MUG and Fpg glycosylases to identify the sites of DNA damage. In adaptive response-induced E. coli cells the majority of DNA lesions recognized by ANPG glycosylase were removed from plasmid DNA within 35 min, while MUG glycosylase excised base modifications only within 50 min, both in a sequence-dependent manner. In non-adapted cells resolution of plasmid topological forms was perturbed, suggesting inhibition of one or more bacterial topoisomerases by unrepaired epsilon-adducts. We also observed delayed consequences of DNA modification with CAA, manifesting as secondary DNA breaks, which appeared 3 h after transformation of damaged DNA into E. coli, and were repaired after 24 h.

Inhibition of DNA repair glycosylases by base analogs and tryptophan pyrolysate, Trp-P-1

DNA base analogs, 2,4,5,6-substituted pyrimidines and 2,6-substituted purines were tested as potential inhibitors of E. coli Fpg protein (formamidopyrimidine -DNA glycosylase). Three of the seventeen compounds tested revealed inhibitory properties. 2-Thioxanthine was the most efficient, inhibiting 50% of 2,6-diamino-4-hydroxy-5N-methyl-formamidopyrimidine (Fapy-7MeG) excision activity at 17.1 microM concentration. The measured K(i) was 4.44 +/- 0.15 microM. Inhibition was observed only when the Fpg protein was first challenged to its substrate followed by the addition of the base analog, suggesting uncompetitive (catalytic) inhibition. For two other compounds, 2-thio- or 2-oxo-4,5,6-substituted pyrimidines, IC(50) was only 343.3 +/- 58.6 and 350 +/- 24.4 microM, respectively. No change of the Fpg glycosylase activity was detected in the presence of Fapy-7MeG, up to 5 microM. We also investigated the effect of DNA structure modified by tryptophan pyrolysate (Trp-P-1) on the activity of base excision repair enzymes: Escherichia coli and human DNA glycosylases of oxidized (Fpg, Nth) and alkylated bases (TagA, AlkA, and ANPG), and for bacterial AP endonuclease (Xth protein). Trp-P-1, which changes the secondary DNA structure into non-B, non-Z most efficiently inhibited excision of alkylated bases by the AlkA glycosylase (IC(50) = 1 microM). The ANPG, TagA, and Fpg proteins were also inhibited although to a lesser extent (IC(50) = 76.5 microM, 96 microM, and 187.5 microM, respectively). Trp-P-1 also inhibited incision of DNA at abasic sites by the beta-lyase activity of the Fpg and Nth proteins, and to a lesser extent by the Xth AP endonuclease. Thus, DNA conformation is critical for excision of damaged bases and incision of abasic sites by DNA repair enzymes.

Helicobacter pylori eradication as prevention against chronic peptic ulcer disease in children

The changes caused by Helicobacter pylori are a slow, progressing inflammatory process developing from several to dozen years. H. pylori infection leads to an inflammatory response in the gastric mucosa with granulocyte infiltrates in an acute form of the inflammation, and lymphocytes, plasmatic, macrophages and eosinophils in a chronic form inducing the development of gastric and duodenal ulcers and gastric cancer in some patients. The frequency and the type of morphological changes in the gastric mucosa were analyzed in children with positive IgG against H. pylori and the incidence of gastric and duodenal ulcers in family members of children examined was evaluated in our study. Gastritis was reported in 68.8% of children with positive IgG against H. pylori. Gastric ulcer was confirmed in 37.1% of families of children included in the study. Duodenal ulcers were found in 22.9% of families. The results obtained, indicate the usefulness of long-term observation and clinical follow-up of children with chronic gastritis of H. pylori ethiology taking into consideration bacterium eradication as prophylaxis of peptic ulceration.

Inhibition of DNA repair glycosylases by base analogs and tryptophan pyrolysate, Trp-P-1

DNA base analogs, 2,4,5,6-substituted pyrimidines and 2,6-substituted purines were tested as potential inhibitors of E. coli Fpg protein (formamidopyrimidine -DNA glycosylase). Three of the seventeen compounds tested revealed inhibitory properties. 2-Thioxanthine was the most efficient, inhibiting 50% of 2,6-diamino-4-hydroxy-5N-methyl-formamidopyrimidine (Fapy-7MeG) excision activity at 17.1 microM concentration. The measured K(i) was 4.44 +/- 0.15 microM. Inhibition was observed only when the Fpg protein was first challenged to its substrate followed by the addition of the base analog, suggesting uncompetitive (catalytic) inhibition. For two other compounds, 2-thio- or 2-oxo-4,5,6-substituted pyrimidines, IC(50) was only 343.3 +/- 58.6 and 350 +/- 24.4 microM, respectively. No change of the Fpg glycosylase activity was detected in the presence of Fapy-7MeG, up to 5 microM. We also investigated the effect of DNA structure modified by tryptophan pyrolysate (Trp-P-1) on the activity of base excision repair enzymes: Escherichia coli and human DNA glycosylases of oxidized (Fpg, Nth) and alkylated bases (TagA, AlkA, and ANPG), and for bacterial AP endonuclease (Xth protein). Trp-P-1, which changes the secondary DNA structure into non-B, non-Z most efficiently inhibited excision of alkylated bases by the AlkA glycosylase (IC(50) = 1 microM). The ANPG, TagA, and Fpg proteins were also inhibited although to a lesser extent (IC(50) = 76.5 microM, 96 microM, and 187.5 microM, respectively). Trp-P-1 also inhibited incision of DNA at abasic sites by the beta-lyase activity of the Fpg and Nth proteins, and to a lesser extent by the Xth AP endonuclease. Thus, DNA conformation is critical for excision of damaged bases and incision of abasic sites by DNA repair enzymes.

Long-chain adducts of trans-4-hydroxy-2-nonenal to DNA bases cause recombination, base substitutions and frameshift mutations in M13 phage

Oxidative stress enhances lipid peroxidation (LPO) implicated in the promotion and progression of carcinogenesis. One of the major LPO products is trans-4-hydroxy-2-nonenal (HNE), which was shown to react with guanosine and under peroxidizing conditions also with adenosine. We show here that all four DNA bases are targets for HNE, although displaying different reactivity: dG > dC > dA approximately equal to dT. HPLC and mass spectrometry analyses of HNE reactions with deoxynucleosides showed in each case the formation of several products, with mass peaks corresponding to HNE-dN adducts at a 1:1 and also 2:1 and 3:1 ratios. In the dA, dC and dG reactions, mass peaks corresponding to heptyl-substituted etheno-adducts were also detected, indicating HNE oxidation to its epoxide by air oxygen. In DNA pretreated with HNE, DNA synthesis by T7 DNA polymerase was stopped in a sequence-dependent manner at G > or = C > A and T sites. HNE increased the mutation rates in the lac Z gene of M13 phage transfected into wild type Escherichia coli. The most frequent event was the recombination between lacZ gene sequences in M13 and the E. coli F' factor DNA. Base substitutions and frameshifts were also observed in approximately similar numbers. Over 50% of base substitutions were the C-->T transitions, followed by the G-->C and A-->C transversions. In the E. coli recA strain recombination was not observed, although one mutational G-->T hot-spot appeared within the DNA fragment undergoing recombination in the wild type E. coli. We conclude that long chain HNE adducts to DNA bases arrest DNA synthesis and cause recombination, base substitutions and frameshift mutations in ssDNA.

Opposite base specificity in excision of pyrimidine ring-opened 1,N6-ethenoadenine by thymine glycol-DNA-glycosylases

A highly mutagenic DNA lesion, 1,N6-ethenoadenine ( epsilon A) is chemically unstable and either depurinates or converts to a pyrimidine ring-opened product upon water molecule addition to the C(2)z.sbnd;N(3) bond in epsilon dA (compound B). Compound B subsequently undergoes deformylation to yield compound C, which depurinates in the final step of the epsilon A rearrangement pathway. We have previously shown that epsilon A rearrangement products are not repaired by human N-methylpurine-DNA-glycosylase, which excises parental epsilon A. Compound B was shown to be eliminated from a B:T pair by Escherichia coli formamidopyrimidine-DNA-glycosylase (Fpg protein) and endonuclease III (Nth protein). Fpg protein excised B also from a B:C pair, and much less efficiently from B:A and B:G pairs [J. Biol. Chem. 276 (2001) 21821]. Here we show that efficiency of B excision by the Nth protein also depends on the opposite base in the pair. Most efficient repair is observed when this derivative is paired with dG (Km=18nM, kcat=12) and is less favourable when paired with dC (Km=40nM, kcat=13) and dT (Km=32nM, kcat=11). In physiological conditions, compound B is probably not excised by the Nth-glycosylase from a B:A pair, or from a single-stranded DNA, since kinetic constants in these conditions are an order or two orders of magnitude higher than when B is paired with T, C or G. A similar specificity for B excision was found for Saccharomyces cerevisiae Ntg2-glycosylase. Thus, when paired with A, an epsilon A derivative might be more persistent than when paired with other bases and give rise to AT-->TA transversions.

Localization of chloroacetaldehyde-induced DNA damage in human p53 gene by DNA polymerase fingerprint analysis

Chloroacetaldehyde (CAA) reacts with DNA bases, forming hydroxyethano derivatives of different stability, which are subsequently converted into etheno (epsilon) adducts: epsilon A, epsilon C, epsilon G. DNA polymerase fingerprint analysis was used to study the distribution of CAA-induced modifications in the p53 sequence. A plasmid bearing cDNA containing the human p53 gene was reacted in vitro with CAA, then dehydrated for conversion of hydroxyethano into etheno adducts, and primer extension by T7 DNA polymerase in the presence of four dNTPs was performed. The DNA repair enzymes methylpurine-DNA glycosylase and Escherichia coli exonuclease III were used to convert epsilon A residues in the template into DNA strand breaks, which enabled precise localization of the epsilon A residues within the p53 gene. Hydroxyethano derivatives of adenine and cytosine in a template blocked T7 DNA polymerase and caused premature chain termination opposite adenine or one base before cytosine. After dehydration, both epsilon A and epsilon C were much more easily by-passed by T7 DNA polymerase. Formation of epsilon G was identified as 'stop bands' one base before guanine residues. Modification of cytosine and guanine was additionally recognized by weakening or disappearance of non-specific stops on an undamaged template, probably due to steric hindrance by the tertiary DNA structure for polymerase. Etheno adduction of cytosine and guanine relaxed the compact DNA structure and enabled DNA polymerase to by-pass. In exons 5-8 of p53, 143 out of 500 sites appeared to be damaged by CAA, with four particularly densely modified regions between codons 135-147, 218-222, 234-255 and 284-292. The pattern of modification followed the pattern of p53 mutations found in vinyl chloride-associated liver angiosarcomas in humans and rats, but only in regions that showed 100% homology with the human sequence. The factors that influence DNA damage and induction of mutations in the p53 gene by CAA and vinyl chloride are discussed.

Identification of a site necessary for allosteric regulation in T4-phage deoxycytidylate deaminase

An allosteric inhibitor of dCMP deaminase, dTTP, forms a photolabile covalent bond with T4-phage dCMP deaminase in the presence of UV light at 254 nm. The importance of the methyl group in this process is supported by the findings that dUTP, also an allosteric inhibitor, does not photofix to the enzyme and that tritium is released from [methyl-3H dTTP during the course of the photofixation. That the bond formed is photolabile is demonstrated by the fact that tritium is released by about 10-fold over the amount of nucleotide that is photofixed. The amino acid that covalently binds dTTP in T4-dCMP deaminase was identified as Phe112. On conversion of Phe112 to an alanine by site-directed mutagenesis, there was a dramatic change in the enzyme's response to its allosteric effectors when measured early in the reaction, in that the mutant enzyme was as active as the wild-type even in the absence of dCTP and was only weakly inhibited by dTTP. However, after 10-15% of the substrate had been deaminated, the reaction rate fell off rather markedly, indicating either that an inhibitor was being accumulated on the enzyme or that the enzyme was being irreversibly inactivated with time. That the latter was not the case was shown by the addition of dCTP to the reaction, which restored the rate to that expected when it was present initially. Furthermore, we showed that, consistent with the observed loss of allosteric regulation by dCTP and dTTP, the affinity of the mutant enzyme for dTTP and dCTP as determined by binding studies was greatly reduced relative to the wild-type enzyme.(ABSTRACT TRUNCATED AT 250 WORDS)

Cyclic phosphates of some antiviral acyclonucleosides: relationship between conformation and substrate/inhibitor properties in some enzyme systems

Solution conformations, and substrate/inhibitor properties towards several phosphodiesterases and other nucleolytic enzymes, have been investigated for the cyclic phosphates of various acyclonucleosides, some with known antiviral activity, including 9-[(1,3-dihydroxy-2-propoxy)methyl]guanine (DHPG) and its carbocyclic congener, 9-(3,4-dihydroxybutyl)guanine (DHBG),9-[4-hydroxy-2-(hydroxymethyl)- butyl]-guanine (2HM-HBG), and 9-(2,3-dihydroxypropyl)guanine (HPG). Conformations of the cyclic phosphate rings were derived from analysis of the 1H-1H and 1H-31P vicinal coupling constants in the 1H n.m.r. spectra, subsequently optimalized by minimalization of the internal energy. The resulting structures were examined with respect to their ability to recognize various specific phosphodiesterases and nucleases, and some structural parameters were delineated for acyclonucleotide interactions. Qualitative data are presented for inhibitory properties of the acyclonucleoside cyclic phosphates, and, in those instances where they were substrates, kinetic constants were evaluated. An unusual finding was the apparent ability of nuclease P1 to hydrolyse a five-membered cyclic phosphate ring of an acyclonucleoside.