Integrated analysis of mRNA-m6A-protein profiles reveals novel insights into the mechanisms for cadmium-induced urothelial transformation

METTL3-mediated m6A mRNA modification was involved in cadmium-induced liver injury

Cadmium is an environmental pollutant that has extensive deleterious effects. However, the mechanisms underlying the hepatotoxicity induced by long-term exposure to cadmium remained undefined. In the present study, we explored the role of m6A methylation in the development of cadmium-induced liver disease. We showed a dynamic change of RNA methylation in liver tissue from mice administrated with cadmium chloride (CdCl2) for 3, 6 and 9 months, respectively. Particularly, the METTL3 expression was declined in a time-dependent manner, associated with the degree of liver injury, indicating the involvement of METTL3 in hepatotoxicity induced by CdCl2. Moreover, we established a mouse model with liver-specific over-expression of Mettl3 and administrated these mice with CdCl2 for 6 months. Notably, METTL3 highly expressed in hepatocytes attenuated CdCl2-induced steatosis and liver fibrosis in mice. In vitro assay also showed METTL3 overexpression ameliorated the CdCl2-induced cytotoxicity and activation of primary hepatic stellate cells. Furthermore, transcriptome analysis identified 268 differentially expressed genes both in mice liver tissue treated with CdCl2 for 3 months and 9 months. Among them, 115 genes were predicted to be regulated by METTL3 determined by m6A2Target database. Further analysis revealed the perturbation of metabolic pathway, glycerophospholipid metabolism, ErbB signaling pathway, Hippo signaling pathway, and choline metabolism in cancer, and circadian rhythm, led to hepatotoxicity induced by CdCl2. Collectively, our findings reveal new insight into the crucial role of epigenetic modifications in hepatic diseases caused by long-term exposure to cadmium.

The emerging role of N6-methyladenine RNA methylation in metal ion metabolism and metal-induced carcinogenesis

N⁶-methyladenine (m⁶A) is the most common and abundant internal modification in eukaryotic mRNAs, which can regulate gene expression and perform important biological tasks. Metal ions participate in nucleotide biosynthesis and repair, signal transduction, energy generation, immune defense, and other important metabolic processes. However, long-term environmental and occupational exposure to metals through food, air, soil, water, and industry can result in toxicity, serious health problems, and cancer. Recent evidence indicates dynamic and reversible m⁶A modification modulates various metal ion metabolism, such as iron absorption, calcium uptake and transport. In turn, environmental heavy metal can alter m⁶A modification by directly affecting catalytic activity and expression level of methyltransferases and demethylases, or through reactive oxygen species, eventually disrupting normal biological function and leading to diseases. Therefore, m⁶A RNA methylation may play a bridging role in heavy metal pollution-induced carcinogenesis. This review discusses interaction among heavy metal, m⁶A, and metal ions metabolism, and their regulatory mechanism, focuses on the role of m⁶A methylation and heavy metal pollution in cancer. Finally, the role of nutritional therapy that targeting m⁶A methylation to prevent metal ion metabolism disorder-induced cancer is summarized.

Interaction between N6-methyladenosine (m6A) modification and environmental chemical-induced diseases in various organ systems

A wide variety of chemicals are ubiquitous in the environment and thus exposure to these environmental chemicals poses a serious threat to public health. Particularly, environmental factors such as air pollution, heavy metals, and endocrine-disrupting chemicals (EDCs) can lead to diseases in various organ systems. Recent research in environmental epigenetics has demonstrated that N6-methyladenosine (m6A) modification is a key mechanism of environment-related diseases. m6A modification is the most abundant chemical modification in mRNAs, which can specifically regulate gene expression by affecting RNA translation, stability, processing, and nuclear export. In this review, we discussed how environmental chemicals affected m6A modification and mediated environment-related disease occurrence by classifying the diseases of various systems. Here, we conclude that environmental chemicals alter the levels of m6A and its modulators, which then participate in the occurrence of diseases in various systems by regulating gene expression and downstream signaling pathways such as METTL3/m6A ZBTB4/YTHDF2/EZH2, Foxo3a/FTO/m6A ephrin-B2/YTHDF2, and HIF1A/METTL3/m6A BIRC5/IGF2BP3/VEGFA. Considering the significant role of m6A and its modulators in response to environmental chemicals, they are expected to be used as biomarkers of environment-related diseases. Additionally, targeting m6A modulators using small molecule inhibitors and activators is expected to be a new method for the treatment of environment-related diseases. This review systematically and comprehensively clarifies the important role of m6A in diseases caused by environmental chemicals, thus establishing a scientific basis for the treatment of diseases in various organ systems.

Fibronectin 1 as a Key Gene in the Genesis and Progression of Cadmium-Related Bladder Cancer

Exposure to cadmium (Cd), a non-essential heavy metal, leads to the malignant transformation of urothelial cells and promotes bladder cancer (BC) development, but the mechanisms are unclear. Therefore, we aimed to explore the possible molecules associated with Cd-related BC. By analyzing and mining biological big data in public databases, we screened genes associated with the malignant transformation of uroepithelial cells caused by Cd and further screened the key gene associated with BC prognosis from these genes. The possible roles of the key gene in BC progression were then further explored through biological big data analysis and cellular experiments. Data mining yielded a total of 387 malignant transformation-related genes, which were enriched in multiple cancer-related signaling pathways, such as cytokine-cytokine receptor interaction, Toll-like receptor signaling pathway, and Jak-STAT signaling pathway. Further screening identified Fibronectin 1 (FN1) as the key gene. High expression of FN1 was associated with the advanced pathologic stage, T stage, N stage, and M stage and predicted an unfavorable outcome in BC patients. FN1 expression was positively associated with the infiltration of several types of immune cells, particularly tumor-associated macrophages and cancer-associated fibroblasts. Overexpression of FN1 could be detected in Cd-treated urothelial cells and BC cell lines. Interestingly, silencing of FN1 impaired the proliferation and invasive capacity of BC cells. In conclusion, the present study provides new insight into the mechanism of Cd-related BC. FN1 might be a prognostic marker and therapeutic target for BC. Future studies are needed to confirm these results.

Epigenetic Regulation in Chromium-, Nickel- and Cadmium-Induced Carcinogenesis

Environmental and occupational exposure to heavy metals, such as hexavalent chromium, nickel, and cadmium, are major health concerns worldwide. Some heavy metals are well-documented human carcinogens. Multiple mechanisms, including DNA damage, dysregulated gene expression, and aberrant cancer-related signaling, have been shown to contribute to metal-induced carcinogenesis. However, the molecular mechanisms accounting for heavy metal-induced carcinogenesis and angiogenesis are still not fully understood. In recent years, an increasing number of studies have indicated that in addition to genotoxicity and genetic mutations, epigenetic mechanisms play critical roles in metal-induced cancers. Epigenetics refers to the reversible modification of genomes without changing DNA sequences; epigenetic modifications generally involve DNA methylation, histone modification, chromatin remodeling, and non-coding RNAs. Epigenetic regulation is essential for maintaining normal gene expression patterns; the disruption of epigenetic modifications may lead to altered cellular function and even malignant transformation. Therefore, aberrant epigenetic modifications are widely involved in metal-induced cancer formation, development, and angiogenesis. Notably, the role of epigenetic mechanisms in heavy metal-induced carcinogenesis and angiogenesis remains largely unknown, and further studies are urgently required. In this review, we highlight the current advances in understanding the roles of epigenetic mechanisms in heavy metal-induced carcinogenesis, cancer progression, and angiogenesis.

N6-methyladenosine-mediated downregulation of miR-374c-5p promotes cadmium-induced cell proliferation and metastasis by targeting GRM3 in breast cancer cells

Cadmium (Cd) is a toxic heavy metal that can facilitate the development and progression of breast cancer (BC). Emerging evidence has indicated that the progression of Cd-exposed BC is related to the dysregulation of microRNAs (miRNAs). The purpose of our study was to investigate the expression pattern and underlying mechanisms of miR-374c-5p in Cd-mediated BC progression. In this study, T-47D cells and MCF-7 cells were treated with different concentrations of Cd (0.1, 1 and 10 μM) for 72 h. MiR-374c-5p expression was downregulated, and transfection of miR-374c-5p mimics significantly decreased BC cell proliferation, migration and invasion induced by 10 μM Cd. Importantly, we used the Cytoscape software plugin cytoHubba to analyse the intersected genes between our RNA-Seq results and the mirDIP database, and six hub genes (CNR1, CXCR4, GRM3, RTN1, SLC1A6 and ZEB1) were identified as potential direct targets of miR-374c-5p in our model; however, luciferase reporter assays indicated that miR-374c-5p only repressed GRM3 by directly binding to its 3'-untranslated region (UTR). Of note, we verified that suppression of N6-methyladenosine (m6A) modification led to miR-374c-5p downregulation by decreasing its RNA transcript stability. Together, these findings demonstrated that m6A modification of pri-miRNA-374c blocks miRNA-374c-5p maturation and then activates GRM3 expression, which drives BC cell metastasis after Cd exposure.

Genes involved in mRNA surveillance are induced in Brachypodium distachyon under cadmium toxicity

BACKGROUND

Cd accumulation in plant cells results in dramatic problems including oxidative stress and inhibition of vital enzymes. It also affects mineral uptakes by disrupting membrane permeability. Interaction among Cd and other plant nutrient elements changes the nutritional contents of crops and reduces their yield.

METHODS AND RESULTS

In the present study, Cd stress in Brachypodium distachyon led to the upregulation of some heavy metal transport genes (influx or efflux) encoding cation-efflux proteins, heavy metal-associated proteins and NRAMP proteins. The Arabidopsis orthologs of the differentially expressed B. distachyon genes (DEGs) under Cd toxicity were identified, which exhibited Bradi4g26905 was an ortholog of AtALY1-2. Detailed co-expression network and gene ontology analyses found the potential involvement of the mRNA surveillance pathway in Cd tolerance in B. distachyon. These genes were shown to be downregulated by sulfur (S) deficiency.

CONCLUSIONS

This is the first transcriptomic study investigating the effect of Cd toxicity in B. distachyon, a model plant for genomic studies in Poaceae (Gramineae) species. The results are expected to provide valuable information for more comprehensive research related to heavy metal toxicity in plants.

Coordination of m6A mRNA methylation and gene transcriptome in rice response to cadmium stress

N⁶-methyladenosine (m⁶A) is the most prevalent internal modification present in the mRNAs of all higher eukaryotes. However, the role of the m⁶A methylomes in rice is still poorly understood. With the development of the MeRIP-seq technique, the in-depth identification of mRNAs with m⁶A modification has become feasible. A study suggested that m⁶A modification is crucial for posttranscriptional regulation related to Cd²⁺-induced malignant transformation, but the association between m⁶A modification in plants and Cd tolerance has not been reported. We investigated the m⁶A methylomes in the roots of a cadmium (Cd)-treated group and compared them with the roots in the control (CK) group by m⁶A sequencing of cv. 9311 and cv. Nipponbare (NIP) plants. The results indicated that Cd leads to an altered modification profile in 3,406 differential m⁶A peaks in cv. 9311 and 2,065 differential m⁶A peaks in cv. NIP. KEGG pathway analysis of the genes with differentially modified m⁶A peaks indicated that the "phenylalanine", "tyrosine and tryptophan biosynthesis", "glycine", "adherens junctions", "glycerophospholipid metabolism" and "threonine metabolism" signalling pathways may be associated with the abnormal root development of cv. 9311 rice due to exposure to Cd. The "arginine", "proline metabolism", "glycerolipid", and "protein processing in endoplasmic reticulum" metabolism pathways were significantly enriched in genes with differentially modified m⁶A peaks in cv. NIP. Unlike that in Arabidopsis, the m⁶A-modified nucleotide position on mRNAs (m⁶A peak) distribution in rice exhibited a preference towards both the stop codon and 3' untranslated regions (3' UTRs). These findings provide a resource for plant RNA epitranscriptomic studies and further increase our knowledge on the function of m⁶A modification in RNA in plants.