title: Bortezomib inhibits STAT5-dependent degradation of LEF-1, inducing granulocytic differentiation in congenital neutropenia CD34(+) cells.
abstract: The transcription factor lymphoid enhancer-binding factor 1 (LEF-1), which plays a definitive role in granulocyte colony-stimulating factor (G-CSF) receptor-triggered granulopoiesis, is downregulated in granulocytic progenitors of severe congenital neutropenia (CN) patients. However, the exact mechanism of LEF-1 downregulation is unclear. CN patients are responsive to therapeutically high doses of G-CSF and are at increased risk of developing acute myeloid leukemia. The normal expression of LEF-1 in monocytes and lymphocytes, whose differentiation is unaffected in CN, suggests the presence of a granulopoiesis-specific mechanism downstream of G-CSF receptor signaling that leads to LEF-1 downregulation. Signal transducer and activator of transcription 5 (STAT5) is activated by G-CSF and is hyperactivated in acute myeloid leukemia. Here, we investigated the effects of activated STAT5 on LEF-1 expression and functions in hematopoietic progenitor cells. We demonstrated that constitutively active STAT5a (caSTAT5a) inhibited LEF-1-dependent autoregulation of the LEF-1 gene promoter by binding to the LEF-1 protein, recruiting Nemo-like kinase and the E3 ubiquitin-ligase NARF to LEF-1, leading to LEF-1 ubiquitination and a reduction in LEF-1 protein levels. The proteasome inhibitor bortezomib reversed the defective G-CSF-triggered granulocytic differentiation of CD34(+) cells from CN patients in vitro, an effect that was accompanied by restoration of LEF-1 protein levels and LEF-1 messenger RNA autoregulation. Taken together, our data define a novel mechanism of LEF-1 downregulation in CN patients via enhanced ubiquitination and degradation of LEF-1 protein by hyperactivated STAT5.
authors.affiliation: Department of Molecular Hematopoiesis, and.
authors.forename: Kshama
authors.initials: K
authors.lastname: Gupta
authors.forename: Inna
authors.initials: I
authors.lastname: Kuznetsova
authors.forename: Olga
authors.initials: O
authors.lastname: Klimenkova
authors.forename: Maksim
authors.initials: M
authors.lastname: Klimiankou
authors.forename: Johann
authors.initials: J
authors.lastname: Meyer
authors.forename: Malcolm A S
authors.initials: MA
authors.lastname: Moore
authors.forename: Cornelia
authors.initials: C
authors.lastname: Zeidler
authors.forename: Karl
authors.initials: K
authors.lastname: Welte
authors.forename: Julia
authors.initials: J
authors.lastname: Skokowa
mesh_terms: D018952:Antigens, CD34 / Q000378:metabolism; D001897:Boronic Acids / Q000494:pharmacology*; D000069286:Bortezomib; D002454:Cell Differentiation / Q000187:drug effects* / Q000235:genetics; D002478:Cells, Cultured; D000080984:Congenital Bone Marrow Failure Syndromes; D006098:Granulocytes / Q000187:drug effects* / Q000473:pathology / Q000502:physiology; D057809:HEK293 Cells; D006410:Hematopoiesis / Q000187:drug effects / Q000235:genetics; D006412:Hematopoietic Stem Cells / Q000187:drug effects* / Q000378:metabolism / Q000502:physiology; D006801:Humans; D051821:Lymphoid Enhancer-Binding Factor 1 / Q000235:genetics / Q000378:metabolism*; D009503:Neutropenia / Q000151:congenital* / Q000235:genetics / Q000378:metabolism / Q000473:pathology; D059748:Proteolysis / Q000187:drug effects*; D011719:Pyrazines / Q000494:pharmacology*; D050799:STAT5 Transcription Factor / Q000502:physiology
chemical_list: D018952:Antigens, CD34; D001897:Boronic Acids; C497573:LEF1 protein, human; D051821:Lymphoid Enhancer-Binding Factor 1; D011719:Pyrazines; D050799:STAT5 Transcription Factor; D000069286:Bortezomib