Modulation of nuclear pore topology by transport modifiers

The nuclear pore complex (NPC) represents the only pathway for macromolecular communication between the nuclear and cytoplasmic compartments of the cell. Nucleocytoplasmic transport requires the interaction of transport receptors with phenylalanine-glycine (FG)-repeats that line the transport pathway through the NPC. Here we examine the effects of transport receptors and amphipathic alcohols on NPC topology using scanning force microscopy. We show that transport receptors that irreversibly bind FG-repeats increase NPC vertical aspect, whereas transport receptors that weakly interact with FG-repeats increase NPC diameter. Interestingly, small polar alcohols likewise increase NPC diameter. These opposing effects agree with the inhibition or enhancement of nuclear transport, respectively, previously ascribed to these agents.     

Hydrogen-oxidizing capabilities of Helicobacter hepaticus and in vivo availability of the substrate

Hydrogen-oxidizing hydrogenase activity was detected in Helicobacter hepaticus and compared to the activity in Helicobacter pylori for characteristics associated with hydrogen uptake respiratory hydrogenases. Intact whole cells could couple H(2) oxidation to oxygen uptake, and no H(2) uptake was observed without oxygen available to complete the respiratory pathway. The H. hepaticus enzyme coupled H(2) oxidation to reduction of many positive potential acceptors, and it underwent anaerobic or reductive activation. H. hepaticus had a strong affinity for molecular H(2) (apparent K(m) of 2.5 micro M), and microelectrode measurements on the livers of live mice demonstrated that H(2) is available in the host tissue at levels 20-fold greater than the apparent whole-cell K(m) value.     

LcrV is a channel size-determining component of the Yop effector translocon of Yersinia

Delivery of Yop effector proteins by pathogenic Yersinia across the eukaryotic cell membrane requires LcrV, YopB and YopD. These proteins were also required for channel formation in infected erythrocytes and, using different osmolytes, the contact-dependent haemolysis assay was used to study channel size. Channels associated with LcrV were around 3 nm, whereas the homologous PcrV protein of Pseudomonas aeruginosa induced channels of around 2 nm in diameter. In lipid bilayer membranes, purified LcrV and PcrV induced a stepwise conductance increase of 3 nS and 1 nS, respectively, in 1 M KCl. The regions important for channel size were localized to amino acids 127-195 of LcrV and to amino acids 106-173 of PcrV. The size of the channel correlated with the ability to translocate Yop effectors into host cells. We suggest that LcrV is a size-determining structural component of the Yop translocon.     

Inhibition of natural killer cells results in acceptance of cardiac allografts in CD28-/- mice

Successful transplantation of allogeneic organs is an important objective in modern medicine. However, sophisticated immune defense mechanisms, primarily evolved to combat infections, often work against medical transplantation. To investigate the roles of natural and adaptive immune responses in transplant rejection, we functionally inactivated key effector systems of the innate (NK cells) and the adaptive immune system (CD28-mediated costimulation of T cells) in mice. Neither of these interventions alone led to acceptance of allogeneic vascularized cardiac grafts. In contrast, inhibition of NK-receptor-bearing cells combined with CD28-costimulation blockade established long-term graft acceptance. These results indicate a concerted interplay between innate and adaptive immune surveillance for graft rejection. Thus we suggest that inactivation of NK-receptor-bearing cells could be a new strategy for successful survival of solid-organ transplants.     

Stereoselective effects of (R)- and (S)-carvedilol in humans

Carvedilol is currently used as the racemic mixture, (R,S)-carvedilol, consisting of equal amounts of (R)-carvedilol, an alpha-blocker, and (S)-carvedilol, an alpha- and beta-blocker, which have never been tested in their optically pure forms in human subjects. We performed a randomized, double-blind, placebo-controlled, crossover study in 12 healthy male volunteers. Subjects received single oral doses of 25 mg (R,S)-carvedilol, 12.5 mg (R)-carvedilol, 12.5 mg (S)-carvedilol, and placebo at 8 AM as well as at 8 PM. Exercise was performed at 11 AM, and heart rate and blood pressure were measured at rest and after 10 min of exercise. Urine was collected between 10 AM and 6 PM, as well as between 10 PM and 6 AM, and the amounts of urinary 6-hydroxy-melatonin sulfate (aMT6s) were determined by RIA. Compared to placebo, (R)-carvedilol increased heart rate during exercise (+4%, P < 0.05) and recovery (+10%, P < 0.05); (S)-carvedilol decreased heart rate during exercise (-14%, P < 0.05) and recovery (-6%, P < 0.05), and systolic blood pressure during exercise (-12%, P < 0.05); (R,S)-carvedilol decreased heart rate during exercise (-11%, P < 0.05), and systolic blood pressure at rest (-7%, P < 0.05) and during exercise (-10%, P < 0.05). None of the agents had any significant effect on the release of aMT6s. Our results indicate that only (S)-carvedilol causes beta-blockade, whereas (R)-carvedilol appears to increase sympathetic tone, presumably as a physiological reaction to the decrease of blood pressure caused by alpha-blockade. None of the drugs had any influence on melatonin release. The weak clinical net effect of beta-blockade of (R,S)-carvedilol at rest might be one reason why this drug causes fewer side effects than other beta-blockers, such as a reduction of nocturnal melatonin release.     

Integration of hypoxic dilation signaling pathways for skeletal muscle resistance arteries

Mediator contributions to hypoxic dilation of rat gracilis muscle resistance arteries were determined by measuring dilation, vascular smooth muscle hyperpolarization, and metabolite production after incremental hypoxia. Nitric oxide (NO) synthase inhibition abolished responses to mild hypoxia, whereas COX inhibition impaired responses to more severe hypoxia by 77%. Blocking 20-hydroxyeicosatetraenoic acid (20-HETE) impaired responses to moderate hypoxia. With only NO systems intact, responses were maintained with mild hypoxia (88% normal) mediated via K(Ca) channels. When only COX pathways were intact, responses to moderate-severe hypoxia were largely retained (79% of normal) mediated via K(ATP) channels. Vessel responses to moderate hypoxia were retained with only 20-HETE systems intact mediated via K(Ca) channels. NO production increased 5.6-fold with mild hypoxia; greater hypoxia was without further effect. With increased hypoxia, 20-HETE levels fell to 40% of control values. 6-keto-PGF(1alpha) levels were not altered with mild hypoxia, but increased 4.6-fold with severe hypoxia. These results suggest vascular reactivity to progressive hypoxia represents an integration of NO production (mild hypoxia), PGI(2) production (severe hypoxia), and reduced 20-HETE levels (moderate hypoxia).     

Antihypertensive effect of mechanism-based inhibition of renal arachidonic acid omega-hydroxylase activity

The cytochrome P-450 eicosanoid 20-hydroxyeicosatetraenoic acid (20-HETE) is a potent vasoconstrictor that is implicated in the regulation of blood pressure. The identification of selective inhibitors of renal 20-HETE formation for use in vivo would facilitate studies to determine the systemic effects of this eicosanoid. We characterized the acetylenic fatty acid sodium 10-undecynyl sulfate (10-SUYS) as a potent and selective mechanism-based inhibitor of renal 20-HETE formation. A single dose of 10-SUYS caused an acute reduction in mean arterial blood pressure in 8-wk-old spontaneously hypertensive rats. The decrease in mean arterial pressure was maximal 6 h after 10-SUYS treatment (17.9 +/- 3.2 mmHg; P < 0.05), and blood pressure returned to baseline levels within 24 h after treatment. Treatment with 10-SUYS was associated with a decrease in urinary 20-HETE formation in vivo and attenuation of the vasoconstrictor response of renal interlobar arteries to ANG II in vitro. These results provide further evidence that 20-HETE plays an important role in the regulation of blood pressure in the spontaneously hypertensive rat.     

Sphingomyelin and cholesterol promote HIV-1 gp41 pretransmembrane sequence surface aggregation and membrane restructuring

The interfacial sequence DKWASLWNWFNITNWLWYIK, preceding the transmembrane anchor of gp41 glycoprotein subunit, has been shown to be essential for fusion activity and incorporation into virions. HIV(c), a peptide representing this region, formed lytic pores in liposomes composed of the main lipids occurring in the human immunodeficiency virus, type 1 (HIV-1), envelope, i.e. 1-palmitoyl-2-oleoylphosphatidylcholine (POPC):sphingomyelin (SPM):cholesterol (Chol) (1:1:1 mole ratio), at low (>1:10,000) peptide-to-lipid mole ratio, and promoted the mixing of vesicular lipids at >1:1000 peptide-to-lipid mole ratios. Inclusion of SPM or Chol in POPC membranes had different effects. Whereas SPM sustained pore formation, Chol promoted fusion activity. Even if partitioning into membranes was not affected in the absence of both SPM and Chol, HIV(c) had virtually no effect on POPC vesicles. Conditions described to disturb occurrence of lateral separation of phases in these systems reproduced the high peptide-dose requirements for leakage as found in pure POPC vesicles and inhibited fusion. Surface aggregation assays using rhodamine-labeled peptides demonstrated that SPM and Chol promoted HIV(c) self-aggregation in membranes. Employing head-group fluorescent phospholipid analogs in planar supported lipid layers, we were able to discern HIV(c) clusters associated to ordered domains. Our results support the notion that the pretransmembrane sequence may participate in the clustering of gp41 monomers within the HIV-1 envelope, and in bilayer architecture destabilization at the loci of fusion.