Balance of MafB and PU.1 specifies alternative macrophage or dendritic cell fate

Abstract

Macrophages and myeloid dendritic cells (DCs) represent alternative differentiation options of bone marrow progenitors and blood monocytes. This choice profoundly influences the immune response under normal and pathological conditions, but the underlying transcriptional events remain unresolved. Here, we show that experimental activation of the transcription factors PU.1 and MafB in transformed chicken myeloid progenitors triggered alternative DC or macrophage fate, respectively. PU.1 activation also was instructive for DC fate in the absence of cytokines in human HL-60 cell-derived myeloid progenitor and monocyte clones. Differentiation of normal human monocytes to DCs led to a rapid increase of PU.1 to high levels that preceded phenotypic changes, but no MafB expression, whereas monocyte-derived macrophages expressed MafB and only moderate levels of PU.1. DCs inducing levels of PU.1 inhibited MafB expression in monocytes, which appeared to be required for DC specification, since constitutive MafB expression inhibited DC differentiation. Consistent with this, PU.1 directly bound to MafB, inhibited its transcriptional activity in macrophages, and repressed its ability to induce macrophage differentiation in chicken myeloid progenitors. We propose that high PU.1 activity favors DCs at the expense of macrophage fate by inhibiting expression and activity of the macrophage factor MafB. IntroductionDendritic cells (DCs) serve a crucial function in the immune system as the major antigen presenting cells with the unique ability to activate naive T cells, 1 a capacity that has made them the major target of therapeutic manipulation in vaccination and cancer immunotherapy protocols. 1 They can develop from myeloid progenitors in the bone marrow or circulating blood monocytes. 2 When exiting the blood stream, monocytes can give rise to inflammatory macrophages or to antigen presenting DCs. 3 A disturbance of this balance in favor of DC differentiation has been observed in autoimmune disease, 4 whereas tumors can skew it toward the macrophage option. 5 Cytokine conditions favoring outgrowth of DCs in vitro have been well defined in mouse and human cells, most commonly culture of bone marrow progenitors with granulocyte-macrophage colony-stimulating factor (GM-CSF), CD34 ϩ progenitors with GM-CSF and tumor necrosis factor ␣ (TNF␣), or stimulation of blood monocytes with GM-CSF and interleukin-4 (IL-4). 2 By contrast M-CSF, 5 5,[6][7][8][9][10]7 and interferon-␥ (IFN-␥) 8 favor macrophage differentiation at the expense of DC fate.In contrast to the cytokine requirements, the transcriptional events controlling the choice of macrophage versus DC fate have remained unresolved. Some transcription factor knockout mice show defects in DC differentiation 9,10 but also in other lineages, making it difficult to determine at what stage the differentiation block occurred. Certain transcription factor oncogenes have been shown to be capable of transforming DCs or their progenitors, but how this relates to the normal differentiation prog...

E2a/Pbx1 oncogene inhibits terminal differentiation but not myeloid potential of pro-T cells

“…For this purpose, EGER-Fms cells were infected with a bicistronic retroviral vector expressing EGFP and an estradiol-inducible fusion protein of PU.1 (PUER) or a control vector (Bakri et al, 2005). Infected cells were selected by FACS on EGFP expression and Western blot analysis confirmed the correlation between EGFP and PUER fusion protein expressions (Figure 7c).…”

“…For obtaining BMMP, BMCs were cultivated in IMDM supplemented with 10% FBS and 5 ng/ml of Flt3 ligand (PeproTech, France) as described previously (Arnaud et al, 2002). For PU.1 enforced expression, EGER-Fms cells were infected for 2 days by coculture with PlatE packaging cells transfected either with the MFG-EGFP, or the MFG-PUER-EGFP retroviral vectors (Bakri et al, 2005), in the presence of 4 mg/ml of polybrene (Sigma). Infected cells were selected by FACS for EGFP expression.…”

Exogenous heat shock protein 27 uniquely blocks differentiation of monocytes to dendritic cells

“…In contrast, exogenous HSP-27 (a small HSP) predominantly stimulates MO IL-10 [12]. HSP-27 may have a dominant immunosuppressive/antiinflammatory function since IL-10 powerfully depresses MO to immature DC (iDC) (MO?iDC) differentiation and subsequent DC function [13][14][15]. IL-10 also depresses macrophage (MU) production of proinflammatory cytokines [16].…”

“…Differentiating MO are the primary source of human DC and MU [14,16,19]. Myeloid DC are pivotal cells not only in induction of adaptive immune responses, but also in maintaining self tolerance [20][21][22].…”

Everolimus restrains the IL-17A-dependent osteoclast-like transdifferentiation of dendritic cells in multiple myeloma

“…Finally, IL)17A promotes the fusion of DCs, resulting in the multinucleated bone resorbing giant cells in Langherans histiocytosis while enhances the sensitivity of OC precursors to RANK)L (11,12) IL)17A stimulates with high affinity the IL)17RA that drives the OC)like transdifferentiation of iDCs through the CEBPB (CCAAT/enhancer)binding protein beta) factor, thus leading the transcription of NFATc1 (nuclear factor of activated T)cells, cytoplasmic))1, MITF (microphthalmia) associated transcription factor) and cFos while modulates MAFB (musculoaponeurotic fibrosarcoma oncogene homolog B) as the negative regulator of OC maturation (14,15). In addition, IL)17A regulates the OC polarization and bone remodelling priming the CEBPB expression for the balance of Lip/Lap isoforms while restrains experimental and human osteoclastogenesis by MAFB up)regulation (14).…”