title: Lnk inhibits erythropoiesis and Epo-dependent JAK2 activation and downstream signaling pathways.
abstract: Erythropoietin (Epo), along with its receptor EpoR, is the principal regulator of red cell development. Upon Epo addition, the EpoR signaling through the Janus kinase 2 (JAK2) activates multiple pathways including Stat5, phosphoinositide-3 kinase (PI-3K)/Akt, and p42/44 mitogen-activated protein kinase (MAPK). The adaptor protein Lnk is implicated in cytokine receptor signaling. Here, we showed that Lnk-deficient mice have elevated numbers of erythroid progenitors, and that splenic erythroid colony-forming unit (CFU-e) progenitors are hypersensitive to Epo. Lnk(-/-) mice also exhibit superior recovery after erythropoietic stress. In addition, Lnk deficiency resulted in enhanced Epo-induced signaling pathways in splenic erythroid progenitors. Conversely, Lnk overexpression inhibits Epo-induced cell growth in 32D/EpoR cells. In primary culture of fetal liver cells, Lnk overexpression inhibits Epo-dependent erythroblast differentiation and induces apoptosis. Lnk blocks 3 major signaling pathways, Stat5, Akt, and MAPK, induced by Epo in primary erythroblasts. In addition, the Lnk Src homology 2 (SH2) domain is essential for its inhibitory function, whereas the conserved tyrosine near the C-terminus and the pleckstrin homology (PH) domain of Lnk are not critical. Furthermore, wild-type Lnk, but not the Lnk SH2 mutant, becomes tyrosine-phosphorylated following Epo administration and inhibits EpoR phosphorylation and JAK2 activation. Hence, Lnk, through its SH2 domain, negatively modulates EpoR signaling by attenuating JAK2 activation, and regulates Epo-mediated erythropoiesis.
authors.affiliation: Whitehead Institute for Biomedical Research, Cambridge, MA 02142, USA.
authors.forename: Wei
authors.initials: W
authors.lastname: Tong
authors.forename: Jing
authors.initials: J
authors.lastname: Zhang
authors.forename: Harvey F
authors.initials: HF
authors.lastname: Lodish
mesh_terms: D048868:Adaptor Proteins, Signal Transducing; D000818:Animals; D017209:Apoptosis; D001798:Blood Proteins / Q000737:chemistry; D015153:Blotting, Western; D002453:Cell Cycle; D002454:Cell Differentiation; D002469:Cell Separation; D003433:Crosses, Genetic; D004268:DNA-Binding Proteins / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D004789:Enzyme Activation; D015672:Erythroid Precursor Cells / Q000378:metabolism; D004920:Erythropoiesis / Q000502:physiology*; D004921:Erythropoietin / Q000378:metabolism*; D005434:Flow Cytometry; D049452:Green Fluorescent Proteins / Q000378:metabolism; D047908:Intracellular Signaling Peptides and Proteins; D053614:Janus Kinase 2; D008099:Liver / Q000196:embryology; D020935:MAP Kinase Signaling System; D008565:Membrane Proteins; D051379:Mice; D008807:Mice, Inbred BALB C; D008810:Mice, Inbred C57BL; D008822:Mice, Transgenic; D008894:Milk Proteins / Q000378:metabolism; D019950:Mitogen-Activated Protein Kinase 1 / Q000378:metabolism; D048052:Mitogen-Activated Protein Kinase 3 / Q000378:metabolism; D009154:Mutation; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D010750:Phosphoproteins / Q000737:chemistry; D010766:Phosphorylation; D017434:Protein Structure, Tertiary; D011505:Protein-Tyrosine Kinases / Q000378:metabolism*; D011506:Proteins / Q000378:metabolism / Q000502:physiology*; D011518:Proto-Oncogene Proteins / Q000378:metabolism*; D017467:Receptors, Erythropoietin / Q000378:metabolism; D012190:Retroviridae / Q000235:genetics; D050799:STAT5 Transcription Factor; D015398:Signal Transduction; D013154:Spleen / Q000166:cytology; D013234:Stem Cells; D013997:Time Factors; D015534:Trans-Activators / Q000378:metabolism; D014443:Tyrosine / Q000737:chemistry; D018909:src Homology Domains
chemical_list: D048868:Adaptor Proteins, Signal Transducing; D001798:Blood Proteins; D004268:DNA-Binding Proteins; D004921:Erythropoietin; D049452:Green Fluorescent Proteins; D047908:Intracellular Signaling Peptides and Proteins; D053614:Janus Kinase 2; D008565:Membrane Proteins; D008894:Milk Proteins; D019950:Mitogen-Activated Protein Kinase 1; D048052:Mitogen-Activated Protein Kinase 3; D019869:Phosphatidylinositol 3-Kinases; D010750:Phosphoproteins; D011505:Protein-Tyrosine Kinases; D011506:Proteins; D011518:Proto-Oncogene Proteins; D017467:Receptors, Erythropoietin; D050799:STAT5 Transcription Factor; D015534:Trans-Activators; D014443:Tyrosine; C490777:Lnk protein, mouse; C039077:platelet protein P47; C507926:Jak2 protein, mouse