Benzo(a)pyrene (BaP) is a polycyclic aromatic hydrocarbon that specifically causes cancer and is widely distributed in the environment. Poly (ADP-ribosylation), as a key post-translational modification in BaP-induced carcinogenesis, is mainly catalyzed by poly (ADP-ribose) glycohydrolase (PARG) in eukaryotic organisms. Previously, it is found that PARG silencing can counteract BaP-induced carcinogenesis in vitro , but the mechanism remained unclear. In this study, we further examined this process in vivo by using heterozygous PARG knockout mice (PARG +/− ). Wild-type and PARG +/− mice were individually treated with 0 or 10 μg/m 3 BaP for 90 or 180 days by dynamic inhalation exposure. Pathological analysis of lung tissues showed that, with extended exposure time, carcinogenesis and injury in the lungs of WT mice was progressively worse; however, the injury was minimal and carcinogenesis was not detected in the lungs of PARG +/− mice. These results indicate that PARG gene silencing protects mice against lung cancer induced by BaP inhalation exposure. Furthermore, as the exposure time was extended, the protein phosphorylation level was down-regulated in WT mice, but up-regulated in PARG +/− mice. The relative expression of Wnt2b and Wnt5b mRNA in WT mice were significantly higher than those in the control group, but there was no significant difference in PARG +/− mice. Meanwhile, the relative expression of Wnt2b and Wnt5b proteins, as assessed by immunohistochemistry and Western blot analysis, was significantly up-regulated by BaP in WT mice; while in PARG +/− mice it was not statistically affected. Our work provides initial evidence that PARG silencing suppresses BaP induced lung cancer and stabilizes the expression of Wnt ligands, PARG gene and Wnt ligands may provide new options for the diagnosis and treatment of lung cancer.

Poly(ADP‐ribose) glycohydrolase (PARG) as a main enzyme hydrolyzing poly(ADP‐ribose) in eukaryotes, and its silencing can inhibit benzo(a)pyrene (BaP)‐induced carcinogenesis. A thorough understanding of the mechanism of PARG silenced inhibition of BaP‐induced carcinogenesis provides a new therapeutic target for the prevention and treatment of environmental hazard induced lung cancer. We found that the expression of several subtypes of the histone H2B was downregulated in BaP‐induced carcinogenesis via PARG silencing as determined by label‐free proteomics and confirmed by previous cell line‐ and mouse model‐based studies. Analysis using the GEPIA2 online tool indicated that the transcription levels of H2BFS, HIST1H2BD, and HIST1H2BK in lung adenocarcinoma (LUAD) tissues and squamous cell lung carcinoma (LUSC) tissues were higher than those in normal lung tissues, while the transcription levels of HIST1H2BH in LUSC tissues were higher than those in normal lung tissues. The expression levels of HIST1H2BB, HIST1H2BH, and HIST1H2BL were significantly different in different lung cancer (LC) stages. Moreover, the expression of H2BFS, HIST1H2BD, HIST1H2BJ, HIST1H2BK, HIST1H2BL, HIST1H2BO, HIST2H2BE, and HIST2H2BF was positively correlated with that of PARG in LC tissues. Analysis of the Kaplan‐Meier plotter database indicated that high H2B levels predicted low survival in all LC patients suggesting that H2B could be a new biomarker for determining the prognosis of the LC, and that its expression can be inhibited by PARG silencing in BaP‐induced carcinogenesis.

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