 At present, the most well-established function of EpoR is to promote proliferation and rescue of erythroid (red blood cell) progenitors from apoptosis.The cytoplasmic domains of the EpoR contain a number of phosphotyrosines that are phosphorylated by Jak2 and serve as docking sites for a variety of intracellular pathway activators and Stats (such as Stat5).In addition to activating Ras/AKT and ERK/MAP kinase, phosphatidylinositol 3-kinase/AKT pathway and STAT transcription factors, phosphotyrosines also serve as docking sites for phosphatases that negatively affect EpoR signaling in order to prevent overactivation that may lead to such disorders as erythrocytosis.