The nuclear aryl hydocarbon receptor is involved in regulation of DNA repair and cell survival following treatment with ionizing radiation

Gene Expression and Activity of Selected Antioxidant and DNA Repair Enzymes in the Prefrontal Cortex of Sheep as Affected by Kynurenic Acid

The prefrontal cortex (PCx) is involved in many higher-order cognitive processes, including decision making, reasoning, personality expression, and social cognition. These functions are associated with high energy demand and the production of harmful oxygen radicals. Recent studies indicate that kynurenic acid (KYNA) exerts neuroprotective effects, largely due to its anti-inflammatory and antioxidant properties. To further evaluate the antioxidant potential of this compound, we tested the hypothesis that increasing KYNA levels in the sheep cerebroventricular circulation would positively affect the mRNA expression and activity of selected antioxidant and DNA repair enzymes in the distal part of the brain, i.e., the PCx. Anestrous sheep were infused intracerebroventricularly with a series of two KYNA doses: lower (4 × 5 μg/60 μL/30 min) and higher (4 × 25 μg/60 μL/30 min) at 30 min intervals. The results demonstrated that KYNA exerted significant dose-dependent stimulatory effects on the activity of superoxide dismutase 2, catalase, and glutathione peroxidase 1 while inhibiting their transcription in a similar manner. In addition, KYNA was also found to dose-dependently activate the base excision repair pathway, as determined by the increased transcript levels of glycosylases: N-methylpurine DNA glycosylase, thymine-DNA glycosylase, 8-oxoguanine DNA glycosylase-1, and apurinic/apyrimidinic endonuclease 1. The excision efficiency of damaged nucleobases, such as εA, εC and 8-oxoG, by these enzymes was also increased in response to central KYNA infusion. These findings expand the knowledge on KYNA as a potential protective factor against oxidative stress in the central nervous system.

A microbiota and dietary metabolite integrates DNA repair and cell death to regulate embryo viability and aneuploidy during aging

During aging, environmental stressors and mutations along with reduced DNA repair cause germ cell aneuploidy and genome instability, which limits fertility and embryo development. Benevolent commensal microbiota and dietary plants secrete indoles, which improve healthspan and reproductive success, suggesting regulation of germ cell quality. We show that indoles prevent aneuploidy and promote DNA repair and embryo viability, which depends on age and genotoxic stress levels and affects embryo quality across generations. In young animals or with low doses of radiation, indoles promote DNA repair and embryo viability; however, in older animals or with high doses of radiation, indoles promote death of the embryo. These studies reveal a previously unknown quality control mechanism by which indole integrates DNA repair and cell death responses to preclude germ cell aneuploidy and ensure transgenerational genome integrity. Such regulation affects healthy aging, reproductive senescence, cancer, and the evolution of genetic diversity in invertebrates and vertebrates.

LINC00665 knockdown confers sensitivity in irradiated non-small cell lung cancer cells through the miR-582-5p/UCHL3/AhR axis

Background

The resistance to radiotherapy remains a major obstacle that limits the efficacy of radiotherapy in non-small cell lung cancer (NSCLC). This study aims to illustrate the molecular mechanism underlying the role of LINC00665 in the radiosensitivity of NSCLC, which involves ubiquitin C-terminal hydrolase L3 (UCHL3).

Methods and results

The expression of UCHL3 was determined in clinical tissue samples collected from NSCLC patients and NSCLC cell lines. We found that UCHL3 overexpression occurred in both NSCLC tissues and cells, associated with poor prognosis in NSCLC patients. Mechanistically, UCHL3 stabilized aryl hydrocarbon receptor (AhR) protein through deubiquitination, thereby promoting PD-L1 expression. UCHL3 reduced the radiosensitivity of NSCLC cells by stabilizing AhR protein. Upstream microRNAs (miRNAs) and lncRNAs of UCHL3 were predicted by microarray profiling and validated by functional experiments. LINC00665 functioned as a sponge of miR-582-5p and thus up-regulated the expression of the miR-582-5p target UCHL3. Gain- and loss- of function assays were performed to assess the effects of LINC00665, UCHL3 and miR-582-5p on the in vitro cell malignant behaviors and immune escape as well as on the in vivo tumor growth. Silencing LINC00665 or overexpressing miR-582-5p enhanced the sensitivity of NSCLC cells to radiotherapy. LINC00665 augmented the immune escape of NSCLC cells in vitro and in vivo through stabilizing AhR protein via the miR-582-5p/UCHL3 axis.

Conclusions

Overall, LINC00665 reduced the radiosensitivity of NSCLC cells via stabilization of AhR through the miR-582-5p/UCHL3 axis.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12967-022-03516-2.

Intestinal Radiation Protection and Mitigation by Second-Generation Probiotic Lactobacillus-reuteri Engineered to Deliver Interleukin-22

(1) Background: The systemic administration of therapeutic agents to the intestine including cytokines, such as Interleukin-22 (IL-22), is compromised by damage to the microvasculature 24 hrs after total body irradiation (TBI). At that time, there is significant death of intestinal microvascular endothelial cells and destruction of the lamina propria, which limits drug delivery through the circulation, thus reducing the capacity of therapeutics to stabilize the numbers of Lgr5+ intestinal crypt stem cells and their progeny, and improve survival. By its direct action on intestinal stem cells and their villus regeneration capacity, IL-22 is both an ionizing irradiation protector and mitigator. (2) Methods: To improve delivery of IL-22 to the irradiated intestine, we gavaged Lactobacillus-reuteri as a platform for the second-generation probiotic Lactobacillus-reuteri-Interleukin-22 (LR-IL-22). (3) Results: There was effective radiation mitigation by gavage of LR-IL-22 at 24 h after intestinal irradiation. Multiple biomarkers of radiation damage to the intestine, immune system and bone marrow were improved by LR-IL-22 compared to the gavage of control LR or intraperitoneal injection of IL-22 protein. (4) Conclusions: Oral administration of LR-IL-22 is an effective protector and mitigator of intestinal irradiation damage.

Triclosan (TCS) affects the level of DNA methylation in the human oral squamous cell carcinoma (SCC-15) cell line in a nontoxic concentration

The oral cancer is presumably caused by genetic factors and exposure to substances derived from cosmetics and disinfectants. Triclosan (TCS) is widely spread in many consumer products and oral care products. Since TCS can affect DNA methylation, which is one of the key mechanisms of gene expression that may lead to cancerogenesis, it is necessary to study this mechanism in oral cell carcinoma. The aim of the present study was to evaluate the impact of TCS on metabolic parameters, oxidative stress, gene expression, and DNA methylation and hydroxymethylation in the SCC-15 cell line. The experiments have shown TCS toxicity to SCC-15 cells only in the highest concentrations of 50 and 100 µM. TCS in a wide range of concentrations increases ROS production and caspase-3 activity. Our experiments have shown that TCS in the nontoxic concentrations of 10 µM exerts an impact on SOD2 mRNA expression and SOD activity in the SCC-15 cell line. Finally, our experiments have demonstrated that 6-h treatment with TCS decreases the mRNA expression of DNMT3A and DNMT3B. After 72-h exposure to TCS, an increased level of 5-methylcytosine and 5-hydroxymethylcytosine was observed in the SCC-15 cell line, but it was abolished by the NAC treatment. However, it is very likely that these results can be an effect of TET enzyme activity, especially in the case of the decrease in 5mC and the increase in 5hmC after the 48-h exposure to TCS, which was accompanied with a decrease in the mRNA expression of DNMT3A and DNMT3B.

Detection of double-stranded DNA breaks and apoptosis induced by bleomycin in mouse intestine

The gastrointestinal tract is exposed to a myriad of mutagens, making the DNA damage response (DDR) essential to maintain intestinal homeostasis. In vivo models to study DDRs are necessary to understand the mechanisms of disease development caused by genetic disorders such as colorectal cancer. A double-stranded break (DSB) in DNA is the most toxic type of DNA damage; it can be induced by either X-rays or chemicals, including anticancer agents. If DSBs in DNA cannot be repaired, cells can die by apoptosis to be removed from tissues. Here, we show that the DDRs observed as the phosphorylation of H2AX (γH2AX) and caspase-3-dependent apoptosis-induction are under critical control in the intestine of C57BL mice that were injected intraperitoneally with bleomycin, a natural glycopeptide used clinically as an antitumor agent. We found a significant increase in γH2AX expression 2-6 hr post-treatment in mouse ileum, cecum, and colon tissues by Western blotting and immunostaining. Apoptotic cells were observed after 6-24 hr by terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) assay and immunofluorescence of active caspase-3. We observed that γH2AX expression and apoptotic cells were distributed in the lower part of the crypt. The experimental protocol described here is a simple procedure that can be used generally as an in vivo intestinal toxicity assay. Our experimental approach provides a useful method for examining the effects of various bioactive compounds on the DDR, which is essential for understanding intestinal homeostasis.

Impact of DNA repair and reactive oxygen species levels on radioresistance in pancreatic cancer

PURPOSE

Radioresistance in pancreatic cancer patients remains a critical obstacle to overcome. Understanding the molecular mechanisms underlying radioresistance may achieve better response to radiotherapy and thereby improving the poor treatment outcome. The aim of the present study was to elucidate the mechanisms leading to radioresistance by detailed characterization of isogenic radioresistant and radiosensitive cell lines.

METHODS

The human pancreatic cancer cell lines, Panc-1 and MIA PaCa-2 were repeatedly exposed to radiation to generate radioresistant (RR) isogenic cell lines. The surviving cells were expanded, and their radiosensitivity was measured using colony formation assay. Tumor growth delay after irradiation was determined in a mouse pancreatic cancer xenograft model. Gene and protein expression were analyzed using RNA sequencing and Western blot, respectively. Cell cycle distribution and apoptosis (Caspase 3/7) were measured by FACS analysis. Reactive oxygen species generation and DNA damage were analyzed by detection of CM-H₂DCFDA and γH2AX staining, respectively. Transwell chamber assays were used to investigate cell migration and invasion.

RESULTS

The acquired radioresistance of RR cell lines was demonstrated in vitro and validated in vivo. Ingenuity pathway analysis of RNA sequencing data predicted activation of cell viability in both RR cell lines. RR cancer cell lines demonstrated greater DNA repair efficiency and lower basal and radiation-induced reactive oxygen species levels. Migration and invasion were differentially affected in RR cell lines.

CONCLUSIONS

Our data indicate that repeated exposure to irradiation increases the expression of genes involved in cell viability and thereby leads to radioresistance. Mechanistically, increased DNA repair capacity and reduced oxidative stress might contribute to the radioresistant phenotype.

Targeting the Aryl Hydrocarbon Receptor Signaling Pathway in Breast Cancer Development

Activation of the aryl hydrocarbon receptor (AhR) through environmental exposure to known human carcinogens including dioxins can lead to the promotion of breast cancer. While the repressor protein of the AhR (AhRR) blocks the canonical AhR pathway, the function of AhRR in the development of breast cancer is not well-known. In the current study we examined the impact of suppressing AhR activity using its dedicated repressor protein AhRR. AhRR is a putative tumor suppressor and is silenced in several cancer types, including breast, where its loss correlates with shorter patient survival. Using the AhRR transgenic mouse, we demonstrate that AhRR overexpression opposes AhR-driven and inflammation-induced growth of mammary tumors in two different murine models of breast cancer. These include a syngeneic model using E0771 mammary tumor cells as well as the Polyoma Middle T antigen (PyMT) transgenic model. Further AhRR overexpression or knockout of AhR in human breast cancer cells enhanced apoptosis induced by chemotherapeutics and inhibited the growth of mouse mammary tumor cells. This study provides the first in vivo evidence that AhRR suppresses mammary tumor development and suggests that strategies which lead to its functional restoration and expression may have therapeutic benefit.

β-Naphthoflavone Activation of the Ah Receptor Alleviates Irradiation-Induced Intestinal Injury in Mice

Radiotherapy induced gastrointestinal syndrome results from the acute damage of intestinal stem cells, impaired crypts reconstruction, and subsequent breakdown of the mucosal barrier. The toxicity of ionizing radiation is associated with oxidative stress in the intestinal epithelial cells (IECs). Moreover, the rapid proliferation of IECs is a risk factor for radiation damage. β-naphthoflavone (BNF) is an agonist of the aryl hydrocarbon receptor (AhR) and possesses potential antioxidative activity. We investigated BNF radioprotection in IECs experiencing γ-ray exposure, contributed to mitigation of radiation enteritis. BNF significantly enhanced cell viability and suppressed cell apoptosis in an AhR activation-dependent manner. The mechanism of BNF reducing the IECs radiosensitivity was associated with cell cycle arrest and suppression of cell proliferation. In contrast, AhR antagonist CH-223191 significantly blocked BNF-induced cell cycle arrest. Cyp1a1 mRNA levels are induced after irradiation in a dose-dependent manner, and CYP1A1 protein expression increased in the irradiated intestinal tract as well. BNF also reduces DNA strand breaks induced by irradiation. These studies demonstrate that BNF pretreatment prolonged median survival time of mice upon exposure to a lethal dose of radiation and alleviated irradiation-induced toxicity within the bowel.

The circ_VCAN with radioresistance contributes to the carcinogenesis of glioma by regulating microRNA-1183

Circular RNAs (circRNAs), a widespread type of noncoding RNA, are produced by reverse splicing with a circular loop structure. Circ_VCAN (hsa_circ_0073237) acts as a novel circRNA, although its roles in the progression and radioresistance of glioma remain unknown.Expressions of circ_VCAN and microRNA-1183 (miR-1183) were analyzed by quantitative real-time PCR, and the functions of circ_VCAN and irradiate in glioma cell proliferation, apoptosis, migration, and invasion were assessed using cell counting kit-8, flow cytometry, Wound healing, and Transwell assays. The interaction between circ_VCAN and miR-1183 was validated dual-luciferase reporter assay.Our results revealed that circ_VCAN was significantly upregulated in radioresistant glioma tissues compared with radiosensitive tissues, and that circ_VCAN expression was negatively correlated with miR-1183 expression in glioma tissues. We also determined that circ_VCAN expression was decreased and miR-1183 expression was increased in U87 and U251 cells after irradiation. Both knockdown of circ_VCAN and treatment with miR-1183 mimics inhibited proliferation, migration, and invasion, and accelerated apoptosis of the irradiated U87 and U251 cells. In addition, luciferase reporter assays revealed that circ_VCAN might function as a sponge for miR-1183. Finally, overexpression of circ_VCAN expedited carcinogenesis and reduced glioma radiosensitivity by regulating miR-1183.Circ_VCAN serves as a potential oncogene of glioma by regulating miR-1183, and plays an essential role in the radioresistance of glioma.

Reduced exosomal L-Plastin is responsible for radiation-induced bystander effect

Radiation-induced bystander effects (RIBE) are discussed as relevant processes during radiotherapy. Irradiated cells are suggested to release growth-inhibitory/DNA-damaging factors transported to non-irradiated cells. However, the molecular nature of this phenomenon has not yet been resolved. We aimed at identifying the growth-inhibitory factor(s) transmitted to non-irradiated cells. RIBE-competent PC3 cells were used to produce conditioned medium (CM) after exposure to ionizing radiation. Indicator cells were incubated with CM and clonogenic survival as well as cell proliferation were determined as endpoints. A549 indicator cells exhibited a bystander effect upon incubation with CM from irradiated PC3 cells. This bystander effect was not due to DNA-damaging factors, but a radiation-triggered reduction of mitogenic/clonogenic activity present in CM. Several tumor cells, but not normal fibroblasts secrete this factor, whose release is reduced by irradiation. We identified L-Plastin to be responsible for the mitogenic/clonogenic activity. Removal of L-Plastin from CM by immunoprecipitation or siRNA-mediated knockdown of L-Plastin expression resulted in loss or reduction of mitogenic/clonogenic activity transmitted via CM, respectively. Exosome-transported L-Plastin was constitutively Ser5-phosphorylated, indicative of its bioactive conformation. In summary, we observed production and exosomal secretion of L-Plastin by cancer cells. Via exosome-transmitted L-Plastin, tumors induce clonogenic and mitogenic activity in cancer and normal cells of the tumor microenvironment. Irradiation inhibits L-Plastin production targeting both cancer cells and the tumor niche and may explain the high impact of radiotherapy in tumor control.

Silencing of heat shock protein 27 increases the radiosensitivity of non‑small cell lung carcinoma cells

Radiotherapy is a useful treatment for malignant tumors, including lung carcinoma; however, non‑small cell lung carcinoma (NSCLC) is frequently insensitive to radiation. It has been reported that heat shock protein 27 (HSPB1) is a radioresistance‑associated protein in nasopharyngeal carcinoma. In the present study, the role of HSPB1 in NSCLC cells induced by irradiation was investigated. The viability of cells was determined by a Cell Counting Kit‑8 assay. The apoptotic activity, cell cycle distribution and mitochondrial membrane potential (MMP) of cells were evaluated via flow cytometry. Reverse transcription‑quantitative polymerase chain reaction and western blot analyses were employed to measure the expression of various genes and proteins. It was observed that knockdown of HSPB1 with small interfering RNA (si‑HSPB1) markedly decreased the viability of A549 NSCLC cells and induced cell cycle arrest in the G2/M phase following exposure to 6 Gy irradiation. Furthermore, it was revealed that si‑HSPB1 significantly downregulated cyclin B1 and cyclin G1 expression. Additionally, si‑HSPB1 promoted apoptosis and depolarized the MMP of cells exposed to 6 Gy irradiation. The expression levels of B‑cell lymphoma‑2 (Bcl‑2), mitochondrial cytochrome c (cyto c) and pro‑caspase‑8 were downregulated, whereas those of Bcl‑2 associated X protein (Bax), cytosolic cyto c and cleaved‑caspase‑8 were upregulated. Collectively, silencing of HSPB1 increased the radiosensitivity of NSCLC cells by reducing cell viability, depolarizing the MMP, arresting the cell cycle in the G2/M phase and promoting cell apoptosis. Therefore, HSPB1 may be a novel target for increasing radiosensitivity in the treatment of NSCLC.

The AHR represses nucleotide excision repair and apoptosis and contributes to UV-induced skin carcinogenesis

Ultraviolet B (UVB) radiation induces mutagenic DNA photoproducts, in particular cyclobutane pyrimidine dimers (CPDs), in epidermal keratinocytes (KC). To prevent skin carcinogenesis, these DNA photoproducts must be removed by nucleotide excision repair (NER) or apoptosis. Here we report that the UVB-sensitive transcription factor aryl hydrocarbon receptor (AHR) attenuates the clearance of UVB-induced CPDs in human HaCaT KC and skin from SKH-1 hairless mice. Subsequent RNA interference and inhibitor studies in KC revealed that AHR specifically suppresses global genome but not transcription-coupled NER. In further experiments, we found that the accelerated repair of CPDs in AHR-compromised KC depended on a modulation of the p27 tumor suppressor protein. Accordingly, p27 protein levels were increased in AHR-silenced KC and skin biopsies from AHR^−/− mice, and critical for the improvement of NER. Besides increasing NER activity, AHR inhibition was accompanied by an enhanced occurrence of DNA double-strand breaks triggering KC apoptosis at later time points after irradiation. The UVB-activated AHR thus acts as a negative regulator of both early defense systems against carcinogenesis, NER and apoptosis, implying that it exhibits tumorigenic functions in UVB-exposed skin. In fact, AHR^−/− mice developed 50% less UVB-induced cutaneous squamous cell carcinomas in a chronic photocarcinogenesis study than their AHR^+/+ littermates. Taken together, our data reveal that AHR influences DNA damage-dependent responses in UVB-irradiated KC and critically contributes to skin photocarcinogenesis in mice.

Aryl hydrocarbon receptor (AhR) a possible target for the treatment of skin disease

Aryl hydrocarbon receptor (AhR) is a transcription factor expressed in all skin cells type. It responds to exogenous and endogenous chemicals by inducing/repressing the expression of several genes with toxic or protective effects in a wide range of species and tissues. In healthy skin, AhR signalling contributes to keratinocytes differentiation, skin barrier function, skin pigmentation, and mediates oxidative stress. In the last years, some studies have shown that AhR seems to be involved in the pathogenesis of some skin diseases, even if the currently available data are contradictory. Indeed, while the blocking the AhR signalling activity could prevent or treat skin cancer, the AhR activation seems to be advantageous for the treatment of inflammatory skin diseases. Therefore, for its multifaceted role in skin diseases, AhR seems to be an attractive therapeutic target. Indeed, recently some molecules have been identified for the prevention of skin cancer and the treatment of inflammatory skin diseases.

Hydroxystilbenes and methoxystilbenes activate human aryl hydrocarbon receptor and induce CYP1A genes in human hepatoma cells and human hepatocytes

Natural polyphenol resveratrol (trihydroxystilbene) is a partial agonist of human aryl hydrocarbon receptor AhR, thereby, displaying a plethora of biological effects. Biological activities of metoxylated and hydroxylated stilbenes were studied in the past. The aim of the current study was to describe the effects of 13 different hydroxy- and methoxystilbenes, including their cis/trans isomers on the transcriptional activity of AhR and the expression of CYP1A genes in hepatic cancer cells HepG2 and in primary human hepatocytes. Techniques of gene reporter assays, qRT-PCR, Simple Western blotting by Sally Sue™ and electrophoretic mobility shift assay EMSA were employed. All compounds activated AhR, but their efficacies, potencies and dose-response profiles differed substantially. The strongest activators of AhR and inducers of CYP1A1 in HepG2 cells were DMU-212 ((E)-3,4,5,4´-tetramethoxystilbene), trans-piceatannol, cis-piceatannol, trans-trismethoxyresveratrol and trans-pinostilbene. While DMU-212 and trans-trismethoxyresveratrol also induced CYP1A1 and CYP1A2 in primary human hepatocytes, the effects of trans-piceatannol, cis-piceatannol and trans-pinostilbene weaned off. On the other hand, trans-4-methoxystilbene was strong CYP1A inducer in hepatocytes but not in HepG2 cells. Differences between effects of stilbenes in HepG2 cells and human hepatocytes are probably due to the extensive phase I and phase II xenobiotic metabolism in human hepatocytes. The data obtained may be of toxicological relevance.