Oncogene (2007) 26, 6816–6828 & 2007 Nature Publishing Group All rights reserved 0950-9232/07 $30.00 www.nature.com/onc REVIEW Transcriptional control of granulocyte and monocyte development AD Friedman Division of Pediatric Oncology, Johns Hopkins University, Baltimore, MD, USA PU.1 directs the hematopoietic stem cell to the lymphoid- progenitor (GMP; Akashi et al., 2000; Traver et al., 2001). myeloid progenitor (LMP) and interacts with GATA- The GMP population includes granulocyte-, monocyte- and binding protein 1 to inhibit commitment to the mega- predominantly granulocyte/monocyte-colony forming units karyocyte-erythroid progenitor. The CCAAT/enhancer- (CFU-G, CFU-M and CFU-GM). CFU-G and CFU-M binding protein (C/EBP)a then directs the LMP to the likely arise from CFU-GM, though direct development of granulocyte-monocyte progenitor (GMP) stage, while CFU-M or CFU-G from CMP or HSC under some inhibiting lymphoid development via cross-inhibition of circumstances remains a formal possibility. GMPs also arise Pax5 and potentially other regulators. Increased PU.1 from a linÀKit þ Sca þ IL7Raþ CD34 þ Flt3 þ lymphoid-mye- activity favors monocytic commitment of the GMP. loid progenitor (LMP; Adolfsson et al., 2005). Fetalliverand Induction of PU.1 by C/EBPa and interaction of PU.1 adult marrow also harbor cells with combined B-lineage and with c-Jun elevates PU.1 activity. Zippering of C/EBPa monocyte/macrophage potential(Lacaud et al., 1998; with c-Jun or c-Fos also contributes to monocyte lineage Montecino-Rodriguez et al., 2001; Traver et al., 2001). specification. An additional factor, potentially an Id1- Monocytes not only develop into macrophages, but in regulated basic helix–loop–helix protein, may be required addition give rise to osteoclasts and myeloid dendritic cells for the GMP to commit to the granulocyte lineage. Egr-1, (Roodman, 1996; Manz et al., 2001). Egr-2, Vitamin D Receptor, MafB/c: Fos and PU.1:in- An earlier review provided an overview of the terferon regulatory factor 8 complexes direct further transcriptionalregulation of immature and mature monocytic maturation, while retinoic acid receptor (RAR) granulocyte and monocyte lineage-specific genes (Fried- and C/EBPe direct granulopoiesis. Both C/EBPa and man, 2002). From that survey, it was apparent that RARs induce C/EBPe, and PU.1 is also required, albeit at CCAAT/enhancer-binding proteins (C/EBPs) and PU.1 lower levels, for granulocytic maturation. HoxA10 and regulate the large majority of myeloid genes and that CAAT displacement protein act as transcriptional repres- AP-1 proteins activate at least a subset of monocytic sors to delay expression of terminal differentiation. Gfi-1 genes. Although Runx1 and c-Myb regulate several and Egr-1,2/Nab2 complexes repress each other to genes in immature myeloid cells, they likely play a maintain myeloid lineage fidelity. NF-jB directly binds greater role in HSC biology. The current review will and cooperates with C/EBPb to induce the inflammatory focus on progress over the last 5 years on regulation of response in mature myeloid cells and potentially also myeloid lineage development by C/EBPa and PU.1 and cooperates with C/EBPa to regulate early myelopoiesis. by transcription factors and cytokine signals that Oncogene (2007) 26, 6816–6828; doi:10.1038/sj.onc.1210764 interact directly or indirectly with these factors or further downstream in granulocyte or monocyte lineage Keywords: granulocyte; monocyte; differentiation; C/EBPa; development. PU.1 CCAAT/enhancer-binding protein a, b and e Introduction The C/EBPs homo- and heterodimerize via their C-terminalleucine zipper (LZ) domains and bind DNA Polymorphonuclear and mononuclear phagocytes func- as obligate dimers via the adjacent basic regions (BR) tion in host defense against infections and recognize, (Landschulz et al., 1989). The co-crystalstructure of the ingest and destroy foreign materials and organisms. C/EBPa BR-LZ (bZIP) domain with its cognate binding Pluripotent hematopoietic stem cells (HSC) give rise to a site confirms that the bZIP domain is a continuous linÀIL7RaÀKit þ Sca-1ÀCD34 þ FcgRlo common myeloid a-helix with residues 286–300 entering the major groove progenitor (CMP), which in turn gives rise to a to make direct contact with the base pairs and the linÀIL7RaÀKit þ Sca-1ÀCD34 þ FcgRhi granulocyte-monocyte phosphate backbone (Miller et al., 2003). The consensus binding site is 50-T(T/G)NNGNAA(T/G)-30. C/EBPa, C/EBPb and C/EBPd have N-terminal trans-activation Correspondence: Dr AD Friedman, Division of Pediatric Oncology, Johns Hopkins University, Cancer Research Building I, Room 253, domains, and translation initiation from internal methio- 1650 Orleans Street, Baltimore, MD 21231, USA. nines produces truncated, dominant-inhibitory polypep- E-mail: [email protected] tides that retain the bZIP domain, but have an altered Myeloid development AD Friedman 6817 spectrum of preferred DNA-binding sites (Friedman C/EBPa–ER fusion protein even in cycloheximide, sug- et al., 1989; Friedman and McKnight, 1990; Descombes gesting direct gene activation (Wang et al., 1999). Indeed, and Schibler, 1991; Lin et al., 1993; Calkhoven et al., C/EBPa binds and activates the PU.1 promoter and distal 2000; Cleaves et al., 2004). The Notch-induced protein enhancer, and the role of this activation in myelopoiesis Trib2 binds the 42 kDa but not the 30 kDa isoform of will be discussed further below (Kummalue and Friedman, C/EBPa to induce its proteasome-mediated degradation 2003; Yeamans et al., 2007). C/EBPe(À/À) mice develop (Keeshan et al., 2006). Phosphorylation of C/EBPa all of the hematopoietic lineages, but have a defect in serine 21 by extracellular signal-regulated kinase sup- terminalneutrophilmaturation resemblinghuman cases of presses its activity (Ross et al., 2004). C/EBPe has both secondary granule deficiency (SGD; Yamanaka et al., trans-activation and trans-repression domains and is 1997; Chumakov et al., 1997), and human cases of SGD expressed as several alternatively spliced isoforms harboring C/EBPe point mutations have been described (Williamson et al., 1998; Lekstrom-Himes, 2001). (Lekstrom-Himes et al., 1999; Gombart et al., 2001). Within hematopoiesis, C/EBPa, C/EBPb and C/EBPd Defects in macrophage function are also present in are predominantly expressed in the granulocyte, mono- C/EBPe(À/À) mice (Gombart et al., 2005). C/EBPa binds cyte and eosinophillineages(Scott et al., 1992; Muller the promoter of micro-RNA 223, which in turn suppresses et al., 1995; Radomska et al., 1998). C/EBPa expression translation of nuclear factor I-A to favor granulocytic predominates in immature cells and is detected in the maturation (Fazi et al., 2005). C/EBPa also binds and HSC, CMP and GMP, but not the common lymphoid activates its own promoter, perhaps reflecting a feed- (CLP) or megakeryocyte-erythroid progenitor (MEP) forward mechanism to fix commitment decisions (Christy populations (Traver et al., 2001). C/EBPe is found in et al., 1991). As a further means of stabilizing commitment later-stage granulocytes (Antonson et al., 1996). CHOP, decisions, cross-inhibition of C/EBPa and Pax5 expression a dominant-inhibitory C/EBP isoform is not expressed may stabilize transition of LMP to either the CLP or during normalgranulopoiesis, but is induced by DNA GMP stages, although the extent of such competition and damage or ER-stress and participates in the inflamma- the mechanisms involved require further investigation tory response (Friedman, 1996; Endo et al., 2006). (Heavey et al., 2003; Xie and Graf, 2004; Hsu et al., 2006; C/EBPa(À/À) neonatalmice lackneutrophilsand Anderson et al., 2007). Pax5 also represses the MCSFR eosinophils; although they retain monocytes in their promoter through direct interaction (Tagoh et al., 2006). peripheralblood, Mac-1 þ /Gr-1À monocytes are reduced Under some circumstances, C/EBPb can compensate in their fetaland newborn livers, and marrow CFU-M for loss of C/EBPa during myelopoiesis. Expression of numbers are reduced twofold despite expression of the C/EBPb from the C/EBPa locus leads to normal macrophage colony stimulating factor receptor hematopoiesis (Jones et al., 2002). C/EBPa(À/À) fetal (MCSFR; Zhang et al., 1997). Consistent with these liver cells exposed in vivo to GM-CSF and IL-3 generate observations, Mx1-CRE-mediated deletion of C/EBPa neutrophils, whereas knockdown of C/EBPb in these in adult mice results in a block of the CMP to GMP cells reduces their ability to do so (Hirai et al., 2006). transition (Zhang et al., 2004). A separate study C/EBPb(À/À) marrow cells generate 25–50% reduced investigated myelopoiesis in independently generated numbers of myeloid colonies compared with C/EBPa(À/À) mice similarly concludes that lack of C/EBPb( þ /À) cells in various cytokine conditions, C/EBPa leads to a block between the CMP and GMP and the colonies formed are smaller, potentially reflect- stage, based on increased CFU-S but reduced CFU-GM, ing an ability of C/EBPb to stimulate the proliferation neutrophils and monocyte/macrophages (Heath et al., of myeloid cells, as has been seen with other cell types 2004). Lack of myelopoiesis in vivo from C/EBPa(À/À) (Hirai et al., 2006; Sebastian and Johnson, 2006). progenitors may in part reflect reduced expression of the Induction of C/EBPb in vitro may account for the M-CSF and G-CSF Receptors, as each of their ability of C/EBPa(À/À) cells cultured in IL-3 or GM- promoters depends upon C/EBPa for expression (Zhang CSF, or transduced with the G-CSF receptor and et al., 1994; Smith et al., 1996). A global inhibitor of cultured in G-CSF, to generate neutrophils (Zhang C/EBP-induced trans-activation, KRAB-C/EBPa-ER, et al., 1998, 2002). inhibits murine CFU-G, CFU-M and CFU-GM forma- In contrast to C/EBPb, C/EBPa potently inhibits G1 tion in interleukin (IL)-3 or GM-CSF and prevents 32Dcl3 to S cell cycle progression in a variety of lineages, granulocytic differentiation even in the presence of including myeloid cells (Umek et al., 1991; Wang et al., exogenous G-CSF receptor, indicating that C/EBP family 1999).