Phospholipase D2 is a positive regulator of sirtuin 1 and modulates p53-mediated apoptosis via sirtuin 1

Sirtuin 1 (SIRT1) is a nicotinamide adenine dinucleotide-dependent histone deacetylase that plays diverse physiological roles. However, little is known about the regulation of SIRT1 activity. Here, we show that phospholipase D2 (PLD2), but not PLD1, selectively interacts with SIRT1 and increases the deacetylase activity of SIRT1. PLD2 does not interact with the other isozymes of SIRT (SIRT2–7). Two leucine residues in the LXXLL motif (L173 and L174) in the phox domain of PLD2 interact with the region essential for SIRT1 activity. PLD2 stimulates the SIRT1-mediated deacetylation of p53 independent of its lipase activity. In our study, mutagenesis of the LXXLL motif suppressed the interaction of PLD2 with SIRT1 and inhibited SIRT1-mediated p53 deacetylation and p53-induced transactivation of proapoptotic genes. Ultimately, overexpression of wild-type PLD2 but not that of LXXLL-mutant PLD2 protected cells against etoposide-induced apoptosis. Moreover, PLD2 did not protect against apoptosis induced by SIRT1 depletion under genotoxic stress. Collectively, our results suggest that PLD2 is a positive regulator of SIRT1 and modulates p53-mediated apoptosis via SIRT1.Subject terms: Lipid signalling, Cancer metabolism     

Paclitaxel Induces the Apoptosis of Prostate Cancer Cells via ROS-Mediated HIF-1α Expression

Prostate cancer (PCa) is the most common malignancy to endanger the health of male genitourinary system. Clinically, paclitaxel (PTX) (C47H51NO14), a diterpene alkaloid, is commonly used as an effective natural antineoplastic drug during the treatment of PCa. However, the mechanism and pathway involved in the function of PTX are poorly understood. In the current study, we employed the CCK-8 assay, revealing that PTX can inhibit the survival and induce the apoptosis of PC3M cells (a human prostate cancer cell line) in a concentration-dependent manner. Reactive oxygen species (ROS), as a metabolic intermediate produced by the mitochondrial respiratory chain, are highly accumulated under the PTX treatment, which results in a sharp decrease of the mitochondrial membrane potential in PC3M cells. Additionally, the migration and invasion of PC3M cells are weakened due to PTX treatment. Further analysis reveals that N-acetylcysteine (NAC), which functions as an antioxidant, not only rescues the decreased mitochondrial membrane potential induced by the abnormal ROS level, but also restores the migration and invasion of PC3M cells. In a subsequent exploration of the detailed mechanism, we found that hypoxia-inducible factor (HIF)-1α works as a downstream gene that can respond to the increased ROS in PC3M cells. Under PTX treatment, the expression levels of HIF-1α mRNA and protein are significantly increased, which stimulate the activation of JNK/caspase-3 signaling and promote the apoptosis of PC3M cells. In summary, we demonstrate that PTX regulates the expression of HIF-1α through increased ROS accumulation, thereby promoting the activation of JNK/caspase-3 pathway to induce the apoptosis of PCa cells. This study provides new insights into the mechanism of antineoplastic action of taxanes and unveils the clinical benefit of the ROS-HIF-1α signaling pathway, which may offer a potential therapeutic target to prevent the development of PCa.     

Synthesis of chiral (alpha,alpha-difluoroalkyl)phosphonate analogues of (lyso)phosphatidic acid via hydrolytic kinetic resolution

The hydrolytic kinetic resolution of 1,1-difluoro-3,4-epoxy-butylphosphonate using a chiral salen-Co complex was employed as a key step to obtain enantiomeric diols in 99% ee as key intermediates. The enantiomerically homogeneous (alpha,alpha-difluoroalkyl)phosphonates were obtained after selective esterification and deprotection of the corresponding phosphonates. These compounds are novel phosphatase-resistant analogues of lysophosphatidic acid and phosphatidic acid. [reaction: see text]     

Phospholipase D is involved in oxidative stress-induced migration of vascular smooth muscle cells via tyrosine phosphorylation and protein kinase C

Oxidative stress has been implicated in mediation of vascular disorders. In the presence of vanadate, H(2)O(2) induced tyrosine phosphorylation of PLD1, protein kinase C-alpha (PKC-alpha), and other unidentified proteins in rat vascular smooth muscle cells (VSMCs). Interestingly, PLD1 was found to be constitutively associated with PKC-alpha in VSMCs. Stimulation of the cells by H(2)O(2) and vanadate showed a concentration-dependent tyrosine phosphorylation of the proteins in PLD1 immunoprecipitates and activation of PLD. Pretreatment of the cells with the protein tyrosine kinase inhibitor, genistein resulted in a dose-dependent inhibition of H(2)O(2)-induced PLD activation. PKC inhibitor and down-regulation of PKC abolished H(2)O(2)-stimulated PLD activation. The cells stimulated by oxidative stress (H(2)O(2)) caused increased cell migration. This effect was prevented by the pretreatment of cells with tyrosine kinase inhibitors, PKC inhibitors, and 1-butanol, but not 3-butanol. Taken together, these results suggest that PLD might be involved in oxidative stress-induced migration of VSMCs, possibly via tyrosine phosphorylation and PKC activation.     

2D spatially periodic architectures via the drying of 1D holographically photopatterned polymer solutions

We demonstrate an efficient and versatile method for selectively generating 1D and 2D periodic polymer structures in the submicron to tens of micron range by the directed drying of 1D photopatterned polymer solutions. Ultraviolet (UV) holographic lithography (Xia et al. Chem. Rev. 1999, 99, 1823-1848) is initially used to create 1D periodic cross-link and density variations in the polymer/volatile solvent solutions. These variations act as anisotropic barriers (walls) that direct the subsequent solvent evaporation process. Somewhat akin to directional drying (Allain and Limat Phys. Rev. Lett. 1995, 74, 2981-2984) and directional solidification (Pelc, P. Dynamics of Curved Fronts; Academic Press: San Diego, CA, 1988) experiments, the drying exhibits channel-like interface propagation behavior. The combination of the instabilities and minimization of the interface area during drying can be effectively used to produce larger scale 2D pseudohexagonal polymer-strut structures, or by the addition of a monomeric component to the polymer solution, the instabilities can be suppressed, resulting in the formation of 1D linear gratings.     

Construction of two 3D homochiral frameworks with 1D chiral pores via chiral recognition

The reactions of a pair of enantiomers of macrocyclic nickel(II) complexes with racemic penicillamine generated two 3D hydrogen-bonded homochiral frameworks of {[Ni(f-(SS)-L)](2)(l-pends)(ClO(4))(2)}(n) (Λ-1) and {[Ni(f-(RR)-L)](2)(d-pends) (ClO(4))(2)}(n) (Δ-1). The frameworks possess 1D tubular pores and opposite right/left-handed helical porous surfaces (L = 5,5,7,12,12,14-hexamethyl-1,4,8,11-tetraazacyclotetradecane; pends(2-) = penicillaminedisulfide anion).     

Polysusbtituted 1-hydroxycyclopentane carboxylic acid derivatives via a group-selective radical annulation

A radical annulation procedure based on a highly stereoselective conjugated addition of a cyclic 1-hydroxyacid derivative to methyl acrylate followed by a fully group selective cyclization is reported. The 1,3-stereoinduction during the cyclization step is the only component of this process that is not fully controlled. The reaction furnished only two out of the 16 possible diastereomers. This reaction opens a new approach for the preparation of polysubstituted 1-hydroxycyclopentane carboxylic acid derivatives.     

Mechanistic evidence for an alpha-oxoketene pathway in the formation of beta-ketoamides/esters via Meldrum's acid adducts

A practical, one-pot process for the preparation of beta-keto amides via a three-component reaction, including Meldrum's acid, an amine, and a carboxylic acid, has been developed. Key to development of an efficient, high-yielding process was an in-depth understanding of the mechanism of the multistep process. Kinetic studies were carried out via online IR monitoring and subsequent principal component analysis which provided a means of profiling the concentration of both the anionic and free acid forms of the Meldrum's adduct 6 in real time. These studies, both in the presence and absence of nucleophiles, strongly suggest that formation of beta-keto amides from acyl Meldrum's acids occurs via alpha-oxoketene species 2 and rule out other possible reaction pathways proposed in the literature, such as via protonated alpha-oxoketene intermediates 3 or nucleophilic addition-elimination pathways.     

Antioxidant activity of the anti-inflammatory compound ebselen: a reversible cyclization pathway via selenenic and seleninic acid intermediates

A revised mechanism that accounts for the glutathione peroxidase (GPx)-like catalytic activity of the organoselenium compound ebselen is described. It is shown that the reaction of ebselen with H(2)O(2) yields seleninic acid as the only oxidized product. The X-ray crystal structure of the seleninic acid shows that the selenium atom is involved in a noncovalent interaction with the carbonyl oxygen atom. In the presence of excess thiol, the Se--N bond in ebselen is readily cleaved by the thiol to produce the corresponding selenenyl sulfide. The selenenyl sulfide thus produced undergoes a disproportionation in the presence of H(2)O(2) to produce the diselenide, which upon reaction with H(2)O(2), produces a mixture of selenenic and seleninic acids. The addition of thiol to the mixture containing selenenic and seleninic acids leads to the formation of the selenenyl sulfide. When the concentration of the thiol is relatively low in the reaction mixture, the selenenic acid undergoes a rapid cyclization to produce ebselen. The seleninic acid, on the other hand, reacts with the diselenide to produce ebselen as the final product. DFT calculations show that the cyclization of selenenic acids to the corresponding selenenyl amides is more favored than that of sulfenic acids to the corresponding sulfenyl amides. This indicates that the regeneration of ebselen under a variety of conditions protects the selenium moiety from irreversible inactivation, which may be responsible for the biological activities of ebselen.     

Sensitivity enhancement in 1D heteronuclear NMR spectroscopy via single-scan inverse experiments.

Measuring the nuclear magnetic resonance spectra of low-gamma heteronuclei such as 15N constitutes an important analytical tool for the characterization of molecular structure and dynamics. The reduced resonance frequencies and magnetic moments of these heteronuclei, however, make the sensitivity of this kind of spectroscopy inherently lower than that of comparable H NMR observations. A well-known solution to this sensitivity problem is indirect detection: a 2D NMR technique capable of enhancing the sensitivity of heteronuclear NMR by porting the actual data acquisition from the low-gamma nucleus to neighboring protons. This has become the standard method of observation in biomolecular NMR, where the resolution introduced by 2D spectroscopy is always a sought-after commodity. Indirect detection, however, has not gained a wide appeal in organic chemistry or in in vivo investigations, where one-dimensional heteronuclear NMR information usually suffices. The present study explores the possibility of retaining certain advantages derived from indirect detection while not giving up on the simple one-dimensional nature of heteronuclear NMR, by relying on the spatial-encoding scheme we have recently demonstrated for implementing single-scan multi-dimensional NMR spectroscopy. Preliminary results based on a 1D modification of this experiment confirm theoretical calculations suggesting that the sensitivity of 1D 15N NMR can be enhanced significantly in this manner; the relevance of this experiment given the advent of dedicated H-observing cryogenic probeheads with very high sensitivities is briefly discussed.     

Designed Synthesis of a 1D Polymer in Twist-Stacked Topology via Single-Crystal-to-Single-Crystal Polymerization

To synthesize a fully organic 1D polymer in a novel twist-stacked topology, we designed a peptide monomer HC≡CCH₂-NH-Ile-Leu-N₃, which crystallizes with its molecules H-bonded along a six-fold screw axis. These H-bonded columns pack parallelly such that molecules arrange head-to-tail, forming linear non-covalent chains in planes perpendicular to the screw axis. The chains arrange parallelly to form molecular layers which twist-stack along the screw axis. Crystals of this monomer, on heating, undergo single-crystal-to-single-crystal (SCSC) topochemical azide–alkyne cycloaddition (TAAC) polymerization to yield an exclusively 1,4-triazole-linked polymer in a twist-stacked layered topology. This topologically defined polymer shows better mechanical strength and thermal stability than its unordered form, as evidenced by nanoindentation studies and thermogravimetric analysis, respectively. This work illustrates the scope of topochemical polymerizations for synthesizing polymers in pre-decided topologies.     

Low-dose UVB irradiation stimulates matrix metalloproteinase-1 expression via a BLT2-linked pathway in HaCaT cells

Skin exposure to low-dose ultraviolet B (UVB) light up-regulates the expression of matrix metalloproteinase-1 (MMP-1), thus contributing to premature skin aging (photo-aging). Although cyclooxygenase-2 (COX- 2) and its product, prostaglandin E(2) (PGE((2))), have been associated with UVB-induced signaling to MMP expression, very little are known about the roles of lipoxygenases and their products, especially leukotriene B((4)) (LTB((4))) and 12(S)-hydroxyeicosatetraenoic acid (12(S)-HETE), in MMP-1 expression in skin keratinocytes. In the present study, we demonstrate that BLT2, a cell surface receptor for LTB((4)) and 12(S)-HETE, plays a critical role in UVB-mediated MMP-1 upregulation in human HaCaT keratinocytes. Moreover, our results demonstrated that BLT2-mediated MMP-1 upregulation occurs through a signaling pathway dependent on reactive oxygen species (ROS) production and the subsequent stimulation of ERK. Blockage of BLT2 via siRNA knockdown or with the BLT2-antagonist LY255283 completely abolished the up-regulated expression of MMP-1 induced by low-dose UVB irradiation. Finally, when HaCaT cells were transiently transfected with a BLT2 expression plasmid, MMP-1 expression was significantly enhanced, along with ERK phosphorylation, suggesting that BLT2 overexpression alone is sufficient for MMP-1 up-regulation. Together, our results suggest that the BLT2-ROS- ERK-linked cascade is a novel signaling mechanism for MMP-1 upregulation in low-dose UVB- irradiated keratinocytes and thus potentially contributes to photo-aging.     

Total synthesis of actinomycin D(C1) via a ring-opening reaction of aziridine

Actinomycin D(C₁) has been synthesized by a route involving the ester formation between two peptide fragments, (2S,3S)-1-(2-nitro-3-benzyloxy-4-methylbenzoyl)-3-methyl-2-aziridine-carbonyl-D-valylproline t-butyl ester and N-benzyloxycarbonylsarcosyl-N-methylvaline, via a ring-opening reaction of aziridine. Cyclization, followed by reduction and oxidation, gave actinomycin D(C₁). The synthetic actinomycin D(C₁) was indistinguishable from natural substance with respect to physical properties and biological activity.     

Synthesis of C-19-functionalized 1alpha-hydroxyvitamin D(2) analogues via ring-closing metathesis

A heteroatom-tethered regioselective ring-closing metathesis reaction was used for the C-19 functionalization of 1alpha-hydroxy-5,6-trans-vitamin D(2) analogues. Applications of the reaction to form a range of analogues by manipulation of the tether using both organolithium reagents and Diels-Alder cycloadditions are described.     

Thermally Conductive Poly(lactic acid) Composites with Superior Electromagnetic Shielding Performances via 3D Printing Technology

This work proposes a facile fabrication strategy for thermally conductive graphite nanosheets/poly(lactic acid) sheets with ordered GNPs(o-GNPs/PLA) via fused deposition modeling(FDM) 3 D printing technology.Further combinations of o-GNPs/PLA with Ti₃ C₂ T_x films prepared by vacuum-assisted filtration were carried out by "layer-by-layer stacking-hot pressing" to be the thermally conductive Ti₃ C₂ T_x/(oGNPs/PLA) composites with superior electromagnetic interference shielding effectiveness(EMI SE).When the content of GNPs was 18.60 wt%and 4 layers of Ti₃ C₂ T_x(6.98 wt%) films were embedded,the in-plane thermal conductivity coefficient(λ_Ⅱ) and EMI SE(EMI SE_Ⅱ) values of the thermally conductive Ti₃ C₂ T_x/(o-GNPs/P LA) composites significantly increa sed to 3.44 W·m^-1·K^-1 and 65 d B(3.00 mm),increased by 1223.1% and2066.7%,respectively,compared with λ_Ⅱ(0.26 W·m^-1·K^-1) and EMI SE_Ⅱ(3 d B) of neat PLA matrix.This work offers a novel and easily route for designing and manufacturing highly thermally conductive polymer composites with superior EMI SE for broader application.     

Enhanced diastereoselectivity via confinement: photoisomerization of 2,3-diphenylcyclopropane-1-carboxylic acid derivatives within zeolites

From the perspective of asymmetric induction, the photochemistry of 24 chiral esters and amides of cis-2,3-diphenylcyclopropane-1-carboxylic acid from excited singlet and triplet states has been investigated within zeolites. The chiral auxiliaries placed at a remote location from the isomerization site functioned far better within a zeolite than in solution. Generally, chiral auxiliaries with an aromatic or a carbonyl substituent performed better than the ones containing only alkyl substituents. A model based on cation-binding-dependent flexibility of the chiral auxiliary accounts for the observed variation in de between aryl (and carbonyl) and alkyl chiral auxiliaries within zeolites. Cation-dependent diastereomer switch was also observed in select examples.