Production of granulocyte colony-stimulating factor by THP-1 cells in response to retinoic acid and phorbol ester is mediated through the autocrine production of interleukin-1

Nuclear hormone receptors enable macrophages and dendritic cells to sense their lipid environment and shape their immune response

A key issue in the immune system is to generate specific cell types, often with opposing activities. The mechanisms of differentiation and subtype specification of immune cells such as macrophages and dendritic cells are critical to understand the regulatory principles and logic of the immune system. In addition to cytokines and pathogens, it is increasingly appreciated that lipid signaling also has a key role in differentiation and subtype specification. In this review we explore how intracellular lipid signaling via a set of transcription factors regulates cellular differentiation, subtype specification, and immune as well as metabolic homeostasis. We introduce macrophages and dendritic cells and then we focus on a group of transcription factors, nuclear receptors, which regulate gene expression upon receiving lipid signals. The receptors we cover are the ones with a recognized physiological function in these cell types and ones which heterodimerize with the retinoid X receptor. These are as follows: the receptor for a metabolite of vitamin A, retinoic acid: retinoic acid receptor (RAR), the vitamin D receptor (VDR), the fatty acid receptor: peroxisome proliferator-activated receptor γ (PPARγ), the oxysterol receptor liver X receptor (LXR), and their obligate heterodimeric partner, the retinoid X receptor (RXR). We discuss how they can get activated and how ligand is generated and eliminated in these cell types. We also explore how activation of a particular target gene contributes to biological functions and how the regulation of individual target genes adds up to the coordination of gene networks. It appears that RXR heterodimeric nuclear receptors provide these cells with a coordinated and interrelated network of transcriptional regulators for interpreting the lipid milieu and the metabolic changes to bring about gene expression changes leading to subtype and functional specification. We also show that these networks are implicated in various immune diseases and are amenable to therapeutic exploitation.

Multiple signaling pathways are involved in the interleukine-4 regulated expression of DC-SIGN in THP-1 cell line

Dendritic cell-specific intercellular adhesion molecule-3 grabbing nonintegrin (DC-SIGN) is an important pattern recognition receptor on dendritic cells (DCs), and its expression shows significant cytological and histological specificity, being interleukine-4 (IL-4) dependent. The signaling pathways through which IL-4 regulates expression of DC-SIGN are still unclear. We used phorbol 12-myristate 13-acetate- (PMA-) differentiated THP-1 cells as the in vitro model of monocyte/macrophage cells to study the signaling pathways involved in IL-4-regulated expression of DC-SIGN. We found that a high expression of DC-SIGN could be induced by IL-4 at the levels of mRNA and cell surface protein. Upregulated expression of DC-SIGN was almost completely blocked by the specific inhibitor of ERK pathway, and partly reduced by the specific inhibitors of JAK-STAT and NF-κB pathways. The activation of the three signaling pathways was directly confirmed by testing the phosphorylation of protein kinase within the cytoplasm and nucleus over time. The analysis of cis-acting elements of DC-SIGN promoter showed that the activity of DC-SIGN promoter without Ets-1 transcription factors binding site almost completely disappeared. Our results demonstrated that multiple signaling pathways are involved in IL-4 induced high expression of DC-SIGN on THP-1 cells, in which ERK pathway is the main signaling pathway and mediated by the Ets-1 transcription factors binding site.

Retinoid pathway and cancer therapeutics

The retinoids are a class of compounds that are structurally related to vitamin A. Retinoic acid, which is the active metabolite of retinol, regulates a wide range of biological processes including development, differentiation, proliferation, and apoptosis. Retinoids exert their effects through a variety of binding proteins including cellular retinol-binding protein (CRBP), retinol-binding proteins (RBP), cellular retinoic acid-binding protein (CRABP), and nuclear receptors i.e. retinoic acid receptor (RAR) and retinoid x receptor (RXR). Because of the pleiotropic effects of retinoids, understanding the function of these binding proteins and nuclear receptors assists us in developing compounds that have specific effects. This review summarizes our current understanding of how retinoids are processed and act with an emphasis on the application of retinoids in cancer treatment and prevention.

MAIL regulates human monocyte IL-6 production

IL-6 is a pleiotropic cytokine implicated in the pathogenesis of disorders such as sepsis and cancer. We noted that human monocytes are excellent producers of IL-6 as compared with monocyte-derived macrophages. Because macrophages from molecule containing ankyrin repeats induced by LPS (MAIL) knockout animals have suppressed IL-6 production, we hypothesized that regulation of MAIL is key to IL-6 production in humans and may explain the differences between human monocytes and macrophages. To test this hypothesis fresh human monocytes and monocyte-derived macrophages were compared for MAIL expression in response to LPS. LPS-induced monocyte MAIL expression was highly inducible and transient. Importantly for our hypothesis MAIL protein expression was suppressed during differentiation of monocytes to macrophages. Of note, the human MAIL protein detected was the 80 kDa MAIL-L form and human MAIL showed nuclear localization. Human MAIL-L bound to p50 subunit of the NF-kappaB and increased IL-6 luciferase promoter activity in a cEBPbeta, NF-kappaB, and AP-1-dependent fashion. Like the differences in MAIL induction, monocytes produced 6-fold more IL-6 compared with macrophages (81.7 +/- 29.7 vs 12.6 +/- 6.8 ng/ml). Furthermore, suppression of MAIL by small interfering RNA decreased the production of IL-6 significantly in both THP-1 cells and in primary monocytes. Costimulation of monocytes with LPS and muramyl dipeptide induced an enhanced IL-6 response that was suppressed by siMAIL. Our data suggests that MAIL is a key regulator of IL-6 production in human monocytes and plays an important role in both TLR and NOD-like receptor ligand induced inflammation.

The effect of particle wear debris on NFkappaB activation and pro-inflammatory cytokine release in differentiated THP-1 cells

Orthopedic wear debris has been thought to be an important factor associated with osteolysis and loosening of total joint arthroplasties. Previous in vitro studies have reported that particles of wear debris induce the release of pro-inflammatory cytokines and other inflammatory mediators from macrophages and other cells. Several recent investigations, however, have suggested that the wear particles themselves may not be primarily responsible for the inflammatory cellular responses, but that the observed cytokine release in vitro may be caused by endotoxin adsorbed to commercially available particle preparations. The intracellular pathways involved in macrophage signal transduction also are poorly understood. The purposes of this study are to use isolated orthopedic wear debris particles to evaluate pro-inflammatory cytokine release and nuclear factor kappa B (NFkappaB) activation from macrophages. Cells from human monocyte/macrophage cell line (THP-1) were differentiated and incubated with particles of debris that had been isolated from a failed human total hip arthroplasty. The titanium-alloy particles did not evoke release of TNF-alpha or IL-1beta whereas lipopolysaccharide (LPS) or LPS-treated debris particles induced both TNF-alpha and IL-1beta. LPS-treated particles, but not particles alone, stimulated NFkappaB activation. Our results suggest that at the concentrations tested in this study, endotoxin-free wear debris particles may not themselves initiate inflammatory cellular responses in differentiated THP-1 cells. It is unclear whether adsorbed endotoxin is clinically associated with osteolysis and/or loosening in total joint arthroplasties, but several factors, including adsorbed endotoxin, need to be investigated to explore the cellular responses responsible for osteolysis and/or loosening.

Regulation of granulocyte colony-stimulating factor and parathyroid hormone-related protein production in lung carcinoma cell line OKa-C-1

Previously we have established a clonal squamous cell carcinoma cell line OKa-C-1 derived from lung cancer of a patient with marked leukocytosis and hypercalcemia. OKa-C-1 cells simultaneously produce granulocyte colony-stimulating factor (G-CSF) and parathyroid hormone-related protein (PTHrP) at the single cell level and cause paraneoplastic syndromes in nude mice bearing the tumor. It is known that the production of G-CSF and PTHrP is individually regulated by inflammatory cytokines in various malignant cells. To investigate the common factors in the regulation of G-CSF and PTHrP production in OKa-C-1 cells, we examined the effects of some inflammatory agents [lipopolysaccharide (LPS), phorbol-12-myristate-13-acetate (PMA), tumor necrosis factor-alpha (TNF-alpha), interleukin-1 (IL-1) beta and IL-6] on G-CSF and PTHrP production, by means of enzyme-linked immunosorbent assay (ELISA), immunoradiometric assay (IRMA) and quantitative reverse transcription-polymerase chain reaction (RT-PCR). TNF-alpha or IL-1beta induced both G-CSF and PTHrP production in the conditioned medium. TNF-alpha synergized with IL-1beta to significantly increase G-CSF production. In addition, TNF-alpha and IL-1beta strongly induced G-CSF mRNA with peaks at 2 and 6 h respectively. Although PTHrP production was also strongly induced by TNF-a PTHrP mRNA expression was more strongly induced by PMA than by TNF-alpha. Thus, TNF-alpha and IL-1beta could be common factors that individually and synergistically regulate G-CSF and PTHrP production in OKa-C-1 cells. Moreover, G-CSF and PTHrP production could be not only transcriptionally, but also posttranscriptionally regulated by other factors.

Dexamethasone and interleukin-1 potently synergize to stimulate the production of granulocyte colony-stimulating factor in differentiated THP-1 cells

The human monocytic leukemic cell line, THP-1, which differentiates toward macrophages in response to phorbol 12-myristate 13-acetate (PMA) was investigated for its ability to produce granulocyte colony-stimulating factor (G-CSF). G-CSF protein was neither produced during PMA-induced differentiation nor in response to dexamethasone (Dex) alone. However, when combined, PMA and Dex synergistically stimulated THP-1 cells to produce G-CSF. The synergistic interaction between PMA and Dex on G-CSF production appeared to be mediated through the production of interleukin-1 (IL-1) since neutralization of IL-1 activity completely inhibited G-CSF production. Further experiments demonstrated that in THP-1 cells pretreated with PMA, Dex potently synergized with IL-1 to stimulate G-CSF production.