Activation of the transcription factor NF-kappaB by the erythropoietin receptor: structural requirements and biological significance.
The transcription factor nuclear factor kappa B (NF-kappaB) has been implicated in the regulation of genes mainly involved in inflammation and immune response. We analysed the role of NF-kappaB in signalling pathways induced by the hematopoietic growth factor erythropoietin (EPO). Our data, obtained by electrophoretic mobility shift assays (EMSA) and reporter gene assays, show that the intracellular domain of the EPO receptor (EPOR) transmits signals leading to the activation of NF-kappaB. Studies employing an inhibitor specific for the EPOR-associated tyrosine kinase JAK2 suggest that JAK2-dependent pathways are not involved. The induction of an NF-kappaB-triggered reporter gene construct was inhibited by cotransfection of dominant negative forms of the src kinase Lyn, but not by dominant negative JAK2. Using epidermal growth factor (EGF)/EPOR hybrids containing mutant forms of the EPOR intracellular domain, we were able to further define the critical structures for the induction of NF-kappaB. The data show that although the activity of JAK2 seems to be dispensable, its association to the receptor, as well as the phosphorylation of membrane proximal tyrosine residues, are essential. Furthermore, the functional analysis of different receptor forms revealed a correlation of the abilities to induce NF-kappaB activity and to generate antiapoptotic signals.
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Institute of Medical Biochemistry and Molecular Biology, Medical Faculty, University of Rostock, Schillingallee 70, PF100888, 18055 Rostock, Germany. thomas.bittorf@med.uni-rostock.de
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Jaster
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Brock
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D000818:Animals; D017209:Apoptosis; D002460:Cell Line; D004742:Enhancer Elements, Genetic; D004791:Enzyme Inhibitors / Q000494:pharmacology; D004921:Erythropoietin / Q000494:pharmacology; D017930:Genes, Reporter; D053614:Janus Kinase 2; D051379:Mice; D009154:Mutation; D016328:NF-kappa B / Q000378:metabolism*; D019000:Phosphotyrosine / Q000502:physiology; D017434:Protein Structure, Tertiary; D011505:Protein-Tyrosine Kinases / Q000037:antagonists & inhibitors / Q000235:genetics; D011518:Proto-Oncogene Proteins; D017467:Receptors, Erythropoietin / Q000737:chemistry* / Q000235:genetics / Q000502:physiology*; D015398:Signal Transduction; D020032:Tyrphostins / Q000494:pharmacology; D019061:src-Family Kinases / Q000235:genetics
D004791:Enzyme Inhibitors; D016328:NF-kappa B; D011518:Proto-Oncogene Proteins; D017467:Receptors, Erythropoietin; D020032:Tyrphostins; C095512:alpha-cyano-(3,4-dihydroxy)-N-benzylcinnamide; D004921:Erythropoietin; D019000:Phosphotyrosine; D011505:Protein-Tyrosine Kinases; C507926:Jak2 protein, mouse; D053614:Janus Kinase 2; C060902:lyn protein-tyrosine kinase; D019061:src-Family Kinases