Raf-1 is not required for megakaryocytopoiesis or TPO-induced ERK phosphorylation.
Thrombopoietin stimulates extracellular signal-related kinase 1/2 (ERK1/2) phosphorylation in megakaryocytes, and the classic mitogen-activated protein (MAP) kinase (Raf/mitogen-induced extracellular kinase [MEK]/ERK) pathway has been implicated directly and indirectly to play a critical role in megakaryocytopoiesis. However, the involvement of specific Raf family members in megakaryocytopoiesis is unknown. raf-1(-/-) mice were therefore used to directly determine the role of Raf-1 in megakaryocytopoiesis. Surprisingly, raf-1(-/-) mice have a modestly higher platelet count than their raf-1(+/+) littermates. Nonetheless, the absence of Raf-1 does not alter thrombopoietin-induced expansion of primary megakaryocyte-lineage cells, the development of apoptotic megakaryocytes in the presence or absence of thrombopoietin, or the development of megakaryocyte DNA ploidy distribution. Moreover, raf-1(-/-) megakaryocytes do not have a compensatory increase in A-Raf or B-Raf expression, and thrombopoietin-induced ERK1/2 phosphorylation is similar in raf-1(-/-) and raf-1(+/+) megakaryocytes. These unexpected findings demonstrate that Raf-1 is dispensable for megakaryocytopoiesis, and for thrombopoietin-induced ERK1/2 activation in primary megakaryocyte-lineage cells.
Department of Laboratory Medicine, University of California, San Francisco, CA 94143-0100, USA.
Tamihiro
T
Kamata
Catrin A
CA
Pritchard
Andrew D
AD
Leavitt
D000818:Animals; D003433:Crosses, Genetic; D004920:Erythropoiesis / Q000502:physiology*; D008533:Megakaryocytes / Q000166:cytology* / Q000187:drug effects / Q000502:physiology*; D051379:Mice; D018345:Mice, Knockout; D019950:Mitogen-Activated Protein Kinase 1 / Q000378:metabolism*; D048052:Mitogen-Activated Protein Kinase 3; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism*; D010766:Phosphorylation; D019908:Proto-Oncogene Proteins c-raf / Q000172:deficiency / Q000235:genetics / Q000502:physiology*; D013921:Thrombocytopenia / Q000235:genetics; D013926:Thrombopoietin / Q000494:pharmacology*
D013926:Thrombopoietin; D019908:Proto-Oncogene Proteins c-raf; D019950:Mitogen-Activated Protein Kinase 1; D048052:Mitogen-Activated Protein Kinase 3; D020928:Mitogen-Activated Protein Kinases