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C M Burns

Publications and source records attributed to C M Burns.

At least 37 records · Page 2Linked to original sources
PubMed1997

Regulation of serotonin-2C receptor G-protein coupling by RNA editing.

The neurotransmitter serotonin (5-hydroxytryptamine, 5-HT) elicits a wide array of physiological effects by binding to several receptor subtypes. The 5-HT2 family of receptors belongs to a large group of seven-transmembrane-spanning G-protein-coupled receptors and includes three receptor subtypes (5-HT2A, 5-HT(2B) and 5-HT(2C)) which are linked to phospholipase C, promoting the hydrolysis of membrane phospholipids and a subsequent increase in the intracellular levels of inositol phosphates and diacylglycerol. Here we show that transcripts encoding the 2C subtype of serotonin receptor (5-HT(2C)R) undergo RNA editing events in which genomically encoded adenosine residues are converted to inosines by the action of double-stranded RNA adenosine deaminase(s). Sequence analysis of complementary DNA isolates from dissected brain regions have indicated the tissue-specific expression of seven major 5-HT(2C) receptor isoforms encoded by eleven distinct RNA species. Editing of 5-HT(2C)R messenger RNAs alters the amino-acid coding potential of the predicted second intracellular loop of the receptor and can lead to a 10-15-fold reduction in the efficacy of the interaction between receptors and their G proteins. These observations indicate that RNA editing is a new mechanism for regulating serotonergic signal transduction and suggest that this post-transcriptional modification may be critical for modulating the different cellular functions that are mediated by other members of the G-protein-coupled receptor superfamily.

3T3 Cells↗
PubMed1997

DNA binding is not sufficient for H-NS-mediated repression of proU expression.

H-NS is a major component of bacterial chromatin and influences the expression of many genes. H-NS has been shown to exhibit a binding preference for certain AT-rich curved DNA elements in vitro. In this study we have addressed the factors that determine the specificity of H-NS action in vitro and in vivo. In bandshift studies, H-NS showed a slight binding preference for all curved sequences tested whether GC-based or AT-based; the specific architecture of the curve also influenced H-NS binding. In filter retention assays little difference in affinity could be detected for any sequence tested, including the downstream regulatory element (DRE) a downstream curved DNA element required for H-NS to repress transcription of the Salmonella typhimurium proU operon in vivo. A Kd of 1-2 microM was estimated for binding of H-NS to each of these sequences. In vivo, the distance between the proU promoter and the DRE, their relative orientations on the face of the DNA helix, and translation of the DRE had no major effect on proU regulation. None of the synthetic curved sequences tested could functionally replace the DRE in vivo. These data show that differential binding to curved DNA cannot account for the specificity of H-NS action in vivo. Furthermore, binding of H-NS to DNA per se is insufficient to repress the proU promoter. Thus, the DRE does not simply act as an H-NS binding site but must have a more specific role in mediating H-NS regulation of proU transcription.

Amino Acid Transport Systems↗
PubMed1997

Function of the novel subdomain in the RNA binding domain of transcription termination factor Rho from Micrococcus luteus.

Transcription termination factor Rho from Micrococcus luteus, a high G + C Gram-positive bacterium, contains an unusual extra sequence within its RNA binding domain that is rich in Arg, Glu, and Asp residues and deficient in hydrophobic residues. To determine the role of this extra sequence, we compared the biochemical properties of a variant lacking nearly all the extra sequence, des(60-300) Rho, to that of wild-type M. luteus Rho. The two forms had very similar properties except that the des(60-300) Rho was unable to terminate transcription with Escherichia coli RNA polymerase at the promoter proximal sites used by the wild-type Rho on a lambda cro DNA template but could cause termination at more distal sites and did cause termination at proximal sites when ITP replaced GTP in the reaction mixture. The RNA binding properties of the two forms of this Rho with normal and inosine-substituted RNAs were found to correlate fully with their termination properties. These results indicate that the arginine-rich extra sequence is directly involved in the selection of the termination site and support the hypothesis that the sequence is present in M. luteus Rho to facilitate its binding to M. luteus transcripts, which are likely to have a high degree of base-paired secondary structure because of their high proportion of G residues.

Adenosine Triphosphatases↗
PubMed1997

Very low calorie diet (VLCD): a useful alternative in the treatment of the obese NIDDM patient.

Conventional treatment of obese noninsulin dependent diabetes mellitus (NIDDM) patients is often unsatisfactory. In this study the efficacy of Modifast, a commercial very low calorie diet (VLCD), was evaluated in a population of obese poorly controlled NIDDM patients. The mechanisms of action of VLCD in these patients were also studied by comparing: (i) Plasma insulin and glucose profiles after a VLCD and an isocaloric mixed meal and (ii) plasma amino acid levels, both at baseline and after four weeks of VLCD treatment. A total of 14 obese NIDDM patients (M/F 7/7. median body mass index (BMI) 38.7 kg-2, interquartile range (IQ) 34.7-46.5 kg-2, waist circumference 116 cm, IQ 106-139 cm, insulin treated 7/14) with poor diabetic control (HbA1c 8.6%, IQ 7.8-10%) were studied. Patients were given a VLCD (425 kcal/day) for 12 weeks. At baseline, VLCD and isocaloric meal tests were performed on consecutive mornings. Fasting plasma amino acid levels were also determined at baseline and after 4 weeks of VLCD treatment. Weight, waist circumference, HbA1c, blood pressure, fasting plasma insulin, total cholesterol and triglyceride levels all fell significantly following VLCD treatment. Insulin therapy was able to be ceased in the seven insulin treated patients. Oral hypoglycaemic agent dosage fell from a median of eight (IQ 6-12) to two (IQ 0-8) tablets per day (P = 0.03) in patients initially on this form of therapy. Insulin secretion was higher after VLCD than isocaloric meal (P = 0.04). Fasting plasma alanine level fell from 512.0 (IQ 412.0-563.0) to 374.0 (IQ 342-472.0) mumol/l (P = 0.04) following VLCD treatment. In conclusion, the short term use of a VLCD is very effective in rapidly improving glycaemic control and promoting substantial weight loss in obese NIDDM patients. Moreover, a VLCD diet increases insulin secretion and reduces substrate for gluconeogenesis. Thus, VLCD treatment may improve glycaemic control by factors more than caloric restriction alone.

Adult↗
PubMed1997

Implementing a quality assurance program using a risk assessment tool on dairy operations.

Concerns and perceptions about antibiotic residues in milk prompted the dairy industry to develop a voluntary program to support rational antibiotic use on dairy farms. One deficiency of this program is the inability of producers to identify easily the weaknesses in antibiotic management in order to develop control plans. To overcome this deficiency, an educational approach was designed. The program centered on an on-farm risk assessment tool used by the producer and an industry educator to determine the current risk for residue violation. The risk assessment tool was tested by 25 field personnel working with northeastern milk receivers and 250 producers in seven states. The participants in the study identified a lack of adequate treatment records as being the highest risk factor for antibiotic residues, followed by deficiencies in understanding how to use antibiotics and poor relationships between veterinarians and their clients. When field representatives utilized the risk assessment tool, for most producers, risk of antibiotic residue decreased by approximately 19%. In particular, more farms kept written records or more complete records. Finally, producers with reported histories of antibiotic residues were less likely to implement management changes to reduce the risk of antibiotic residue.

Animal Husbandry↗
PubMed1996

Anti-CD40 ligand antibody treatment prevents the development of lupus-like nephritis in a subset of New Zealand black x New Zealand white mice. Response correlates with the absence of an anti-antibody response.

Systemic lupus erythematosus is characterized by B cell production of pathogenic autoantibodies dependent upon cooperation from CD4+ Th cells. The interaction between CD40 on B cells and CD40 ligand (CD40L) on Th cells is necessary for normal thymus-dependent Ab production. An anti-murine CD40L mAb blocks binding of CD40L to CD40 and prevents primary and secondary immune responses to thymus-dependent Ags. In this study, New Zealand Black x New Zealand White lupus-prone mice treated with this anti-CD40L Ab from ages 4 to 10 mo had reduced anti-DNA autoantibody production and renal disease and significantly prolonged survival compared with control mice. Pathologic examination verified the absence of significant renal damage or immune deposition in responding mice. Mice that responded to treatment did not develop an Ab response to the administered Ab. Long-term survivors mounted a substantial Ab response to keyhole limpet hemocyanin after completion of anti-CD40L Ab treatment, suggesting that some of the immunosuppressive effects of the Ab may be reversible. These results suggest a human form of this Ab may have therapeutic utility in human systemic lupus erythematosus.

Animals↗
PubMed1996

Differential basal protein tyrosine phosphorylation in natural killer (NK) and T cells: a biochemical correlate of lymphoid functional activity.

Despite the similarities between natural killer (NK) and T cells, these lymphocytes have dramatically different functional phenotypes. To identify potential biochemical parameters that correlate with the "primed" NK phenotype, we have investigated protein tyrosine phosphorylation in NK and T cells. Examination of tyrosyl phosphorylation in NK cells showed that they have higher levels of phosphorylation than resting T cells. Consistent with this, the concentrations of the tyrosine kinase inhibitor, herbimycin A, required to inhibit FcR-mediated Ca2+ flux in NK cells were much higher than those required for inhibition of T cell receptor-mediated Ca2+ mobilization. Differences in phosphorylation were not due to purification artifact lymphocyte src-family kinase, p56lck or the protein tyrosine phosphatase CD45. Thus, we have identified high basal tyrosyl phosphorylation as a striking biochemical feature of NK cells that correlates with the unique functions of this subset.

CD4-Positive T-Lymphocytes↗
PubMed1996

Residues in the RNP1-like sequence motif of Rho protein are involved in RNA-binding affinity and discrimination.

The termination of transcription in Escherichia coli by action of Rho factor is dependent on the ability of this homohexameric protein to make productive interactions with the nascent RNA molecule to be terminated. The roles of two residues in a phylogenetically conserved sequence motif in the RNA-binding domain of Rho, Asp60 and Phe62, were analyzed by studies of the biochemical properties of pure mutant proteins. F62S Rho had greatly reduced affinity for lambda cro RNA, very poor ability to terminate transcription in vitro by itself and only partial termination activity (at a level consistent with its in vivo defect) in the presence of NusG. D60G Rho had a high affinity for lambda cro RNA but a much lower ability to discriminate against RNA molecules lacking cis-acting Rho-utilization sequences, and a reduced efficiency of termination that was not improved by NusG. These results indicate a major role for Phe62 in stabilizing the binding of Rho to RNA through hydrophobic interactions, while Asp60 provides an electrostatic repulsive force that allows a rapid dissociation of non-productive complexes with RNA.

Adenosine Triphosphatases↗
PubMed1996

Anticonvulsant activity of novel derivatives of 2- and 3-piperidinecarboxylic acid in mice and rats.

The relative ability of derivatives of 2-piperidinecarboxylic acid (2-PC; pipecolic acid) and 3-piperidinecarboxylic acid (3-PC; nipecotic acid) to block maximal electroshock (MES)-induced seizures, elevate the threshold for electroshock-induced seizures and be neurotoxic in mice was investigated. Protective index (PI) values, based on the MES test and rotorod performance, ranged from 1.3 to 4.5 for 2-PC benzylamides and from < 1 to > 7.2 for 3-PC derivatives. PI values based on elevation of threshold for electroshock-induced seizures and rotorod performance ranged from > 1.6 to > 20 for both types of derivatives. Since preliminary data indicated that benzylamide derivatives of 2-PC displace [3H]1-[1-(2-thienyl)-cyclohexyl]piperidine (TCP) binding to the phencyclidine (PCP) site of the N-methyl-D-aspartate (NMDA) receptor in the micromolar range and such low affinity uncompetitive antagonists of the NMDA receptor-associated ionophore have been shown to be effective anticonvulsants with low neurological toxicity, the 2-PC derivatives were evaluated in rat brain homogenates for binding affinity to the PCP site. Although all compounds inhibited [3H]TCP binding, a clear correlation between pharmacological activity and binding affinity was not apparent. Select compounds demonstrated minimal ability to protect against pentylenetetrazol-, 4-aminopyridine- and NMDA-induced seizures in mice. Corneal and amygdala kindled rats exhibited different sensitivities to both valproic acid and the nonsubstituted 2-PC benzylamide, suggesting a difference in these two models. Enantiomers of the alpha-methyl substituted benzylamide of 2-PC showed some ability to reduce seizure severity in amygdala kindled rats.

4-Aminopyridine↗
PubMed1996

Changes in glucose and lipid metabolism following weight loss produced by a very low calorie diet in obese subjects.

OBJECTIVE: To study the effects of a very low calorie diet (VLCD) on glucose and lipid metabolism in obese subjects, in particular, the effects on insulin sensitivity and the activities of the key enzymes of glucose disposal, glycogen synthase (GS) and the pyruvate dehydrogenase complex (PDHC). DESIGN: Clinical dietary intervention study (1.67 MJ (400 kcal)/day) until weight loss of > 10%. SUBJECTS: 11 (seven male, four female) non-diabetic, obese subjects (age: 27-62 y; BMI: 40.5 +/- 1.4 kg/m2). MEASUREMENTS: Whole body glucose disposal (by euglycemic hyperinsulinemic clamp), respiratory quotient (RQ), resting energy expenditure (REE), glucose and lipid oxidation (by indirect calorimetry), insulin-stimulated PDHC and GS activity (in muscle biopsies) both before and immediately after VLCD (i.e. while still in a hypocaloric state), serum hormone and metabolite levels throughout the dietary period. RESULTS: Weight loss was accompanied by reduced insulin and elevated NEFA levels, improved insulin sensitivity due to increased nonoxidative glycolysis with no increase in PDHC or GS activities. The rate of weight loss was inversely related to the initial RQ. PDHCa was strongly age-related. CONCLUSION: A low RQ may be used as a predictor of the efficacy of VLCD treatment and that while VLCD improves nonoxidative glycolytic flux, changes in oxidative glucose disposal and muscle glucose storage are prevented by high NEFA availability during this catabolic phase of dietary intervention.

Adult↗
PubMed1995

NusG is required to overcome a kinetic limitation to Rho function at an intragenic terminator.

Rho-dependent transcription termination at certain terminators in Escherichia coli also depends on the presence of NusG [Sullivan, S. L. & Gottesman, M. E. (1992) Cell 68, 989-994]. We have found that termination at the first intragenic terminator in lacZ (tiZ1) is strongly dependent on NusG when transcription is done in vitro with the concentrations of NTPs found in vivo. With a lower level of NTPs, and consequently a slower rate of RNA-chain growth, Rho causes some termination by itself that is enhanced with NusG. These results suggest that NusG serves to overcome a kinetic limitation of Rho to function at certain terminators. At a second intragenic terminator within the lacZ reading frame (tiZ2) the efficiency of Rho-mediated termination was unaffected by either NusG or by RNA polymerase elongation kinetics. Thus, using purified components and intracellular levels of NTPs, we have confirmed the in vivo finding that certain Rho-dependent terminators also depend on NusG, whereas others do not.

Bacterial Proteins↗
PubMed1995

p53-dependent growth arrest of REF52 cells containing newly amplified DNA.

The rat cell line REF52 is not permissive for gene amplification. Simian virus 40 tumor (T) antigen converts these cells to a permissive state, as do dominant negative mutants of p53, suggesting that the effect of T antigen is due mainly to its ability to bind to p53. To manipulate permissivity, we introduced a temperature-sensitive mutant of T antigen (tsA58) into REF52 cells and selected for resistance to N-(phosphonacetyl)-L-aspartate (PALA). Most freshly isolated PALA-resistant colonies, each of approximately 200 cells, selected at a permissive temperature, arrested when shifted to a nonpermissive temperature. Growth arrest was stable, with no evidence of apoptosis, as long as T antigen was absent but was reversed when T antigen was restored. In contrast, PALA-resistant clones grown to approximately 10(7) cells at a permissive temperature did not arrest when shifted to a nonpermissive temperature. All PALA-resistant clones examined had amplified carbamoyl-phosphate synthetase-aspartate transcarbamoylase-dihydroorotase (CAD) genes, present in structures consistent with a mechanism involving bridge-breakage-fusion (BBF) cycles. We propose that p53-mediated growth arrest operates only early during the complex process of gene amplification, when newly formed PALA-resistant cells contain broken DNA, generated in BBF cycles. During propagation under permissive conditions, the broken DNA ends are healed, and, even though the p53-mediated pathway is still intact at a nonpermissive temperature and the cells contain amplified DNA, they are not arrested in the absence of broken DNA. The data support the hypothesis that BBF cycles are an important mechanism of amplification and that the broken DNA generated in each cycle is a key signal that regulates permissivity for gene amplification.

Animals↗
PubMed1995

Glutamate receptor RNA editing in vitro by enzymatic conversion of adenosine to inosine.

RNA encoding the B subunit of the alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) subtype of ionotropic glutamate receptor (GluR-B) undergoes a posttranscriptional modification in which a genomically encoded adenosine is represented as a guanosine in the GluR-B complementary DNA. In vitro editing of GluR-B RNA transcripts with HeLa cell nuclear extracts was found to result from an activity that converts adenosine to inosine in regions of double-stranded RNA by enzymatic base modification. This activity is consistent with that of a double-stranded RNA-specific adenosine deaminase previously described in Xenopus oocytes and widely distributed in mammalian tissues.

Adenosine↗
PubMed1995

ECT for OCD.

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Comorbidity↗
PubMed1994

CD45 regulation of tyrosine phosphorylation and enzyme activity of src family kinases.

Previous analyses have suggested that the CD45 tyrosine phosphatase activates src family tyrosine kinases p56lck and p59fyn by dephosphorylating regulatory COOH-terminal residues. We have examined the status of p56lck and p59fyn in murine and human CD45- T cell lines. Surprisingly, despite the fact that p56lck and p59fyn were spontaneously hyperphosphorylated, the tyrosine kinase activity of both enzymes was increased in CD45- versus CD45+ cells. In vitro exposure of hyperphosphorylated p56lck to CD45 decreased enzyme activity to near-basal levels. Lck from CD45- cells was hyperphosphorylated on the cyanogen bromide digestion fragment that contains the negative regulatory residue Tyr-505, and the identity of this site of phosphorylation was confirmed by trypsin digestion followed by high performance liquid chromatography. Loss of CD45 results, therefore, in a paradoxical hyperphosphorylation of the COOH-terminal tyrosine and increased src family kinase enzymatic activity.

Amino Acid Sequence↗