Poly (ADP-ribose) glycohydrolase silencing-mediated maintenance of H2A and downregulation of H2AK9me protect human bronchial epithelial cells from benzo(a)pyrene-induced carcinogenesis.

ABSTRACT

Poly (ADP-ribosylation) is a key post-translational modification (PTM), and poly (ADP-ribose) glycohydrolase (PARG) is the main enzyme that hydrolyzes poly (ADP-ribose) in eukaryotic organisms. Our previous findings suggested that knockdown of PARG attenuates benzo(a)pyrene (BaP) carcinogenesis. However, the mechanisms underlying PARG-mediated protective effects remain limited. In this study, the expression levels of histones were analyzed by Western blotting and immunofluorescence. Histone H2A levels were abnormally decreased by BaP-induced carcinogenesis, but were maintained by knockdown of PARG in the 16HBE human bronchial epithelial cell line. The interaction between poly (ADP-ribose) and H2A was confirmed by co-immunoprecipitation. PARG-related modifications in H2A were profiled by immune antibody enrichment coupled with mass spectrometry. H2AK5ac, H2AK9ac, H2AK13ac, H2A.ZK4K7K11ac, and H2AK9me were expressed in BaP-transformed 16HBE (BTC-16HBE) cells, but were not detectable in normal 16HBE or BaP-transformed 16HBE cells with knockdown of PARG (BTC-shPARG). Further verification by Western blotting indicated that H2AK9me was elevated in BTC-16HBE cells but decreased in BTC-shPARG cells. These findings suggest that knockdown of PARG protects against BaP-induced carcinogenesis in 16HBE cells by downregulating H2AK9me. Our in vivo studies confirmed that PARG silencing decreased H2AK9me levels, thereby countering the carcinogenic teratogenic effects induced by BaP.