The GM-CSF receptor utilizes β-catenin and Tcf4 to specify macrophage lineage differentiation

GM-CSF receptor expression determines opposing innate memory phenotypes at different stages of myelopoiesis

ABSTRACT

Inflammatory responses must be tightly coordinated with the activation of emergency myelopoiesis to produce potent myeloid cells that fight infection without causing excessive host damage. Here, we show that granulocyte-macrophage colony-stimulating factor (GM-CSF) programs myeloid-committed progenitors to produce trained macrophages (increased cytokine response), but programs the upstream noncommitted LKS+ progenitors (defined as Lin- c-Kit+ Sca-1+ cells) to produce tolerized macrophages (decreased cytokine response). In myeloid progenitors, GM-CSF strongly activates signal transducer and activator of transcription 5 (STAT5), Ras-Raf-extracellular signal regulated kinase (ERK), and Akt-mTOR signaling pathways, which are essential to establish a training program, whereas in LKS+ progenitors, GM-CSF induces NF-κB translocation to the nucleus to establish a tolerization program. These differences arise from higher GM-CSF receptor expression in myeloid progenitors compared with LKS+ cells. We demonstrate that β-catenin regulation of NF-κB nuclear translocation is central in this process. In myeloid progenitors, glycogen synthase kinase 3 (GSK3) inactivation by strong ERK and phosphatidylinositol 3 kinase (PI3K)-Akt signaling increases cytoplasmic β-catenin levels to block NF-κB nuclear translocation. In contrast, when ERK and PI3K-Akt signaling are weak, active GSK3 causes a decrease in β-catenin, allowing NF-κB nuclear translocation in LKS+ progenitors. Finally, GM-CSF-induced LKS+ tolerization takes place in several murine models of trained immunity and in human CD34+ CD38- progenitors. Our study reveals that in addition to activating myelopoiesis, GM-CSF also programs early and immediate myeloid progenitors to produce opposing immune memory phenotypes. We propose that the inflammatory response from immediate myeloid progenitors may be balanced by the tolerized phenotype of early progenitors, thus providing a mechanism for appropriate resolution of inflammation and protection against a prolonged cytokine storm.

Wnt signaling: Modulating tumor-associated macrophages and related immunotherapeutic insights

Wnt signaling pathways are highly conserved cascades that mediate multiple biological processes through canonical or noncanonical pathways, from embryonic development to tissue maintenance, but they also contribute to the pathogenesis of numerous cancers. Recent studies have revealed that Wnt signaling pathways critically control the interplay between cancer cells and tumor-associated macrophages (TAMs) in the tumor microenvironment (TME) and potentially impact the efficacy of cancer immunotherapy. In this review, we summarize the evidence that Wnt signaling pathways boost the maturation and infiltration of macrophages for immune surveillance in the steady state but also polarize TAMs toward immunosuppressive M2-like phenotypes for immune escape in the TME. Both cancer cells and TAMs utilize Wnt signaling to transmit signals, and this interaction is crucial for the carcinogenesis and progression of common solid cancers, such as colorectal, gastric, hepatocellular, breast, thyroid, prostate, kidney, and lung cancers; osteosarcoma; and glioma. Specifically, compared with those in solid cancers, Wnt signaling pathways play a distinct role in the pathogenesis of leukemia. Efforts to develop Wnt-based drugs for cancer treatment are still ongoing, and some indeed enhance the anticancer immune response. We believe that the combination of Wnt signaling-based therapy with conventional or immune therapies is a promising therapeutic approach and can facilitate personalized treatment for most cancers.

Recognition of granulocyte-macrophage colony-stimulating factor by specific S100 proteins

Granulocyte-macrophage colony-stimulating factor (GM-CSF) is a pleiotropic myelopoietic growth factor and proinflammatory cytokine, clinically used for multiple indications and serving as a promising target for treatment of many disorders, including cancer, multiple sclerosis, rheumatoid arthritis, psoriasis, asthma, COVID-19. We have previously shown that dimeric Ca2+-bound forms of S100A6 and S100P proteins, members of the multifunctional S100 protein family, are specific to GM-CSF. To probe selectivity of these interactions, the affinity of recombinant human GM-CSF to dimeric Ca2+-loaded forms of 18 recombinant human S100 proteins was studied by surface plasmon resonance spectroscopy. Of them, only S100A4 protein specifically binds to GM-CSF with equilibrium dissociation constant, Kd, values of 0.3-2 μM, as confirmed by intrinsic fluorescence and chemical crosslinking data. Calcium removal prevents S100A4 binding to GM-CSF, whereas monomerization of S100A4/A6/P proteins disrupts S100A4/A6 interaction with GM-CSF and induces a slight decrease in S100P affinity for GM-CSF. Structural modelling indicates the presence in the GM-CSF molecule of a conserved S100A4/A6/P-binding site, consisting of the residues from its termini, helices I and III, some of which are involved in the interaction with GM-CSF receptors. The predicted involvement of the 'hinge' region and F89 residue of S100P in GM-CSF recognition was confirmed by mutagenesis. Examination of S100A4/A6/P ability to affect GM-CSF signaling showed that S100A4/A6 inhibit GM-CSF-induced suppression of viability of monocytic THP-1 cells. The ability of the S100 proteins to modulate GM-CSF activity is relevant to progression of various neoplasms and other diseases, according to bioinformatics analysis. The direct regulation of GM-CSF signaling by extracellular forms of the S100 proteins should be taken into account in the clinical use of GM-CSF and development of the therapeutic interventions targeting GM-CSF or its receptors.

Modulation of recovery from neonatal hyperoxic lung injury by sex as a biological variable

Recovery from lung injury during the neonatal period requires the orchestration of many biological pathways. The modulation of such pathways can drive the developing lung towards proper repair or persistent maldevelopment that can lead to a disease phenotype. Sex as a biological variable can regulate these pathways differently in the male and female lung exposed to neonatal hyperoxia. In this study, we assessed the contribution of cellular diversity in the male and female neonatal lung following injury. Our objective was to investigate sex and cell-type specific transcriptional changes that drive repair or persistent injury in the neonatal lung and delineate the alterations in the immune-endothelial cell communication networks using single cell RNA sequencing (sc-RNAseq) in a murine model of hyperoxic injury. We generated transcriptional profiles of >55,000 cells isolated from the lungs of postnatal day 1 (PND 1; pre-exposure), PND 7, and PND 21neonatal male and female C57BL/6 mice exposed to 95 % FiO2 between PND 1-5 (saccular stage of lung development). We show the presence of sex-based differences in the transcriptional states of lung endothelial and immune cells at PND 1 and PND 21. Furthermore, we demonstrate that biological sex significantly influences the response to injury, with a greater number of differentially expressed genes showing sex-specific patterns than those shared between male and female lungs. Pseudotime trajectory analysis highlighted genes needed for lung development that were altered by hyperoxia. Finally, we show intercellular communication between endothelial and immune cells at saccular and alveolar stages of lung development with sex-based biases in the crosstalk and identify novel ligand-receptor pairs. Our findings provide valuable insights into the cell diversity, transcriptional state, developmental trajectory, and cell-cell communication underlying neonatal lung injury, with implications for understanding lung development and possible therapeutic interventions while highlighting the crucial role of sex as a biological variable.

Modulation of Recovery from Neonatal Hyperoxic Lung Injury by Sex as a Biological Variable

Recovery from lung injury during the neonatal period requires the orchestration of many biological pathways. The modulation of such pathways can drive the developing lung towards proper repair or persistent maldevelopment that can lead to a disease phenotype. Sex as a biological variable can regulate these pathways differently in the male and female lung exposed to neonatal hyperoxia. In this study, we assessed the contribution of cellular diversity in the male and female neonatal lung following injury. Our objective was to investigate sex and cell-type specific transcriptional changes that drive repair or persistent injury in the neonatal lung and delineate the alterations in the immune-endothelial cell communication networks using single cell RNA sequencing (sc-RNAseq) in a murine model of hyperoxic injury. We generated transcriptional profiles of >55,000 cells isolated from the lungs of postnatal day 1 (PND 1) and postnatal day 21 (PND 21) neonatal male and female C57BL/6 mice exposed to 95% FiO 2 between PND 1-5 (saccular stage of lung development). We show the presence of sex-based differences in the transcriptional states of lung endothelial and immune cells at PND 1 and PND 21. Furthermore, we demonstrate that biological sex significantly influences the response to injury, with a greater number of differentially expressed genes showing sex-specific patterns than those shared between male and female lungs. Pseudotime trajectory analysis highlighted genes needed for lung development that were altered by hyperoxia. Finally, we show intercellular communication between endothelial and immune cells at saccular and alveolar stages of lung development with sex-based biases in the crosstalk and identify novel ligand-receptor pairs. Our findings provide valuable insights into the cell diversity, transcriptional state, developmental trajectory, and cell-cell communication underlying neonatal lung injury, with implications for understanding lung development and possible therapeutic interventions while highlighting the crucial role of sex as a biological variable.

Wnt3a-Modified Nanofiber Scaffolds Facilitate Tendon Healing by Driving Macrophage Polarization during Repair

Inflammation is part of the natural healing response, but persistent inflammatory events tend to contribute to pathology changes of tendon or ligament. Phenotypic switching of macrophages within the inflammatory niche is crucial for tendon healing. One viable strategy to improve the functional and biomechanical properties of ruptured tendons is to modulate the transition from inflammatory to regenerative signals during tendon regeneration at the site of injury. Here, we developed a tendon repair scaffold made of biodegradable polycaprolactone by electrospinning, which was modified to deliver Wnt3a protein and served as an implant to improve tendon healing in a rat model of Achilles tendon defect. During the in vitro study, Wnt3a protein promoted the polarization of M2 macrophages. In the in vivo experiment, Wnt3a scaffold promoted the early recruitment and counting curve of macrophages and increased the proportion of M2 macrophages. Achilles function index and mechanical properties showed that the implantation effect of the Wnt3a group was better than that of the control group. We believe that this type of scaffold can be used to repair tendon defects. This work highlights the beneficial role of local delivery of biological factors in directing inflammatory responses toward regenerative strategies in tendon healing.

Myeloid Wls expression is dispensable for skin wound healing and blood vessel regeneration

Wnt signaling controls blood vessel growth, regression and patterning during embryonic and postnatal life. Macrophages are major producers of Wnt ligands and angiogenic growth factors. It regulates vascular development and specification during embryogenesis and wound healing. Macrophage dysregulation in wound healing impairs vessel regeneration and delay wound closure. During cutaneous wound healing, the endovascular progenitors (EVPs) proliferate and differentiate into mature endothelial (D) cells in response to signals produced by perivascular cells, including macrophages, governing blood vessels regeneration. However, the role of macrophage's Wnt production on endothelial cells, especially the EVPs during wound healing is currently unknown. Here we used a cutaneous excisional wound model in mice with conditional deletion of Wnt secretion by myeloid cells (Wls^fl/flLysM-Cre⁺ ) to assess the kinetics of endothelial subpopulations (including EVP), myeloid infiltration, collagen deposition and wound closure. Deletion of Wls expression by myeloid cells did not affect wound closure and collagen deposition, indicating that myeloid Wls expression does not promote wound healing and regeneration. Myeloid-specific Wls deletion elevated the EVP population during the peak of angiogenesis, yet without affecting blood vessel density. Wounds in Wls^fl/flLysM-Cre⁺ animals showed unperturbed myeloid infiltration and differentiation. Overall, our data indicate that macrophage Wnt production shapes EVP kinetics without major relevance to wound healing. These findings extend the knowledge of macrophage and endothelial molecular crosstalk and position myeloid-derived Wnt production as a regulator of endovascular progenitor.

Calming the inflammatory storm in severe COVID-19 infections: Role of biologics- A narrative review

The risk of Coronavirus infection continues, and the fear of resurgence indicates the lack of a successful therapeutic strategy. In severe COVID-19 infection, many immune cells and their products are involved, making management difficult. The abundant release of cytokines and chemokines in severe COVID-19 patients leads to profound hyper inflammation and the mobilization of immune cells, triggering the cytokine storm. The complications associated with the cytokine storm include severe respiratory distress, intravascular coagulation, multi-organ failure, and death. The enormous formation of interleukin (IL)-6 and hemopoietic factors such as granulocyte-macrophage colony-stimulating factor (GM-CSF) are implicated in the severity of the infection. Moreover, these inflammatory cytokines and factors signal through the Janus kinase (JAK)-signal transducer and activator of transcription (STAT) pathway causing the activation of cytokine-related genes. The neutralization of these proteins could be of therapeutic help in COVID-19 patients and could mitigate the risk of mortality. IL-6 antagonist, IL-6 receptor antagonists, GM-CSF receptor inhibitors, and JAK-STAT inhibitors are being investigated to prevent intense lung injury in COVID-19 patients and increase the chances of survival. The review focuses the role of IL-6, GM-CSF, and JAK-STAT inhibitors in regulating the immune response in severely affected COVID-19 patients.

Tumour-derived CSF2/granulocyte macrophage colony stimulating factor controls myeloid cell accumulation and progression of gliomas

BACKGROUND

Malignant tumours release factors, which attract myeloid cells and induce their polarisation to pro-invasive, immunosuppressive phenotypes. Brain-resident microglia and peripheral macrophages accumulate in the tumour microenvironment of glioblastoma (GBM) and induce immunosuppression fostering tumour progression. Macrophage colony stimulating factors (CSFs) control the recruitment of myeloid cells during peripheral cancer progression, but it is disputable, which CSFs drive their accumulation in gliomas.

METHODS

The expression of CSF2 (encoding granulocyte-macrophage colony stimulating factor) was determined in TCGA datasets and five human glioma cell lines. Effects of stable CSF2 knockdown in glioma cells or neutralising CSF2 or receptor CSF2Rα antibodies on glioma invasion were tested in vitro and in vivo.

RESULTS

CSF2 knockdown or blockade of its signalling reduced microglia-dependent glioma invasion in microglia-glioma co-cultures. CSF2-deficient human glioma cells encapsulated in cell-impermeable hollow fibres and transplanted to mouse brains, failed to attract microglia, but stimulated astrocyte recruitment. CSF2-depleted gliomas were smaller, attracted less microglia and macrophages, and provided survival benefit in tumour-bearing mice. Apoptotic microglia/macrophages were detected in CSF2-depleted tumours.

CONCLUSIONS

CSF2 is overexpressed in a subset of mesenchymal GBMs in association with high immune gene expression. Tumour-derived CSF2 attracts, supports survival and induces pro-tumorigenic polarisation of microglia and macrophages.

Macrophages as a Source and Recipient of Wnt Signals

Macrophages are often viewed through the lens of their core functions, but recent transcriptomic studies reveal them to be largely distinct across tissue types. While these differences appear to be shaped by their local environment, the key signals that drive these transcriptional differences remain unclear. Since Wnt signaling plays established roles in cell fate decisions, and tissue patterning during development and tissue repair after injury, we consider evidence that Wnt signals both target and are affected by macrophage functions. We propose that the Wnt gradients present in developing and adult tissues effectively shape macrophage fates and phenotypes. We also highlight evidence that macrophages, through an ability to dispatch Wnt signals, may couple tissue debridement and matrix remodeling with stem cell activation and tissue repair.

Crosstalk between hepatic tumor cells and macrophages via Wnt/β-catenin signaling promotes M2-like macrophage polarization and reinforces tumor malignant behaviors

Tumor-associated macrophages (TAMs) are a major component of tumor microenvironment (TME) and play pivotal roles in the progression of hepatocellular carcinoma (HCC). Wnt signaling is evolutionarily conserved and participates in liver tumorigenesis. Several studies have shown that macrophage-derived Wnt ligands can activate Wnt signaling in tumor cells. However, whether Wnt ligands secreted by tumor cells can trigger Wnt signaling in macrophages is still elusive. In this study, we first verified that canonical Wnt/β-catenin signaling was activated during monocyte-to-macrophage differentiation and in M2-polarized macrophages. Knockdown of β-catenin in M2 macrophages exhibited stronger antitumor characteristics when cocultured with Hepa1-6 HCC cells in a series of experiments. Activation of Wnt signaling promoted M2 macrophage polarization through c-Myc. Moreover, co-culturing naïve macrophages with Hepa1-6 HCC cells in which Wnt ligands secretion was blocked by knockdown of Wntless inhibited M2 polarization in vitro. Consistently, the growth of HCC tumor orthotopically inoculated with Wntless-silenced Hepa1-6 cells was impeded, and the phenotype of M2-like TAMs was abrogated due to attenuated Wnt/β-catenin signaling in TAMs, leading to subverted immunosuppressive TME. Finally, we confirmed the correlation between M2 macrophage polarization and nuclear β-catenin accumulation in CD68⁺ macrophages in human HCC biopsies. Taken together, our study indicates that tumor cells-derived Wnt ligands stimulate M2-like polarization of TAMs via canonical Wnt/β-catenin signaling, which results in tumor growth, migration, metastasis, and immunosuppression in HCC. To block Wnts secretion from tumor cells and/or Wnt/β-catenin signal activation in TAMs may be potential strategy for HCC therapy in future.

Wnt/β-Catenin-Promoted Macrophage Alternative Activation Contributes to Kidney Fibrosis

The Wnt/β-catenin pathway is crucial in normal development and throughout life, but aberrant activation of this pathway has been linked to kidney fibrosis, although the mechanisms involved remain incompletely determined. Here, we investigated the role of Wnt/β-catenin in regulating macrophage activation and the contribution thereof to kidney fibrosis. Treatment of macrophages with Wnt3a exacerbated IL-4- or TGFβ1-induced macrophage alternative (M2) polarization and the phosphorylation and nuclear translocation of STAT3 in vitro Conversely, inhibition of Wnt/β-catenin signaling prevented these IL-4- or TGFβ1-induced processes. In a mouse model, induced deletion of β-catenin in macrophages attenuated the fibrosis, macrophage accumulation, and M2 polarization observed in the kidneys of wild-type littermates after unilateral ureter obstruction. This study shows that activation of Wnt/β-catenin signaling promotes kidney fibrosis by stimulating macrophage M2 polarization.

Biological role of granulocyte macrophage colony-stimulating factor (GM-CSF) and macrophage colony-stimulating factor (M-CSF) on cells of the myeloid lineage

M-CSF and GM-CSF are 2 important cytokines that regulate macrophage numbers and function. Here, we review their known effects on cells of the macrophage-monocyte lineage. Important clues to their function come from their expression patterns. M-CSF exhibits a mostly homeostatic expression pattern, whereas GM-CSF is a product of cells activated during inflammatory or pathologic conditions. Accordingly, M-CSF regulates the numbers of various tissue macrophage and monocyte populations without altering their "activation" status. Conversely, GM-CSF induces activation of monocytes/macrophages and also mediates differentiation to other states that participate in immune responses [i.e., dendritic cells (DCs)]. Further insights into their function have come from analyses of mice deficient in either cytokine. M-CSF signals through its receptor (CSF-1R). Interestingly, mice deficient in CSF-1R expression exhibit a more significant phenotype than mice deficient in M-CSF. This observation was explained by the discovery of a novel cytokine (IL-34) that represents a second ligand of CSF-1R. Information about the function of these ligands/receptor system is still developing, but its complexity is intriguing and strongly suggests that more interesting biology remains to be elucidated. Based on our current knowledge, several therapeutic molecules targeting either the M-CSF or the GM-CSF pathways have been developed and are currently being tested in clinical trials targeting either autoimmune diseases or cancer. It is intriguing to consider how evolution has directed these pathways to develop; their complexity likely mirrors the multiple functions in which cells of the monocyte/macrophage system are involved.

Regulation of gene expression in the bovine blastocyst by colony stimulating factor 2

Background

Colony stimulating factor 2 can have multiple effects on the function of the preimplantation embryo that include increased potential to develop to the blastocyst stage, reduced apoptosis, and enhanced ability of inner cell mass (ICM) to remain pluripotent after culture. The objective of the current experiment was to identify genes regulated by CSF2 in the ICM and trophectoderm (TE) of the bovine blastocyst with the goal of identifying possible molecular pathways by which CSF2 increases developmental competence for survival. Embryos were produced in vitro and cultured from Day 6 to 8 in serum-free medium containing 10 ng/ml recombinant bovine CSF2 or vehicle. Blastocysts were harvested at Day 8 and ICM separated from TE by magnetic-activated cell sorting. RNA was purified and used to prepare amplified cDNA, which was then subjected to high-throughput sequencing using the SOLiD 4.0 system. Three pools of amplified cDNA were analyzed per treatment.

Results

The number of genes whose expression was regulated by CSF2, using P < 0.05 and >1.5-fold difference as cut-offs, was 945 in the ICM (242 upregulated by CSF2 and 703 downregulated) and 886 in the TE (401 upregulated by CSF2 and 485 downregulated). Only 49 genes were regulated in a similar manner by CSF2 in both cell types. The three significant annotation clusters in which genes regulated by ICM were overrepresented were related to membrane signaling. Genes downregulated by CSF2 in ICM were overrepresented in several pathways including those for ERK and AKT signaling. The only significant annotation cluster containing an overrepresentation of genes regulated by CSF2 in TE was for secreted or extracellular proteins. In addition, genes downregulated in TE were overrepresented in TGFβ and Nanog pathways.

Conclusions

Differentiation of the blastocyst is such that, by Day 8 after fertilization, the ICM and TE respond differently to CSF2. Analysis of the genes regulated by CSF2 in ICM and TE are suggestive that CSF2 reinforces developmental fate and function of both cell lineages.

Electronic supplementary material

The online version of this article (doi:10.1186/s13104-016-2038-y) contains supplementary material, which is available to authorized users.

Selective phosphorylation during early macrophage differentiation

The differentiation of macrophages from monocytes is a tightly controlled and complex biological process. Although numerous studies have been conducted using biochemical approaches or global gene/protein profiling, the mechanisms of the early stages of differentiation remain unclear. Here we used SILAC-based quantitative proteomics approach to perform temporal phosphoproteome profiling of early macrophage differentiation. We identified a large set of phosphoproteins and grouped them as PMA-regulated and non-regulated phosphoproteins in the early stages of differentiation. Further analysis of the PMA-regulated phosphoproteins revealed that transcriptional suppression, cytoskeletal reorganization and cell adhesion were among the most significantly activated pathways. Some key involved regulators of these pathways are mTOR, MYB, STAT1 and CTNNB. Moreover, we were able to classify the roles and activities of several transcriptional factors during different differentiation stages and found that E2F is likely to be an important regulator during the relatively late stages of differentiation. This study provides the first comprehensive picture of the dynamic phosphoproteome during myeloid cells differentiation, and identifies potential molecular targets in leukemic cells.

Retinoic acid and GM-CSF coordinately induce retinal dehydrogenase 2 (RALDH2) expression through cooperation between the RAR/RXR complex and Sp1 in dendritic cells

Retinoic acid (RA)-producing dendritic cells (DCs) play critical roles in gut immunity. Retinal dehydrogenase 2 (RALDH2) encoded by Aldh1a2 is a key enzyme for generating RA in DCs. Granulocyte–macrophage colony-stimulating factor (GM-CSF) potently induces RALDH2 expression in DCs in an RA-dependent manner, and RA alone weakly induces the expression. However, how GM-CSF and RA induce RALDH2 expression remains unclear. Here, we show that GM-CSF-induced activation of the transcription factor Sp1 and RA-dependent signaling via the RA receptor (RAR)/retinoid X receptor (RXR) complex contribute to Aldh1a2 expression. The RAR antagonist LE540 and the Sp1 inhibitor mithramycin A inhibited GM-CSF-induced Aldh1a2 expression in fms-related tyrosine kinase 3 ligand-generated bone marrow-derived DCs (BM-DCs). ERK and p38 MAPK inhibitors suppressed GM-CSF-induced nuclear translocation of Sp1 and Aldh1a2 expression. Sp1 and the RARα/RXRα complex bound to GC-rich Sp1-binding sites and an RA response element (RARE) half-site, respectively, near the TATA box in the mouse Aldh1a2 promoter. The DNA sequences around these sites were highly conserved among different species. In the presence of RA, ectopic expression of RARα/RXRα and Sp1 synergistically enhanced Aldh1a2 promoter-reporter activity. GM-CSF did not significantly induce Aldh1a2 expression in plasmacytoid DCs, peritoneal macrophages, or T cells, and the Aldh1a2 promoter in these cells was mostly unmethylated. These results suggest that GM-CSF/RA-induced RALDH2 expression in DCs requires cooperative binding of Sp1 and the RAR/RXR complex to the Aldh1a2 promoter, and can be regulated by a DNA methylation-independent mechanism.

Interleukin-3-mediated regulation of β-catenin in myeloid transformation and acute myeloid leukemia

Aberrant activation of β-catenin is a common event in AML and is an independent predictor of poor prognosis. Although increased β-catenin signaling in AML has been associated with oncogenic translocation products and activating mutations in the FLT3R, the mechanisms that activate β-catenin in AML more broadly are still unclear. Here, we describe a novel link between IL-3 signaling and the regulation of β-catenin in myeloid transformation and AML. In a murine model of HoxB8 and IL-3 cooperation, we show that β-catenin protein levels are modulated by IL-3 and that Cre-induced deletion of β-catenin abolishes IL-3-dependent growth and colony formation. In IL-3-dependent leukemic TF-1.8 cells, we observed increased β-catenin protein levels and nuclear localization in response to IL-3, and this correlated with transcriptional induction of β-catenin target genes. Furthermore, IL-3 promoted β-catenin accumulation in a subset of AML patient samples, and gene-expression profiling of these cells revealed induction of WNT/β-catenin and TCF4 gene signatures in an IL-3-dependent manner. This study is the first to link β-catenin activation to IL-3 and suggests that targeting IL-3 signaling may be an effective approach for the inhibition of β-catenin activity in some patients with AML.

γ-Catenin is overexpressed in acute myeloid leukemia and promotes the stabilization and nuclear localization of β-catenin

Canonical Wnt signaling regulates the transcription of T-cell factor (TCF)-responsive genes through the stabilization and nuclear translocation of the transcriptional co-activator, β-catenin. Overexpression of β-catenin features prominently in acute myeloid leukemia (AML) and has previously been associated with poor clinical outcome. Overexpression of γ-catenin mRNA (a close homologue of β-catenin) has also been reported in AML and has been linked to the pathogenesis of this disease, however, the relative roles of these catenins in leukemia remains unclear. Here we report that overexpression and aberrant nuclear localization of γ-catenin is frequent in AML. Significantly, γ-catenin expression was associated with β-catenin stabilization and nuclear localization. Consistent with this, we found that ectopic γ-catenin expression promoted the stabilization and nuclear translocation of β-catenin in leukemia cells. β-Catenin knockdown demonstrated that both γ- and β-catenin contribute to TCF-dependent transcription in leukemia cells. These data indicate that γ-catenin expression is a significant factor in the stabilization of β-catenin in AML. We also show that although normal cells exclude nuclear translocation of both γ- and β-catenin, this level of regulation is lost in the majority of AML patients and cell lines, which allow nuclear accumulation of these catenins and inappropriate TCF-dependent transcription.