• Journal of Life Science
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• v.29 no.9
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• pp.949-954
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• 2019

Membrane topology is a key characteristic of membrane proteins. We previously reported the cloning of the chromosome 4 open-reading frame 32 (C4orf32) gene as a potential membrane protein; however, the cellular localization and membrane topology of C4orf32 was as yet unknown. In this study, we found that green fluorescent protein (GFP) fused to the C-terminus of C4orf32 (C4orf32-GFP) was localized to the endoplasmic reticulum (ER). We applied three tools to identify determinants of C4orf32 topology: protease protection, fluorescence protease protection (FPP), and an inducible system using the ternary complex between FK506 binding protein 12 (FKBP), rapamycin, and the rapamycin-binding domain of mTOR (FRB) (the FRB-rapamycin-FKBP system). Using protease protection and FPP assays, we found that the GFP tag in C4orf32-GFP was localized to the cytoplasmic surface of the ER membrane of HeLa cells. Protease protection and FPP assays are useful and complimentary tools for identifying the topology of GFP fusion membrane proteins. The FRB-rapamycin-FKBP system was also used to study the topology of C4orf32. In the absence of rapamycin, a monomeric red fluorescent protein-FKBP fusion (mRFP-FKBP) and C4orf32-GFP-FRB were localized to the cytoplasm and the ER membrane, respectively. However, in the presence of rapamycin, the mRFP-FKBP was shifted from the cytoplasm to the ER and colocalized with the C4orf32-GFP-FRB. These results indicate that the FRB moiety is facing the cytoplasmic surface of ER membrane. Overall, our results clearly suggest that C4orf32 belongs to the family of type I ER resident membrane proteins.

• Mass Spectrometry Letters
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• v.2 no.4
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• pp.92-95
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• 2011

Pyrophosphates are the key intermediates in the biosynthesis of isoprenoids, and their concentrations could reveal the benefits of statins in cardiovascular diseases. Quantitative analysis of five pyrophosphates, including isopentenyl pyrophosphate (IPP), dimethylallyl pyrophosphate (DMAPP), geranyl pyrophosphate (GPP), farnesyl pyrophosphate (FPP), and geranylgeranyl pyrophosphate (GGPP), was performed using liquid chromatography-tandem mass spectrometry (LC-MS/MS) in negative ionization mode. After dilution with methanol, samples were separated on a 3 ${\mu}m$ particle multi-modal $C_{18}$ column ($50{\times}2$ mm) and quantified within 10 min. The gradient elution consists of 10 mM ammonium bicarbonate and 0.5% triethylamine (TEA) in water and 0.1% TEA in 80% acetonitrile was used at the flow rate of 0.4 mL/min. Overall recoveries were 51.4-106.6%, while the limit of quantification was 0.05 ${\mu}g$/mL for GPP and FPP and 0.1 ${\mu}g$/mL for IPP, DMAPP, and GGPP. The precision (% CV) and accuracy (% bias) of the assay were 1.9-12.3% and 89.6-111.8%, respectively, in 0.05-10 ${\mu}g$/mL calibration ranges ($R^2$ > 0.993). The devised LC-MS/MS technique with the multi-modal $C_{18}$ column can be used to estimate the biological activity of pyrophosphates in plasma and may be applicable to cardiovascular events with cholesterol metabolism as well as the drug efficacy of statins.

• YAKHAK HOEJI
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• v.52 no.1
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• pp.62-66
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• 2008

In this study, we examined the inhibitory effects of propenone derivatives, 1,3-diphenyl-propenone (DPhP), 3-phenyl-1-thiophen-2-yl-propenone (PhT2P), 3-phenyl-1-thiophen-3-yl-propenone (PhT3P) and 1-furan-2-yl-3-phenyl-propenone (FPhP), on $TNF-{\alpha}$-induced nuclear factor (NF)-${\kappa}B$ activity and interleukin (IL)-8-induced monocyte adhesion to colon epithelial cells. 1-Furan-2-yl-3-pyridin-2-yl-propenone (FPP-3) that is previously reported as a $NF-{\kappa}B$ inhibitor suppressed $TNF-{\alpha}$-induced monocyte-epithelial cell adhesion in a concentration-dependent manner. The propenone derivatives, DPhP, PhT2P, PhT3P, FPhP, also inhibited $TNF-{\alpha}$-induced $NF-{\kappa}B$ activation in a similar degree to FPP-3. In a DPPH radical scavenging assay, none of the compounds showed DPPH radical scavenging activity, indicating that the inhibitory actions of the propenone derivatives on redox-sensitive $NF-{\kappa}B$ activity is not due to a simple free radical scavenging activity. In addition, the propenone derivatives also suppressed the IL-8-induced monocyte adhesion to colon epithelial cells. Furthermore, the effective concentrations of the propenone derivatives on both $NF-{\kappa}B$ activation as well as IL-8 induced monocyte-epithelial cell adhesion were 1000 times lower than 5-aminosalicylic acid (5-ASA), a clinically used drug for inflammatory bowel disease. These results suggest that the propenone derivatives may be a potential lead having a strong inhibitory activity against inflammatory cytokine-induced epithelial inflammation.