Differential epigenetic and transcriptional profile in MCF-7 breast cancer cells exposed to cadmium
Introduction
Cadmium (Cd) was a confirmed carcinogen involving in breast carcinogenesis (Benbrahim-Tallaa et al., 2009; Ponce et al., 2015; He et al., 2017; Wei and Shaikh, 2017). However, the underlying mechanism was not clarified yet. Cd was able to cause DNA mutation only at a high concentration which induced apoptosis in more than half of exposed cells (Waalkes, 2003). At an ordinary exposure level, Cd hardly bound to DNA or induced reactive oxygen species to cause any mutagenesis and DNA damage (Takiguchi et al., 2003; Huang et al., 2008; Suzuki et al., 2017), suggesting that Cd was weakly genotoxic and mutagenic. Therefore, epigenetic modification has been supposed as the main way of Cd-induced breast tumorigenesis (Chen et al., 2019).
Accumulating evidences indicated that Cd caused multiple epigenetic changes, especially aberrant DNA methylation and non-coding RNA deregulation. It has been reported that Cd exposure was associated with gene-specific DNA methylation (such as MGMT, DNMT3B, and MT2A) as well as global DNA methylation in blood (Virani et al., 2016). Cd-induced DNA methylation of some cancer-related genes were also observed in rat liver (Hirao-Suzuki et al., 2018) and human cancer cell lines including prostate (Pelch et al., 2015) and lung (Zhou et al., 2012). Non-coding RNAs, including microRNAs (miRNAs) and long non-coding RNAs (lncRNAs), have also received attention as novel mechanisms for Cd toxicity. It has been found that Cd modified the expressions of the non-coding RNAs related to oxidative stress, inflammatory processes, cell proliferation, and DNA repair, in leukocytes and bronchial epithelial cells (Bollati et al., 2010; Zhou et al., 2015; Huang et al., 2017). A few studies also examined the Cd-induced miRNA profiles in liver cancer and bronchial epithelial cells (Fabbri et al., 2012; Liu et al., 2015). However, there was no study using breast cancer cells to explore the epigenetic modifications caused by Cd, particularly on a genome-wide scale.
In the current study, we firstly obtained the Cd-induced profiles of epigenome (including DNA methylation, miRNA, and lncRNA) and transcriptome, through comparing Cd-treated and untreated MCF-7 cells. We then integrated the predicted target genes of epigenetic marks with transcriptional data to cross-verify the target genes likely to be epigenetically regulated by Cd. Thereafter, these target genes were further validated by associating with tumor progression in a breast cancer cohort. We further identified the critical pathways and genes through a series of bioinformatic analyses. The study strategy was detailed in Fig. 1. The results would provide more evidences for epigenetic mechanism of breast carcinogenesis induced by Cd.
Section snippets
Cell culture and treatment
We selected human breast cancer cell line (MCF-7) to examine the Cd-induced epigenetic modifications, considering that: 1) MCF-7 cell was hormone positive, representing the main subtype of breast cancer (∼75%) (Setiawan et al., 2009); 2) hormone positive breast cancer was associated with Cd more pronouncedly (Grioni et al., 2019); 3) MCF-7 cells possessed the molecular features of both breast cancer cells and normal breast epithelial cells (Do et al., 2010). MCF-7 breast cancer cell line was
Profiles of epigenome and transcriptome caused by Cd
By comparing the Cd-treated and untreated breast cancer cells, we obtained the profiles of epigenome and transcriptome caused by Cd. As summarized in Table 1 aberrant methylated probes (3720 hypermethylated and 2023 hypomethylated probes were identified, representing 3260 hypermethylated and 1859 hypomethylated genes. We also obtained 2 decreased miRNAs and predicted 112 miRNA-related target genes. As for lncRNA, we identified 213 differentially expressed lncRNAs (149 increased and 64
Discussion
In the present study, we found that the Cd-induced epigenetic modifications altered the expressions of 997 target genes in breast cancer cells and 400 of them were validated to be associated with breast cancer progression. Functional analyses revealed that these validated genes were related to several pathways, such as Wnt signaling pathway, metabolic pathways, and regulation of cell death, which were well-known contributors to carcinogenesis. We further identified that TXNRD1 and CCT3 were the
Conclusions
Our study suggested that Cd was associated with breast carcinogenesis by epigenetically regulating several cancer-related pathways, such as the Wnt signaling pathways and metabolic pathways. Furthermore, TXNRD1 and CCT3 were identified as the critical genes, which might act as therapeutic target and biomarker in breast cancer. Our results also suggested that Cd-induced epigenome and HPV infection might jointly participate in breast carcinogenesis, providing new clues to explore the etiology of
Credit author statement
Zhuo-Zhi Liang, Conceptualization, Formal analysis, Data curation, Writing - original draft. Rui-Mei Zhu, Conceptualization, Methodology, Investigation, Writing - review & editing. Yue-Lin Li, Investigation. Hong-Mei Jiang, Investigation. Ruo-Bi Li, Investigation. Lu-Ying Tang, Methodology. Qing Wang: Supervision, Project administration and Writing - review & editing. Ze-Fang Ren, Supervision, Project administration, Writing - review & editing and Funding acquisition.
Declaration of competing interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgement
This work was supported by the National Natural Science Foundation of China (81773515 and 81973115) and Science and Technology Planning Project of Guangdong Province, China (2019B030316002).
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2022, Toxicology LettersCitation Excerpt :They also identified several Cd-induced carcinogenesis-related pathways, such as Wnt signaling, the metabolic pathway, regulation of cell death and critical genes such as TXNRD1 and CCT3. Interestingly, they found that the Cd-induced epigenome regulates target genes associated with HPV infection, suggesting that Cd and HPV infection may co-participate in breast carcinogenesis, anticipating new clues about breast tumor formation (Liang et al., 2020). Few studies point to the interference of Cd with DNA methylation along with histone modifications in BrC.
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2022, Toxicology ReportsCitation Excerpt :Indirect damage to mitochondria linked to cadmium exposure, resulting in epigenetic alterations has also been suggested [66]. Another study suggested the association of cadmium with the development of breast cancer through epigenetic regulation of Wnt and metabolic signaling pathways, with TXNRD1 and CCT3 identified as critical genes [67]. A summary of the studies examining cadmium effects on miRNA was published recently by Wallace et al. in 2020 [68].
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These authors contributed equally to this work.