Nanowire nanosensors for highly sensitive and selective detection of biological and chemical species

Boron-doped silicon nanowires (SiNWs) were used to create highly sensitive, real-time electrically based sensors for biological and chemical species. Amine- and oxide-functionalized SiNWs exhibit pH-dependent conductance that was linear over a large dynamic range and could be understood in terms of the change in surface charge during protonation and deprotonation. Biotin-modified SiNWs were used to detect streptavidin down to at least a picomolar concentration range. In addition, antigen-functionalized SiNWs show reversible antibody binding and concentration-dependent detection in real time. Lastly, detection of the reversible binding of the metabolic indicator Ca2+ was demonstrated. The small size and capability of these semiconductor nanowires for sensitive, label-free, real-time detection of a wide range of chemical and biological species could be exploited in array-based screening and in vivo diagnostics.

Fabry - Perot interference in a nanotube electron waveguide

The behaviour of traditional electronic devices can be understood in terms of the classical diffusive motion of electrons. As the size of a device becomes comparable to the electron coherence length, however, quantum interference between electron waves becomes increasingly important, leading to dramatic changes in device properties. This classical-to-quantum transition in device behaviour suggests the possibility for nanometer-sized electronic elements that make use of quantum coherence. Molecular electronic devices are promising candidates for realizing such device elements because the electronic motion in molecules is inherently quantum mechanical and it can be modified by well defined chemistry. Here we describe an example of a coherent molecular electronic device whose behaviour is explicitly dependent on quantum interference between propagating electron waves-a Fabry-Perot electron resonator based on individual single-walled carbon nanotubes with near-perfect ohmic contacts to electrodes. In these devices, the nanotubes act as coherent electron waveguides, with the resonant cavity formed between the two nanotube-electrode interfaces. We use a theoretical model based on the multichannel Landauer-Büttiker formalism to analyse the device characteristics and find that coupling between the two propagating modes of the nanotubes caused by electron scattering at the nanotube-electrode interfaces is important.

Nanometre-scale thermometry in a living cell

Sensitive probing of temperature variations on nanometre scales is an outstanding challenge in many areas of modern science and technology. In particular, a thermometer capable of subdegree temperature resolution over a large range of temperatures as well as integration within a living system could provide a powerful new tool in many areas of biological, physical and chemical research. Possibilities range from the temperature-induced control of gene expression and tumour metabolism to the cell-selective treatment of disease and the study of heat dissipation in integrated circuits. By combining local light-induced heat sources with sensitive nanoscale thermometry, it may also be possible to engineer biological processes at the subcellular level. Here we demonstrate a new approach to nanoscale thermometry that uses coherent manipulation of the electronic spin associated with nitrogen-vacancy colour centres in diamond. Our technique makes it possible to detect temperature variations as small as 1.8 mK (a sensitivity of 9 mK Hz(-1/2)) in an ultrapure bulk diamond sample. Using nitrogen-vacancy centres in diamond nanocrystals (nanodiamonds), we directly measure the local thermal environment on length scales as short as 200 nanometres. Finally, by introducing both nanodiamonds and gold nanoparticles into a single human embryonic fibroblast, we demonstrate temperature-gradient control and mapping at the subcellular level, enabling unique potential applications in life sciences.

Activation of BTK by a phosphorylation mechanism initiated by SRC family kinases

Bruton's tyrosine kinase (BTK) is pivotal in B cell activation and development through its participation in the signaling pathways of multiple hematopoietic receptors. The mechanisms controlling BTK activation were studied here by examination of the biochemical consequences of an interaction between BTK and SRC family kinases. This interaction of BTK with SRC kinases transphosphorylated BTK on tyrosine at residue 551, which led to BTK activation. BTK then autophosphorylated at a second site. The same two sites were phosphorylated upon B cell antigen receptor cross-linking. The activated BTK was predominantly membrane-associated, which suggests that BTK integrates distinct receptor signals resulting in SRC kinase activation and BTK membrane targeting.

Analysis of upstream elements in the HuC promoter leads to the establishment of transgenic zebrafish with fluorescent neurons

HuC encodes an RNA binding protein homologous to Drosophila elav that serves as an excellent early marker for differentiating neurons. We have characterized the promoter of the zebrafish HuC gene by examining the ability of 5'-upstream fragments to drive expression of green fluorescent protein (GFP) in live embryos. We determined that 2.8 kb of the 5'-flanking sequence is sufficient to restrict GFP gene expression to neurons. The core promoter spans 251 base pairs and contains a CCAAT box and one SP1 sequence but no TATA box is present near the transcription start site. A putative MyT1 binding site and at least 17 E-box sequences are necessary to maintain the neuronal specificity of HuC expression. Interestingly, sequential removal of the putative MyT1 binding site and 14 distal E boxes does not appear to abolish neuronal expression; rather, it leads to a progressive expansion of GFP expression into muscle cells. Further removal of the three proximal E boxes eliminates neuronal and muscle specificity of GFP expression and leads to ubiquitous expression of GFP in the whole body. Identification of key components of the HuC promoter has led to the establishment of a stable zebrafish transgenic line (HuC-GFP) in which GFP is expressed specifically in neurons. We crossed mind bomb (mib) fish with this line to visualize their neurogenic phenotype in live mib(-/-) mutant embryos. This cross illustrates how HuC-GFP fish could be used in the future to identify and analyze zebrafish mutants with an aberrant pattern of early neurons.

DTI and MTR abnormalities in schizophrenia: analysis of white matter integrity

Diffusion tensor imaging (DTI) studies in schizophrenia demonstrate lower anisotropic diffusion within white matter due either to loss of coherence of white matter fiber tracts, to changes in the number and/or density of interconnecting fiber tracts, or to changes in myelination, although methodology as well as localization of such changes differ between studies. The aim of this study is to localize and to specify further DTI abnormalities in schizophrenia by combining DTI with magnetization transfer imaging (MTI), a technique sensitive to myelin and axonal alterations in order to increase specificity of DTI findings. 21 chronic schizophrenics and 26 controls were scanned using Line-Scan-Diffusion-Imaging and T1-weighted techniques with and without a saturation pulse (MT). Diffusion information was used to normalize co-registered maps of fractional anisotropy (FA) and magnetization transfer ratio (MTR) to a study-specific template, using the multi-channel daemon algorithm, designed specifically to deal with multidirectional tensor information. Diffusion anisotropy was decreased in schizophrenia in the following brain regions: the fornix, the corpus callosum, bilaterally in the cingulum bundle, bilaterally in the superior occipito-frontal fasciculus, bilaterally in the internal capsule, in the right inferior occipito-frontal fasciculus and the left arcuate fasciculus. MTR maps demonstrated changes in the corpus callosum, fornix, right internal capsule, and the superior occipito-frontal fasciculus bilaterally; however, no changes were noted in the anterior cingulum bundle, the left internal capsule, the arcuate fasciculus, or inferior occipito-frontal fasciculus. In addition, the right posterior cingulum bundle showed MTR but not FA changes in schizophrenia. These findings suggest that, while some of the diffusion abnormalities in schizophrenia are likely due to abnormal coherence, or organization of the fiber tracts, some of these abnormalities may, in fact, be attributed to or coincide with myelin/axonal disruption.

Synthesis of superporous hydrogels: hydrogels with fast swelling and superabsorbent properties

We have been interested in the synthesis of hydrogels with fast swelling kinetics and superabsorbent properties. To increase the water absorption rate, interconnected pores were introduced to the hydrogels. Since the pore size in the dried hydrogels is in the order of hundreds of micrometers, these hydrogels are called "superporous" hydrogels. Superporous hydrogels were synthesized by crosslinking polymerization of various vinyl monomers in the presence of gas bubbles formed by the chemical reaction of acid and NaHCO3. The polymerization process was optimized to capture the gas bubbles inside the synthesized hydrogels. The use of the NaHCO3/acid system allowed easy control of timing for gelation and foam formation. We found that PF127 was the best foam stabilizer for most of the monomer systems used in our study. Scanning electron microscope (SEM) pictures showed interconnected pores forming capillary channels. The capillary channels, which were critical for fast swelling, were preserved during drying by dehydrating water-swollen hydrogels with ethanol before drying. The ethanol-dehydrated superporous hydrogels reached equilibrium swelling within minutes. The equilibrium swelling time could be reduced to less than a minute with the use of a wetting agent. In our study, water moisture was used as a wetting agent since the amount of moisture content in the dried hydrogels easily could be controlled. Preparation of superporous hydrogels using the right blowing system, foam stabilizer, drying method, and wetting agent makes it possible to reduce the swelling time to less than a minute regardless of the size of the dried gels. The superporous hydrogels can be used where fast swelling and superabsorbent properties are critical.

Bioadhesive polymers as platforms for oral controlled drug delivery II: synthesis and evaluation of some swelling, water-insoluble bioadhesive polymers

A series of cross-linked, swellable polymers was sythesized from monomers such as acrylic acid, methacrylic acid, and others with various cross-linking agents to produce a range of polymers differing in charge densities and hydrophobicity. The densities, rate, and extent of hydration of the polymers were determined. An increase in the number of hydrophobic groups in the polymer structure reduced hydration whereas the density of the polymer was unaffected. A sensitive in vitro method for measuring adhesion of polymer to tissue from the rabbit stomach was developed. Polymers of acrylic acid loosely cross-linked (0.3%, w/w) with three different agents, divinyl glycol, 2,5-dimethyl-1,5-hexadiene, and divinylbenzene, showed the same degree of bioadhesion while poly(methacrylic acid-divinylbenzene) showed reduced bioadhesion. The small percent of cross-linking agent, irrespective of physicochemical properties, did not contribute substantially to bioadhesion, whereas the starting monomer had a large effect. The effect of pH on the bioadhesion of poly(acrylic acid-divinyl glycol) was studied at constant temperature, ionic strength, and osmolality. The polymer showed maximum adhesion at pH 5 and 6 and a minimum at pH 7. Gastrointestinal transit studies of cross-linked polymers in rats were studied. Poly(acrylic acid-divinyl glycol) and poly(methacrylic acid-divinylbenzene) were shown to have substantially longer GI transit times than the control, Amberlite 200 resin beads. The delay in transit time was due to bioadhesion of the polymer to the mucin-epithelial cell surface which was clearly observable on animal autopsy. The acrylic acid polymer showed a longer GI transit time than the methacrylic acid polymer, and this in vivo GI transit result is consistent with in vitro bioadhesion test results.

Mechanisms of mucoadhesion of poly(acrylic acid) hydrogels

It has been proposed that mucoadhesives which adhere to the gastric mucus layer may be used to prolong gastric retention time of oral dosage forms. Preliminary studies, using acrylic hydrogels, have established that the density of carboxyl groups on the polymer chain is important for mucoadhesion. To understand the role(s) of the carboxyl groups in mucoadhesion, acrylic acid-acrylamide random copolymers [P(AA-co-AM)] were synthesized, and the adhesion strength of the cross-linked polymers to the gastric mucus layer was examined as a function of the pH, initial concentration of the cross-linking agent, degree of swelling, and carboxyl-group density. From the study on mucoadhesion of various P(AA-co-AM), it was found that at least 80% of the vinyl groups of the polymer must possess carboxyl groups in the protonated form. The dependence of mucoadhesion on pH and carboxyl-group density suggests that mucoadhesion occurs through hydrogen bonding. In addition, the density of the cross-linking agent significantly affects mucoadhesion. As the density of the cross-linking agent is lowered, the mucoadhesive strength increases, although the density of carboxyl groups in the test surface area is reduced. It is concluded that for mucoadhesion to occur, polymers must have functional groups that are able to form hydrogen bonds above the critical concentration (80% for vinyl polymers), and the polymer chains should be flexible enough to form as many hydrogen bonds as possible.

Regulation of Btk function by a major autophosphorylation site within the SH3 domain

Bruton's tyrosine kinase (Btk) plays a crucial role in B cell development. Overexpression of Btk with a Src family kinase increases tyrosine phosphorylation and catalytic activity of Btk. This occurs by transphosphorylation at Y551 in the Btk catalytic domain and the enhancement of Btk autophosphorylation at a second site. A gain-of-function mutant called Btk* containing E41 to K change within the pleckstrin homology domain induces fibroblast transformation. Btk* enhances the transphosphorylation of Y551 by endogenous Src family tyrosine kinases and autophosphorylation at the second site. We mapped the major Btk autophosphorylation site to Y223 within the SH3 domain. Mutation of Y223 to F blocks Btk autophosphorylation and dramatically potentiates the transforming activity of Btk* in fibroblasts. The location of Y223 in a potential ligand-binding pocket suggests that autophosphorylation regulates SH3-mediated signaling by Btk.

NMR structure of the histidine kinase domain of the E. coli osmosensor EnvZ

Bacteria live in capricious environments, in which they must continuously sense external conditions in order to adjust their shape, motility and physiology. The histidine-aspartate phosphorelay signal-transduction system (also known as the two-component system) is important in cellular adaptation to environmental changes in both prokaryotes and lower eukaryotes. In this system, protein histidine kinases function as sensors and signal transducers. The Escherichia coli osmosensor, EnvZ, is a transmembrane protein with histidine kinase activity in its cytoplasmic region. The cytoplasmic region contains two functional domains: domain A (residues 223-289) contains the conserved histidine residue (H243), a site of autophosphorylation as well as transphosphorylation to the conserved D55 residue of response regulator OmpR, whereas domain B (residues 290-450) encloses several highly conserved regions (G1, G2, F and N boxes) and is able to phosphorylate H243. Here we present the solution structure of domain B, the catalytic core of EnvZ. This core has a novel protein kinase structure, distinct from the serine/threonine/tyrosine kinase fold, with unanticipated similarities to both heatshock protein 90 and DNA gyrase B.

Solution structure of the homodimeric core domain of Escherichia coli histidine kinase EnvZ

Escherichia coli osmosensor EnvZ is a protein histidine kinase that plays a central role in osmoregulation, a cellular adaptation process involving the His-Asp phosphorelay signal transduction system. Dimerization of the transmembrane protein is essential for its autophosphorylation and phosphorelay signal transduction functions. Here we present the NMR-derived structure of the homodimeric core domain (residues 223-289) of EnvZ that includes His 243, the site of autophosphorylation and phosphate transfer reactions. The structure comprises a four-helix bundle formed by two identical helix-turn-helix subunits, revealing the molecular assembly of two active sites within the dimeric kinase.

Observation of a narrow charmoniumlike state in exclusive B+/--->K+/-pi+pi-J/psi decays

We report the observation of a narrow charmoniumlike state produced in the exclusive decay process B+/--->K+/-pi(+)pi(-)J/psi. This state, which decays into pi(+)pi(-)J/psi, has a mass of 3872.0+/-0.6(stat)+/-0.5(syst) MeV, a value that is very near the M(D0)+M(D(*0)) mass threshold. The results are based on an analysis of 152M B-Bmacr; events collected at the Upsilon(4S) resonance in the Belle detector at the KEKB collider. The signal has a statistical significance that is in excess of 10sigma.

Purification and characterization of a fibrinolytic enzyme produced from Bacillus sp. strain CK 11-4 screened from Chungkook-Jang

Bacillus sp. strain CK 11-4, which produces a strongly fibrinolytic enzyme, was screened from Chungkook-Jang, a traditional Korean fermented-soybean sauce. The fibrinolytic enzyme (CK) was purified from supernatant of Bacillus sp. strain CK 11-4 culture broth and showed thermophilic, hydrophilic, and strong fibrinolytic activity. The optimum temperature and pH were 70 degrees C and 10.5, respectively, and the molecular weight was 28,200 as determined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The first 14 amino acids of the N-terminal sequence of CK are Ala-Gin-Thr-Val-Pro-Tyr-Gly-Ile-Pro-Leu-Ile-Lys-Ala-Asp. This sequence is identical to that of subtilisin Carlsberg and different from that of nattokinase, but CK showed a level of fibrinolytic activity that was about eight times higher than that of subtilisin Carlsberg. The amidolytic activity of CK increased about twofold at the initial state of the reaction when CK enzyme was added to a mixture of plasminogen and substrate (H-D-Val-Leu-Lys-pNA). A similar result was also obtained from fibrin plate analysis.

TAR RNA-binding protein is an inhibitor of the interferon-induced protein kinase PKR

A cDNA encoding a double-stranded-RNA (dsRNA)-binding protein was isolated by screening a HeLa cell cDNA expression library for proteins that bind the HIV-1 Rev-responsive-element RNA. The cDNA encoded a protein that was identical to TRBP, the previously reported cellular protein that binds the transactivation response element (TAR) RNA of human immunodeficiency virus type 1. TRBP inhibited phosphorylation of the interferon-induced ribosome-associated protein kinase PKR and of the eukaryotic translation initiation factor eIF-2 alpha in a transient-expression system in which the translation of a reporter gene was inhibited by the localized activation of PKR. TRBP expression in HeLa cells complemented the growth and protein-synthesis defect of a vaccinia virus mutant lacking the expression of the dsRNA-binding protein E3L. These results implicate TRBP as a cellular regulatory protein that binds RNAs containing specific secondary structure(s) to mediate the inhibition of PKR activation and stimulate translation in a localized manner.

AMPK as a metabolic switch in rat muscle, liver and adipose tissue after exercise

An increasing body of evidence has revealed that activation of adenosine monophosphate (AMP)-activated protein kinase (AMPK)-activated protein kinase increases fatty acid oxidation by lowering the concentration of malonyl coenzyme A (CoA), an inhibitor of carnitine palmitoyl transferase 1. Studies carried out primarily in skeletal muscle suggest that AMPK modulates the concentration of malonyl CoA by concurrently phosphorylating and inhibiting acetyl CoA carboxylase (ACC), the rate limiting enzyme in malonyl CoA synthesis, and phosphorylating and activating malonyl CoA decarboxylase (MCD), an enzyme involved in its degradation. We have recently observed that AMPK and MCD activities are increased and ACC activity diminished in skeletal muscle, liver and, surprisingly, in adipose tissue 30 min following exercise (treadmill run) in normal rats. In liver and adipose tissue these changes were associated with a decrease in the activity of glycerol-3-phosphate acyltransferase (GPAT), which catalyses the first committed reaction in glycerolipid synthesis and, which like ACC, is phosphorylated and inhibited by AMPK. Similar changes in ACC, MCD and GPAT were observed following the administration of 5-aminoimidazole 4-carboxamide-riboside (AICAR), further indicating that the exercise-induced alterations in these enzymes were AMPK-mediated.

CONCLUSIONS

(1) AMPK plays a major role in regulating lipid metabolism in multiple tissues following exercise. (2) The net effect of its activation is to increase fatty acid oxidation and diminish glycerolipid synthesis. (3) The relevance of these findings to the regulation of muscle glycogen repletion in the post-exercise state and to the demonstrated ability of AMPK activation to decrease adiposity and increase insulin sensitivity in rodents remains to be determined.

Gastric retention properties of superporous hydrogel composites

In many applications, usefulness of conventional hydrogels is limited by their slow swelling. To improve the swelling property of the conventional hydrogels, we have synthesized superporous hydrogels (SPHs) which swell fast to equilibrium size in minutes due to water uptake by capillary wetting through numerous interconnected open pores. The swelling ratio was also large in the range of hundreds. The mechanical strength of the highly swollen SPHs was increased by adding a composite material during the synthesis. The composite material used in the synthesis of SPH composites was Ac-Di-Sol((R)) (croscarmellose sodium). The gastric retention property of the prepared SPH composites was tested in dogs both in fasted and fed conditions. The SPH composites were placed in a hard gelatin capsule (size 000) for oral administration. All dogs tested were fasted for 36 h before experiments. Under the fasted condition, the SPH composite remained in the stomach for 2-3 h after before breaking into two pieces and being emptied. When food was given before the experiment just once following 36 h of fasting, the SPH composite remained in the stomach for more than 24 h, even though the fed condition was maintained only for the first few hours. Our study indicated that SPH composites possessed three properties necessary for gastric retention: fast swelling; superswelling; and high mechanical strength. While more improvements need to be made, the SPH composites provide the basis for the development of effective long-term gastric retention devices.

Involvement of specific calmodulin isoforms in salicylic acid-independent activation of plant disease resistance responses

The Ca2+ signal is essential for the activation of plant defense responses, but downstream components of the signaling pathway are still poorly defined. Here we demonstrate that specific calmodulin (CaM) isoforms are activated by infection or pathogen-derived elicitors and participate in Ca2+-mediated induction of plant disease resistance responses. Soybean CaM (SCaM)-4 and SCaM-5 genes, which encode for divergent CaM isoforms, were induced within 30 min by a fungal elicitor or pathogen, whereas other SCaM genes encoding highly conserved CaM isoforms did not show such response. This pathogen-triggered induction of these genes specifically depended on the increase of intracellular Ca2+ level. Constitutive expression of SCaM-4 and SCaM-5 in transgenic tobacco plants triggered spontaneous induction of lesions and induces an array of systemic acquired resistance (SAR)-associated genes. Surprisingly, these transgenic plants have normal levels of endogenous salicylic acid (SA). Furthermore, coexpression of nahG gene did not block the induction of SAR-associated genes in these transgenic plants, indicating that SA is not involved in the SAR gene induction mediated by SCaM-4 or SCaM-5. The transgenic plants exhibit enhanced resistance to a wide spectrum of virulent and avirulent pathogens, including bacteria, fungi, and virus. These results suggest that specific CaM isoforms are components of a SA-independent signal transduction chain leading to disease resistance.

Glutamine-dependent antiapoptotic interaction of human glutaminyl-tRNA synthetase with apoptosis signal-regulating kinase 1

Glutamine has been known to be an apoptosis suppressor, since it blocks apoptosis induced by heat shock, irradiation, and c-Myc overexpression. Here, we demonstrated that HeLa cells were susceptible to Fas-mediated apoptosis under the condition of glutamine deprivation. Fas ligation activated apoptosis signal-regulating kinase 1 (ASK1) and c-Jun N-terminal kinase (JNK; also known as stress-activated protein kinase (SAPK)) in Gln-deprived cells but not in normal cells, suggesting that Gln might be involved in the activity control of ASK1 and JNK/SAPK. As one of the possible mechanisms for the suppressive effect of Gln on ASK1, we investigated the molecular interaction between human glutaminyl-tRNA synthetase (QRS) and ASK1 and found the Gln-dependent association of the two molecules. While their association was enhanced by the elevation of Gln concentration, they were dissociated by Fas ligation within 5 min. The association involved the catalytic domains of the two enzymes. The ASK1 activity was inhibited by the interaction with QRS as determined by in vitro kinase and transcription assays. Finally, we have shown that QRS inhibited the cell death induced by ASK1, and this antiapoptotic function of QRS was weakened by the deprivation of Gln. Thus, the antiapoptotic interaction of QRS with ASK1 is controlled positively by the cellular concentration of Gln and negatively by Fas ligation. The results of this work provide one possible explanation for the working mechanism of the antiapoptotic activity of Gln and suggest a novel function of mammalian ARSs.

Regulation of senescence associated signaling mechanisms in chondrocytes for cartilage tissue regeneration

Adult articular chondrocytes undergo slow senescence and dedifferentiation during in vitro expansion, restricting successful cartilage regeneration. A complete understanding of the molecular signaling pathways involved in the senescence and dedifferentiation of chondrocytes is essential in order to better characterize chondrocytes for cartilage tissue engineering applications. During expansion, cell fate is determined by the change in expression of various genes in response to aspects of the microenvironment, including oxidative stress, mechanical stress, and unsuitable culture conditions. Rapid senescence or dedifferentiation not only results in the loss of the chondrocytic phenotype but also enhances production of inflammatory mediators and matrix-degrading enzymes. This review focuses on the two groups of genes that play direct and indirect roles in the induction of senescence and dedifferentiation. Numerous degenerative signaling pathways associated with these genes have been reported. Upregulation of the genes interleukin 1 beta (IL-1β), p53, p16, p21, and p38 mitogen-activated protein kinase (MAPK) is responsible for the direct induction of senescence, whereas downregulation of the genes transforming growth factor-beta (TGF-β), bone morphogenetic protein-2 (BMP-2), SRY (sex determining region Y)-box 9 (SOX9), and insulin-like growth factor-1 (IGF-1), indirectly induces senescence. In senescent and dedifferentiated chondrocytes, it was found that TGF-β, BMP-2, SOX9, and IGF-1 are downregulated, while the levels of IL-1β, p53, p16, p21, and p38 MAPK are upregulated followed by inhibition of the normal molecular functioning of the chondrocytes. This review helps to elucidate the underlying mechanism in degenerative cartilage disease, which may help to improve cartilage tissue regeneration techniques.

Plasma membrane cholesterol is a key molecule in shear stress-dependent activation of extracellular signal-regulated kinase

Shear stress, the dragging force generated by fluid flow, differentially activates extracellular signal-regulated kinase (ERK) and c-Jun NH2-terminal kinase (JNK) in bovine aortic endothelial cells (BAEC) (Jo, H., Sipos, K., Go, Y. M., Law, R., Rong, J., and McDonald, J. M. (1997) J. Biol. Chem. 272, 1395-1401). Here, we examine whether cholesterol-enriched compartments in the plasma membrane are responsible for such differential regulation. Pretreatment of BAEC with a cholesterol-binding antibiotic, filipin, did not inhibit shear-dependent activation of JNK. In contrast, filipin and other membrane-permeable cholesterol-binding agents (digitonin and nystatin), but not the lipid-binding agent xylazine, inhibited shear-dependent activation of ERK. The effect of cholesterol-binding drugs did not appear to be due to membrane permeabilization, since treatment of BAEC with a detergent, Triton X-100 which also permeabilizes membranes, did not inhibit shear-dependent activation of ERK. Furthermore, shear-dependent activation of ERK, but not JNK, was inhibited by cyclodextrin, a membrane-impermeable cholesterol-binding agent, which removes cell-surface cholesterol. Moreover, the effects of cyclodextrin were prevented by adding cholesterol during the incubation. These results indicate that cholesterol or cholesterol-sensitive compartments in the plasma membrane play a selective and essential role in activation of ERK, but not JNK, by shear stress. Although exposure to shear stress (1 h) increased the number of caveolae by 3-fold, treatment with filipin had no effect in either control or shear-exposed cells suggesting that caveolae density per se is not a crucial determinant in shear-dependent ERK activation. In summary, the current study suggests that cholesterol-sensitive microdomains in the plasma membrane, such as caveolae-like domains, play a critical role in differential activation of ERK and JNK by shear stress.

Signal transduction via the histidyl-aspartyl phosphorelay

The histidyl-aspartyl phosphorelay, formerly described as the two-component system, is the predominant mode of signal transduction in bacteria. Adaptation to environmental changes occurs through a sensor histidine protein kinase and a response regulator. The histidine protein kinase is usually a transmembrane receptor and the response regulator is a cytoplasmic protein. Together the histidyl-aspartyl phosphorelay proteins mediate reversible phosphorylation events that control downstream effectors. Following autophosphorylation at a conserved histidine residue, the histidine kinase serves as a phospho-donor for the response regulator. Once phosphorylated, the response regulator mediates changes in gene expression or cellular locomotion. The EnvZ-OmpR phosphorelay system in Escherichia coli, which monitors external osmolarity and responds by differentially modulating the expression of the OmpF and OmpC major outer membrane porins, will be described as a model system. While histidine kinases were thought to be present only in prokaryotes, they have recently been identified in eukaryotic systems. Here, we review the unique and conserved features of this growing family of signal transducers.

Activation of Bruton's tyrosine kinase (BTK) by a point mutation in its pleckstrin homology (PH) domain

Bruton's tyrosine kinase (BTK) is a nonreceptor tyrosine kinase critical for B cell development and function. Mutations in BTK result in X-linked agammaglobulinemia (XLA) in humans and X-linked immunodeficiency (xid) in mice. Using a random mutagenesis scheme, we isolated a gain-of-function mutant called BTK* whose expression drives growth of NIH 3T3 cells in soft agar. BTK* results from a single point mutation in the pleckstrin homology (PH) domain, where a Glu is replaced by Lys at residue 41. BTK* shows an increase in phosphorylation on tyrosine residues and an increase in membrane targeting. Transforming activity requires kinase activity, a putative autophosphorylation site, and a functional PH domain. Mutation of the SH2 or SH3 domains did not affect the activity of BTK*. Expression of BTK* could also relieve IL-5 dependence of a B lineage cell line. These results show that transformation activation and regulation of BTK are critically dependent on the PH domain.