Epigenetic regulation of peroxiredoxins: Implications in the pathogenesis of cancer

Silencing of peroxiredoxin III inhibits formaldehyde-induced oxidative damage of bone marrow cells in BALB/c mice

BACKGROUND

Formaldehyde (FA) is associated with the occurrence of leukemia, and oxidative stress is considered to be a major reason. As an endogenous biomarker of oxidative stress, few studies focus on the relationship between peroxiredoxin III (PrxIII) and FA toxicity. Our previous research observed high expression of PrxIII occurred in the process of apoptosis of bone marrow cells (BMCs) induced by FA, however the exact mechanism is unclear. Therefore, this paper aimed to explore the possible association between FA toxicity and PrxIII gene.

METHODS

We first, used a Cell Counting Kit-8 (CCK-8) to detect the viability of BMCs after they were exposed to different doses of FA (50, 100, 200 μmol/L) for different exposure time (12, 24, 48 h), then chose 24 h as an exposure time to detect the expression of PrxIII for exposing different doses of FA by Quantitative reverse transcription-PCR (qRT-PCR) and Western blot analysis. Based on our preliminary experimental results, we chose 100 μmol/L FA as an exposure dose to expose for 24 h, and used a small interfering RNA (siRNA) to silenced PrxIII to examine the cell viability by CCK-8, reactive oxygen species (ROS) level by DCFH-DA, apoptosis by Annexin V/PI double staining and cell cycle by flow cytometry (FCM) so as to explore the possible regulatory effect of PrxIII silencing on FA-induced bone marrow toxicity.

RESULTS

High expression of PrxIII occurred in the process of FA-induced oxidative stress. Silencing of PrxIII prevented FA from inducing oxidative stress, thus increasing cell viability, decreasing ROS level, rescuing G0 -G1 and G2 -M arrest, and reducing cell apoptosis.

CONCLUSION

PrxIII silencing might be a potential target for alleviating FA-induced oxidative damage.

ent-Kaurane diterpenoids induce apoptosis and ferroptosis through targeting redox resetting to overcome cisplatin resistance

Reactive oxygen species (ROS) induction is an effective mechanism to kill cancer cells for many chemotherapeutics, while resettled redox homeostasis induced by the anticancer drugs will promote cancer chemoresistance. Natural ent-kaurane diterpenoids have been found to bind glutathione (GSH) and sulfhydryl group in antioxidant enzymes covalently, which leads to the destruction of intracellular redox homeostasis. Therefore, redox resetting destruction by ent-kaurane diterpenoids may emerge as a viable strategy for cancer therapy. In this study, we isolated 30 ent-kaurane diterpenoids including 20 new samples from Chinese liverworts Jungermannia tetragona Lindenb and studied their specific targets and possible application in cancer drug resistance through redox resetting destruction. 11β-hydroxy-ent-16-kaurene-15-one (23) possessed strong inhibitory activity against several cancer cell lines. Moreover, compound 23 induced both apoptosis and ferroptosis through increasing cellular ROS levels in HepG2 cells. ROS accumulation induced by compound 23 was caused by inhibition of antioxidant systems through targeting peroxiredoxin I/II (Prdx I/II) and depletion of GSH. Furthermore, compound 23 sensitized cisplatin (CDDP)-resistant A549/CDDP cancer cells in vitro and in vivo by inducing apoptosis and ferroptosis. Thus, the ent-kaurane derivative showed potential application for sensitizing CDDP resistance by redox resetting destruction through dual inhibition of Prdx I/II and GSH in cancer chemotherapy.

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Thirty ent-kaurane diterpenoids were isolated from the Chinese liverworts, Jungermannia tetragona.

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11β-hydroxy-ent-16-kaurene-15-one (23) was identified to induce apoptosis and ferroptosis for the first time.

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Compound 23 could disorder the intracellular redox system by directly targeting Prdx I/II and GSH.

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Compound 23 could sensitize A549/CDDP cancer cells in vitro and in vivo through redox resetting destruction.

Exercise, redox homeostasis and the epigenetic landscape

Physical exercise represents one of the strongest physiological stimuli capable to induce functional and structural modifications in all biological systems. Indeed, beside the traditional genetic mechanisms, physical exercise can modulate gene expression through epigenetic modifications, namely DNA methylation, post-translational histone modification and non-coding RNA transcripts.

Initially considered as merely damaging molecules, it is now well recognized that both reactive oxygen (ROS) and nitrogen species (RNS) produced under voluntary exercise play an important role as regulatory mediators in signaling processes. While robust scientific evidences highlight the role of exercise-associated redox modifications in modulating gene expression through the genetic machinery, the understanding of their specific impact on epigenomic profile is still at an early stage. This review will provide an overview of the role of ROS and RNS in modulating the epigenetic landscape in the context of exercise-related adaptations.

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Physical exercise can modulate gene expression through epigenetic modifications.

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Epigenetic regulation of ROS/RNS generating, sensing and neutralizing enzymes can impact the cellular levels of ROS and RNS.

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ROS might act as modulators of epigenetic machinery, interfering with DNA methylation, hPTMs and ncRNAs expression.

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Redox homeostasis might hold a relevant role in the epigenetic landscape modulating exercise-related adaptations.

Peroxiredoxin V Inhibits Emodin-induced Gastric Cancer Cell Apoptosis via the ROS/Bcl2 Pathway

BACKGROUND/AIM

Peroxiredoxin (Prx) protein family is aberrantly expressed in various cancers including gastric cancer. Among the six family members, Prx V has been known as an antioxidant enzyme which scavenges intracellular reactive oxygen species (ROS) and modulates cellular apoptosis. This study aimed at investigating the role of Prx V in apoptosis of gastric cancer cells.

MATERIALS AND METHODS

Stably constructed Prx V knockdown, over-expression and mock AGS cells (a human gastric adenocarcinoma cell line) were used to study the effect of Prx V on emodin-induced apoptosis by western blotting, cell viability, apoptosis and ROS detection assays.

RESULTS

Overexpression of Prx V significantly decreased emodin-induced cellular apoptosis and ROS levels compared to Mock and Prx V knockdown AGS cells. Also, overexpression of Prx V down-regulated the expression of pro-apoptotic proteins, Bad and cleaved PARP, and increased the expression of anti-apoptotic protein, Bcl2.

CONCLUSION

Prx V suppresses AGS cell apoptosis via scavenging intracellular ROS and modulating apoptosis-related markers.

Small interfering RNA targeting of peroxiredoxinⅡ gene enhances formaldehyde-induced toxicity in bone marrow cells isolated from BALB/c mice

BACKGROUDS

Formaldehyde (FA) is an important chemicals that can induce sick house syndrome and may be an incentive of childhood leukemia, however the exact mechanism is unclear. Oxidative stress may be an underlying reason of cancer occurring, while diverse antioxidants can protect the bone marrow cells (BMCs) from damaged. PeroxiredoxinⅡ (PrxⅡ) is an important member of the peroxiredoxin family, can remove reactive oxygen species (ROS), and is closely related with the occurrence of tumor. The present study aimed to detect a possible relationship between PrxⅡ gene and FA-induced bone marrow toxicity.

METHODS

The BMCs were taken out from BALB/c mice, then exposed to control and different doses of FA (50, 100, 200 μmol/L). The cell viability, ROS level and expressions of PrxⅡ gene were examined. Afterwards, we used a small interfering RNA (siRNA) to inhibit the expression of PrxⅡ gene, and chose 100 μmol/L FA for exposure dose, to examine the cell viability, ROS level, cell cycle, apoptotic rate, expressions of PrxⅡ gene in BMCs.

RESULTS

After a 24 h exposure to different doses of FA, the cell viability, expressions of PrxⅡ gene were decreased with the increasing of FA concentration, while the ROS level was increased. Inhibiting PrxⅡ gene's expression could enhance above FA-induced events. Additionally, siRNA targeting of PrxⅡcould aggravate cell cycle arrest to inhibit cell's growth and development, as well as increase apoptotic rates induced by FA.

CONCLUSION

These results demonstrated that PrxⅡ gene was involved in FA-induced bone marrow toxicity, and siRNA targeting of PrxⅡcould enhance this toxic process.

Downregulation of peroxiredoxin II suppresses the proliferation and metastasis of gastric cancer cells

Peroxiredoxin (Prx) II is an imperative member of the superfamily of peroxidases. It serves an essential role in scavenging organic hydroperoxide and H2O2. It is involved in the development of various malignant tumors. In order to investigate the significance of Prx II expressions level in gastric cancer (GC), downregulation of Prx II was performed to investigate its role in the proliferation and migration of gastric adenocarcinoma cells. In GC cells and 45 GC specimens, the mRNA and protein expression levels of Prx II were determined using reverse transcription-quantitative polymerase chain reaction (RT-qPCR) and western blot analysis, respectively. The Prx II expression profile in another 116 GC specimens was also detected with immunohistochemistry (IHC). The changes in the proliferation and migration of MKN45 and MGC-803 cells folllowing transfection with small interfering RNA (siRNA) were detected by cell counting kit (CCK)-8, western blot analysis, and Transwell migration and invasion assays. The results revealed that the expression of Prx II in GC tissues and GC cells were significantly upregulated compared with the normal control. There was a significant association between the expression level of Prx II and various factors, including tumor size, histological differentiation, the depth of invasion, the stage of tumor-node-metastasis (TNM) and lymph node metastasis in GC (P<0.05). Survival in patients with higher Prx II expression was significantly decreased compared with those with lower Prx II expression (P<0.01). Prx II, depth of invasion, lymph node metastasis and distant metastasis were identified as independent prognosis factors of GC (P<0.05). Knockdown of Prx II significantly suppressed the proliferation and the migration of GC cells. These experiments revealed that Prx II promotes the development of GC, affecting the survival of patients with GC.

Peroxiredoxin II Regulates Cancer Stem Cells and Stemness-Associated Properties of Cancers

Cancer stem cells (CSCs) represent a sub-population of cancer cells with the ability to regulate stemness-associated properties which are specifically responsible for unlimited growth of cancers, generation of diverse cancer cells in differentiated state and resistance to existing chemotherapy and radiotherapy. Even though, current therapies destroy majority of cancer cells, it is believed to leave CSCs without eradicating which may be the conceptualization for chemoresistance and radio-resistance. Reactive oxygen species (ROS) maintain stem cells and regulate the stemness-associated properties of cancers. Beyond the maximum limit, ROS can damage cellular functions of cancers by subjecting them to oxidative stress. Thus, maintenance of ROS level plays an important role in cancers to regulate stemness-associated properties. Peroxiredoxin II (Prx II) is a member of peroxiredoxin antioxidant enzyme family which considers as a regulator of ROS in cellular environments by modulating redox status to maintain CSC phenotype and stemness properties. Prx II has cell type-dependent expression in various types of cancer cells and overexpression or silenced expression of Prx II in cancers is associated with stem cell phenotype and stemness-associated properties via activation or deactivation of various signaling pathways. In this review, we summarized available studies on Prx II expression in cancers and the mechanisms by which Prx II takes parts to regulate CSCs and stemness-associated properties. We further discussed the potential therapeutic effects of altering Prx II expression in cancers for better anticancer strategies by sensitizing cancer cells and stem cells to oxidative stress and inhibiting stemness-associated properties.

ent-Jungermannenone C Triggers Reactive Oxygen Species-Dependent Cell Differentiation in Leukemia Cells

Acute myeloid leukemia (AML) is a hematologic malignancy that is characterized by clonal proliferation of myeloid blasts. Despite the progress that has been made in the treatment of various malignant hematopoietic diseases, the effective treatment of AML remains very challenging. Differentiation therapy has emerged as a promising approach for leukemia treatment, and new and effective chemical agents to trigger the differentiation of AML cells, especially drug-resistant cells, are urgently required. Herein, the natural product jungermannenone C, a tetracyclic diterpenoid isolated from liverworts, is reported to induce cell differentiation in AML cells. Interestingly, the unnatural enantiomer of jungermannenone C (1) was found to be more potent than jungermannenone C in inducing cell differentiation. Furthermore, compound 1 targets peroxiredoxins I and II by selectively binding to the conserved cysteine residues and leads to cellular reactive oxygen species accumulation. Accordingly, ent-jungermannenone C (1) shows potential for further investigation as an effective differentiation therapy against AML.

Circadian and Metabolic Perspectives in the Role Played by NADPH in Cancer

Physiological activity in healthy conditions requires a coordinated interaction between the molecular circadian clock and the network of biochemical pathways. An important metabolic parameter in the interface between these two entities is the redox state. Among the redox coenzymes that regulate the fluxes of enzymatic reactions is the NADP⁺/NADPH pair. Indeed, the main biosynthetic pathways need NADPH to serve as an electron donor for cellular anabolic transformations. The existence of a metabolic circadian clock is well established, and it was first identified in mammalian red blood cells. The metabolic circadian clock is independent of transcriptional activity and is sustained by the enzymatic complex peroxiredoxin/thioredoxin/NADPH. This complex shows 24-h redox fluctuations metabolizing H₂O₂ in various tissues and species (fungi, insects, and mammals). Although this NADPH-sensitive metabolic clock is autonomous in erythrocytes that lack a nucleus, it functions in concert with the transcriptional circadian clock in other cell types to accomplish the task of timing cellular physiology. During carcinogenesis, circadian alterations influence cell cycle onset and promote tumoral growth. These alterations also deregulate cellular energetics through a process known as aerobic glycolysis, or the Warburg effect. The Warburg effect is a typical response of cancer cells in which the metabolism turns into glycolysis even in the presence of functional mitochondria. This alteration has been interpreted as a cellular strategy to increase biomass during cancer, and one of its main factors is the availability of NADPH. This minireview explores the potential role of NADPH as a circadian and cancer-promoting metabolite.

Peroxiredoxin 5 promotes the epithelial-mesenchymal transition in colon cancer

Globally, colorectal cancer (CRC) is common cause of cancer-related deaths. The high mortality rate of patients with colon cancer is due to cancer cell invasion and metastasis. Initiation of the epithelial-to-mesenchymal transition (EMT) is essential for the tumorigenesis. Peroxiredoinxs (PRX1-6) have been reported to be overexpressed in various tumor tissues, and involved to be responsible for tumor progression. However, the exact role of PRX5 in colon cancer remains to be investigated enhancing proliferation and promoting EMT properties. In this study, we constructed stably overexpressing PRX5 and suppressed PRX5 expression in CRC cells. Our results revealed that PRX5 overexpression significantly enhanced CRC cell proliferation, migration, and invasion. On the other hand, PRX5 suppression markedly inhibited these EMT properties. PRX5 was also demonstrated to regulate the expression of two hallmark EMT proteins, E-cadherin and Vimentin, and the EMT-inducing transcription factors, Snail and Slug. Moreover, in the xenograft mouse model, showed that PRX5 overexpression enhances tumor growth of CRC cells. Thus, our findings first provide evidence in CRC that PRX5 promotes EMT properties by inducing the expression of EMT-inducing transcription factors. Therefore, PRX5 can be used as a predictive biomarker and serves as a putative therapeutic target for the development of clinical treatments for human CRC.