Measuring the Local Velocity along Transition Paths during the Folding of Single Biological Molecules.

Transition paths are the most interesting part of folding reactions but remain little studied. We measured the local velocity along transition paths in DNA hairpin folding using optical tweezers. The velocity distribution agreed well with diffusive theories, yielding the diffusion coefficient. We used the average velocity to calculate the transmission factor in transition-state theory (TST), finding observed rates that were ∼10^{5}-fold slower than predicted by TST. This work quantifies the importance of barrier recrossing events and highlights the effectiveness of the diffusive model of folding.

Fostering supportive learning environments in long-term care: the case of WIN A STEP UP.

The education of direct care workers (DCWs) is key to improving job quality and the quality of care in long-term care (LTC). This paper describes the successful integration of a supervisory training program into a continuing education intervention (WIN A STEP UP) for DCWs, identifies the factors that appear to influence the integration of the learning into practice, and discusses the implications for educators. The WIN A STEP UP program achieved its strongest results when the DCW curriculum was paired with Coaching Supervision. Attention to pre-training, training and post-training conditions is necessary to successfully integrate learning into practice in LTC.

Isolation and characterisation of a novel spirochaete from severe virulent ovine foot rot.

A novel spirochaete was isolated from a case of severe virulent ovine foot rot (SVOFR) by immunomagnetic separation with beads coated with polyclonal anti-treponemal antisera and prolonged anaerobic broth culture. The as yet unnamed treponeme differs considerably from the only other spirochaete isolated from ovine foot rot as regards morphology, enzymic profile and 16S rDNA sequence. On the basis of 16S rDNA, it was most closely related to another unnamed spirochaete isolated from cases of bovine digital dermatitis in the USA, raising the possibility of cross-species transmission. Further information is required to establish this novel ovine spirochaete as the cause of SVOFR.

The epithelial Na(+)/H(+) exchanger, NHE3, is internalized through a clathrin-mediated pathway.

Trafficking of the Na(+)/H(+) exchanger isoform 3 (NHE3) between sub-apical vesicles and apical membrane of epithelial cells is a suggested mechanism of regulation of NHE3 activity. When epitope-tagged NHE3 was stably expressed in NHE-deficient Chinese hamster ovary cells, a sizable fraction was found in recycling endosomes. This system was used to analyze the mechanism of endocytosis of NHE3. Immunofluorescence and radiolabeling experiments showed that inhibition of clathrin-mediated endocytosis using hypertonicity, acid treatment, or K(+) depletion inhibited internalization of NHE3. Moreover, transient transfection of an inhibitory mutant of dynamin (DynS45N) blocked the clathrin-mediated uptake of transferrin, as well as the endocytosis of NHE3. In ileal villus cells, endogenous NHE3 was also found to co-purify with isolated clathrin-coated vesicles, thereby confirming their association in native tissues. The role of COP-I subunits in the intracellular traffic of NHE3 was evaluated using ldlF cells, which bear a temperature-sensitive mutation in the epsilon-COP subunit. At the permissive temperature, NHE3 distributed normally, whereas at the restrictive temperature, which induces rapid degradation of epsilon-COP, NHE3 was still internalized, but its subcellular distribution was altered. These results indicate that endocytosis of NHE3 occurs primarily via clathrin-coated pits and vesicles and that normal intracellular trafficking of NHE3 involves an epsilon-COP-dependent step.

ATP dependence is not an intrinsic property of Na+/H+ exchanger NHE1: requirement for an ancillary factor.

Na+/H+ exchange is a passive process not requiring expenditure of metabolic energy. Nevertheless, depletion of cellular ATP produces a marked inhibition of the antiport. No evidence has been found for direct binding of nucleotide to exchangers or alteration in their state of phosphorylation, suggesting ancillary factors may be involved. This possibility was tested by comparing the activity of dog red blood cells (RBC) and their resealed ghosts. Immunoblotting experiments using isoform-specific polyclonal and monoclonal antibodies indicated RBC membranes express Na+/H+ exchanger isoform 1 (NHE1). In intact RBC, uptake of Na+ was greatly stimulated when the cytosol was acidified. The stimulated uptake was largely eliminated by amiloride and by submicromolar concentrations of the benzoyl guanidinium compound HOE-694, consistent with mediation by NHE1. Although exchange activity could also be elicited by acidification in resealed ghosts containing ATP, the absolute rate of transport was markedly diminished at comparable pH. Dissipation of the pH gradient was ruled out as the cause of diminished transport rate in ghosts. This was accomplished by a "pH clamping" procedure based on continued export of base equivalents by the endogenous anion exchanger. These observations suggest a critical factor required to maintain optimal Na+/H+ exchange activity is lost or inactivated during preparation of ghosts. Depletion of ATP, achieved by incubation with 2-deoxy-D-glucose, inhibited Na+/H+ exchange in intact RBC, as reported for nucleated cells. In contrast, the rate of exchange was similar in control and ATP-depleted resealed ghosts. Interestingly, the residual rate of Na+/H+ exchange in ATP-depleted but otherwise intact cells was similar to the transport rate of ghosts. Therefore, we tentatively conclude that full activation of NHE1 requires both ATP and an additional regulatory factor, which may mediate the action of the nucleotide. Ancillary phosphoproteins or phospholipids or the kinases that mediate their phosphorylation are likely candidates for the regulatory factor(s) that is inactivated or missing in ghosts.

Proline-rich motifs of the Na+/H+ exchanger 2 isoform. Binding of Src homology domain 3 and role in apical targeting in epithelia.

The NHE2 isoform of the Na+/H+ exchanger (NHE) displays two proline-rich sequences in its C-terminal region that resemble SH3 (Src homology 3)-binding domains. We investigated whether these regions (743PPSVTPAP750, termed Pro-1, and 786VPPKPPP792, termed Pro-2) can bind to SH3 domains and whether they are essential for NHE2 function and targeting. A fusion protein containing the Pro-1 region showed promiscuous binding to SH3 domains of several proteins in vitro, whereas a Pro-2 fusion bound preferentially to domains derived from kinases. In contrast, cytoplasmic regions of NHE1, NHE3, or NHE4 failed to interact. When expressed in antiporter-deficient cells, truncated NHE2 lacking both Pro-rich regions catalyzed Na+/H+ exchange, retained sensitivity to intracellular ATP, and was activated by hyperosmolarity, resembling full-length NHE2. The role of the Pro-rich regions in subcellular targeting was examined by transfection of epitope-tagged forms of NHE2 in porcine renal epithelial LLC-PK1 cells. Both full-length and Pro-2-truncated NHE2 localized almost exclusively to the apical membrane. By contrast, a mutant devoid of both Pro-1 and Pro-2 was preferentially sorted to the basolateral surface but also accumulated intracellularly. These observations indicate that the region encompassing Pro-1 is essential for appropriate subcellular targeting of NHE2.

Regulation of phagosomal acidification. Differential targeting of Na+/H+ exchangers, Na+/K+-ATPases, and vacuolar-type H+-atpases.

Vacuolar-type (V) ATPases are thought to be the main determinant of phagosomal acidification. In phagosomes containing mycobacteria, which ostensibly impair the delivery of V-ATPases to the phagosomal membrane, the pH would be expected to be near neutral. This prediction was tested by microfluorescence ratio imaging using macrophages from mice susceptible to mycobacterial infection. Although less acidic than their counterparts containing dead bacteria, phagosomes containing live Mycobacteria bovis were nearly 1 pH unit more acidic than the cytosol, suggesting the existence of alternate H+ transport mechanisms. We therefore investigated whether Na+/H+ exchange (NHE) contributes to phagosomal acidification. Immunoblotting, reverse transcriptase-polymerase chain reaction, and pharmacological studies indicated that NHE1 is the predominant isoform of the exchanger in macrophages. Fractionation revealed that NHE1 is incorporated into the phagosomal membrane, and measurements of pH indicated that it is functional in this location. Nevertheless, acidification of the lumen of phagosomes containing either latex beads or live M. bovis was insensitive to (3-methylsulfonyl-4-piperidinobenzoyl)-guanidine methanesulfonate, a potent inhibitor of NHE1. This may have been due to the absence of an appropriate lumen to cytosol Na+ gradient, because the phagosomal membrane was found to be devoid of Na+/K+ pumps. Unexpectedly, the acidification of M. bovis phagosomes was fully reversed by specific inhibitors of the vacuolar H+-ATPase, suggesting that ATPases are present only transiently or in reduced quantities in the phagosomal membrane. Alternatively, acid equivalents accumulated in endosomes by V-ATPases may be delivered to the mycobacterial phagosome by carrier vesicles devoid of ATPases.

Sphingosylphosphorylcholine activates an amiloride-insensitive Na+-H+-exchange mechanism in GH4C1 cells.

The effect of sphingosylphosphorylcholine (SphPCho) on the intracellular pH (pHi) in GH4C1 cells was investigated. SphPCho evoked a very slow increase in basal pHi. In cells acidified with nigericin, SphPCho induced a rapid alkalinization of the cells. The effect was inhibited in a Na+-free buffer solution, but was insensitive to ethylisopropyl amiloride, a potent inhibitor of Na+-H+ exchangers (NHE). Reverse transcription and PCR showed that the predominant isoform of the antiport expressed in GH4C1 cells is NHE-1. The rate of alkalinization after stimulation with propionate, and after addition of Na+ to cells acidified with NH4Cl, was enhanced in cells treated with SphPCho. The initial rate of alkalinization after addition of Na+ to acidified cells treated with SphPCho gave an apparent Km value of 15 +/- 2 mM for Na+. The Vmax value was 9 +/- 2 mM H+/min. The effect was insensitive to ouabain, staurosporine and bafilomycin A. However, the SphPCho-evoked alkalinization was abolished in cells treated with 2-deoxy-D-glucose. The effect was not due to the charge of the molecule, as stearylamine increased pHi in Na+-containing and Na+-free buffer. The results show that SphPCho may activate Na+-H+ exchange, and that this effect is mediated via an amiloride-insensitive exchange mechanism.

Calreticulin is essential for integrin-mediated calcium signalling and cell adhesion.

Integrins are important mediators of cell adhesion to extracellular ligands and can transduce biochemical signals both into and out of cells. The cytoplasmic domains of integrins interact with several structural and signalling proteins and consequently participate in the regulation of cell shape, motility, growth and differentiation. It has been shown that calreticulin associates with the cytoplasmic domains of integrin alpha-subunits and that this interaction can influence integrin-mediated cell adhesion to extracellular matrix. We have now developed calreticulin-deficient embryonic stem (ES) cells and isolated embryonic fibroblasts from calreticulin mutant mice. We find that in both cell types integrin-mediated adhesion is severely impaired, although integrin expression is unaltered. Expression of recombinant calreticulin in double knockout ES cells by complementary DNA transfection rescued integrin-mediated adhesion. In wild-type cells, engagement of surface integrins induced a transient elevation in cytosolic calcium concentration owing to influx of extracellular calcium. This calcium transient was absent in calreticulin-deficient cells. In contrast, the amount of calcium in endomembrane stores, which is sensitive to both inositol 1,4,5-trisphosphate and thapsigargin, was indistinguishable in the two cell types. Our results indicate that calreticulin is an essential modulator both of integrin adhesive functions and integrin-initiated signalling, but that it may not play a significant role in the storage of luminal calcium.

Modulation of the retinoic acid and retinoid X receptor signaling pathways in P19 embryonal carcinoma cells by calreticulin.

Calreticulin is a widely expressed calcium binding protein that can bind to an amino acid sequence motif, KXGFFKR, which is present in the cytoplasmic domain of all integrin alpha-subunits. Closely related sequences, KXFFKR and KXFFRR, are encoded in the DNA-binding domain of all members of the steroid/thyroid/retinoid receptor superfamily and it has recently been demonstrated that calreticulin inhibits their activity both in vitro and in vivo. Here we present novel evidence that calreticulin can interfere directly with the retinoic acid (RARs) and retinoid X (RXRs) receptor pathways. Calreticulin exhibits the ability to inhibit DNA-binding activity of both heterodimeric RAR/RXR and homodimeric RXR complexes in vitro. Inhibition of RXR binding to DNA is achieved with a concentration of calreticulin that is approximately fourfold lower than that required for inhibition of RAR/RXR binding to a cognate binding site. Coprecipitation experiments suggest a direct protein:protein interaction between calreticulin and retinoid receptors. Stable overexpression of calreticulin in P19 embryonal carcinoma cells significantly decreases the rapid activation of the endogenous RA-responsive RARbeta gene, abrogates the ability of endogenous RAR/RXR complexes to bind to DNA, and inhibits the emergence of the RA-induced differentiated phenotype. These data demonstrate that calreticulin can interfere with the two distinct retinoid signaling pathways through a mechanism likely involving direct protein:protein interactions and that disruption of the retinoid signal alters biological processes in vivo.

Muscarinic agonists induce phosphorylation-independent activation of the NHE-1 isoform of the Na+/H+ antiporter in salivary acinar cells.

Cholinergic agonists stimulate isotonic fluid secretion in the parotid gland. This process is driven by the apical exit of Cl-, which enters the cells partly via Cl-/HCO-3 exchange across the basolateral membrane. Acidification of the cytosol by the extrusion of HCO-3 is prevented by the concomitant activation of the Na+/H+ exchanger (NHE), which is directly activated by cholinergic stimulation. Multiple isoforms of the NHE have been described in mammalian cells, but the particular isoform(s) present in salivary glands and their mechanism of activation have not been defined. Reverse transcriptase-polymerase chain reaction with isoform-specific primers was used to establish that NHE-1 and NHE-2, but not NHE-3 or NHE-4, are expressed in parotid glands. The presence of NHE-1 was confirmed by immunoblotting and immunofluorescence, which additionally demonstrated that this isoform is abundant in the basolateral membrane of acinar cells. The predominant role of NHE-1 in carbachol-induced Na+/H+ exchange was established pharmacologically using HOE694, an inhibitor with differential potency toward the individual isoforms. Because muscarinic agonists induce stimulation of protein kinases in acinar cells, we assessed the role of phosphorylation in the activation of the antiport. Immunoprecipitation experiments revealed that, although NHE-1 was phosphorylated in the resting state, no further phosphorylation occurred upon treatment with carbachol. Similar phosphopeptide patterns were observed in control and carbachol-treated samples. Together, these findings indicate that NHE-1, the predominant isoform of the antiporter in the basolateral membrane of acinar cells, is activated during muscarinic stimulation by a phosphorylation-independent event. Other processes, such as association of Ca2+-calmodulin complexes to the cytosolic domain of the antiporter, may be responsible for the activation of Na+/H+ exchange.

Experimental evaluation of "The Images Within": an alcohol education and prevention program.

A program titled "The Images Within" was implemented and evaluated in three sites on the east coast of the United States. This school curriculum uses art work developed by children of alcoholics to stimulate classroom discussions of the problems of parental alcohol abuse. The evaluation with 278 experimental and 310 control students indicated increased knowledge about the effects of alcohol and improved skills in coping with alcohol problems and help seeking behavior. Process data indicated that related programs were initiated, students were stimulated by the program and teachers were positive in their perceptions of the program. Schools implementing this program need to have developed referral networks to handle the individual concerns that are expressed as a result of participation in "The Images Within."

Prevention of endotoxin-induced mortality by antitissue factor immunization.

BACKGROUND: Microvascular thrombosis with intravascular fibrin deposition is a characteristic pathologic alteration during endotoxic shock. This effect is predominantly mediated by expression of the cellular procoagulant tissue factor by endothelial cells and cells of monocyte or macrophage lineage, resulting in acceleration of the coagulation cascade and fibrin deposition. OBJECTIVE: To determine whether modulation of this response by treatment with an antitissue factor antibody might have beneficial effects. DESIGN: A polyclonal antibody to murine tissue factor was prepared by injecting rabbits with a synthesized peptide sequence of murine tissue factor. To determine the activity of the antibody, elicited murine peritoneal macrophages were treated for 4 hours with 10-micrograms/mL lipopolysaccharide (LPS), and procoagulant activity was determined via a clotting assay (milliunits of activity per 10(6) macrophages). RESULTS: The tissue factor antibody abrogated LPS-induced macrophage procoagulant activity, confirming activity of the antibody (macrophages, 236 +/- 28 mU/10(6) macrophages; macrophages/LPS, 3801 +/- 190* mU/10(6) macrophages; macrophages/LPS/alpha-tissue factor, 753 +/- 92* mU/10(6) macrophages; n = 3; the asterisk indicates P < .05 by an analysis of variance). Additionally, antibody-protein affinity was confirmed by Western blot analysis. Having determined the activity of the antibody in vitro, we tested its efficacy in vivo in a lethal endotoxemia model. Mice were immunized with 200 microL of antiserum intraperitoneally 2 hours before injection with 250 micrograms of LPS intraperitoneally and 24 hours later. Control animals received 200 microL of saline solution. All animals initially exhibited lethargy and piloerection, characteristic of the predicted response to LPS. However, immunized animals had a significantly (P < .05) reduced mortality compared with control animals. Fibrinogen levels were significantly (P < .05) higher in the immunized mice, suggesting decreased consumption of coagulation factors, a finding consistent with an antitissue factor effect. Further, plasma tumor necrosis factor levels 90 minutes after LPS injection were similar in both groups, suggesting normal induction of the cytokine cascade. CONCLUSIONS: Modulation of microvascular fibrin deposition by abrogating tissue factor-mediated coagulation significantly (P < .05) improved survival in this model without attenuating the initiation of the cytokine cascade. These findings suggest a pathogenic role for coagulation in the induction of acute organ injury during sepsis.

Severity of medical and neurologic complications as a determinant of neurodevelopmental outcome at 6 and 12 months in very low birth weight infants.

Very low birth weight (n = 154) and term infants (n = 119) had neurologic and developmental assessment at 6 and 12 months of age. Preterm infants with severe neonatal complications were considered to be at high risk, and those with milder complications were considered to be at low risk, for neurodevelopmental abnormality. Compared to term infants, high- and low-risk infants had abnormalities at 6 months in total neurologic score, cranial nerves, motor tone, motor coordination, and reflexes (P < .001). At 12 months, all groups had improved. However, high-risk infants had persistent abnormalities in the same subcategories (P < .001), whereas low-risk infants differed from term infants only in motor tone (P < .001). Bayley developmental scores were different for all groups at 6 months (P < .001), but at 12 months only high-risk infants differed from term infants (P < .01). These results demonstrate improvement in neurologic and developmental scores over time in very low birth weight infants. The degree of neurodevelopmental abnormality and improvement over time is related to severity of neonatal complications in preterm infants.

The mammalian Na+/H+ antiporters NHE-1, NHE-2, and NHE-3 are electroneutral and voltage independent, but can couple to an H+ conductance.

Na+/H+ exchange in vertebrates is thought to be electroneutral and insensitive to the membrane voltage. This basic concept has been challenged by recent reports of antiport-associated currents in the turtle colon epithelium (Post and Dawson, 1992, 1994). To determine the electrogenicity of mammalian antiporters, we used the whole-cell patch clamp technique combined with microfluorimetric measurements of intracellular pH (pHi). In murine macrophages, which were found by RT-PCR to express the NHE-1 isoform of the antiporter, reverse (intracellular Na(+)-driven) Na+/H+ exchange caused a cytosolic acidification and activated an outward current, whereas forward (extracellular Na(+)-driven) exchange produced a cytosolic alkalinization and reduced a basal outward current. The currents mirrored the changes in pHi, were strictly dependent on the presence of a Na+ gradient and were reversibly blocked by amiloride. However, the currents were seemingly not carried by the Na+/H+ exchanger itself, but were instead due to a shift in the voltage dependence of a preexisting H+ conductance. This was supported by measurements of the reversal potential (Erev) of tail currents, which identified H+ (equivalents) as the charge carrier. During Na+/H+ exchange, Erev changed along with the measured changes in pHi (by 60-69 mV/pH). Moreover, the current and Na+/H+ exchange could be dissociated. Zn2+, which inhibits the H+ conductance, reversibly blocked the currents without altering Na+/H+ exchange. In Chinese hamster ovary (CHO) cells, which lack the H+ conductance, Na+/H+ exchange produced pHi changes that were not accompanied by transmembrane currents. Similar results were obtained in CHO cells transfected with either the NHE-1, NHE-2, or NHE-3 isoforms of the antiporter, indicating that exchange through these isoforms is electroneutral. In all the isoforms tested, the amplitude and time-course of the antiport-induced pHi changes were independent of the holding voltage. We conclude that mammalian NHE-1, NHE-2, and NHE-3 are electroneutral and voltage independent. In cells endowed with a pH-sensitive H+ conductance, such as macrophages, activation of Na(+)-H+ exchange can modulate a transmembrane H+ current. The currents reported in turtle colon might be due to a similar "cross-talk" between the antiporter and a H+ conductance.

Prediction of 12-month neurodevelopmental outcome from a 6-month neurologic examination in premature infants.

This study examined whether a neurologic examination at 6 months of age is predictive of neurodevelopmental outcome at 12 months in very-low-birth-weight (VLBW) infants. A neurologic examination and the Bayley Scales of Infant Development were performed at 6 and 12 months with VLBW infants and full-term (FT) controls. VLBW infants were categorized based on early medical complications. High-risk (HR) infants had diagnoses of bronchopulmonary dysplasia, pulmonary immaturity, grade III or IV intraventricular hemorrhage, and/or periventricular leukomalacia. VLBW infants with other diagnoses were placed in the low-risk (LR) group. Total neurologic scores (NS) improved over time for all three groups but improved more for HR infants, who had more abnormal NS at both time points; NS at 6 months predicted neurologic and developmental scores at 12 months for all three groups, but the relation between 6- and 12-month outcomes was strongest for the HR infants. The neurologic examination may be helpful in assessing VLBW infants' need for referral to early childhood intervention programs.

ATP dependence of NHE-1, the ubiquitous isoform of the Na+/H+ antiporter. Analysis of phosphorylation and subcellular localization.

ATP is not hydrolyzed during the transport cycle of the Na+/H+ exchanger (NHE), yet depletion of the nucleotide drastically reduces the rate of cation exchange. The mechanism underlying this inhibition was investigated in fibroblasts transfected with NHE-1, the growth factor-sensitive isoform of the antiport. NHE-1 was found to be phosphorylated in serum-starved, unstimulated cells. Acute ATP depletion induced a profound inhibition of transport without detectable changes in NHE-1 phosphorylation. Analysis of cells transfected with truncated mutants of NHE-1 indicated that the carboxyl-terminal cytosolic domain of the antiport is required for expression of its ATP dependence. To define whether inhibition of Na+/H+ exchange resulted from internalization of NHE-1, extracellularly exposed proteins were labeled with impermeant biotin derivatives. The proportion of NHE-1 exposed to the surface was comparable before and after ATP depletion. Immunofluorescence determinations revealed focal accumulations of NHE-1 on the membrane of untreated cells. NHE-1 redistributed following ATP depletion, showing a more homogeneous localization. F-actin, which co-localizes with the antiport in untreated cells, also redistributed when cells were ATP depleted. These findings suggest an interaction of NHE-1 with the cytoskeleton. Accordingly, disassembly of actin filaments with cytochalasin D induced redistribution of the antiport. However, Na+/H+ exchange activity was unaltered by cytochalasin D. We propose that ancillary proteins confer ATP sensitivity to the antiporter and may also mediate its association with the cytoskeleton. Depletion of the nucleotide would alter the interaction between NHE-1 and the putative regulator, inhibiting Na+/H+ exchange and inducing subcellular redistribution. However, disruption of the cytoskeleton at distal sites, such as induced by cytochalasins, is insufficient to inactivate the antiport.

Focal localization of the NHE-1 isoform of the Na+/H+ antiport: assessment of effects on intracellular pH.

Na+/H+ exchange (antiport) is a major pathway for the regulation of intracellular pH. Antiport activity is stimulated when suspended cells adhere to the substratum. In this report, immunofluorescence was used to study the subcellular localization of the ubiquitous NHE-1 isoform of the antiport. NHE-1 was not distributed homogeneously on the surface of the cells. Instead, antiports were found to accumulate along the border of lamellipodia and near the edge of finer processes. Dual immunofluorescence experiments demonstrated that vinculin, talin and F-actin are concentrated at sites of NHE-1 accumulation. A mutated construct of NHE-1 lacking residues 566-635 of the cytosolic domain also accumulated near marginal lamellae. In contrast, the focal distribution observed in adherent cells was not detectable in cells grown in suspension. Fluorescence ratio imaging was used to define the functional consequences of focal accumulation of NHE-1. In the steady state, the pH was virtually identical throughout the cytosol. Moreover, no pH gradients were found to develop when cells recovered from an acid load by activation of Na+/H+ exchange. This is probably because of the presence of high concentrations of mobile buffers in the cytosol. The focal accumulation of antiporters near the cell margins may be involved in stimulation by adherence and/or generation of local osmotic gradients.