Article

HOXB4's road map to stem cell expansion.

Department of Experimental Hematology, Hannover Medical School, Carl-Neuberg-Strasse 1, 30625 Hannover, Germany.
Proceedings of the National Academy of Sciences (Impact Factor: 9.81). 11/2007; 104(43):16952-7. DOI: 10.1073/pnas.0703082104
Source: PubMed

ABSTRACT Homeodomain-containing transcription factors are important regulators of stem cell behavior. HOXB4 mediates expansion of adult and embryo-derived hematopoietic stem cells (HSCs) when expressed ectopically. To define the underlying molecular mechanisms, we performed gene expression profiling in combination with subsequent functional analysis with enriched adult HSCs and embryonic derivatives expressing inducible HOXB4. Thereby, we identified a set of overlapping genes that likely represent "universal" targets of HOXB4. A substantial number of loci are involved in signaling pathways important for controlling self-renewal, maintenance, and differentiation of stem cells. Functional assays performed on selected pathways confirmed the biological coherence of the array results. HOXB4 activity protected adult HSCs from the detrimental effects mediated by the proinflammatory cytokine TNF-alpha. This protection likely contributes to the competitive repopulation advantage of HOXB4-expressing HSCs observed in vivo. The concept of TNF-alpha inhibition may also prove beneficial for patients undergoing bone marrow transplantation. Furthermore, we demonstrate that HOXB4 activity and FGF signaling are intertwined. HOXB4-mediated expansion of adult and ES cell-derived HSCs was enhanced by specific and complete inhibition of FGF receptors. In contrast, the expanding activity of HOXB4 on hematopoietic progenitors in day 4-6 embryoid bodies was blunted in the presence of basic FGF (FGF2), indicating a dominant negative effect of FGF signaling on the earliest hematopoietic cells. In summary, our results strongly suggest that HOXB4 modulates the response of HSCs to multiple extrinsic signals in a concerted manner, thereby shifting the balance toward stem cell self-renewal.

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    • "Crcareva et al. (2005) confirmed that FGF-1 stimulates ex vivo expansion of HSCs and showed that the expanded cells were efficiently transduced by retrovirus vectors. Conditional derivatives of FGF receptor-1 have also been used to support short-term HSC expansion and long-term HSC survival in culture (Schiedlmeier et al, 2007). However, the role of the FGF pathway in regulating adult HSCs or embryonic hematopoietic development is controversial as the same authors showed that the treatment of purified mouse HSCs that ectopically express HoxB4 with the fibroblast growth factor receptor (FGFR) inhibitor SU5402 enhanced HSC repopulating activity. "
    Advances in Hematopoietic Stem Cell Research, 01/2012; , ISBN: 978-953-307-930-1
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    • "Examples are the apical surface of endodermal cells (detected by the Dll4 antibody; fig. 3 b, f) and a few cells from mesodermal territories (detected by both Dll1 + 4 and by J1 antibodies; fig. 3 e, g). HoxB4 induction during EB differentiation is known to upregulate Dll3 and J2 [Schiedlmeier et al., 2007] (online suppl. fig. "
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    ABSTRACT: We portrayed the Notch system in embryonic stem cell (ESC)-derived embryoid bodies (EBs) differentiating under the standard protocols used to assess yolk sac (YS) hematopoiesis in vitro. Notch receptors and Notch ligands were detected in virtually all cells throughout EB development. Notch 1 and Notch 2, but not Notch 4, were visualized in the nucleus of EB cells, and all these receptors were also observed as patent cytoplasmic foci. Notch ligands (Delta-like 1 and 4, Jagged 1 and 2) were immunodetected mostly as cytoplasmic foci. Widespread Notch 1 activation was evident at days 2-4 of EB differentiation, the time window of hemangioblast generation in this in vitro system. EBs experienced major spatial remodeling beyond culture day 4, the time point coincident with the transition between primitive and multilineage waves of YS hematopoiesis in vitro. At day 6, where definitive YS hematopoiesis is established in EBs, these exhibit an immature densely packed cellular region (DCR) surrounded by a territory of mesodermal-like cells and an outer layer of endodermal cells. Immunolabeling of Notch receptors and ligands was usually higher in the DCR. Our results show that Notch system components are continuously and abundantly expressed in the multicellular environments arising in differentiating EBs. In such an active Notch system, receptors and ligands do not accumulate extensively at the cell surface but instead localize at cytoplasmic foci, an observation that fits current knowledge on endocytic modulation of Notch signaling. Our data thus suggest that Notch may function as a territorial modulator during early development, where it may eventually influence YS hematopoiesis.
    Cells Tissues Organs 11/2010; 193(4):239-52. DOI:10.1159/000320572 · 2.14 Impact Factor
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    • "Hoxb4 might protect adult HSCs from detrimental effects mediated by the proinflammatory cytokine TNF-α. This protection also likely contributes to the competitive repopulation advantage of hoxb4-expressing HSCs observed in vivo (Schiedlmeier et al, 2007). "
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    ABSTRACT: In this study six versions of recombinant human hoxb4 proteins were produced and their effectiveness evaluated in expanding human haematopoietic stem and progenitor cells in vitro and in vivo. An N-terminal-tat and C-terminal histidine-tagged version of hoxb4 (T-hoxb4-H) showed the highest activity in expanding colony forming cells (CFCs) and long-term culture-initiating cells (LTC-ICs) when used at 50 nmol/l concentration in cell culture. Human cord blood CD34(+) cells cultured with 50 nmol/l T-hoxb4-H showed a significant increase in severe-combined immunodeficient mouse-repopulating cells (SRCs). In a mouse model of immune-mediated bone marrow (BM) failure, T-hoxb4-H showed an additive effect with cyclosporine in alleviating pancytopenia. In addition, T-hoxb4-H expanded CFC and LTC-IC on BM samples from patients with refractory severe aplastic anaemia and myelodysplastic syndromes: after culturing with 50 nmol/l T-hoxb4-H for 4 d, BM cells from 10 of the 11 patients showed increases in CFC and LTC-IC, and the increase in LTC-IC was statistically significant in samples from four patients. Recombinant human hoxb4 could be a promising therapeutic agent for BM failure.
    British Journal of Haematology 02/2009; 144(4):603-12. DOI:10.1111/j.1365-2141.2008.07509.x · 4.96 Impact Factor

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