Identification of K-ras as the major regulator for cytokine-dependent Akt activation in erythroid progenitors in vivo.
Despite intensive investigation, controversial results have been obtained concerning the precise signaling pathway(s) regulated by K-ras in different cell types. We show that in primary fetal liver erythroid progenitors, erythropoietin activates all three Ras isoforms, but preferentially N- and K-ras. In K-ras(-/-) fetal liver cells (FLC), erythropoietin- or stem cell factor-dependent Akt activation is greatly reduced, whereas other pathways including Stat5 and p44/p42 MAP kinase are activated normally. We further studied the effects of reduced cytokine-dependent Akt activation in erythroid differentiation. We find that freshly isolated K-ras(-/-) FLC show an approximately 7-fold increase of apoptosis and delayed erythroid differentiation, but only at the stage of erythroid progenitors and very early erythroblasts. When K-ras(-/-) erythroid progenitors are cultured in vitro, there is a significant delay in erythroid differentiation but little increase in apoptosis. Furthermore, we show that partial pharmacologic inhibition of the phosphatidylinositol 3-kinase/Akt pathway in wild-type erythroid progenitors leads to a delay in erythroid differentiation similar to that observed in K-ras(-/-) FLC. Taken together, our data identify K-ras as the major regulator for cytokine-dependent Akt activation, which is important for erythroid differentiation in vivo.
Zhang
Jing
J
Whitehead Institute for Biomedical Research, Nine Cambridge Center, Cambridge, MA 02142, USA.
Lodish
Harvey F
HF
D000818:Animals; D015153:Blotting, Western; D002454:Cell Differentiation / Q000187:drug effects / Q000502:physiology*; D002867:Chromones / Q000494:pharmacology; D016207:Cytokines / Q000378:metabolism; D004789:Enzyme Activation / Q000187:drug effects / Q000502:physiology; D015672:Erythroid Precursor Cells / Q000378:metabolism*; D005260:Female; D005434:Flow Cytometry; D047468:Immunoprecipitation; D051379:Mice; D008807:Mice, Inbred BALB C; D018345:Mice, Knockout; D009025:Morpholines / Q000494:pharmacology; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism*; D015398:Signal Transduction / Q000502:physiology*; D018631:ras Proteins / Q000378:metabolism*
D002867:Chromones; D016207:Cytokines; D009025:Morpholines; C085911:2-(4-morpholinyl)-8-phenyl-4H-1-benzopyran-4-one; D051057:Proto-Oncogene Proteins c-akt; D018631:ras Proteins