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S Thompson

Publications and source records attributed to S Thompson.

At least 19 recordsLinked to original sources
PubMed1992

Seven, eight and nine-membered anticodon loop mutants of tRNA(2Arg) which cause +1 frameshifting. Tolerance of DHU arm and other secondary mutations.

The mutant tRNA(2Arg) encoded by the genetically-selected frameshift suppressor, sufT621, inserts arginine and causes a +1 reading-frame shift at the proline codon, CCG(U). There is an extra base, G36.1, in argV beta, one of the four identical genes for tRNA(2Arg) in the position between bases 36 and 37, corresponding to the 3' side of the anticodon. The new four-base anticodon, predicted from DNA sequencing to be 3' GGCA 5', is complementary to the four-base codon CCGU. Quadruplet translocation promoted by mutant argV does not require perfect complementarity between the codon and the anticodon since synthetic genes encoding derivatives of tRNA(2Arg) and tRNA(1Pro), with four-base anticodons complementary to three out of the four bases of CCGU, were also shown to be capable of frameshifting. Two other mutants of argV, inferred to have normal-size, seven-base anticodon loops, were also found to be capable of four-base-decoding demonstrating that quadruplet translocation promoted by mutant argV does not require an enlarged anticodon loop. Other alleles of argV, predicted to have nine bases in the anticodon loop, were also found to cause frameshifting. The DNA sequence of two of these showed in addition, either a deletion of G24, or a ten-base duplication in the region corresponding to the TFC arm. A general finding is that mutations in the DHU arm of tRNA(2Arg) are compatible with, and in one case necessary for, frameshifting.

Amino Acid Sequence↗
PubMed1992

Mapping of epitopes, glycosylation sites, and complement regulatory domains in human decay accelerating factor.

Decay accelerating factor (DAF, CD55) is a glycophospholipid-anchored membrane protein that protects cells from complement-mediated damage by inhibiting the formation and accelerating the decay of C3/C5 convertases. DAF deletion mutants lacking each of the four short consensus repeats (SCR) or the serine/threonine-rich region (S/T) were created by site-directed mutagenesis. These deletion mutants were expressed by stable transfection in Chinese hamster ovary cells for the purpose of mapping important structural and functional sites in DAF. The epitopes on DAF for 16 murine mAb were mapped by immunoprecipitation studies as follows: SCR1, 6; SCR2, 3; SCR3, 3; SCR4, 3; S/T, 1. Testing of 13 mAb showed complete blocking of DAF function only by 1C6 and 1H4, both directed at SCR3. The single N-linked glycosylation site was confirmed at a location between SCR1 and SCR2, and the multiple O-linked oligosaccharides were localized to the S/T region. Functional activity of DAF mutants was assessed by the ability of these transfected constructs to protect Chinese hamster ovary cells from cytotoxicity induced by rabbit antibody plus human complement. Removal of SCR1 had no effect on DAF function, but individual deletion of SCR2, SCR3, or SCR4 totally abolished DAF function. Surprisingly, deletion of the S/T region totally abrogated DAF function, but this could be restored by a fusion construct placing the four SCR domains of DAF onto the HLA-B44 molecule, implying that the O-glycosylated S/T region serves as an important but nonspecific spacer projecting the DAF functional domains above the plasma membrane. Overall, the creation of DAF deletion mutants has elucidated important structure-function relations in the DAF molecule.

Animals↗
PubMed1992

Increased fucosylation and other carbohydrate changes in haptoglobin in ovarian cancer.

Cancer sera have high levels of an abnormal form of haptoglobin (Hp) that can be extracted from blood using the fucose-specific lectin, Lotus tetragonolobus. In order to investigate the carbohydrate abnormality that is responsible for this effect, the monosaccharide composition of Hp has been measured in Hp preparations isolated from blood samples of healthy women and women with ovarian cancer. The fucose content (g/100 g protein) of Hp was considerably elevated (7-fold) in ovarian cancer; whereas the concentrations of the other sugars were not significantly increased. There were significant increases in the galactose and N-acetylglucosamine contents of the 'cancer' Hp if the levels were expressed relative to the mannose content. This latter finding suggests that there are more oligosaccharide branches on the 'cancer' Hp. The results indicate that Hp is extracted by lotus lectin from ovarian cancer sera because of the increased fucose levels and provide further support for a disturbance in fucose metabolism in cancer.

Aged↗
PubMed1992

Parallel changes in the blood levels of abnormally-fucosylated haptoglobin and alpha 1,3 fucosyltransferase in relationship to tumour burden: more evidence for a disturbance of fucose metabolism in cancer.

Levels of an abnormally-fucosylated form of the serum glycoprotein, haptoglobin (FHp) and an enzyme, alpha 1,3 fucosyltransferase (FT) have been measured in blood specimens from women with carcinoma of the ovary or breast who are undergoing chemotherapy. The levels of FHp and FT increased if the women had progressive disease and decreased if they showed complete response to therapy. The statistical correlation between the blood concentrations of these two substances is very strong (P less than 0.0001, chi 2 test). These results and recent studies of fucosyltransferases and cell adhesion molecules from other laboratories, suggest that there are important changes in fucose metabolism in cancer which are worthy of further investigation.

Biomarkers, Tumor↗
PubMed1992

Application of an organic solvent extraction to the determination of catechol-O-methyltransferase activity by high-performance liquid chromatography in human mononuclear cells.

We report here a method for measuring mononuclear cell catechol-O-methyltransferase (COMT) activity which is ideally adapted to clinical studies. The method measures the O-methylation of dopamine to 3-methoxytyramine and 4-methoxy-3-hydroxyphenethylamine. Whole mononuclear cell sonicate is incubated with saturating concentrations of dopamine, S-adenosyl-L-methionine and magnesium chloride in sodium-potassium phosphate buffer at pH 7.3. An organic solvent extraction using ethyl acetate is then used for product separation, followed by high-performance liquid chromatography with electrochemical detection for product separation and quantification. This method allows both O-methylated products, 3-methoxytyramine and 4-methoxy-3-hydroxyphenethylamine, to be isolated and quantified separately. The apparent Michaelis constants for dopamine and S-adenosyl-L-methionine using this method are similar to values reported previously (0.51 and 14 microM, respectively). The optimal concentration of magnesium chloride is eight to ten times higher than previously reported. No endogenous inhibitors were apparent using this assay. The within-day coefficient of variation using this method is 7% when measuring 3-methoxytyramine and 5% when measuring 4-methoxy-3-hydroxyphenethylamine. The between-day coefficient of variation is 11%. Mononuclear cell COMT activity can be detected using protein concentrations as low as 0.75 mg/ml, corresponding to 2-3 ml of whole blood. The small amount of blood required per sample allows multiple sample analysis from a single patient, including infants.

Adult↗
PubMed1992

Effects of endothelin-1 on signal transduction in UMR-106 osteoblastic cells.

Endothelin-1 is now recognized to affect the functions of a number of tissues and to activate calcium/phospholipid second messenger pathways in target cells. In the present study, we characterized its effects on signal transduction in UMR-106 cells. To study calcium transients elicited by endothelin-1, cells were loaded either with fluo-3 (for the measurement of cytosolic free calcium) or chlortetracycline (for the measurement of intracellularly stored calcium) as fluorescent probes. Intracellular production of inositol phosphates and cyclic AMP was also measured. Endothelin-1 elicited dose-dependent cytosolic calcium transients with an ED50 of 20 nM. This effect was also seen in EGTA-containing or calcium-free medium; however, the signals were reduced in magnitude. The dihydropyridine calcium channel antagonist nifedipine did not affect the response. Repeated administration of endothelin-1 resulted in homologous desensitization of the response. A 4 minute pretreatment with phorbol ester reduced the initial response to endothelin-1 in both calcium-containing and calcium-free media. A 24 h pretreatment with indomethacin had no effect on response. Using chlortetracycline as an indicator, a significant reduction in intracellularly stored calcium by endothelin-1 was observed. This was prevented by 8-(N,N-diethylamino)octyl-3,4,5-trimethoxybenzoate, a blocker of calcium release from internal stores. Endothelin-1 also stimulated the dose-dependent production of inositol phosphates by UMR-106 cells. Indomethacin was also without effect on this process. The increase in inositol trisphosphates was seen within the same time frame as the increase in cytosolic calcium. Endothelin-1 did not influence cyclic AMP production over 5 minutes in these cells.(ABSTRACT TRUNCATED AT 250 WORDS)

Calcium↗
PubMed1992

Amitriptyline, clovoxamine and cognitive function: a placebo-controlled comparison in depressed outpatients.

No longer prescribed only for vegetative signs of depression, tricyclic antidepressants also lessen depressive cognitive distortions. Less clear is whether they ameliorate depressed patients' other cognitive deficits in memory, information processing speed, and psychomotor performance. We tested the alternative hypothesis that amitriptyline, because of its anticholinergic and sedative properties, would exacerbate depressed patients' cognitive disturbances. Depressed outpatients received double-blind placebo (n = 15), amitriptyline (n = 10), or clovoxamine fumarate (n = 10), a serotonin reuptake inhibitor relatively lacking in anticholinergic properties. Depression, memory, and psychomotor performance were assessed at baseline and after 7 and 28 days of drug treatment. Depression was alleviated after all treatments, including placebo. Only amitriptyline impaired performance on tests of memory, producing a significant decrement, relative to placebo, after 4 weeks of treatment. None of the treatments adversely affected performance on psychomotor tasks. These findings add to the evidence that antidepressant drugs with high anticholinergic activity can impair memory, despite alleviation of depression.

Acoustic Stimulation↗
PubMed1992

A-type potassium channel clusters revealed using a new statistical analysis of loose patch data.

The spatial distribution of ion channels over the surface of a neuron is an important determinant of its excitable properties. We introduce two measures of channel clustering for use in patch-clamp experiments: a normalized chi-squared statistic (eta) and the number of zero-channel patches in a data set (Z). These statistics were calculated for data sets describing the distribution of A-type potassium channels on neurons of the nudibranch Doriopsilla and measurements of Ca-dependent outward current channels on bullfrog hair cells, as well as simulated channel distributions. When channels are clustered, eta is approximately equal to the amount of current in a cluster. The analysis shows that somatic A-channels in the nudibranch are distributed in clusters of approximately 50 channels each. The clusters are < 2 microns wide and are separated, on average, by 3.2 microns. Outward current channels on hair cells occur in clusters of approximately 27 channels each, in agreement with the original analysis. Channel clustering may reflect properties of the insertion or regulation of channels in the membrane.

Animals↗
PubMed1992

p53, c-erbB-2 and the epidermal growth factor receptor in the benign and malignant prostate.

Expression of the p53, the epidermal growth factor receptor (c-erbB-1) and c-erbB-2 protein was studied in 34 men with benign prostatic hyperplasia and 29 men with locally advanced prostate cancer by means of an immuno-histochemical method. Strong staining for p53 was found in five of 29 prostate cancers (17%; mean 21% +/- 7% of malignant cells stained in the positive tumours), but no staining was found in benign prostatic hyperplasia (p less than 0.05). On the other hand, the epithelium in benign glands was stained positively for c-erbB-2 in 18% (6/34) and for the epidermal growth factor receptor in 88% (30/34); whereas malignant epithelium stained strongly for c-erbB-2 in 21% (6/29) and for the epidermal growth factor receptor in only 17% (5/29). Prostate cancer was associated with a significant decrease in epidermal growth factor receptor staining (p less than 0.0001) and a significant increase in p53 staining (p less than 0.05). Most of the tumours were advanced and no significant relationship was observed between tumour stage and grade and expression of p53, the epidermal growth factor receptor or c-erbB-2. These findings demonstrate that altered expression of the epidermal growth factor receptor and p53 protein occurs in prostate cancer, but were not associated with other features of prognostic importance such as stage or grade.

Aged↗
PubMed1992

A dynamic dual isotope radionuclear method of quantifying penile blood flow.

A new radionuclear method of quantifying arterial and venous blood flow of the penis is described. The technique is based on the simultaneous recording of the change in blood volume and venous outflow in the flaccid and erect states, which is produced pharmacologically. The change in penile blood volume is determined by measuring the change in the technetium-labeled red blood cell activity with time. Venous outflow is recorded with a xenon washout technique. The isotope data are used to compute arterial and venous flows with a complex computerized mathematical formula. Three basic blood flow patterns have been noted that distinguish normal patients from those with arterial insufficiency and venous leakage. The study is relatively easy and noninvasive to perform, and it appears to quantify penile blood flow accurately.

Adult↗
PubMed1992

Social rehabilitation and return to work after cardiac transplantation--a multicenter survey.

As the medical results of heart transplantation steadily improve, the social rehabilitation of patients, in particular, their ability to return to some form of employment, is becoming increasingly important. Two-hundred fifty patients were therefore surveyed at 7 heart transplant centers (5 of which were Medicare certified) from different geographic regions in the U.S.A. Over all, 45% were employed, 36% were unemployed, 13% were medically disabled, and 6% were retired. Of those employed, 87% had returned to their previous employment, and only 13% had secured new employment. Of the unemployed, 16% had made job applications, and no fewer than 63% had no current plan to seek employment. Factors found to negatively influence a return to work included the following: (1) length of medical disability prior to transplantation; (2) a patient's self-perception of being physically unable to work; and (3) the potential loss of health insurance and/or disability income. At 2 centers, where there was a definite policy of not supporting a patient's claim for medical disability in the absence of an absolute indication, there were significantly increased numbers who (1) secured new employment and (2) planned to seek employment. More serious attention must be paid to aspects of employment if heart transplant recipients are to become fully productive members of the community.

Adult↗
PubMed1992

Practical screening priorities for hearing impairment among children in developing countries.

Routine screening for hearing impairment in childhood is now widespread in industrial countries, although there is considerable controversy over the most efficient techniques and procedures. In most developing countries, however, routine screening programmes for hearing impairment do not currently exist. The problems involved in implementing screening programmes in developing and industrial countries are very different, and in selecting screening procedures for a particular population the following factors have to be taken into consideration: the environmental test conditions; the availability of resources for equipment and the training of testers; the local attitudes towards disability; the level of hearing impairment that may cause handicaps; and the major types of pathology causing hearing impairment. We suggest that in developing countries children should be screened at school entry using a simple field audiometer and that the external ear be inspected for the presence of a discharge. There is an urgent need to develop reliable and simple screening procedures for infants and young children; where possible, all children should be screened for severe or significant hearing impairment before the age of 2 years. No screening should, however, be implemented until appropriate follow-up services are available.

Acoustic Impedance Tests↗
PubMed1992

A dual-radioisotope technique for the evaluation of penile blood flow during tumescence.

A technique is described for concomitant study of both arterial and venous penile blood flow during tumescence. Dual-isotope acquisition is started after labeling red cells in vivo with 99mTc. Xenon-133 in saline is then injected into the corpus cavernosum followed with vasoactive drugs to induce an erection. The resulting xenon and technetium time-activity curves are inputs for a one-compartment model. In 14 subjects, the average peak arterial flow rate (PAF) for normal males was calculated as 13.0 +/- 1.28 ml/min (avg +/- s.d.) compared to 16.1 +/- 5.14 and 5.02 +/- 1.78 ml/min for patients with venous leak (VL) or arterial insufficiency (AI), respectively. Peak venous flows (PVF) were 4.25 +/- 1.17, 12.1 +/- 3.75, and 3.78 +/- 1.00 ml/min for normal, VL and AL respectively. Al patients have significantly lower PAF than normal (p = 0.002) or VL patients (p = 0.018), and VL patients had significantly higher PVF than normal (p = 0.012) or Al (p = 0.018). The technique may be helpful in the study of impotence.

Adult↗