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Biomedical subjects

E Hoppe

Publications and source records attributed to E Hoppe.

At least 19 recordsLinked to original sources
PubMed2001

Truncated trkB.T1 is dominant negative inhibitor of trkB.TK+-mediated cell survival.

Truncated trkB.T1 (T1) neurotrophin receptor inhibits full-length trkB.TK+ (TK+) signaling. At least two possible mechanisms have been proposed for this action: T1 could trap the ligand or function as a dominant negative receptor. To differentiate between these possibilities we have studied survival of serum-deprived PC12-trkB cells stably expressing TK+. PC12-trkB cells were observed to display constitutive trkB kinase activity which leads to survival of a cell subpopulation in the absence of added brain-derived neurotrophic factor (BDNF) and serum. Exogenous BDNF significantly increased cell survival, and this increase was inhibited by BDNF neutralizing antibody. The antibody treatment had no effect on the constitutive TK+ activity. Transfected T1 completely inhibited survival by BDNF or constitutive trkB kinase activity in PC12-trkB cells similarly to tyrosine kinase inhibitor K252a. In addition, T1 coimmunoprecipitated with TK+ and inhibited its autophosphorylation by BDNF. These data suggest that truncated T1 inhibits TK+ signaling by dominant negative action.

Animals↗
PubMed2000

Down-regulation of the neurotrophin receptor TrkB following ligand binding. Evidence for an involvement of the proteasome and differential regulation of TrkA and TrkB.

This study examines the mechanisms by which the tyrosine kinase receptor TrkB is down-regulated following binding of brain-derived neurotrophic factor (BDNF). In primary cultures of cerebellar granule neurons, BDNF-induced reduction of TrkB receptors was largely prevented by the addition of specific proteasome inhibitors. HN10 cells, a neuronal cell line that can be readily transfected, also showed a marked down-regulation of cell surface TrkB following BDNF exposure. In addition, we observed that prolonged exposure to nerve growth factor of TrkA-transfected cells did not lead to the down-regulation seen with BDNF and TrkB. TrkA and TrkB chimeric molecules were therefore expressed in HN10 cells and tested for ligand-induced regulation. These experiments led to the conclusion that the motives responsible for down-regulation are contained in the cytoplasmic domain of TrkB, and a short sequence in the juxtamembrane domain of TrkB was identified that confers nerve growth factor-induced down-regulation when inserted into TrkA.

Animals↗
PubMed1999

Activated human T cells, B cells, and monocytes produce brain-derived neurotrophic factor in vitro and in inflammatory brain lesions: a neuroprotective role of inflammation?

Brain-derived neurotrophic factor (BDNF) has potent effects on neuronal survival and plasticity during development and after injury. In the nervous system, neurons are considered the major cellular source of BDNF. We demonstrate here that in addition, activated human T cells, B cells, and monocytes secrete bioactive BDNF in vitro. Notably, in T helper (Th)1- and Th2-type CD4(+) T cell lines specific for myelin autoantigens such as myelin basic protein or myelin oligodendrocyte glycoprotein, BDNF production is increased upon antigen stimulation. The BDNF secreted by immune cells is bioactive, as it supports neuronal survival in vitro. Using anti-BDNF monoclonal antibody and polyclonal antiserum, BDNF immunoreactivity is demonstrable in inflammatory infiltrates in the brain of patients with acute disseminated encephalitis and multiple sclerosis. The results raise the possibility that in the nervous system, inflammatory infiltrates have a neuroprotective effect, which may limit the success of nonselective immunotherapies.

Autoantigens↗
PubMed1999

Biochemical and functional interactions between the neurotrophin receptors trk and p75NTR.

Neurotrophins bind to two structurally unrelated receptors, the trk tyrosine kinases and the neurotrophin receptor p75(NTR). Ligand activation of these two types of receptor can lead to opposite actions, in particular the prevention or activation of programmed cell death. Many cells co-express trk receptors and p75(NTR), and we found that p75(NTR) was co-precipitated with trkA, trkB and trkC in cells transfected with both receptor types. Co-precipitation of p75(NTR) was not observed with the epidermal growth factor receptor. Experiments with deletion constructs of trkB (the most abundant trk receptor in the brain) and p75(NTR) revealed that both the extracellular and intracellular domains of trkB and p75(NTR) contribute to the interaction. Blocking autophosphorylation of trkB substantially reduced the interactions between p75(NTR) and trkB constructs containing the intracellular, but not the extracellular, domains. We also found that co-expression of p75(NTR) with trkB resulted in a clear increase in the specificity of trkB activation by brain-derived neurotrophic factor, compared with neurotrophin-3 and neurotrophin-4/5. These results indicate a close proximity of the two neurotrophin receptors within cell membranes, and suggest that the signalling pathways they initiate may interact soon after their activation.

Animals↗
PubMed1996

Protein kinase cross-talk: membrane targeting of the beta-adrenergic receptor kinase by protein kinase C.

The beta-adrenergic receptor kinase (betaARK) is the prototypical member of the family of cytosolic kinases that phosphorylate guanine nucleotide binding-protein-coupled receptors and thereby trigger uncoupling between receptors and guanine nucleotide binding proteins. Herein we show that this kinase is subject to phosphorylation and regulation by protein kinase C (PKC). In cell lines stably expressing alpha1B- adrenergic receptors, activation of these receptors by epinephrine resulted in an activation of cytosolic betaARK. Similar data were obtained in 293 cells transiently coexpressing alpha1B- adrenergic receptors and betaARK-1. Direct activation of PKC with phorbol esters in these cells caused not only an activation of cytosolic betaARK-1 but also a translocation of betaARK immunoreactivity from the cytosol to the membrane fraction. A PKC preparation purified from rat brain phospborylated purified recombinant betaARK-1 to a stoichiometry of 0.86 phosphate per betaARK-1. This phosphorylation resulted in an increased activity of betaARK-1 when membrane-bound rhodopsin served as its substrate but in no increase of its activity toward a soluble peptide substrate. The site of phosphorylation was mapped to the C terminus of betaARK-1. We conclude that PKC activates betaARK by enhancing its translocation to the plasma membrane.

Amino Acid Sequence↗
PubMed1996

Decreased skeletal muscle phosphotyrosine phosphatase (PTPase) activity towards insulin receptors in insulin-resistant Zucker rats measured by delayed Europium fluorescence.

In order to measure the phosphotyrosine phosphatase (PTPase) activity in small muscle biopsies, a sandwich-immunofluorescence assay was developed using the phosphorylated human insulin receptor as a substrate, a C-terminal insulin receptor antibody as catching antibody and Europium-labelled anti-phosphotyrosine as detecting antibody. Soluble and particulate muscle fractions were prepared from soleus muscle of obese, diabetic (fa/fa) Zucker rats and their lean littermates (Fa/-). In the soluble muscle fractions of the obese (fa/fa) rats PTPase activity was significantly reduced compared to control (Fa/-) rats (45.2 +/- 2.6% vs 61.3 +/- 4.7%, p < 0.02). This reduction was completely prevented by 24 days of metformin treatment which decreased plasma glucose and plasma insulin levels. In particulate muscle fractions, however, no difference in PTPase activity was found among any groups of rats examined. These results show that the alterations in soluble PTPase activity in the insulin-resistant, diabetic Zucker rat vary with the abnormality in glucose homeostasis.

Adenosine Triphosphate↗
PubMed1996

A year in the life: Southern California College of Optometry student experience in the Indian Health Service.

BACKGROUND: The Indian Health Service offers an excellent opportunity for health professions students to enhance their professional growth and knowledge. The Southern California College of Optometry began its relationship with the Indian Health Service in 1974. Today, SCCO has Memoranda of Understanding for clinical education of its students with nine of the 12 IHS area offices across the country. METHODS/RESULTS: In 1994-95, 37.6 percent of SCCO's graduating class received a portion of their senior year clinical training in externships with the Indian Health Service. A total of 15,834 patient encounters were logged by the students while they were at the IHS sites. Fifty different types of procedures were reported by the students, reflecting an extensive clinical experience. The types of patients seen and the complexity of the patient mix, varied across the different student externships. CONCLUSIONS: The Indian Health Service is truly a great resource for the education of our future doctors of optometry.

California↗
PubMed1995

Selective down-regulation of the insulin receptor signal by protein-tyrosine phosphatases alpha and epsilon.

Binding of insulin to its receptor (IR) causes rapid autophosphorylation with concomitant activation of its tyrosine kinase which transmits the signal by phosphorylating cellular substrates. The IR activity is controlled by protein-tyrosine phosphatases, but those directly involved in regulating the insulin receptor and its signaling pathways have not yet been identified. Using baby hamster kidney cells overexpressing the IR and a novel insulin-based selection principle, we established stable cell lines with functionally coupled expression of the IR and protein-tyrosine phosphatases. The two closely related protein-tyrosine phosphatases alpha and epsilon were identified as negative regulators of IR tyrosine kinase.

Animals↗
PubMed1994

Expression, purification and crystallization of human phosphotyrosine phosphatase 1B.

Protein phosphotyrosine phosphatases are believed to be involved in the regulation of the activity of cellular proteins, such as receptor tyrosine kinases, by controlling their phosphorylation status. One of the best described and characterized protein of this class of enzymes is the phosphotyrosine phosphatase 1B. To obtain sufficient quantities for structural investigations, truncated forms of PTP1B encompassing the catalytic domain were over-expressed in Escherichia coli and purified to apparent homogeneity by conventional chromatography. The activity of these purified enzymes has been compared with the wild-type enzyme expressed in mammalian cells. By measuring the activities against p-nitrophenyl phosphate, the pH dependence of this activity, and responses to different modulators, it could be demonstrated that the truncated forms of PTP1B retained the same characteristics as the full-length mammalian enzyme, but are not subject to inhibition of enzymic activity mediated by the C-terminus. Due to their improved solubility, it can be assumed that the catalytic domains are advantageous for crystallization studies in comparison to the natural enzyme. In a screening for crystallization conditions, we obtained protein crystals indicating that the quality of the purified protein is sufficient for crystallographic studies.

Base Sequence↗
PubMed1993

The effectivity of Fresnel prisms for visual field enhancement.

An objective method for placement of Fresnel prisms has been used to enhance constricted visual fields at the Eastern Blind Rehabilitation Center in West Haven, CT since 1975. To study the effectiveness of this method, 22 patients fitted with prisms since 1986 participated in a survey regarding their level of satisfaction with the prisms. Nineteen out of 22 patients continued to wear the prisms successfully, resulting in a retention rate of 86.3 percent. Of those still wearing the prisms, their reported overall satisfaction level averaged 3.63 on a scale of 1-4 (4 representing very satisfied). The reported satisfaction levels of the patients wearing the prisms were statistically analyzed with respect to pathology, months of wear, age of the patient, binocular versus monocular fitting, size of the residual field, visual acuity, the power of the prism used, and ocular rotation to enter the prism. No significant predictive value was found with any of these variables in trying to determine the level of satisfaction. However, this may be due to the small sample size. These same variables were used in comparing the patients who continued to wear the prisms with the patients who had discontinued prism use. None of these variables was found to be significant in predicting a successful outcome, possibly in part to small sample size, and the low number of unsuccessful patients. In an effort to make improvements on the existing methods being used for field enhancement, questions were asked regarding technical use of the prisms, mobility with the prisms, the spectacle carrier lens, and the maintenance of the prisms.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1992

Evaluating the laws defining blindness.

The law defining legal blindness was written in 1935, and has not been updated since. A historical view of the background in the development of this law and a comparison to laws used in other countries helps to point out some problems with the current definition. As the population gets older, the prevalence of visual impairment will be increasing. To administer programs, distribute funding, and ensure adequate care, the problems inherent in the definition of legal blindness must be addressed, and the law must be revised.

Blindness↗
PubMed1991

Modulation of A1 adenosine receptor function in rat brain by the polyamine, spermine.

Studies on factors modulating the binding of agonist ligands to A1 adenosine receptors in rat forebrain membranes revealed that the reduction of [3H]cyclohexyladenosine [( 3H]CHA) binding, observed after removing Mg2+ by pretreatment with ethylene-dinitrilo-tetraacetic acid (EDTA), was restored by the polyamine, spermine (1mM). Parallel electrophysiological experiments performed on rat hippocampal slices in Mg(2+)-free medium indicated that spermine also led to a recovery of the depressive effect of 1 microM adenosine on stimulus train-evoked neuronal Ca2+ influx. These observations suggest that the polyamine, spermine is, like Mg2+, able to control the physiological adenosine-mediated modulation of synaptic transmission by changing the affinity state of A1 receptors.

Adenosine↗
PubMed1988

RNA-protein cross-linking in Escherichia coli 50S ribosomal subunits; determination of sites on 23S RNA that are cross-linked to proteins L2, L4, L24 and L27 by treatment with 2-iminothiolane.

RNA-protein cross-links were introduced into E. coli 50S ribosomal subunits by treatment with 2-iminothiolane followed by mild ultraviolet irradiation. After partial digestion of the RNA, the cross-linked RNA-protein complexes were separated by our recently published three-step procedure. In cases where this separation was inadequate, a further purification step was introduced, involving affinity chromatography with antibodies to the ribosomal 50S proteins. Analysis of the isolated complexes enabled four new cross-link sites on the 23S RNA to be identified, as well as re-confirming several previously established sites. The new sites are as follows: Protein L2 is cross-linked within an oligonucleotide at positions 1818-1823 in the 23S RNA, protein L4 within positions 320-325, protein L24 within positions 99-107, and protein L27 within positions 2320-2323.

Base Sequence↗
PubMed1988

[Cytologic urine findings in female genital cancer--before, during and after radiotherapy].

74 cytologic examinations of the urinary sediment were conducted on 57 women with malignant neoplasms of the genital organs in order to evaluate the clinical suspicion of tumor infiltration of the bladder wall. It turned out to be a sensitive indicator of the infiltration of the bladder wall. Prior radiotherapy however let to changes which could be falsly interpreted as indicators of malignant infiltration. In order to enhance the accuracy of cytologic evaluation of the urinary sediment in this clinical setting it is essential that the cytologist must be informed about prior radiation therapy.

Epithelium↗