title: Constitutive activation of the MEK/ERK pathway mediates all effects of oncogenic H-ras expression in primary erythroid progenitors.
abstract: Oncogenic mutations in ras genes frequently occur in patients with myeloid disorders, and in these patients erythropoiesis is often affected. Previously, we showed that expression of oncogenic H-ras in purified mouse primary fetal liver erythroid progenitors blocks terminal erythroid differentiation and supports erythropoietin (Epo)-independent proliferation. As a first step in understanding the underlying molecular mechanisms we examined the signaling pathways downstream of Ras in primary erythroid cells. We found that 3 major pathways are abnormally activated by oncogenic H-ras: Raf/ERK (extracellular signal-regulated kinase), phosphatidyl inositol 3 (PI3)-kinase/Akt, and RalGEF/RalA. However, only constitutive activation of the MEK (MAPK [mitogen-activated protein kinase]/ERK kinase)/ERK pathway alone could recapitulate all of the effects of oncogenic H-ras expression in blocking erythroid differentiation and inducing Epo-independent proliferation. Although expression of a constitutively active Akt kinase (ca.Akt) in erythroid progenitors does not significantly affect erythroid differentiation in the presence of Epo, coexpression of ca.Akt together with a constitutively active MEK causes prolonged Epo-independent proliferation of erythroid progenitors in addition to a block in differentiation. Moreover, the effects of oncogenic H-ras expression on primary erythroid cells are blocked by the addition of U0126, a specific inhibitor of MEK1 and MEK2, allowing normal terminal erythroid proliferation and differentiation. Our data suggest that the interruption of constitutive MEK/ERK signaling is a potential therapeutic strategy to correct impaired erythroid differentiation in patients with myeloid disorders.
authors.affiliation: Whitehead Institute for Biomedical Research, Cambridge, MA, USA.
authors.forename: Jing
authors.initials: J
authors.lastname: Zhang
authors.forename: Harvey F
authors.initials: HF
authors.lastname: Lodish
mesh_terms: D000818:Animals; D002070:Butadienes / Q000494:pharmacology; D002454:Cell Differentiation / Q000187:drug effects; D002455:Cell Division / Q000187:drug effects; D002460:Cell Line; D002478:Cells, Cultured; D004789:Enzyme Activation; D015672:Erythroid Precursor Cells / Q000166:cytology / Q000187:drug effects / Q000201:enzymology / Q000378:metabolism*; D004921:Erythropoietin / Q000494:pharmacology; D005786:Gene Expression Regulation; D011905:Genes, ras / Q000235:genetics*; D006801:Humans; D048369:MAP Kinase Kinase 1; D020935:MAP Kinase Signaling System / Q000187:drug effects; D051379:Mice; D019950:Mitogen-Activated Protein Kinase 1 / Q000037:antagonists & inhibitors / Q000378:metabolism; D048052:Mitogen-Activated Protein Kinase 3; D020929:Mitogen-Activated Protein Kinase Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism*; D020928:Mitogen-Activated Protein Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism*; D009570:Nitriles / Q000494:pharmacology; D017346:Protein Serine-Threonine Kinases / Q000235:genetics / Q000378:metabolism; D011518:Proto-Oncogene Proteins / Q000235:genetics / Q000378:metabolism; D051057:Proto-Oncogene Proteins c-akt; D020725:ral GTP-Binding Proteins / Q000378:metabolism; D018631:ras Proteins / Q000235:genetics / Q000378:metabolism*
chemical_list: D002070:Butadienes; D009570:Nitriles; D011518:Proto-Oncogene Proteins; C113580:U 0126; D004921:Erythropoietin; C494918:AKT1 protein, human; D017346:Protein Serine-Threonine Kinases; D051057:Proto-Oncogene Proteins c-akt; D019950:Mitogen-Activated Protein Kinase 1; D048052:Mitogen-Activated Protein Kinase 3; D020928:Mitogen-Activated Protein Kinases; D048369:MAP Kinase Kinase 1; C482125:MAP2K1 protein, human; C482127:Map2k1 protein, mouse; D020929:Mitogen-Activated Protein Kinase Kinases; D020725:ral GTP-Binding Proteins; D018631:ras Proteins