Interaction of the erythropoietin and stem-cell-factor receptors

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Abstract
MUTATIONS in the KIT transmembrane protein-tyrosine kinase receptor1 affect erythropoiesis, resulting in fewer committed late progenitors (colony-forming unit erythroid, CFU-E) in the fetal liver2. As the survival and proliferation of CFU-Es depend absolutely on erythropoietin (EPO)3, these results suggest that CFU-Es cannot proliferate or mature further unless both the KIT and EPO receptor4 signalling pathways are functional. How KIT affects proliferation or differentiation of CFU-Es is not clear. Here we show that the KIT ligand SCF (for stem-cell factor) can replace EPO in supporting the growth and survival of HCD57 cells, an EPO-dependent erythroid-progenitor cell line expressing high levels of KIT5. SCF supports the proliferation of 32D cells6 that express KIT only if they also express the EPO receptor. In HCD57 cells, SCF rapidly induces tyrosine phosphorylation of the EPO receptor, and KIT physically associates with the extended box 2 region7 in the cytoplasmic domain of the EPO receptor. Our results indi-cate that KIT may activate the EPO receptor by tyrosine phosphorylation to induce further proliferation and maturation of CFU-Es.

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