title: Thrombopoietin and its receptor, c-mpl, are constitutively expressed by mouse liver endothelial cells: evidence of thrombopoietin as a growth factor for liver endothelial cells.
abstract: Present data suggest that the primary site of thrombopoietin (TPO) mRNA is the liver. Previously, we reported that specific murine liver endothelial cells (LEC-1) located in the hepatic sinusoids support in vitro megakaryocytopoiesis from murine hematopoietic stem cells suggesting that these cells may be a source of TPO. We report here that TPO and its receptor, c-mpl, are coexpressed on cloned LEC-1. Enzyme-linked immunosorbent assay (ELISA), biological assay, and flow cytometry studies confirmed the expression of both TPO and its receptor, respectively, at the protein level. TPO activity was enhanced in supernatants from LEC-1 treated with tumor necrosis factor (TNF)-alpha and gamma-interferon (INF). Our results show that TPO through its receptor stimulated the growth of LEC-1 in vitro. These observations establish LEC-1 as a novel source of TPO in the liver. To our knowledge, this is the first report that liver endothelial cells express both TPO and its receptor, c-mpl, and our findings indicate that this cytokine constitutes a growth factor for liver endothelial cells in vitro.
authors.affiliation: Pharmacology and Toxicology Laboratory, Hipple Cancer Research Center, Dayton, OH 45439-2092, USA.
authors.forename: J E
authors.initials: JE
authors.lastname: Cardier
authors.forename: J
authors.initials: J
authors.lastname: Dempsey
mesh_terms: D000818:Animals; D002455:Cell Division; D002478:Cells, Cultured; D017077:Culture Media, Conditioned; D004727:Endothelium / Q000737:chemistry / Q000166:cytology / Q000378:metabolism; D004797:Enzyme-Linked Immunosorbent Assay; D005434:Flow Cytometry; D015870:Gene Expression; D006133:Growth Substances; D007371:Interferon-gamma / Q000494:pharmacology; D008099:Liver / Q000166:cytology / Q000378:metabolism*; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D009363:Neoplasm Proteins; D016133:Polymerase Chain Reaction; D011518:Proto-Oncogene Proteins / Q000032:analysis / Q000235:genetics*; D012333:RNA, Messenger / Q000032:analysis; D018121:Receptors, Cytokine; D053628:Receptors, Thrombopoietin; D013926:Thrombopoietin / Q000235:genetics* / Q000494:pharmacology / Q000502:physiology; D014409:Tumor Necrosis Factor-alpha / Q000494:pharmacology
chemical_list: D017077:Culture Media, Conditioned; D006133:Growth Substances; D009363:Neoplasm Proteins; D011518:Proto-Oncogene Proteins; D012333:RNA, Messenger; D018121:Receptors, Cytokine; D053628:Receptors, Thrombopoietin; D014409:Tumor Necrosis Factor-alpha; C082218:MPL protein, human; D007371:Interferon-gamma; D013926:Thrombopoietin