IL-4 blocks M-CSF-dependent macrophage proliferation by inducing p21Waf1 in a STAT6-dependent way

Proliferating macrophages in human tumours show characteristics of monocytes responding to myelopoietic growth factors

Macrophages play essential roles in maintaining tissue homeostasis and immune defence. However, their extensive infiltration into tumours has been linked to adverse outcomes in multiple human cancers. Within the tumour microenvironment (TME), tumour-associated macrophages (TAMs) promote tumour growth and metastasis, making them prime targets for cancer immunotherapy. Recent single-cell analysis suggest that proliferating TAMs accumulate in human cancers, yet their origins and differentiation pathways remain uncertain. Here, we show that a subpopulation of CD163+ TAMs proliferates in situ within the TME of melanoma, lung cancer, and breast cancer. Consistent with their potential role in suppressing anti-tumour activities of T cells, CD163+ TAMs express a range of potent immunosuppressive molecules, including PD-L1, PD-L2, IL-10, and TGF-β. Other phenotypic markers strongly suggested that these cells originate from CD14+ CCR2+ monocytes, a cell population believed to have minimal capacity for proliferation. However, we demonstrate in vitro that certain myelopoietic cytokines commonly available within the TME induce robust proliferation of human monocytes, especially the combination of interleukin 3 (IL-3) and Macrophage Colony-Stimulating Factor 1 (M-CSF). Monocytic cells cultured with these cytokines efficiently modulate T cell proliferation, and their molecular phenotype recapitulates that of CD163+ TAMs. IL-3-driven proliferation of monocytic cells can be completely blocked by IL-4, associated with the induction of CDKN1A, alongside the upregulation of transcription factors linked to dendritic cell function, such as BATF3 and IRF4. Taken together, our work suggests several novel therapeutic routes to reducing immunosuppressive TAMs in human tumours, from blocking chemokine-mediated recruitment of monocytes to blocking their proliferation.

Distinct Responses to IL4 in Macrophages Mediated by JNK

IL(Interleukin)-4 is the main macrophage M2-type activator and induces an anti-inflammatory phenotype called alternative activation. The IL-4 signaling pathway involves the activation of STAT (Signal Transducer and Activator of Transcription)-6 and members of the MAPK (Mitogen-activated protein kinase) family. In primary-bone-marrow-derived macrophages, we observed a strong activation of JNK (Jun N-terminal kinase)-1 at early time points of IL-4 stimulation. Using selective inhibitors and a knockout model, we explored the contribution of JNK-1 activation to macrophages' response to IL-4. Our findings indicate that JNK-1 regulates the IL-4-mediated expression of genes typically involved in alternative activation, such as Arginase 1 or Mannose receptor, but not others, such as SOCS (suppressor of cytokine signaling) 1 or p21^Waf-1 (cyclin dependent kinase inhibitor 1A). Interestingly, we have observed that after macrophages are stimulated with IL-4, JNK-1 has the capacity to phosphorylate STAT-6 on serine but not on tyrosine. Chromatin immunoprecipitation assays revealed that functional JNK-1 is required for the recruitment of co-activators such as CBP (CREB-binding protein)/p300 on the promoter of Arginase 1 but not on p21^Waf-1. Taken together, these data demonstrate the critical role of STAT-6 serine phosphorylation by JNK-1 in distinct macrophage responses to IL-4.

Metabolic impact of adipose tissue macrophages in the early postnatal life

Adipose tissue macrophages (ATMs) play key roles in metabolic inflammation, insulin resistance, adipose tissue fibrosis, and immune disorders associated with obesity. Research on ATM biology has mostly been conducted in the setting of adult obesity, since adipocyte hypertrophy is associated with a significant increase in ATM number. Signals that control ATM activation toward a proinflammatory or a proresolving phenotype also determine the developmental program and lipid metabolism of adipocytes after birth. ATMs are present at birth and actively participate in the synthesis of mediators, which induce lipolysis, mitobiogenesis, and mitochondrial uncoupling in adipocytes. ATMs in the newborn and the infant promote a lipolytic and fatty acid oxidizing adipocyte phenotype, which is essential to support the lipid-fueled metabolism, to maintain nonshivering thermogenesis and counteract an excessive adipose tissue expansion. Since adipose tissue metabolism in the early postnatal life determines obesity status in adulthood, early-life ATM functions may have a life-long impact.

Inhibition of Cyclin-Dependent Kinase 9 Downregulates Cytokine Production Without Detrimentally Affecting Human Monocyte-Derived Macrophage Viability

Cyclin-dependent kinase (CDK) inhibitor drugs (CDKi), such as R-roscovitine and AT7519, induce neutrophil apoptosis in vitro and enhance the resolution of inflammation in a number of in vivo models. This class of compounds are potential novel therapeutic agents that could promote the resolution of acute and chronic inflammatory conditions where neutrophil activation contributes to tissue damage and aberrant tissue repair. In this study we investigated CDKi effects on macrophage pro-inflammatory mediator production and viability. Treatment of human monocyte-derived macrophages (MDMs) with the CDKi AT7519 and R-roscovitine at concentrations that induce neutrophil apoptosis had no significant effect on control or LPS-activated MDM apoptosis and viability, and did not detrimentally affect MDM efferocytosis of apoptotic cells. In addition, enhanced efferocytosis, induced by the glucocorticoid dexamethasone, was also unaffected after a short time treatment with R-roscovitine. Macrophage cytokine responses to inflammatory stimuli are also of importance during inflammation and resolution. As a key target of CDKi, CDK9, is involved in protein transcription via the RNA polymerase II complex, we investigated the effect of CDKi drugs on cytokine production. Our data show that treatment with AT7519 significantly downregulated expression and release of key MDM cytokines IL-6, TNF, IL-10 and IL-1β, as well as markers of pro-inflammatory macrophage polarisation. R-Roscovitine was also able to downregulate inflammatory cytokine protein secretion from MDMs. Using siRNA transfection, we demonstrate that genetic knock-down of CDK9 replicates these findings, reducing expression and release of pro-inflammatory cytokines. Furthermore, overexpression of CDK9 in THP-1 cells can promote a pro-inflammatory phenotype in these cells, suggesting that CDK9 plays an important role in the inflammatory phenotype of macrophages. Overall, this study demonstrates that pharmacological and genetic targeting of CDK9 inhibits an inflammatory phenotype in human MDMs. As such these data indicate that CDK9 may be key to therapeutically targeting pro-inflammatory macrophage functions during chronic inflammation.

Non-Genomic AhR-Signaling Modulates the Immune Response in Endotoxin-Activated Macrophages After Activation by the Environmental Stressor BaP

Emerging studies revealed that the Aryl hydrocarbon receptor (AhR), a receptor sensing environmental contaminants, is executing an immunomodulatory function. However, it is an open question to which extent this is achieved by its role as a transcription factor or via non-genomic signaling. We utilized a multi-post-translational modification-omics approach to examine non-genomic AhR-signaling after activation with endogenous (FICZ) or exogenous (BaP) ligand in endotoxin-activated (LPS) monocyte-derived macrophages. While AhR activation affected abundances of few proteins, regulation of ubiquitination and phosphorylation were highly pronounced. Although the number and strength of effects depended on the applied AhR-ligand, both ligands increased ubiquitination of Rac1, which participates in PI3K/AKT-pathway-dependent macrophage activation, resulting in a pro-inflammatory phenotype. In contrast, co-treatment with ligand and LPS revealed a decreased AKT activity mediating an anti-inflammatory effect. Thus, our data show an immunomodulatory effect of AhR activation through a Rac1ubiquitination-dependent mechanism that attenuated AKT-signaling, resulting in a mitigated inflammatory response.

Limosilactobacillus fermentum CECT5716: Mechanisms and Therapeutic Insights

Probiotics microorganisms exert their health-associated activities through some of the following general actions: competitive exclusion, enhancement of intestinal barrier function, production of bacteriocins, improvement of altered microbiota, and modulation of the immune response. Among them, Limosilactobacillus fermentum CECT5716 has become one of the most promising probiotics and it has been described to possess potential beneficial effects on inflammatory processes and immunological alterations. Different studies, preclinical and clinical trials, have evidenced its anti-inflammatory and immunomodulatory properties and elucidated the precise mechanisms of action involved in its beneficial effects. Therefore, the aim of this review is to provide an updated overview of the effect on host health, mechanisms, and future therapeutic approaches.

Identification of tumor-associated macrophage subsets that are associated with breast cancer prognosis

BACKGROUND

Breast cancer is the leading cause of cancer-related deaths in women, demanding new treatment options. With the advent of immune checkpoint blockade, immunotherapy emerged as a treatment option. In addition to lymphocytes, tumor-associated macrophages exert a significant, albeit controversial, impact on tumor development. Pro-inflammatory macrophages are thought to hinder, whereas anti-inflammatory macrophages promote tumor growth. However, molecular markers to identify prognostic macrophage populations remain elusive.

METHODS

We isolated two macrophage subsets, from 48 primary human breast tumors, distinguished by the expression of CD206. Their transcriptomes were analyzed via RNA-Seq, and potential prognostic macrophage markers were validated by PhenOptics in tissue microarrays of patients with invasive breast cancer.

RESULTS

Normal human breast tissue contained mainly CD206+ macrophages, while increased relative amounts of CD206- macrophages were observed in tumors. The presence of CD206+ macrophages correlated with a pronounced lymphocyte infiltrate and subsets of CD206+ macrophages, expressing SERPINH1 and collagen 1, or MORC4, were unexpectedly associated with improved survival of breast cancer patients. In contrast, MHCIIhi CD206- macrophages were linked with a poor survival prognosis.

CONCLUSION

Our data highlight the heterogeneity of tumor-infiltrating macrophages and suggest the use of multiple phenotypic markers to predict the impact of macrophage subpopulations on cancer prognosis. We identified novel macrophage markers that correlate with the survival of patients with invasive mammary carcinoma.

Polyamines and eIF5A Hypusination Modulate Mitochondrial Respiration and Macrophage Activation

How cells adapt metabolism to meet demands is an active area of interest across biology. Among a broad range of functions, the polyamine spermidine is needed to hypusinate the translation factor eukaryotic initiation factor 5A (eIF5A). We show here that hypusinated eIF5A (eIF5AH) promotes the efficient expression of a subset of mitochondrial proteins involved in the TCA cycle and oxidative phosphorylation (OXPHOS). Several of these proteins have mitochondrial targeting sequences (MTSs) that in part confer an increased dependency on eIF5AH. In macrophages, metabolic switching between OXPHOS and glycolysis supports divergent functional fates stimulated by activation signals. In these cells, hypusination of eIF5A appears to be dynamically regulated after activation. Using in vivo and in vitro models, we show that acute inhibition of this pathway blunts OXPHOS-dependent alternative activation, while leaving aerobic glycolysis-dependent classical activation intact. These results might have implications for therapeutically controlling macrophage activation by targeting the polyamine-eIF5A-hypusine axis.

Hepatitis C Virus E2 Envelope Glycoprotein Induces an Immunoregulatory Phenotype in Macrophages

A comprehensive strategy to control hepatitis C virus (HCV) infection needs a vaccine. Our phase I study with recombinant HCV E1/E2 envelope glycoprotein (EnvGPs) as a candidate vaccine did not induce a strong immune response in volunteers. We analyzed the interactions of HCV EnvGPs with human monocyte-derived macrophages as antigen-presenting cells. HCV E2 induced immune regulatory cytokine interleukin (IL)-10 and soluble CD163 (sCD163) protein expression in macrophages from 7 of 9 blood donors tested. Furthermore, HCV E2 enhanced Stat3 and suppressed Stat1 activation, reflecting macrophage polarization toward M2 phenotype. E2-associated macrophage polarization appeared to be dependent of its interaction with CD81 leading endothelial growth factor receptor (EGFR) activation. Additionally, E2 suppressed the expression of C3 complement, similar to HCV-exposed dendritic cells (DCs), implying potential impairment of immune cell priming. Conclusion: Our results suggest that E2 EnvGP may not be an ideal candidate for HCV vaccine development, and discrete domains within E2 may prove to be more capable of elliciting a protective immune response. (Hepatology 2018).

Understanding the Biology of Self-Renewing Macrophages

Macrophages reside in specific territories in organs, where they contribute to the development, homeostasis, and repair of tissues. Recent work has shown that the size of tissue macrophage populations has an impact on tissue functions and is determined by the balance between replenishment and elimination. Macrophage replenishment is mainly due to self-renewal of macrophages, with a secondary contribution from blood monocytes. Self-renewal is a recently discovered trait of macrophages, which can have a major impact on their physiological functions and hence on the wellbeing of the organism. In this review, I discuss our current understanding of the developmental origin of self-renewing macrophages and the mechanisms used to maintain a physiologically stable macrophage pool.

Cytokines Stimulate the Release of Microvesicles from Myeloid Cells Independently from the P2X7 Receptor/Acid Sphingomyelinase Pathway

Microvesicles (MVs) are membrane particles of 200–500 nm released by all cell types constitutively. MVs of myeloid origin are found increased in the cerebrospinal fluid (CSF) of patients suffering from neuroinflammatory disorders, although the factors triggering their production have never been defined. Here, we report that both pro- and anti-inflammatory cytokines, specifically interferon-γ and interleukin-4, are equally able to stimulate the production of MVs from microglia cells and monocytes. Additionally, we found this process to be independent from the best characterized molecular pathway so far described for membrane shedding, which is centered on the purinergic receptor P2X7, whose activation by high concentrations of extracellular ATP (exATP) results in membrane blebbing operated by the secreted enzyme acid sphingomyelinase (ASMase). Moreover, a potent inhibitor of ASMase, injected in a mouse model of multiple sclerosis, failed to reduce the number of MVs in their CSF. This suggests that cytokines, rather than exATP, may exert a long-term control of MV production in the context of chronic inflammation, where both pro- and anti-inflammatory factors play coordinated roles.

Regulation of Epigenetic Modifiers, Including KDM6B, by Interferon-γ and Interleukin-4 in Human Macrophages

Background

Interferon-γ (IFN-γ) or interleukin-4 (IL-4) drives widely different transcriptional programs in macrophages. However, how IFN-γ and IL-4 alter expression of histone-modifying enzymes involved in epigenetic regulation and how this affects the resulting phenotypic polarization is incompletely understood.

Methods and results

We investigated steady-state messenger RNA levels of 84 histone-modifying enzymes and related regulators in colony-stimulating factor-1 differentiated primary human macrophages using quantitative polymerase chain reaction. IFN-γ or IL-4 treatment for 6–48 h changed 11 mRNAs significantly. IFN-γ increased CIITA, KDM6B, and NCOA1, and IL-4 also increased KDM6B by 6 h. However, either cytokine decreased AURKB, ESCO2, SETD6, SUV39H1, and WHSC1, whereas IFN-γ alone decreased KAT2A, PRMT7, and SMYD3 mRNAs only after 18 h, which coincided with decreased cell proliferation. Rendering macrophages quiescent by growth factor starvation or adenovirus-mediated overexpression of p27^kip1 inhibited expression of AURKB, ESCO2, SUV39H1, and WHSC1, and mRNA levels were restored by overexpressing the S-phase transcription factor E2F1, implying their expression, at least partly, depended on proliferation. However, CIITA, KDM6B, NCOA1, KAT2A, PRMT7, SETD6, and SMYD3 were regulated independently of effects on proliferation. Silencing KDM6B, the only transcriptional activator upregulated by both IFN-γ and IL-4, pharmacologically or with short hairpin RNA, blunted a subset of responses to each cytokine.

Conclusion

These findings demonstrate that IFN-γ or IL-4 can regulate the expression of histone acetyl transferases and histone methyl transferases independently of effects on proliferation and that upregulation of the histone demethylase, KDM6B, assists phenotypic polarization by both cytokines.

Nuclear Localization and Cleavage of STAT6 Is Induced by Kaposi's Sarcoma-Associated Herpesvirus for Viral Latency

Emerging evidence implies that STAT6 plays an important role in both the adaptive and innate immune responses to virus infection. Kaposi’s sarcoma-associated herpesvirus (KSHV) is an oncogenic γ-herpesvirus agent associated with several human malignancies, including Kaposi’s sarcoma (KS) and primary effusion lymphomas (PELs). Previously, we demonstrated that KSHV blocks IL-4-induced STAT6 phosphorylation and retains a basal IL-13/STAT6 constitutive activation for cell survival and proliferation. However, the mechanism by which KSHV regulates STAT6 remains largely unknown. Here, we found that KSHV-encoded LANA interacts with STAT6 and promotes nuclear localization of STAT6 independent of the tyrosine 641-phosphorylation state. Moreover, nuclear localization of STAT6 is also dramatically increased in KS tissue. The latent antigen LANA induces serine protease-mediated cleavage of STAT6 in the nucleus, where the cleaved STAT6 lacking transactivation domain functions as a dominant-negative regulator to repress transcription of Replication and Transcription Activator (RTA) and in turn shut off viral lytic replication. Blockade of STAT6 by small interference RNA dramatically enhances expression of RTA, and in turn reduces KSHV-infected endothelial cell growth and colony formation. Taken together, these results suggest that nuclear localization and cleavage of STAT6 is important for modulating the viral latency and pathogenesis of KSHV.

STAT6, a member of the signal transducer and activator of transcription (STAT) family, has been shown to play an important role in viral infection. STAT6 activation is linked to reactivation of oncogenic herpesvirus and their associated cancers. However, the precise mechanism by which KSHV modulates STAT6 regulation remains unclear. In the present study, we demonstrate that KSHV induces nuclear localization and cleavage of STAT6 in both KSHV-infected B lymphoma and endothelial cells. Importantly, this effect is dependent on LANA (a key latent antigen) expression and leads to inhibition of viral lytic replication. Herein, we provide a previously uncharacterized description of how STAT6 plays an inhibitory role in the pathogenesis of oncogenic viruses.

Fully human MAP-fusion protein selectively targets and eliminates proliferating CD64(+) M1 macrophages

Classical immunotoxins compromise a binding component (for example, a ligand, antibody or fragment thereof) and a cytotoxic component, usually derived from bacteria or plants (for example, Pseudomonas exotoxin A or ricin). Despite successful testing in vitro, the clinical development of immunotoxins has been hampered by immunogenicity and unsatisfactory safety profiles. Therefore, research has focused on fully human pro-apoptotic components suitable for the development of cytolytic fusion proteins (CFP). We recently reported that human microtubule-associated protein tau (MAP) can induce apoptosis when delivered to rapidly proliferating cancer cells. Here, we describe a new fully human CFP called H22(scFv)-MAP, which specifically targets CD64(+) cells. We show that H22(scFv)-MAP can efficiently kill proliferating HL-60 pro-monocytic cells in vitro. In addition, the human CFP specifically eliminates polarized M1 macrophages in a transgenic mouse model of cutaneous chronic inflammation. Because M1 macrophages promote the pathogenesis of many chronic inflammatory diseases, targeting this cell population with H22(scFv)-MAP could help to treat diseases such as atopic dermatitis, rheumatoid arthritis and inflammatory bowel disease.

Novel Markers to Delineate Murine M1 and M2 Macrophages

Classically (M1) and alternatively activated (M2) macrophages exhibit distinct phenotypes and functions. It has been difficult to dissect macrophage phenotypes in vivo, where a spectrum of macrophage phenotypes exists, and also in vitro, where low or non-selective M2 marker protein expression is observed. To provide a foundation for the complexity of in vivo macrophage phenotypes, we performed a comprehensive analysis of the transcriptional signature of murine M0, M1 and M2 macrophages and identified genes common or exclusive to either subset. We validated by real-time PCR an M1-exclusive pattern of expression for CD38, G-protein coupled receptor 18 (Gpr18) and Formyl peptide receptor 2 (Fpr2) whereas Early growth response protein 2 (Egr2) and c-Myc were M2-exclusive. We further confirmed these data by flow cytometry and show that M1 and M2 macrophages can be distinguished by their relative expression of CD38 and Egr2. Egr2 labeled more M2 macrophages (~70%) than the canonical M2 macrophage marker Arginase-1, which labels 24% of M2 macrophages. Conversely, CD38 labeled most (71%) in vitro M1 macrophages. In vivo, a similar CD38⁺ population greatly increased after LPS exposure. Overall, this work defines exclusive and common M1 and M2 signatures and provides novel and improved tools to distinguish M1 and M2 murine macrophages.

Tissue macrophage identity and self-renewal

Macrophages are cellular components of the innate immune system that reside in virtually all tissues and contribute to immunity, repair, and homeostasis. The traditional view that all tissue-resident macrophages derive from the bone marrow through circulating monocyte intermediates has dramatically shifted recently with the observation that macrophages from embryonic progenitors can persist into adulthood and self-maintain by local proliferation. In several tissues, however, monocytes also contribute to the resident macrophage population, on which the local environment can impose tissue-specific macrophage functions. These observations have raised important questions: What determines resident macrophage identity and function, ontogeny or environment? How is macrophage proliferation regulated? In this review, we summarize the current knowledge about the identity, proliferation, and turnover of tissue-resident macrophages and how they differ from freshly recruited short-lived monocyte-derived cells. We examine whether macrophage proliferation can be qualified as self-renewal of mature differentiated cells and whether the concepts and molecular pathways are comparable to self-renewal mechanisms in stem cells. Finally, we discuss how improved understanding of macrophage identity and self-renewal could be exploited for therapeutic intervention of macrophage-mediated pathologies by selectively targeting freshly recruited or resident macrophages.

Dendritic cells enhance the activity of human MUC1-stimulated mononuclear cells against breast cancer

Dendritic cells (DCs) are among the most potent antigen-presenting cells (APCs), stimulating peripheral blood mononuclear cells (PBMCs) to generate antigen-specific cytotoxic T lymphocytes (CTLs). The objectives of this study were to determine if interleukin (IL)-4 is beneficial or detrimental for the generation of human DCs in vitro and to understand whether DCs generated in vitro in the presence or absence of IL-4 stimulate the killing of adenocarcinoma cells by CTLs in vivo. Mucin 1 (MUC1), a glycoprotein found on the surface of adenocarcinoma cells was used to load DCs. MUC1-loaded DCs generated in the absence of IL-4 were superior to their counterparts produced with IL-4 in stimulating PBMCs to kill human breast cancer MCF-7 cells in vitro. A corollary in vivo protection experiment was performed by injecting immunodeficient NOD-SCID mice with MCF-7 cells s.c. and MUC1-loaded CTLs, PBMCs, or DCs generated in the absence of IL-4, i.p. Mice that received CTLs and MUC1-loaded DCs on days 0, 2, 4, 9, 14 and 19 were completely protected against the development of MCF-7-derived tumors, while other schedules conferred lower protection. Therefore, tumor antigen-loaded DCs enhance the efficacy of adoptive CTL transfer, and should thus be considered for combinatorial immunotherapeutic regimens.

TRPM7 regulates proliferation and polarisation of macrophages

Ion channels play pivotal roles in regulating important functions of macrophages, such as cytokine and chemokine production, migration, proliferation, phagocytosis and others. In this study, we have identified the transient receptor potential cation channel, subfamily M, member 7 (TRPM7) for the first time in macrophages. TRPM7 activity is differentially regulated in macrophages, i.e. current density in TRPM7 is significantly larger in anti-inflammatory M2-type macrophages than in untreated and in pro-inflammatory M1-type macrophages, whereas mRNA levels of TRPM7 remain unchanged upon cell polarisation. The specific TRPM7 inhibitors NS8593 and FTY720 abolish proliferation of macrophages induced by interleukin-4 (IL-4) and macrophage colony-stimulating factor (M-CSF), respectively, whereas proliferation arrest was not accompanied by induction of apoptosis or necrosis in macrophages. Furthermore, NS8593 and FTY720 prevented polarisation of macrophages towards the anti-inflammatory M2 phenotype. Inhibition of TRPM7 reduced IL-4-induced upregulation of arginase-1 (Arg1) mRNA levels and Arg1 activity, and abolished the inhibitory effects of IL-4 or M-CSF on LPS-induced TNF-α production by macrophages. In summary, our data suggest a main role of TRPM7 in the regulation of macrophage proliferation and polarisation.

CSF-1R signaling in health and disease: a focus on the mammary gland

Colony-stimulating factor-1 (CSF-1), also known as macrophage-colony stimulating factor (M-CSF), is the primary growth factor regulating survival, proliferation and differentiation of macrophages. It is also a potent chemokine for macrophages and monocytes. Signaling via the CSF-1 receptor (CSF-1R) is necessary for the production of almost all tissue resident macrophage populations and these macrophages participate, via trophic mechanisms, in the normal development and homeostasis of tissues and organs in which they reside, including the mammary gland. The drawback of this close interaction between macrophages and parenchymal cells is that dysregulation of macrophage trophic functions assists in the development and progression of many cancers, including breast cancer. Furthermore, tumour cells secrete CSF-1 to attract more macrophages to the tumour microenvironment where CSF-1R signaling frequently drives the behaviour of these tumour-associated macrophages (TAMs) to promote tumour progression and metastasis. Evidence is mounting that treated tumours secrete more CSF-1 and the increased recruitment of TAMs limits treatment efficacy. Thus, therapeutic targeting of the CSF-1R to inhibit TAM function is likely to enhance tumour response and improve patient outcomes in the treatment of cancer, including breast cancer.

Spleen-derived macrophages are readily polarized into classically activated (M1) or alternatively activated (M2) states

Bone marrow derived macrophages (BM-MΦ) that differentiate from precursor cells can be polarized into classically activated pro-inflammatory (M1) or alternatively activated (M2) states depending upon the cytokine microenvironment. We questioned whether tissue MΦ, such as spleen-derived MΦ (Sp-MΦ), have the ability to differentiate into M1 or M2 cells. We show in response to activation with IFN-gamma (IFN-γ) and lipopolysaccharide (LPS), that the Sp-MΦ readily acquired an M1 status indicated by up-regulation of iNOS mRNA, nitric oxide (NO) production, and the co-stimulatory molecule CD86. Conversely, Sp-MΦ exposed to IL-4 exhibited increased levels of mannose receptor (CD 206), arginase-1 (Arg)-1 mRNA expression, and significant urea production typical of M2 cells. At this stage of differentiation, the M2 Sp-MΦ were more efficient at phagocytosis of cell-associated antigens than their M1 counterparts. This polarization was not indefinite as the cells could revert back to their original state upon the removal of stimuli and exhibited flexibility to convert from M2 to M1. Remarkably, both M1 and M2 Sp-MΦ induced more CD4 expression on their cells surface after stimulation. We also demonstrate that adherent macrophages cultured for a short term in IL-4 enhances ARG-1 and YM-1 mRNA along with increasing urea producing capacity: traits indicative of an M2 phenotype. Moreover, in response to in vivo virus infection, the adherent macrophages obtained from spleens rapidly express iNOS. These results provide new evidence for the polarization capabilities of Sp-MΦ when exposed to pro-inflammatory or anti-inflammatory cytokines.

Integrity of the LXXLL motif in Stat6 is required for the inhibition of breast cancer cell growth and enhancement of differentiation in the context of progesterone

Background

Progesterone is essential for the proliferation and differentiation of mammary gland epithelium. Studies of breast cancer cells have demonstrated a biphasic progesterone response consisting of an initial proliferative burst followed by sustained growth arrest. However, the transcriptional factors acting with the progesterone receptor (PR) to mediate the effects of progesterone on mammary cell growth and differentiation remain to be determined. Recently, it was demonstrated that signal transducer and activator of transcription 6 (Stat6) is a cell growth suppressor. Similar to progesterone-bound PR, Stat6 acts by inducing the expression of the G1 cyclin-dependent kinase inhibitors p21 and p27. The possible interaction between Stat6 and progesterone pathways in mammary cells was therefore investigated in the present study.

Methods

ChIP and luciferase were assayed to determine whether Stat6 induces p21 and p27 expression by recruitment at the proximal Sp1-binding sites of the gene promoters. Immunoprecipitation and Western blotting were performed to investigate the interaction between Stat6 and PR-B. The cellular DNA content and cell cycle distribution in breast cancer cells were analyzed by FACS.

Results

We found that Stat6 interacts with progesterone-activated PR in T47D cells. Stat6 synergizes with progesterone-bound PR to transactivate the p21 and p27 gene promoters at the proximal Sp1-binding sites. Moreover, Stat6 overexpression and knockdown, respectively, increased or prevented the induction of p21 and p27 gene expression by progesterone. Stat6 knockdown also abolished the inhibitory effects of progesterone on pRB phosphorylation, G1/S cell cycle progression, and cell proliferation. In addition, knockdown of Stat6 expression prevented the induction of breast cell differentiation markers, previously identified as progesterone target genes. Finally, Stat6 gene expression levels increased following progesterone treatment, indicating a positive auto-regulatory loop between PR and Stat6.

Conclusions

Taken together, these data identify Stat6 as a coactivator of PR mediating the growth-inhibitory and differentiation effects of progesterone on breast cancer cells.

Beyond stem cells: self-renewal of differentiated macrophages

In many mammalian tissues, mature differentiated cells are replaced by self-renewing stem cells, either continuously during homeostasis or in response to challenge and injury. For example, hematopoietic stem cells generate all mature blood cells, including monocytes, which have long been thought to be the major source of tissue macrophages. Recently, however, major macrophage populations were found to be derived from embryonic progenitors and to renew independently of hematopoietic stem cells. This process may not require progenitors, as mature macrophages can proliferate in response to specific stimuli indefinitely and without transformation or loss of functional differentiation. These findings suggest that macrophages are mature differentiated cells that may have a self-renewal potential similar to that of stem cells.

Managing inflammation after spinal cord injury through manipulation of macrophage function

Spinal cord injury (SCI) triggers inflammation with activation of innate immune responses that contribute to secondary injury including oligodendrocyte apoptosis, demyelination, axonal degeneration, and neuronal death. Macrophage activation, accumulation, and persistent inflammation occur in SCI. Macrophages are heterogeneous cells with extensive functional plasticity and have the capacity to switch phenotypes by factors present in the inflammatory microenvironment of the injured spinal cord. This review will discuss the role of different polarized macrophages and the potential effect of macrophage-based therapies for SCI.

Interleukin-4 induces senescence in human renal carcinoma cell lines through STAT6 and p38 MAPK

Interleukin (IL)-4, originally identified as a lymphocyte growth factor, can directly inhibit growth of certain tumor cell types. We reported previously that IL-4 induced cell cycle arrest in G1 phase through an increase in p21(WAF1/CIP1) expression in human renal cell carcinoma (RCC) cell lines. In the present study, we investigated the underlying mechanism of IL-4-induced growth inhibition. In four of six human RCC cell lines, including Caki-1, A498, SNU482, and SNU228, IL-4 induced cellular senescence as demonstrated by enlarged and flattened morphology, increased granularity, and senescence-associated-β-galactosidase (SA-β-gal) staining. Signal tranducer and activator of transcription 6 (STAT6) and p38 MAPK were found to mediate IL-4-induced growth inhibition and cellular senescence. Both of these molecules were activated by 10 min after IL-4 treatment, and inhibition of their activity or expression prevented growth suppression and cellular senescence induced by IL-4. Inhibiting or silencing either STAT6 or p38 MAPK alone partially reduced the effect of IL-4, whereas inhibiting or silencing both molecules exerted an additive effect and almost completely abrogated the effect of IL-4. Thus STAT6 and p38 MAPK appeared to independently mediate IL-4-induced growth inhibition and cellular senescence. The p21(WAF1/CIP1) up-regulation that accompanied growth inhibition and cellular senescence by IL-4 was also attenuated additively when p38 MAPK and STAT6 were silenced. Taken together, these results show that IL-4 induces cellular senescence through independent signaling pathways involving STAT6 and p38 MAPK in some human RCC cell lines.

Stat6 cooperates with Sp1 in controlling breast cancer cell proliferation by modulating the expression of p21(Cip1/WAF1) and p27 (Kip1)

BACKGROUND

The signal transducer and activator of transcription 6 (Stat6), a member of the family of DNA-binding proteins, has been identified as a critical cell differentiation modulator in breast cancer cells. As of yet, the mechanisms underlying this function have remained largely unknown. To further elucidate the role of Stat6 in breast cancer development, we investigated the consequences of exogenous Stat6 expression.

METHODS

Proliferation assays and flow cytometry assays were conducted to evaluate the putative role of Stat6 on cell proliferation. To this end, we produced synchronized cells after a double thymidine block, as confirmed by FACS analysis. mRNA levels of Stat6 were measured by RNase protection analysis. To confirm the interaction among proteins, we employed GST pull-down assays and immunoprecipitation assays. Luciferase assays and ChIP assays were used to assess the transcriptional activity.

RESULTS

Compared to control breast cancer cells, we found that exogenous Stat6 expression plays a critical role in controlling cell proliferation. Also in different breast tumor cell lines, endogenous Stat6 expression was found to be positively related to a lower proliferation rate. Interestingly, in human breast cancer cells Stat6 functions in G1/S cell cycle progression, and the growth-inhibitory effect of Stat6 was shown to be mediated by induction of the G1 cyclin-dependent kinase inhibitors p21(Cip1/WAF1) (p21) and p27(Kip1) (p27). Simultaneously, G1-related cyclin/cyclin-dependent kinase activities and pRB phosphorylation were markedly reduced, and cell cycle progression was blocked in the G1 phase. Stat6 knockdown resulted in enhanced cell proliferation and a decrease in p21 and p27 mRNA levels in the steroid-responsive and non-responsive T-47D and MDA-MB-231 cell lines, respectively. In addition, the stimulatory effect of Stat6 on p21 and p27 gene transcription was found to be associated with interaction of Stat6 with the transcription factor Sp1 at the proximal Sp1-binding sites in their respective promoters.

CONCLUSIONS

Together, these results identify Stat6 as an important cell differentiation regulatory protein functioning, at least in part, by interacting with Sp1 to activate the p21 and p27 gene promoters in breast cancer cells.

In vivo inhibition of c-MYC in myeloid cells impairs tumor-associated macrophage maturation and pro-tumoral activities

Although tumor-associated macrophages (TAMs) are involved in tumor growth and metastasis, the mechanisms controlling their pro-tumoral activities remain largely unknown. The transcription factor c-MYC has been recently shown to regulate in vitro human macrophage polarization and be expressed in macrophages infiltrating human tumors. In this study, we exploited the predominant expression of LysM in myeloid cells to generate c-Myc^fl/fl LysM^cre/+ mice, which lack c-Myc in macrophages, to investigate the role of macrophage c-MYC expression in cancer. Under steady-state conditions, immune system parameters in c-Myc^fl/fl LysM^cre/+ mice appeared normal, including the abundance of different subsets of bone marrow hematopoietic stem cells, precursors and circulating cells, macrophage density, and immune organ structure. In a model of melanoma, however, TAMs lacking c-Myc displayed a delay in maturation and showed an attenuation of pro-tumoral functions (e.g., reduced expression of VEGF, MMP9, and HIF1α) that was associated with impaired tissue remodeling and angiogenesis and limited tumor growth in c-Myc^fl/fl LysM^cre/+ mice. Macrophage c-Myc deletion also diminished fibrosarcoma growth. These data identify c-Myc as a positive regulator of the pro-tumoral program of TAMs and suggest c-Myc inactivation as an attractive target for anti-cancer therapy.

Deacetylation of C/EBPβ is required for IL-4-induced arginase-1 expression in murine macrophages

The amount of arginine available at inflammatory loci is a limiting factor for the growth of several cells of the immune system. IL-4-induced activation of macrophages produced arginase-1, which converts arginine into ornithine, a precursor of polyamines and proline. Trichostatin A (TSA), a pan-inhibitor of histone deacetylases (HDACs), inhibited IL-4-induced arginase-1 expression. TSA showed promoter-specific effects on the IL-4-responsive genes. While TSA inhibited the expression of arginase-1, fizz1, and mrc1, other genes, such as ym,1 mgl1, and mgl2, were not affected. The inhibition of arginase-1 occurred at the transcriptional level with the inhibition of polymerase II binding to the promoter. IL-4 induced STAT6 phosphorylation and binding to DNA. These activities were not affected by TSA treatment. However, TSA inhibited C/EBPβ DNA binding. This inhibitor induced acetylation on lysine residues 215-216, which are critical for DNA binding. Finally, using macrophages from STAT6 KO mice we showed that STAT6 is required for the DNA binding of C/EBPβ. These results demonstrate that the acetylation/deacetylation balance strongly influences the expression of arginase-1, a gene of alternative activation of macrophages. These findings also provide a molecular mechanism to explain the control of gene expression through deacetylase activity.

Circulating cytokine profiles and their relationships with autoantibodies, acute phase reactants, and disease activity in patients with rheumatoid arthritis

Our objective was to analyse the relationship between circulating cytokines, autoantibodies, acute phase reactants, and disease activity in DMARDs-naïve rheumatoid arthritis (RA) patients (n = 140). All cytokines were significantly higher in the RA cohort than in healthy controls. Moderate-to-strong positive intercorrelations were observed between Th1/Th2/macrophage/fibroblast-derived cytokines. RF correlated significantly with IL-1β, IL-2, IL-4, IL-10, IL-12, G-CSF, GM-CSF, IFN-γ, and TNF (P < .0001), and aCCP and aMCV with IL-1β, IL-2, IL-4, and IL-10 (P < .0002), while IL-6 correlated best with the acute phase reactants, CRP, and SAA (P < .0001). In patients with a DAS28 score of ≥5.1, IFN-γ, IL-1β, IL-1Ra, TNF, GM-CSF, and VEGF were significantly correlated (P < .04–.001) with high disease activity (HDA). Circulating cytokines in RA reflect a multifaceted increase in immune reactivity encompassing Th1 and Th2 cells, monocytes/macrophages, and synovial fibroblasts, underscored by strong correlations between these cytokines, as well as their relationships with RF, aCCP, and aMCV, with some cytokines showing promise as biomarkers of HDA.

A polymorphism in the interleukin-4 receptor affects the ability of interleukin-4 to regulate Th17 cells: a possible immunoregulatory mechanism for genetic control of the severity of rheumatoid arthritis

Introduction

Rheumatoid arthritis (RA) is now suspected to be driven by pathogenic Th17 cells that secrete interleukin (IL)-17 and can be regulated by IL-4. A single-nucleotide polymorphism (SNP), I50V, in the coding region of the human IL-4 receptor (IL-4R) is associated with rapid development of erosive disease in RA. The present study was undertaken to determine whether this SNP renders the IL-4R less able to transduce signals that regulate IL-17 production.

Methods

Peripheral blood mononuclear cells were activated under Th17-stimulating conditions in the presence or absence of IL-4, and IL-17 production was measured by both enzyme-linked immunosorbent assay (ELISA) and flow cytometry. Serum IL-17 was also measured by ELISA. Paired comparisons were performed using the two-tailed t-test. IL-4 receptor gene alleles were determined by polymerase chain reaction.

Results

In healthy individuals, IL-4 significantly inhibited IL-17 production by cells from subjects with the I/I genotype (P = 0.0079) and the I/V genotype (P = 0.013), but not the V/V genotype (P > 0.05). In a cross-sectional sample of patients with established RA, the magnitude of the in vitro effect of IL-4 was lower and was not associated with a specific IL-4R allele. Serum IL-17 levels were higher in RA patients than in healthy individuals, as was the percentage of CD4⁺ cells that produced IL-17.

Conclusions

These results indicate that an inherited polymorphism of the IL-4R controls the ability of the human immune system to regulate the magnitude of IL-17 production. However, in established RA, this pattern may be altered, possibly due to secondary effects of both RA itself as well as immunomodulatory medications. Ineffective control of Th17 immune responses is a potential mechanism to explain why IL-4R is an important severity gene in RA, but this issue will require careful study of a cohort of new-onset RA patients.

Genome-wide profiling of interleukin-4 and STAT6 transcription factor regulation of human Th2 cell programming

Dissecting the molecular mechanisms by which T helper (Th) cells differentiate to effector Th2 cells is important for understanding the pathogenesis of immune-mediated diseases, such as asthma and allergy. Because the STAT6 transcription factor is an upstream mediator required for interleukin-4 (IL-4)-induced Th2 cell differentiation, its targets include genes important for this process. Using primary human CD4(+) T cells, and by blocking STAT6 with RNAi, we identified a number of direct and indirect targets of STAT6 with ChIP sequencing. The integration of these data sets with detailed kinetics of IL-4-driven transcriptional changes showed that STAT6 was predominantly needed for the activation of transcription leading to the Th2 cell phenotype. This integrated genome-wide data on IL-4- and STAT6-mediated transcription provide a unique resource for studies on Th cell differentiation and, in particular, for designing interventions of human Th2 cell responses.