4-(Methylnitrosamino)-1-(3-pyridyl)-1-butanone-Induced Histone Acetylation via α7nAChR-Mediated PI3K/Akt Activation and Its Impact on γ-H2AX Generation

A typical tobacco-specific nitrosamine 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) is known as a strong carcinogen. We previously reported that metabolized NNK induced histone H2AX phosphorylation (gamma-H2AX), a DNA damage-induced histone modification. In this study, we found that NNK globally acetylated histone H3, which affected gamma-H2AX generation. Human lung adenocarcinoma A549 was treated with several doses of NNK. NNK induced dose-dependent global histone H3 acetylation (Ac-H3), at 2 to 12 h after the treatment, independent of the cell cycle. The Ac-H3 pattern was not affected by CYP2A13 overexpression unlike gamma-H2AX, indicating no requirement of NNK metabolism to induce Ac-H3. Immunofluorescence staining of Ac-H3 was uniform throughout the nucleus, whereas gamma-H2AX was formed as foci and did not coincide with Ac-H3. Nicotinic receptor antagonist methyllycaconitine inhibited Ac-H3 and also gamma-H2AX. Phosphoinositide-3-kinase (PI3K)/Akt inhibitors, LY294002, wortmannin, and GSK690693, also suppressed both Ac-H3 and gamma-H2AX, whereas KU55933, an inhibitor of ataxia telangiectasia mutated (ATM) upstream of gamma-H2AX, inhibited gamma-H2AX but not Ac-H3. These results suggested that binding of NNK to the nicotinic acetylcholine receptor (alpha 7nAChR) activated the PI3K/Akt pathway, resulting in Ac-H3. The activated pathway leading to Ac-H3 enhanced gamma-H2AX, suggesting that NNK-induced DNA damage is impacted by the alpha 7nAChR-mediated signal transduction pathway.

Automated summary

The study found that NNK globally acetylated histone H3, impacting gamma-H2AX generation. Activation of the nicotinic acetylcholine receptor alpha 7nAChR by NNK activated the PI3K/Akt pathway, leading to Ac-H3. The enhanced Ac-H3 contributed to increased gamma-H2AX, implying that NNK-induced DNA damage is influenced by the alpha 7nAChR-mediated signal transduction pathway.