title: Loss of IKKβ but Not NF-κB p65 Skews Differentiation towards Myeloid over Erythroid Commitment and Increases Myeloid Progenitor Self-Renewal and Functional Long-Term Hematopoietic Stem Cells.
abstract: NF-κB is an important regulator of both differentiation and function of lineage-committed hematopoietic cells. Targeted deletion of IκB kinase (IKK) β results in altered cytokine signaling and marked neutrophilia. To investigate the role of IKKβ in regulation of hematopoiesis, we employed Mx1-Cre mediated IKKβ conditional knockout mice. As previously reported, deletion of IKKβ in hematopoietic cells results in neutrophilia, and we now also noted decreased monocytes and modest anemia. Granulocyte-macrophage progenitors (GMPs) accumulated markedly in bone marrow of IKKβ deleted mice whereas the proportion and number of megakaryocyte-erythrocyte progenitors (MEP) decreased. Accordingly, we found a significantly reduced frequency of proerythroblasts and basophilic and polychromatic erythroblasts, and IKKβ-deficient bone marrow cells yielded a significantly decreased number of BFU-E compared to wild type. These changes are associated with elevated expression of C/EBPα, Gfi1, and PU.1 and diminished Gata1, Klf1, and SCL/Tal1 in IKKβ deficient Lineage-Sca1+c-Kit+ (LSK) cells. In contrast, no effect on erythropoiesis or expression of lineage-related transcription factors was found in marrow lacking NF-κB p65. Bone marrow from IKKβ knockout mice has elevated numbers of phenotypic long and short term hematopoietic stem cells (HSC). A similar increase was observed when IKKβ was deleted after marrow transplantation into a wild type host, indicating cell autonomous expansion. Myeloid progenitors from IKKβ- but not p65-deleted mice demonstrate increased serial replating in colony-forming assays, indicating increased cell autonomous self-renewal capacity. In addition, in a competitive repopulation assay deletion of IKKβ resulted in a stable advantage of bone marrow derived from IKKβ knockout mice. In summary, loss of IKKβ resulted in significant effects on hematopoiesis not seen upon NF-κB p65 deletion. These include increased myeloid and reduced erythroid transcription factors, skewing differentiation towards myeloid over erythroid differentiation, increased progenitor self-renewal, and increased number of functional long term HSCs. These data inform ongoing efforts to develop IKK inhibitors for clinical use.
authors.affiliation: Division of Pediatric Oncology, Johns Hopkins University School of Medicine, Baltimore, Maryland, United States of America.
authors.forename: Jing
authors.initials: J
authors.lastname: Zhang
authors.affiliation: Division of Pediatric Oncology, Johns Hopkins University School of Medicine, Baltimore, Maryland, United States of America.
authors.forename: Li
authors.initials: L
authors.lastname: Li
authors.affiliation: Lineberger Comprehensive Cancer Center and Department of Biology, University of North Carolina, Chapel Hill, North Carolina, United States of America.
authors.forename: Albert S
authors.initials: AS
authors.lastname: Baldwin
authors.affiliation: Division of Pediatric Oncology, Johns Hopkins University School of Medicine, Baltimore, Maryland, United States of America.
authors.forename: Alan D
authors.initials: AD
authors.lastname: Friedman
authors.affiliation: Division of Pediatric Oncology, Johns Hopkins University School of Medicine, Baltimore, Maryland, United States of America.
authors.forename: Ido
authors.initials: I
authors.lastname: Paz-Priel
mesh_terms: D000818:Animals; D002454:Cell Differentiation; D041905:Erythroid Cells / Q000166:cytology*; D006412:Hematopoietic Stem Cells / Q000166:cytology*; D020672:I-kappa B Proteins / Q000235:genetics / Q000378:metabolism*; D051379:Mice; D008822:Mice, Transgenic; D051996:Transcription Factor RelA / Q000235:genetics / Q000378:metabolism*
chemical_list: D020672:I-kappa B Proteins; C498144:Rela protein, mouse; D051996:Transcription Factor RelA