Recombinant Mouse Erythropoietin R Fc Chimera Protein, CF

Erythropoietin (Epo), a glycoprotein produced primarily by the kidney, is the principal factor that regulates erythropoiesis by stimulating the proliferation and differentiation of erythroid progenitor cells. The biological effects of Epo are mediated by the erythropoietin receptor (Epo R). A member of the hematopoietic growth factor receptor superfamily which includes IL-2, IL-3, IL-4, IL-5, IL-6, IL-7, GM-CSF, G-CSF, thrombopoietin, LIF, CNTF, growth hormone, and prolactin, Epo R is expressed not only by erythroid cells but also by embryonic stem cells, endothelial cells, and neural cells (1). Mouse Epo R cDNA encode a type I membrane-spanning protein with 507 amino acid (aa) residues. Mouse Epo R has a 24 aa hydrophobic signal peptide, a 225 aa extracellular domain, a 22 aa transmembrane domain, and a 236 aa intracellular domain. At the protein sequence level, the human Epo R is approximately 82% identical to the mouse protein (2). Mouse and human Epo R both contain 11 cysteine residues and an N-linked glycosylation site. Mouse Epo R, however, contains two disulfide bridges not found with human Epo R. In common with other hematopoietic growth factor receptor superfamily members, mouse Epo R has 4 positionally conserved cysteines in its extracellular domain, a tryptophan-serine-X-tryptophan-serine (WSXWS) motif or its homolog located near the transmembrane region, and lacks kinase motifs in its intracellular domain. Based on its amino acid composition the molecular weight of Epo R would be 55 kDa but after post translational modification including glycosylation and tyrosine and serine-threonine phosphorylation the molecular weight can be as high as 78 kDa (1). As a result of alternative splicing of the Epo R gene, cDNA clones encoding a truncated form of the Epo R as well as a soluble form of Epo R has been found (2, 3). The presence of a soluble form of the Epo R has also been detected in human sera. Recombinant soluble Epo R binds Epo with high affinity and is a potent Epo antagonist (3).