Effect of phosphatidylinositol replacement by diacylglycerol on various physical properties of artificial membranes with respect to the role of phosphatidylinositol response

In an attempt to gain insight into the physiological role of phosphatidylinositol turnover enhanced by extracellular stimuli, the physical properties of artificial membranes (egg yolk phosphatidylcholine/bovine brain phosphatidylserine) containing phosphatidylinositol or diacylglycerol were studied by ESR using spin probes and freeze-fracture electron microscopy. Diacylglycerol lost both the ability to form lipid bilayer structures and its susceptibility to calcium ions. Yeast phosphatidylinositol included in dipalmitoylphosphatidylcholine liposomes lowered the phase transition temperature of dipalmitoylphosphatidylcholine and expanded the temperature range of phase transition. However, diacylglycerol at the same concentration did not undergo the effects caused by phosphatidylinositol but the phase transition temperature was slightly raised. Phase separation of phosphatidylserine induced by calcium ions was enhanced when the phosphatidylinositol was replaced by diacylglycerol in phosphatidylcholine/ phosphatidylserine/phosphatidylinositol (3:5:2, by molar ratio) mixtures. The mobility of phosphatidylcholine spin probe was decreased in phosphatidylcholine/ phosphatidylserine/diacylglycerol (3:5:2, by molar ratio) liposomes compared with phosphatidylcholine/phosphatidylserine/phosphatidylinositol (3:5:2, by molar ratio) liposomes. An additional component from protonated stearic acid spin probes was observed in phosphatidylcholine/phosphatidylinositol (8:2, by molar ratio) liposomes at 40°C, whereas the component was not seen in phosphatidylcholine/diacylglycerol (8:2, by molar ratio) liposomes. This may indicate the alteration of surface charge induced by the replacement of phosphatidylinositol by diacylglycerol. Indeed, in the presence of 1 mM Ca²⁺, the additional component was removed by an electrostatic interaction between Ca²⁺ and phosphatidylinositol molecules in phosphatidylcholine/phosphatidylinositol liposomes at 40°C. These results support the hypothesis that the enhanced turnover of phosphatidylinositol may play a triggering role for various cellular responses to exogenous stimuli by altering membrane physical states.     

Dimerization of DOCK2 Is Essential for DOCK2-Mediated Rac Activation and Lymphocyte Migration

The migratory properties of lymphocytes depend on DOCK2, an atypical Rac activator predominantly expressed in hematopoietic cells. Although DOCK2 does not contain the Dbl homology domain typically found in guanine nucleotide exchange factors (GEFs), DOCK2 mediates the GTP-GDP exchange reaction for Rac via its DOCK homology region (DHR)-2 (also known as CZH2 or Docker) domain. DOCK2 DHR-2 domain is composed of three lobes, and Rac binding site and catalytic center are generated entirely from lobes B and C. On the other hand, lobe A has been implicated in dimer formation, yet its physiological significance remains unknown. Here, we report that lobe A-mediated DOCK2 dimerization is crucial for Rac activation and lymphocyte migration. We found that unlike wild-type DOCK2, DOCK2 mutant lacking lobe A failed to restore motility and polarity when expressed in thymoma cells and primary T cells lacking endogenous expression of DOCK2. Similar results were obtained with the DOCK2 point mutant having a defect in dimerization. Deletion of lobe A from the DHR-2 domain did not affect Rac GEF activity in vitro. However, fluorescence resonance energy transfer analyses revealed that lobe A is required for DOCK2 to activate Rac effectively during cell migration. Our results thus indicate that DOCK2 dimerization is functionally important under the physiological condition where only limited amounts of DOCK2 and Rac are localized to the plasma membrane.     

Inhibitory effects of steroidal allenes on growth,development, and steroid metabolism of the silkworm,Bombyx mori

Steroidal allenes, stigmasta-5,24(28),28-trien-3β-ol (allene-I) and cholesta-5,23,24-trien-3β-ol (allene-II), were tested for their inhibitory effects on growth, development, and steroid metabolism in the silkworm, Bombyx mori. The allenic analogue (I) of stigmasta-5,24(28)-dien-3β-ol (2) was found to be a specific inhibitor for the conversion of stigmast-5-en-3β-ol (1) to stigmasta-5, 24(28)-dien-3β-ol (2) and/or stigmasta-5,24(28)-dien-3β-ol (2) to 24,28-epoxy-stigmast-5-en-3β-ol (3) This inhibitor held the larvae in the second instar for more than 20 days without developing to the third instar, when administered alone or with the dietary sterols of stigmast-5-en-3β-ol (1) or stigmasta-5,24(28)-dien-3β-ol (2). The second allene (II) with a similar structure to cholesta-5,24-dien-3β-ol (4) was also found to be an inhibitor for insect growth and development, but it appeared not to be acting via inhibition of sterol dealkylation.     

Aerobic exercise training reduces plasma endothelin-1 concentration in older women.

Endothelial function deteriorates with aging. On the other hand, exercise training improves the function of vascular endothelial cells. Endothelin-1 (ET-1), which is produced by vascular endothelial cells, has potent constrictor and proliferative activity in vascular smooth muscle cells and, therefore, has been implicated in regulation of vascular tonus and progression of atherosclerosis. We previously reported significantly higher plasma ET-1 concentration in middle-aged than in young humans, and recently we showed that plasma ET-1 concentration was significantly decreased by aerobic exercise training in healthy young humans. We hypothesized that plasma ET-1 concentration increases with age, even in healthy adults, and that lifestyle modification (i.e., exercise) can reduce plasma ET-1 concentration in previously sedentary older adults. We measured plasma ET-1 concentration in healthy young women (21-28 yr old), healthy middle-aged women (31-47 yr old), and healthy older women (61-69 yr old). The plasma level of ET-1 significantly increased with aging (1.02 +/- 0.08, 1.33 +/- 0.11, and 2.90 +/- 0.20 pg/ml in young, middle-aged, and older women, respectively). Thus plasma ET-1 concentration was markedly higher in healthy older women than in healthy young or middle-aged women (by approximately 3- and 2-fold, respectively). In healthy older women, we also measured plasma ET-1 concentration after 3 mo of aerobic exercise (cycling on a leg ergometer at 80% of ventilatory threshold for 30 min, 5 days/wk). Regular exercise significantly decreased plasma ET-1 concentration in the healthy older women (2.22 +/- 0.16 pg/ml, P < 0.01) and also significantly reduced their blood pressure. The present study suggests that regular aerobic-endurance exercise reduces plasma ET-1 concentration in older humans, and this reduction in plasma ET-1 concentration may have beneficial effects on the cardiovascular system (i.e., prevention of progression of hypertension and/or atherosclerosis by endogenous ET-1).     

PLD activation in Chinese hamster ovary (CHO) cells transfected with PGF2α receptor cDNA

Pertussis toxin-insensitive GTP-binding protein was observed to be involved in prostaglandin F2α(PGF2α)-induced phosphoinositide metabolism in Chinese hamster ovary (CHO) cells transfected with PGF2α receptor cDNA (CHO-PGF2α·R cells) (Ito, S. et al. Biochem. Biophys. Res. Commun. 200: 756, 1994). In the present study, we investigated PGF2α-induced PLD activation in CHO-PGF2α·R cells. PLD activation was examined by measuring the production of [³H]phosphatidylbutanol ([³H]PBut), a specific product of the PLD-catalyzed transphosphatidylation reaction. PGF2α-induced [³H]PBut formation was concentration-dependent with the maximal level obtained at 1 μM PGF2α. The maximal [³H]PBut formation was observed at 2 min after addition of PGF2α. Depletion of extracellular Ca²⁺ with EGTA suppressed PGF2α-induced PLD activation by 50%. PKC inhibitors Ro31–8425 and calphostin C inhibited PGF2α-induced [³H]PBut formation by 50%. PTK inhibitors genistein and herbimycin A failed to inhibit PGF2α-induced PLD activation. A combination of maximal effective concentrations of PGF2α (1 μM) and PMA (100 nM) enhanced PLD activation in an additive manner. Pretreatment of the cells with PMA for 2 h down-regulated PKCα and decreased PGF2α-induced PLD activation. These results suggest that PLD activation by PGF2α is mediated by both PKC-dependent and -independent pathways and that PKCα is involved in the former pathway.     

Direct In Vivo Reprogramming with Sendai Virus Vectors Improves Cardiac Function after Myocardial Infarction

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Sesquiterpene constituents from the liverwort Bazzania japonica

The hydrodistillation products of the liverwort Bazzania japonica were separated by preparative gas chromatography (GC) and investigated by spectroscopic methods. Seven unknown compounds were isolated and identified by GC-MS and NMR. Four of them, the norsesquiterpene hydrocarbons 4-epi-11-nor-aristola-1(10),11-diene (1), 4-epi-11-nor-aristola-1,9,11-triene (2), 4-epi-11-nor-aristola-9,11-diene (3), and one oxygenated sesquiterpene, (-)-aristol-1(10)-en-12-ol (5) are new natural compounds, and one, (+)-himachala-2,4-diene (7), has for the first time been isolated from liverworts. The absolute configurations of 5 and 7 were derived by chemical correlation reactions and/or enantioselective GC using cyclodextrin phases. 1, 2 and 3 have identical absolute configuration.     

Establishing an In Vivo Assay System to Identify Components Involved in Environmental RNA Interference in the Western Corn Rootworm

The discovery of environmental RNA interference (RNAi), in which gene expression is suppressed via feeding with double-stranded RNA (dsRNA) molecules, opened the door to the practical application of RNAi-based techniques in crop pest management. The western corn rootworm (WCR, Diabrotica virgifera virgifera) is one of the most devastating corn pests in North America. Interestingly, WCR displays a robust environmental RNAi response, raising the possibility of applying an RNAi-based pest management strategy to this pest. Understanding the molecular mechanisms involved in the WCR environmental RNAi process will allow for determining the rate limiting steps involved with dsRNA toxicity and potential dsRNA resistance mechanisms in WCR. In this study, we have established a two-step in vivo assay system, which allows us to evaluate the involvement of genes in environmental RNAi in WCR. We show that laccase 2 and ebony, critical cuticle pigmentation/tanning genes, can be used as marker genes in our assay system, with ebony being a more stable marker to monitor RNAi activity. In addition, we optimized the dsRNA dose and length for the assay, and confirmed that this assay system is sensitive to detect well-known RNAi components such as Dicer-2 and Argonaute-2. We also evaluated two WCR sid1- like (sil) genes with this assay system. This system will be useful to quickly survey candidate systemic RNAi genes in WCR, and also will be adaptable for a genome-wide RNAi screening to give us an unbiased view of the environmental/systemic RNAi pathway in WCR.