Effect of nitric oxide donor and gamma irradiation on MAPK signaling in murine peritoneal macrophages

Macrophage biology plays a central role during ionizing radiation-elicited tumor response

Radiation therapy is one of the major therapeutic modalities for most solid tumors. The anti-tumor effect of radiation therapy consists of the direct tumor cell killing, as well as the modulation of tumor microenvironment and the activation of immune response against tumors. Radiation therapy has been shown to promote immunogenic cells death, activate dendritic cells and enhance tumor antigen presentation and anti-tumor T cell activation. Radiation therapy also programs innate immune cells such as macrophages that leads to either radiosensitization or radioresistance, according to different tumors and different radiation regimen studied. The mechanisms underlying radiation-induced macrophage activation remain largely elusive. Various molecular players such as NF-κB, MAPKs, p53, reactive oxygen species, inflammasomes have been involved in these processes. The skewing to a pro-inflammatory phenotype thus results in the activation of anti-tumor immune response and enhanced radiotherapy effect. Therefore, a comprehensive understanding of the mechanism of radiation-induced macrophage activation and its role in tumor response to radiation therapy is crucial for the development of new therapeutic strategies to enhance radiation therapy efficacy.

Reprogramming of Tumor-Associated Macrophages with Anticancer Therapies: Radiotherapy versus Chemo- and Immunotherapies

Tumor-associated macrophages (TAMs) play a central role in tumor progression, metastasis, and recurrence after treatment. Macrophage plasticity and diversity allow their classification along a M1–M2 polarization axis. Tumor-associated macrophages usually display a M2-like phenotype, associated with pro-tumoral features whereas M1 macrophages exert antitumor functions. Targeting the reprogramming of TAMs toward M1-like macrophages would thus be an efficient way to promote tumor regression. This can be achieved through therapies including chemotherapy, immunotherapy, and radiotherapy (RT). In this review, we first describe how chemo- and immunotherapies can target TAMs and, second, we detail how RT modifies macrophage phenotype and present the molecular pathways that may be involved. The identification of irradiation dose inducing macrophage reprogramming and of the underlying mechanisms could lead to the design of novel therapeutic strategies and improve synergy in combined treatments.

Ghrelin accelerates wound healing through GHS-R1a-mediated MAPK-NF-κB/GR signaling pathways in combined radiation and burn injury in rats

The therapeutic effect of ghrelin on wound healing was assessed using a rat model of combined radiation and burn injury (CRBI). Rat ghrelin, anti-rat tumor necrosis factor (TNF) α polyclonal antibody (PcAb), or selective antagonists of p38 mitogen-activated protein kinase (MAPK), c-Jun N-terminal kinase (JNK), and growth hormone secretagogue receptor (GHS-R) 1a (SB203580, SP600125, and [D-Lys3]-GHRP-6, respectively), were administered for seven consecutive days. Levels of various signaling molecules were assessed in isolated rat peritoneal macrophages. The results showed that serum ghrelin levels and levels of macrophage glucocorticoid receptor (GR) decreased, while phosphorylation of p38MAPK, JNK, and p65 nuclear factor (NF) κB increased. Ghrelin inhibited the serum induction of proinflammatory mediators, especially TNF-α, and promoted wound healing in a dose-dependent manner. Ghrelin treatment decreased phosphorylation of p38MAPK, JNK, and p65NF-κB, and increased GR levels in the presence of GHS-R1a. SB203580 or co-administration of SB203580 and SP600125 decreased TNF-α level, which may have contributed to the inactivation of p65NF-κB and increase in GR expression, as confirmed by western blotting. In conclusion, ghrelin enhances wound recovery in CRBI rats, possibly by decreasing the induction of TNF-α or other proinflammatory mediators that are involved in the regulation of GHS-R1a-mediated MAPK-NF-κB/GR signaling pathways.

Low-dose ionizing radiation induces direct activation of natural killer cells and provides a novel approach for adoptive cellular immunotherapy

Recent evidence indicates that limited availability and cytotoxicity have restricted the development of natural killer (NK) cells in adoptive cellular immunotherapy (ACI). While it has been reported that low-dose ionizing radiation (LDIR) could enhance the immune response in animal studies, the influence of LDIR at the cellular level has been less well defined. In this study, the authors aim to investigate the direct effects of LDIR on NK cells and the potential mechanism, and explore the application of activation and expansion of NK cells by LDIR in ACI. The authors found that expansion and cytotoxicity of NK cells were markedly augmented by LDIR. The levels of IFN-γ and TNF-α in the supernatants of cultured NK cells were significantly increased after LDIR. Additionally, the effect of the P38 inhibitor (SB203580) significantly decreased the expanded NK cell cytotoxicity, cytokine levels, and expression levels of FasL and perforin. These findings indicate that LDIR induces a direct expansion and activation of NK cells through possibly the P38-MAPK pathway, which provides a potential mechanism for stimulation of NK cells by LDIR and a novel but simplified approach for ACI.

Therapeutic doses of irradiation activate viral transcription and induce apoptosis in HIV-1 infected cells

The highly active antiretroviral therapy reduces HIV-1 RNA in plasma to undetectable levels. However, the virus continues to persist in the long-lived resting CD4(+) T cells, macrophages and astrocytes which form a viral reservoir in infected individuals. Reactivation of viral transcription is critical since the host immune response in combination with antiretroviral therapy may eradicate the virus. Using the chronically HIV-1 infected T lymphoblastoid and monocytic cell lines, primary quiescent CD4(+) T cells and humanized mice infected with dual-tropic HIV-1 89.6, we examined the effect of various X-ray irradiation (IR) doses (used for HIV-related lymphoma treatment and lower doses) on HIV-1 transcription and viability of infected cells. Treatment of both T cells and monocytes with IR, a well-defined stress signal, led to increase of HIV-1 transcription, as evidenced by the presence of RNA polymerase II and reduction of HDAC1 and methyl transferase SUV39H1 on the HIV-1 promoter. This correlated with the increased GFP signal and elevated level of intracellular HIV-1 RNA in the IR-treated quiescent CD4(+) T cells infected with GFP-encoding HIV-1. Exposition of latently HIV-1infected monocytes treated with PKC agonist bryostatin 1 to IR enhanced transcription activation effect of this latency-reversing agent. Increased HIV-1 replication after IR correlated with higher cell death: the level of phosphorylated Ser46 in p53, responsible for apoptosis induction, was markedly higher in the HIV-1 infected cells following IR treatment. Exposure of HIV-1 infected humanized mice with undetectable viral RNA level to IR resulted in a significant increase of HIV-1 RNA in plasma, lung and brain tissues. Collectively, these data point to the use of low to moderate dose of IR alone or in combination with HIV-1 transcription activators as a potential application for the "Shock and Kill" strategy for latently HIV-1 infected cells.

DNA damage response signaling in lung adenocarcinoma A549 cells following gamma and carbon beam irradiation

Carbon beams (5.16MeV/u, LET=290keV/μm) are high linear energy transfer (LET) radiation characterized by higher relative biological effectiveness than low LET radiation. The aim of the current study was to determine the signaling differences between γ-rays and carbon ion-irradiation. A549 cells were irradiated with 1Gy carbon or γ-rays. Carbon beam was found to be three times more cytotoxic than γ-rays despite the fact that the numbers of γ-H2AX foci were same. Percentage of cells showing ATM/ATR foci were more with γ-rays however number of foci per cell were more in case of carbon irradiation. Large BRCA1 foci were found in all carbon irradiated cells unlike γ-rays irradiated cells and prosurvival ERK pathway was activated after γ-rays irradiation but not carbon. The noteworthy finding of this study is the early phase apoptosis induction by carbon ions. In the present study in A549 lung adenocarcinoma, authors conclude that despite activation of same repair molecules such as ATM and BRCA1, differences in low and high LET damage responses might be due to their distinct macromolecular complexes rather than their individual activation and the activation of cytoplasmic pathways such as ERK, whether it applies to all the cell lines need to be further explored.

Effects of the acid polysaccharide fraction isolated from a cultivated Cordyceps sinensis on macrophages in vitro

The acid polysaccharide fraction (APSF) extracted from the mycelia of cultivated Cordyceps sinensis is water-soluble polysaccharide. In this study we evaluated the modulating effects of APSF on murine macrophage cell line RAW264.7. Phagocytotic assay by neutral red and FITC-dextran internalization showed that APSF stimulated the phagocytosis of macrophages. The nitrite levels in the culture supernatant determined using Griess reagent revealed the elevation of NO production after treatment with APSF. RT-PCR and immunocytochemistry assay indicated that APSF promoted both the mRNA and protein expressions of inducible nitric oxide synthase (iNOS). Furthermore, Western blotting demonstrated that NF-kappaB levels in nucleuses increased after APSF treatment, suggesting that APSF probably stimulated macrophage activities by activating the IkappaB-NF-kappaB pathway.

Differential activation of mitogen-activated protein kinases following high and low LET radiation in murine macrophage cell line

Mitogen-activated protein kinases have been shown to respond to various stimuli including cytokines, mitogens and gamma irradiation, leading to cell proliferation, differentiation, or death. The duration of their activation determines the specificity of response to each stimulus in various cells. In this study, the crucial intracellular kinases, ERK, JNK, and p38 kinase involved in cell survival, death, or damage and repair were examined for their activity in RAW 264.7 cells at various time points after irradiation with 2 Gy doses of proton ions or X-rays. This is the first report that shows that the MAPK signaling induced after heavy ion or X-ray exposure is not the same. Unlike gamma irradiation, there was prolonged but marginal activation of prosurvival ERK pathway and significant activation of proapoptotic p38 pathway in response to high LET radiation.

Effect of nitric oxide donor and gamma irradiation on modifications of ERK and JNK in murine peritoneal macrophages

Mitogen activated protein kinases (MAPKs) play an important role in activation, differentiation and proliferation of macrophages. Macrophages, upon activation, produce large amounts of nitric oxide that inhibit the growth of variety of microorganisms and tumor cells. This nitric oxide which is known to interfere with tyrosine phosphorylation may result in changes in the pattern of activation of MAPKs. In a previous study we have found that tyrosine phosphorylation of MAPKs was completely abolished in the presence of nitric oxide donor and radiation but this did not affect the function of macrophages. In this study the other post translational modifications namely nitration and ubiquitination of JNK and ERK have been looked at. Both ERK and JNK were found to be nitrated. However, there was no increase in ubiquitination of ERK and JNK, indicating that ubiquitination, in this case was not a natural consequence of nitration and may serve in signaling. Additionally, when the nitration was extensive, phosphorylation was also inhibited. The activation of substrates of ERK and JNK were looked at to determine the consequences of such modifications. Inhibition of phosphorylation and extensive nitration of JNK did not prevent activation of its substrate, c-jun. This study indicates that ERK and JNK may be under regulation by different type of modifications in macrophages.