Disease relevance of EPOR

• We describe a Swedish family with dominant FE in which erythrocytosis segregates with a new truncation in the negative control domain of the EPOR [1].
• Furthermore, we found EPO and EPOR mRNAs as well as EPO protein in K562 cells, a human erythroleukemia cell line [2].
• We also show that EPOR-T mRNA is not detected in erythroid/megakaryocytic leukemia cell lines, but is expressed in nonerythroid/nonmegakaryocytic lines, suggesting the presence of a cell type-specific system by which intron VII of the EPOR transcript is spliced [3].
• We report basal and hypoxia-stimulated expression of EPO and its receptor, EPOR, in human breast cancer cells, and we demonstrate EPO-stimulated tyrosine phosphorylation and the proliferation of these cells in vitro [4].
• In 50 clinical specimens of breast carcinoma, we report high levels of EPO and EPOR associated with malignant cells and tumor vasculature but not with normal breast, benign papilloma, or fibrocystic tissue [4].
• If this finding in non-small cell lung carcinoma is a widespread phenomenon, then impaired erythropoietin receptor downregulation and degradation in tumor cells has clinical implications for those patients receiving erythropoiesis-stimulating agents for cancer-related anemia [5].
• Anemia, however, did not appear to influence EPOR expression on leukemic cells, although children with ETV6/RUNX1-positive leukemias had a lower median hemoglobin than controls [6].

High impact information on EPOR

• EPO and the EPOR are crucial in vivo for the proliferation and survival of CFU-E progenitors and their irreversible terminal differentiation [7].
• Using EPOR mutants, phosphorylation and activation of kinase activity correlate with the induction of mitogenesis [8].
• Two independent cDNA clones encoding the erythropoietin receptor (EPO-R) were isolated from a pXM expression library made from uninduced murine erythroleukemia (MEL) cells [9].
• Although the MEL cell EPO-R has a single affinity with a dissociation constant of approximately 240 pM, the EPO-R cDNA, expressed in COS cells, generates both a high-affinity (30 pM) and a low-affinity (210 pM) receptor [9].
• The Epo receptor required for Epo signaling localizes to photoreceptor cells [10].

Chemical compound and disease context of EPOR

• The erythropoietin receptor (EPO-R), a member of the cytokine receptor superfamily, can be activated to signal cell growth by binding either EPO or F-gp55, the Friend spleen focus-forming virus glycoprotein [11].
• No colocalization was found between EPOR expression and pimonidazole binding indicating that the presence or absence of hypoxia did not necessarily indicate a distinct pattern of EPOR expression [12].
• Erythropoietin-receptor (EpR) expression on bone marrow cells from normal individuals and from patients with chronic myeloid leukemia (CML) was examined by multiparameter flow cytometry after stepwise amplified immunostaining with biotin-labeled Ep, streptavidin-conjugated R-phycoerythrin, and biotinylated monoclonal anti-R-phycoerythrin [13].
• In chloramphenicol acetyl transferase constructs containing the mouse Epo-R promoter, rearranged by retroviral long terminal repeat (LTR) insertion of murine erythroleukemia cell lines, we found that positioning the CCACC motif 3' to the LTR represses the transcriptional activity mediated by the LTR in non-erythroid cells [14].

Biological context of EPOR

• The crystal structure of the extracellular domain of EPOR in its unliganded form at 2.4 angstrom resolution has revealed a dimer in which the individual membrane-spanning and intracellular domains would be too far apart to permit phosphorylation by JAK2 [15].
• This unliganded EPOR dimer is formed from self-association of the same key binding site residues that interact with EPO-mimetic peptide and EPO ligands [15].
• In other words, EPOR appeared to be dispensable for erythropoiesis [16].
• We screened the affected individuals for EPOR gene mutations using SSCP analysis and found a C5964G mutation in exon VIII that changes tyrosine codon 426 to a translation termination codon resulting in an EPOR protein truncated by 83 amino acids [17].
• These data demonstrate that a nonpeptide molecule is capable of inducing EPOR dimerization and mimicking the biological activities of EPO [18].

Anatomical context of EPOR

• The mutant C5964G-EPOR exhibited hypersensitive EPO-dependent proliferation compared to the wild-type EPOR when tested in a murine interleukin-3-dependent myeloid cell line (FDC-P1) [17].
• We find that EPOR is inducible by EPO in primary human endothelial cells of vein (HUVECs) and artery (HUAECs) and cells from a human bone marrow microvascular endothelial line (TrHBMEC) to a much greater extent at low oxygen tension than in room air [19].
• Erythropoietin (EPO) and its receptor (EPOR) are required for the development of mature erythrocytes [20].
• In addition, selected mutant proteins were expressed as full-length EPOR on the surface of COS cells and analyzed for 125I-EPO binding in receptor binding assays [21].
• These results suggest that proinflammatory cytokines regulate expression of EPO and EPOR in human neurons, astrocytes, and microglia and further facilitate interactions among different cell types in the human CNS [22].

Associations of EPOR with chemical compounds

• We first identified compound 1 (N-3-[2-(4-biphenyl)-6-chloro-5-methyl]indolyl-acetyl-L-lysine methyl ester) by screening the in-house chemical collection for inhibitors of EPO binding to human EPOR and then prepared compound 5, which contains eight copies of compound 1 held together by a central core [18].
• However, this did not depend upon the presence of phosphotyrosine sites within the EPOR and was mediated by a mitogenically deficient receptor form (EPOR329) lacking cytoplasmic tyrosine residues [23].
• We found that the 78-kDa erythropoietin receptor (EPOR), a highly modified form of the 66-kDa receptor which is abundant in HCD57 cells, was phosphorylated on serine residues without EPO stimulation [24].
• Contiguous sections from 74 biopsies were analyzed by immunohistochemistry for EPOR and erythropoietin expression and pimonidazole binding [25].
• We introduced tyrosine to phenylalanine substitutions in EPOR-ME, a naturally occurring, mutant human EPOR (G5881T), truncated by 110 carboxy-terminal amino acids and associated with autosomal dominantly inherited PFCP [26].

Physical interactions of EPOR

• Here we show that human SOCS-3 binds to pY401 with a Kd of 9.5 microm while another EpoR tyrosine motif, pY429pY431, can also interact with SOCS-3 but with a ninefold higher affinity than we found for the previously reported motif pY401 [27].
• In a recent paper [Philo et al. (1996), Biochemistry 38, 1681-1691] we described the formation of both 1:1 and 2:1 EPOR/EPO complexes [28].
• Thus, GAB1 could be a scaffold protein able to couple the Epo receptor activation with the stimulation of several intracellular signaling pathways [29].
• Therefore PFCP is presumably brought about as a result of genetic mutations which cause the loss of the SHP-1 binding site in the cytoplasmic region of EpoR [30].
• Activation of the erythropoietin receptor caused specific DNA-binding of Stat 5b, but failed to induce reporter gene transcription [31].

Enzymatic interactions of EPOR

• Erythropoietin-dependent association of phosphatidylinositol 3-kinase with tyrosine-phosphorylated erythropoietin receptor [32].

Regulatory relationships of EPOR

• These data suggest that phosphorylation of either serine or tyrosine residues of the EPOR can enhance the association of the receptor with JAK2, possibly increasing the sensitivity to EPO [24].
• In the erythropoietic process, EPO induces homodimerization of the EPO receptor, which is located on the surface of erythroid progenitor cells [33].
• Here we examined the role of EPOR in erythropoiesis stimulated by SCF, sIL-6R, and IL-6 [16].
• RT-PCR results showed that there was EPO-R but not c-Mpl expression on developing erythroblasts induced by TPO in serum-containing system [34].
• Multiple tyrosine residues in the cytosolic domain of the erythropoietin receptor promote activation of STAT5 [35].

Other interactions of EPOR

• Erythropoietin receptor mutations associated with familial erythrocytosis cause hypersensitivity to erythropoietin in the heterozygous state [1].
• Identification of the human erythropoietin receptor region required for Stat1 and Stat3 activation [36].
• In erythropoietin receptor (EPOR)-mediated signaling, STAT5 is tyrosine-phosphorylated by EPO stimulation [37].
• In this study tyrosine 401 was identified as a binding site for SOCS-3 on the EpoR [27].
• Activation of the mitogen-activated protein kinases Erk1/2 by erythropoietin receptor via a G(i )protein beta gamma-subunit-initiated pathway [38].

Analytical, diagnostic and therapeutic context of EPOR

• We employed both random and site-specific mutagenesis to determine the function of amino acid residues in the extracellular domain (referred to as EPO binding protein, EBP) of the EPOR [21].
• In the present study, we investigated the effects of proinflammatory cytokines on EPO and EPOR expression in highly purified cultures of human neurons, astrocytes, microglia, and oligodendrocytes using reverse transcription-polymerase chain reaction (RT-PCR) and enzyme-linked immunosorbent assay (ELISA) [22].
• Furthermore, administration of EPO-EPOR antagonists delayed the growth of uterine, ovarian, and mammary carcinoma cells in experimental animal models [39].
• Further examination of the inheritance of the EPOR gene alleles and sequence analysis ruled out linkage between the disease phenotype and the EPOR gene; therefore, an abnormality in another gene must be the cause of PFCP in this particular family [40].
• EPOR expression did not significantly change after axotomy [41].

References