Apoptotic cell-derived factors induce arginase II expression in murine macrophages by activating ERK5/CREB.

Apoptotic cell (AC)-derived factors alter the physiology of macrophages (MΦs) towards a regulatory phenotype, characterized by reduced nitric oxide (NO) production. Impaired NO formation in response to AC-conditioned medium (CM) was facilitated by arginase II (ARG II) expression, which competes with inducible NO synthase for L-arginine. Here we explored signaling pathways allowing CM to upregulate ARG II in RAW264.

Sulforaphane potentiates oxaliplatin-induced cell growth inhibition in colorectal cancer cells via induction of different modes of cell death.

The objective of this study was to investigate, whether the plant-derived isothiocyanate Sulforaphane (SFN) enhances the antitumor activities of the chemotherapeutic agent oxaliplatin (Ox) in a cell culture model of colorectal cancer. Caco-2 cells were cultured under standard conditions and treated with increasing concentrations of SFN [1-20 μM] and/or Ox [100 nM-10 μM]. For co-incubation, cells were pre-treated with SFN for 24 h.

A combination of hypoxia and lipopolysaccharide activates tristetraprolin to destabilize proinflammatory mRNAs such as tumor necrosis factor-alpha.

Inflammation is often accompanied by hypoxia because of the high oxygen consumption of invading bacteria and immune cells. During resolution of inflammation, the formation of inflammatory mediators such as tumor necrosis factor-alpha (TNF-alpha), which is produced by macrophages, needs to be terminated. We show in RAW264.

Neuromediators in inflammation--a macrophage/nerve connection.

Macrophages are key players not only during initiation of inflammation but also during its resolution. This is achieved by their high functional plasticity and the demand to recognize an enormous repertoire of danger signals and cytokines/chemokines derived from adaptive immune cells. Studies predominantly conducted over the last two decades implicate that macrophage responses are also modulated by neuronal mediators such as neurotransmitters or neurotrophic factors.

Roles of hypoxia-inducible factor-1alpha (HIF-1alpha) versus HIF-2alpha in the survival of hepatocellular tumor spheroids.

Unlabelled: Hypoxia-inducible factors (HIFs) provoke adaptation to hypoxic stress occurring in rapidly growing tumor tissues. Therefore, overexpression of HIF-1 or HIF-2 is a common feature in hepatocellular carcinoma but their specific function is still controversially discussed. To analyze HIF function in hypoxia-induced cell death we created a stable knockdown of HIF-1alpha and HIF-2alpha in HepG2 cells and generated tumor spheroids as an in vitro hepatocellular carcinoma model.

Technical advance: Generation of human pDC equivalents from primary monocytes using Flt3-L and their functional validation under hypoxia.

The division of labor between DC subsets is evolutionarily well-defined. mDC are efficient in antigen presentation, whereas pDC act as rheostats of the immune system. They activate NK cells, cause bystander activation of mDC, and interact with T cells to induce tolerance.

Knockout of HIF-1α in tumor-associated macrophages enhances M2 polarization and attenuates their pro-angiogenic responses.

Tumor-associated macrophages (TAMs) constitute major infiltrates of solid tumors and express a marker profile that characterizes alternatively activated macrophages (MФs). TAMs accumulate in hypoxic tumor regions, express high amounts of hypoxia-inducible factor-1 (HIF-1) and contribute to tumor angiogenesis and invasiveness. However, the precise role of HIF-1 on MФ infiltration and phenotype alterations remains poorly defined.

Cleavage of sphingosine kinase 2 by caspase-1 provokes its release from apoptotic cells.

Execution of physiologic cell death known as apoptosis is tightly regulated and transfers immunologically relevant information. This ensures efficient clearance of dying cells and shapes the phenotype of their "captors" toward anti-inflammatory. Here, we identify a mechanism of sphingosine-1-phosphate production by apoptotic cells.

High glucose concentrations attenuate hypoxia-inducible factor-1alpha expression and signaling in non-tumor cells.

Hypoxia-inducible factor (HIF) is the major transcription factor mediating adaption to hypoxia e.g. by enhancing glycolysis.

MicroRNA-27b contributes to lipopolysaccharide-mediated peroxisome proliferator-activated receptor gamma (PPARgamma) mRNA destabilization.

Peroxisome proliferator-activated receptor gamma (PPARgamma) gained considerable interest as a therapeutic target during chronic inflammatory diseases. Remarkably, the pathogenesis of diseases such as multiple sclerosis or Alzheimer is associated with impaired PPARgamma expression. Considering that regulation of PPARgamma expression during inflammation is largely unknown, we were interested in elucidating underlying mechanisms.

Casein-kinase-II-dependent phosphorylation of PPARgamma provokes CRM1-mediated shuttling of PPARgamma from the nucleus to the cytosol.

PPARgamma exerts significant anti-inflammatory signaling properties in monocytes and macrophages, which are affected by its intracellular localization. Based on our previous report, which showed that cytosolic localization of PPARgamma attenuates PKCalpha signaling in macrophages, we elucidated the molecular mechanisms provoking cytosolic PPARgamma localization. Using the DsRed-tagged PPARgamma deletion constructs PPARgamma1 Delta1-31 and PPARgamma1 Delta407-475, we observed an exclusive nuclear PPARgamma1 Delta1-31 localization in transfected HEK293 cells, whereas PPARgamma1 Delta407-475 did not alter its cytosolic or nuclear localization.

Phospholipase A2-modified low-density lipoprotein activates macrophage peroxisome proliferator-activated receptors.

Background And Purpose: Peroxisome proliferator-activated receptors (PPARs) are ligand-activated transcription factors modulating metabolic and inflammatory responses of phagocytes to stimuli such as fatty acids and their metabolites. We studied the role of PPARs in macrophages exposed to low-density lipoprotein (LDL) modified by secretory phospholipase A(2) (PLA).

Methods And Results: By analyzing PPAR ligand-binding domain luciferase reporter activation, we observed that PLA-LDL transactivates PPARalpha and PPARdelta, but not PPARgamma.

Role of sestrin2 in peroxide signaling in macrophages.

Reactive oxygen species not only serve as signaling molecules, they also contribute to oxidative stress and cell damage. The thioredoxin and glutaredoxin systems form along with peroxiredoxins a precisely regulated defense system to maintain the cellular redox homeostasis. There is evidence that nitric oxide (NO) protects cells from oxidative stress by preventing inactivation of peroxiredoxins by sulfinylation.

Hypoxic transcription gene profiles under the modulation of nitric oxide in nuclear run on-microarray and proteomics.

Background: Microarray analysis still is a powerful tool to identify new components of the transcriptosome. It helps to increase the knowledge of targets triggered by stress conditions such as hypoxia and nitric oxide. However, analysis of transcriptional regulatory events remain elusive due to the contribution of altered mRNA stability to gene expression patterns as well as changes in the half-life of mRNAs, which influence mRNA expression levels and their turn over rates.

Phospholipase A2-modified low density lipoprotein induces mitochondrial uncoupling and lowers reactive oxygen species in phagocytes.

Low density lipoprotein modified by secretory phospholipase A(2) (PLA-LDL) protects monocytes against oxidative stress. In this study we investigated possible direct effects of PLA-LDL on mitochondrial membrane potential and reactive oxygen species generation. Mitochondrial membrane potential in human monocytic THP-1 cells or primary human monocytes was monitored by flow cytometry using the fluorescent dye 5,5',6,6'-tetrachloro-1,1',3,3'-tetraethylbenzimidazolylcarbocyanine iodide or respirometry.

Redox mechanisms involved in the selective activation of Nrf2-mediated resistance versus p53-dependent apoptosis in adenocarcinoma cells.

We have investigated the role of reactive oxygen species and thiol-oxidizing agents in the induction of cell death and have shown that adenocarcinoma gastric (AGS) cells respond differently to the oxidative challenge according to the signaling pathways activated. In particular, apoptosis in AGS cells is induced via the mitochondrial pathway upon treatment with thiol-oxidizing agents, such as diamide. Apoptosis is associated with persistent oxidative damage, as evidenced by the increase in carbonylated proteins and the expression/activation of DNA damage-sensitive proteins histone H2A.

Regulation of macrophage function by sphingosine-1-phosphate.

The bioactive lipid sphingosine-1-phosphate (S1P) fulfils manifold tasks in the immune system acting in auto- and/or paracrine fashion. This includes regulation of apoptosis, migration and proliferation. Upon its generation by sphingosine kinases from plasma membrane sphingolipids, S1P can either act as a second messenger within cells or can be released from cells to occupy a family of specific G-protein-coupled receptors (S1P1-5).

Sphingosine kinase 2 deficient tumor xenografts show impaired growth and fail to polarize macrophages towards an anti-inflammatory phenotype.

A challenging task of the immune system is to fight cancer cells. However, a variety of human cancers educate immune cells to become tumor supportive. This is exemplified for tumor-associated macrophages (TAMs), which are polarized towards an anti-inflammatory and cancer promoting phenotype.

The supernatant of apoptotic cells causes transcriptional activation of hypoxia-inducible factor-1alpha in macrophages via sphingosine-1-phosphate and transforming growth factor-beta.

Macrophages infiltrating solid tumors exhibit a tumor-supporting phenotype and are critical for tumor development. Little is known which tumor-derived signal provokes this phenotype shift and how these signals are interpreted in macrophages to support tumor growth. We used the supernatant of apoptotic cells and noticed transcriptional, nuclear factor of activated T cells-dependent up-regulation of hypoxia-inducible factor (HIF)-1alpha mRNA, subsequent protein expression, and HIF-1 activity.

Nitric oxide causes macrophage migration via the HIF-1-stimulated small GTPases Cdc42 and Rac1.

Hypoxia-inducible factor 1 (HIF-1) is a key regulator of tumor development. Recently, the tumor microenvironment, with the presence of tumor-associated macrophages (TAMs), has gained considerable interest. The mechanisms of macrophage/TAM migration as well as the role of HIF-1 in macrophages for tumor progression are still under debate.

Attenuated suppression of the oxidative burst by cells dying in the presence of oxidized low density lipoprotein.

Macrophages ingesting apoptotic cells attenuate inflammatory responses, such as reactive oxygen species (ROS) generation. In atherosclerosis, ongoing inflammation and accumulation of apoptotic/necrotic material are observed, suggesting defects of phagocytes in recognizing or responding to dying cells. Modified lipoproteins such as oxidized LDL (oxLDL) are known to promote inflammation and to interfere with apoptotic cell clearance.

The liaison between apoptotic cells and macrophages--the end programs the beginning.

The efficient execution of apoptotic cell death with the clearance of apoptotic debris by phagocytes is a key regulatory mechanism ensuring tissue homeostasis. Failure in this execution program contributes to the pathogenesis of many human diseases. In this review, we describe the current knowledge regarding the interaction of apoptotic cells with their professional 'captors', the macrophages, with special emphasis on the immunological outcome.

HIF-1 in the inflammatory microenvironment.

Hypoxia-inducible factor (HIF) is a transcriptional activator that coordinates adaptive responses to hypoxia. An increased activity is recognized in the majority of clinical relevant hypoxic/ischemic episodes and human cancers. However, studies with HIF-1alpha knockout mice revealed an important role of HIF-1 for physiology such as embryogenesis or glycolytic energy production.

Hypoxia enhances sphingosine kinase 2 activity and provokes sphingosine-1-phosphate-mediated chemoresistance in A549 lung cancer cells.

Hypoxia and signaling via hypoxia-inducible factor-1 (HIF-1) is a key feature of solid tumors and is related to tumor progression as well as treatment failure. Although it is generally accepted that HIF-1 provokes tumor cell survival and induces chemoresistance under hypoxia, HIF-1-independent mechanisms operate as well. We present evidence that conditioned medium obtained from A549 cells, incubated for 24 h under hypoxia, protected naive A549 cells from etoposide-induced cell death.