Staufen1-mediated mRNA decay functions in adipogenesis

The double-stranded RNA binding protein Staufen1 (Stau1) is involved in diverse gene expression pathways. For Stau1-mediated mRNA decay (SMD) in mammals, Stau1 binds to the 3' untranslated region of target mRNA and recruits Upf1 to elicit rapid mRNA degradation. However, the events downstream of Upf1 recruitment and the biological importance of SMD remain unclear. Here we show that SMD involves PNRC2, decapping activity, and 5'-to-3' exonucleolytic activity. In particular, Upf1 serves as an adaptor protein for the association of PNRC2 and Stau1. During adipogenesis, Stau1 and PNRC2 increase in abundance, Upf1 becomes hyperphosphorylated, and consequently SMD efficiency is enhanced. Intriguingly, downregulation of SMD components attenuates adipogenesis in a way that is rescued by downregulation of an antiadipogenic factor, Krüppel-like factor 2 (KLF2), the mRNA of which is identified as a substrate of SMD. Our data thus identify a biological role for SMD in adipogenesis.     

Establishment and characterization of a lung cancer cell line,SMC-L001, from a lung adenocarcinoma

Lung cancer cell lines are a valuable tool for elucidating lung tumorigenesis and developing novel therapies. However, the majority of cell lines currently available were established from tumors in patients of Caucasian origin, limiting our ability to investigate how cancers in patients of different ethnicities differ from one another in terms of tumor biology and drug responses. In this study, we established a human non-small cell lung carcinoma cell line, SMC-L001, and characterized its genome and tumorigenic potential. SMC-L001 cells were isolated from a Korean lung adenocarcinoma patient (male, pStage IIb) and were propagated in culture. SMC-L001 cells were adherent. DNA fingerprinting analysis indicated that the SMC-L001 cell line originated from parental tumor tissue. Comparison of the genomic profile of the SMC-L001 cell line and the original tumor revealed an identical profile with 739 mutations in 46 cancer-related genes, including mutations in TP53 and KRAS. Furthermore, SMC-L001 cells were highly tumorigenic, as evidenced by the induction of solid tumors in immunodeficient mice. In summary, we established a new lung cancer cell line with point mutations in TP53 and KRAS from a Korean lung adenocarcinoma patient that will be useful for investigating ethnic differences in lung cancer biology and drug response.     

Pairwise and Bipartite Entanglements of Three Non-Equally Separated Quantum Dots in Plasmonic Nanowaveguide System

Plasmonics - We theoretically investigate properties of the pairwise and bipartite entanglements of three non-equally separated quantum dots (QDs) coupled to one-dimensional plasmonic nanowaveguide...     

A mass spectrometry-based high-throughput screening method for engineering fatty acid synthases with improved production of medium-chain fatty acids

Microbial cell factories have been extensively engineered to produce free fatty acids (FFAs) as key components of crucial nutrients, soaps, industrial chemicals, and fuels. However, our ability to control the composition of microbially synthesized FFAs is still limited, particularly, for producing medium-chain fatty acids (MCFAs). This is mainly due to the lack of high-throughput approaches for FFA analysis to engineer enzymes with desirable product specificity. Here we report a mass spectrometry (MS)-based method for rapid profiling of MCFAs in Saccharomyces cerevisiae by using membrane lipids as a proxy. In particular, matrix-assisted laser desorption/ionization time-of-flight (MALDI-ToF) MS was used to detect shorter acyl chain phosphatidylcholines from membrane lipids and a higher m/z peak ratio at 730 and 758 was used as an indication for improved MCFA production. This colony-based method can be performed at a rate of ~2 s per sample, representing a substantial improvement over gas chromatography-MS (typically >30 min per sample) as the gold standard method for FFA detection. To demonstrate the power of this method, we performed site-saturation mutagenesis of the yeast fatty acid synthase and identified nine missense mutations that resulted in improved MCFA production relative to the wild-type strain. Colony-based MALDI-ToF MS screening provides an effective approach for engineering microbial fatty acid compositions in a high-throughput manner.     

Modulatory effect of linoleic and oleic acid on cell proliferation and lipid metabolism gene expressions in primary bovine satellite cells

This study was performed to elucidate the effects of linoleic acid (LA), oleic acid (OA) and their combination (LA?+?OA) on cell proliferation, apoptosis, necrosis, and the lipid metabolism related gene expression in bovine satellite cells (BSCs), isolated from bovine muscles. Cell viability was significantly increased with the OA and LA treatment. Furthermore, LA?+?OA enhanced cell proliferation in a dose-dependent manner (10 to 100?µM), whereas it lowered at 250?µM. In addition, a cell-cycle analysis showed that 100?µM of LA and OA markedly decreased the G0/G1 phase proportion (62.58% and 61.33%, respectively), compared to controls (68.02%), whereas the S-phase cells’ proportion was increased. The ratio of G2/M phase cells was not significantly different among the groups. Moreover, analyses with AO/EtBr staining showed that no apoptosis occurred. Necrosis were determined by flow cytometry using Annexin V-FITC/PI staining which revealed no early apoptosis in the cells pretreated with LA or OA, but occurred in the LA?+?OA group. We also analyzed the mRNA expression of lipid metabolizing genes such as peroxisome proliferator receptor alfa (PPARα), peroxisome proliferator receptor gamma (PPARγ), acyl-CoA oxidase (ACOX), lipoprotein lipase (LPL), carnitine palmitoyl transferase (CPT-1), and fatty-acid binding protein4 (FABP4), which were upregulated in LA or OA treated cells compared to the control group. In essence, LA and OA alone promote the cell proliferation without any apoptosis and necrosis, which might upregulate the lipid metabolism related gene expressions, and increase fatty-acid oxidation in the BSCs’ lipid metabolism.     

Inhibition of fructose-1,6-bisphosphatase by a new class of allosteric effectors

A highly constrained pseudo-tetrapeptide (OC252-324) further defines a new allosteric binding site located near the center of fructose-1,6-bisphosphatase. In a crystal structure, pairs of inhibitory molecules bind to opposite faces of the enzyme tetramer. Each ligand molecule is in contact with three of four subunits of the tetramer, hydrogen bonding with the side chain of Asp187 and the backbone carbonyl of residue 71, and electrostatically interacting with the backbone carbonyl of residue 51. The ligated complex adopts a quaternary structure between the canonical R- and T-states of fructose-1,6-bisphosphatase, and yet a dynamic loop essential for catalysis (residues 52-72) is in a conformation identical to that of the T-state enzyme. Inhibition by the pseudo-tetrapeptide is cooperative (Hill coefficient of 2), synergistic with both AMP and fructose 2,6-bisphosphate, noncompetitive with respect to Mg2+, and uncompetitive with respect to fructose 1,6-bisphosphate. The ligand dramatically lowers the concentration at which substrate inhibition dominates the kinetics of fructose-1,6-bisphosphatase. Elevated substrate concentrations employed in kinetic screens may have facilitated the discovery of this uncompetitive inhibitor. Moreover, the inhibitor could mimic an unknown natural effector of fructose-1,6-bisphosphatase, as it interacts strongly with a conserved residue of undetermined functional significance.     

Gating Properties of Inward-Rectifier Potassium Channels: Effects of Permeant Ions

Two inward-rectifier K⁺ channels, ROMK2 (Kir1.1b) and IRK1 (Kir2.1), were expressed in Xenopus oocytes and their gating properties were studied in cell-attached membrane patches. The gating properties depended strongly on the ion being conducted (K⁺, NH₄ ⁺, Rb⁺, or Tl⁺), suggesting tight coupling between permeation and gating. Mean open times were strongly dependent on the nature of the conducted ion. For ROMK2 the order from the longest to the shortest times was K⁺ > Rb⁺ > Tl⁺ > NH₄ ⁺. For IRK1 the sequence was K⁺ > NH₄ ⁺ > Tl⁺. In both cases the open times decreased monotonically as the membrane voltage was hyperpolarized. Both the absolute values and the voltage dependence of closed times were dependent on the conducted species. ROMK2 showed a single closed state whose mean lifetimes were biphasic functions of voltage. The maxima were at various voltages for different ions. IRK1 had at least two closed states whose lifetimes decreased monotonically with K⁺, increased monotonically with Tl⁺, and were relatively constant with NH₄ ⁺ as the conducted ion. We explain the ion-dependence of gating by assuming that the ions bind to a site within the permeation pathway, resulting in a stable, ion-dependent, closed state of the channel. The patterns of voltage-dependence of closed-state lifetimes, which are specific for different ions, can be explained by variations in the rate at which the bound ions leave the pore toward the inside or the outside of the cell. Received: 18 April 2001/Revised: 28 June 2001