Reduced caloric intake decreases arterial blood pressure in healthy individuals and improves endothelium-dependent vasodilation in obese and overweight individuals. The SIRT1 protein deacetylase mediates many of the effects of calorie restriction (CR) on organismal lifespan and metabolic pathways. However, the role of SIRT1 in regulating endothelium-dependent vasomotor tone is not known. Here we show that SIRT1 promotes endotheliumdependent vasodilation by targeting endothelial nitric oxide synthase (eNOS) for deacetylation. SIRT1 and eNOS colocalize and coprecipitate in endothelial cells, and SIRT1 deacetylates eNOS, stimulating eNOS activity and increasing endothelial nitric oxide (NO). SIRT1-induced increase in endothelial NO is mediated through lysines 496 and 506 in the calmodulin-binding domain of eNOS. Inhibition of SIRT1 in the endothelium of arteries inhibits endothelium-dependent vasodilation and decreases bioavailable NO. Finally, CR of mice leads to deacetylation of eNOS. Our results demonstrate that SIRT1 plays a fundamental role in regulating endothelial NO and endothelium-dependent vascular tone by deacetylating eNOS. Furthermore, our results provide a possible molecular mechanism connecting the effects of CR on the endothelium and vascular tone to SIRT1-mediated deacetylation of eNOS.calorie restriction ͉ vasorelaxation ͉ silent information regulator 2 ͉ resveratrol ͉ deacetylation C aloric restriction (CR) is a well recognized nonpharmacological approach to reducing arterial blood pressure. CR not only is capable of independently controlling blood pressure of patients with mild hypertension, but also allows a reduction in the number and dosage of medications used to treat hypertension (1, 2). CR and weight loss resulting from CR also improve endothelium-dependent vascular relaxation in obese and overweight individuals with hypertension (3, 4).In addition, CR prolongs organismal lifespan. In the budding yeast, Saccharomyces cerevisiae, aging of replicating cells is determined by the SIR2 gene (5). Retardation of yeast aging by CR depends on the product of this gene, Sir2 (silent information regulator 2), a class III NAD-dependent histone deacetylase. The mammalian ortholog of Sir2, SIRTUIN 1 (SIRT1), targets histones and many nonhistone proteins (6-10). Resveratrol, a plant polyphenol that stimulates SIRT1 activity (11), activates endothelial nitric oxide synthase (eNOS) (12), improves endothelial function, prevents elevation in blood pressure, and restores vascular eNOS activity in animal models of endothelial dysfunction (13). Hypothesizing that the effects of CR and resveratrol on vascular function are mediated, in part, by SIRT1, we investigated the role of SIRT1 in regulating eNOS activity and endothelium-dependent vascular tone. Results and DiscussionTo determine whether SIRT1 plays an important role in regulating endothelium-dependent vascular tone, vasomotor function of rat aortic rings, in which wild-type SIRT1 or a dominant negative SIRT1 mutant (to inhibit endogenous SIRT1) was adenovi...

Apurinic/apyrimidinic endonuclease-1 (APE1) is an essential enzyme in the base excision repair (BER) pathway. Here, we show that APE1 is a target of the SIRTUIN1 (SIRT1) protein deacetylase. SIRT1 associates with APE1, and this association is increased with genotoxic stress. SIRT1 deacetylates APE1 in vitro and in vivo targeting lysines 6 and 7. Genotoxic insults stimulate lysine acetylation of APE1 which is antagonized by transcriptional upregulation of SIRT1. Knockdown of SIRT1 increases cellular abasic DNA content, sensitizing cells to death induced by genotoxic stress, and this vulnerability is rescued by overexpression of APE1. Activation of SIRT1 with resveratrol promotes binding of APE1 to the BER protein X-ray cross-complementing-1 (XRCC1), while inhibition of SIRT1 with nicotinamide (NAM) decreases this interaction. Genotoxic insult also increases binding of APE1 to XRCC1, and this increase is suppressed by NAM or knockdown of SIRT1. Finally, resveratrol increases APE activity in XRCC1-associated protein complexes, while NAM or knockdown of SIRT1 suppresses this DNA repair activity. These findings identify APE1 as a novel protein target of SIRT1, and suggest that SIRT1 plays a vital role in maintaining genomic integrity through regulation of the BER pathway.

The rac1 GTPase and the p66shc adaptor protein regulate intracellular levels of reactive oxygen species (ROS). We examined the relationship between rac1 and p66shc. Expression of constitutively active rac1 (rac1V12) increased phosphorylation, reduced ubiquitination, and increased stability of p66shc protein. Rac1V12-induced phosphorylation and up-regulation of p66shc was suppressed by inhibiting p38MAPK and was dependent on serine 54 and threonine 386 in p66shc. Phosphorylation of recombinant p66shc by p38MAPK in vitro was also partly dependent on serine 54 and threonine 386. Reconstitution of p66shc in p66shc-null fibroblasts increased intracellular ROS generated by rac1V12, which was significantly dependent on the integrity of residues 54 and 386. Overexpression of p66shc increased rac1V12-inducd apoptosis, an effect that was also partly dependent on serine 54 and threonine 386. Finally, RNA interferencemediated down-regulation of endogenous p66shc suppressed rac1V12-induced cell death. These findings identify p66shc as a mediator of rac1-induced oxidative stress. In addition, they suggest that serine 54 and threonine 386 are novel phosphorylatable residues in p66shc that govern rac1-induced increase in its expression, through a decrease in its ubiquitination and degradation, and thereby mediate rac1-stimulated cellular oxidative stress and death.

The Son of Sevenless 1 protein (sos1) is a guanine nucleotide exchange factor (GEF) for either the ras or rac1 GTPase. We show that p66shc, an adaptor protein that promotes oxidative stress, increases the rac1-specific GEF activity of sos1, resulting in rac1 activation. P66shc decreases sos1 bound to the growth factor receptor bound protein (grb2) and increases the formation of the sos1–eps8–e3b1 tricomplex. The NH2-terminal proline-rich collagen homology 2 (CH2) domain of p66shc associates with full-length grb2 in vitro via the COOH-terminal src homology 3 (C-SH3) domain of grb2. A proline-rich motif (PPLP) in the CH2 domain mediates this association. The CH2 domain competes with the proline-rich COOH-terminal region of sos1 for the C-SH3 domain of grb2. P66shc-induced dissociation of sos1 from grb2, formation of the sos1–eps8–e3b1 complex, rac1-specific GEF activity of sos1, rac1 activation, and oxidative stress are also mediated by the PPLP motif in the CH2 domain. This relationship between p66shc, grb2, and sos1 provides a novel mechanism for the activation of rac1.

Rationale: Low-dose acetylsalicylic acid (aspirin) is widely used in the treatment and prevention of vascular atherothrombosis. Cardiovascular doses of aspirin also reduce systemic blood pressure and improve endotheliumdependent vasorelaxation in patients with atherosclerosis or risk factors for atherosclerosis. Aspirin can acetylate proteins, other than its pharmacological target cyclooxygenase, at lysine residues. The role of lysine acetylation in mediating the effects of low-dose aspirin on the endothelium is not known. Objective:To determine the role of lysine acetylation of endothelial nitric oxide synthase (eNOS) in the regulation of endothelial NO production by low-dose aspirin and to examine whether the lysine deacetylase histone deacetylase (HDAC)3 antagonizes the effect of low-dose aspirin on endothelial NO production by reversing acetylation of functionally critical eNOS lysine residues. Methods and Results: Low concentrations of aspirin induce lysine acetylation of eNOS, stimulating eNOSenzymatic activity and endothelial NO production in a cyclooxygenase-1-independent fashion. Low-dose aspirin in vivo also increases bioavailable vascular NO in an eNOS-dependent and cyclooxygenase-1-independent manner. Low-dose aspirin promotes the binding of eNOS to calmodulin. Lysine 609 in the calmodulin autoinhibitory domain of bovine eNOS mediates aspirin-stimulated binding of eNOS to calmodulin and eNOS-derived NO production. HDAC3 inhibits aspirin-stimulated (1) lysine acetylation of eNOS, (2) eNOS enzymatic activity, (3) eNOS-derived NO, and (4) binding of eNOS to calmodulin. Conversely, downregulation of HDAC3 promotes lysine acetylation of eNOS and endothelial NO generation. Key Words: aspirin Ⅲ endothelial NOS Ⅲ HDAC3 Ⅲ lysine acetylation Ⅲ calmodulin L ow-dose aspirin (81 to 325 mg/d) is a very useful tool in the armamentarium for the treatment of acute coronary syndromes, as well as for the secondary prevention of myocardial infarctions and stroke in high-risk patients. 1 The antithrombotic effects of low-dose aspirin are principally attributed to acetylation of a serine residue in platelet cyclooxygenase (COX)-1, irreversibly inhibiting COX-1 in platelets, and limiting platelet aggregation because of prostanoids produced by COX-1. 2 In addition to preventing thrombosis, low-dose aspirin also improves vasomotor function mediated by the endothelium in humans 3,4 and in animal models of endothelial dysfunction. 5 Although low-dose aspirin is not commonly used in the treatment of hypertension, it is efficacious, when given at bedtime, for reduction of blood pressure in individuals with mild hypertension 6,7 or prehypertension. 8 Suppression of vasoconstricting prostanoids produced by COX-1 could be one mechanism by which low-dose aspirin improves endothelial function and reduces mildly and bor- Low-dose aspirin increases NO produced by blood vessels, 9 but the mechanism responsible for this effect is not fully understood. Cardiovascular doses of aspirin increase nitric oxide synthase (NOS) enzymatic activit...

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Stat3 is an important transcription factor that regulates both proinflammatory and anti-apoptotic pathways in the heart. This study examined the mechanisms of activation of Stat3 in human endothelial cells following hypoxia/reoxygenation (H/R). By expression of constitutively active Rac1 mutant protein, and by RNA silencing of Rac1, we found that Stat3 Y705 and S727 phosphorylation following H/R are dependent on Rac1. Reactive oxygen species produced during H/R, and direct physical association with Rac1 both contribute to Stat3 activation. Stat3 forms a multiprotein complex with Rac1 and PKC in an H/R-dependent manner, which at least in part, appears to regulate Stat3 S727 phosphorylation. Selective inhibition of PKC with calphostin C produces a marked suppression of Stat3 S727 phosphorylation. The association of Stat3 with Rac1 occurs predominantly at the cell membrane, but also inside the nucleus, and occurs through the binding of the coiled-coil domain of Stat3 to the 54 NH2-terminal residues of Rac1. Transfection with a peptide comprising the NH2-terminal 17 amino acid residues of Rac1 inhibits Stat3 S727 phosphorylation after H/R. Thus, Stat3 is activated in endothelial cells by H/R through Rac1-dependent signaling pathways resulting in physical association between Rac1 and Stat3 and the formation of a novel multiprotein complex with PKC.

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