Receptor for erythropoietin. Mediates erythropoietin-induced erythroblast proliferation and differentiation. Upon EPO stimulation, EPOR dimerizes triggering the JAK2/STAT5 signaling cascade. In some cell types, can also activate STAT1 and STAT3. May also activate the LYN tyrosine kinase. Forms homodimers on EPO stimulation. The tyrosine-phosphorylated form interacts with several SH2 domain-containing proteins including LYN, the adapter protein APS, PTPN6, PTPN11, JAK2, PI3 kinases, STAT5A/B, SOCS3 and CRKL. The N-terminal SH2 domain of PTPN6 binds Tyr-453 and inhibits signaling through dephosphorylation of JAK2. APS binding also inhibits the JAK-STAT signaling. Binding to PTPN11, preferentially through the N-terminal SH2 domain, promotes mitogenesis and phosphorylation of PTPN11. Binding of JAK2 (through its N-terminal) promotes cell-surface expression. Interaction with the ubiquitin ligase NOSIP mediates EPO-induced cell proliferation. Interacts with ATXN2L (By similarity). Forms heterooligomers with friend spleen focus-forming virus (FSFFV) gp55, probably via their respective transmembrane domains. Interacts with INPP5D/SHIP1. Additional isoforms seem to exist. Expressed in relatively mature erythroid progenitor cells and in EPO-responsive erythroleukemia cells. The WSXWS motif appears to be necessary for proper protein folding and thereby efficient intracellular transport and cell-surface receptor binding. The box 1 motif is required for JAK interaction and/or activation. Contains 1 copy of a cytoplasmic motif that is referred to as the immunoreceptor tyrosine-based inhibitor motif (ITIM). This motif is involved in modulation of cellular responses. The phosphorylated ITIM motif can bind the SH2 domain of several SH2-containing phosphatases. The identity of the C-linked hexose on the WXXW motif has not been determined. It is probably mannose. On EPO stimulation, phosphorylated on C-terminal tyrosine residues by JAK2. The phosphotyrosine motifs are also recruitment sites for several SH2-containing proteins and adapter proteins which mediate cell proliferation. Phosphorylation on Tyr-453 is required for PTPN6 interaction, Tyr-425 for PTPN11. Tyr-425 is also required for SOCS3 binding, but Tyr-453/Tyr-455 motif is the preferred binding site (By similarity). Ubiquitinated by NOSIP; appears to be either multi-monoubiquitinated or polyubiquitinated. Ubiquitination mediates proliferation and survival of EPO-dependent cells (By similarity). Ubiquitination at Lys-280 mediates receptor internalization, whereas ubiquitination at Lys-452 promotes trafficking of activated receptors to the lysosomes for degradation. Interaction with FSFFV envelope-like membrane glycoprotein gp55 leads to ligand-independent activation of EPOR and to the abnormally rapid proliferation of erythroid precursor cells. Viral promoter integration by Friend spleen focus-forming virus (F-SFFVP) in the murine erythroleukemia cell line F5-5, results in aberrant EPOR sequences and EPOR overexpression in erythroid progenitor cells. Belongs to the type I cytokine receptor family. Type 1 subfamily.