The intron 5-inserted form of rat erythropoietin receptor is expressed as a membrane-bound form

PCFamily: a web server for searching homologous protein complexes

The proteins in a cell often assemble into complexes to carry out their functions and play an essential role of biological processes. The PCFamily server identifies template-based homologous protein complexes [called protein complex family (PCF)] and infers functional modules of the query proteins. This server first finds homologous structure complexes of the query using BLASTP to search the structural template database (11 263 complexes). PCFamily then searches the homologous complexes of the templates (query) from a complete genomic database (Integr8 with 6 352 363 protein sequences in 2274 species). According to these homologous complexes across multiple species, this sever infers binding models (e.g. hydrogen-bonds and conserved amino acids in the interfaces), functional modules, and the conserved interacting domains and Gene Ontology annotations of the PCF. Experimental results demonstrate that the PCFamily server can be useful for binding model visualizations and annotating the query proteins. We believe that the server is able to provide valuable insights for determining functional modules of biological networks across multiple species. The PCFamily sever is available at http://pcfamily.life.nctu.edu.tw.

Optimal neuroprotection by erythropoietin requires elevated expression of its receptor in neurons

Erythropoietin receptor (EpoR) binding mediates neuroprotection by endogenous Epo or by exogenous recombinant human (rh)Epo. The level of EpoR gene expression may determine tissue responsiveness to Epo. Thus, harnessing the neuroprotective power of Epo requires an understanding of the Epo-EpoR system and its regulation. We tested the hypothesis that neuronal expression of EpoR is required to achieve optimal neuroprotection by Epo. The ventral limbic region (VLR) in the rat brain was used because we determined that its neurons express minimal EpoR under basal conditions, and they are highly sensitive to excitotoxic damage, such as occurs with pilocarpine-induced status epilepticus (Pilo-SE). We report that (i) EpoR expression is significantly elevated in nearly all VLR neurons when rats are subjected to 3 moderate hypoxic exposures, with each separated by a 4-day interval; (ii) synergistic induction of EpoR expression is achieved in the dorsal hippocampus and neocortex by the combination of hypoxia and exposure to an enriched environment, with minimal increased expression by either treatment alone; and (iii) rhEpo administered after Pilo-SE cannot rescue neurons in the VLR, unless neuronal induction of EpoR is elicited by hypoxia before Pilo-SE. This study thus demonstrates using environmental manipulations in normal rodents, the strict requirement for induction of EpoR expression in brain neurons to achieve optimal neuroprotection. Our results indicate that regulation of EpoR gene expression may facilitate the neuroprotective potential of rhEpo.

Erythropoietin receptor spliced forms differentially expressed in blind subterranean mole rats

Erythropoietin (Epo) is the primary regulator of erythropoiesis, controlling the proliferation, maturation, and survival of erythroid progenitor cells. The functions of Epo are mediated through its specific receptor (EpoR) expressed mainly on the surface of erythroid progenitor cells, and the expression of both responds to hypoxia. The subterranean mole rat (Spalax) is a unique model system to study the molecular mechanisms for adaptation to hypoxia. Here, we cloned two forms of Spalax EpoR: a complete EpoR cDNA as well as a novel truncated bone marrow specific EpoR form. In the full-length Spalax EpoR (sEpoR), two out of the eight conserved tyrosine- phosphorylation sites were substituted (Y481F and Y499G), suggesting that Spalax Epo signaling pathways may be modulated. The level of the sEpoR mRNA in the spleen and in bone marrow was relatively low and similar in Spalax newborns and adults, with no significant response to hypoxia. The truncated sEpoR was not detected in the spleen and comprised only approximately 1% of the sEpoR expressed in the bone marrow. In Rattus, the truncated EpoR form was approximately 15% of the total expressed receptor. The level of Rattus EpoR in newborn spleens was three- to fourfold higher than in Spalax newborns and decreased toward adulthood. Severe hypoxia induces a significant increase in adult Rattus EpoR. Our data provide further insight into the adaptive mechanisms of Spalax to the extreme conditions of hypoxia in its subterranean environment.

Expression of erythropoietin receptor splice variants in human cancer

Erythropoietin (EPO) regulates mammalian erythropoiesis by binding to its transmembrane receptor EPOR. Recent studies demonstrated functional EPOR expression in human cancer cells. Recombinant human EPO was reported to stimulate the proliferation of monolayer cultures of breast and renal carcinoma cells. Furthermore, administration of EPO-EPOR antagonists delayed the growth of uterine, ovarian, and mammary carcinoma cells in experimental animal models. In this study, we show EPOR transcript and protein expression in breast, colon, lung, ovary, and prostate cancer cells. Using reverse transcription-polymerase chain reaction, we isolated and characterized several novel cDNAs for EPOR splice variants expressed in cancer cells. Deduced amino acid sequences of the cDNAs revealed splice variants encoding soluble EPOR or membrane-bound EPOR peptides with intra-cytoplasmic, carboxy-terminal truncations. These findings indicate the expression of multiple EPOR isoforms in human cancer cells that may modulate the cellular effects of recombinant human EPO or EPO-EPOR antagonists.

Quantitation of the mRNA levels of Epo and EpoR in various tissues in the ovine fetus

A partial cDNA of the sheep erythropoietin receptor (EpoR) was obtained and used in real-time PCR to quantitate mRNA levels in placenta, liver and kidney throughout development (term=150 days). This was compared with Epo mRNA levels in the same tissues. Both Epo and EpoR mRNA were present in the placenta throughout gestation at low levels from 66 days onwards and these did not vary throughout gestation. Compared with the expression levels in the placenta, the levels of EpoR gene expression in the liver at 66, 99 and 140 days were, median (range)-288 (120-343), 278 (63-541) and 7 (3-15), respectively, reflecting the disappearance of erythropoiesis after 130 days. Low levels of EpoR gene expression were seen in the kidney at 3 (2-5), 5 (2-7), and 7 (2-10) times that in the placenta at 66, 99, and 140 days, respectively. By hybridization histochemistry the EpoR mRNA was located in the proximal tubular cells of the mesonephros and metanephros at 42 days. Epo mRNA levels in the kidney were 215 (116-867), 528 (113-765) and 46 (15-204) times those in the placenta at 69, 99, and 140 days, respectively. In the liver at the same ages the concentrations of mRNA were lower than in the kidney, the liver/placenta ratios being 50 (11-90), 17 (3-39), 9 (5-14). At 130 days Epo/EpoR levels in the hippocampus were 6+/-3 and 8+/-3 times that in the term placenta, respectively. These studies demonstrate that the ovine placenta expresses the Epo gene from at least 66 days of gestation. However, gene expression levels are very low compared with those in the liver and kidney, and even the hippocampus.