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: Kshama Gupta, Inna Kuznetsova, Olga Klimenkova, Maksim Klimiankou, Johann Meyer, Malcolm A S Moore, Cornelia Zeidler, Karl Welte, Julia Skokowa
• Journal: Blood (Blood) Vol. 123 Issue 16 Pg. 2550-61 (Apr 17 2014) ISSN: 1528-0020 [Electronic] United States
• PMID: 24394665 (Publication Type: Journal Article)

Chemical References

• Antigens, CD34
• Boronic Acids
• LEF1 protein, human
• Lymphoid Enhancer-Binding Factor 1
• Pyrazines
• STAT5 Transcription Factor
• Bortezomib

Topics

• Antigens, CD34 (metabolism)
• Boronic Acids (pharmacology)
• Bortezomib
• Cell Differentiation (drug effects, genetics)
• Cells, Cultured
• Congenital Bone Marrow Failure Syndromes
• Granulocytes (drug effects, pathology, physiology)
• HEK293 Cells
• Hematopoiesis (drug effects, genetics)
• Hematopoietic Stem Cells (drug effects, metabolism, physiology)
• Humans
• Lymphoid Enhancer-Binding Factor 1 (genetics, metabolism)
• Neutropenia (congenital, genetics, metabolism, pathology)
• Proteolysis (drug effects)
• Pyrazines (pharmacology)
• STAT5 Transcription Factor (physiology)