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Biomedical subjects

S Linn

Publications and source records attributed to S Linn.

At least 127 records · Page 7Linked to original sources
PubMed1987

Prognostic significance of plasma cell morphology in multiple myeloma.

The effect of bone marrow plasma cell morphology at diagnosis on survival time was evaluated in 139 patients with multiple myeloma. According to the morphological classification scheme the patients were categorized as mature (30 patients), immature (76 patients) or plasmablastic (33 patients). The plasmablastic group had an estimated median survival (Kaplan-Meier method) of 10.9 months, compared with 32.2 months for immature and 60 months for mature types (P = 0.0000). The prognostic value of a morphologic classification in multiple myeloma was further demonstrated by means of a multivariate linear regression analysis of survival data. Expected survival was calculated using clinical features and morphologic subtypes. The estimated survival time for plasmablastic myeloma was shorter by 51.4 months and for immature myeloma patients by 35 months, compared with mature myeloma patients with similar clinical characteristics. Plasma cell morphology at diagnosis is an important predictor of survival duration in patients with multiple myeloma.

Bone Marrow↗
PubMed1987

Exposure of HeLa DNA polymerase alpha to protein kinase C affects its catalytic properties.

Protein kinase C (Ca2+/phospholipid-dependent protein kinase) purified from rat brain or endogenous to cell-free extracts from HeLa cells stimulates, by a factor of 2-3, HeLa DNA polymerase alpha but not beta or gamma. Monoclonal antibody to the kinase prevents the stimulation, and monoclonal antibody to human DNA polymerase alpha neutralizes the enhanced activity. Reduced DNA polymerase alpha activity is obtained from noncycling HeLa cells and this activity has lower fidelity when copying synthetic primer-templates than that obtained from log phase cultures. After exposure to the kinase, the fidelities and activities of the polymerase from both sources increase by 2- to 3-fold. This improved accuracy is not accompanied by the appearance of triphosphatase or DNase activities. Exposure to the protein kinase reduces the Km for activated DNA and for poly(dA-dT) but not for dNTPs. Moreover, the Vmax for activated DNA but not for poly(dA-dT) is increased approximately 2- to 3-fold. These alterations suggest a role for protein phosphorylation in modulating DNA polymerase alpha.

Animals↗
PubMed1987

DNA alkylation repair and the induction of cell death and sister chromatid exchange in human cells.

Mer- human cells, which lack O6-methylguanine DNA methyltransferase activity, are extremely sensitive to alkylation induced killing, mutation and sister chromatid exchange. We have analyzed a Mer+, a Mer-, and a Mer- revertant HeLa cell line and found that the methyltransferase deficiency correlates with increased levels of mutation and sister chromatid exchange, but does not correlate with increased killing of Mer- HeLa cells by alkylating agents. Furthermore, we show that HeLa Mer- cells repair N-3-methylguanine and N-3-methyladenine just as efficiently as HeLa Mer+ cells.

Adenine↗
PubMed1987

Mutagenesis and stress responses induced in Escherichia coli by hydrogen peroxide.

Killing of Escherichia coli by hydrogen peroxide proceeds by two modes. Mode one killing appears to be due to DNA damage, has a maximum near 1 to 3 mM H2O2, and requires active metabolism during exposure. Mode two killing is due to uncharacterized damage, occurs in the absence of metabolism, and exhibits a classical multiple-order dose-response curve up to at least 50 mM H2O2 (J. A. Imlay and S. Linn, J. Bacteriol. 166:519-527, 1986). H2O2 induces the SOS response in proportion to the degree of killing by the mode one pathway, i.e., induction is maximal after exposure to 1 to 3 mM H2O2. Mutant strains that cannot induce the SOS regulon are hypersensitive to peroxide. Analysis of the sensitivities of mutants that are deficient in individual SOS-regulated functions suggested that the SOS-mediated protection is due to the enhanced synthesis of recA protein, which is rate limiting for recombinational DNA repair. Specifically, strains wholly blocked in both SOS induction and DNA recombination were no more sensitive than mutants that are blocked in only one of these two functions, and strains carrying mutations in uvrA, -B, -C, or -D, sfiA, umuC or -D, ssb, or dinA, -B, -D, -F, -G, -H, -I, or -J were not abnormally sensitive to killing by H2O2. After exposure to H2O2, mutagenesis and filamentation also occurred with the dose response characteristic of SOS induction and mode one killing, but these responses were not dependent on the lexA-regulated umuC mutagenesis or sfiA filamentation functions, respectively. Exposure of E. coli to H2O2 also resulted in the induction of functions under control of the oxyR regulon that enhance the scavenging of active oxygen species, thereby reducing the sensitivity to H2O2. Catalase levels increased 10-fold during this induction, and katE katG mutants, which totally lack catalase, while not abnormally sensitive to killing by H2O2 in the naive state, did not exhibit the induced protective response. Protection equal to that observed during oxyR induction could be achieved by the addition of catalase to cultures of naive cells in an amount equivalent to that induced by the oxyR response. Thus, the induction of catalase is necessary and sufficient for the observed oxyR-directed resistance to killing by H2O2. Although superoxide dismutase appeared to be uninvolved in this enhanced protective response, sodA sodB mutants, which totally lack superoxide dismutase, were especially sensitive to mode one killing by H2O2 in the naive state. gshB mutants, which lack glutathione, were not abnormally sensitive to killing by H2O2.

Catalase↗
PubMed1987

Toxicity, mutagenesis and stress responses induced in Escherichia coli by hydrogen peroxide.

Two modes of killing of Escherichia coli by hydrogen peroxide can be distinguished. Mode-one killing is maximal at 1-2 mM; at higher concentrations the killing rate is approximately half-maximal and is independent of H2O2 concentration but first order with respect to exposure time. Mutagenesis and induction of a phage lambda lysogen are similarly affected by H2O2 concentration, with reduced levels of response above 1-2 mM-H2O2. Mutagenesis is not affected by inactivation of umuC. Mode-one killing requires active metabolism during the H2O2 challenge and it results in sfiA-independent filamentation of both cells that survive and those that are killed by the challenge. This mode of killing is enhanced in xth, polA, recA and recB strains; however, it is unaffected by mutations in the nth, uvrA, uvrB, uvrC, uvrD, rep, gyrA, htpR and rel loci. Mode-one killing is normal in strains totally lacking catalase activity (katE, katG), glutathione reductase (gor) or glutathione synthetase (gshB), but enhanced in a strain lacking NADH dehydrogenase (ndh). Mode-one killing is accelerated by the presence of CN- or by an unidentified function that is induced by anoxic growth and is under the control of the fnr locus. A strain carrying both xth and recA mutations and certain polA mutants appear to undergo spontaneous mode-one killing only under aerobic conditions. Taken together, these observations imply that mode-one killing results from DNA damage that normally occurs at a low, non-lethal level during aerobic growth. Models for the resistance to mode-one killing at dose above 1-2 mM-H2O2 will be discussed. Mode-two killing occurs at high concentrations of H2O2 and longer times. It does not require active metabolism, and cells that are killed do not filament, although survivors demonstrate a dose-dependent growth lag followed by a period of filamentation. Mode-two killing is accompanied by enhanced mutagenesis, but strains with DNA repair defects were not observed to be especially sensitive to this mode of killing.

Cell Survival↗
PubMed1986

Purification and properties of a single strand-specific endonuclease from mouse cell mitochondria.

A nuclease was purified from mitochondria of the mouse plasmacytoma cell line, MCP-11 which acts on single-stranded DNA endonucleolytically and appears to have no activity upon native DNA. It degrades unordered RNA somewhat more effectively than it does DNA. The enzyme activity and the major detectable polypeptide migrate to a position corresponding to an Mr of 37,400 on denaturing polyacrylamide gels; in its native form the activity has an S value of 4.7, which corresponds to a molecular weight of roughly 73,000. The single-strand DNase activity has a pH optimum near 7.5, requires a divalent cation and is inhibited by EDTA, phosphate, KCl and NaCl. The enzyme is remarkably similar to fungal mitochondrial enzymes whose absence in various mutants correlates with defective DNA repair and recombination. It reacts weakly with antibody to a form of such an enzyme from Neurospora crassa.

Animals↗
PubMed1986

Studies of DNA polymerases alpha and beta from cultured human cells in various replicative states.

DNA polymerase activities from HeLa cells and from cultured diploid human fibroblasts in various growth states were compared. alpha-Polymerase activities from log phase fibroblasts treated with sodium butyrate and from stationary phase HeLa cells had DEAE-cellulose elution patterns that differed from those of polymerases from dividing cells. Moreover, alpha- and beta-polymerases from nondividing cells replicated synthetic polymers less faithfully. Although similar changes were observed previously for polymerases from late-passage and postconfluent early passage fibroblasts, amounts of alpha-polymerase activity recovered from nondividing cells in this study did not dramatically decline as they had in the former cases. The alpha-polymerase activities from HeLa cells and fibroblasts in various growth states sedimented near 7.5S in 0.4 M KCI and could be inhibited by a monoclonal IgG fraction prepared against KB cell alpha-polymerase. By several criteria, there was no significant differences in levels of UV-stimulated repair synthesis observed in early or late-passage postconfluent fibroblasts or in log phase fibroblasts treated with sodium butyrate. In summary, levels of alpha-polymerase do not necessarily correlate either with replicative activity or with apparent levels of repair synthesis. However, cells with decreased replicative activity always yielded enzyme with decreased fidelity in vitro and altered chromatographic behavior. It appears, therefore, that the alterations observed for alpha-polymerase from late-passage cells may be attributed more generally to the nondividing nature of these cells.

Cell Line↗
PubMed1986

Levels of uracil DNA glycosylase and AP endonuclease in murine B- and T-lymphocytes do not change with age.

Two DNA repair enzyme activities, uracil DNA glycosylase and AP endonuclease, were measured in extracts of T- and B-lymphocytes isolated from mice ranging in age from 3 to 24 months. T- and B-lymphocytes had roughly equal levels of AP endonuclease which did not change appreciably with age. T-lymphocytes had roughly twice as high a level of uracil DNA glycosylase as B-lymphocytes; these levels were not affected by age either. This constancy with age contrasts dramatically with increases in both enzymes--roughly 3-fold on a protein basis or 50-fold on a per cell basis--in a transformed line (MPC-11) derived from a carcinogen-induced lymphocytoma. These results are similar to those obtained with cultured murine fibroblasts, wherein a relative constancy was noted with passage of non-transformed cells, followed by dramatic changes upon transformation (La Belle, M & Linn, S, Mutat res 132 (1984) 51). Hence these enzyme assays do not support the notion of a drop in base excision DNA repair capacity as being a causative factor in aging, but suggest instead that DNA repair properties might differ dramatically in transformed vs non-transformed cells.

Aging↗
PubMed1986

Dietary soya lecithin decreases plasma triglyceride levels and inhibits collagen- and ADP-induced platelet aggregation.

Elevated plasma lipid concentrations and increased platelet activation are risk factors in the development of atherosclerosis. Nine patients with type IIa hyperlipoproteinemia and nine patients with type IV hyperlipoproteinemia were given soya lecithin, 12 g/day, for 3 months. Plasma cholesterol and triglycerides were reduced by 15 and 23%, respectively, and HDL-cholesterol increased by 16% in the hypercholesterolemic patients. Platelet function was unchanged. In the hypertriglyceridemic patients, total cholesterol fell by 18%, triglycerides by 36%, and HDL-cholesterol increased by 14%. There was a 27% reduction in platelet aggregation (P less than 0.01). Seventeen hypertriglyceridemic patients then received increasing doses of soya lecithin for 1-month periods (6, 12, and 18 g/day). The optimal lipoprotein-lowering effect was achieved with a daily dose of 12 g soya lecithin per day. Both low-density lipoprotein and very-low-density lipoprotein levels were reduced, and HDL-cholesterol and apolipoprotein levels were reduced, and HDL-cholesterol and apolipoprotein A-I concentrations were increased. Platelet aggregation in response to collagen and ADP was significantly reduced, parallel with the reduction in triglyceride level. Soya lecithin supplementing the diet may be useful in the management of the hypertriglyceridemic patient.

Adenosine Diphosphate↗
PubMed1986

Auditory brainstem evoked potentials in asymptomatic lead-exposed subjects.

Auditory Brainstem Evoked Potentials (ABEP) were recorded from 29 adults and children, accidentally exposed to lead through food until approximately a year prior to this study. ABEP were recorded in response to 75 dBHL clicks presented at rates of 10/sec. and 55/sec. Average values were calculated for peak latency and for interpeak latency differences. Average values of the effect of increasing stimulus rate were calculated as well. Similar values were calculated for normative child and adult control groups. IPLD(I-III) showed the most significant and recurring results, with longer intervals in lead-exposed children compared with their control group. Increasing stimulus rate, on the other hand, affected the adult lead-exposed subjects more than the children. These results may imply an impairment of the peripheral portion of the auditory system with axonal and myelin involvement. ABEP is suggested as a sensitive detector of subclinical lead exposure effects on the nervous system.

Adolescent↗
PubMed1986

Bimodal pattern of killing of DNA-repair-defective or anoxically grown Escherichia coli by hydrogen peroxide.

Two modes of killing of Escherichia coli K-12 by hydrogen peroxide can be distinguished. Mode-one killing was maximal with hydrogen peroxide at a concentration of 1 to 2 mM. At higher concentrations the killing rate was approximately half maximal and was independent of H2O2 concentration but first order with respect to exposure time. Mode-one killing required active metabolism during the H2O2 challenge, and it resulted in sfiA-independent filamentation of both cells which survived and those which were killed by the challenge. This mode of killing was enhanced in xth, polA, recA, and recB strains and was accelerated in all strains by an unidentified, anoxia-induced cell function. A strain carrying both xth and recA mutations appeared to undergo spontaneous mode-one killing only under aerobic conditions. Mode-one killing appeared to result from DNA damage which normally occurs at a low, nonlethal level during aerobic growth. Mode-two killing occurred at higher doses of H2O2 and exhibited a multihit dependence on both H2O2 concentration and exposure time. Mode-two killing did not require active metabolism, and killed cells did not filament, although survivors demonstrated a dose-dependent growth lag. Strains with DNA-repair defects were not especially susceptible to mode-two killing.

Chloramphenicol↗
PubMed1985

The DNA restriction endonuclease of Escherichia coli B. I. Studies of the DNA translocation and the ATPase activities.

Electron microscopic examination of DNA intermediates formed by the restriction endonuclease of Escherichia coli B revealed supercoiled loops that are presumably formed during an ATP-dependent DNA translocation process in which the enzyme remains bound to the recognition site while tracking along the DNA helix to a cleavage site. The rate of DNA translocation during this process is at least 5000 base pairs/min at 37 degrees C. Even after all cleavages have been completed, complexes are seen that contain terminal loops or loop plus tail structures. During this later phase of the reaction, ATP is hydrolyzed at a rate which is dependent upon the size of the largest possible loop (or loop plus tail); this ATP hydrolysis can be terminated by one double-strand cleavage within the loop region between the recognition site and the terminus. To explain these results, it is hypothesized that after cleavage the enzyme cycles between a tracking (and possibly back-tracking) mode which is fueled by ATP hydrolysis and a relatively long static period in which ATP hydrolysis does not occur. While tracking, the enzyme would be bound both to the recognition site and to a distal site but, while static, the enzyme would be bound only at the recognition site of nonlooped molecules. This post-nuclease phase of the reaction is hypothesized to reflect a reaction whereby the enzyme initially scans DNA molecules before making a strand cleavage.

Adenosine Triphosphatases↗
PubMed1985

The DNA restriction endonuclease of Escherichia coli B. II. Further studies of the structure of DNA intermediates and products.

The DNA intermediates and final products formed by the Type I restriction endonuclease, EcoB, were further characterized. DNA cleaved on only one strand (hemi-restricted DNA) contains gaps of approximately 70-100 nucleotides, while the fully restricted products contain 3'-single-stranded tails averaging approximately 70-100 nucleotides for each strand cleaved. The gaps and tails are formed with the release of an equal number of nucleotides as small oligonucleotides that are soluble in acid. After purification, neither the hemi-restricted nor the fully restricted DNAs are cleaved again by EcoB. There is no apparent specificity for which strand of a duplex is initially cleaved by EcoB, nor is there specificity with respect to the composition of the 3'-terminal nucleotide formed on the DNA or the 3'- or 5'-terminal nucleotides of the acid-soluble oligonucleotides released during DNA cleavage. The structure formed at the 5' terminus of the DNA product which blocks phosphorylation by T4 polynucleotide kinase remains unknown, but its removal with phage lambda exonuclease allows at least some reutilization of recognition sites by EcoB as well as phosphorylation of the newly formed 5' termini. To explain the complex mechanism of this enzyme, it is suggested that the unidentified 5'-tails prevent wasteful rerestriction from occurring, whereas the 3'-single-stranded tails create DNA which, when nonhomologous to chromosomal DNA, cannot be rescued because such tails are not substrate for DNA polymerases. However, when homologous chromosomal DNA exists, the randomly cleaved large fragments with these tails can easily be assimilated by recA-mediated genetic recombination, thus stimulating DNA exchange between related organisms.

Animals↗
PubMed1985

Characterization of DNA polymerase I*, a form of DNA polymerase I found in Escherichia coli expressing SOS functions.

DNA polymerase I* is a form of the DNA polymerase I isolated from Escherichia coli which are expressing recA/lexA (SOS) functions. Induction of recA or polA1 cells by nalidixic acid does not result in the appearance of pol I*, but lexA or recA mutants that are constitutive for SOS functions constitutively express pol I* and mutants which lack functional recA protein produce pol I* when they carry a lexA mutation which renders the lexA repressor inoperative. Pol I* has been induced by nalidixic acid in dinA, dinD, dinF, and umuC mutants. Polymerase I* has a lower affinity for single-stranded DNA-agarose than polymerase I and it sediments through sucrose gradients in a dispersed manner between 6.6-10.5 S, whereas polymerase I sediments at 5 S. Whereas pol I* migrates significantly faster than pol I in nondenaturing polyacrylamide gels, the active polypeptide of both forms migrates at the same rate in denaturing polyacrylamide gels. Compared with polymerase I, polymerase I* has an enhanced capacity to incorporate the adenine analog, 2-amino-purine, into activated salmon sperm DNA and a relatively low fidelity in replicating synthetic polydeoxyribonucleotides. Both the 3'----5' (proofreading) and 5'----3' (nick-translational) exonuclease activities of pol I* and pol I are indistinguishable. Estimates of processivity give a value of approximately 6 for both forms of the enzyme.

Centrifugation, Density Gradient↗
PubMed1985

Hypocholesterolaemia and abnormal high-density lipoprotein in rheumatoid arthritis.

Plasma lipid and lipoprotein patterns were determined in 54 female patients with rheumatoid arthritis (RA). The patients were divided into four groups, on the basis of the treatment that was being administered (gold, penicillamine, hydroxychloroquine and nonsteroidal anti-inflammatory drugs). Plasma cholesterol levels were significantly reduced in all groups. The reduced plasma cholesterol level was a result of 26% and 36% reductions in low- and high-density lipoproteins (LDL and HDL), respectively. Very-low-density lipoprotein cholesterol was reduced only in the group receiving hydroxychloroquine, and this was associated with decreased plasma triglycerides in this group. Plasma apolipoprotein (apo) B, the LDL protein moiety, demonstrated a pattern similar to that shown for LDL cholesterol. Plasma apo A-I, the major HDL protein, was, however, in the normal range, suggesting an abnormal HDL fraction. Even though reduced HDL cholesterol was found in RA patients, the HDL/LDL ratio was normal and the apo A-I/apo B ratio was increased, suggesting that these patients are not at increased risk for atherosclerosis.

Anti-Inflammatory Agents↗
PubMed1985

Assessment of intestinal and cardiorespiratory function in children with congenital heart disease on high-caloric formulas.

Fourteen infants with congenital heart disease were investigated for failure to thrive. Assessment of intestinal function revealed minor absorptive abnormalities (mild steatorrhea in three patients, bile salt loss in four patients), delayed gastric emptying, and abnormal triglyceride loading tests. Low caloric intake (88.3 +/- 19.3 kcal/kg/day) seemed the main reason for failure to gain weight. Weight accession and cardiorespiratory rates were monitored daily during voluntary intake, a high-caloric diet by mouth, and nasogastric tube feeding. Providing 169 +/- 29 kcal/kg/day by tube resulted in weight gain with mild and transient elevation of respiratory rate at the end of the meal and increased heart rate 90 min after the meal. This regimen is a metabolically inexpensive and efficient method of supporting weight gain in children with congenital heart disease.

Age Factors↗