Functional analysis of Tpr: identification of nuclear pore complex association and nuclear localization domains and a role in mRNA export

Tpr is a 270-kD coiled-coil protein localized to intranuclear filaments of the nuclear pore complex (NPC). The mechanism by which Tpr contributes to the structure and function of the nuclear pore is currently unknown. To gain insight into Tpr function, we expressed the full-length protein and several subdomains in mammalian cell lines and examined their effects on nuclear pore function. Through this analysis, we identified an NH2-terminal domain that was sufficient for association with the nucleoplasmic aspect of the NPC. In addition, we unexpectedly found that the acidic COOH terminus was efficiently transported into the nuclear interior, an event that was apparently mediated by a putative nuclear localization sequence. Ectopic expression of the full-length Tpr caused a dramatic accumulation of poly(A)+ RNA within the nucleus. Similar results were observed with domains that localized to the NPC and the nuclear interior. In contrast, expression of these proteins did not appear to affect nuclear import. These data are consistent with a model in which Tpr is tethered to intranuclear filaments of the NPC by its coiled coil domain leaving the acidic COOH terminus free to interact with soluble transport factors and mediate export of macromolecules from the nucleus.

The novel murine calmodulin-binding protein Sha1 disrupts mitotic spindle and replication checkpoint functions in fission yeast

Entry into mitosis is normally blocked in eukaryotic cells that have not completed replicative DNA synthesis; this ‘S-M’ checkpoint control is fundamental to the maintenance of genomic integrity. Mutants of the fission yeast Schizosaccharomyces pombe defective in the S-M checkpoint fail to arrest the cell cycle when DNA replication is inhibited and hence attempt mitosis and cell division with unreplicated chromosomes, resulting in the ‘cut’ phenotype. In an attempt to identify conserved molecules involved in the S-M checkpoint we have screened a regulatable murine cDNA library in S. pombe and have identified cDNAs that induce the cut phenotype in cells arrested in S phase by hydroxyurea. One such cDNA encodes a novel protein with multiple calmodulin-binding motifs that, in addition to its effects on the S-M checkpoint, perturbed mitotic spindle functions, although spindle pole duplication was apparently normal. Both aspects of the phenotype induced by this cDNA product, which we term Sha1 (for spindle and hydroxyurea checkpoint abnormal), were suppressed by simultaneous overexpression of calmodulin. Sha1 is structurally related to the product of the Drosophila gene abnormal spindle (asp). These data suggest that calmodulin-binding protein(s) are important in the co-ordination of mitotic spindle functions with mitotic entry in fission yeast, and probably also in multicellular eukaryotes.

High level inhibition of HIV replication with combination RNA decoys expressed from an HIV-Tat inducible vector

Intracellular immunization, an antiviral gene therapy approach based on the introduction of DNA into cells to stably express molecules for the inhibition of viral gene expression and replication, has been suggested for inhibition of HIV infection. Since the Tat and Rev proteins play a critical role in HIV regulation, RNA decoys and ribozymes of these sequences have potential as therapeutic molecular inhibitors. In the present study, we have generated several anti-HIV molecules; a tat-ribozyme, RRE, RWZ6 and TAR decoys and combinations of decoys, and tested them for inhibition of HIV-1 replication in vitro. We used T cell specific CD2 gene elements and regulatory the HIV inducible promoter to direct high level expression and a 3' UTR sequence for mRNA stabilization. We show that HIV replication was most strongly inhibited with the combination TAR + RRE decoy when compared with the single decoys or the tat-ribozyme. We also show that the Tat-inducible HIV promoter directs a higher level of steady-state transcription of decoys and inhibitors and that higher levels of expression directly relate to increased levels of inhibition of HIV infection. Furthermore, a stabilization of the 3' end of TAR + RRE inhibitor transcripts using a beta-globin 3' UTR sequence leads to an additional 15-fold increase in steady-state RNA levels. This cassette when used to express the best combination decoy inhibitor TAR + RRE, yields high level HIV inhibition for greater than 3 weeks. Taken together, both optimization for high level expression of molecular inhibitors and use of combinations of inhibitors suggest better therapeutic application in limiting the spread of HIV.

An atomic model of fimbrin binding to F-actin and its implications for filament crosslinking and regulation

Using a new procedure that combines electron-density correlation with biochemical information, we have fitted the crystal structure of the N-terminal actin-binding domain of human T-fimbrin to helical reconstructions of fimbrin-decorated actin filaments. The map locates the N-terminal calcium-binding domain and identifies actin-binding site residues on the two calponin-homology domains of fimbrin. Based on this map, we propose a model of a fimbrin crosslink in an actin bundle and its regulation by calcium.

Dimerization of P-selectin glycoprotein ligand-1 (PSGL-1) required for optimal recognition of P-selectin

Interactions between P-selectin, expressed on endothelial cells and activated platelets, and its leukocyte ligand, a homodimer termed P-selectin glycoprotein ligand-1 (PSGL-1), mediate the earliest adhesive events during an inflammatory response. To investigate whether dimerization of PSGL-1 is essential for functional interactions with P-selectin, a mutant form of PSGL-1 was generated in which the conserved membrane proximal cysteine was mutated to alanine (designated C320A). Western blotting under both denaturing and native conditions of the C320A PSGL-1 mutant isolated from stably transfected cells revealed expression of only a monomeric form of PSGL-1. In contrast to cells cotransfected with alpha1-3 fucosyltransferase-VII (FucT-VII) plus PSGL-1, K562 cells expressing FucT-VII plus C320A failed to bind COS cells transfected with P-selectin in a low shear adhesion assay, or to roll on CHO cells transfected with P-selectin under conditions of physiologic flow. In addition, C320A transfectants failed to bind chimeric P-selectin fusion proteins. Both PSGL-1 and C320A were uniformly distributed on the surface of transfected K562 cells. Thus, dimerization of PSGL-1 through the single, conserved, extracellular cysteine is essential for functional recognition of P-selectin.

Inhibition of Tat-mediated transactivation and HIV replication with Tat mutant and repressor domain fusion proteins

Strategies to inhibit the spread of HIV infection consist of a number of specific molecular approaches. Since viral production is dependent upon Tat-mediated transactivation of the HIV promoter through the Tat activating region (TAR), tat antisense RNA, anti-tat ribozymes, TAR decoys and dominant negative Tat mutant proteins have been suggested as therapeutic inhibitors. We produced and tested several Tat mutant proteins, including a newly generated form Tat delta 58, for the ability to inhibit Tat-mediated transactivation and HIV production. In addition, we generated a new Tat fusion mutant between a C-terminus truncated form of Tat (Tat delta 53) and the Drosophila Engrailed (Eng) transcription repressor domain to test the hypothesis that transcriptional repression can be targeted to the HIV promoter. This fusion mutant was also examined for its capacity to block both Tat-mediated transactivation and HIV replication. We show that three mutants Tat delta 53. Tat delta 58 and Tat delta 53/Eng result in a transdominant phenotype inhibiting wild-type Tat-mediated transactivation, and that the inhibiting potential is increased by the presence of the entire basic domain or the fusion of a repressor domain. However, only the transdominant mutants Tat delta 58 and Tat delta 53/Eng significantly inhibit HIV-1 replication after infection of transfected T cell lines. These results demonstrate the potent inhibiting activity of Tat mutants on HIV replication, and suggest a synergistic effect of Tat transdominant mutant fusion with the Drosophila Engrailed transcription repressor domain.

An sLex-deficient variant of HL60 cells exhibits high levels of adhesion to vascular selectins: further evidence that HECA-452 and CSLEX1 monoclonal antibody epitopes are not essential for high avidity binding to vascular selectins

Selectins are carbohydrate-binding cell adhesion molecules that play a key role in the initiation of inflammatory responses. Several studies have suggested that the sialylated, fucosylated tetrasaccharide sialyl Lewis X (sLex) is an important component of leukocyte ligands for E- and P-selectin. We have identified a stable variant of the HL60 cell line, HL60var, which displays a nearly complete absence of staining with several mAb directed against sLex and/or sLex-related structures. HL60var also exhibits a concomitant increase in reactivity with mAb directed against the unsialylated Lewis X (Lex/CD15) structure. Despite this sLex deficiency, HL60var binds well to both E- and P-selectin. No significant differences in expression of alpha1,3-fucosyltransferases, C2GnT (Core2 transferase), or P-selectin glycoprotein ligand-1 between HL60var and typical sLex(high) HL60 cells were detected. Although the precise molecular basis for the sLex(-/low) phenotype of HL60var remains uncertain, flow cytometric analysis with the sialic acid-specific Limax flavus lectin revealed a sharp reduction in HL60var surface sialylation. Thus, the loss in mAb reactivity may result from a loss of sialic acid residues from the mAb carbohydrate epitope. However, binding of HL60var to E- and P-selectin remains sensitive to neuraminidase treatment. Taken together, these data indicate that high levels of surface sLex and/or related epitopes are not essential for interactions with vascular selectins, implying that as yet unidentified sialylated, fucosylated structures serve as physiologically relevant ligands for E- and P-selectin.

MKK6 activates myocardial cell NF-kappaB and inhibits apoptosis in a p38 mitogen-activated protein kinase-dependent manner

In cardiac myocytes the stimulation of p38 mitogen-activated protein kinase activates a hypertrophic growth program and the induction of the cardiac-specific genes associated with this program. This study focused on determining whether these novel growth-promoting effects are accompanied by the p38-mediated inhibition of apoptosis, and if so, what signaling pathways might be responsible. Primary neonatal rat ventricular myocytes were driven into apoptosis by treatments known to induce apoptosis in other cell types, e.g. incubation with anisomycin or overexpression constitutively active MEKK-1 (MEKK-1COOH), a protein that strongly activates extracellular signal-regulated kinase and N-terminal c-Jun kinase, but not p38. Overexpression of constitutively active MKK6, MKK6 (Glu), which selectively activates p38 in cardiac myocytes, protected cells from either anisomycin- or MEKK-1COOH-induced apoptosis. This protection was blocked by SB 203580, a selective p38 inhibitor. MKK6 (Glu) also activated transcription mediated by NF-kappaB, a factor which protects other cell types from apoptosis. The activation of NF-kappaB and the protection from apoptosis mediated by MKK6 (Glu) were both blocked by SB 203580. Interestingly, overexpression of a mutant form of I-kappaBalpha, which inhibits nuclear translocation of NF-kappaB, completely blocked MKK6 (Glu)-activated NF-kappaB but had little effect on MKK6s anti-apoptotic effects. These findings suggest that, in part, the overexpression of MKK6 (Glu) may foster growth and survival of cardiac myocytes by protecting them from apoptosis in a p38-dependent manner. Additionally, while NF-kappaB is activated in myocardial cells by p38, this does not appear to be the major mechanism by which MKK6 (Glu) exerts its anti-apoptotic effects in this cell type, suggesting a novel pathway for p38-mediated protection from apoptosis.

Towards an atomic model of the thick filaments of muscle

The thick filaments of muscle and non-muscle cells are polymers of myosin molecules whose energy-transducing heads lie on the filament surface, where they interact with actin to generate force. A key structural question is how the myosin heads are arranged in the relaxed state, and how this arrangement changes on activation of contraction. We have fitted the atomic structure of the myosin head to the three-dimensional structure of myosin filaments of tarantula muscle determined by electron microscopy to produce a near-atomic model of the head arrangement. A good fit is obtained only when the two heads from a myosin molecule run along the helical tracks antiparallel to each other. Oppositely oriented heads from axially adjacent molecules in a helix interact with each other, with their nucleotide-binding pockets opposed. This arrangement, supported also by crosslinking evidence, suggests a simple mechanism for the stabilization of myosin head helices in relaxed muscle via the formation of intermolecular "dimers" of heads from axially adjacent myosin molecules.

Visualization of caldesmon on smooth muscle thin filaments

Caldesmon, a narrow, elongated actin-binding protein, is found in both nonmuscle and smooth muscle cells. It inhibits actomyosin ATPase and filament severing in vitro, and is thus a putative regulatory protein. To elucidate its function, we have used electron microscopy and three-dimensional image reconstruction to reveal the location of caldesmon on isolated smooth muscle thin filaments. Caldesmon density was clearly delineated in reconstructions and found to occur peripherally, on the extreme outer edge of actin subdomains-1 and 2, without making obvious contacts with tropomyosin strands on the inner domains of actin. When the reconstructions were fitted to the atomic model of F-actin, caldesmon appeared to cover potentially weak sites of myosin interaction with actin, while, together with tropomyosin, it flanked strong sites of myosin interaction, without covering them. These interactions are unlike those of troponin-tropomyosin and therefore inhibition of actomyosin ATPase by caldesmon-tropomyosin and by troponin-tropomyosin cannot occur in the same way. The location of caldesmon would allow it to compete with a number of cellular actin-binding proteins, including those known to sever or sequester actin.

Fibroblast growth factor-2 inhibits endothelial cell apoptosis by Bcl-2-dependent and independent mechanisms

Intact endothelium acts as a sensor and transducer of signals and also provides a nonthrombogenic surface at the blood-vascular wall interface. Hence, mechanisms that maintain the integrity of the endothelium are of interest in physiological and pathological states. In this study we show that apoptosis induced by growth factor and serum deprivation of endothelial cells occurs at all phases of the cell cycle and can be blocked by fibroblast growth factor-2 (FGF-2) independently of its mitogenic activity. As the Bcl-2 family of proteins plays a prominent role in regulating cell survival, we attempted to identify Bcl-2 homologues expressed in endothelial cells. Here we demonstrate that, in addition to the previously identified A1, four other members of the Bcl-2 family, Bcl-2, Mcl-1, Bcl-X(L), and Bax, are expressed in endothelial cells. Of these family members, only Bcl-2 is induced by FGF-2. Overexpression of Bcl-2, using a retroviral vector, protects endothelial cells from serum and growth factor deprivation. There is no difference in FGF-2-induced proliferation between Bcl-2-overexpressing cells and those transduced with the empty retroviral vector. At early time points Bcl-2 is not up-regulated, but FGF-2 still has a protective effect. However, FGF-2 protects only adherent endothelial cells but not those that are cultured in suspension. The early effect of FGF-2 is dependent on tyrosine phosphorylation but not on activation of the MAP kinase pathway. Thus, FGF-2 inhibits endothelial cell apoptosis by Bcl-2-dependent and independent mechanisms.

Resistance to diverse drugs and ultraviolet light conferred by overexpression of a novel human 26 S proteasome subunit

We have investigated the usefulness of the fission yeast Schizosaccharomyces pombe as a model organism for the discovery of novel modes of drug resistance in human cells. In fission yeast, overexpression of the essential pad1(+) gene confers pleiotropic drug resistance through a pathway involving an AP-1 transcription factor encoded by pap1(+). We have identified POH1, a human pad1 homologue that can substitute fully for pad1(+) and induce AP-1-dependent drug resistance in fission yeast. POH1 also confers P-glycoprotein-independent resistance to taxol (paclitaxel), doxorubicin, 7-hydroxystaurosporine, and ultraviolet light when transiently overexpressed in mammalian cells. Poh1 is a previously unidentified component of the human 26 S proteasome, a multiprotein complex that degrades proteins targeted for destruction by the ubiquitin pathway. Hence, Poh1 is part of a conserved mechanism that determines cellular susceptibility to cytotoxic agents, perhaps by influencing the ubiquitin-dependent proteolysis of transcription factors.

3-D image reconstruction of reconstituted smooth muscle thin filaments containing calponin: visualization of interactions between F-actin and calponin

Calponin is a putative thin filament regulatory protein of smooth muscle that inhibits actomyosin ATPase in vitro. We have used electron microscopy and three-dimensional reconstruction to elucidate the structural organization of calponin on actin and actin-tropomyosin filaments. Calponin density was clearly delineated in the reconstructions and found to occur peripherally along the long-pitch actin-helix. The main calponin mass was located over sub-domain 2 of actin, and connected axially adjacent actin monomers by binding to the "upper" and "lower" edges of sub-domains 1 of each actin. When the reconstructions were fitted to the atomic model of F-actin, calponin appeared to contact actin near the N terminus and at residues 349 to 352 close to the C terminus of sub-domain 1 on one monomer. It also touched residues 92 to 95 of sub-domain 1 on the axially neighboring actin and continued up the side of this monomer as far as residues 43 to 48 of sub-domain 2. These positions are consensus binding sites for a number of actin-associated proteins and are also near to sites of weak myosin interaction. Calponin did not appear to block strong myosin binding sites on actin. In contrast to the calponin mass which appeared monomeric in reconstructions, tropomyosin formed a continuous strand of added density along F-actin. When added to tropomyosin-containing filaments, calponin caused a shift of tropomyosin away from sub-domain 1 towards sub-domain 3 of actin, exposing strong myosin-binding sites that were previously covered by tropomyosin. This structural effect is unlike that of troponin and therefore inhibition of actomyosin ATPase by calponin and troponin cannot be strictly analogous. The location of calponin would allow it to directly compete or interact with a number of actin-binding proteins.

Expression of leukocyte fucosyltransferases regulates binding to E-selectin: relationship to previously implicated carbohydrate epitopes

E-selectin is a carbohydrate-binding endothelial cell adhesion molecule that reportedly interacts with several related sialylated and fucosylated carbohydrates. The activity of leukocyte alpha1,3-fucosyltransferases (FucT-IV or FucT-VII) is an essential step in the synthesis of E-selectin ligands. Using a panel of stably transfected hemopoietic cell lines, we have investigated the role of alpha1,3-fucosyltransferases in generating E-selectin ligands, and the relationship between adhesion to E-selectin and expression of mAb-defined carbohydrates. Expression of FucT-VII was always sufficient for binding to E- and P-selectin, while the ability of FucT-IV to construct E-selectin ligands varied among different cell types. Furthermore, FucT-IV was unable to support any binding to P-selectin in a lymphoid cell line, even when expressed at levels equivalent to those in myeloid cells. FucT-IV expression generated high levels of surface Le(x)/CD15 and CDw65, whereas expression of FucT-VII correlated with a subset of mAb-defined sialyl Lewis X (sLex)-like structures. FucT-IV-associated epitopes were present on both binding and nonbinding cells, whereas all cells that expressed FucT-VII-associated epitopes bound E-selectin. However, treatment of HL60 cells with neuraminidase destroyed FucT-VII-associated epitopes at a faster rate than E-selectin binding sites. Surface expression of a subset of mAb-defined sLex-like carbohydrates is therefore a good marker for high levels of FucT-VII activity, but these carbohydrates are not themselves required for recognition of E-selectin.

Expression of leukocyte fucosyltransferases regulates binding to E-selectin: relationship to previously implicated carbohydrate epitopes

E-selectin is a carbohydrate-binding endothelial cell adhesion molecule that reportedly interacts with several related sialylated and fucosylated carbohydrates. The activity of leukocyte alpha1,3-fucosyltransferases (FucT-IV or FucT-VII) is an essential step in the synthesis of E-selectin ligands. Using a panel of stably transfected hemopoietic cell lines, we have investigated the role of alpha1,3-fucosyltransferases in generating E-selectin ligands, and the relationship between adhesion to E-selectin and expression of mAb-defined carbohydrates. Expression of FucT-VII was always sufficient for binding to E- and P-selectin, while the ability of FucT-IV to construct E-selectin ligands varied among different cell types. Furthermore, FucT-IV was unable to support any binding to P-selectin in a lymphoid cell line, even when expressed at levels equivalent to those in myeloid cells. FucT-IV expression generated high levels of surface Le(x)/CD15 and CDw65, whereas expression of FucT-VII correlated with a subset of mAb-defined sialyl Lewis X (sLex)-like structures. FucT-IV-associated epitopes were present on both binding and nonbinding cells, whereas all cells that expressed FucT-VII-associated epitopes bound E-selectin. However, treatment of HL60 cells with neuraminidase destroyed FucT-VII-associated epitopes at a faster rate than E-selectin binding sites. Surface expression of a subset of mAb-defined sLex-like carbohydrates is therefore a good marker for high levels of FucT-VII activity, but these carbohydrates are not themselves required for recognition of E-selectin.

Polymerization of myosin on activation of rat anococcygeus smooth muscle

The in vivo state of assembly of myosin in vertebrate smooth muscle is controversial. In vitro studies on purified smooth muscle myosin show that it is monomeric (10S) under relaxing conditions and filamentous under contraction conditions. Electron microscopic and antibody labelling studies of intact smooth muscles, on the other hand, suggest that myosin is filamentous in the relaxed as well as the contracting state and that 10S myosin occurs only in trace amounts. However, birefringence, conventional EM and X-ray diffraction evidence suggests that in certain smooth muscles in vivo (e.g. rat anococcygeus), while myosin filaments exist in the relaxed state, their number increases on contraction. Here, we have used low temperature electron microscopic techniques (rapid freezing followed by freeze-substitution), which preserve labile components in close to their in vivo state, to detect any change in filament number on contraction. The results from rat anococcygeus have been compared with those from guinea pig taenia coli, in which other techniques have revealed no change in filament number. In the anococcygeus, we find evidence for a 23% increase in filament density in transverse sections of contracting muscle compared with relaxed muscle. In the taenia coli we find no change. These results are in qualitative agreement with earlier findings. They provide evidence for polymerization of myosin in contracting rat anococcygeus, and suggest that this process is subtle and occurs only in some smooth muscles.

Three-dimensional image reconstruction of reconstituted smooth muscle thin filaments: effects of caldesmon

Caldesmon inhibits actomyosin ATPase and filament sliding in vitro, and therefore may play a role in modulating smooth and non-muscle motile activities. A bacterially expressed caldesmon fragment, 606C, which consists of the C-terminal 150 amino acids of the intact molecule, possesses the same inhibitory properties as full-length caldesmon and was used in our structural studies to examine caldesmon function. Three-dimensional image reconstruction was carried out from electron micrographs of negatively stained, reconstituted thin filaments consisting of actin and smooth muscle tropomyosin both with and without added 606C. Helically arranged actin monomers and tropomyosin strands were observed in both cases. In the absence of 606C, tropomyosin adopted a position on the inner edge of the outer domain of actin monomers, with an apparent connection to sub-domain 1 of actin. In 606C-containing filaments that inhibited acto-HMM ATPase activity, tropomyosin was found in a different position, in association with the inner domain of actin, away from the majority of strong myosin binding sites. The effect of caldesmon on tropomyosin position therefore differs from that of troponin on skeletal muscle filaments, implying that caldesmon and troponin act by different structural mechanisms.

Steric-model for activation of muscle thin filaments

The structural basis of thin filament-linked regulation of muscle contraction is not yet understood. Here we have used electron microscopy and three-dimensional image reconstruction to observe the effects of Ca2+ and myosin head binding on thin filament structure, especially on the position of tropomyosin. Thin filaments isolated in EGTA were treated with Ca2+ or myosin heads (S-1) and negatively stained. Tropomyosin strands were directly visualized in electron micrographs, and distinct EGTA, Ca2+ and S-1-dependent positions were apparent in reconstructions. By fitting reconstructions to the atomic model of F-actin, clusters of amino acids on actin lying beneath tropomyosin were defined under each set of conditions. In the presence of Ca2+, tropomyosin moved 25 degrees away from its low Ca2+ position, exposing most, but not all, of the previously blocked myosin-binding sites. Saturation of filaments with myosin heads produced a further 10 degrees shift in tropomyosin position, thereby exposing the entire myosin-binding site. Our results thus suggest that full switching-on of thin filaments by reversal of steric-blocking requires both Ca2+ and the binding of myosin heads, acting in sequence. By using filaments which were partially decorated with heads, tropomyosin movement was shown to be cooperative, and the size of the actin-tropomyosin cooperative unit was estimated directly. Our results provide direct structural support for previous models of thin filament activation based on kinetics of actin-myosin interaction.

The expression of bacterial nitroreductase in transgenic mice results in specific cell killing by the prodrug CB1954

The enzyme nitroreductase, isolated from Escherichia coli B, converts CB1954 ((5-aziridin-1-yl)-2,4-dinitro-benzamide) into a cytotoxic DNA interstrand cross-linking agent. The E. coli B gene (nfnB, NTR) encoding nitroreductase (NTR) was cloned into eukaryotic expression vectors. When driven by a CMV promoter, 5-10% of the stably transfected mouse fibroblasts expressed the NTR enzyme. These cells were killed at a concentration of 20 microM CB1954 in comparison to nonexpressing cells which were killed at a much higher concentration (500 microM). We subsequently generated transgenic mice to test the prodrug system in vivo. Nitroreductase was expressed specifically in T cells driven by the control elements of the human CD2 locus. Upon CB1954 treatment, transgenic mice show extensive cell depletion in thymus and spleen (14-16% of normal cell numbers), whereas all other tissues are unaffected by prodrug administration. These results raise the possibility of using the NTR gene in anticancer therapy.

P-selectin glycoprotein ligand-1 is essential for adhesion to P-selectin but not E-selectin in stably transfected hematopoietic cell lines

P-selectin (CD62P) is a member of the selectin family of adhesion molecules involved in the regulation of leukocyte traffic. P-selectin glycoprotein ligand-1 (PSGL-1) is a mucin-like molecule that is thought to be a primary ligand for P-selectin. The interaction of P-selectin with PSGL-1 results in leukocyte rolling and recruitment of leukocytes to sites of inflammation and tissue injury. However, expression of PSGL-1 protein alone is insufficient for binding to P-selectin. Several posttranslational modifications of PSGL-1, including sialylation, sulfation, and fucosylation by alpha 1,3-fucosyltransferase(s) (FucT), are required for functional interaction with P-selectin. Recently, several groups have reported that PSGL-1 might also serve as a ligand for E-selectin. Differential posttranslational modifications of PSGL-1 may determine whether it can interact with either P- or E-selectin or both. To determine whether PSGL-1 is essential for adhesion to P- or E-selectin, we have constructed and analyzed a panel of stably transfected K562 cells. K562 cells express FucT-IV but not FucT-VII or PSGL-1, and do not bind to either E- or P-selectin. K562 cells transfected with PSGL-1 cDNA also did not bind to either P- or E-selectin. Binding to P-selectin occurred only when K562 cells were cotransfected with both FucT-VII and PSGL-1. In contrast, expression of FucT-VII alone was sufficient for E-selectin binding. These data demonstrate that expression of PSGL-1 is not required for adhesion of a stably transfected hematopoietic cell line to E-selectin, and suggest that FucT-IV alone cannot properly modify PSGL-1, expressed in transfected K562 cells, to bind P-selectin.

Thoracoscopic pleurodesis with minocycline vs talc in the porcine model

BACKGROUND

Eighteen adult pigs (Sus scrofa) underwent thoracoscopy and were placed into one of three groups: no sclerosant, talc pleurodesis, or minocycline pleurodesis.

METHODS

Animals were then sacrificed at matched time intervals. Gross inspection of the pleural cavity estimated percentage of pleural symphysis (>25% was considered substantial) and allowed assignment of a pleurodesis score based on a scale described by Bresticker. Microscopic examination evaluated degree of fibrosis as mild, moderate, or severe.

RESULTS

The talc group had significantly better pleurodesis than the minocycline group as determined by (1) the proportion of animals with substantial surface pleural symphysis (5/6 vs 1/6, p < 0.01), (2) a higher pleurodesis score (3 vs 1.3, p < 0.05), and (3) the proportion of animals with moderate fibrosis (5/6 vs 0/6, p < 0. 01).

CONCLUSIONS

The authors conclude that instillation of aerosolized talc produces significantly better fibrosis and pleural symphysis than atomized minocycline in this animal model.

A comparison between epidural anaesthesia using alkalinized solution and spinal (combined spinal/epidural) anaesthesia for elective caesarean section

In a double-blind investigation, 40 women undergoing elective lower segment caesarean section were randomly divided into two groups. Group I (n = 20) received spinal anaesthesia with 2.0 ml hyperbaric 0.5% bupivacaine using a single space combined spinal epidural technique. Group II (n = 20) received epidural anaesthesia with a local anaesthetic mixture consisting of 0.5% bupivacaine plain 10 ml and 2% lignocaine plain 10 ml to which was added 0.1 ml of adrenaline 1 in 1000 and 2 ml of 8.4% sodium bicarbonate. The mean onset times of sensory block to T4 and grade 3 motor blockade were 7.9 min and 9.5 min respectively in the spinal group, compared to 13.1 min and 16.3 min in the epidural group. These differences were both significant (P < 0.05). There was no difference between the two groups in the quality of analgesia or the incidence of hypotension and nausea. The relatively rapid onset of the pH adjusted epidural solution may provide an attractive alternative to spinal anaesthesia. Moreover, this study underlines the important role of pH adjusted epidural solutions in parturients progressing to emergency caesarean section with epidural catheters previously inserted for labour analgesia.

Polarization-dependent noise in photon-number squeezed light generated by quantum-well lasers

Amplitude noise spectra from the nonclassical output of an injection-locked low-temperature quantum-well laser analyzed along orthogonal polarization axes reveals correlated polarization-dependent noise. Using polarization-preserving balanced homodyne detection to suppress these effects, we demonstrate photon-number fluctuations 4.5 dB below the semiclassical shot-noise limit (within 95% of the expected squeezing based on the device efficiency). Polarization mixing through birefringent components and, more significantly, correlated fluctuations originating in the laser gain medium are shown to account for the observations.