Date Published: December 22, 2009
Publisher: Public Library of Science
Author(s): Nargis Nasrin, Virendar K. Kaushik, Eric Fortier, Daniel Wall, Kevin J. Pearson, Rafael de Cabo, Laura Bordone, Laura N. Rusche. http://doi.org/10.1371/journal.pone.0008414
Abstract: SIRT1 is a NAD-dependent deacetylase that regulates a variety of pathways including the stress protection pathway. SIRT1 deacetylates a number of protein substrates, including histones, FOXOs, PGC-1α, and p53, leading to cellular protection. We identified a functional interaction between cJUN N-terminal kinase (JNK1) and SIRT1 by coimmunoprecipitation of endogenous proteins. The interaction between JNK1 and SIRT1 was identified under conditions of oxidative stress and required activation of JNK1 via phosphorylation. Modulation of SIRT1 activity or protein levels using nicotinamide or RNAi did not modify JNK1 activity as measured by its ability to phosphorylate cJUN. In contrast, human SIRT1 was phosphorylated by JNK1 on three sites: Ser27, Ser47, and Thr530 and this phosphorylation of SIRT1 increased its nuclear localization and enzymatic activity. Surprisingly, JNK1 phosphorylation of SIRT1 showed substrate specificity resulting in deacetylation of histone H3, but not p53. These findings identify a mechanism for regulation of SIRT1 enzymatic activity in response to oxidative stress and shed new light on its role in the stress protection pathway.
Partial Text: Sirtuins are NAD+-dependent deacetylases (or ADP-ribosyltransferases) that remove acetyl groups from (or add ADP-ribose to) protein substrates, thereby regulating the biological function of their targets . By catalyzing these reactions, sirtuins increase tissue and organism survival in a diversity of species, ranging from yeast to mammals , , . The prototypical sirtuin, yeast Sir2p, is a NAD-dependent deacetylase that removes acetyl groups from histones to regulate chromatin structure . In humans, the Sir2p homolog SIRT1 deacetylates transcription factors such as p53, FOXOs, and nuclear factor Kappa B (NFkB) mediating stress resistance, apoptosis, and inflammatory responses among other pathways. Evidence from uni- and multicellular organisms indicates that SIRT1 has evolved to mediate signaling initiated by stressors, such as nutrient deprivation, to produce adaptation to enhance organism survival . Consistent with this concept, extra copies of sirtuin genes increase survival in model organisms, including yeast, flies, and worms , , .
In this paper we describe a novel mechanism whereby oxidative stress, via JNK1, regulates SIRT1 activity by altering its subcellular localization and activity. First, we demonstrated that SIRT1 and JNK1 functionally interact, but only when JNK1 is activated by anisomycin or H2O2. Second, we showed that SIRT1 localization changes after treatment with H2O2, an effect blocked by treatment of cells with a JNK1 inhibitor. Third, we confirmed JNK1 as a kinase involved in phosphorylating SIRT1 at previously identified sites (Ser27 and Ser47), and identified a novel JNK1 phosphorylation site (Thr530) on SIRT1. Fourth, we demonstrated a functional role of JNK1 phosphorylation of SIRT1, selective deacetylation of histone H3 but not another SIRT1 substrate, namely p53. Mutations of these sites into alanines abolished JNK1-mediated phosphorylation of SIRT1 and abrogated the functional changes seen with respect to histone H3. Finally, we determined that the SIRT1:JNK1 interaction did not lead to a change in JNK1 activity, as measured by levels of phosphorylated cJun.