title: Ral is both necessary and sufficient for the inhibition of myeloid differentiation mediated by Ras.
abstract: Hyperactivation of Ras is one of the most common abnormalities in acute myeloid leukemia. In experimental models, Ras inhibits myeloid differentiation, which is characteristic of leukemia; however, the mechanism through which it disrupts hematopoiesis is poorly understood. In multipotent FDCP-mix cells, Ras inhibits terminal neutrophil differentiation, thereby indefinitely extending their proliferative potential. Ras also strongly promotes the sensitivity of these cells to granulocyte-macrophage colony-stimulating factor (GM-CSF). Using this model, we have dissected the signaling elements downstream of Ras to determine their relative contribution to the dysregulation of hematopoiesis. Cells expressing Ras mutants selectively activating Raf (Ras*T35S) or phosphatidylinositol 3-kinase (Ras*Y40C) did not significantly affect differentiation or proliferative capacity, whereas Ras*E37G (which selectively activates RalGEFs) perpetuated proliferation and blocked neutrophil development in a manner similar to that of Ras. Correspondingly, expression of constitutively active versions of these effectors confirmed the overriding importance of Ral guanine nucleotide exchange factors. Cells expressing Ras demonstrated hyperactivation of Ral, which itself was able to exactly mimic the phenotype of Ras, including hypersensitivity to GM-CSF. Conversely, dominant negative Ral promoted spontaneous neutrophil development. Ral, in turn, appears to influence differentiation through multiple effectors. These data show, for the first time, the importance of Ral in regulating differentiation and self-renewal in hematopoietic cells.
authors.affiliation: Department of Haematology, School of Medicine, Cardiff School of Biosciences, Cardiff University, Museum Avenue, Cardiff, United Kingdom. OmidvarN@cf.ac.uk
authors.forename: Nader
authors.initials: N
authors.lastname: Omidvar
authors.forename: Lorna
authors.initials: L
authors.lastname: Pearn
authors.forename: Alan K
authors.initials: AK
authors.lastname: Burnett
authors.forename: Richard L
authors.initials: RL
authors.lastname: Darley
mesh_terms: D000818:Animals; D015153:Blotting, Western; D018929:Cell Culture Techniques; D002454:Cell Differentiation; D045744:Cell Line, Tumor; D049109:Cell Proliferation; D002999:Clone Cells; D004305:Dose-Response Relationship, Drug; D004789:Enzyme Activation; D015973:Gene Expression Regulation, Leukemic; D011905:Genes, ras; D016178:Granulocyte-Macrophage Colony-Stimulating Factor / Q000494:pharmacology; D007951:Leukemia, Myeloid / Q000235:genetics / Q000503:physiopathology*; D051379:Mice; D009154:Mutation; D009504:Neutrophils / Q000166:cytology / Q000378:metabolism; D012190:Retroviridae / Q000235:genetics; D020726:ral Guanine Nucleotide Exchange Factor / Q000235:genetics / Q000502:physiology*; D018631:ras Proteins / Q000502:physiology*
chemical_list: D020726:ral Guanine Nucleotide Exchange Factor; D016178:Granulocyte-Macrophage Colony-Stimulating Factor; D018631:ras Proteins