Evidence that Gsta4 modifies susceptibility to skin tumor development in mice and humans

Colonic expression of glutathione S-transferase alpha 4 and 4-hydroxynonenal adducts is correlated with the pathology of murine colitis-associated cancer

Chronic inflammation-induced oxidative stress is an important driving force for developing colitis-associated cancer (CAC). 4-hydroxynonenal (4-HNE) is a highly reactive aldehyde derived from lipid peroxidation of ω-6 polyunsaturated fatty acids that contributes to colorectal carcinogenesis. Glutathione S-transferase alpha 4 (Gsta4) specifically conjugates glutathione to 4-HNE and thereby detoxifies 4-HNE. The correlation of these oxidative biomarkers with the pathological changes in CAC is, however, unclear. In this study, we investigated the expression of Gsta4 and 4-HNE adducts in azoxymethane/dextran sulfate sodium (AOM/DSS)-induced murine CAC, and analyzed the correlations of 4-HNE and Gsta4 with inflammatory cytokines and the pathological scores in the colon biopsies. Real-time quantitative PCR showed that expression of IL6, TNFα, and Gsta4 sequentially increased in colon tissues for mice treated with DSS for 1, 2, and 3 cycles, respectively. Moreover, immunohistochemical staining showed remarkably increased expression of 4-HNE adducts, Gsta4, TNFα, and IL6 in the colon biopsies after 3 cycles of DSS treatment. Correlation analysis demonstrated that 4-HNE adducts in the colon biopsies were positively correlated with Gsta4 expression. Additionally, the expression of Gsta4 and 4-HNE adducts were strongly correlated with the pathological changes of colon, as well as the expression of TNFα and IL6 in colon tissues. These results provide evidence for the association of oxidative biomarkers Gsta4 and 4-HNE with the pathological changes of CAC and may help developing novel histopathological biomarkers and prevention targets for CAC.

Role of endogenous and exogenous antioxidants in risk of six cancers: evidence from the Mendelian randomization study

Background: Although oxidative stress is known to contribute to cancer, and endogenous and exogenous antioxidants are thought to prevent tumorigenesis by suppressing oxidative stress-induced DNA damage, antioxidants have also been reported to show negative effects on tumor formation, necessitating characterization of the causal associations between antioxidants and cancer risk. Methods: In this study, Mendelian randomization (MR) analysis, primarily inverse-variance weighted MR, was used to assess the causal effect of six endogenous and five exogenous diet-derived antioxidants on the risk of six cancers. MR-Egger intercept test and Cochran's Q statistic were utilized to assess pleiotropy and heterogeneity, respectively. Results: For endogenous antioxidants, a bidirectional two-sample MR analysis was conducted. Our findings suggested that serum albumin has a negative causal association with the risk of prostate cancer [odds ratio (OR) = 0.78, 95% confidence interval (CI): 0.68-0.91, p = 0.001]. The risks of the six cancers showed no significant associations with endogenous antioxidants in the converse MR analysis. For exogenous antioxidants, the unidirectional two-sample MR analysis exhibited a nominal relationship between the serum retinol level and non-small-cell lung cancer risk (OR = 0.29, 95% CI: 0.11-0.76, p = 0.011). Conclusions: Thus, our study revealed the protective effects of genetic susceptibility to high circulating albumin levels on prostate cancer, providing potential targeted interventions for prostate cancer prevention.

Glutathione S-Transferase Alpha 4 Promotes Proliferation and Chemoresistance in Colorectal Cancer Cells

Glutathione S-transferase alpha 4 (GSTA4) is a phase II detoxifying enzyme that is overexpressed in colorectal cancer (CRC) and regulated by the oncogenic transcription factor AP-1. However, the role of GSTA4 in these CRC cells remains unclear. In this study, we investigated the roles of GSTA4 in the CRC cells by inactivating GSTA4 in HCT116 human CRC cells (Defined as HCT116^ΔGSTA4) using the CRISPR/Cas9 gene editing. Cell proliferation, clonogenicity, and susceptibility to chemotherapeutic drugs were analyzed in vitro and in a xenograft model. The results showed that loss of GSTA4 significantly decreased cell proliferation and clonogenicity, whereas it increased intracellular reactive oxygen species and cell susceptibility to 5-fluorouracil (5-FU) and oxaliplatin. Additionally, exposure of HCT116^ΔGSTA4 cells to 5-FU increased the expression of γH2AX, a hallmark of double-stranded DNA breaks. In contrast, no remarkably increased γH2AX was noted in oxaliplatin-treated HCT116^ΔGSTA4 cells compared with HCT116 cells. Moreover, loss of GSTA4 blocked the AKT and p38 MAPK pathways, leading to proliferative suppression. Finally, the xenograft model showed decreased tumor size for HCT116^ΔGSTA4 cells compared with HCT116 cells, confirming in vitro findings. These findings suggest that GSTA4 is capable of promoting proliferation, tumorigenesis, and chemoresistance and is a potential target for CRC therapy.

Curzerene suppresses progression of human glioblastoma through inhibition of glutathione S-transferase A4

Aims

Glioblastoma is the central nervous system tumor with the highest mortality rate, and the clinical effectiveness of chemotherapy is low. Curzerene can inhibit the progression of non‐small‐cell lung cancer, but its role in glioma has not been reported. The purpose of this study was to clarify the effect of curzerene on glioma progression and further explore its potential mechanism.

Methods

The expression of glutathione S‐transferase A4 (GSTA4) in glioblastoma and the effect of curzerene on the expression of GSTA4 and matrix metalloproteinase 9 and the activation of the mTOR pathway were detected by Western blotting and RT‐PCR, and the effects of curzerene treatment on glioma malignant character were detected by cell biological assays. The in vivo antitumor effects of curzerene were analyzed in a nude mouse xenograft model.

Results

Curzerene was found to inhibit the expression of GSTA4 mRNA and protein in U251 and U87 glioma cells, and this effect correlated with a downregulation of the proliferation of these cells in a time‐ and dose‐dependent manner. Invasion and migration were also inhibited, and curzerene treatment correlated with induction of apoptosis. Curzerene inhibited the activation of the mTOR pathway and the expression of matrix metalloproteinase 9, and it correlated with increased 4‐hydroxynonenal levels. In vivo, curzerene was found to significantly inhibit tumor growth in nude mice and to prolong the survival time of tumor‐bearing nude mice.

Conclusion

In conclusion, inhibition of GSTA4 correlates with positive outcomes in glioma models, and thus, this molecule is a candidate drug for the treatment of glioma.

Identification of differentially expressed methylated genes in melanoma versus nevi using bioinformatics methods

Background

Melanoma is a highly invasive malignant skin tumor. While melanoma may share some similarities with that of melanocytic nevi, there also exist a number of distinct differences between these conditions. An analysis of these differences may provide a means to more effectively evaluate the etiology and pathogenesis of melanoma. In particular, differences in aberrant methylation expression may prove to represent a critical distinction.

Methods

Data from gene expression datasets (GSE3189 and GSE46517) and gene methylation datasets (GSE86355 and GSE120878) were downloaded from the GEO database. GEO2R was used to obtain differentially expressed genes (DEGs) and differentially methylation genes (DMGs). Function and pathway enrichment of selected genes were performed using the DAVID database. A protein-protein interaction (PPI) network was constructed by STRING while its visualization was achieved with use of cytoscape. Primary melanoma samples from TCGA were used to identify significant survival genes.

Results

There was a total of 199 genes in the hypermethylation-low expression group, while 136 genes in the hypomethylation-high expression group were identified. The former were enriched in the biological processes of transcription regulation, RNA metabolism and regulation of cell proliferation. The later were highly involved in cell cycle regulation. 13 genes were screened out after survival analysis and included: ISG20, DTL, TRPV2, PLOD3, KIF3C, DLGAP4, PI4K2A, WIPI1, SHANK2, SLC16A10, GSTA4O, LFML2A and TMEM47.

Conclusion

These findings reveal some of the methylated differentially expressed genes and pathways that exist between melonoma and melanocytic nevi. Moreover, we have identified some critical genes that may help to improve the diagnosis and treatment of melanoma.

The Complex Interplay between Antioxidants and ROS in Cancer

Reactive oxygen species (ROS) play important roles in tissue homeostasis, cellular signaling, differentiation, and survival. In this review, we discuss the types ofROS, their impact on cellular processes, and their pro- and antitumorigenic effects. Further, we discuss recent advances in our understanding of both endogenous and exogenous antioxidants in tumorigenic processes. Finally, wediscuss how aberrant activation of antioxidant programs by the transcription factor NFE2-related factor 2 (NRF2) influences tumorigenesis and metastasis, and where the current gaps in our knowledge remain.

Reduced Expression of Glutathione S-Transferase 4 Promotes Vascular Neointimal Hyperplasia in CKD

Neointima formation is the leading cause of arteriovenous fistula (AVF) failure. We have shown that CKD accelerates this process by transforming the vascular smooth muscle cells (SMCs) lining the AVF from a contractile to the synthetic phenotype. However, the underlying mechanisms affecting this transformation are not clear. Previous studies have shown that the α-class glutathione transferase isozymes have an important role in regulating 4-hydroxynonenal (4-HNE)-mediated proliferative signaling of cells. Here, using both the loss- and gain-of-function approaches, we investigated the role of glutathione S-transferase α4 (GSTA4) in modulating cellular 4-HNE levels for the transformation and proliferation of SMCs. Compared with non-CKD controls, mice with CKD had downregulated expression of GSTA4 at the mRNA and protein levels, with concomitant increase in 4-HNE in arteries and veins. This effect was associated with upregulated phosphorylation of MAPK signaling pathway proteins in proliferating SMCs. Overexpressing GSTA4 blocked 4-HNE-induced SMC proliferation. Additionally, inhibitors of MAPK signaling inhibited the 4-HNE-induced responses. Compared with wild-type mice, mice lacking GSTA4 exhibited increased CKD-induced neointima formation in AVF. Transient expression of an activated form of GSTA4, achieved using a combined Tet-On/Cre induction system in mice, lowered levels of 4-HNE and reduced the proliferation of SMCs. Together, these results demonstrate the critical role of GSTA4 in blocking CKD-induced neointima formation and AVF failure.

Regulatory roles of glutathione-S-transferases and 4-hydroxynonenal in stress-mediated signaling and toxicity

Glutathione-S-Transferases (GSTs) have primarily been thought to be xenobiotic metabolizing enzymes that protect cells from toxic drugs and environmental electrophiles. However, in last three decades, these enzymes have emerged as the regulators of oxidative stress-induced signaling and toxicity. 4-Hydroxy-trans 2-nonenal (HNE) an end-product of lipid peroxidation, has been shown to be a major determinant of oxidative stress-induced signaling and toxicity. HNE is involved in signaling pathways, including apoptosis, proliferation, modulation of gene expression, activation of transcription factors/repressors, cell cycle arrest, and differentiation. In this article, available evidence for a major role of GSTs in the regulation of HNE-mediated cell signaling processes through modulation of the intracellular levels of HNE is discussed.

Glutathione S-transferase alpha 4 induction by activator protein 1 in colorectal cancer

Glutathione S-transferase alpha 4 (GSTA4) is a phase II detoxifying enzyme that metabolizes electrophiles and carcinogens including 4-hydroxy-2-nonenal (4-HNE), an endogenous carcinogen that contributes to colorectal carcinogenesis. In this study, we investigated GSTA4 expression and regulation in murine primary colonic epithelial cells, microbiome-driven murine colitis and human carcinomas. Exposure of YAMC cells to 4-HNE induced Gsta4 expression. Using an inflammation-associated model of colorectal cancer (CRC), Gsta4 expression increased in vivo in colon macrophages and serum after 2 weeks of colonization of IL-10 deficient (Il10^-/-) mice with Enterococcus faecalis. Increased expression was noted after 9 months of colonization in colon macrophages and epithelia in areas of inflammation. In human colon biopsies, immunohistochemistry showed no GSTA4 expression in normal epithelial cells, whereas GSTA4 was strongly expressed in the neoplastic epithelia of invasive carcinomas. For tubular adenomas, increased expression was primarily noted in stromal macrophages. Increased GSTA4 was confirmed in established human CRC cell lines and associated with 4-HNE-protein adducts in human colon adenomas and CRC. Next, we showed that 4-HNE induced activation of c-Jun and Nrf2, two components of the oncogenic transcription factor AP-1. AP-1 inhibitors and gene-specific small interfering RNAs partially suppressed GSTA4 expression. Co-immunoprecipitation confirmed interactions between c-Jun and Nrf2 supporting a role for AP-1 in regulating 4-HNE-induced GSTA4 expression. These findings demonstrate GSTA4 activation during 4-HNE-induced neoplastic transformation in colorectal carcinogenesis. GSTA4 is a potential surrogate biomarker for CRC screening and should provide novel approaches for chemoprevention.

Fine mapping reveals that promotion susceptibility locus 1 (Psl1) is a compound locus with multiple genes that modify susceptibility to skin tumor development

Although it is well known that the majority of human cancers occur as the result of exposure to environmental carcinogens, it is clear that not all individuals exposed to a specific environmental carcinogen have the same risk of developing cancer. Considerable evidence indicates that common allelic variants of low-penetrance, tumor susceptibility genes are responsible for this interindividual variation in risk. We previously reported a skin tumor promotion susceptibility locus, Psl1, which maps to the distal portion of chromosome 9, that modified skin tumor promotion susceptibility in the mouse. Furthermore, Psl1 was shown to consist of at least two subloci (i.e., Psl1.1 and Psl1.2) and that glutathione S-transferase alpha 4 (Gsta4), which maps to Psl1.2, is a skin tumor promotion susceptibility gene. Finally, variants of human GSTA4 were found to be associated with risk of nonmelanoma skin cancer. In the current study, a combination of nested and contiguous C57BL/6 congenic mouse strains, each inheriting a different portion of the Psl1 locus from DBA/2, were tested for susceptibility to skin tumor promotion with 12-O-tetradecanoylphorbol-13-acetate. These analyses indicate that Psl1 is a compound locus with at least six genes, including Gsta4, that modify skin tumor promotion susceptibility. More than 550 protein-coding genes map within the Psl1 locus. Fine mapping of the Psl1 locus, along with two-strain haplotype analysis, gene expression analysis, and the identification of genes with amino acid variants, has produced a list of fewer than 25 candidate skin tumor promotion susceptibility genes.

4-Hydroxynonenal induces G2/M phase cell cycle arrest by activation of the ataxia telangiectasia mutated and Rad3-related protein (ATR)/checkpoint kinase 1 (Chk1) signaling pathway

4-Hydroxynonenal (HNE) has been widely implicated in the mechanisms of oxidant-induced toxicity, but the detrimental effects of HNE associated with DNA damage or cell cycle arrest have not been thoroughly studied. Here we demonstrate for the first time that HNE caused G2/M cell cycle arrest of hepatocellular carcinoma HepG2 (p53 wild type) and Hep3B (p53 null) cells that was accompanied with decreased expression of CDK1 and cyclin B1 and activation of p21 in a p53-independent manner. HNE treatment suppressed the Cdc25C level, which led to inactivation of CDK1. HNE-induced phosphorylation of Cdc25C at Ser-216 resulted in its translocation from nucleus to cytoplasm, thereby facilitating its degradation via the ubiquitin-mediated proteasomal pathway. This phosphorylation of Cdc25C was regulated by activation of the ataxia telangiectasia and Rad3-related protein (ATR)/checkpoint kinase 1 (Chk1) pathway. The role of HNE in the DNA double strand break was strongly suggested by a remarkable increase in comet tail formation and H2A.X phosphorylation in HNE-treated cells in vitro. This was supported by increased in vivo phosphorylation of H2A.X in mGsta4 null mice that have impaired HNE metabolism and increased HNE levels in tissues. HNE-mediated ATR/Chk1 signaling was inhibited by ATR kinase inhibitor (caffeine). Additionally, most of the signaling effects of HNE on cell cycle arrest were attenuated in hGSTA4 transfected cells, thereby indicating the involvement of HNE in these events. A novel role of GSTA4-4 in the maintenance of genomic integrity is also suggested.

Naturally occurring variation in the Glutathione-S-Transferase 4 gene determines neurodegeneration after traumatic brain injury

AIM

Genetic factors are important for outcome after traumatic brain injury (TBI), although exact knowledge of relevant genes/pathways is still lacking. We here used an unbiased approach to define differentially activated pathways between the inbred DA and PVG rat strains. The results prompted us to study further if a naturally occurring genetic variation in glutathione-S-transferase alpha 4 (Gsta4) affects the outcome after TBI.

RESULTS

Survival of neurons after experimental TBI is increased in PVG compared to the DA strain. Global expression profiling analysis shows the glutathione metabolism pathway to be the most regulated between the strains, with increased Gsta4 in PVG among top regulated transcripts. A congenic strain (R5) with a PVG genomic insert containing the Gsta4 gene on DA background displays a reversal of the strain pattern for Gsta4 expression and increased survival of neurons compared to DA. Gsta4 is known to effectively reduce 4-hydroxynonenal (4-HNE), a noxious by-product of lipid peroxidation. Immunostaining of 4-HNE was evident in both rat and human TBI. Intracerebral injection of 4-HNE resulted in neurodegeneration with increased levels of a marker for nerve injury in cerebrospinal fluid of DA compared to R5.

INNOVATION

These findings provide strong support for the notion that the inherent capability of coping with increased 4-HNE after TBI affects outcome in terms of nerve cell loss.

CONCLUSION

A naturally occurring variation in Gsta4 expression in rats affects neurodegeneration after TBI. Further studies are needed to explore if genetic variability in Gsta4 can be associated to outcome also in human TBI.

Sulforaphane induces phase II detoxication enzymes in mouse skin and prevents mutagenesis induced by a mustard gas analog

Mustard gas, used in chemical warfare since 1917, is a mutagenic and carcinogenic agent that produces severe dermal lesions for which there are no effective therapeutics; it is currently seen as a potential terrorist threat to civilian populations. Sulforaphane, found in cruciferous vegetables, is known to induce enzymes that detoxify compounds such as the sulfur mustards that react through electrophilic intermediates. Here, we observe that a single topical treatment with sulforaphane induces mouse epidermal levels of the regulatory subunit of glutamate-cysteine ligase, the rate-limiting enzyme in glutathione biosynthesis, and also increases epidermal levels of reduced glutathione. Furthermore, a glutathione S-transferase, GSTA4, is also induced in mouse skin by sulforaphane. In an in vivo model in which mice are given a single mutagenic application of the sulfur mustard analog 2-(chloroethyl) ethyl sulfide (CEES), we now show that therapeutic treatment with sulforaphane abolishes the CEES-induced increase in mutation frequency in the skin, measured four days after exposure. Sulforaphane, a natural product currently in clinical trials, shows promise as an effective therapeutic against mustard gas.

Proteomic and pathway analyses reveal a network of inflammatory genes associated with differences in skin tumor promotion susceptibility in DBA/2 and C57BL/6 mice

Genetic susceptibility to two-stage skin carcinogenesis is known to vary significantly among different stocks and strains of mice. In an effort to identify specific protein changes or altered signaling pathways associated with skin tumor promotion susceptibility, a proteomic approach was used to examine and identify proteins that were differentially expressed in epidermis between promotion-sensitive DBA/2 and promotion-resistant C57BL/6 mice following treatment with 12-O-tetradecanoylphorbol-13-acetate (TPA). We identified 19 differentially expressed proteins of which 5 were the calcium-binding proteins annexin A1, parvalbumin α, S100A8, S100A9, and S100A11. Further analyses revealed that S100A8 and S100A9 protein levels were also similarly differentially upregulated in epidermis of DBA/2 versus C57BL/6 mice following topical treatment with two other skin tumor promoters, okadaic acid and chrysarobin. Pathway analysis of all 19 identified proteins from the present study suggested that these proteins were components of several networks that included inflammation-associated proteins known to be involved in skin tumor promotion (e.g. TNF-α, NFκB). Follow-up studies revealed that Tnf, Nfkb1, Il22, Il1b, Cxcl1, Cxcl2 and Cxcl5 mRNAs were highly expressed in epidermis of DBA/2 compared with C57BL/6 mice at 24h following treatment with TPA. Furthermore, NFκB (p65) was also highly activated at the same time point (as measured by phosphorylation at ser276) in epidermis of DBA/2 mice compared with C57BL/6 mice. Taken together, the present data suggest that differential expression of genes involved in inflammatory pathways in epidermis may play a key role in genetic differences in susceptibility to skin tumor promotion in DBA/2 and C57BL/6 mice.

Modes of retrotransposition of long interspersed element-1 by environmental factors

Approximately 42% of the human genome is composed of endogenous retroelements, and the major retroelement component, long interspersed element-1 (L1), comprises ∼17% of the total genome. A single human cell has more than 5 × 10(5) copies of L1, 80∼100 copies of which are competent for retrotransposition (RTP). Notably, L1 can induce RTP of other retroelements, such as Alu and SVA, and is believed to function as a driving force of evolution. Although L1-RTP during early embryogenesis has been highlighted in the literature, recent observations revealed that L1-RTP also occurs in somatic cells. However, little is known about how environmental factors induce L1-RTP. Here, we summarize our current understanding of the mechanism of L1-RTP in somatic cells. We have focused on the mode of L1-RTP that is dependent on the basic helix-loop-helix/per-arnt-sim (bHLH/PAS) family of transcription factors. Along with the proposed function of bHLH/PAS proteins in environmental adaptation, we discuss the functional linking of L1-RTP and bHLH/PAS proteins for environmental adaptation and evolution.

Involvement of retrotransposition of long interspersed nucleotide element-1 in skin tumorigenesis induced by 7,12-dimethylbenz[a]anthracene and 12-O-tetradecanoylphorbol-13-acetate

Tumor development induced by 7,12-dimethylbenz[a]anthracene (DMBA) plus 12-O-tetradecanoylphorbol-13-acetate (TPA) is a well-characterized model of multistep carcinogenesis. DMBA mutates the Ha-ras gene, whereas TPA promotes the growth of transformed cells by activating cellular signaling molecules. It remains to be clarified how repeated TPA treatment endows transformed cells with autonomous cell growth. Long interspersed nucleotide element-1 (L1) is an endogenous retroelement, and 80-100 copies of L1 function as autonomous mobile elements. Although the L1 retrotransposition (RTP) has been found in various human tumors, implying the possible mobility of L1 during carcinogenesis, little is known about how L1-RTP arises in tumor cells, owing to a lack of experimental models. To dissect the mechanism of L1-RTP during carcinogenesis, we established a line of transgenic mice carrying human L1 and enhanced green fluorescent protein (hL1-EGFP mice) and subjected them to DMBA/TPA-induced skin tumorigenesis. Of 15 skin tumors examined, 13 were positive for L1-RTP; L1-RTP was not detected in normal skin tissues adjacent to the tumors. Moreover, nine L1-RTP-positive tumors were positive for activated Ha-ras, and immunohistochemical analysis revealed cells positive for both L1-RTP and phosphorylated Stat3, a marker of tumor cells. Additional in vivo experiments suggested that L1-RTP occurred during tumor promotion by TPA. This is the first report on the involvement of L1-RTP in chemical carcinogenesis. We propose hL1-EGFP mice as a versatile system for investigating the mode of L1-RTP in tumor development and discuss the possible role of L1-RTP in tumorigenesis.