D Assefa

Publications (6)16.17 Total impact

• Source

  Available from: Sven Gudmund Hinderaker

  Article: Intensified tuberculosis case finding among people living with the human immunodeficiency virus in a hospital clinic in Ethiopia.

  D Assefa, Z Melaku, T Gadissa, A Negash, S G Hinderaker, A D Harries
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  ABSTRACT: Intensified tuberculosis case finding (ICF) is used in people living with the human immunodeficiency virus (PLHIV) to reduce the burden of tuberculosis (TB). We conducted a retrospective study in 300 PLHIV attending an HIV care clinic in Ethiopia to assess ICF performance during a 12-month period. Between 80% and 95% of patients were screened for TB at enrolment and at each 3-month follow-up visit. Thirty-four (11%) patients were diagnosed with TB, of whom 27 (79%) were identified in the first 6 months. This study assessed serial ICF in routine settings, showing that TB screening had its largest diagnostic yield in the first 6 months.
  The international journal of tuberculosis and lung disease: the official journal of the International Union against Tuberculosis and Lung Disease 03/2011; 15(3):411-3. · 2.73 Impact Factor
• Article: The lack of gonadotrophin-releasing hormone (GnRH) receptor desensitisation in alphaT3-1 cells is not due to GnRH receptor reserve or phosphatidylinositol 4,5-bis-phosphate pool size.

  W Forrest-Owen, G B Willars, S R Nahorski, D Assefa, J S Davidson, J Hislop, C A McArdle
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  ABSTRACT: The phospholipase C (PLC)-activating gonadotrophin-releasing hormone (GnRH) receptor is thought not to rapidly desensitise in alphaT3-1 cells. This extremely unusual characteristic raises the concern that it might be a feature of the cell type, rather than the receptor per se. Here we have used video imaging to establish whether the effects of endogenous PLC-activating G-protein coupled receptors (GPCRs) on Ca2+ ion concentration [Ca2+]i desensitise in these cells. Oxytocin, endothelin-1, methacholine, and UTP all caused [Ca2+]i increases which underwent rapid homologous desensitisation in that they were transient and responses to repeat stimuli were attenuated whereas subsequent responses to GnRH were not. To test whether receptor reserve obscures functional desensitisation of GnRH receptors, a photoaffinity antagonist (Pant-1), was used to effect a partial and irreversible receptor blockade. UV crosslinking in medium with 1000 nM Pant-1 reduced GnRH receptor number to 20 +/- 5% and reduced maximal buserelin-stimulated [3H]IP(X) accumulation to 57 +/- 5%, demonstrating removal of receptor reserve. In control alphaT3-1 cells the initial rate of GnRH-stimulated [3H]IP(X) accumulation was maintained for at least 5 min and GnRH caused a sustained increase in Ins(1,4,5)P3 mass (confirming the resistance of GnRH receptors to desensitisation) and Pant-1 pre-treatment reduced the magnitude of these responses without altering their temporal profiles. In alphaT3-1 cells stably transfected with recombinant human muscarinic receptors (alphaT3-1/M3), responses to methacholine were characteristic of desensitising GPCRs (transient Ins(1,4,5)P3 and curvilinear [3H]IP(X) responses) and were unaltered by Pant-1. To test the relevance of phospholipid pool size, alphaT3-1/M3 cells were pre-treated with GnRH or methacholine in medium with LiCl (to deplete PtdIns(4,5)P2 pools). These pre-treatments reduced subsequent responses to methacholine and GnRH comparably, indicating access to a shared PtdIns(4,5)P2 pool. Partial depletion of this pool (GnRH pre-treatment in medium with LiCl) reduced the magnitude of the [3H]IP(X) and Ins(1,4,5)P3 responses to methacholine and GnRH, without altering their temporal profiles. Thus the GnRH receptor does not undergo rapid homologous desensitisation in alphaT3-1 cells in spite of the fact that they can desensitise other endogenous (and recombinant) PLC-activating GPCRs, and the lack of desensitisation cannot be attributed to the existence of GnRH receptor reserve or access to an atypically large or rapidly re-cycled PtdIns(4,5)P2 pool. This unique functional characteristic (mammalian GnRH receptors are the only PLC-activating GPCRs known not to rapidly desensitise) almost certainly therefore reflects the atypical structure of these receptors (mammalian GnRH receptors are the only PLC-activating GPCRs known to lack C-terminal tails).
  Molecular and Cellular Endocrinology 02/1999; 147(1-2):161-73. · 4.19 Impact Factor
• Article: Irreversible activation of the gonadotropin-releasing hormone receptor by photoaffinity cross-linking: localization of attachment site to Cys residue in N-terminal segment.

  J S Davidson, D Assefa, A Pawson, P Davies, J Hapgood, I Becker, C Flanagan, R Roeske, R Millar
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  ABSTRACT: Photoaffinity cross-linking with [azidobenzoyl-d-Lys6]GnRH leads to irreversible activation of the gonadotropin-releasing hormone (GnRH) receptor. In order to localize the cross-linking site, the disulfide bridge structure was initially probed by mutagenesis. A consistent pattern of changes in the ability of GnRH to stimulate signal transduction after Ser substitutions of extracellularly located Cys residues indicated that Cys14 in the N-terminal domain is connected to Cys200 in the second extracellular loop, while Cys196 in this loop is connected to the highly conserved Cys114 at the extracellular end of transmembrane helix 3. Protein chemical analysis of radioactive fragments of cross-linked GnRH receptor following deglycosylation and enzymatic digest with endoproteinase Glu-C and trypsin before and after introduction or elimination of potential protease cleavage sites indicated that 125I[azidobenzoyl-d-Lys6]GnRH cross-links to a segment comprising residues 12-18 of the N-terminal domain. The existence of the Cys114-Cys196 bridge was directly confirmed as a labeled fragment, including that Cys114 was resolvable only under reducing conditions. The observation that the cross-linked N-terminal enzymatic fragments had identical apparent size under non-reducing conditions shows that the cross-linking reaction disconnected the disulfide bridge between Cys14 and Cys200 and indicates that Cys14 is probably the residue involved in cross-linking of the ligand. It is concluded that covalent tethering of GnRH through a photoreactive side chain located at position 6 in the middle of the peptide leads to continued activation of the receptor presumably through covalent binding to Cys14 in the N-terminal domain of the receptor.
  Biochemistry 11/1997; 36(42):12881-9. · 3.42 Impact Factor
• Article: Protein kinase activities in Leishmania aethiopica: control by growth, transformation and inhibitors.

  D Assefa, Y Worku, G Skoglund
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  ABSTRACT: Promastigotes of L. aethiopica express an ectokinase activity preferring histone V-S as substrate. A soluble kinase activity utilizing protamine and histone V-S, as well as a particulate fraction associated kinase activity preferring protamine are also expressed. The soluble histone kinase activity, but not the ectokinase, was expressed at a higher level in cells from late phases of growth, as compared to early log phase cultures. Transformation of L. aethiopica to an amastigote-like stage, resulted in almost complete loss of the kinase activities, with retained viability of the cells. Formycin-ATP only weakly inhibited the kinases while effectively inhibiting cell growth and thymidine incorporation. Staurosporin efficiently blocked the kinase activities and cell growth without affecting thymidine incorporation.
  Biochimica et Biophysica Acta 05/1995; 1270(2-3):157-62. · 4.66 Impact Factor
• Article: Septic cavernous sinus thrombosis following infection of ethmoidal and maxillary sinuses: a case report.

  D Assefa, E Dalitz, W Handrick, R Lietz, W Braun, H Michalski
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  ABSTRACT: A 10-year-old boy with a unilateral septic cavernous sinus thrombosis complicating infection of the ethmoidal and maxillary sinuses is described. The causative agents identified were Eikenella corrodens and Staphylococcus aureus. The disease was cured without any sequelae.
  International Journal of Pediatric Otorhinolaryngology 07/1994; 29(3):249-55. · 1.17 Impact Factor
• Article: The lack of gonadotrophin-releasing hormone (GnRH) receptor desensitisation in αT3-1 cells is not due to GnRH receptor reserve or phosphatidylinositol 4,5-bis-phosphate pool size

  W. Forrest-Owen, G.B. Willars, S.R. Nahorski, D. Assefa, J.S. Davidson, J. Hislop, C.A. McArdle
  [show abstract] [hide abstract]
  ABSTRACT: The phospholipase C (PLC)-activating gonadotrophin-releasing hormone (GnRH) receptor is thought not to rapidly desensitise in αT3-1 cells. This extremely unusual characteristic raises the concern that it might be a feature of the cell type, rather than the receptor per se. Here we have used video imaging to establish whether the effects of endogenous PLC-activating G-protein coupled receptors (GPCRs) on Ca2+ ion concentration [Ca2+]i desensitise in these cells. Oxytocin, endothelin-1, methacholine, and UTP all caused [Ca2+]i increases which underwent rapid homologous desensitisation in that they were transient and responses to repeat stimuli were attenuated whereas subsequent responses to GnRH were not. To test whether receptor reserve obscures functional desensitisation of GnRH receptors, a photoaffinity antagonist (Pant-1), was used to effect a partial and irreversible receptor blockade. UV crosslinking in medium with 1000 nM Pant-1 reduced GnRH receptor number to 20±5% and reduced maximal buserelin-stimulated [3H]IPX accumulation to 57±5%, demonstrating removal of receptor reserve. In control αT3-1 cells the initial rate of GnRH-stimulated [3H]IPX accumulation was maintained for at least 5 min and GnRH caused a sustained increase in Ins(1,4,5)P3 mass (confirming the resistance of GnRH receptors to desensitisation) and Pant-1 pre-treatment reduced the magnitude of these responses without altering their temporal profiles. In αT3-1 cells stably transfected with recombinant human muscarinic receptors (αT3-1/M3), responses to methacholine were characteristic of desensitising GPCRs (transient Ins(1,4,5)P3 and curvilinear [3H]IPX responses) and were unaltered by Pant-1. To test the relevance of phospholipid pool size, αT3-1/M3 cells were pre-treated with GnRH or methacholine in medium with LiCl (to deplete PtdIns(4,5)P2 pools). These pre-treatments reduced subsequent responses to methacholine and GnRH comparably, indicating access to a shared PtdIns(4,5)P2 pool. Partial depletion of this pool (GnRH pre-treatment in medium with LiCl) reduced the magnitude of the [3H]IPX and Ins(1,4,5)P3 responses to methacholine and GnRH, without altering their temporal profiles. Thus the GnRH receptor does not undergo rapid homologous desensitisation in αT3-1 cells in spite of the fact that they can desensitise other endogenous (and recombinant) PLC-activating GPCRs, and the lack of desensitisation cannot be attributed to the existence of GnRH receptor reserve or access to an atypically large or rapidly re-cycled PtdIns(4,5)P2 pool. This unique functional characteristic (mammalian GnRH receptors are the only PLC-activating GPCRs known not to rapidly desensitise) almost certainly therefore reflects the atypical structure of these receptors (mammalian GnRH receptors are the only PLC-activating GPCRs known to lack C-terminal tails).
  Molecular and Cellular Endocrinology.