title: Functional erythropoietin receptor is undetectable in endothelial, cardiac, neuronal, and renal cells.
abstract: Erythropoiesis stimulating agents (ESAs) have been reported to activate erythropoietin receptors (EpoR) on cell types, including endothelial, neuronal, renal tubule, and cardiac cells. ESAs have also been reported to promote angiogenesis. However, those findings are controversial and confounded by methodologic issues. We show that EpoR mRNA was detected in essentially all cell types examined, including primary human endothelial, renal, cardiac, and neuronal cells but 10- to 100-fold lower than Epo-responsive cells using quantitative reverse-transcribed polymerase chain reaction. Total endothelial EpoR protein examined using a new monoclonal antibody was low to undetectable. Surface EpoR on endothelial cells was not detected using [(125)I]-rHuEpo surface-binding studies. There was no evidence of ESA-induced intracellular signaling in endothelial cells. There was a similar lack of EpoR expression and signaling in other cell types examined. Experiments were performed examining ESA function on these cells. An in vivo rat corneal angiogenesis assay demonstrated neo-vessel formation in response to recombinant human vascular endothelial growth factor (rHuVEGF). However, recombinant mouse Epo did not induce vessel formation. Similarly, ESAs did not reproducibly provide cytoprotection to neuronal, renal, or cardiac cells. Taken together, our data challenge the notion of presence or function of EpoR on nonhematopoietic cells, and call into question the preclinical basis for clinical studies exploring direct, "pleiotropic" actions of ESAs.
authors.affiliation: Department of Hematology, Amgen Inc, Thousand Oaks, CA, USA. anguss@amgen.com
authors.forename: Angus M
authors.initials: AM
authors.lastname: Sinclair
authors.forename: Angela
authors.initials: A
authors.lastname: Coxon
authors.forename: Ian
authors.initials: I
authors.lastname: McCaffery
authors.forename: Stephen
authors.initials: S
authors.lastname: Kaufman
authors.forename: Katherine
authors.initials: K
authors.lastname: Paweletz
authors.forename: Liqin
authors.initials: L
authors.lastname: Liu
authors.forename: Leigh
authors.initials: L
authors.lastname: Busse
authors.forename: Susan
authors.initials: S
authors.lastname: Swift
authors.forename: Steven
authors.initials: S
authors.lastname: Elliott
authors.forename: C Glenn
authors.initials: CG
authors.lastname: Begley
mesh_terms: D000818:Animals; D001483:Base Sequence; D002460:Cell Line; D002478:Cells, Cultured; D017931:DNA Primers / Q000235:genetics; D042783:Endothelial Cells / Q000187:drug effects / Q000378:metabolism*; D004921:Erythropoietin / Q000378:metabolism / Q000494:pharmacology; D006397:Hematinics / Q000494:pharmacology; D006801:Humans; D007687:Kidney Tubules, Proximal / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D051379:Mice; D032383:Myocytes, Cardiac / Q000187:drug effects / Q000378:metabolism*; D018919:Neovascularization, Physiologic / Q000187:drug effects; D009474:Neurons / Q000187:drug effects / Q000378:metabolism*; D016716:PC12 Cells; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D051381:Rats; D017467:Receptors, Erythropoietin / Q000235:genetics / Q000378:metabolism*; D011994:Recombinant Proteins / Q000494:pharmacology; D015398:Signal Transduction / Q000187:drug effects; D014018:Tissue Distribution; D042442:Vascular Endothelial Growth Factors / Q000494:pharmacology
chemical_list: D017931:DNA Primers; D006397:Hematinics; D012333:RNA, Messenger; D017467:Receptors, Erythropoietin; D011994:Recombinant Proteins; D042442:Vascular Endothelial Growth Factors; D004921:Erythropoietin