DNA damage response impacts macrophage functions

Helicobacter pylori triggers inflammation and oncogenic transformation by perturbing the immune microenvironment

The immune microenvironment plays a critical regulatory role in the pathogenesis of Helicobacter pylori (H. pylori). Understanding the mechanisms that drive the transition from chronic inflammation to cancer may provide new insights for early detection of gastric cancer. Although chronic inflammation is frequent in precancerous gastric conditions, the monitoring function of the inflammatory microenvironment in the progression from H. pylori-induced chronic inflammation to gastric cancer remains unclear. This literature review summarizes significant findings on how H. pylori triggers inflammatory responses and facilitates cancer development through the immune microenvironment. Furthermore, the implications for future research and clinical applications are also addressed. The review is divided into four main sections: inflammatory response and immune evasion mechanisms induced by H. pylori, immune dysregulation associated with gastric cancer, therapeutic implications, and future perspectives on H. pylori-induced gastric carcinogenesis with a focus on the immune microenvironment.

DNA-dependent protein kinase regulates cytosolic double-stranded DNA secretion from irradiated macrophages to increase radiosensitivity of tumors

BACKGROUND AND PURPOSE

To investigate the molecular mechanism by which irradiated macrophages secrete cytosolic double-stranded DNA (c-dsDNA) to increase radiosensitivity of tumors.

MATERIALS AND METHODS

Irradiated bone marrow-derived macrophages (BMDM) were co-incubated with irradiated EO771 or MC38 cancer cells to determine clonogenic survival. c-dsDNA were measured by agarose gel or enzyme-linked immunosorbent assay. BMDM or cancer cells were analyzed with immunostaining or western blot. Subcutaneously implanted MC38 cells in myeloid-specific Prkdc knockout (KO) mice or littermate control mice were irradiated with 8 Gy to determine radiosensitivity of tumors.

RESULTS

We observed that irradiated BMDM significantly increased radiosensitivity of cancer cells. By performing immunostaining, we found that there was a dose-dependent increase in the formation of c-dsDNA and phosphorylation in DNA-dependent protein kinase (DNA-PK) in irradiated BMDM. Importantly, c-dsDNA in irradiated BMDM could be secreted to the extracellular milieu and this process required DNA-PK, which phosphorylated myosin light chain to regulate the secretion. The secreted c-dsDNA from irradiated BMDM then activated toll-like receptor-9 and subsequent nuclear factor kappa-light-chain-enhancer of activated B cells signaling in the adjacent cancer cells inhibiting radiation-induced DNA double strand break repair. Lastly, we observed that irradiated tumors in vivo had a significantly increased number of tumor-associated macrophages (TAM) with phosphorylated DNA-PK expression in the cytosol. Furthermore, tumors grown in myeloid-specific Prkdc KO mice, in which TAM lacked phosphorylated DNA-PK expression were significantly more radioresistant than those of the wild-type control mice.

CONCLUSIONS

Irradiated macrophages can increase antitumor efficacy of radiotherapy through secretion of c-dsDNA under the regulation of DNA-PK.

Less Severe Polymicrobial Sepsis in Conditional mgmt-Deleted Mice Using LysM-Cre System, Impacts of DNA Methylation and MGMT Inhibitor in Sepsis

The O6-methylguanine-DNA methyltransferase (MGMT) is a DNA suicide repair enzyme that might be important during sepsis but has never been explored. Then, the proteomic analysis of lipopolysaccharide (LPS)-stimulated wild-type (WT) macrophages increased proteasome proteins and reduced oxidative phosphorylation proteins compared with control, possibly related to cell injury. With LPS stimulation, mgmt null (mgmt^flox/flox; LysM-Cre^cre/-) macrophages demonstrated less profound inflammation; supernatant cytokines (TNF-α, IL-6, and IL-10) and pro-inflammatory genes (iNOS and IL-1β), with higher DNA break (phosphohistone H2AX) and cell-free DNA, but not malondialdehyde (the oxidative stress), compared with the littermate control (mgmt^flox/flox; LysM-Cre^-/-). In parallel, mgmt null mice (MGMT loss only in the myeloid cells) demonstrated less severe sepsis in the cecal ligation and puncture (CLP) model (with antibiotics), as indicated by survival and other parameters compared with sepsis in the littermate control. The mgmt null protective effect was lost in CLP mice without antibiotics, highlighting the importance of microbial control during sepsis immune modulation. However, an MGMT inhibitor in CLP with antibiotics in WT mice attenuated serum cytokines but not mortality, requiring further studies. In conclusion, an absence of mgmt in macrophages resulted in less severe CLP sepsis, implying a possible influence of guanine DNA methylation and repair in macrophages during sepsis.

Less Severe Lipopolysaccharide-Induced Inflammation in Conditional mgmt-Deleted Mice with LysM-Cre System: The Loss of DNA Repair in Macrophages

Despite the known influence of DNA methylation from lipopolysaccharide (LPS) activation, data on the O6-methylguanine-DNA methyltransferase (MGMT, a DNA suicide repair enzyme) in macrophages is still lacking. The transcriptomic profiling of epigenetic enzymes from wild-type macrophages after single and double LPS stimulation, representing acute inflammation and LPS tolerance, respectively, was performed. Small interfering RNA (siRNA) silencing of mgmt in the macrophage cell line (RAW264.7) and mgmt null (mgmt^flox/flox; LysM-Cre^cre/-) macrophages demonstrated lower secretion of TNF-α and IL-6 and lower expression of pro-inflammatory genes (iNOS and IL-1β) compared with the control. Macrophage injury after a single LPS dose and LPS tolerance was demonstrated by reduced cell viability and increased oxidative stress (dihydroethidium) compared with the activated macrophages from littermate control mice (mgmt^flox/flox; LysM-Cre^-/-). Additionally, a single LPS dose and LPS tolerance also caused mitochondrial toxicity, as indicated by reduced maximal respiratory capacity (extracellular flux analysis) in the macrophages of both mgmt null and control mice. However, LPS upregulated mgmt only in LPS-tolerant macrophages but not after the single LPS stimulation. In mice, the mgmt null group demonstrated lower serum TNF-α, IL-6, and IL-10 than control mice after either single or double LPS stimulation. Suppressed cytokine production resulting from an absence of mgmt in macrophages caused less severe LPS-induced inflammation but might worsen LPS tolerance.

Ataxia telangiectasia mutated kinase inhibition promotes irradiation-induced PD-L1 expression in tumour-associated macrophages through IFN-I/JAK signalling pathway

Tumour-associated macrophages (TAMs) are one of the primary sources of PD-L1 expression in the tumour microenvironment (TME). Ionizing radiation (IR) promotes PD-L1 expression in tumour cells. However, the effect of IR on macrophage PD-L1 expression and the underlying mechanisms remain unclear. ATM kinase, as the key kinase for initiating DNA damage repair (DDR) process, is associated with innate immune STING axis activation. Here, we explored the molecular mechanism implicated in macrophage PD-L1 expression regulated by IR as well as the role of ATM kinase in this process. IR-regulated PD-L1 expression in macrophages and associated signalling pathways were explored by in vitro studies using murine and human macrophage cell lines. A colorectal xenograft murine model was employed to demonstrate the impact of targeting ATM and PD-L1 expression in TAMs following IR on growth of tumour in vivo. IR up-regulated PD-L1 expression in macrophages, which was further augmented by ATM kinase inhibition. ATM inhibition increased IR-induced DNA damage, which activated STING/interferon regulatory factor 3 (IRF3) signalling pathway and up-regulated type I interferon (IFN-I) expression in macrophages. IFN-I bound to the IFN α receptor 1 on macrophages, activated the downstream JAK1 and STAT1/3 signalling and eventually led to PD-L1 up-expression. ATM inhibition augmented IR-induced PD-L1 expression in macrophages and CD8⁺ T cell infiltration, and promoted anti-tumour efficacy in vivo. These results suggested that ATM inhibition promoted IR-induced PD-L1 expression through the activation of innate immunity in TAMs, which provided a novel approach to enhance the anti-tumour efficacy of RT.

Impairment of sirtuin 1-mediated DNA repair is involved in bisphenol A-induced aggravation of macrophage inflammation and atherosclerosis

Bisphenol A (BPA), an environmental pollutant, has received considerable attention worldwide for its hazardous effects of promoting atherosclerosis and increasing the risk of cardiovascular diseases (CVDs). However, the mechanisms involved are unclear. We aimed to investigate the mechanisms underlying BPA-aggravated atherosclerosis and potential preventive treatments. Four-week-old male Ldlr^-/- C57BL/6 mice were administered 250 μg/L BPA via drinking water for 30 weeks with or without a Western diet and/or resveratrol (RESV) for 12 weeks. Chronic BPA exposure significantly aggravated atherosclerosis, enhanced the production of inflammatory cytokines but not lipid levels, promoted macrophage infiltration into plaque areas. Moreover, peritoneal macrophages isolated from BPA-exposed mice exhibited a more pro-inflammatory phenotype in response to cholesterol crystal treatment than those from control mice. The comet assay revealed that the DNA repair capacity of BPA-exposed macrophages was impaired, and western blotting showed that sirtuin 1 and Nijmegen breakage syndrome 1 (NBS1) expression was reduced. However, restoring sirtuin 1 by RESV administration significantly blocked the BPA-induced decrease in NBS1 and subsequently attenuated the BPA-induced impairment of DNA repair and apoptosis, as indicated by phosphorylated H2AX expression and staining and PARP expression. Moreover, RESV administration significantly ameliorated BPA-aggravated NOD-like receptor pyrin domain 3 and caspase 1 activation and interleukin-1β production, which were abolished by NBS1 knockdown. Furthermore, RESV administration prevented BPA-induced aggravation of atherosclerosis. Our findings indicate that impairment of sirtuin 1-mediated DNA repair is involved in BPA-induced aggravation of macrophage inflammation and atherosclerosis and that RESV might be a promising preventive and therapeutic agent for BPA-related CVDs.

Gephyromycin C, a novel small-molecule inhibitor of heat shock protein Hsp90, induces G2/M cell cycle arrest and apoptosis in PC3 cells in vitro

Gephyromycin C (GC), a natural compound isolated from a marine-derived actinomycete Streptomyces sp. SS13I, which exerts anti-proliferative effect on PC3 cells. However, its underlying mechanism of the anti-cancer effect remains unknown. The results of SRB assays showed that GC inhibited the proliferation of PC3 cells with an IC₅₀ value of 1.79 ± 0.28 μM. GC also induced G2/M cell cycle arrest which was accompanied by declining levels of cyclin proteins. Possible mechanisms were investigated and it was found that GC bound to Hsp90 and caused the degradation of Hsp90 client proteins (AKT, CHK1, P53, CDK4, Raf-b, and Raf-1). The fluorescent polarization assay with FITC-labeled geldanamycin (FITC-GA) demonstrated that GC was able to compete with FITC-GA in binding to wild type Hsp90 with an IC₅₀ of 2.15 μM. Results of a docking study also suggested that GC interacted with the N-terminal domain of Hsp90. Our results showed that GC could bind to Hsp90, which resulted in down-regulation of Hsp90 client proteins and G2/M arrest in PC3 cells. Since the antitumor effects of this kind of angucycline via targeting Hsp90 has not been reported before, our results indicate that GC is a novel inhibitor of Hsp90 from marine resources and worthy of further study.

Inflammation, DNA Damage, Helicobacter pylori and Gastric Tumorigenesis

Helicobacter pylori (H. pylori) is a Gram negative bacterium that colonizes the stomach of almost half human population. It has evolved to escape immune surveillance, establishes lifelong inflammation, predisposing to genomic instability and DNA damage, notably double strand breaks. The epithelial host cell responds by activation of DNA damage repair (DDR) machinery that seems to be compromised by the infection. It is therefore now accepted that genetic damage is a major mechanism operating in cases of H. pylori induced carcinogenesis. Here, we review the data on the molecular pathways involved in DNA damage and DDR activation during H. pylori infection.