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Increasing environmental genotoxic chemicals have been shown to induce epigenetic alterations. However, the interaction between genetics and epigenetics in chemical carcinogenesis is still not fully understood. Here, we constructed an in vitro human lung carcinogenesis model (16HBE-T) by treating human bronchial epithelial cells with a typical significant carcinogen benzo(a)pyrene (BaP). We identified a novel circular RNA, circ0087385, which was overexpressed in 16HBE-T and human lung cancer cell lines, as well as in lung cancer tissues and serum exosomes from lung cancer patients. The upregulated circ0087385 after exposure to BaP promoted DNA damage in the early stage of chemical carcinogenesis and affected the cell cycle, proliferation, and apoptosis of the malignantly transformed cells. Overexpression of circ0087385 enhanced the expression of cytochrome P450 1A1 (CYP1A1), which is crucial for metabolically activating BaP. Interfering with circ0087385 or CYP1A1 reduced the levels of ultimate carcinogen benzo(a)pyrene diol epoxide (BPDE) and BPDE-DNA adducts. Interfering with CYP1A1 partially reversed the DNA damage induced by high expression of circ0087385, as well as decreased the level of BPDE and BPDE-DNA adducts. These findings provide novel insights into the interaction between epigenetics and genetics in chemical carcinogenesis which are crucial for understanding the epigenetic and genetic toxicity of chemicals. [ABSTRACT FROM AUTHOR]

Benzo [a]pyrene (B [a]P) is a widespread environmental chemical pollutant that has been linked to the development of various diseases. However, the specific mechanism of action remains unclear. In this study, human bronchial epithelial 16HBE and BEAS-2B cells were exposed to B [a]P at 0–32 μM to assess the DNA-damaging effects. B [a]P exposure resulted in elevated expression of γ-H2AX, a marker of DNA damage. The m6A RNA methylation assay showed that B [a]P exposure increased the extent of m6A modification and the demethylase ALKBH5 played an integral role in this process. Moreover, the results of the comet assay and Western blot analysis showed an increase in m6A modification mediated by ALKBH5 that promoted DNA damage. Furthermore, the participation of a novel circular RNA, circ_0003552, was assessed by high-throughput sequencing under the condition of high m6A modification induced by B [a]P exposure. In subsequent functional studies, an interference/overexpression system was created to confirm that circ_0003552 participated in regulation of DNA damage. Mechanistically, circ_0003552 had an m6A binding site that could regulate its generation. This study is the first to report that B [a]P upregulated circ_0003552 through m6A modification, thereby promoting DNA damage. These findings revealed that epigenetics played a key role in environmental carcinogen-induced DNA damage, and the quantitative changes it brought might provide an early biomarker for future medical studies of genetic-related diseases and a new platform for investigations of the interaction between epigenetics and genetics. [Display omitted] • B [a]P induces DNA damage in bronchial epithelial cells. • B [a]P upregulates the degree of m6A modification by suppressing ALKBH5 expression. • Both ALKBH5 and circ_0003552 can regulate the B [a]P-induced DNA damage. • M6A modification promotes circ_0003552 production through the m6A binding site. [ABSTRACT FROM AUTHOR]

• B[ a ]P induces DNA damage response (DDR) in bronchial epithelial cells. • B[ a ]P upregulates circ_0057504 through suppressing DNMT3A-mediated DNA methylation. • Circ_0057504 promotes B[ a ]P-induced DDR via modulating NONO-SFPQ complex formation. Benzo[ a ]pyrene (B[ a ]P) is a class I carcinogen and hazardous environmental pollutant with genetic toxicity. Understanding the molecular mechanisms underlying genetic deterioration and epigenetic alterations induced by environmental contaminants may contribute to the early detection and prevention of cancer. However, the role and regulatory mechanisms of circular RNAs (circRNAs) in the B[ a ]P-induced DNA damage response (DDR) have not been elucidated. In this study, human bronchial epithelial cell lines (16HBE and BEAS-2B) were exposed to various concentrations of B[ a ]P, and BALB/c mice were treated with B[ a ]P intranasally. B[ a ]P exposure was found to induce DNA damage and upregulate circular RNA hsa_circ_0057504 (circ_0057504) expression in vitro and in vivo. In addition, B[ a ]P upregulated TMEM194B mRNA and circ_0057504 expression through inhibition of DNA methyltransferase 3 alpha (DNMT3A) expression in vitro. Modulation (overexpression or knockdown) of circ_0057504 expression levels using a lentiviral system in human bronchial epithelial cells revealed that circ_0057504 promoted B[ a ]P-induced DNA damage. RNA pull-down and western blot assays showed that circ_0057504 interacted with non-POU domain-containing octamer-binding (NONO) and splicing factor proline and glutamine rich (SFPQ) proteins and regulated formation of the NONO-SFPQ protein complex. Thus, our findings indicate that circ_0057504 acts as a novel regulator of DNA damage in human bronchial epithelial cells exposed to B[ a ]P. The current study reveals novel insights into the role of circRNAs in the regulation of genetic damage, and describes the effect and regulatory mechanisms of circ_0057504 on B[ a ]P genotoxicity. [ABSTRACT FROM AUTHOR]