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S Mohr

Publications and source records attributed to S Mohr.

At least 37 records · Page 2Linked to original sources
PubMed2000

Characterization of an unusual tRNA-like sequence found inserted in a Neurospora retroplasmid.

We characterized an unusual tRNA-like sequence that had been found inserted in suppressive variants of the mitochondrial retroplasmid of Neurospora intermedia strain Varkud. We previously identified two forms of the tRNA-like sequence, one of 64 nt (TRL-64) and the other of 78 nt (TRL-78) containing a 14-nt internal insertion in the anticodon stem at a position expected for a nuclear tRNA intron. Here, we show that TRL-78 is encoded in Varkud mitochondrial (mt)DNA within a 7 kb sequence that is not present in Neurospora crassa wild-type 74 A mtDNA. This 7-kb insertion also contains a perfectly duplicated tRNA(Trp)gene, segments of several mitochondrial plasmids and numerous GC-rich palindromic sequences that are repeated elsewhere in the mtDNA. The mtDNA-encoded copy of TRL-78 is transcribed and apparently undergoes 5'- and 3'-end processing and 3' nucleotide addition by tRNA nucleotidyl transferase to yield a discrete tRNA-sized molecule. However, the 14 nt intron-like sequence in TRL-78, which is missing in the TRL-64 form, is not spliced detectably in vivo or in vitro. Our results show that TRL-78 is an unusual tRNA-like species that could be incorporated into suppressive retroplasmids by the same reverse transcription mechanism used to incorporate mt tRNAs. The tRNA-like sequence may have been derived from an intron-containing nuclear tRNA gene or it may serve some function, like mtRNA. Our results suggest that mt tRNAs or tRNA-like species may be integrated into mtDNA via reverse transcription, analogous to SINE elements in animal cells.

Base Sequence↗
PubMed2000

Controlled human exposure to methyl tertiary butyl ether in gasoline: symptoms, psychophysiologic and neurobehavioral responses of self-reported sensitive persons.

The 1990 Clean Air Act mandated oxygenation of gasoline in regions where carbon monoxide standards were not met. To achieve this standard, methyl tertiary butyl ether (MTBE) was increased to 15% by volume during winter months in many locations. Subsequent to the increase of MTBE in gasoline, commuters reported increases in symptoms such as headache, nausea, and eye, nose, and throat irritation. The present study compared 12 individuals selected based on self-report of symptoms (self-reported sensitives; SRSs) associated with MTBE to 19 controls without self-reported sensitivities. In a double-blind, repeated measures, controlled exposure, subjects were exposed for 15 min to clean air, gasoline, gasoline with 11% MTBE, and gasoline with 15% MTBE. Symptoms, odor ratings, neurobehavioral performance on a task of driving simulation, and psychophysiologic responses (heart and respiration rate, end-tidal CO(2), finger pulse volume, electromyograph, finger temperature) were measured before, during, and immediately after exposure. Relative to controls, SRSs reported significantly more total symptoms when exposed to gasoline with 15% MTBE than when exposed to gasoline with 11% MTBE or to clean air. However, these differences in symptoms were not accompanied by significant differences in neurobehavioral performance or psychophysiologic responses. No significant differences in symptoms or neurobehavioral or psychophysiologic responses were observed when exposure to gasoline with 11% MTBE was compared to clean air or to gasoline. Thus, the present study, although showing increased total symptoms among SRSs when exposed to gasoline with 15% MTBE, did not support a dose-response relationship for MTBE exposure nor the symptom specificity associated with MTBE in epidemiologic studies.

Adult↗
PubMed2000

Effect of aging on saccadic eye movements to visual and auditory targets.

Elderly patients with diseases of the central nervous system often show saccadic disorders. Before these disorders can be called pathological, they must be distinguished from the physiological effects of aging. The purpose of this study was to determine the effect of aging on visual and auditory saccadic eye movements. Ninety healthy volunteers were divided into three groups (younger than 30 years; 30-50 years; older than 50 years), with 30 volunteers in each group. Visual and auditory predictive 15-degree saccades were evoked and recorded with electrooculography. Recorded parameters were peak velocity, duration, and latency. Both stimuli showed increasing latencies with increasing age and a higher peak velocity in the middle group as compared to the oldest group. The latter result was significant only for saccades to visual targets. Duration was almost identical for both patterns and all age groups. Between the age groups, latencies were significantly shorter for the saccades to auditory targets, and no differences in peak velocity occurred. The results stress the importance of an age-related assessment for saccadic parameters. The increasing latency and decreasing peak velocity in elderly people probably result from age-related degenerative changes in central nervous system parts that are involved in the generation of saccadic eye movements. We found no indications of a different effect of aging through either the visual or the auditory pathway for saccadic parameters.

Acoustic Stimulation↗
PubMed1999

Nitric oxide-induced S-glutathionylation and inactivation of glyceraldehyde-3-phosphate dehydrogenase.

S-Nitrosylation of protein thiol groups by nitric oxide (NO) is a widely recognized protein modification. In this study we show that nitrosonium tetrafluoroborate (BF4NO), a NO+ donor, modified the thiol groups of glyceraldehyde-3-phosphate dehydrogenase (GAPDH) by S-nitrosylation and caused enzyme inhibition. The resultant protein-S-nitrosothiol was found to be unstable and to decompose spontaneously, thereby restoring enzyme activity. In contrast, the NO-releasing compound S-nitrosoglutathione (GSNO) promoted S-glutathionylation of a thiol group of GAPDH both in vitro and under cellular conditions. The GSH-mixed protein disulfide formed led to a permanent enzyme inhibition, but upon dithiothreitol addition a functional active GAPDH was recovered. This S-glutathionylation is specific for GSNO because GSH itself was unable to produce protein-mixed disulfides. During cellular nitrosative stress, the production of intracellular GSNO might channel signaling responses to form protein-mixed disulfide that can regulate intracellular function.

Animals↗
PubMed1998

Comparison of the complete protein sets of worm and yeast: orthology and divergence.

Comparative analysis of predicted protein sequences encoded by the genomes of Caenorhabditis elegans and Saccharomyces cerevisiae suggests that most of the core biological functions are carried out by orthologous proteins (proteins of different species that can be traced back to a common ancestor) that occur in comparable numbers. The specialized processes of signal transduction and regulatory control that are unique to the multicellular worm appear to use novel proteins, many of which re-use conserved domains. Major expansion of the number of some of these domains seen in the worm may have contributed to the advent of multicellularity. The proteins conserved in yeast and worm are likely to have orthologs throughout eukaryotes; in contrast, the proteins unique to the worm may well define metazoans.

Animals↗
PubMed1998

Propensity for macrophage apoptosis is related to the pattern of expression and function of integrin extracellular matrix receptors.

Ligation of integrins to an extracellular matrix activates signal transduction systems which produce multiple responses in different cell types. Adhesion often provides a survival signal to cells; disruption of adhesion frequently results in apoptosis. Our laboratory has utilized apoptosis-sensitive and -resistant cell lines to investigate the role of integrin expression and function in regulation of apoptosis in macrophages. Chronic exposure of murine macrophage-like RAW264.7 cells to apoptosis-inducing agents (bacterial lipopolysaccharide and interferon-gamma) resulted in the generation of a derivative cell line (RES) resistant to apoptosis. Observation of RAW and RES cultures indicated a difference in adhesion between the two cell types. The two cell lines also exhibit significant differences in expression of integrins previously characterized to be important in apoptosis.

Animals↗
PubMed1998

Macrophages resistant to endogenously generated nitric oxide-mediated apoptosis are hypersensitive to exogenously added nitric oxide donors: dichotomous apoptotic response independent of caspase 3 and reversal by the mitogen-activated protein kinase kinase (MEK) inhibitor PD 098059.

Nitric oxide (NO) induction through the inducible NO synthase has been demonstrated to cause cell death in macrophages. We demonstrate that, in macrophages that have been rendered resistant to apoptosis induced by inducible NO synthase (RES cells), exposure to exogenous NO donors results in a hypersensitive apoptosis reaction when compared with the parental RAW 264.7 cells. The apoptosis induced via exogenous NO donors was found to be caspase 3-independent. Although caspase 3 activity was stimulated in the apoptotic macrophages, inhibition of caspase 3 by the inhibitor DEVD-CHO (N-acetyl-Asp-Glu-Val-Asp-aldehyde) did not reverse the apoptosis induced by the NO donor S-nitrosoglutathione (GSNO). This suggests that although caspase 3 activity is stimulated during apoptosis in macrophages, this signal is not sufficient to induce apoptosis. Cleavage of the enzyme poly(ADP ribose) polymerase mirrors our results of the caspase activity. Interestingly, we show that exogenous NO donation results in an accumulation of cells at the G2/M-phase border. Here, we demonstrate that the mitogen activated protein kinase kinase (MEK) inhibitor PD 098059 can be used to reverse the G2/M-phase block and show that this treatment also inhibits the observed apoptosis in RES macrophages. Treatment with the MEK inhibitor also reversed both the caspase 3 activity and poly(ADP ribose) polymerase cleavage in cells treated with GSNO. This result indicates that the mitogen-activated protein kinase pathway may be involved in regulation of the caspase cascade. Alternatively, it may suggest an activity for the MEK inhibitor heretofore not observed, that of a cyclin kinase inhibitor. Our results suggest that selection of macrophages by resistance to endogenously generated NO may cause hypersensitivity to exogenous NO donors. These findings have relevant implications for the treatment of apoptotic-resistant cell populations that may occur in both cancer and atheroma.

Animals↗
PubMed1998

Phenotype-dependent differences in apolipoprotein E metabolism and in cholesterol homeostasis in human monocyte-derived macrophages.

In this study, we investigated the impact of the common apoE polymorphism on apoE metabolism and cholesterol homeostasis in monocyte-derived macrophages isolated from E2/2, E3/3, and E4/4 subjects. Unloaded cells of all genotypes contained similar amounts of free cholesterol, cholesteryl ester, and apoE mRNA. E3/3 cells secreted 77 and 30% more apoE than E2/2 or E4/4 cells, respectively. Pulse-chase studies confirmed that the apoE secretion rate was greatest in E3/3 and least in E2/2 cells and showed that a portion of apoE2, but not apoE3 or apoE4, was degraded intracellularly. Surface binding of apoE was greatest in E4/4 cells, as revealed by heparinase treatment. On cholesterol loading with acetylated LDL, apoE mRNA levels and protein secretion rose most in E4/4 and least in E2/2 cells. Cholesterol and cholesteryl ester content, however, rose most in E2/2 and least in E3/3 cells. Incubations with 3H-cholesterol-labeled acetylated LDL revealed that E2/2 cells were most efficient at secreting cholesterol. The greatest reuptake of 3H-cholesterol-rich particles was from E4/4 macrophage- conditioned media. Thus, E2/2 macrophages, despite a low apoE secretion rate, are protected from cholesterol storage by apoE-mediated cholesterol efflux. In E3/3 macrophages, cholesterol accumulation is lessened by a high basal apoE secretion rate. E4/4 macrophages secrete the most apoE but lack effective net cholesterol efflux due to enhanced surface binding and reuptake of cholesterol-rich particles.

Adult↗
PubMed1998

Sequential and rapid activation of select caspases during apoptosis of normal intestinal epithelial cells.

Detachment-induced cell death (DICD) is considered to be one of the means by which intestinal epithelial cells (IEC) die of apoptosis as they reach the lumen and are shed. Caspases, a family of cysteine proteases, play a central role in initiating, amplifying, and executing apoptosis; however, the pattern of caspase activation in response to distinct apoptotic stimuli remains unknown. We investigated the kinetics of caspase activation during DICD in freshly isolated human IEC. DNA fragmentation is observed 90 min after detachment and is preceded by the sequential activation of preformed members of the CPP32 family of caspases. Activation of caspase 6 and cleavage of the endogenous caspase substrate poly(ADP-ribose) polymerase (EC 2.4.2.30) are detected within 15 min of detachment, 30-45 min before caspase 3 activation. Caspase 1 and caspase 10 are present as proenzymes, yet they remain inactive in response to this trigger of apoptosis. Human IEC are primed to rapidly undergo detachment-induced apoptosis involving the selective and sequential activation of preformed caspases. This study may enhance our understanding of physiological events occurring as IEC are shed. Their rapid apoptotic response to detachment may facilitate the high turnover of cells and ensure homeostasis in the intestinal epithelium.

Apoptosis↗
PubMed1998

Developmental remodeling and shortening of the cardiac outflow tract involves myocyte programmed cell death.

The embryonic outflow tract is a simple tubular structure that connects the single primitive ventricle with the aortic sac and aortic arch arteries. This structure undergoes a complex sequence of morphogenetic processes to become the portion of the heart that aligns the right and left ventricles with the pulmonary artery and aorta. Abnormalities of the outflow tract are involved in many clinically significant congenital cardiac defects; however, the cellular and molecular processes governing the development of this important structure are incompletely understood. Histologic and tissue-tagging studies indicate that the outflow tract tissues compact and are incorporated predominantly into a region of the right ventricle. The hypothesis tested in the current study was that cell death or apoptosis in the muscular portion of the outflow tract is an important cellular mechanism for outflow tract shortening. The tubular outflow tract myocardium was specifically marked by infecting myocytes of the chicken embryo heart with a recombinant replication-defective adenovirus expressing beta-galactosidase (beta-gal) under the control of the cytomegalovirus promoter. Histochemical detection of the beta -gal-labeled outflow tract myocytes revealed that the tubular structure shortened to become a compact ring at the level of the pulmonic infundibulum over several days of development (stages 25-32, embryonic days 4-8). The appearance of apoptotic cardiomyocytes was correlated with OFT shortening by two histologic assays, TUNEL labeling of DNA fragments and AnnexinV binding. The rise and fall in the number of apoptotic myocytes detected by histologic analyses paralleled the change in activity levels of Caspase-3, a protease in the apoptotic cascade, measured in outflow tract homogenates. These results suggest that the elimination of myocytes by programmed cell death is one mechanism by which the outflow tract myocardium remodels to form the proper connection between the ventricular chambers and the appropriate arterial trunks.

Adenoviridae↗
PubMed1997

Peroxynitrite protects RAW 264.7 macrophage from Lipopolysaccharide/Interferon-gamma-induced cell death.

Peroxynitrite, formed by the interaction of superoxide with nitric oxide, has previously been implicated mostly as a cytotoxic agent. In contrast, its physiological and, possibly, beneficial effects are largely unknown. We have previously shown [Journal of Biological Chemistry, 1997, 272, 7253] that RAW 264.7 macrophages can be selected to be resistant toward lipopolysaccharide (LPS)/interferon-gamma (IFN-gamma)-induced cytotoxicity. Resistant cells produced comparable amount of nitric oxide, but showed increased formation of superoxide, which might lead to increased production of peroxynitrite. We utilized this well characterized cell model to seek evidence that peroxynitrite might cause protection of RAW cells from cytokine toxicity. Exogenous peroxynitrite (30-50 microM), applied to RAW cells before cytokine stimulation, dramatically reduced LPS/IFN-gamma toxicity. Measurement of cell viability after overnight incubation with a mixture of LPS (10 microg/ml) and IFN-gamma (100 U/ml), showed that pretreatment with 40 microM peroxynitrite completely reverted LPS/IFN-gamma cytotoxicity. Differently, pretreatment of RAW cells with peroxynitrite (10-60 microM) did not prevent cytotoxicity induced by the nitric oxide-donors S-Nitroso-L-glutathione (0.2-1 mM), or spermine NONOate (0.2-2 mM), and by Actimomycin D (0.5-1 microg/ml), suggesting that the protective effect is specific for the LPS/IFN-gamma pathway. These results were confirmed through extensive controlled studies aimed to optimize cell exposure to peroxynitrite, and showed that peroxynitrite protects macrophages from cytokine-induced cytotoxicity.

Animals↗
PubMed1997

Inhibition of caspase-3 by S-nitrosation and oxidation caused by nitric oxide.

Apoptotic signaling cascades converge in the activation of caspases (interleukin-1beta converting enzyme like proteases). Treatment of the human promyelocytic leukaemia cell line U937 with actinomycin D resulted in the activation of caspase-3 also known as CPP32. Protease activity was measured in cytosolic extracts by fluorometric analysis of the time-dependent cleavage of acetyl-Asp-Glu-Val-Asp-aminomethylcoumarin (DEVD-AMC), a caspase-3 substrate. Caspase activity was inhibited by thiol modifying agents such as N-ethylmaleimide or iodoacetamide and NO donors such as S-nitrosoglutathione (GSNO), BF4NO, and spermine-NO. NO-mediated enzyme inhibition was fully reversible upon the addition of DTT (dithiothreitol). NO. itself was not primarily responsible for downregulation of caspase-3, as we found no correlation between rates of NO* release and the magnitude of enzyme inhibition. It is likely that S-nitrosation accounts for enzyme inhibition by various NO donors. SIN-1 and peroxynitrite were inhibitory as well. In this case, however, enzyme activity was not restored upon DTT addition, suggesting oxidation as an additional thiol modification mechanism. Our studies provide evidence that caspases are targeted by NO via S-nitrosation and oxidation of critical thiol groups.

Apoptosis↗
PubMed1997

Parental and novel copies of the mitochondrial orf25 gene in the hybrid crop-plant triticale: predominant transcriptional expression of the maternal gene copy.

Triticale, an intergeneric hybrid crop-plant, is generated when female wheat lines are fertilised with pollen from rye. We have investigated the mitochondrial DNA organisation and the expression of a total of 11 different triticale genotypes, varying in their nuclear and cytoplasmic backgrounds. In Southern hybridisations using probes homologous to the upstream flanking sequences, mtDNA fragments characteristic of both wheat and rye mtDNA can be detected in all triticale lines analysed. In addition, clones isolated fom a triticale lambda library exhibit either a maternal-like or paternal-like organisation of the orf25 gene region. By PCR cloning, four different orf25 gene copies were identified in triticale, three of which correspond to maternal (85%) or paternal (12%) orf25 sequences. Three percent of all clones represent a novel type, that might have arisen by homologous recombination. Although these data suggest biparental inheritance of mtDNA in wheat/rye crosses, paternal-like gene copies can also be detected in maternal wheat mitochondria. Their stoichiometry as assayed by competitive PCR is about 0.1% of total orf25 gene copies. The high abundance of paternal-like sequences in the F1 hybrid might therefore be due to either the transmission of rye mtDNA in the intergeneric cross and/or the amplification of sequences in triticale that persist in sub-stoichiometric amounts in wheat. These data suggest that amplification and recombination of sub-genomic mitochondrial molecules are affected by different nuclear genotypes. Interestingly, sequence analysis of triticale RT-PCR clones indicates a selective transcription of maternal-like orf25 gene copies in triticale. Mitochondrial gene expression may therefore possess mechanisms to compensate for the variation of mtDNA organisation.

Base Sequence↗
PubMed1997

Cerebral vasomotor changes in the transient syndrome of headache with neurologic deficits and CSF lymphocytosis (HaNDL).

We report two patients with the recently described transient syndrome of headache with neurologic deficits and CSF lymphocytosis (HaNDL). Transcranial Doppler sonography performed during and after attacks of HaNDL showed asymmetrical decreases or increases in blood flow velocity of the middle cerebral artery, accompanied by increases or decreases in pulsatility suggesting fluctuations of arteriolar tone. The findings demonstrate focal vasomotor disturbances that link the transient headaches and deficits of HaNDL with attacks of migraine.

Adult↗
PubMed1997

Downregulation of the selectin ligand-producing fucosyltransferases Fuc-TIV and Fuc-TVII during foam cell formation in monocyte-derived macrophages.

Identification of genes expressed during foam cell formation is important for understanding the molecular basis of atherosclerosis. We used polymerase chain reaction (PCR)-based differential display to isolate differentially expressed cDNA species in foam cells induced by incubation of human monocyte-derived macrophages in the presence of acetylated or oxidized LDL. This led to identification of a 306-bp cDNA with 100% homology to type IV fucosyltransferase (Fuc-TIV), which was downregulated by factors of 20 and 3 in acetylated LDL- and oxidized LDL-loaded macrophages, respectively. This enzyme is sufficient for the expression of Lewis X and sialyl Lewis X, carbohydrate adhesion molecules that bind to receptors of the selectin family. Expression of a second fucosyltransferase (Fuc-TVII) that synthesizes sialyl Lewis X but not Lewis X was shown by quantitative reverse transcription-PCR to also be reduced, by 40% and 20% in acetylated LDL- and oxidized LDL-loaded macrophages, respectively. alpha-(1,3)-Fucosyltransferase enzyme activity was reduced in lysates from both acetylated LDL- and oxidized LDL-loaded cells. Analysis by flow cytometry showed reduced expression of the CD15 (corresponding to Lewis X) and CD15s (sialyl Lewis X) antigens on the surface of cells loaded with either acetylated or oxidized LDL. Transformation of macrophages into foam cells results in reduced expression of selectin-binding ligands on the surface of such cells.

Acetylation↗