Physiology and function of the erythropoietin receptor.

Interaction between erythropoietin (EPO) and its membrane receptor induces the proliferation and differentiation of erythroid progenitors. Targeted disruption of the EPO receptor (EPOR) gene have clearly demonstrated the importance of the EPO/EPOR system for definitive erythroid cell survival and proliferation; however, in vitro rescue experiments have revealed that it is not essential for differentiation. The three-dimensional structure of the EPOR has been determined, and a biologically active 20 amino acid peptide has been shown to cause dimerization of the extracellular domain of EPOR. EPO activates the JAK2-STAT5 pathway, and two tyrosine residues (Y343, Y401) in the cytoplasmic domain of EPOR are important for STAT5 activation. However, the physiologic role of STAT5 in erythroid cell proliferation and differentiation is still controversial. Mutations that result in C-terminal deletion of EPOR are frequently found in familial erythrocytosis. Hematopoietic cell phosphatase, which binds to the C-terminal region, could be involved in negative regulation of EPOR function.