Expression of the early growth response 1 and 2 zinc finger genes during induction of monocytic differentiation

Temporal Analysis Reveals the Transient Differential Expression of Transcription Factors That Underlie the Trans-Differentiation of Human Monocytes to Macrophages

The activation of monocytes and their trans-differentiation into macrophages are critical processes of the immune response. Prior work has characterized the differences in the expression between monocytes and macrophages, but the transitional process between these cells is poorly detailed. Here, we analyzed the temporal changes of the transcriptome during trans-differentiation of primary human monocytes into M0 macrophages. We find changes with many transcription factors throughout the process, the vast majority of which exhibit a maximally different expression at the intermediate stages. A few factors, including AP-1, were previously known to play a role in immunological transitions, but most were not. Thus, these findings indicate that this trans-differentiation requires the dynamic expression of many transcription factors not previously discussed in immunology, and provide a foundation for the delineation of the molecular mechanisms associated with healthy or pathological responses that involve this transition.

Role of Systemic Lupus Erythematosus Risk Variants With Opposing Functional Effects as a Driver of Hypomorphic Expression of TNIP1 and Other Genes Within a Three-Dimensional Chromatin Network

OBJECTIVE

Genetic variants in the region of tumor necrosis factor-induced protein 3-interacting protein 1 (TNIP1) are associated with autoimmune disease and reduced TNIP1 gene expression. The aim of this study was to define the functional genetic mechanisms driving TNIP1 hypomorphic expression imparted by the systemic lupus erythematosus-associated TNIP1 H1 risk haplotype.

METHODS

Dual luciferase expression and electrophoretic mobility shift assays were used to evaluate the allelic effects of 11 risk variants on enhancer function and nuclear protein binding in immune cell line models (Epstein-Barr virus [EBV]-transformed human B cells, Jurkat cells, and THP-1 cells), left in a resting state or stimulated with phorbol 12-myristate 13-acetate/ionomycin. HiChIP was used to define the regulatory 3-dimensional (3-D) chromatin network of the TNIP1 haplotype by detecting in situ long-range DNA contacts associated with H3K27ac-marked chromatin in EBV B cells. Then, quantitative reverse transcription-polymerase chain reaction (qRT-PCR) was used to determine the expression of genes within the 3-D chromatin network.

RESULTS

Bioinformatics analyses of 50 single-nucleotide polymorphisms on the TNIP1 H1 risk haplotype identified 11 non-protein-coding variants with a high likelihood of influencing TNIP1 gene expression. Eight variants in EBV B cells, 5 in THP-1 cells, and 2 in Jurkat cells exhibited various allelic effects on enhancer activation, resulting in a cumulative suppressive effect on TNIP1 expression (net effect of risk variants -7.14 fold, -6.80 fold, and -2.44 fold, respectively; n > 3). Specifically, in EBV B cells, only 2 variants (rs10057690 and rs13180950) exhibited allele-specific loss of both enhancer activity and nuclear protein binding (each P < 0.01 relative to nonrisk alleles). In contrast, the rs10036748 risk allele reduced binding affinities of the transcriptional repressors basic helix-loop-helix family member 40/differentially expressed in chondrocytes 1 (bHLHe40/DEC1) (P < 0.05 relative to nonrisk alleles) and CREB-1 (P not significant) in EBV B cells, resulting in a gain of enhancer activity (P < 0.05). HiChIP and qRT-PCR analyses revealed that overall transcriptional repression of the TNIP1 haplotype extended to the neighboring genes DCTN4 and GMA2, both of which also showed decreased expression in the presence of the TNIP1 risk haplotype (P < 0.001 and P < 0.01, respectively, relative to the nonrisk haplotype); notably, it was found that these genes share a 3-D chromatin network.

CONCLUSION

Hypomorphic TNIP1 expression results from the combined concordant and opposing effects of multiple risk variants carried on the TNIP1 risk haplotype, with the strongest regulatory effect in B lymphoid lineage cells. Furthermore, the TNIP1 risk haplotype effect extends to neighboring genes within a shared chromatin network.

CDK6 Inhibition: A Novel Approach in AML Management

Acute myeloid leukemia (AML) is a complex disease with an aggressive clinical course and high mortality rate. The standard of care for patients has only changed minimally over the past 40 years. However, potentially useful agents have moved from bench to bedside with the potential to revolutionize therapeutic strategies. As such, cell-cycle inhibitors have been discussed as alternative treatment options for AML. In this review, we focus on cyclin-dependent kinase 6 (CDK6) emerging as a key molecule with distinct functions in different subsets of AML. CDK6 exerts its effects in a kinase-dependent and -independent manner which is of clinical significance as current inhibitors only target the enzymatic activity.

Signs of Deregulated Gene Expression Are Present in Both CD14+ and CD14- PBMC From Non-Obese Men With Family History of T2DM

AIM

Development of type 2 diabetes (T2DM) is associated with disturbances in immune and metabolic status that may be reflected by an altered gene expression profile of peripheral blood mononuclear cells (PBMC). To reveal a potential family predisposition to these alterations, we investigated the regulation of gene expression profiles in circulating CD14⁺ and CD14^- PBMC in fasting conditions and in response to oral glucose tolerance test (OGTT) in glucose tolerant first-degree relatives (FDR) of T2DM patients and in control subjects.

MATERIALS AND METHODS

This work is based on the clinical study LIMEX (NCT03155412). Non-obese 12 non-diabetic (FDR), and 12 control men without family history of diabetes matched for age and BMI underwent OGTT. Blood samples taken before and at the end of OGTT were used for isolation of circulating CD14⁺ and CD14^- PBMC. In these cells, mRNA levels of 94 genes related to lipid and carbohydrate metabolism, immunity, and inflammation were assessed by qPCR.

RESULTS

Irrespectively of the group, the majority of analyzed genes had different mRNA expression in CD14⁺ PBMC compared to CD14^- PBMC in the basal (fasting) condition. Seven genes (IRS1, TLR2, TNFα in CD14⁺ PBMC; ABCA1, ACOX1, ATGL, IL6 in CD14^- PBMC) had different expression in control vs. FDR groups. OGTT regulated mRNA levels of nine genes selectively in CD14⁺ PBMC and of two genes (ABCA1, PFKL) selectively in CD14^-PBMC. Differences in OGTT-induced response between FDR and controls were observed for EGR2, CCL2 in CD14⁺ PBMC and for ABCA1, ACOX1, DGAT2, MLCYD, and PTGS2 in CD14^- PBMC.

CONCLUSION

This study revealed a different impact of glucose challenge on gene expression in CD14⁺ when compared with CD14^- PBMC fractions and suggested possible impact of family predisposition to T2DM on basal and OGTT-induced gene expression in these PBMC fractions. Future studies on these putative alterations of inflammation and lipid metabolism in fractionated PBMC in larger groups of subjects are warranted.

The molecular mechanism study of insulin in promoting wound healing under high-glucose conditions

BACKGROUND

Wound healing is a complex process in bone development. The aim of this study was to explore the molecular mechanism study of insulin in promoting wound healing.

METHODS

Firstly, the acute human monocyte leukemia cell lines were induced to differentiate into macrophages. Secondly, the porphyromonas gingivalis was applied to mix with the differentiated macrophages. Thirdly, the effect of different concentrations of insulin (0 ng/mL, 5 ng/mL, 50 ng/mL, 100 ng/mL, 200 ng/mL, 500 ng/mL, and 1,000 ng/mL) on the phagocytosis of macrophages and production of reactive oxygen species was investigated. Depending on these experiments, the optimal insulin concentration was used to treat the macrophages at different time points (0 hours and 0.5 hours) to identify the differentially expressed mRNAs. Finally, functional analysis including gene ontology (GO) and the Kyoto Encyclopedia of Genes and Genomes (KEGG) and protein-protein interaction (PPI) analysis was carried out to explore the biological function of these differentially expressed mRNAs.

RESULTS

The test of phagocytosis function and production of reactive oxygen species showed that 200 ng/mL insulin treatment had a significant influence on antibacterial and production of reactive oxygen species. In RNA sequencing, a total of 415 (245 upregulated and 170 downregulated) differentially expressed mRNAs were identified between different time points. Two important signaling pathways including endocytosis and systemic lupus erythematosus were found in the KEGG enrichment analysis. In the PPI network, several hub proteins encoded by differentially expressed mRNA including ALB, HIP1R, RAB5A, HIST1H2BJ, HIST1H3G, and HIST1H2BO were identified.

CONCLUSION

Our work demonstrated that several differentially expressed mRNAs, such as EGR1, RAB34, ALB, HIP1R, RAB5A, HIST1H2BJ, HIST1H3G, and HIST1H2BO and two important signaling pathways including endocytosis and systemic lupus erythematosus may play important roles in the bone wound healing.

MicroRNAs as regulators and effectors of hematopoietic transcription factors

Hematopoiesis is a highly-regulated development process orchestrated by lineage-specific transcription factors that direct the generation of all mature blood cells types, including red blood cells, megakaryocytes, granulocytes, monocytes, and lymphocytes. Under homeostatic conditions, the hematopoietic system of the typical adult generates over 10¹¹ blood cells daily throughout life. In addition, hematopoiesis must be responsive to acute challenges due to blood loss or infection. MicroRNAs (miRs) cooperate with transcription factors to regulate all aspects of hematopoiesis, including stem cell maintenance, lineage selection, cell expansion, and terminal differentiation. Distinct miR expression patterns are associated with specific hematopoietic lineages and stages of differentiation and functional analyses have elucidated essential roles for miRs in regulating cell transitions, lineage selection, maturation, and function. MiRs function as downstream effectors of hematopoietic transcription factors and as upstream regulators to control transcription factor levels. Multiple miRs have been shown to play essential roles. Regulatory networks comprised of differentially expressed lineage-specific miRs and hematopoietic transcription factors are involved in controlling the quiescence and self-renewal of hematopoietic stem cells as well as proliferation and differentiation of lineage-specific progenitor cells during erythropoiesis, myelopoiesis, and lymphopoiesis. This review focuses on hematopoietic miRs that function as upstream regulators of central hematopoietic transcription factors required for normal hematopoiesis. This article is categorized under: RNA in Disease and Development > RNA in Development Regulatory RNAs/RNAi/Riboswitches > Regulatory RNAs.

Role of early growth response 1 in arteriogenesis: Impact on vascular cell proliferation and leukocyte recruitment in vivo

Based on previous findings that early growth response 1 (Egr-1) participates in leukocyte recruitment and cell proliferation in vitro, this study was designed to investigate its mode of action during arteriogenesis in vivo. In a model of peripheral arteriogenesis, Egr-1 was significantly upregulated in growing collaterals of wild-type (WT) mice, both on mRNA and protein level. Egr-1−/− mice demonstrated delayed arteriogenesis after femoral artery ligation. They further showed increased levels of monocytes and granulocytes in the circulation, but reduced levels in adductor muscles under baseline conditions. After femoral artery ligation, elevated numbers of macrophages were detected in the perivascular zone of collaterals in Egr-1−/− mice and mRNA of leukocyte recruitment mediators was upregulated. Other Egr family members (Egr-2 to -4) were significantly upregulated only in Egr-1−/− mice, suggesting a mechanism of counterbalancing Egr-1 deficiency. Moreover, splicing factor-1, downregulated in WT mice after femoral artery ligation in the process of increased vascular cell proliferation, was upregulated in Egr-1−/− mice. αSM-actin on the other hand, significantly downregulated in WT mice, showed no differential expression in Egr-1−/− mice. While cell cycle regulator cyclin E and cdc20 were upregulated in Egr-1−/− mice, cyclin D1 expression decreased below the detection limit in collaterals, and the proliferation marker ki67 was not differentially expressed. In conclusion, compensation for deficiency in Egr-1 function in leukocyte recruitment can presumably be mediated by other transcription factors; however, Egr-1 is indispensable for effective vascular cell cycle progression in arteriogenesis.

Egr-1 regulates RTA transcription through a cooperative involvement of transcriptional regulators

Kaposi's sarcoma associated herpesvirus (KSHV) regulates the host cellular environment to establish life-long persistent infection by manipulating cellular signaling pathways, with approximately 1- 5% of cells undergoing lytic reactivation during the course of infection. Egr-1 (Early Growth Response Factor-1) is one such cellular transcription factor, which gets phosphorylated during the lytic phase of viral life cycle to perpetrate its function. This study demonstrates the mechanism of how Egr-1 mediates transcription of the immediate early gene, RTA (Replication and transcription activator), which is the lytic switch gene of KSHV. Egr-1 depleted KSHV infected cells exhibited reduced expression of RTA. Also, an increase in Egr-1 phosphorylation led to a higher virion production, which was suppressed in the presence of p38 and Raf inhibitors. Reporter assays showed that coexpression of Egr-1 and CBP (CREB-binding protein) enhances RTA promoter activity as compared to the expression of either Egr-1 or CBP alone. Binding of Egr-1 and CBP at RTA promoter was analyzed by chromatin immunoprecipitation assay (ChIP), which showed an enhanced accumulation during viral reactivation. Mutation in Egr-1 binding site of the RTA promoter eliminated Egr-1 response on promoter activation. Furthermore, de novo infection of THP-1 (monocytic) and HUVECs (endothelial) cells showed an upregulation of Egr-1 phosphorylation, whereas depletion of Egr-1 reduced the mRNA levels of RTA during primary infection. Together, these results demonstrate a cooperative role of Egr-1 and CBP in mediating RTA transcription, which significantly improves our understanding of the involvement of cellular factors controlling RTA transcription in KSHV pathogenesis.

Gene expression profiles and signaling mechanisms in α2B-adrenoceptor-evoked proliferation of vascular smooth muscle cells

BACKGROUND

α2-adrenoceptors are important regulators of vascular tone and blood pressure. Regulation of cell proliferation is a less well investigated consequence of α2-adrenoceptor activation. We have previously shown that α2B-adrenoceptor activation stimulates proliferation of vascular smooth muscle cells (VSMCs). This may be important for blood vessel development and plasticity and for the pathology and therapeutics of cardiovascular disorders. The underlying cellular mechanisms have remained mostly unknown. This study explored pathways of regulation of gene expression and intracellular signaling related to α2B-adrenoceptor-evoked VSMC proliferation.

RESULTS

The cellular mechanisms and signaling pathways of α2B-adrenoceptor-evoked proliferation of VSMCs are complex and include redundancy. Functional enrichment analysis and pathway analysis identified differentially expressed genes associated with α2B-adrenoceptor-regulated VSMC proliferation. They included the upregulated genes Egr1, F3, Ptgs2 and Serpine1 and the downregulated genes Cx3cl1, Cav1, Rhoa, Nppb and Prrx1. The most highly upregulated gene, Lypd8, represents a novel finding in the VSMC context. Inhibitor library screening and kinase activity profiling were applied to identify kinases in the involved signaling pathways. Putative upstream kinases identified by two different screens included PKC, Raf-1, Src, the MAP kinases p38 and JNK and the receptor tyrosine kinases EGFR and HGF/HGFR. As a novel finding, the Src family kinase Lyn was also identified as a putative upstream kinase.

CONCLUSIONS

α2B-adrenoceptors may mediate their pro-proliferative effects in VSMCs by promoting the activity of bFGF and PDGF and the growth factor receptors EGFR, HGFR and VEGFR-1/2. The Src family kinase Lyn was also identified as a putative upstream kinase. Lyn is known to be expressed in VSMCs and has been identified as an important regulator of GPCR trafficking and GPCR effects on cell proliferation. Identified Ser/Thr kinases included several PKC isoforms and the β-adrenoceptor kinases 1 and 2. Cross-talk between the signaling mechanisms involved in α2B-adrenoceptor-evoked VSMC proliferation thus appears to involve PKC activation, subsequent changes in gene expression, transactivation of EGFR, and modulation of kinase activities and growth factor-mediated signaling. While many of the identified individual signals were relatively small in terms of effect size, many of them were validated by combining pathway analysis and our integrated screening approach.

MicroRNA-146a modulates B-cell oncogenesis by regulating Egr1

miR-146a is a NF-κB induced microRNA that serves as a feedback regulator of this critical pathway. In mice, deficiency of miR-146a results in hematolymphoid cancer at advanced ages as a consequence of constitutive NF-κB activity. In this study, we queried whether the deficiency of miR-146a contributes to B-cell oncogenesis. Combining miR-146a deficiency with transgenic expression of c-Myc led to the development of highly aggressive B-cell malignancies. Mice transgenic for c-Myc and deficient for miR-146a were characterized by significantly shortened survival, increased lymph node involvement, differential involvement of the spleen and a mature B-cell phenotype. High-throughput sequencing of the tumors revealed significant dysregulation of approximately 250 genes. Amongst these, the transcription factor Egr1 was consistently upregulated in mice deficient for miR-146a. Interestingly, transcriptional targets of Egr1 were enriched in both the high-throughput dataset and in a larger set of miR-146a-deficient tumors. miR-146a overexpression led to downregulation of Egr1 and downstream targets with concomitant decrease in cell growth. Direct targeting of the human EGR1 by miR-146a was seen by luciferase assay. Together our findings illuminate a bona fide role for miR-146a in the modulation of B-cell oncogenesis and reveal the importance of understanding microRNA function in a cell- and disease-specific context.

Lactic acid delays the inflammatory response of human monocytes

Lactic acid (LA) accumulates under inflammatory conditions, e.g. in wounds or tumors, and influences local immune cell functions. We previously noted inhibitory effects of LA on glycolysis and TNF secretion of human LPS-stimulated monocytes. Here, we globally analyze the influence of LA on gene expression during monocyte activation. To separate LA-specific from lactate- or pH-effects, monocytes were treated for one or four hours with LPS in the presence of physiological concentrations of LA, sodium lactate (NaL) or acidic pH. Analyses of global gene expression profiles revealed striking effects of LA during the early stimulation phase. Up-regulation of most LPS-induced genes was significantly delayed in the presence of LA, while this inhibitory effect was attenuated in acidified samples and not detected after incubation with NaL. LA targets included genes encoding for important monocyte effector proteins like cytokines (e.g. TNF and IL-23) or chemokines (e.g. CCL2 and CCL7). LA effects were validated for several targets by quantitative RT-PCR and/or ELISA. Further analysis of LPS-signaling pathways revealed that LA delayed the phosphorylation of protein kinase B (AKT) as well as the degradation of IκBα. Consistently, the LPS-induced nuclear accumulation of NFκB was also diminished in response to LA. These results indicate that the broad effect of LA on gene expression and function of human monocytes is at least partially caused by its interference with immediate signal transduction events after activation. This mechanism might contribute to monocyte suppression in the tumor environment.

Cell-Type Specific Determinants of NRAMP1 Expression in Professional Phagocytes

The Natural resistance-associated macrophage protein 1 (Nramp1 or Solute carrier 11 member 1, Slc11a1) transports divalent metals across the membrane of late endosomes and lysosomes in professional phagocytes. Nramp1 represents an ancient eukaryotic cell-autonomous defense whereas the gene duplication that yielded Nramp1 and Nramp2 predated the origin of Sarcopterygians (lobe-finned fishes and tetrapods). SLC11A1 genetic polymorphisms associated with human resistance to tuberculosis consist of potential regulatory variants. Herein, current knowledge of the regulation of SLC11A1 gene expression is reviewed and comprehensive analysis of ENCODE data available for hematopoietic cell-types suggests a hypothesis for the regulation of SLC11A1 expression during myeloid development and phagocyte functional polarization. SLC11A1 is part of a 34.6 kb CTCF-insulated locus scattered with predicted regulatory elements: a 3' enhancer, a large 5' enhancer domain and four elements spread around the transcription start site (TSS), including several C/EBP and PU.1 sites. SLC11A1 locus ends appear mobilized by ETS-related factors early during myelopoiesis; activation of both 5' and 3' enhancers in myelo-monocytic cells correlate with transcription factor binding at the TSS. Characterizing the corresponding cis/trans determinants functionally will establish the mechanisms involved and possibly reveal genetic variation that impacts susceptibility to infectious or immune diseases.

Caveolin-1 plays a critical role in the differentiation of monocytes into macrophages

OBJECTIVE

Monocyte to macrophage differentiation is an essential step in atherogenesis. The structure protein of caveolae, caveolin-1, is increased in primary monocytes after its adhesion to endothelium. We explore the hypothesis that caveolin-1 plays a role in monocyte differentiation to macrophages.

METHODS AND RESULTS

Both phorbol myristate acetate-induced THP-1 and colony-stimulating factor-induced primary monocyte differentiation was associated with an increase in cellular caveolin-1 expression. Overexpression of caveolin-1 by transfection increased macrophage surface markers and inflammatory genes, whereas caveolin-1 knockdown by small interfering RNA or knockout reduced these. Also, caveolin-1 knockdown inhibited the differentiation-induced nuclear translocation of early growth response 1 (EGR-1) through extracellular signal-regulated kinase phosphorylation, further decreased the binding of EGR-1 to CD115 promoter, thus decreasing EGR-1 transcriptional activity. In functional assays, caveolin-1 inhibited transmigration but promoted phagocytosis in the monocyte-macrophage lineage. Decreasing caveolin-1 inhibited the uptake of modified low-density lipoprotein and reduced cellular lipid content. Finally, we showed that caveolin-1 knockout mice displayed less monocyte differentiation than wild-type mice and that EGR-1 transcription activity was also decreased in these mice because of the inhibition of extracellular signal-regulated kinase phosphorylation.

CONCLUSIONS

Caveolin-1 promotes monocyte to macrophage differentiation through the regulation of EGR-1 transcriptional activity, suggesting that phagocytic caveolin-1 may be critical for atherogenesis.

Phospholipase D2 (PLD2) shortens the time required for myeloid leukemic cell differentiation: mechanism of action

Cell differentiation is compromised in acute leukemias. We report that mammalian target of rapamycin (mTOR) and S6 kinase (S6K) are highly expressed in the undifferentiated promyelomonocytic leukemic HL-60 cell line, whereas PLD2 expression is minimal. The expression ratio of PLD2 to mTOR (or to S6K) is gradually inverted upon in vitro induction of differentiation toward the neutrophilic phenotype. We present three ways that profoundly affect the kinetics of differentiation as follows: (i) simultaneous overexpression of mTOR (or S6K), (ii) silencing of mTOR via dsRNA-mediated interference or inhibition with rapamycin, and (iii) PLD2 overexpression. The last two methods shortened the time required for differentiation. By determining how PLD2 participates in cell differentiation, we found that PLD2 interacts with and activates the oncogene Fes/Fps, a protein-tyrosine kinase known to be involved in myeloid cell development. Fes activity is elevated with PLD2 overexpression, phosphatidic acid or phosphatidylinositol bisphosphate. Co-immunoprecipitation indicates a close PLD2-Fes physical interaction that is negated by a Fes-R483K mutant that incapacitates its Src homology 2 domain. All these suggest for the first time the following mechanism: mTOR/S6K down-regulation→PLD2 overexpression→PLD2/Fes association→phosphatidic acid-led activation of Fes kinase→granulocytic differentiation. Differentiation shortening could have a clinical impact on reducing the time of return to normalcy of the white cell counts after chemotherapy in patients with acute promyelocytic leukemia.

Cooperative and redundant signaling of leukotriene B4 and leukotriene D4 in human monocytes

BACKGROUND

Leukotriene B(4) (LTB(4)) and cysteinyl leukotrienes (cysLTs) are important immune mediators, often found concomitantly at sites of inflammation. Although some of the leukotriene-mediated actions are distinctive (e.g., bronchial constriction for cysLTs), many activities such as leukocyte recruitment to tissues and amplification of inflammatory responses are shared by both classes of leukotrienes.

OBJECTIVE

We used human monocytes to characterize leukotriene-specific signaling, gene expression signatures, and functions and to identify interactions between LTB(4)- and cysLTs-induced pathways.

METHODS

Responsiveness to leukotrienes was assessed using oligonucleotide microarrays, real-time PCR, calcium mobilization, kinase activation, and chemotaxis assays.

RESULTS

Human monocytes were found to express mRNA for high- and low-affinity LTB(4) receptors, BLT(1) and BLT(2), but signal predominantly through BLT(1) in response to LTB(4) stimulation as shown using selective agonists, inhibitors, and gene knock down experiments. LTB(4) acting through BLT(1) coupled to G-protein α inhibitory subunit activated calcium signaling, p44/42 mitogen-activated protein kinase, gene expression, and chemotaxis. Twenty-seven genes, including immediate early genes (IEG), transcription factors, cytokines, and membrane receptors were significantly up-regulated by LTB(4). LTB(4) and LTD(4) had similar effects on signaling, gene expression, and chemotaxis indicating redundant cell activation pathways but costimulation with both lipid mediators was additive for many monocyte functions.

CONCLUSION

Leukotriene B(4) and LTD(4) display both redundant and cooperative effects on intracellular signaling, gene expression, and chemotaxis in human monocytes. These findings suggest that therapies targeting either leukotriene alone may be less effective than approaches directed at both.

Live in vivo imaging of Egr-1 promoter activity during neonatal development, liver regeneration and wound healing

BACKGROUND

The zinc finger transcription factor Egr-1 (Early growth response 1) is central to several growth factors and represents an important activator of target genes not only involved in physiological processes like embryogenesis and neonatal development, but also in a variety of pathophysiological processes, for example atherosclerosis or cancer. Current options to investigate its transcription and activation in vivo are end-point measurements that do not provide insights into dynamic changes in the living organism.

RESULTS

We developed a transgenic mouse (Egr-1-luc) in which the luciferase reporter gene is under the control of the murine Egr-1 promoter providing a versatile tool to study the time course of Egr-1 activation in vivo. In neonatal mice, bioluminescence imaging revealed a high Egr-1 promoter activity reaching basal levels three weeks after birth with activity at snout, ears and paws. Using a model of partial hepatectomy we could show that Egr-1 promoter activity and Egr-1 mRNA levels were increased in the regenerating liver. In a model of wound healing, we demonstrated that Egr-1 promoter activity was upregulated at the site of injury.

CONCLUSION

Taken together, we have developed a transgenic mouse model that allows real time in vivo imaging of the Egr-1 promoter activity. The ability to monitor and quantify Egr-1 activity in the living organism may facilitate a better understanding of Egr-1 function in vivo.

Early growth response transcription factors and the modulation of immune response: implications towards autoimmunity

Early Growth Response (EGR) zinc finger transcription factors are induced under diverse mitogenic signals on different cell types such as lymphocytes. Their genetic expression does not require de novo protein synthesis, which suggests its role as immediate response mediators between cell surface receptor signaling and gene expression regulation. EGR factors are involved in modulating the immune response, by means of the induction of differentiation of lymphocyte precursors, activation of T and B cells, as well as their involvement in central and peripheral tolerance. The maturation state, particularly for B cells, and signaling through the T or B cell receptors seems to be quite relevant for the induction of the expression of these transcription factors. EGR-1 functions as a positive regulatory factor for B and T cells mediated by transcriptional regulation of key cytokines and costimulatory molecules, and its interaction with NFAT. On the opposite, EGR-2 and 3 act as negative regulators involved in anergy induction and apoptosis. EGR-2 and 3 deficiency has been related to the development of lupus like disease in murine models. The deficiency of these transcription factors has been associated to deficient Cbl-b expression, a resistant to anergy phenotype, and expansion of effector and activated T cells.

Genome-wide investigation of in vivo EGR-1 binding sites in monocytic differentiation

A Genome-wide analysis of EGR-1 binding sites reveals co-localization with CpG islands and histone H3 lysine 9 binding. SP-1 binding occupancies near EGR-1 binding sites are dramatically altered.

Background

Immediate early genes are considered to play important roles in dynamic gene regulatory networks following exposure to appropriate stimuli. One of the immediate early genes, early growth response gene 1 (EGR-1), has been implicated in differentiation of human monoblastoma cells along the monocytic commitment following treatment with phorbol ester. EGR-1 has been thought to work as a modifier of monopoiesis, but the precise function of EGR-1 in monocytic differentiation has not been fully elucidated.

Results

We performed the first genome-wide analysis of EGR-1 binding sites by chromatin immunoprecipitation with promoter array (ChIP-chip) and identified EGR-1 target sites in differentiating THP-1 cells. By combining the results with previously reported FANTOM4 data, we found that EGR-1 binding sites highly co-localized with CpG islands, acetylated histone H3 lysine 9 binding sites, and CAGE tag clusters. Gene Ontology (GO) analysis revealed enriched terms, including binding of molecules, in EGR-1 target genes. In addition, comparison with gene expression profiling data showed that EGR-1 binding influenced gene expression. Moreover, observation of in vivo occupancy changes of DNA binding proteins following PMA stimulation indicated that SP1 binding occupancies were dramatically changed near EGR-1 binding sites.

Conclusions

We conclude that EGR-1 mainly recognizes GC-rich consensus sequences in promoters of active genes. GO analysis and gene expression profiling data confirm that EGR-1 is involved in initiation of information transmission in cell events. The observations of in vivo occupancy changes of EGR-1 and SP1 suggest that several types of interplay between EGR-1 and other proteins result in multiple responses to EGR-1 downstream genes.

Effects of hypoxia on transcription factor expression in human monocytes and macrophages

The presence of multiple areas of hypoxia (low oxygen tension) is a hallmark feature of human and experimental tumours. Monocytes are continually recruited into tumours where they differentiate into tumour-associated macrophages (TAM) and often accumulate in hypoxic and/or necrotic areas. A number of recent studies have shown that macrophages respond to hypoxia by up-regulating transcription factors such as HIF-1alpha and HIF-2alpha, which in turn up-regulate the expression of a broad array of mitogenic, pro-invasive, pro-angiogenic and pro-metastatic genes. Here we show that primary human macrophages but not monocytes rapidly up-regulate HIF-1alpha and HIF-2alpha proteins upon exposure to hypoxia, and that these proteins then translocate to the nucleus. We also demonstrate differences in the temporal expression and responses to re-oxygenation for HIF-1alpha and HIF-2alpha in macrophages. Here we found that, compared to HIF-1alpha, HIF-2alpha expression was prolonged and persisted with re-oxygenation. ATF-4 and Egr-1 were also found to be hypoxia-responsive transcription factors in macrophages but not monocytes, but only early after exposure to hypoxia. Taken together, these findings indicate that a number of transcription factors work together in a tightly regulated fashion to control macrophage activities in ischaemic areas of diseased tissues.

IL-10 inhibits cysteinyl leukotriene-induced activation of human monocytes and monocyte-derived dendritic cells

The immunoregulatory cytokine IL-10 plays an essential role in down-modulating adaptive and innate immune responses leading to chronic inflammatory diseases. In contrast, cysteinyl leukotrienes (cysLTs), important proinflammatory mediators of cell trafficking and innate immune responses, are thought to enhance immune reactions in the pathogenesis of diseases, such as bronchial asthma, atherosclerosis, and pulmonary fibrosis. The aim of this study was to determine the IL-10 regulatory role in cysLT-induced activation of human monocytes and monocyte-derived dendritic cells. Herein we show that cysLT-induced activation and chemotaxis of human monocytes and monocyte-derived immature dendritic cells (iDC) are inhibited by IL-10 pretreatment. IL-10 down-regulated cysLT type 1 and 2 receptors' mRNA in a time- and concentration-dependent fashion. cysLT-induced activation of monocytes and iDCs measured by intracellular calcium flux and immediate-early gene expression (FBJ murine osteosarcoma viral oncogen homolog B and early growth response-2) was potently decreased by IL-10 and by the cysLT antagonist MK571. Chemotaxis of monocytes and iDCs to increasing concentrations of leukotriene D(4) (LTD(4)) was also inhibited by IL-10. LTD(4) enhanced iDC migration in response to CCL5. IL-10 selectively inhibited LTD(4)-induced chemotaxis without affecting migration to CCL5. These data indicate that cysLT-induced activation of human monocytes and dendritic cells may be specifically inhibited by IL-10, suggesting a direct link between the 5-lipoxygenase proinflammatory pathway and IL-10 regulatory mechanisms. Antileukotriene therapies may reproduce some regulatory mechanisms played by IL-10 in inflammatory processes.

Endothelium, inflammation, and diabetes

The normal endothelium produces a number of vasodilator substances such as nitric oxide (NO) and prostacyclin (PGI2) that regulate vasomotor tone, reduce platelet aggregation, and inhibit the recruitment and activity of inflammatory cells. The functions of vascular endothelial cells are disturbed in diabetic patients. The major cause for mortality and a great percent of morbidity in patients with diabetes mellitus is atherosclerosis. Insulin has recently been shown to stimulate NO release and the expression of NO synthase by the endothelium. Insulin is thus a vasodilator, has anti-platelet activity, and now has been shown to be anti-inflammatory and thus, potentially anti-atherogenic. Similar anti-inflammatory effects of thiazolidenediones (TZDs), troglitazone, and rosiglitazone suggest that they too may have potential anti-atherogenic effects. These effects of insulin and TZDs are of importance since the two major states of insulin resistance, obesity and type 2 diabetes, are associated with a marked increase in atherosclerosis, coronary heart disease, and stroke. These recent observations have extremely important implications for the understanding of the pathogenesis of atherosclerosis in insulin-resistant states and for a rational approach to their comprehensive treatment, including the prevention of atherosclerosis and its complications. This review challenges the previously proposed hypothesis that hyperinsulinemia represents a common pathophysiological pathway of diabetic complications and advances our hypothesis that insulin, through its effect on the endothelium, leucocytes, and platelets, has anti-inflammatory and thus potentially anti-atherogenic properties. Furthermore, through its anti-inflammatory effects, its use improves clinical outcomes in at least two clinical states characterized by profound inflammation-acute myocardial infarction and sepsis.

Leukotriene D(4) induces gene expression in human monocytes through cysteinyl leukotriene type I receptor

BACKGROUND

Cysteinyl leukotrienes (CysLTs) are important mediators of innate immune responsiveness and chronic inflammatory diseases. CysLTs acting through CysLT receptors can influence the migration and activity of cells, such as eosinophils, monocytes, and dendritic cells.

OBJECTIVE

We sought to determine the gene expression signature of human monocytes in response to CysLTs and to elucidate the signaling pathways involved in monocyte activation.

METHODS

Gene expression was analyzed by using oligonucleotide microarrays. Responsiveness to CysLTs was assessed by using real-time PCR, calcium flux, kinase activation, and chemotaxis assays.

RESULTS

CysLT type 1 receptor (CysLTR(1)) transcript 1 is predominantly expressed in human monocytes, and CysLTs signal through CysLTR(1) in these cells. Several immediate-early genes, including early growth response 2 and 3, FBJ murine osteosarcoma viral oncogene homolog B, activating transcription factor 3, and nuclear receptor subfamily 4 were significantly induced by leukotriene (LT) D(4). This effect was mediated by CysLTR(1) coupled to the G protein alpha inhibitory subunit, activation of phospholipase C, and inositol-1,4,5-triphosphate and store-operated calcium channels. LTD(4) induced p38 mitogen-activated protein kinase phosphorylation, a pathway also involved in the regulation of immediate-early gene expression in monocytes. LTD(4) stimulated monocyte chemotactic activity that was fully blocked by a selective CysLTR(1) inhibitor, MK571, and pertussis toxin, suggesting that CysLTR(1) coupled to the G protein alpha inhibitory subunit is a dominant functional pathway in human monocytes.

CONCLUSION

Our data show that CysLTs acting through CysLTR(1) can significantly influence the activation and migration of human monocytes and that these effects can be fully inhibited by CysLTR(1) antagonists.

Early growth response transcriptional regulators are dispensable for macrophage differentiation

Early growth response (Egr) proteins comprise a family of transcriptional regulators (Egr1-4) that modulate gene expression involved in the growth and differentiation of many cell types. In particular, Egr1 is widely believed to have an essential role in regulating monocyte/macrophage differentiation. However, Egr1-deficient mice have normal numbers of functional macrophages, an observation that has led to the hypothesis that other Egr proteins may compensate for Egr1 function in vivo. We examined whether other Egr transcription factors have a functionally redundant role in monocyte/macrophage differentiation. Egr1 and Egr3 expression was found to be induced in myeloid cells when they were differentiated into macrophages by treatment with M-CSF, whereas Egr2 was minimally induced and Egr4 was not detected. In either Egr1/Egr3 or Egr1/Egr2 double homozygous mutant mice, macrophage differentiation and function remained unimpaired. Additionally, the expression of molecules that broadly inhibit Egr function failed to block commitment to the monocytic lineage or inhibit the maturation of monocyte precursors. Finally, several hemopoietic growth factors were found to induce Egr gene expression, indicating that Egr gene expression is not cell lineage specific. Taken together, these results demonstrate that Egr transcription factors are neither essential for nor specific to monocyte/macrophage differentiation.

A two-step, PU.1-dependent mechanism for developmentally regulated chromatin remodeling and transcription of the c-fms gene

Hematopoietic stem cells and multipotent progenitors exhibit low-level transcription and partial chromatin reorganization of myeloid cell-specific genes including the c-fms (csf1R) locus. Expression of the c-fms gene is dependent on the Ets family transcription factor PU.1 and is upregulated during myeloid differentiation, enabling committed macrophage precursors to respond to colony-stimulating factor 1. To analyze molecular mechanisms underlying the transcriptional priming and developmental upregulation of the c-fms gene, we have utilized myeloid progenitors lacking the transcription factor PU.1. PU.1 can bind to sites in both the c-fms promoter and the c-fms intronic regulatory element (FIRE enhancer). Unlike wild-type progenitors, the PU.1(-/-) cells are unable to express c-fms or initiate macrophage differentiation. When PU.1 was reexpressed in mutant progenitors, the chromatin structure of the c-fms promoter was rapidly reorganized. In contrast, assembly of transcription factors at FIRE, acquisition of active histone marks, and high levels of c-fms transcription occurred with significantly slower kinetics. We demonstrate that the reason for this differential activation was that PU.1 was required to promote induction and binding of a secondary transcription factor, Egr-2, which is important for FIRE enhancer activity. These data suggest that the c-fms promoter is maintained in a primed state by PU.1 in progenitor cells and that at FIRE PU.1 functions with another transcription factor to direct full activation of the c-fms locus in differentiated myeloid cells. The two-step mechanism of developmental gene activation that we describe here may be utilized to regulate gene activity in a variety of developmental pathways.

Induction of the early growth response 1 gene by Epstein-Barr virus lytic transactivator Zta

Early growth response 1 (Egr-1) is a cellular transcription factor involved in diverse biologic functions. Egr-1 has been associated with Epstein-Barr virus (EBV) infection, but it is still unknown whether any EBV protein regulates Egr-1 expression. In this study, we first showed that EBV reactivation is involved in upregulation of Egr-1 and that Egr-1 can be induced by Zta, an EBV lytic transactivator. Zta not only binds to the Egr-1 promoter but also activates the ERK signaling pathway to trigger binding of Elk-1 to the Egr-1 promoter. In addition, knockdown of Egr-1 significantly reduces the spontaneous expression of Zta and Rta in EBV-infected 293 cells, suggesting that a positive-feedback network involving Egr-1 is required for EBV reactivation. This study also implies that Zta has the potential to affect expression of certain genes through Egr-1.

Quantitative production of macrophages or neutrophils ex vivo using conditional Hoxb8

Differentiation mechanisms and inflammatory functions of neutrophils and macrophages are usually studied by genetic and biochemical approaches that require costly breeding and time-consuming purification to obtain phagocytes for functional analysis. Because Hox oncoproteins enforce self-renewal of factor-dependent myeloid progenitors, we queried whether estrogen-regulated Hoxb8 (ER-Hoxb8) could immortalize macrophage or neutrophil progenitors that would execute normal differentiation and normal innate immune function upon ER-Hoxb8 inactivation. Here we describe methods to derive unlimited quantities of mouse macrophages or neutrophils by immortalizing their respective progenitors with ER-Hoxb8 using different cytokines to target expansion of different committed progenitors. ER-Hoxb8 neutrophils and macrophages are functionally superior to those produced by many other ex vivo differentiation models, have strong inflammatory responses and can be derived easily from embryonic day 13 (e13) fetal liver of mice exhibiting embryonic-lethal phenotypes. Using knockout or small interfering RNA (siRNA) technologies, this ER-Hoxb8 phagocyte maturation system represents a rapid analytical tool for studying macrophage and neutrophil biology.

Protein tyrosine phosphatase 1B negatively regulates macrophage development through CSF-1 signaling

Protein tyrosine phosphatase 1B (PTP-1B) is a ubiquitously expressed cytosolic phosphatase with the ability to dephosphorylate JAK2 and TYK2, and thereby down-regulate cytokine receptor signaling. Furthermore, PTP-1B levels are up-regulated in certain chronic myelogenous leukemia patients, which points to a potential role for PTP-1B in myeloid development. The results presented here show that the absence of PTP-1B affects murine myelopoiesis by modifying the ratio of monocytes to granulocytes in vivo. This bias toward monocytic development is at least in part due to a decreased threshold of response to CSF-1, because the PTP-1B -/- bone marrow presents no abnormalities at the granulocyte-monocyte progenitor level but produces significantly more monocytic colonies in the presence of CSF-1. This phenomenon is not due to an increase in receptor levels but rather to enhanced phosphorylation of the activation loop tyrosine. PTP-1B -/- cells display increased inflammatory activity in vitro and in vivo through the constitutive up-regulation of activation markers as well as increased sensitivity to endotoxin. Collectively, our data indicate that PTP-1B is an important modulator of myeloid differentiation and macrophage activation in vivo and provide a demonstration of a physiological role for PTP-1B in immune regulation.

An efficient strategy to identify early TPA-responsive genes during differentiation of HL-60 cells

We have adopted a special experimental strategy to identify early responsive genes during 12-O-tetradecanoylphorbol-13-acetate (TPA)-induced macrophage-like differentiation of human myeloid leukemia cells (HL-60). This was performed in cells that were synchronized by nocodazole and treated with TPA in the presence of a protein synthesis inhibitor, cycloheximide, to prevent activation of secondary targets and therefore increase the probability of early transcripts in total RNA pool. The expression alteration was analyzed by microarray and the selection criteria of candidate genes were adjusted by real-time PCR validation to increase its reliability. Finally, 56 genes were identified as early TPA-responsive genes in this multiscreening step approach. Furthermore, upregulation of three candidate genes (NFIL3, SKIL, and JMJD3) was shown to be dosage and time dependent with TPA treatment and was found to be directly regulated by TPA through PKC-dependent signaling. These results revealed that our screenings provide a useful and efficient approach to identify early TPA-responsive genes and these genes might involve the regulation of TPA-induced differentiation program of HL-60 cells as primary

Down-modulation of poly(ADP-ribose) polymerase-1 (PARP-1) in human TUR leukemia cells restores transcriptional responsiveness for differentiation and cell cycle arrest

Aggressive tumor developing human TUR myeloid leukemia cells continued cell cycle progression in the presence of the differentiation-inducing phorbol ester 12-O-tetradecanoylphorbol-13-acetate (TPA). Similar results were obtained after stable transfection of TUR cells with the pTracer control vector (pTracer TUR cells). In contrast, TUR transfectants containing a constitutively active poly(ADP-ribose) polymerase-1 (PARP-1) gene fragment in antisense orientation within the pTracer vector (asPARP TUR cells) demonstrated increasing cell attachment and differentiation after TPA treatment. Moreover, asPARP TUR cells ceased to divide upon TPA stimulation. Cell cycle analysis revealed a predominant G0/G1 arrest and a partial G2/M arrest in TPA-treated asPARP TUR cells, whereas little if any population was detectable in S phase. Microarray gene expression analysis exhibited a significant down-regulation of cell cycle genes in phorbol ester-stimulated asPARP TUR and markedly elevated levels of differentiation-associated factors in contrast to TPA-incubated wild-type TUR cells. Whereas PARP-1 can associate with the 20S proteasome in leukemia cells, a significant reduction of this proteolytic activity was observed in asPARP TUR cells. Conversely, protein levels of manganese superoxide dismutase and the matrix metalloproteinases MMP-1 and MMP-9 were progressively increased in TPA-treated asPARP TUR cells, respectively. These findings underscore an important function of PARP-1 in human leukemia cells to connect cell cycle progression and control of differentiation.

Glucose intake induces an increase in activator protein 1 and early growth response 1 binding activities, in the expression of tissue factor and matrix metalloproteinase in mononuclear cells, and in plasma tissue factor and matrix metalloproteinase concentrations

BACKGROUND

Glucose intake has been shown to cause an increase in intranuclear nuclear factor-kappa B and a decrease in inhibitor kappa B that are consistent with a proinflammatory effect. We investigated the effect of glucose intake on 2 other proinflammatory transcription factors, activator protein 1 (AP-1) and early growth response 1 (Egr-1), and on the genes regulated by them, ie, the genes for matrix metalloproteinases 2 (MMP-2) and 9 (MMP-9) and tissue factor (TF), respectively.

OBJECTIVE

The objective of the study was to ascertain whether the intake of 75 g glucose induces an increase in AP-1, Egr-1, and the genes regulated by them.

DESIGN

Eight healthy subjects were given 75 g glucose dissolved in 300 mL water to drink. Blood samples were collected before and 1, 2, and 3 h after glucose intake. Four weeks later, the same subjects were given 300 mL water sweetened with saccharine, and blood samples were collected at the same time points. Mononuclear cells (MNCs) were separated, and nuclear fractions were isolated.

RESULTS

AP-1 and Egr-1 binding activities were significantly higher 1 and 2 h after glucose intake and then decreased toward the baseline by 3 h. The expression of MMP-2 and TF in MNC homogenates also was significantly higher at 2 and 3 h. Plasma concentrations of MMP-2 were significantly higher at 3 h, whereas those of MMP-9 were significantly higher at 1, 2, and 3 h. In addition, TF was significantly higher at 2 and 3 h. Intake of saccharine-sweetened water had no significant effect on the inflammatory mediators measured in this study.

CONCLUSION

Glucose induces proinflammatory changes, including increases in AP-1, Egr-1, MMPs, and TF, the factors that regulate processes that are potentially relevant to atherosclerotic plaque rupture and thrombosis.

Regulation of tissue factor and inflammatory mediators by Egr-1 in a mouse endotoxemia model

In septic shock, tissue factor (TF) activates blood coagulation, and cytokines and chemokines orchestrate an inflammatory response. In this study, the role of Egr-1 in lipopolysaccharide (LPS) induction of TF and inflammatory mediators in vivo was evaluated using Egr-1(+/+) and Egr-1(-/-) mice. Administration of LPS transiently increased the steady-state levels of Egr-1 mRNA in the kidneys and lungs of Egr-1(+/+) mice with maximal induction at one hour. Egr-1 was expressed in epithelial cells in the kidneys and lungs in untreated and LPS-treated mice. LPS induction of monocyte chemoattractant protein mRNA in the kidneys and lungs of Egr-1(-/-) mice was not affected at 3 hours, but its expression was significantly reduced at 8 hours compared with the expression observed in Egr-1(+/+) mice. Similarly, LPS induction of TF mRNA expression in the kidneys and lungs at 8 hours was reduced in Egr-1(-/-) mice. However, Egr-1 deficiency did not affect plasma levels of tumor necrosis factor alpha in endotoxemic mice. Moreover, Egr-1(+/+) and Egr-1(-/-) mice exhibited similar survival times in a model of acute endotoxemia. These data indicate that Egr-1 does not contribute to the early inflammatory response in the kidneys and lungs or the early systemic inflammatory response in endotoxemic mice. However, Egr-1 does contribute to the sustained expression of inflammatory mediators and to the maximal expression of TF at 8 hours in the kidneys and lungs.

Early gene activation in chronic leukemic B lymphocytes induced toward a plasma cell phenotype

Chronic lymphocytic leukemia (CLL) is characterized by the accumulation of lymphocytes that are arrested at an intermediate stage of B lymphocyte development. CLL B lymphocytes transform (mature) to a plasmacytic phenotype with loss of CD19 and CD20 and the appearance of cytoplasmic immunoglobulin when treated in vitro with phorbol esters. We have used array hybridization technology to describe gene expression patterns for untreated and tetradecanoyl phorbol acetate (TPA)-treated CLL B cells at 5, 10, and 20 min following initial TPA exposure. Three genes, early growth response factor 1 (EGR-1), dual specificity phosphatase 2, and CD69 (early T-cell activation antigen), showed a 2.0-fold or greater increase in mRNA transcription at four or more of six time points in two studies. Upregulation of expression of these genes was confirmed by real-time polymerase chain reaction in the TPA-treated cells of four CLL patients. A progressive increase in gene expression was observed during the 20-min time course for all three genes. In addition, protein expression of EGR-1 and CD69 was increased as measured by immunofluorescence cell analysis. Several genes (PKC, n-myc, jun D, and BCL-2) previously reported as overexpressed in CLL lymphocytes were overexpressed in these studies also, but were not altered by TPA treatment. Genes for proteins whose upregulation requires hours of TPA exposure (the 4F2hc component of the L-system amino acid transporter, prohibition, and hsp60) were assessed, and their later expression contrasted with the early expression of EGR-1, dual specificity phosphatase 2, and CD69. EGR-1 encodes a zinc-finger transcription factor that is induced by pokeweed mitogen and TPA and promotes B lymphocyte maturation. The dual specificity phosphatase 2 encodes an enzyme that reverses mitogen activated protein kinase cell activation by dephosphorylation. The CD69 protein is induced by TPA in thymocytes and is a type II transmembrane signaling molecule in hematopoietic cells. These findings suggest that the products of these three genes may be central to early steps in the TPA-induced evolution of CLL B cells to a plasmacytic phenotype.

Gene expression of TPA induced differentiation in HL-60 cells by DNA microarray analysis

The tumor promoter 12-O-tetradecanoylphorbol-13-acetate (TPA) is a potent inducer of differentiation in human promyelocytic leukemia cells. Recently, TPA has been successfully administered to patients with myelocytic leukemia and has produced therapeutic effects that led to temporary remission. These studies demonstrated the potential efficacy of TPA in cancer chemotherapy. We now seek to understand the biological effects and molecular mechanisms of differentiation in response to TPA treatment in leukemia cells by expression profiling using DNA microarray. Our results show distinct temporal and coordinated gene changes that are consistent with differentiation and activation of multiple biochemical pathways in HL-60 cells exposed to TPA. Alterations of gene expression in HL-60 cells include various transcription factors, cytokines and protein markers that are consistent with the induction of differentiation elicited by TPA. These temporal patterns of gene expression were abolished or greatly diminished in an HL-60 derived TPA- resistant variant cell line (HL-525), thus revealing transcriptional and consequential biochemical changes that may be required for TPA-induced differentiation. In addition, certain genes were upregulated by TPA in TPA-resistant HL-525 cells but not in TPA-sensitive HL-60 cells suggesting that these genes may play a role in the resistant phenotype. These patterns of gene expression may be important for predicting response to TPA.

Augmented expression of P-gp/multi-drug resistance gene by all-trans retinoic acid in monocytic leukemic cells

P-glycoprotein (P-gp)/multi-drug resistance 1 (MDR1) gene is recognized to be, at least in part, responsible for the refractoriness to chemotherapy of leukemia. The transcriptional mechanism of MDR1 gene is largely unknown. However, recent reports have clarified that early growth response 1 gene (Egr1) positively regulates MDR1 transcription, while Wilms' tumor suppressor gene (WT1) does negative regulation of MDR1 gene expression in 12-O-tetradecanoylphorbol-13-acetate treated K562 cells. In addition, Egr1 and WT1 are structurally related transcription factors and bind to quite similar DNA sequences. Our study of mRNA expression profile of Egr1, WT1 and MDR1 in fresh AML samples demonstrated that there are disease-specific patterns. Egr1 mRNA was frequently and strongly expressed in monocytic leukemia cells, especially in AML M4 cells. WT1 mRNA was undetectable in t(8;21) AML cells. mRNA expression of MDR1 was frequent in AML M1 and t(8;21) AML cells, in which the expression level was highest in AML M1 and was low in monocytic leukemia (M4 and M5). Then, expression level of MDR1 was inversely correlated with Egr1. By liquid culture of leukemia cell lines and fresh AML cells with the addition of all-trans retinoic acid (ATRA), modulation of P-gp/MDR1 and Egr1 was observed and the pattern of modulation was divided into four groups: (1) blastic AML type, in which distinct expression of P-gp/MDR1 and CD34 was not influenced by ATRA; (2) t(8;21)AML type, in which P-gp/MDR1 expression was augmented by ATRA, while CD34 was kept high; (3) AML M3 type, in which P-gp/MDR1 expression was reduced with granulocytic differentiation by ATRA; (4) monocytic AML type, in which P-gp/MDR1 expression was augmented by ATRA, while CD34 expression decreased, and strong Egr1 expression was downregulated just prior to the augmentation of P-gp/MDR1 expression. WT1 expression was not influenced by the addition of ATRA in each group. Previous reports have suggested that P-gp/MDR1 plays an important role in resistance to chemotherapy, and is recognized as one of the stem cell marker. However, P-gp/MDR1 expression augmented by ATRA, which was observed in monocytic AML, was recognized as a functional molecule of mature monocyte/macrophage, because CD34 expression decreased and CD13 expression increased by ATRA. Finally, expression of P-gp/MDR1 in monocytic leukemia, which was functionally confirmed by Rh123 efflux study, was thought to be closely related to the characteristic modulation of Egr1 expression by ATRA.

Mitochondrial targeting of JNK/SAPK in the phorbol ester response of myeloid leukemia cells

Treatment of human U-937 myeloid leukemia cells with 12-O-tetradecanoylphorbol-13-acetate (TPA) is associated with activation of the stress-activated protein kinase (SAPK) and induction of terminal monocytic differentiation. The present studies demonstrate that TPA targets SAPK to mitochondria by a mechanism dependent on activation of protein kinase C (PKC) beta. Translocation of SAPK to mitochondria in response to TPA is associated with release of cytochrome c, caspase-3 activation and induction of apoptosis. The results show that TPA induces the association of SAPK with the mitochondrial anti-apoptotic Bcl-x(L) protein. Overexpression of Bcl-x(L) attenuated the apoptotic response to TPA treatment. Moreover, expression of Bcl-x(L) mutated at sites of SAPK phosphorylation (Thr-47, -115) was more effective than wild-type Bcl-x(L) in abrogating TPA-induced cytochrome c release and apoptosis. By contrast, expression of Bcl-x(L) had little effect on induction of the monocytic phenotype. These findings indicate that myeloid leukemia cells respond to TPA with targeting of SAPK to mitochondria and that this response contributes to terminal differentiation through the release of cytochrome c and induction of apoptosis.

Distinct PKC isozymes regulate bufalin-induced differentiation and apoptosis in human monocytic cells

Bufalin, an Na(+)-K(+)-ATPase inhibitor, simultaneously induced cell differentiation and apoptosis in human monocytic leukemia THP-1 cells. In this study, we investigated the regulatory role of protein kinase C (PKC) isozymes in bufalin-induced cell differentiation and apoptosis. A PKC-specific but isozyme-nonselective inhibitor, Ro-31-8220, and a cPKC selective inhibitor, Gö-6976, caused significant attenuation of bufalin-induced interleukin-1beta (IL-1beta) gene expression, a mature monocytic marker, indicating that cPKC participates in the bufalin-induced cell differentiation. On the other hand, cPKCbeta- and nPKCdelta-defective THP-1/TPA cells displayed strong resistance to the bufalin-induced DNA ladder formation. Rottlerin, an nPKCdelta-specific inhibitor, partially attenuated preapoptotic effects of bufalin, such as the limited proteolysis of nPKCdelta and poly(ADP-ribose) polymerase and the cell staining by terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling, suggesting that nPKCdelta is involved, at least in part, in bufalin-induced apoptosis. In contrast, Gö-6976 and rottlerin significantly augmented bufalin-induced apoptosis and differentiation, respectively. The findings suggest that bufalin-induced cell differentiation and apoptosis are interlinked and that distinct PKC isozymes are involved in the fate of the cell.

Thrombospondin-1 inhibits TCR-mediated T lymphocyte early activation

Biological activities of the matrix glycoprotein thrombospondin-1 (TSP1) are cell type specific and depend on the relative expression or activation of several TSP1 receptors. Although engaging individual TSP1 receptors in T lymphocytes can elicit costimulating signals, in this study we show that intact TSP1 inhibits TCR-mediated T cell activation, assessed globally using cDNA microarrays. TSP1 signaling suppressed expression of several genes induced in Jurkat T cells, including the T cell activation markers CD69, early growth response gene-1 (Egr-1), and phosphatase of activated cells (PAC-1). TCR-stimulated and CD47-costimulated IL-2 secretion and cell surface CD69 expression were also inhibited by TSP1. The specific inhibitory effect of TSP1 was verified in freshly isolated human PBMCs. TSP1 inhibited TCR-mediated but not protein kinase C-mediated T cell activation. Using CD69 expression as a marker, we demonstrated that the inhibitory activity of TSP1 depended on two TSP1 receptors, CD47 and integrin-associated protein heparan sulfate proteoglycans. Signals from these receptors inhibited TCR signaling downstream of ZAP70, but upstream of NF-AT. Therefore, the expression of TSP1 induced during wound repair and in tumor stroma may limit T cell activation at these sites.

Phorbol ester-induced generation of reactive oxygen species is protein kinase cbeta -dependent and required for SAPK activation

Treatment of human U-937 myeloid leukemia cells with 12-O-tetradecanoylphorbol-13-acetate (TPA) is associated with protein kinase C (PKC) betaII-mediated activation of the stress-activated protein kinase (SAPK) pathway. The present studies demonstrate that the TPA response of U-937 cells includes the generation of reactive oxygen species (ROS). By contrast, the TPA-resistant U-937 cell variant (TUR), which is deficient in PKCbetaII expression, failed to respond to TPA with the induction of ROS. Moreover, we show that TPA-induced ROS production is restored in TUR cells stably transfected to express PKCbetaII. The results also demonstrate that TPA-induced ROS production is required for activation of the MEK kinase-1 (MEKK-1)--> SAPK pathway. In concert with this observation, treatment of U-937 with H(2)O(2) as a source of ROS is associated with activation of the MEKK-1-->SAPK cascade. These findings indicate that PKCbetaII is required for TPA-induced ROS production and that the MEKK-1-->SAPK pathway is activated by a ROS-mediated mechanism.

Granulocyte colony-stimulating factor induces Egr-1 up-regulation through interaction of serum response element-binding proteins

Granulocyte colony-stimulating factor (G-CSF) stimulates the proliferation and maturation of myeloid progenitor cells both in vitro and in vivo. We showed that G-CSF rapidly and transiently induces expression of egr-1 in the NFS60 myeloid cell line. Transient transfections of NFS60 cells with recombinant constructs containing various deletions of the human egr-1 promoter identified the serum response element (SRE) between nucleotides (nt) -418 and -391 as a critical G-CSF-responsive sequence. The SRE (SRE-1) contains a CArG box, the binding site for the serum response factor (SRF), which is flanked at either side by an ETS protein binding site. We demonstrated that a single copy of the wild-type SRE-1 in the minimal promoter plasmid, pTE2, is sufficient to induce transcriptional activation in response to G-CSF and that both the ETS protein binding site and the CArG box are required for maximal transcriptional activation of the pTE2-SRE-1 construct. In electromobility shift assays using NFS60 nuclear extracts, we identified SRF and the ETS protein Fli-1 as proteins that bind the SRE-1. We also demonstrated through electrophoretic mobility shift assays, using an SRE-1 probe containing a CArG mutation, that Fli-1 binds the SRE-1 independently of SRF. Our data suggest that SRE-binding proteins potentially play a role in G-CSF-induced egr-1 expression in myeloid cells.

Alteration of Egr-1 mRNA during multistage carcinogenesis in mouse skin

Immediate early genes, including fos, jun, and early growth response-1 (Egr-1), are induced during cellular response to changes in extracellular environment. These immediate early genes are believed to mediate processes of cell growth and differentiation. In particular, Egr-1 is induced during mitogenic stimulation of a variety of cell types, including fibroblasts, B cells, and epithelial cells. In the present study, we examined Egr-1 gene expression during multistage carcinogenesis in mouse skin. After a single topical treatment with the tumor promoter 12-O-tetradecanoylphorbol-13-acetate (TPA) to SENCAR mouse skin, Egr-1 mRNA was induced, and maximal induction was observed at 2 h in both epidermis and dermis. Induction of Egr-1 mRNA by TPA was inhibited by fluocinolone acetonide, a potent inhibitor of tumor promotion by TPA. Egr-1 mRNA was present in primary keratinocytes derived from adult SENCAR mice. The keratinocyte cultures were maintained in low Ca(2+) medium, and Egr-1 mRNA levels became significantly elevated after the cultures were switched to high Ca(2+) medium. Additionally, a large proportion of primary papillomas and carcinomas generated from SENCAR mice by standard initiation-promotion regimens exhibited elevated Egr-1 mRNA compared with normal epidermis. Taken together, these data suggest a possible role of Egr-1 during multistage carcinogenesis in mouse skin.

The biology of 5-lipoxygenase: function, structure, and regulatory mechanisms

5-Lipoxygenase (5-LO) catalyzes the two-step conversion of arachidonic acid to leukotriene A4 (LTA4). The first step consists of the oxidation of arachidonic acid to the unstable intermediate 5-hydroperoxyeicosatetraenoic acid (5-HPETE), and the second step is the dehydration of 5-HPETE to form LTA4. These events are the first committed reactions leading to the synthesis of all leukotrienes and play a critical role in controlling leukotriene production. 5-LO has evolved many complex structural features and regulatory mechanisms to allow it to fulfill this highly specialized role. The biology of 5-LO is reviewed here with an emphasis on enzymatic function, protein and gene structure, essential cofactors, and the many regulatory mechanisms controlling its expression.

cDNA cloning and expression analysis of mouse zf9, a Krüppel-like transcription factor gene that is induced by adipogenic hormonal stimulation in 3T3-L1 cells

Using a differential hybridization method, we have cloned a zinc finger transcription factor gene whose expression was enhanced by adipogenic hormones in preadipocyte 3T3-L1 cells. Cloning of this gene revealed that it encodes a mouse homologue of rat Zf9 and human CPBP/GBF, previously identified as a wound-induced transcription factor and GC-rich binding protein, respectively. The mRNA for this clone consisted of 0.9 kb coding region and 3.2 kb long 3' untranslated region. Northern blot analysis revealed that it was ubiquitously expressed, among adult tissues, in which abundant expression was observed in lung, ovary and thymus. The transcript was transiently induced by different stimuli such as serum, cAMP and 12-O-tetradecanoylphorbol 13-acetate. Nuclear run-on and RNA synthesis inhibitor chase experiments indicated that the transient induction of the mRNA was regulated both at transcriptional and post-transcriptional levels.

Ternary complex factors Elk-1 and Sap-1a mediate growth hormone-induced transcription of egr-1 (early growth response factor-1) in 3T3-F442A preadipocytes

In our search for transcription factors induced by GH, we have analyzed immediate early gene activation in a model of GH-dependent differentiation. Here we describe the activation of early growth response factor-1 (egr-1) in GH-stimulated 3T3-F442A preadipocytes and the transcription factors responsible for its transactivation. Binding activity of egr-1 in electrophoretic mobility shift assay (EMSA) increased transiently 1 h after GH stimulation, accompanied by a concomitant increase in egr-1 mRNA. egr-1 induction appeared not to be related to proliferation since it was amplified in quiescent preadipocytes at a time when cells were refractive to GH-stimulated DNA synthesis. Truncations of the proximal 1 kb of the egr-1 promoter revealed that a 374-bp region (-624 to -250) contributes about 80% of GH inducibility in 3T3-F442A cells and approximately 90% inducibility in CHO-K1 cells. This region contains three juxtaposed SRE (serum response element)/Ets site pairs known to be important for egr-1 activity in response to exogenous stimuli. Site-specific mutations of individual SRE and Ets sites within this region each reduced GH inducibility of the promoter. Use of these site-specific mutations in EMSA showed that disruption of either Ets or SRE sites abrogated ternary complex formation at the composite sites. DNA binding of ternary complexes, but not binary complexes, in EMSA was rapidly and transiently increased by GH. EMSA supershifts indicated these ternary complexes contained serum response factor (SRF) and the Ets factors Elk-1 and Sap-1a. Coexpression of Sap-1a and Elk-1 resulted in a marked increase in GH induction of egr-1 promoter activity, although transfection with expression vectors for either Ets factor alone did not significantly enhance the GH response. We conclude that GH stimulates transcription of egr-1 primarily through activation of these Ets factors at multiple sites on the promoter and that stabilization of ternary complexes with SRF at these sites maximizes this response.