Erythropoietin (EPO) is the major glycoprotein hormone regulator of mammalian erythropoiesis , and is produced by kidney and liver in an oxygen-dependent manner. The biological effects of EPO are mediated by the specific erythropoietin receptor (EPOR) on bone marrow erythroblasts, which transmits signals important for both proliferation and differentiation along the erythroid lineage. EPOR is a type 1 single-transmembrane cytokine receptor, and belongs to the homodimerizing subclass which functions as ligand-induced or ligand-stabilized homodimers. EPOR pre-exists as dimers which upon binding of a 34 kDa ligand erythropoietin (Epo), changes its homodimerized state. These conformational changes result in the autophosphorylation of Jak2 kinases that are pre-associated with the receptor. Erythropoietin is necessary to maintain endothelial cells and to promote tumor angiogenesis, hence the dysregulation of EpoR may affect the growth of certain tumors. EpoR signaling prevents neuronal death and ischemic injury.