This study maps specific functional domains within the cytoplasmic region of the human TPO receptor (c-Mpl) that govern megakaryocytic proliferation, differentiation, and DNA synthesis.
Delineates c-Mpl domains in megakaryopoiesis; leaves open therapeutic targeting pending in vivo validation.
To identify the functional domains of the human thrombopoietin (TPO) receptor essential for proliferation and megakaryocytic differentiation, we introduced human wild type c-mpl cDNA and deletion mutants of c-mpl cDNA into the human erythropoietin (EPO)-dependent cell line UT-7/EPO that does not express endogenous c-Mpl. TPO induced the proliferation and megakaryocytic differentiation of UT-7/EPO expressing wild type c-Mpl, as evidenced by increased levels of the CD41 antigen specific for cells of the megakaryocytic lineage and by changes in morphology. Mutational analysis of the cytoplasmic domain of c-Mpl identified four functional regions: (a) two C-terminal regions (amino acids 575-586 and 615-630) containing a domain essential for cell proliferation and megakaryocytic differentiation but not for DNA synthesis; (b) a region (amino acids 587-614) containing a negative domain for TPO-induced cell proliferation and megakaryocytic differentiation; and (c) a region (amino acids 565-574) including a box2 motif that is required for DNA synthesis. These deletion mutants will provide useful materials for analyzing the signals specific for TPO-induced proliferation and megakaryocytic differentiation.
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Takatoku et al. (1997) studied this question.
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