ABSTRACT
We found that hematopoietic cell-specific Lyn substrate 1 (HCLS1 or HS1) is highly expressed in human myeloid cells and that stimulation with granulocyte colony-stimulating factor (G-CSF) leads to HCLS1 phosphorylation. HCLS1 binds the transcription factor lymphoid-enhancer binding factor 1 (LEF-1), transporting LEF-1 into the nucleus upon G-CSF stimulation and inducing LEF-1 autoregulation. In patients with severe congenital neutropenia, inherited mutations in the gene encoding HCLS1-associated protein X-1 (HAX1) lead to profound defects in G-CSF-triggered phosphorylation of HCLS1 and subsequently to reduced autoregulation and expression of LEF-1. Consistent with these results, HCLS1-deficient mice are neutropenic. In bone marrow biopsies of the majority of tested patients with acute myeloid leukemia, HCLS1 protein expression is substantially elevated, associated with high levels of G-CSF synthesis and, in some individuals, a four-residue insertion in a proline-rich region of HCLS1 protein known to accelerate intracellular signaling. These data demonstrate the importance of HCLS1 in myelopoiesis in vitro and in vivo.
Subject(s)
Adaptor Proteins, Signal Transducing/genetics , Blood Proteins/metabolism , Granulocyte Colony-Stimulating Factor/metabolism , Lymphoid Enhancer-Binding Factor 1/metabolism , Myelopoiesis , Neutropenia/congenital , Active Transport, Cell Nucleus , Adaptor Proteins, Signal Transducing/metabolism , Animals , Base Sequence , Blood Proteins/genetics , Cell Line , Cell Proliferation , Congenital Bone Marrow Failure Syndromes , Female , Granulocytes/metabolism , HEK293 Cells , Humans , Leukemia, Myeloid, Acute/genetics , Leukemia, Myeloid, Acute/metabolism , Male , Mice , Mice, Inbred C57BL , Mice, Knockout , Mutation , Myelopoiesis/genetics , Neutropenia/genetics , Neutropenia/physiopathology , Phosphorylation , RNA Interference , RNA, Small Interfering , Receptors, Granulocyte Colony-Stimulating Factor/genetics , Sequence Analysis, DNA , Signal TransductionABSTRACT
BACKGROUND: Inhibitors of nicotinamide phosphoribosyltransferase have recently been validated as therapeutic targets in leukemia, but the mechanism of leukemogenic transformation downstream of this enzyme is unclear. DESIGN AND METHODS: Here, we evaluated whether nicotinamide phosphoribosyltransferase's effects on aberrant proliferation and survival of myeloid leukemic cells are dependent on sirtuin and delineated the downstream signaling pathways operating during this process. RESULTS: We identified significant upregulation of sirtuin 2 and nicotinamide phosphoribosyltransferase levels in primary acute myeloid leukemia blasts compared to in hematopoietic progenitor cells from healthy individuals. Importantly, specific inhibition of nicotinamide phosphoribosyltransferase or sirtuin 2 significantly reduced proliferation and induced apoptosis in human acute myeloid leukemia cell lines and primary blasts. Intriguingly, we found that protein kinase B/AKT could be deacetylated by nicotinamide phosphoribosyltransferase and sirtuin 2. The anti-leukemic effects of the inhibition of nicotinamide phosphoribosyltransferase or sirtuin 2 were accompanied by acetylation of protein kinase B/AKT with subsequent inhibition by dephosphorylation. This leads to activation of glycogen synthase kinase-3 ß via diminished phosphorylation and, ultimately, inactivation of ß-catenin by phosphorylation. CONCLUSIONS: Our results provide strong evidence that nicotinamide phosphoribosyltransferase and sirtuin 2 participate in the aberrant proliferation and survival of leukemic cells, and suggest that the protein kinase B/AKT/ glycogen synthase kinase-3 ß/ß-catenin pathway is a target for inhibition of nicotinamide phosphoribosyltransferase or sirtuin 2 and, thereby, leukemia cell proliferation.
