Rabbit EPO gene and cDNA: expression of rabbit EPO after intramuscular injection of pDNA

The influence of artificially introduced N-glycosylation sites on the in vitro activity of Xenopus laevis erythropoietin

Erythropoietin (EPO), the primary regulator of erythropoiesis, is a heavily glycosylated protein found in humans and several other mammals. Intriguingly, we have previously found that EPO in Xenopus laevis (xlEPO) has no N-glycosylation sites, and cross-reacts with the human EPO (huEPO) receptor despite low homology with huEPO. In this study, we introduced N-glycosylation sites into wild-type xlEPO at the positions homologous to those in huEPO, and tested whether the glycosylated mutein retained its biological activity. Seven xlEPO muteins, containing 1–3 additional N-linked carbohydrates at positions 24, 38, and/or 83, were expressed in COS-1 cells. The muteins exhibited lower secretion efficiency, higher hydrophilicity, and stronger acidic properties than the wild type. All muteins stimulated the proliferation of both cell lines, xlEPO receptor-expressing xlEPOR-FDC/P2 cells and huEPO receptor-expressing UT-7/EPO cells, in a dose-dependent manner. Thus, the muteins retained their in vitro biological activities. The maximum effect on xlEPOR-FDC/P2 proliferation was decreased by the addition of N-linked carbohydrates, but that on UT-7/EPO proliferation was not changed, indicating that the muteins act as partial agonists to the xlEPO receptor, and near-full agonists to the huEPO receptor. Hence, the EPO-EPOR binding site in X. laevis locates the distal region of artificially introduced three N-glycosylation sites, demonstrating that the vital conformation to exert biological activity is conserved between humans and X. laevis, despite the low similarity in primary structures of EPO and EPOR.

Hypoxic stress tolerance of the blind subterranean mole rat: expression of erythropoietin and hypoxia-inducible factor 1 alpha

Blind subterranean mole rats (Spalax, Spalacidae) evolved adaptive strategies to cope with hypoxia that climaxes during winter floods in their burrows. By using real-time PCR, we compared gene expression of erythropoietin (Epo), a key regulator of circulating erythrocytes, and hypoxia-inducible factor 1 alpha (HIF-1 alpha), Epo expression inducer, in the kidneys of Spalax and white rats, Rattus norvegicus. Our results show significantly higher, quicker, and longer responses to different O(2) levels in Spalax compared with Rattus. (i) In normoxia, both Spalax and Rattus kidneys produce small amounts of Epo. Maximal expression of Rattus Epo is noticed after a 4-h hypoxia at 6% O(2). Under these conditions, Spalax Epo levels are 3-fold higher than in Rattus. After 24 h of 10% O(2), Spalax Epo reaches its maximal expression, remarkably 6-fold higher than the maximum in Rattus; (ii) the HIF-1 alpha level in normoxia is 2-fold higher in Spalax than in Rattus. Spalax HIF-1 alpha achieves maximal expression after 4-h hypoxia at 3% O(2), a 2-fold increase compared with normoxia, whereas no significant change was detected in Rattus HIF-1 alpha at any of the conditions studied; (iii) at 6% O(2) for 10 h, in which Rattus cannot survive, Epo and HIF-1 alpha levels in Spalax galili, living in heavily flooded soils, are higher than in Spalax judaei, residing in light aerated soil. We suggest that this pattern of Epo and HIF-1 alpha expression is a substantial contribution to the adaptive strategy of hypoxia tolerance in Spalax, evolved during 40 million years of evolution to cope with underground hypoxic stress.

Nucleotide sequence of equine erythropoietin and characterization of region-specific antibodies

OBJECTIVE

To determine the full-length complementary DNA (cDNA) sequence of equine erythropoietin (EPO) and to develop region-specific antibodies to differentiate equine EPO (eEPO) and human EPO (hEPO).

SAMPLE POPULATION

RNA and lysate extracted from renal tissues of an adult Thoroughbred.

PROCEDURE

Full-length cDNA was determined by use of a reverse transcriptase-polymerase chain reaction assay and a rapid amplification of cDNA ends method. The deduced amino acid sequence was compared with sequences of EPO reported for other species. Furthermore, 4 synthetic peptides were designed in 2 distinctive parts of the eEPO and hEPO amino acid sequences to obtain antibodies specific for eEPO and hEPO. Specificity of the antibodies was tested against supernatant of homogenized equine kidney and recombinant hEPO (rhEPO) by use of western immunoblotting techniques.

RESULTS

Analysis of the 1,181 bp in the nucleotide sequence revealed that eEPO was a residue of 192 amino acids. Similarity of eEPO with amino acid sequences of EPO from other species was 81.0% to 90.6%. Antibodies were specifically recognized by eEPO or rhEPO molecules. Anti-hEPO (161 to 165) antibody specifically recognized rhEPO. In contrast, anti-eEPO (133 to 144) antibody reacted with the equine kidney lysate.

CONCLUSIONS AND CLINICAL RELEVANCE

We determined the cDNA and amino acid sequence of eEPO and developed region-specific antibodies that specifically recognized eEPO or rhEPO. These antibodies may be useful in distinguishing rhEPO from eEPO in a test to detect the misuse of rhEPO in racehorses.