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Biomedical subjects

R J O'Connor

Publications and source records attributed to R J O'Connor.

At least 19 recordsLinked to original sources
PubMed1994

Mutually exclusive interaction of the adenovirus E4-6/7 protein and the retinoblastoma gene product with internal domains of E2F-1 and DP-1.

The binding of E2F to the adenovirus (Ad) E2a promoter is stimulated by the Ad E4-6/7 protein. E2F DNA binding activity is composed of a heterodimer of related but distinct proteins of the E2F-1 and DP-1 families. The E4-6/7 protein induces the cooperative and stable binding of E2F to an inverted repeat binding site in the E2a promoter apparently by providing a dimerization interface to two adjacent E2F heterodimers. The product of the retinoblastoma gene product (Rb) represses the transcriptional activity of E2F by direct protein-protein interaction. In this report, we have examined the regions of E2F-1 and DP-1 that are required for the induction of cooperative E2F binding to the E2a promoter by the E4-6/7 protein. Our results demonstrate that an internal segment of E2F-1, that is conserved among members of the E2F family, is required for functional interaction with the E4-6/7 product. Consistent with this observation, other members of the E2F family (E2F-2 and E2F-3) productively interact with E4-6/7. DP-1 also is necessary for stable interaction with E4-6/7 and an internal segment of DP-1 is required that is positioned in a location similar to that of the conserved E2F-1 domain. Interestingly, the binding of E4-6/7 and the binding of Rb to E2F are mutually exclusive, and our results show that the same internal segments of E2F-1 and DP-1 that are required for E4-6/7 binding are also required for stable interaction with Rb. These results suggest that the Ad E4-6/7 protein mimics Rb in part for the protein interaction requirements for E2F binding, although with different functional consequences. While Rb binding represses E2F activity, the E4-6/7 protein stimulates transactivation of the Ad E2a promoter.

Adenoviridae↗
PubMed1994

The adenovirus E4-6/7 protein transactivates the E2 promoter by inducing dimerization of a heteromeric E2F complex.

Binding of the mammalian transcription factor E2F to the adenovirus E2a early promoter is modulated through interaction with the viral E4-6/7 protein. E4-6/7 induces the cooperative and stable binding of E2F in vitro to two correctly spaced and inverted E2F binding sites in the E2a promoter (E2F induction) by physical interaction in the protein-DNA complex. The E2a promoter is transactivated in vivo by the E4-6/7 product. The C-terminal 70 amino acids of E4-6/7 are necessary and sufficient for induction of E2F binding and for transactivation. To assess the mechanism(s) of E2a transactivation and the induction of cooperative E2F binding by the E4-6/7 protein, we have analyzed a series of point mutants in the functional C-terminal domain of E4-6/7. Two distinct segments of E4-6/7 are required for interaction with E2F. Additionally, and E4-6/7 mutant with a phenylalanine-to-proline substitution at amino acid 125 (F-125-P) efficiently interacts with E2F but does not induce E2F binding to the E2a promoter and is defective for transactivation. Induction of E2F stable complex formation at the E2a promoter by the F-125-P mutant protein is restored by divalent E4-6/7-specific monoclonal antibodies, but not a monovalent Fab fragment, or by appending a heterologous dimerization domain to the N terminus of the mutant protein. These and other data support the involvement of E4-6/7 dimerization in the induction of cooperative and stable E2F binding and transactivation of the E2a promoter. We present evidence that at least two cellular components are involved in E2F DNA binding activity and that both are required for E2F induction by the E4-6/7 product. The recently cloned E2F-related activities E2F-1 and DP-1 individually bind to an E2F binding site weakly, but when combined generate an activity that is indistinguishable from endogenous cellular E2F. Recombinant E2F-1, DP-1, and E4-6/7 are sufficient to form the induced E2F complex at the E2a promoter.

Adenovirus E2 Proteins↗
PubMed1992

Regeneration of functional hemoglobin from iron(III) hemoglobin by reduction with hydrogen and a heterogeneous catalyst.

Functional hemoglobin was regenerated from partially autoxidized hemoglobin by reduction with molecular hydrogen in the presence of a heterogeneous catalyst consisting of elemental platinum embedded in an electroactive polymer. The visible spectrum of the regenerated hemoglobin was identical to that of native iron(II) hemoglobin. The regenerated hemoglobin displayed highly cooperative oxygen-binding characteristics. P50 values for oxidized-regenerated hemoglobin samples were not different from native hemoglobin. The Hill coefficients for regenerated hemoglobin were slightly lower than the controls, possibly because of small amounts of irreversibly oxidized hemoglobin arising during the initial autoxidation. The advantages of the reduction system include: (1) the heterogeneous catalyst avoids the problem of protein adsorption onto bare platinum, (2) catalyst and reducing agent are easily removed from the protein, and (3) the by-product H+ is buffered easily.

Buffers↗
PubMed1991

The C-terminal 70 amino acids of the adenovirus E4-ORF6/7 protein are essential and sufficient for E2F complex formation.

E2F is a cellular transcription factor that binds to the adenovirus (Ad) E1A enhancer and E2aE promoter regions, to the cellular c-myc P2 and dihydrofolate reductase promoters, and to other viral and cellular regulatory regions. The binding activity of E2F to the Ad E2aE promoter is dramatically increased during an adenovirus infection (termed E2F induction). E2F induction is dependent on the expression of the 150 amino acid E4-ORF6/7 protein which forms a direct, physical complex with E2F to mediate the cooperative and stable binding of E2F to inverted sites in the E2aE promoter. Using in vitro DNA binding assays to measure the formation of the infection-specific complexes, we have defined the minimal domain of the E4-ORF6/7 protein, the C-terminal 70 amino acids, required to complex with E2F and stabilize its binding at the E2aE promoter. The ability of mutant E4-ORF6/7 proteins to form the stable E2F-E2aE promoter complex in vitro correlated well with their ability to trans-activate E2 transcription in vivo. These observations support a model in which the E4-ORF6/7 protein binds to E2F to induce the cooperative binding of two E2F molecules to the E2aE promoter thereby activating E2 transcription.

Adenovirus Early Proteins↗
PubMed1991

Substituent effects on the binding constants of arsenical-dithiol adducts.

Proton nuclear magnetic resonance spectroscopy (1H NMR) was used to determine the relative binding constants for several arsenical-dithiol adducts. The compounds investigated were 2,3-dimercaptopropanol (British anti-lewisite; BAL), 1,2-ethane dithiol (ET), and 1,2-propane dithiol (PDT). It was found that PDT has a significantly higher affinity than ET or BAL for phenyldichloroarsine (PDA) in methanol.

Arsenicals↗
PubMed1987

One-dimensional and two-dimensional nuclear magnetic resonance studies of the reaction of phenyldichloroarsine with glutathione.

14C-labeled phenyldichloroarsine (PDA) enters the red blood cell and forms a 1:2 adduct with intracellular glutathione. Upon gel filtration of the hemolysate, [14C]PDA was recovered with the glutathione-containing fractions. One-dimensional and two-dimensional nuclear magnetic resonance spectroscopy were used to confirm the structure of the adduct and elucidate its stereochemistry, stability, and reactivity.

Arsenicals↗
PubMed1987

Caval tumor thrombus complicating renal cell carcinoma: a surgical challenge.

The surgical challenge of resection of renal cell carcinoma with vena caval invasion may require close cooperation between the urologist and cardiovascular surgeon. From 1977 to 1986, 13 patients with renal cell carcinoma and tumor thrombus invading the inferior vena cava (IVC) underwent radical surgical resection. In three of 13 patients the thrombus extended into the heart (right atrium two patients and right ventricle one patient). The tumor originated in the right kidney in 10 patients and in the left kidney in three patients. There were 10 men and three women with a mean age of 64 years (range, 46 to 75 years). Surgical management included midline incision, seven, with median sternotomy, four, and thoracoabdominal, two. After exposure of the renal vessels and IVC, all patients underwent radical nephrectomy. Two patients had caval sleeve resection, one had a partial caval resection, and seven had a 1 cm caval cuff. Planned cardiopulmonary bypass was used in three patients. The tumor thrombus was extracted by simultaneous atrial and caval approaches. One patient underwent unplanned emergency cardiopulmonary bypass after intraoperative cardiac arrest caused by a large tumor embolus of the pulmonary artery. No operative deaths occurred. Postoperative morbidity was significant in five of 13 patients, caval thrombosis in one, lower limb swelling in two, renal failure in one, and pulmonary edema in one patient. Two patients required long-term anticoagulation therapy for confirmed pulmonary emboli within 1 month of surgery. These complications resolved. The follow-up period ranged from 7 to 64 months with a mean of 36 months. Two patients died of metastatic disease at 24 and 48 months after surgery. Three patients are alive with metastatic disease at 6 to 64 months while one patient had a solitary metastatic lesion removed from the frontal lobe 4 years after nephrectomy and has been disease free a subsequent 18 months. Eight of 11 patients are disease free at 7 to 64 months (four patients greater than 52 months). Our 83% survival rate at a mean follow-up of 36 months suggests that this group of patients should not be denied aggressive resection. Documentation of tumor source and caval extension are essential to plan operative procedures, including use of cardiopulmonary bypass.

Aged↗
PubMed1984

Prediction of improvement in ankle blood pressure following arterial bypass.

Percutaneous femoral artery pressures and lower extremity segmental Doppler-derived blood pressures in 116 lower extremities were analyzed to determine if postbypass ankle/brachial indices (ABIs) could be predicted based on preoperative pressures. Predicted ABIs were calculated by increasing the prebypass ABI by the same percentage that the extremity/brachial index at the distal end of the bypass would be increased, assuming a postbypass index of 1.0 at the distal graft. The correlation between predicted ABI and actual postbypass ABI was strong for aortofemoral bypass (r = 0.8735) and moderate for infrainguinal bypass (r = 0.5961), with 75% of the postinfrainguinal bypass ABIs being greater than predicted. Minimum postoperative increases in ABI can be predicted based on preoperative hemodynamic measurements, thus providing important information relative to choosing the appropriate level of revascularization in patients with multisegmental disease.

Ankle↗
PubMed1983

Persistent sciatic artery. Clinical aspects and operative management.

Abnormal persistent of the embryonic axial blood supply to the leg, the sciatic artery, is a rare but often clinically important condition. The sciatic artery may vary from a small collateral in the upper thigh to a very large vessel that is the leg's sole arterial blood supply. The abnormal artery is prone to aneurysmal dilatation and atherosclerotic occlusion, and different patterns of anatomic development in the sciatic and femoral artery systems pose significant diagnostic and therapeutic problems. Advances in preoperative hemodynamic assessment, arteriography, and vascular surgical technique have improved the results of management of persistent sciatic artery and its complications. The world literature has been reviewed, including one additional case, with emphasis on embryologic development, anatomic variations, and clinical presentation, as well as diagnosis, therapy, and results.

Adult↗
PubMed1982

Erythrocyte filterability, fragility, and membrane proteins in folic acid deficient guinea pigs.

The purpose of this study was to determine if erythrocytes from folic acid-deficient guinea pigs could be used as a model for the study of defects which have been reported in megaloblastic anemic patients. Reported defects include decreased deformability and abnormal membrane proteins. Red cell filterability was studied with polycarbonate sieves and cellulose filters. Membrane proteins were analyzed by polyacrylamide gel electrophoresis in sodium in sodium dodecyl sulfate. Severe folate deficiency in guinea pigs caused no change in erythrocyte filterability or membrane proteins. Thus, the defects which have been reported in human folic acid or vitamin B-12 deficiency are not present in all animals with the same nutrient deficiency. Folate deficiency, however, did cause guinea pig erythrocytes to be markedly less susceptible to hypotonic lysis than cells from control animals, a feature which is not characteristic of human megaloblastic anemia.

Animals↗
PubMed1982

Predictive value of distal perfusion pressure in the healing of amputation of the digits and the forefoot.

To evaluate the role of distal perfusion pressure in predicting the healing of 31 digit and forefoot amputations preoperative digital, transmetatarsal and ankle systolic pressures were retrospectively compared with the eventual results of amputation. A photoplethysmography transducer placed distal to an occluding cuff was used to measure digital and transmetatarsal level systolic blood pressure. Ankle pressures were measured with Doppler ultrasound. Twenty-six amputations healed initially, whereas, four required reamputation proximal to the ankle. There was no difference in mean ankle Doppler pressure between the healed and failed groups. Mean photoplethysmography derived transmetatarsal pressure was significantly higher in the healed group, 116 +/- 47 millimeters of mercury as compared with the failed group, 44 +/- 88 millimeters of mercury. The difference in mean photoplethysmography digital pressure in the healed and failed groups--75 +/- 36 and 4 +/- 9 millimeters of mercury, respectively--was highly significant, p less than 0.001. Failure of digit or forefoot amputation occurred in all limbs with photoplethysmography derived pressures of less than 20 millimeters of mercury. A transmetatarsal or digital photoplethysmography pressure of greater than 20 millimeters of mercury was associated with amputation healing in all instances. These data suggest that photoplethysmography distal perfusion pressures may be valid predictors of the healing potential of minor foot amputations for end stage ischemia.

Adult↗
PubMed1982

Utility of wide and narrow blood pressure cuffs in the hemodynamic assessment of aortoiliac occlusive disease.

One hundred lower extremities were evaluated by measurement of common femoral intra-arterial pressure and high-thigh Doppler-derived segmental pressures using wide and narrow blood pressure cuffs to assess the accuracy of high-thigh pressures in the evaluation of aortoiliac disease. Sixty-four extremities were also studied by arteriography. The results were analyzed using the common femoral intra-arterial pressure as the standard. The accuracy was poor for both the wide (52%) and narrow (73%) cuff techniques. No significant differences between the two techniques were evident in regard to the incidence of false positive (wide cuff, 75%; narrow cuff, 65%) and false negative (wide cuff, 3%; narrow cuff, 8%) tests. Superficial femoral artery disease was found to be responsible for all false positive tests using the narrow cuff technique (20 of 20) and all but one of the false positive tests using the wide cuff technique (34 of 35). These data indicate that segmental high-thigh pressures are useful primarily as a screening technique (low false negative rate) to exclude hemodynamically significant aortoiliac occlusive disease at rest.

Aortic Diseases↗
PubMed1979

Red cell membrane in hemolytic disease. Studies on variables affecting electrophoretic analysis.

Significant alterations in the spectrin: band 3 and band 4.1a: band 4.1b ratios and an occasional decrease in the peak height of band 4.2 with respect to band 4.1 were found in electrophoretic patterns of red cell membranes from patients with hereditary xerocytosis. Electrophoretic comparison of whole cell, cytoplasm and membrane polypeptides implied that atypical partitioning at hemolysis could account for some, but not all, of the alterations seen in membrane patterns of xerocytes. A decrease in band 4.2 peak height as well as a variation in the profile of band 3 were produced in controls by specific manipulations of the electrophoresis protocol. Metabolic depletion of normal cells produced the type of alterations in bands 3 and 4.1 found in xerocyte membranes, whereas Heinz body production, addition of calcium to the hemolysis buffer and incubation of membranes in detergent under conditions designed to promote proteolysis did not. The presence of a higher peak height of band 4.1b with respect to that of band 4.1a in membranes of patients with various other red cell disorders correlated with an increase in the percentage of reticulocytes in peripheral circulation. The appearance of both band 3 and 4.1 abnormalities in the patterns of control cells which had been enriched in young cells by density gradient centrifugation suggested that these alterations in hemolytic disease are related to the predominance of young cells in the population.

Adenosine Triphosphate↗