Erythropoietin hypersensitivity in primary familial and congenital polycythemia: Role of tyrosines Y-285 and Y-344 in erythropoietin receptor cytoplasmic domain

摘要

Erythropoietin receptor (EPOR) gene mutations leading to truncations of the cytoplasmic, carboxy-terminal region of EPOR have been described in some patients with primary familial and congenital polycythemia (PFCP), a disorder characterized by isolated erythrocytosis and increased sensitivity of erythroid progenitors to Epo. We studied the role of EPOR in the pathogenesis of PFCP and the requirement for intracytoplasmic tyrosine residues Y-285 and Y-344 in generation of Epo hypersensitivity phenotype. Interleukin-3-dependent hematopoietic cells were engineered to express variant human EPORs using retrovirus-mediated gene transfer. 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. Cells expressing EPOR-ME exhibited increased Epo sensitivity compared to cells expressing wild type EPOR. Mutation of Y-285 alone had a relatively minor effect on Epo hypersensitivity whereas mutation of Y-344 resulted in loss of increased Epo sensitivity. Expression of a tyrosine-null truncated EPOR conferred further decrease of Epo-mediated proliferation suggesting that both Y-285 and Y-344 may contribute to proliferation signals. In the context of EPOR-ME, Y-344 was required for Epo-induced Stat5 tyrosine phosphorylation. The positive effect of either Y-285 or Y-344 on cellular proliferation was associated with Epo-induced tyrosine phosphorylation of Stat1. These findings suggest that both tyrosine residues Y-285 and Y-344 in the cytoplasmic domain of EPOR-ME may contribute to increased Epo sensitivity that is characteristic of PFCP phenotype. (c) 2005 Elsevier B.V. All rights reserved.