Bryostatin 1 (bryo1)-induced monocytic differentiation in THP-1 human leukemia cells is associated with enhanced c-fyn tyrosine kinase and M-CSF receptors

Anti-inflammatory mechanisms in cancer research: Characterization of a distinct M2-like macrophage model derived from the THP-1 cell line

AIMS

Macrophages play an essential role in cancer development. Tumor-associated macrophages (TAMs) have predominantly M2-like attributes that are associated with tumor progression and poor patient survival. Numerous methods have been reported for differentiating and polarizing macrophages in vitro, but there is no standardized and validated model for creating TAMs. Primary cells show varying cytokine responses depending on their origin and functional studies utilizing these cells may lack generalization and validity. A distinct cell line-derived TAM-like M2 subtype is required to investigate the mechanisms mediated by anti-inflammatory TAMs in vitro. Our previous work demonstrated a standardized protocol for creating an M2 subtype derived from a human THP-1 cell line. The cell expression profile, however, has not been validated. The aim of this study was to characterize and validate the TAM-like M2 subtype macrophage created based on our protocol to introduce them as a standardized model for cancer research.

METHODS AND RESULTS

Using qRT-PCR and ELISA, we demonstrated that proinflammatory, anti-inflammatory, and tumor-associated marker expression changed during THP-1-derived marcrophage development in vitro, mimicking a TAM-related profile (e.g., TNFα, IL-1β). The anti-inflammatory marker IL-8/CXCL8, however, is most highly expressed in young M0 macrophages. Flow cytometry showed increased expression of CD206 in the final TAM-like M2 macrophage. Single-cell RNA-sequencing analysis of primary human monocytes and colon cancer tissue macrophages demonstrated that cell line-derived M2 macrophages resembled a TAM-related gene profile.

CONCLUSIONS

The THP-1-derived M2 macrophage based on a standardized cell line model represents a distinct anti-inflammatory TAM-like phenotype with an M2a subtype profile. This model may provide a basis for in vitro investigation of functional mechanisms in a variety of anti-inflammatory settings, particularly colon cancer development.

The phosphatase PPM1A controls monocyte-to-macrophage differentiation

Differentiation of circulating monocytes into tissue-bound or tissue-resident macrophages is a critical regulatory process affecting host defense and inflammation. However, the regulatory signaling pathways that control the differentiation of monocytes into specific and distinct functional macrophage subsets are poorly understood. Herein, we demonstrate that monocyte-to-macrophage differentiation is controlled by the Protein Phosphatase, Mg2+/Mn2+-dependent 1A (PPM1A). Genetic manipulation experiments demonstrated that overexpression of PPM1A attenuated the macrophage differentiation program, while knockdown of PPM1A expression accelerated the ability of monocytes to differentiate into macrophages. We identify imiquimod and Pam3CSK4 as two Toll-like receptor agonists that induce PPM1A expression, and show that increased expression of PPM1A at the onset of differentiation impairs cellular adherence, reduces expression of inflammatory (M1) macrophage-specific markers, and inhibits the production of inflammatory cytokines. Our findings reveal PPM1A as a negative threshold regulator of M1-type monocyte-to-macrophage differentiation, establishing it as a key phosphatase that orchestrates this program.

Regulation of monocyte differentiation by specific signaling modules and associated transcription factor networks

Monocyte/macrophages are important players in orchestrating the immune response as well as connecting innate and adaptive immunity. Myelopoiesis and monopoiesis are characterized by the interplay between expansion of stem/progenitor cells and progression towards further developed (myelo)monocytic phenotypes. In response to a variety of differentiation-inducing stimuli, various prominent signaling pathways are activated. Subsequently, specific transcription factors are induced, regulating cell proliferation and maturation. This review article focuses on the integration of signaling modules and transcriptional networks involved in the determination of monocytic differentiation.

PMA withdrawal in PMA-treated monocytic THP-1 cells and subsequent retinoic acid stimulation, modulate induction of apoptosis and appearance of dendritic cells

OBJECTIVES

To analyse proliferation, differentiation and apoptosis in THP-1 cells after stimulation with phorbol 12-myristate 13-acetate (PMA) and retinoic acid (RA).

MATERIALS AND METHODS

PMA and RA were used in a three-step-procedure: (i) treatment with 6, 30, 60 nm PMA, that induced initial, intermediate and advanced levels of monocyte-macrophage transition, respectively; (ii) recovery in PMA-free medium; (iii) incubation with 4 μm RA. Cultures were characterized cytokinetically (flow cytometry/bromodeoxyuridine uptake) and immunocytochemically (static cytometry) for expression of CD14, CD11b (monocyte-macrophage) and DC-SIGN (dendritic cell: DCs) markers.

RESULTS

Some treatments determined appearance of monocyte/macrophage, dendritic and apoptotic phenotypes, percentages of which were related to PMA dose used in step 1, and dependent on presence/absence of PMA and RA. PMA withdrawal induced dedifferentiation and partial restoration of proliferative activity, specially in 6 and 30 nm PMA-derived cells. Recovery in the presence of serum (fundamental to DC appearance) indicated that depending on differentiation level, cell proliferation and apoptosis were inversely correlated. Treatment with 30 nm PMA induced intermediate levels of monocytic-macrophagic differentiation, with expression of alternative means of differentiation and acquisition of DCs without using cytokines, after PMA withdrawal and RA stimulation.

CONCLUSIONS

Our experimental conditions favoured differentiation, dedifferentiation and transdifferentiational pathways, in monocytic THP-1 cells, the balance of which could be related to both cell proliferation and cell death.

Characterization of Mycobacterium tuberculosis Beijing isolates from the Mediterranean area

BACKGROUND

The Beijing lineage of Mycobacterium tuberculosis is causing concern due to its global distribution and its involvement in severe outbreaks. Studies focused on this lineage are mainly restricted to geographical settings where its prevalence is high, whereas those in other areas are scarce. In this study, we analyze Beijing isolates in the Mediterranean area, where this lineage is not prevalent and is mainly associated with immigrant cases.

RESULTS

Only 1% (N = 26) of the isolates from two population-based studies in Spain corresponded to Beijing strains, most of which were pan-susceptible and from Peruvian and Ecuadorian patients. Restriction fragment length polymorphism typing with the insertion sequence IS6110 identified three small clusters (2-3 cases). Mycobacterial interspersed repetitive unit-variable number tandem repeat typing (MIRU-15) offered low discriminatory power, requiring the introduction of five additional loci. A selection of the Beijing isolates identified in the Spanish sample, together with a sample of Beijing strains from Italy, to broaden the analysis context in the Mediterranean area, were assayed in an infection model with THP-1 cells. A wide range of intracellular growth rates was observed with only two isolates showing an increased intracellular replication, in both cases associated with contained production of TNF-alpha. No correlation was observed between virulence and the Beijing phylogenetic group, clustered/orphan status, or resistance. The Beijing strain responsible for extensive spread on Gran Canaria Island was also identified in Madrid, but did not lead to secondary cases and did not show high infectivity in the infection model.

CONCLUSIONS

The Beijing lineage in our area is a non-homogeneous family, with only certain highly virulent representatives. The specific characterization of Beijing isolates in different settings could help us to accurately identify the virulent representatives before making general assumptions about this lineage.

Survival of monocytes and macrophages and their role in health and disease

Macrophages are versatile cells involved in health and disease. These cells act as scavengers to rid the body of apoptotic and senescent cells and debris through their phagocytic function. Although this is a primary function of these cells, macrophages play vital roles in inflammation and repair of damaged tissue. Macrophages secrete a large number of cytokines, chemokines and growth factors that recruit and activate a variety of cell types to inflamed tissue compartments. These cells are also critical in cell-mediated immunity and in the resolution of inflammation. Since macrophages, and their precursors, blood monocytes, are important in regulating and resolving inflammation, prolonged cellular survival in tissue compartments could be detrimental. Thus, factors that regulate the fate of monocyte and macrophage survival are important in cellular homeostasis. In this article, we will explore stimuli and the intracellular pathways important in regulating macrophage survival and implication in human disease.

Efficacy of selected natural products as therapeutic agents against cancer

With emerging sophistication in the exploration of ocean environment, a number of marine bioactive products have been identified with promising anticancer activity. Many of these are in active phase I or phase II clinical trials or have been terminated because of adverse side effects, mainly hematological in nature. Nonetheless, the information derived has aided enormously in providing leads for laboratory synthesis with modifications in the parent structure affecting compound solubility, absorption, and toxicity, resulting in less severe toxicity while achieving maximum efficacy in smaller doses. We describe herein, a few of the compounds obtained from marine and terrestrial sources [bryostatin 1 ( 1), dolastatin 10 ( 2), auristatin PE ( 3), and combretastatin A4 ( 4)] that have been extensively investigated in our laboratory and continue to be investigated for their sensitization effects with other cytotoxic agents in several different site-specific tumors employing murine models or human subjects.

Comparative gene expression analysis of a chronic myelogenous leukemia cell line resistant to cyclophosphamide using oligonucleotide arrays and response to tyrosine kinase inhibitors

Acquired imatinib resistance in chronic myelogenous leukemia (CML) can be the consequence of mutations in the kinase domain of BCR-ABL or increased protein levels. However, as in other malignancies, acquired resistance to cytostatic drugs is a common reason for treatment failure or disease progression. As a model for drug resistance, we developed a CML cell line resistant to cyclophosphamide (CP). Using oligonucleotide arrays, we examined changes in global gene expression. Selected genes were also examined by real-time PCR and flow cytometry. Neither the parent nor the resistant lines had mutations in their ATP binding domain. Filtering genes with a low-base line expression, a total of 239 genes showed significant changes (162 up- and 77 down-regulated) in the resistant clone. Most of the up-regulated genes were associated with metabolism, signal transduction, or encoded enzymes. The gene for aldehyde dehydrogenase 1 was over-expressed more than 2000-fold in the resistant clone. BCR-ABL was expressed in both cell lines to a comparable extent. When exposed to the tyrosine kinase inhibitors imatinib and nilotinib, both lines were sensitive. In conclusion, we found multiple genetic changes in a CML cell line resistant to CP related to metabolism, signal transduction or apoptosis. Despite these changes, the resistant cells retained sensitivity to tyrosine kinase inhibitors.

The antineoplastic agent bryostatin-1 differentially regulates IFN-gamma receptor subunits in monocytic cells: transcriptional and posttranscriptional control of IFN-gamma R2

Bryostatin-1 (Bryo-1) is a potent ligand and modulator of protein kinase C that exerts antineoplastic and immunomodulatory activities both in vitro and in vivo. We have previously reported that Bryo-1 synergized with IFN-gamma to induce NO synthase and NO by macrophages. To determine whether this effect was associated with changes in levels of IFN-gammaR, we investigated the effects of Bryo-1 on the expression and regulation of IFN-gammaR chains in monocytic cells. Northern blot analysis revealed that Bryo-1 treatment of the human monocytic cell lines MonoMac6 and THP-1 and human monocytes enhanced the expression of IFN-gammaR2 mRNA but did not affect IFN-gammaR1 mRNA expression. Bryo-1 increased IFN-gammaR2 mRNA in a dose-dependent manner as early as 3 h posttreatment. Bryo-1-induced up-regulation of IFN-gammaR2 mRNA levels is not dependent on de novo protein synthesis as shown by cell treatment with the protein-synthesis inhibitor cycloheximide. Bryo-1 treatment increased the IFN-gammaR2 mRNA half-life by 2 h. EMSA analysis from Bryo-1-treated MonoMac6 cells showed an increased nuclear protein binding to the NF-kappaB motif present in the 5' flanking region of the human IFN-gammaR2 promoter that was markedly decreased by pretreatment with the NF-kappaB inhibitor SN50. These results show for the first time that Bryo-1 up-regulates IFN-gammaR2 expression in monocytic cells. Given the pivotal role that IFN-gamma exerts on monocyte activation and in the initiation and outcome of the immune response, the induction of IFN-gammaR2 by Bryo-1 has significant implications in immunomodulation and could overcome some of the immune defects observed in cancer patients.

Src family tyrosine kinases are activated by Flt3 and are involved in the proliferative effects of leukemia-associated Flt3 mutations

OBJECTIVE

The hematopoietic growth factor receptor, Fms-like tyrosine kinase-3 (Flt3), modulates survival and proliferation of myeloid and B-cell precursors. Activating mutations of Flt3 are the most common molecular abnormalities in acute myeloid leukemia (AML) and have an apparent role in leukemogenesis. However, signaling pathways mediating Flt3 effects are incompletely understood. The role of Src kinases is unknown, although some, such as Lyn, have also been linked to leukemogenesis. This study examines the role of Src kinases in Flt3 signaling and the oncogenic effects of leukemia-associated Flt3 mutations.

MATERIALS AND METHODS

We examined the activation and functional roles of Src kinases in human leukemic myeloid cell lines expressing wild-type Flt3 or a constitutively active mutant, and in cells stably transduced with human wild-type or mutant Flt3.

RESULTS

Flt3 ligand stimulation of wild-type Flt3 increased phosphorylation of Src kinase Lyn. Constitutive Lyn phosphorylation and activation was found in cells expressing constitutively active Flt3 mutants. Src kinases are implicated in downregulation of closely related receptors, but Src inhibitors had no effect on ligand-stimulated Flt3 degradation, or on the rapid degradation of an Flt3 mutant. However, growth-factor-independent proliferation resulting from mutant Flt3 expression did depend on the activity of Src kinases.

CONCLUSION

Our studies reveal for the first time the involvement of Src kinases in Flt3 signaling, with activation of Lyn by constitutively active Flt3 mutants as well as ligand-stimulated wild-type receptor, and show that Src kinase inhibitors block proliferative effects of Flt3 mutants found in AML. Thus, Src kinases may represent targets for inhibitor therapy in Flt3-related AML.

Cbl-mediated degradation of Lyn and Fyn induced by constitutive fibroblast growth factor receptor-2 activation supports osteoblast differentiation

Fibroblast growth factors (FGFs) play an important regulatory role in skeletal development and bone formation. However, the FGF signaling mechanisms controlling osteoblast function are poorly understood. Here, we identified a role for the Src family members Lyn and Fyn in osteoblast differentiation promoted by constitutive activation of FGF receptor-2 (FGFR2). We show that the overactive FGFR2 S252W mutation induced decreased Src family kinase tyrosine phosphorylation and activity associated with decreased Lyn and Fyn protein expression in human osteoblasts. Pharmacological stimulation of Src family kinases or transfection with Lyn or Fyn vectors repressed alkaline phosphatase (ALP) up-regulation induced by overactive FGFR2. Inhibition of proteasome activity restored normal Lyn and Fyn expression and ALP activity in FGFR2 mutant osteoblasts. Immunoprecipitation studies showed that Lyn, Fyn, and FGFR2 interacted with the ubiquitin ligase c-Cbl and ubiquitin. Transfection with c-Cbl in which the RING finger was disrupted or with c-Cbl with a point mutation that abolishes the binding ability of the Cbl phosphotyrosine-binding domain restored Src kinase activity and Lyn, Fyn, and FGFR2 levels and reduced ALP up-regulation in mutant osteoblasts. Thus, constitutive FGFR2 activation induces c-Cbl-dependent Lyn and Fyn proteasome degradation, resulting in reduced Lyn and Fyn kinase activity, increased ALP expression, and FGFR2 down-regulation. This reveals a common Cbl-mediated negative feedback mechanism controlling Lyn, Fyn, and FGFR2 degradation in response to overactive FGFR2 and indicates a role for Cbl-dependent down-regulation of Lyn and Fyn in osteoblast differentiation induced by constitutive FGFR2 activation.

Regulated Expression of the Pathogen Receptor Dendritic Cell-specific Intercellular Adhesion Molecule 3 (ICAM-3)-grabbing Nonintegrin in THP-1 Human Leukemic Cells, Monocytes, and Macrophages

Dendritic cell-specific ICAM-3-grabbing nonintegrin (DC-SIGN) is a type II C-type lectin that functions as an adhesion receptor and mediates binding and internalization of pathogens such as virus (human immunodeficiency virus, hepatitis C), bacteria (Mycobacterium), fungi, and parasites. DC-SIGN expression in vivo is primarily restricted to interstitial dendritic cells (DC) and certain tissue macrophages. We now report that leukemic THP-1 cells, widely used as a model for monocyte-macrophage differentiation, express very low basal levels of DC-SIGN and that DC-SIGN expression in THP-1 cells is regulated during differentiation. Differentiation-inducing agents (phorbol ester, bryostatin) conveyed THP-1 cells with the ability to up-regulate DC-SIGN mRNA levels and cell surface expression in response to interleukin-4 (IL-4) or IL-13. DC-SIGN up-regulation required a functional JAK-STAT signaling pathway, was inhibited in the presence of lipopolysaccharide (LPS) or tumor necrosis factor-alpha (TNF-alpha), and conferred THP-1 cells with increased pathogen recognition and T cell stimulatory capabilities. The up-regulation of DC-SIGN on THP-1 cells resembles its inducible expression on monocytes and macrophages, where DC-SIGN expression is also induced by IL-4/IL-13 and negatively regulated by TNF-alpha, LPS, and vitamin D(3). These results point to THP-1 cells as a useful cellular system to characterize the pathogen-binding capabilities of DC-SIGN and to dissect the molecular mechanisms that control its regulated and tissue-specific expression in myeloid dendritic cells, and the results suggest that DC-SIGN constitutes a marker for both DC and alternatively activated macrophages.

1α,25-dihydroxyvitamin D3 and bryostatin-1 synergize to induce monocytic differentiation of NB4 acute promyelocytic leukemia cells by modulating cell cycle progression

This study examines the role of 1alpha,25-dihydroxyvitamin D(3) (1,25(OH)(2)D(3)) and the natural compound, bryostatin-1, on the monocytic differentiation of NB4 acute promyelocytic leukemia cells. We previously showed that 1,25(OH)(2)D(3) primes NB4 cells to mature along the monocyte/macrophage pathway in response to the tumor-promoting phorbol ester, 12-O-tetradecanoylphorbol-13-acetate (TPA). This maturation response involves protein kinase C (PKC) signaling, activation of the transcription factor nuclear factor kappaB (NFkB), and intracellular calcium and calpain activity. The natural compound, bryostatin-1, exhibits some of the effects of TPA but lacks its tumor-promoting nature. 1,25(OH)(2)D(3) treatment followed by bryostatin-1 induces monocytic differentiation of NB4 cells, however,this effect is less pronounced than the combination of 1,25(OH)(2)D(3) and TPA. Maturation is accompanied by decreased proliferation, changes in cellular morphology, increased plastic adherence, and expression of the cell surface marker CD14. Changes in the cell cycle traverse occur before the morphological and biochemical changes associated with differentiation. Within 24 h of bryostatin-1 addition, NB4 cells begin arresting, predominantly in G(1) phase. Changes in the cell cycle traverse were accompanied by changes in the expression of several cell cycle regulatory proteins. Combination 1,25(OH)(2)D(3) and bryostatin-1 treatment, resulted in decreased expression of the cyclin-dependent kinases Cdk2, Cdk1, and Cdk4, of cyclins E and D3, and of the retinoblastoma binding protein (RBBP). Levels of the cyclin-dependent kinase inhibitors p21 and p27 as well as Cyclin D1 were undetectable in NB4 cell lysates, suggesting that they do not participate in the differentiation response or cell cycle control in this model.

Bryostatin-1: a novel PKC inhibitor in clinical development

Modulation of PKC represents a novel approach to cancer therapy. Bryostatin-1 is a macrocyclic lactone derived from a marine invertebrate that binds to the regulatory domain of protein kinase C. Short-term exposure to bryostatin-1 promotes activation of PKC, whereas prolonged exposure promotes significant downregulation of PKC. In numerous hematological and solid tumor cell lines, bryostatin-1 inhibits proliferation, induces differentiation, and promotes apoptosis. Furthermore, preclinical studies indicate that bryostatin-1 potently enhances the effect of chemotherapy. In many cases, this effect is sequence specific. Bryostatin-1 is currently in phase I and phase II clinical trials. The major toxicities are myalgias, nausea, and vomiting. Although there is minimal single-agent activity, combinations with standard chemotherapy are providing very encouraging results and indicate a new direction in cancer therapy.

Activation of the MEK/MAPK pathway is involved in bryostatin1-induced monocytic differenciation and up-regulation of X-linked inhibitor of apoptosis protein

Induction of monocytic differentiation by bryostatin1 (bryo1) conferred on THP-1 leukemia cells the ability to resist Z-LLL-CHO-induced apoptosis. The mechanism of resistance developed during this process was investigated. Apoptosis resistance was associated with an enhanced expression of X-linked inhibitor of apoptosis protein (XIAP), an endogenous caspase inhibitor, in differentiated THP-1 cells. Bryo1 also increased the level of c-IAP-1, yet decreased the level of c-IAP-2 in THP-1 cells, indicating that distinct regulatory mechanisms are operative. In addition, treatment of THP-1 cells with bryo1 induced a rapid and sustained activation of MEK, prior to the upregulation of XIAP and monocytic differentiation. Pretreatment of THP-1 cells with MEK inhibitors (U0126 and PD98059) prior to bryo1 induction blocked the expression of both XIAP and the c-fms product (M-CSF receptor), a hallmark of monocytic differentiation, but not Bcl-2. In addition, the expression of XIAP in bryo1-treated cells was inhibited by CAPE, a NF-kappaB-specific inhibitor, indicating that its expression is under the transcriptional regulation of NF-kappaB downstream of the MEK/MAPK pathway. The importance of XIAP in mediating apoptosis resistance was illustrated in cells transiently transfected with XIAP, which conferred on THP-1 cells the ability to resist Z-LLL-CHO-induced apoptosis. These findings suggest that the expression of XIAP is linked to monocytic differentiation in bryo1-treated THP-1 cells and represents one of the potential antiapoptotic mechanisms acquired during this process.

Induction of macrophage colony-stimulating factor receptor up-regulation in THP-1 human leukemia cells is dependent on the activation of c-fyn protein tyrosine kinase

We investigated the role of fyn kinase on the expression of macrophage colony-stimulating factor (M-CSF) receptors (M-CSFR) and macrophage differentiation using a human myelomonocytic leukemic cell line THP-1. Treatment of THP-1 cells with Bryostatin 1 (bryo 1), a potent protein kinase C (PKC) activator, caused a major fraction of them to become adherent (AD) with distinct monocyte/macrophage characteristics. The differentiation was associated with an enhanced expression of M-CSFR and fyn tyrosine kinase activity, occurring primarily on cells in the AD fraction. Scatchard plot analysis showed that the enhanced expression of M-CSFR binding activity was due to an increase in total receptor number per AD cell, rather than an increase in the binding affinity. Fyn antisense (AS) phosphorothioate oligonucleotides (s-oligos) inhibited the up-regulation of both M-CSFR and c-fms transcripts in bryo 1-treated THP-1 cells. In contrast, fyn sense s-oligos did not affect the up-regulation of either M-CSFR or c-fms mRNA in bryo 1-treated cells. In addition, fyn AS s-oligos blocked the expression of AD capacity in bryo 1-treated THP-1 cells. The efficacy of fyn AS s-oligos as macromolecular inhibitors was verified by their ability to lower fyn-associated tyrosine kinase and in vitro autophosphorylation activity in bryo 1-treated THP-1 cells. Taken together, our results show a strong correlation between M-CSFR expression and monocytic differentiation in THP-1 cells, and suggest a possible role of c-fyn tyrosine kinase in mediating these processes.