Sirtuin, an oxidant sensitive deacetylase, is post‐translationally modified and degraded by the proteasome in response to cigarette smoke in lung epithelial cells

Abstract

Sirtuin1 (Sirt1) is a class III histone/protein deacetylase that has anti‐aging and anti‐inflammatory properties. We have previously shown that cigarette smoke (CS) decreased Sirt1 protein level in rat lung and human monocyte/macrophages leading to increased NF‐κB dependent pro‐inflammatory cytokine release. As CS contains greater than 1015–17 free radicals, we hypothesized that the cell's redox status influences Sirt1 protein level in response to CS, leading to post‐translational modifications and degradation. Human bronchial epithelial cells (BEAS.2B) were exposed for 24 hrs to different concentrations of cigarette smoke extract (CSE 0.5–1%) in the presence or absence of buthionine sulfoximine (BSO) or N‐acetyl‐L‐cysteine (NAC), an inhibitor and precursor for glutathione biosynthesis respectively. CSE decreased nuclear Sirt1 levels; co‐treatment with BSO further decreased Sirt1, whereas treatment with NAC rescued CSE depletion. Furthermore, CSE caused 4‐hydroxy‐2‐nonenol adduct formation on Sirt1, which was increased by BSO treatment and decreased by NAC. Decreased Sirt1 level was also found to be due to proteasomal degradation as proteasomal inhibitors (ALLN and MG132) attenuated CSE‐mediated degradation of Sirt1. These data suggest that oxidants in CSE modify Sirt1 post‐translationally, marking the protein for proteasomal degradation in lung epithelial cells, which may contribute to the pro‐inflammatory effect of cigarette smoke.Supported by the NIEHS Center Grant ES01247 and Toxicology Training Program Grant ES07026.