IDENTIFICATION OF TYROSINE RESIDUES WITHIN THE INTRACELLULAR DOMAIN OF THE ERYTHROPOIETIN RECEPTOR CRUCIAL FOR STAT5 ACTIVATION

FDCP-1 cells are hematopoietic progenitor cells which require interleu kin-3 for survival and proliferation, FDCP-1 cells stably transfected with the murine erythropoietin receptor cDNA survive and proliferate i n the presence of erythropoietin. Erythropoietin induces the activatio n of the short forms (80 kDa) of STAT5 in the cells. Erythropoietin-in duced activation of STAT5 was strongly reduced in cells expressing mut ated variants of the erythropoietin receptors in which tyrosine residu es in their intracellular domain have been eliminated. We determined t hat the erythropoietin receptor tyrosine residues 343 and 401 are inde pendently necessary for STAT5 activation. The amino acid sequences sur rounding these two tyrosine residues are very similar, Peptides compri sing either phosphorylated Tyr343 or phosphorylated Tyr401, but not th eir unphosphorylated counterparts, inhibited the STAT5 activation. We propose that these two tyrosine residues of the erythropoietin recepto r constitute docking sites for the STAT5 SH2 domain, The growth stimul us mediated by erythropoietin was decreased in cells expressing erythr opoietin receptors lacking both Tpr343 and Tyr401. This suggests that STAT5 activation could be involved in the growth control of FDCP-1 cel ls.