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Background: Benzene and its metabolite hydroquinone (HQ) are widely used in daily life, and long‐term exposure to benzene or HQ can induce acute myeloid leukemia (AML). Circular RNAs (circRNAs) are mostly produced by reverse splicing of gene exon mRNA precursors. The modulation of circRNA expression is connected to leukemia progression; however, the molecular mechanism is still unknown. Materials and methods: In this study, the cells were divided into four groups: PBS control group (PBS‐TK6), TK6 malignantly transformed cells induced by 10.0 μmol/L HQ (HQ‐TK6), and HQ‐TK6 cells treated with 5 μmol/L 5‐AzaC (DNA methyltransferase inhibitor) for 24 h (HQ + 5‐AzaC). HQ‐TK6 cells were treated with 200 nmol/L TSA (histone deacetylation inhibitor) for 24 h (HQ + TSA). qRT–PCR was used to identify the differential hsa_circ_401351 expression between the four groups. We further determined the hsa_circ_401351 promoter methylation level with methylation‐specific PCR. DNMT1 and DNMT3b were knocked down by CRISPR/Cas9 to elucidate the specific molecular mechanism of hsa_circ_401351 in HQ‐TK6 cells. CCK‐8 and flow cytometry detected cell proliferation and apoptosis, respectively, after hsa_circ_401351 was overexpressed in HQ‐TK6 cells. Results: Compared with the PBS‐TK6 group, the expression of hsa_circ_401351 was found to be lower in the HQ‐TK6 group. Nevertheless, treatment with 5‐AzaC or TSA increased hsa_circ_401351 expression, with the upregulation being more pronounced in the TSA group. The expression of hsa_circ_401351 in the DNMT1 knockdown group was dramatically increased by 50% compared to that in the control group, and the DNA methylation level of the hsa_circ_401351 promoter region was decreased. When hsa_circ_401351 was overexpressed, HQ‐TK6 cell proliferation was significantly slowed after 48 h compared with the control group. Flow cytometry showed that cells were mainly arrested in G1 phase, and apoptosis was significantly enhanced. Similarly, qRT–PCR and Western blot data showed significant reductions in Caspase‐3 mRNA and protein production, and Bcl‐2 mRNA levels were also elevated. Conclusions: Overall, our research showed that elevated DNMT1 expression in HQ‐TK6 cells increased methylation levels and decreased expression of the hsa_circ_401351 promoter region, limiting its ability to suppress HQ‐TK6 cell growth and enhance apoptosis. [ABSTRACT FROM AUTHOR]

Hydroquinone (HQ), one of the main active metabolites of benzene, can induce the abnormal expression of long non-coding RNA (lncRNA). Studies have shown that lncRNA plays an important role in the occurrence of hematologic tumors induced by benzene or HQ. However, the molecular mechanism remains to be elucidated. Here, we investigated the molecular mechanism by which poly(ADP-ribose)polymerase 1 (PARP-1) interacts with DNA methyltransferase 1 (DNMT1) to regulate promoter methylation mediated linc01132 expression in HQ-induced TK6 malignant transformed cells (HQ-MT). The results revealed that the expression of linc01132 was increased in benzene-exposed workers and HQ-MT cells. The methylation of linc01132 promoter region was inhibited. Furthermore, in HQ-MT cells treated with 5-Aza-2′-deoxycytidine (5-AzaC) (DNA methyltransferase inhibitor) or trichostatin A (TSA) (histone deacetylation inhibitor), the expression of linc01132 was increased due to the regulation of DNA promoter methylation level by inhibiting DNMT1 expression. The methylation level of linc01132 promoter was correlated negatively with the expression of linc01132 in benzene-exposed workers, indicating that DNA methylation may contribute the expression of linc01132. Knockout of DNMT1, not DNMT3b, increased the expression of linc01132 as well as the demethylation of linc01132 promoter in HQ-MT cells. It was found that by knockdown PARP-1, the expression of DNMT1 in the nucleus was increased by immunofluorescence confocal microscopy, leading to the inhibition of hypermethylation in the promoter region of linc01132. Therefore, PARP-1 inhibits DNA methyltransferase (DNMT)-mediated promoter methylation and plays a role in linc01132 expression in benzene-exposed workers or HQ-MT cells, and is associated with benzene or HQ induced leukemia progression. [ABSTRACT FROM AUTHOR]

Hydroquinone (HQ) is one of the major metabolites of benzene and can cause abnormal gene expression. It is a known carcinogen that alters cell cycle disruption and cell proliferation. However, its chemical mechanism remain a mystery. Circular RNAs (circRNAs) are a subtype of noncoding RNAs (ncRNAs) that play a variety of roles in biological processes. Hsa_circ_001944 expression was upregulated in 30 leukemia patients and HQ‐induced malignant transformed TK6 cells. Hsa_circ_001944 silencing inhibited the growth of HQ‐TK6 cells and halted the cell cycle. The silencing of hsa_circ_0001944 led to increased cell accumulation in G1 versus S phase, increased apoptosis in the sh1944 versus the shNC group, and increased levels of DNA damage (γ‐H2AX), leading to cell cycle arrest. In summary, inhibition of hsa_circ_001944 restricted cell growth by inhibiting cell cycle arrest and induced growth of HQ‐TK6 cells by modulating PARP1 expression. Hsa_circ_0001944 targeted HuR, which is a kind of RNA‐binding protein, to control PARP1 expression via RNAinter, RBPmap, and RBPdb. Fluorescence in situ hybridization combined with immunofluorescent labeling and western blotting experiments showed that hsa_circ_001944 was able to dissociate HuR and PARP1 binding in HQ‐TK6 cells, control PARP1 production, and ultimately alter the PARP1/H‐Ras pathway. [ABSTRACT FROM AUTHOR]

Mitogen-activated protein kinase kinase 4 (MKK4) is a critical mediator of stress-activated protein kinase signals that regulate apoptosis, inflammations and tumorigenesis. Several polymorphisms have been identified in the MKK4 gene. We hypothesized that genetic variants in the MKK4 promoter may alter its expression and thus cancer risk. In a case-control study of 1056 lung cancer cases and 1056 sex and age frequency-matched cancer-free controls, we genotyped two common polymorphisms in the MKK4 promoter region (-1304T>G and -1044A>T) with the Taqman assay, and we found that compared with the most common -1304TT genotype, carriers of -1304G variant genotypes had a decreased risk of lung cancer [odds ratio (OR) = 0.74; 95% confidence interval (CI) = 0.61-0.90 for TG, and OR = 0.62; 95% CI = 0.41-0.94 for GG] in an allele dose-response manner (adjusted P(trend) = 0.0005). Further stratification analysis showed that the protective role of the -1304G variant allele was more evident in low or normal body mass index (BMI) but restrained in the overweighters and that the -1304G variant genotypes interacted with BMI in reducing cancer risk (adjusted P(interaction) = 0.003). Moreover, the luciferase assay showed that the G allele in the promoter significantly increased the transcription activity of the MKK4 gene in vitro and that the MKK4 protein expression levels of the G variant carriers was significantly higher in tumor tissues than those of the -1304TT genotype. However, no significant association was observed between the -1044A>T polymorphism and risk of lung cancer. Our data suggest that the functional -1304G variant in the MKK4 promoter contributes to a decreased risk of lung cancer by increasing the promoter activity and that the G variant may be a marker for susceptibility to lung cancer.