Structural and biological properties of erythropoietin in Xenopus laevis

Objective. Erythropoietin (EPO) and its receptor (EPOR) are key regulators of red blood cell production in mammals and fish. We aimed to investigate the structural and functional conservation of the EPO-EPOR system in amphibian erythropoiesis, using Xenopus laevis as a model. Materials and Methods. X. laevis epo (xlepo) complementary DNA was identified by referring to the Xenopus tropicalis genome database. Biological activity of recombinant x/EPO expressed in COS-1 cells was evaluated using x/EPOR-expressing murine FDC/P2 cells and human EPO-dependent UT-7/EPO cells. Expression of xlepo messenger RNA in adult X. laevis tissues in the normal state and under the condition of phenylhydrazine-induced anemia was evaluated by real-time reverse transcription polymerase chain reaction. Results. In the encoded protein, the positions of four cysteine residues were conserved; however, x/EPO had only 38% identity with human EPO.N-glycosylation sites were absent. Recombinant x/EPO induced proliferation of cell lines expressing x/EPOR and UT-7/EPO, confirming biological activity and cross-species reactivity. Despite little primary amino acid sequence similarity, the evolutionary highly conserved sequence NFLRGK was identified in the EPOR-binding site 1 region as in the human EPO protein. Strong expression of xlepo messenger RNA was detected in the lung and liver, especially in fractionated hepatocytes. No marked increase in xlepo expression was seen in the lung and liver of phenylhydrazine-induced anemic X. laevis. Conclusion. We confirmed that x/EPO is the ligand to the previously reported x/EPOR in X. laevis. x/EPO shares structural and functional similarities and differences with mammalian counterparts, and regulation of xlepo expression and its influence on the erythropoietic system appears to be unique. (C) 2010 ISEH - Society for Hematology and Stem Cells. Published by Elsevier Inc.