Specific interaction of wild-type and truncated mouse N-methylpurine-DNA glycosylase with ethenoadenine-containing DNA

N-Methylpurine-DNA glycosylase (MPG), a ubiquitous DNA repair enzyme, is responsible for the removal of a wide variety of alkylated base lesions in DNA, e.g., N-alkylpurines and cyclic ethenoadducts of adenine, guanine, and cytosine. These lesions, some of which are mutagenic and toxic, are generated endogenously or by genotoxic agents such as N-alkylnitrosamines and vinyl chloride. Wild-type mouse MPG, expressed from recombinant baculovirus, was purified to near homogeneity for studying its specific interaction with substrate, 1,N6-ethenoadenine- (epsilonA-) containing DNA. Electrophoretic mobility shift assays (EMSA) indicated that MPG formed a specific complex with a 50-mer epsilonA-containing duplex oligonucleotide. This complex was shown to be a transient reaction intermediate, because it could be formed only with the unreacted substrate and contained active enzyme molecules. DNA footprinting studies confirmed the specific binding of the protein to the epsilonA-containing duplex oligonucleotide; eight nucleotides on the epsilonA-containing strand and 16-17 nucleotides in the complementary strand spanning the base adduct were protected from DNase I digestion. A systematic deletion analysis of MPG was carried out in order to determine the minimally sized polypeptide capable of forming a stable substrate complex that is also suitable for characterization by NMR spectroscopy and X-ray crystallography. A truncated polypeptide (NDelta100CDelta18) lacking 100 and 18 amino acid residues from the amino and carboxyl termini, respectively, was found to be the minimal size that retained activity. The truncated and wild-type enzymes have similar kinetic properties. Moreover, both EMSA and DNase I footprinting studies indicated identical pattern of specific binding by the truncated and full-length polypeptides. Removal of five and nine additional residues from the amino- and carboxyl-termini of this polypeptide, respectively, resulted in a complete loss of activity. These results suggest that minimal structural change occured as a result of truncation in the NDelta100CDelta18 mutant, which may thus be suitable for elucidating the structure and mechanism of MPG.

Effect of 17 beta-estradiol, retinoic acid and tamoxifen upon primary and transplanted thyroid tumor in B6C3F1 mice fed an iodine deficient diet

This study was aimed to establish TSH dependent, transplantable thyroid tumor (TT) in B6C3F1 (BCF1) mice. In addition, transplanted TT was examined for its growth in mice given 17 beta-estradiol (E2), retinoic acid (RA), tamoxifen (TAM), T3 and T4. Both sexes of BCF1 mice were observed for 12 months under IDD and distilled water (DW), starting at 4 weeks of age. Groups of mice received an i.p. injection of radioactive iodine (131I) once at a dose of 60 mu Ci/head and/or given 0.25 mg E2 pellet s.c. One piece of induced pituitary or thyroid tumor was individually dissected aseptically and s.c. grafted under the fat pad of one site of the neck in the same strain of mice at 5 weeks of age. All mice were sacrificed between 7.5 to 13.5 months after grafting the tumors depending on the experiments. The transplantability of both pituitary and thyroid tumor was 100% in IDD mice, but TT was about 50% with a combined treatment of IDD plus E2. A supplement of thyroid hormones of T3 or T4 in mice with IDD completely inhibited the growth of in situ or grafted thyroid tumors. The growth of in situ thyroid gland was significantly promoted by the oral administration of RA in both sexes, whereas the growth of transplanted TT was significantly increased by RA in the female, but not in the male. Oral administration of TAM proved inhibitory upon in in situ and transplanted TT in the male, but not in the female. Thyroid tumor induced by IDD could grow only in mice with IDD and was partially regulated of its growth by RA and TAM.

Efflux systems and increased trypanothione levels in arsenite-resistant Leishmania

The mechanism of resistance to the metal arsenite has been studied and compared in L. mexicana, L. tropica, and L. tarentolae selected in a step by step manner for arsenite resistance. Amplification of the ABC transporter gene pgpA was found to be a frequent resistance mechanism in all species. Transfection of pgpA genes into different species indicated that both the origin of the pgpA gene and the recipient strain into which the gene is transfected seem important for resistance. An increase in the levels of trypanothione was also correlated with metal resistance in different Leishmania species. The mechanism used to increase the levels of trypanothione seems to differ, however, between the different species. This study points to a key role of transporters and thiol levels in metal resistance in Leishmania.

Characterization of a chloride-selective channel from rough endoplasmic reticulum membranes of rat hepatocytes: evidence for a block by phosphate

We have characterized the conduction and blocking properties of a chloride channel from rough endoplasmic reticulum membranes of rat hepatocytes after incorporation into a planar lipid bilayer. Our experiments revealed the existence of a channel with a mean conductance of 164 +/- 5 pS in symmetrical 200 mm KCl solutions. We determined that the channel was ten times more permeable for Cl- than for K+, calculated from the reversal potential using the Goldman-Hodgkin-Katz equation. The channel was voltage dependent, with an open probability value ranging from 0.9 at -20 mV to 0.4 at +60 mV. In addition to its fully open state, the channel could also enter a flickering state, which appeared to involve rapid transitions to zero current level. Our results showed a decrease of the channel mean open time combined with an increase of the channel mean closed time at positive potentials. An analysis of the dwell time distributions for the open and closed intervals led to the conclusion that the observed fluctuation pattern was compatible with a kinetic scheme containing a single open state and a minimum of three closed states. The permeability sequence for test halides determined from reversal potentials was Br- > Cl- > I- approximately F-. The voltage dependence of the open probability was modified by the presence of halides in trans with a sequence reflecting the permeability sequence, suggesting that permeant anions such as Br- and Cl- have access to an internal site capable of controlling channel gating. Adding NPPB to the cis chamber inhibited the channel activity by increasing fast flickering and generating long silent periods, whereas channel activity was not affected by 50 microM DNDS in trans. The channel was reversibly inhibited by adding phosphate to the trans chamber. The inhibitory effect of phosphate was voltage-dependent and could be reversed by addition of Cl-. Our results suggest that channel block involves the interaction of HPO2-4 with a site located at 70% of the membrane span.

Evaluation of donor skin disinfection methods

BACKGROUND

Because most bacteria isolated from contaminated platelet concentrates are thought to originate from the donor's skin, the efficacy of four methods of skin disinfection was compared.

STUDY DESIGN AND METHODS

Contact plates were used for antecubital skin cultures after they were demonstrated to be easier to use and at least as sensitive as a swab system. One antecubital fossa of each subject was disinfected by a standard method, the use of a povidone-iodine swabstick containing 0.75-percent available iodine followed by the use of a povidone-iodine swabstick containing 1-percent available iodine. The other arm was disinfected with either a 70-percent isopropyl alcohol scrub followed by an ampoule of 2-percent iodine tincture (Group 1; n = 126); a green-soap sponge followed by a 70-percent isopropyl alcohol swab, used for donors who are allergic to iodine (Group 2; n = 30); or a 0.5-percent chlorhexidine gluconate and 70-percent isopropyl alcohol sponge followed by an ampoule of 0.5-percent chlorhexidine gluconate and 70-percent isopropyl alcohol (Group 3; n = 40). Contact plate cultures were done before and after disinfection, and colonies counted after a 48-hour 37 degrees C incubation period.

RESULTS

Similar numbers of bacteria grew from both antecubital fossae of the same subject before disinfection (p = 0.71). Compared to the standard povidoneiodine method, isopropyl alcohol and tincture of iodine resulted in significantly less bacterial growth (p < 0.001), the green soap and isopropyl alcohol method resulted in significantly more bacterial growth (p < 0.001), and the chlorhexidine gluconate and isopropyl alcohol method resulted in similar amounts of bacterial growth (p > 0.3).

CONCLUSION

Isopropyl alcohol scrub followed by iodine tincture is more efficacious than povidone-iodine as measured by contact plate cultures. For donors who are allergic to iodine, chlorhexidine gluconate and isopropyl alcohol is more efficacious than green soap and isopropyl alcohol.

Quantitative reverse transcriptase polymerase chain reaction for measuring the N-methylpurine-DNA glycosylase mRNA level in rodent cells

A modified quantitative reverse transcriptase polymerase chain reaction (QRT-PCR) procedure was developed for measuring mRNA concentration, in rodent cells, of the N-methylpurine-DNA glycosylase (MPG), a ubiquitous DNA repair protein responsible for the removal of N-alkylpurines and ethenoadducts of adenine, guanine, and cytosine from DNA. The method, applicable for quantitation of any mRNA, is based on the standard approach of comparing the relative amounts of PCR products of the experimental mRNA and a known amount of an exogenous reference RNA which is nearly identical to the experimental RNA. However, unlike in the earlier procedures in which deletion or insertion sequences were added to the reference RNA template, which may affect the efficiency of PCR but are needed to generate different size PCR products, experimental and reference RNAs yield PCR products of the same size in the new method. However, prior digestion with EcoRI allows separation of the two products because a unique EcoRI site was created in the reference RNA vector by point mutations. The QRT-PCR procedure is particularly useful for studying expression of the MPG gene whose mRNA level is very low and difficult to quantitate by Northern blot analysis. The number of MPG mRNA molecules/cell in late log-phase cultures varied from about 6 to 30 in several rodent lines. The SSV-NRK rat cell line has 6 +/- 0. 2 molecules/cell, while mouse NIH3T3 cells have about 30 +/- 1 molecules/cell. If the mRNA level is indicative of the level of the active MPG enzyme, these results may imply a variation in the capacity of various lines to remove the cytotoxic and mutagenic adducts from DNA.

Facteurs génétiques et environnementaux affectant la qualité de la semence de jeunes taureaux Holstein

Semen traits were measured from 294 young Holstein bulls between the ages of 10 and 18 mo. Bulls were sampled between the years 1987 and 1989 and the first four suitable ejaculates from each bull were retained for study. The season of the year, the year and the sire of each bull were used as factors and the age of the bulls and the inbreeding coefficient were used as co-factors for the analyses of variance and covariance. The sire effect was declared significant for the volume (P < 0.001), concentration (P < 0.05) and the number of motile spermatozoa per ejaculate (P < 0.001). Intraclass regression studies indicated that each increase of 1 d of age in young bulls increased the volume of the ejaculate by 0.004 mL, the concentration and the motility of the ejaculate by 0.024 × 108 spermatozoa mL−1 and 0.034% and the number of motile spermatozoa by 0.091 × 108 per ejaculate. A 1% increase in the inbreeding coefficient (F) decreased the motility of spermatozoa by 0.30% and the concentration of the ejaculate by 0.14 × 108 mL, resulting in a decreased total number of inseminations possible by 13.83 doses. It also increased the number of rejected samples by 0.25 and delayed sexual maturity by 3 d. Heritability estimates of semen traits varied from 0.25 and 0.79. The genetic and phenotipic correlations were respectively −0.72 and −0.47 for the correlations between volume and concentration, 0.140 and 0.07 between volume and motility and −0.22 and −0.01 between motility and concentration. Key words: Inbreeding, semen, bull, holstein

Characterization of stable RNAs from the resected intestinal tissues of individuals with either Crohn's disease or ulcerative colitis

Circular RNAs reminiscent of viroids and the human hepatitis delta virus have been proposed as possible nonconventional pathogens responsible for Crohn's disease and ulcerative colitis, two inflammatory bowel diseases. Consequently, RNA was extracted from various areas of intestinal tissues from individuals with either Crohn's disease or ulcerative colitis as well as several appropriate control diseases, and analyzed by two-dimensional gel electrophoresis. No circular viroid-like RNAs (< 1500 nucleotides) were detected, confirming a previous report that was limited to the investigation of small RNAs (< 300 nucleotides). However, three small, unusually stable, linear RNAs were shown to be associated to both Crohn's disease and ulcerative colitis tissues: a specific 28S ribosomal RNA cleavage product characterized previously; a 5.8S ribosomal RNA conformer; and a fragment homologous to transcripts from DNA CpG islands. The two last RNAs were detected prior to visible morphological tissue alterations, suggesting that they are produced early during the inflammation and that they have value as molecular diagnostic tools for the inflammatory bowel diseases. The potential cellular mechanisms producing these RNAs and their involvement in inflammatory bowel disease are discussed.

Childhood renal tumours with intravascular extension

OBJECTIVE

To assess whether pre-operative chemotherapy reduces operative morbidity in children with intravascular extension of renal tumours.

PATIENTS AND METHODS

Thirty children with intravascular extension of their renal tumour, treated in 10 different centres in the UK, were reviewed retrospectively.

RESULTS

Twenty-nine patients had nephroblastoma and one child had clear cell sarcoma (favourable histology in 23, unfavourable histology in six). Patients were classified into stage II (17 patients), stage III (three patients) and stage IV (10 patients). Ultrasonography had been performed in 29 patients and had correctly diagnosed intravascular extension in 11 (40%); computed tomography (CT) was accurate in 93% of patients. A pre-operative diagnosis was made accurately in 24 patients, with caval extension in 18 and atrial extension in six. Nine patients underwent primary surgery, whilst 21 had pre-operative chemotherapy followed by delayed nephrectomy. In the latter group, the intravascular thrombus diminished in 16 patients. Five patients died, one from tumour rupture and four from extensive or progressive tumour disease; the overall 2-year survival was 83%. Unfavourable histology did not adversely affect survival, and patients having pre-operative chemotherapy appeared to have a better outcome.

CONCLUSION

CT remains the best imaging modality to assess intravascular tumour extension. Pre-operative chemotherapy is recommended for patients with intra-caval extension of tumour. Those with intra-atrial extension or with hepatic vein obstruction (Budd-Chiari syndrome) may require a cardiopulmonary bypass and primary surgery.

Volume-sensitive chloride channels blocked by neuroprotective drugs in human glial cells (U-138MG)

Glial cell swelling in hypotonic media activates an anionic channel that was found previously to be permeable to amino acids. It is possible that the same channel is also activated when glial cells swell in pathologic conditions, like ischemia or hypoxia, and it could be partly responsible for the release of glutamate appearing in such conditions. Many drugs have been developed to block glutamate release during ischemia. Six of these drugs were tested on human glial cells (U-138MG) in vitro to determine if they could block the swelling-activated anionic channels. Three of them, phenytoin, lidocaine, and flunarizine, had no effect. The other three could block the anionic channels: riluzole, nizofenone, and BW1003C87. Such blocking was reversible and the half inhibition concentration (IC50) of each of these drugs was within that observed for their inhibition of glutamate release by various authors. An important advantage of these three drugs is their capacity to inhibit glutamate release after the beginning of ischemia. It is concluded that the volume-sensitive anionic channel could be partly responsible for glutamate release during a cerebral ischemia.

[Vaccination against influenza in elderly persons: some current presumptions]

A telephone survey in March 1994 revealed that only 70% of 185 persons surveyed aged 65 and over were offered influenza vaccine during the last flu shot campaign; the sample was taken among non-institution residents of the Quebec City area who were likely to have regular health professional contact. Misinformation concerning influenza infection and vaccine remains widespread: 30% of the people surveyed still believe that the vaccine can transmit the virus and 21% consider the vaccine ineffective. Incorrect beliefs are significantly more prevalent among the unvaccinated population: 12% stated that they were allergic to the vaccine; in fact, true allergies are rare. Health professionals should recognize that elderly people, though in regular contact with the health care system, may not have been offered the influenza vaccine and may have inadequate information or incorrect beliefs regarding influenza and its preventability.

Gene disruption of the P-glycoprotein related gene pgpa of Leishmania tarentolae

Transfection of pgpA into Leishmania confers resistance to arsenite and antimonials. By gene targeting mediated by homologous recombination the two alleles of the pgpA gene of a L. tarentolae wild-type cell were disrupted sequentially with the neomycin and hygromycin phosphotransferase genes. This pgpA null mutant showed an increased sensitivity to arsenite and antimonite. In addition, the L. tarentolae pgpA null mutant exhibited a decreased intracellular survival inside murine macrophages. The observed phenotypes were reverted to levels not statistically different than wild-type when an intact pgpA gene was introduced into the null mutant. Disruption of the pgpA chromosomal locus in an arsenite resistant mutant indicated that PgpA is not essential for resistance to oxyanions, although it might be required in the early steps of selection when resistance is being established.

Formation of extrachromosomal circular amplicons with direct or inverted duplications in drug-resistant Leishmania tarentolae

Selection for methotrexate resistance in Leishmania spp. is often associated with amplification of the H locus short-chain dehydrogenase-reductase gene ptr1 as part of extrachromosomal elements. Extensive sequences are always coamplified and often contain inverted duplications, most likely formed by the annealing of inverted repeats present at the H locus. By gene targeting mediated by homologous recombination, several repeated sequences were introduced in the vicinity of ptr1. Selection for methotrexate resistance in these transfectants led to ptr1 amplification as part of small circles with direct or inverted duplications whether the integrated sequences consisted of direct or inverted repeats. Hence, for a region to he amplified in L. tarentolae during drug selection, a drug resistance gene is required and must be flanked by (any) homologous repeated sequences. The distance between these repeats and their orientation will determine the length of the amplicon and whether it contains direct or inverted duplications.

Direct regulation of ZAP-70 by SHP-1 in T cell antigen receptor signaling

The threshold at which antigen triggers lymphocyte activation is set by the enzymes that regulate tyrosine phosphorylation. Upon T cell activation, the protein tyrosine phosphatase SHP-1 was found to bind to the protein tyrosine kinase ZAP-70. This interaction resulted in an increase in SHP-1 phosphatase activity and a decrease in ZAP-70 kinase activity. Expression of a dominant negative mutant of SHP-1 in T cells increased the sensitivity of the antigen receptor. Thus, SHP-1 functions as a negative regulator of the T cell antigen receptor and in setting the threshold of activation.

Thioesterase and protein deacylase activities of porcine pancreatic phospholipase A2

The thioesterase activity of porcine pancreatic phospholipase A2 has been investigated with non-phospholipid substrates. The acyl-CoA hydrolase activity towards acyl-CoA derivatives is specific for long chain fatty acids (14 C, 16 C) but is unable to hydrolyze short chain acyl-CoA compounds (below 8 C). The same enzyme also shows protein deacylase activity liberating [3H]palmitic acid from [3H]palmitoyl-acyl carrier protein.

[Delivery of public health services. Proposal for a frame of reference]

This article proposes a framework for the delivery of public health services by the health care system. Considering the many factors associated with a population's health status and well-being, health care systems must provide public health services in addition to clinical preventive health care services. Public health services are distinctive in that they are supplied in response to community as opposed to individual needs. The delivery of public health services is carried out, in partnership with groups and organizations, through the use of strategies that enable, advocate and educate. These strategies, taking place at the earliest possible moment in the natural history of problems, act as catalysts in the process of change towards health and well-being.

Influence of paternal (252) Cf neutron exposure on abnormal sperm, embryonal lethality, and liver tumorigenesis in the F(1) offspring of mice

Experiments were conducted to determine whether neutron-induced genetic damage in parental germline cells can lead to development of cancer in the offspring. Seven-week-old C3H male mice were irradiated with (252) Cf neutrons at a dose of 0, 50, 100, or 200 cGy. Two weeks or three months after irradiation, the male mice were mated with virgin 9-week-old C57BL females. Two weeks after irradiation, the irradiated male mice showed an increased incidence of sperm abnormalities, which led to embryo lethalities in a dose-dependent manner when they were mated with unirradiated female mice. Furthermore, liver tumors in male offspring of male mice in the 50 cGy group were significantly increased in 19 of 44 (43.2%) animals, in clear contrast to the unirradiated group (1 of 31; 3.2%) (P < 0.01). In the 100 cGy group, 6 of 39 (15%) mice had lesions. At 3 months after irradiation abnormal sperm and embryonal lethality were not significantly increased. The incidences of liver tumors in male offspring from the 50 cGy, 100 and 200 cGy groups were 6 of 20 (30%), 5 of 22 (23%) and 1 of 19 (5%), respectively, which are not significantly increased compared with the control. It is concluded that increased hepatic tumor risk in the F(1) generation may be caused by genetic transmission of hepatoma-associated trait(s) induced by (252) Cf neutron irradiation.

Amino acid current through anion channels in cultured human glial cells

During volume regulation in hypotonic media, glial cells release a large portion of their amino acids. These amino acid losses appear to be mediated by a diffusion type of transport and a swelling-activated chloride channel seems to be involved. The objective of this project was to provide direct evidence that amino acids could diffuse through a Cl- channel. Using a human glial cell line, Cl- currents activated in hypotonic media were measured in whole-cell patch clamp. To measure the currents produced by amino acids, it was necessary to increase the pH of external solutions to basic values reaching 9.6 and 10.0 to raise the concentration of the anionic form of these amino acids. Introducing external hypotonic media containing high concentrations of amino acids, like glycine, taurine, glutamine and glutamate, it was possible to measure their respective current-voltage curves with NMDG-Cl-filled pipettes. From the reversal potentials, their permeability ratios with respect to chloride were determined. It was found that the low molecular weight amino acids, like glycine, were most permeant, while the larger ones, like glutamine, had a lower permeability with respect to chloride. The amino acids with two carboxyl groups, like glutamate, had a much lower permeability ratio. The reversal potentials for some metabolites, like lactate and malate were also measured for comparison. These results demonstrate that amino acids can diffuse through anion channels and that activation of these channels in pathological conditions could be at least partly responsible for the observed increase in external amino acids.

Effect of thyroxine on experimental bronchospasm in guinea pigs

Effect of Thyroxine was studied in histamine induced bronchospasm in guinea pigs. Chronic treatment with the drug significantly protected against experimental bronchospasm. Thyroxine also potentiated salbutamol evoked bronchodilation in this experimental model. Up-regulation of beta-2 adrenoceptors in bronchial smooth muscle may be the probable mechanism of action of thyroxine.

Structural organization of the mouse DNA repair gene, N-methylpurine-DNA glycosylase

N-Methylpurine-DNA glycosylase (MPG), a ubiquitous DNA repair enzyme, removes N-alkylpurines and other purine lesions induced in DNA by simple alkylating carcinogens. A mouse MPG cDNA clone was isolated from a lambda recombinant phage library of BALB/c mouse lung cell and characterized. Using the mouse MPG cDNA as a probe, the complete mouse MPG gene was isolated in two overlapping lambda recombinant genomic clones. The 6-kb gene has four exons containing 1,002 bp of coding sequence. The transcription start site was identified in the genomic sequence by primer extension of MPG mRNA from a mouse lung fibroblast cell line. The location of this transcription start site was confirmed by in vitro transcription with the promoter-containing plasmid template. Promoter function of the sequence 5' upstream of the transcription initiation site was shown by transient expression of the firefly luciferase reporter gene under the control of this sequence in transfected human and mouse cells. The mouse MPG promoter contains no TATA box, but has a CAAT element and is G.C-rich with putative AP2 elements and SP1-complementary sequences.