Differential alternative splicing activity of isoforms of polypyrimidine tract binding protein (PTB)

Polypyrimidine tract binding protein (PTB) is an RNA-binding protein that regulates splicing by repressing specific splicing events. It also has roles in 3'-end processing, internal initiation of translation, and RNA localization. PTB exists in three alternatively spliced isoforms, PTB1, PTB2, and PTB4, which differ by the insertion of 19 or 26 amino acids, respectively, between the second and third RNA recognition motif domains. Here we show that the PTB isoforms have distinct activities upon alpha-tropomyosin (TM) alternative splicing. PTB1 reduced the repression of TM exon 3 in transfected smooth muscle cells, whereas PTB4 enhanced TM exon 3 skipping in vivo and in vitro. PTB2 had an intermediate effect. The PTB4 > PTB2 > PTB1 repressive hierarchy was observed in all in vivo and in vitro assays with TM, but the isoforms were equally active in inducing skipping of alpha-actinin exons and showed the opposite hierarchy of activity when tested for activation of IRES-driven translation. These findings establish that the ratio of PTB isoforms could form part of a cellular code that in turn controls the splicing of various other pre-mRNAs.

Small molecule peptidomimetics containing a novel phosphotyrosine bioisostere inhibit protein tyrosine phosphatase 1B and augment insulin action

Protein tyrosine phosphatase 1B (PTP1B) attenuates insulin signaling by catalyzing dephosphorylation of insulin receptors (IR) and is an attractive target of potential new drugs for treating the insulin resistance that is central to type II diabetes. Several analogues of cholecystokinin(26)(-)(33) (CCK-8) were found to be surprisingly potent inhibitors of PTP1B, and a common N-terminal tripeptide, N-acetyl-Asp-Tyr(SO(3)H)-Nle-, was shown to be necessary and sufficient for inhibition. This tripeptide was modified to reduce size and peptide character, and to replace the metabolically unstable sulfotyrosyl group. This led to the discovery of a novel phosphotyrosine bioisostere, 2-carboxymethoxybenzoic acid, and to analogues that were >100-fold more potent than the CCK-8 analogues and >10-fold selective for PTP1B over two other PTP enzymes (LAR and SHP-2), a dual specificity phosphatase (cdc25b), and a serine/threonine phosphatase (calcineurin). These inhibitors disrupted the binding of PTP1B to activated IR in vitro and prevented the loss of tyrosine kinase (IRTK) activity that accompanied PTP1B-catalyzed dephosphorylation of IR. Introduction of these poorly cell permeant inhibitors into insulin-treated cells by microinjection (oocytes) or by esterification to more lipophilic proinhibitors (3T3-L1 adipocytes and L6 myocytes) resulted in increased potency, but not efficacy, of insulin. In some instances, PTP1B inhibitors were insulin-mimetic, suggesting that in unstimulated cells PTP1B may suppress basal IRTK activity. X-ray crystallography of PTP1B-inhibitor complexes revealed that binding of an inhibitor incorporating phenyl-O-malonic acid as a phosphotyrosine bioisostere occurred with the mobile WPD loop in the open conformation, while a closely related inhibitor with a 2-carboxymethoxybenzoic acid bioisostere bound with the WPD loop closed, perhaps accounting for its superior potency. These CCK-derived peptidomimetic inhibitors of PTP1B represent a novel template for further development of potent, selective inhibitors, and their cell activity further justifies the selection of PTP1B as a therapeutic target.

Is inflammation good for the ischemic heart--perspectives beyond the ordinary

In recent years, early reperfusion of the myocardial infarct has become the mainstay of optimal therapeutic management since it limits ventricular injury and infarct expansion and improves patient survival [14]. It has become clear that reperfusion promotes effective tissue repair and decreases ventricular remodeling even under circumstances where reperfusion is effected at too late a time to limit myocardial necrosis [4]. One of the striking differences between reperfused and non-reperfused myocardial infarctions is that the early intense inflammatory reaction which ensues immediately upon reperfusion has been demonstrated to potentially extend myocardial injury [9]. Substantial evidence suggests that this inflammatory reaction is important in tissue repair, leading to an obvious paradox with regard to the role of the inflammatory reaction. This communication takes the position that inflammatory injury occurring upon reperfusion of the infarcted myocardium results from the overwhelming of tissue defenses against inflammation resulting from the sudden entry of large amounts of neutrophils to an area of infarction where chemotactic factors have built up to high concentration. However, we hypothesize that inflammation fundamentally evolved as a protective mechanism to promote tissue healing and protect jeopardized myocardium. In this presentation, we will discuss our approach and data designed to evaluate potential protective roles of the inflammatory reaction after reperfusion.

Retrograde cardiovascular angiography in infants, using a 3.6 French catheter

Diagnostic retrograde arterial catheterization in infants, and small children has been constrained by the risk of arterial thrombosis and the low flow rate of catheters less than #5 French. We performed retrograde arterial catheterization (percutaneous technique in 21 of 24 patients) on 24 infants and small children (median age 3 months, median weight 4.1 kg), using a 3.6 French performed polyethylene catheter. Systemic heparinization was used. Among the group, we performed 23 aortograms, and 4 selective injections into a bronchial artery; all angiograms were of diagnostic quality. Injection rates ranged from 3 cc/sec to 10 cc/sec (median 5 cc/sec) with a peak developed pressure of 300 PSI to 900 PSI (median 700 PSI). No catheter-related complications were encountered during the study. Four of 24 patients developed a decreased pulse, noted immediately following the catheterization; however, pulses returned to normal within 24 hours, and late blood pressure assessment revealed no abnormalities in the catheterized leg. We now recommend this catheter for infants less than 10 kg when the following angiograms are required: 1. retrograde aortography (truncus arteriosus, pulmonary atresia, aortic stenosis, coarctation, coronary anomalies) 2. selective injections of bronchial arteries 3. retrograde catheterization of surgical shunts.

Induction of the synthesis of the C-X-C chemokine interferon-gamma-inducible protein-10 in experimental canine endotoxemia

Endotoxemia is associated with a systemic inflammatory response leading to organ-specific leukocyte recruitment and tissue injury. Chemokine expression has been demonstrated in various models of sepsis and may mediate tissue infiltration with inflammatory cells. In this study we examined expression of the C-X-C chemokine interferon-gamma-inducible protein-10 (IP-10), a potent T-lymphocyte chemoattractant, in a canine model of endotoxemia and investigated mechanisms of cytokine-mediated IP-10 induction in endothelial cells. Control canine tissues showed negligible expression of IP-10 message, with the exception of the spleen. Endotoxemic dogs demonstrated a robust induction of IP-10 mRNA in the heart, lung, kidney, liver, and spleen. Immunohistochemical studies indicated that IP-10 was predominantly localized in cardiac venular endothelial cells, bronchial epithelial cells, renal mesangial cells, and in the splenic red pulp of endotoxemic dogs. In addition, IP-10 expression was associated with T-lymphocyte infiltration in canine tissues. Tumor necrosis factor-alpha (TNF-alpha) and interleukin-1 beta (IL-1 beta) induced a marked upregulation of IP-10 message in canine venular endothelial cells. IP-10 expression in TNF-alpha-stimulated endothelial cells peaked at 6 h of stimulation and returned to baseline levels after 24 h. In addition, macrophage colony-stimulating factor (M-CSF) induced a dose-dependent induction of IP-10 mRNA in canine endothelial cells. M-CSF-mediated IP-10 expression peaked after 6 h of incubation and returned to baseline levels after 24 h. Canine endotoxemia is associated with a robust early expression of IP-10 in multiple tissues. IP-10 induction may be important in regulating lymphocyte recruitment and function. TNF-alpha, IL-1 beta, and M-CSF are potent inducers of IP-10 in canine endothelial cells and may indirectly mediate lymphocyte chemotaxis and activation in inflammatory processes.

Possible steps involved in the transition to stationary adhesion of rolling neutrophils: a brief review

The transition from rolling to firm adhesion is a phenomenon frequently observed when neutrophils are interacting with activated endothelium in vitro or in vivo under physiologically relevant shear stress. The mechanisms leading to this activation are poorly understood, though selectin-dependent tethering and CD18-integrin-dependent adhesion are known to be involved. This transition may involve a sequence of interactions that trigger sufficient integrin activation to allow cell arrest under flow. Recent evidence is reviewed in support of the concept that integrin (Mac-1 and LFA-1) activation results from signaling that occurs through selectin binding, chemotactic factor stimulation, and, possibly, LFA-1 binding.

Antiorthostatic suspension for 14 days does not diminish the oxidative response of neutrophils in mice

The effects of long-term spaceflight on inflammatory responses have not been well-studied in either humans or animals. It is thus important to determine if the functions of immune and inflammatory cells are altered in models of spaceflight. One such animal model is antiorthostatic suspension (AOS), in which the experimental animal is subjected to a head-down tilt that mimics both the stress and the cephalad fluid shift experienced in spaceflight. A previous study reported that the peritoneal neutrophils from mice experiencing AOS generated less superoxide than unsuspended controls. We expanded on this study using several different stimuli and measuring the oxidative response of murine neutrophils in a variety of ways. These responses included the rate, lag period, and dose/response characteristics for superoxide generation, FACS analysis with dihydrodichlorofluorescein as a substrate, and a chemiluminescence response with luminol as a substrate. We also examined phagocytosis of three different microorganisms. While some effects of orthostatic suspension (attributable to the stress of the apparatus) were observed, no clear effects of AOS on oxidative function of the peritoneal neutrophils were seen.

Pathophysiologic importance of E- and L-selectin for neutrophil-induced liver injury during endotoxemia in mice

Neutrophils can cause parenchymal cell injury in the liver during ischemia-reperfusion and endotoxemia. Neutrophils relevant for the injury accumulate in sinusoids, transmigrate, and adhere to hepatocytes. To investigate the role of E- and L-selectin in this process, C3Heb/FeJ mice were treated with 700 mg/kg galactosamine and 100 microgram/kg endotoxin (Gal/ET). Immunogold labeling verified the expression of E-selectin on sinusoidal endothelial cells 4 hours after Gal/ET injection. In addition, Gal/ET caused up-regulation of Mac-1 (CD11b/CD18) and shedding of L-selectin from circulating neutrophils. Gal/ET induced hepatic neutrophil accumulation (422 +/- 32 polymorphonuclear leukocytes [PMN]/50 high power fields [HPF]) and severe liver injury (plasma alanine transaminase [ALT] activities: 4,120 +/- 960 U/L; necrosis: 44 +/- 3%) at 7 hours. Treatment with an anti-E-selectin antibody (3 mg/kg, intravenously) at the time of Gal/ET administration did not significantly affect hepatic neutrophil accumulation and localization. However, the anti-E-selectin antibody significantly attenuated liver injury as indicated by reduced ALT levels (-84%) and 43% less necrotic hepatocytes. In contrast, animals treated with an anti-L-selectin antibody or L-selectin gene knock out mice were not protected against Gal/ET-induced liver injury. However, E-, L-, and P-selectin triple knock out mice showed significantly reduced liver injury after Gal/ET treatment as indicated by lower ALT levels (-65%) and reduced necrosis (-68%). Previous studies showed that circulating neutrophils of E-selectin-overexpressing mice are primed and activated similar to neutrophils adhering to E-selectin in vitro. Therefore, we conclude that blocking E-selectin or eliminating this gene may have protected against Gal/ET-induced liver injury in vivo by inhibiting the full activation of neutrophils during the transmigration process.

The hind wing of the desert locust (Schistocerca gregaria Forskal). III. A finite element analysis of a deployable structure

Finite element analysis is used to model the automatic cambering of the locust hind wing during promotion: the umbrella effect. It was found that the model required a high degree of sophistication before replicating the deformations found in vivo. The model has been validated using experimental data and the deformations recorded both in vivo and ex vivo. It predicts that even slight modifications to the geometrical description used can lead to significant changes in the deformations observed in the anal fan. The model agrees with experimental data and produces deformations very close to those seen in free-flying locusts. The validated model may be used to investigate the varying geometries found in orthopteran anal fans and the stresses found throughout the wing when loaded.

The hind wing of the desert locust (Schistocerca gregaria Forskal). II. Mechanical properties and functioning of the membrane

As part of an investigation of the functional mechanics of the hind wing of the desert locust Schistocerca gregaria, the Young's modulus of the membrane was measured using a newly developed universal materials test machine capable of testing very small specimens of cuticle, down to 1 mm gauge length. Strain was measured optically. Specimens were cut from various locations around the wing and tested under controlled temperature and humidity. The modulus of the membrane was typically between 1 and 5 GPa, but both this and the membrane thickness varied around the wing, with the remigium and the anal fan showing markedly different properties. The membrane was tested for chitin using two methods: a gas pyrolysis/mass spectrometry assay, and a gold-labelled immunoassay specific to chitin. None was detected, and the membrane may consist of epicuticle alone. The wings were examined for evidence of crystalline material using standard polarising microscopy and an advanced technique that distinguishes between three components of the polarised image. Birefringence was detected in the membrane of the anterior part of the wing, but vanished when the membrane was separated from the surrounding veins, suggesting that it was due to pre-stress rather than to ultrastructure. The implications are discussed.

The hind wing of the desert locust (Schistocerca gregaria Forskal). I. Functional morphology and mode of operation

Detailed morphological investigation, mechanical testing and high-speed cinematography and stroboscopic examination of desert locusts, Schistocerca gregaria, in flight show that their hind wings are adapted to deform cyclically and automatically through the wing stroke and that the deformations are subtly dependent on the wings' structure: their shape, venation and vein design and the local properties of the membrane. The insects predominantly fly fast forwards, generating most force on the downstroke, and the hind wings generate extra lift by peeling apart at the beginning of the downstroke and by developing a cambered section during the stroke's translation phase through the ‘umbrella effect’ - an automatic consequence of the active extension of the wings' expanded posterior fan. Bending experiments indicate that most of the hind wing is more rigid to forces from below than from above and demonstrate that the membrane acts as a stressed skin to stiffen the structure.

Syntaxin 7 is localized to late endosome compartments, associates with Vamp 8, and Is required for late endosome-lysosome fusion

Protein traffic from the cell surface or the trans-Golgi network reaches the lysosome via a series of endosomal compartments. One of the last steps in the endocytic pathway is the fusion of late endosomes with lysosomes. This process has been reconstituted in vitro and has been shown to require NSF, alpha and gamma SNAP, and a Rab GTPase based on inhibition by Rab GDI. In Saccharomyces cerevisiae, fusion events to the lysosome-like vacuole are mediated by the syntaxin protein Vam3p, which is localized to the vacuolar membrane. In an effort to identify the molecular machinery that controls fusion events to the lysosome, we searched for mammalian homologues of Vam3p. One such candidate is syntaxin 7. Here we show that syntaxin 7 is concentrated in late endosomes and lysosomes. Coimmunoprecipitation experiments show that syntaxin 7 is associated with the endosomal v-SNARE Vamp 8, which partially colocalizes with syntaxin 7. Importantly, we show that syntaxin 7 is specifically required for the fusion of late endosomes with lysosomes in vitro, resulting in a hybrid organelle. Together, these data identify a SNARE complex that functions in the late endocytic system of animal cells.

IL-10 is induced in the reperfused myocardium and may modulate the reaction to injury

Reperfusion of the ischemic myocardium is associated with a dramatic inflammatory response leading to TNF-alpha release, IL-6 induction, and subsequent neutrophil-mediated cytotoxic injury. Because inflammation is also an important factor in cardiac repair, we hypothesized the presence of components of the inflammatory reaction with a possible role in suppressing acute injury. Thus, we investigated the role of IL-10, an anti-inflammatory cytokine capable of modulating extracellular matrix biosynthesis, following an experimental canine myocardial infarction. Using our canine model of myocardial ischemia and reperfusion, we demonstrated significant up-regulation of IL-10 mRNA and protein in the ischemic and reperfused myocardium. IL-10 expression was first detected at 5 h and peaked following 96-120 h of reperfusion. In contrast, IL-4 and IL-13, also associated with suppression of acute inflammation and macrophage deactivation, were not expressed. In the ischemic canine heart, CD5-positive lymphocytes were the predominant source of IL-10 in the myocardial infarct. In the absence of reperfusion, no significant induction of IL-10 mRNA was noted. In addition, IL-12, a Th1-related cytokine associated with macrophage activation, was not detected in the ischemic myocardium. In vitro experiments demonstrated late postischemic cardiac-lymph-induced tissue inhibitor of metalloproteinases (TIMP)-1 mRNA expression in isolated canine mononuclear cells. This effect was inhibited when the incubation contained a neutralizing Ab to IL-10. Our findings suggest that lymphocytes infiltrating the ischemic and reperfused myocardium express IL-10 and may have a significant role in healing by modulating mononuclear cell phenotype and inducing TIMP-1 expression.

Laser diode facet modal reflectivity measurements

A simple and accurate method for measuring the front facet modal reflectivity of a Fabry-Perot laser diode is presented. In this method, optical feedback from an external mirror of known reflectivity, R(ext), is used to alter the laser diode threshold current. The effect of the external mirror and front facet reflectivities on the threshold current then allows for a measurement of the front facet modal reflectivity of the laser diode and is theoretically and experimentally studied. This method was used to measure a facet reflectivity of R(2) = 0.0151(+0.0018/-0.0032) [R(2) = 0.00592(+0.00085/-0.00123)] for a commercially antireflection-coated facet of a laser diode with a center wavelength of 795 nm (935 nm). The results of the reflectivity measurements based on the threshold current as a function of the external mirror reflectivity are compared with the results of the reflectivity measurements based on modulation depth of the optical spectrum [IEEE J. Quantum Electron. QE-19, 493 (1983)].

Alternative pre-mRNA splicing: the logic of combinatorial control

Alternative splicing of mRNA precursors is a versatile mechanism of gene expression regulation that accounts for a considerable proportion of proteomic complexity in higher eukaryotes. Its modulation is achieved through the combinatorial interplay of positive and negative regulatory signals present in the RNA, which are recognized by complexes composed of members of the hnRNP and SR protein families.

LFA-1 (CD11a/CD18) triggers hydrogen peroxide production by canine neutrophils

The respiratory burst of neutrophils stimulated by chemotactic factors is markedly augmented by Mac-1-dependent adhesion such as the interaction of Mac-1 (CD11b/CD18) with intercellular adhesion molecule-1 (ICAM-1; CD54) expressed on the surface of parenchymal cells (e.g., cardiac myocytes). In the current study, we evaluate the hypothesis that lymphocyte function-associated antigen-1 (LFA-1; CD11a/CD18) can also trigger the respiratory burst in neutrophils. To isolate LFA-1/ICAM-1 interactions from Mac-1/ ICAM-1 interactions, full-length chimeric ICAM-1 was developed and expressed in L cells with domains 1 and 2 from canine ICAM-1 and domains 3-5 from human ICAM-1 (C1,2;H3-5). We have shown that canine neutrophils do not bind to human ICAM-1. We demonstrated that chimeric ICAM-1 C1,2;H3-5 supported only LFA-1-dependent adhesion of canine neutrophils and that such adhesion triggered rapid onset of H2O2 production from canine neutrophils. The following seven experimental conditions distinguished LFA-1-dependent H2O2 production from Mac-1-dependent production: It did not require exogenous chemotactic stimulation; H2O2 release was more rapid, but the amount released was <40% of that mediated by Mac-1 adhesion; it was inhibited by anti-CD11a and anti-ICAM-1 antibodies; in contrast to that mediated by Mac-1, it was not inhibited by anti-CD11b antibody, neutrophil inhibitory factor (NIF), or cytochalasin B or H7. Thus, canine neutrophils seem to be able to utilize two members of the beta2 integrin family to interact with ICAM-1 and signal H2O2 production, with LFA-1 at an early stage without prior chemotactic stimulation and Mac-1 at a later stage requiring chemotactic stimulation.

Preferential sites for stationary adhesion of neutrophils to cytokine-stimulated HUVEC under flow conditions

Neutrophils form CD18-dependent adhesions to endothelial cells at sites of inflammation. This phenomenon was investigated under conditions of flow in vitro using isolated human neutrophils and monolayers of HUVEC. The efficiency of conversion of neutrophil rolling to stable adhesion in this model was >95%. Neither anti-CD11a nor anti-CD11b antibodies significantly altered the extent of this conversion, but a combination of both antibodies inhibited the arrest of rolling neutrophils by >95%. The efficiency of transendothelial migration of arrested neutrophils was >90%, and the site of transmigration was typically <6 microm from the site of stationary adhesion. Approximately 70% of transmigrating neutrophils migrated at tricellular corners between three adjacent endothelial cells. A model of neutrophils randomly distributed on endothelium predicted a significantly greater migration distance to these preferred sites of transmigration, but a model of neutrophils adhering to endothelial borders is consistent with observed distances. It appears that stable adhesions form very near tricellular corners.

Multilocus interactions restrict gene introgression in interspecific populations of polyploid Gossypium (cotton)

Experimental advanced-generation backcross populations contain individuals with genomic compositions similar to those resulting from interspecific hybridization in nature. By applying a detailed restriction fragment length polymorphism (RFLP) map to 3662 BC3F2 plants derived from 24 different BC1 individuals of a cross between Gossypium hirsutum and G. barbadense, large and widespread deficiencies of donor (G. barbadense) chromatin were found, and seven independent chromosomal regions were entirely absent. This skewed chromatin transmission is best accounted for by multilocus epistatic interactions affecting chromatin transmission. The observed frequencies of two-locus genotypes were significantly different from Mendelian expectations about 26 times more often than could be explained by chance (P < or = 0.01). For identical pairs of loci, different two-locus genotypes occurred in excess in different BC3 families, implying the existence of higher-order interlocus interactions beyond the resolution of these data. Some G. barbadense markers occurred more frequently than expected by chance, indicating that genomic interactions do not always favor host chromatin. A preponderance of interspecific allelic interactions involved one locus each in the two different subgenomes of (allotetraploid) Gossypium, thus supporting several other lines of evidence suggesting that intersubgenomic interactions contribute to unique features that distinguish tetraploid cotton from its diploid ancestors.

Expression of adhesion molecules in kidney with experimental chronic obstructive uropathy: the pathogenic role of ICAM-1 and VCAM-1

BACKGROUND

Chronic obstructive uropathy induced by maintained unilateral ureter ligation in the rat is characterized morphologically by interstitial inflammation, interstitial fibrosis, and tubular atrophy. Infiltrating mononuclear inflammatory cells, particularly T lymphocytes and macrophages, may contribute to the progression of this lesion by mediating tubular injury and by the activation of interstitial fibroblasts, with resultant tubular atrophy and interstitial fibrosis, respectively. Altered expression and activation of adhesion molecules by leukocytes, vascular endothelial cells, and parenchymal cells likely contributes both to the infiltration of inflammatory cells into the tubulointerstitial compartment and to the interaction of activated inflammatory cells with parenchymal cells.

METHODS

In the current study, we examined changes in the expression of intercellular adhesion molecule-1 (ICAM-1) and vascular cell adhesion molecule-1 (VCAM-1) in a 90-day model of maintained unilateral ureter ligation in male Sprague-Dawley rats.

RESULTS

Rat kidneys showed constitutive expression of ICAM-1 mRNA and constitutive immunostaining for ICAM-1 in peritubular capillaries, glomeruli, and a small percentage of cortical tubules. Ureter ligation resulted in a rapid increase in ICAM-1 mRNA, which was almost 2-fold greater than those of the contralateral and control kidneys as early as 3 h and which was maintained at a 4- to 6-fold higher level in the ligated vs. contralateral kidneys throughout the entire 90-day time course. There was a marked increase in ICAM-1 immunostaining within the tubular epithelium, with up to 80% of both cortical and medullary tubular cross-sections showing strong apical immunostaining from day 6 to 25, with a subsequent decrease throughout the remainder of the experiment. ICAM-1 immunostaining in the expanding interstitium in the ligated kidneys showed a gradual increase throughout the duration of the experiment. In contrast, glomerular immunostaining for ICAM-1 was decreased in the ligated compared to the contralateral kidneys throughout the entire experiment. There was a later but prominent increase in VCAM-1 mRNA in ligated kidneys, which was first evident at 2 days and which was maintained 2- to 10-fold greater than the contralateral kidneys throughout the entire time course. VCAM-1 immunostaining increased in the expanding interstitium, but decreased in glomeruli in obstructed vs. contralateral kidneys. Tubular staining for VCAM-1 did not change after ureter ligation.

CONCLUSION

Increased ICAM-1 and VCAM-1 may contribute to the prominent inflammatory cell infiltration in the chronic tubulointerstitial nephritis accompanying maintained unilateral ligation. Tubule expression of ICAM-1, which occurs during a similar time course as previously documented for tubular cell proliferation and especially tubular cell apoptosis in this model, may contribute to injurious interactions of activated inflammatory cells with tubular epithelium.

Identification of a C-terminal cdc25 sequence required for promotion of germinal vesicle breakdown

Glutathione S-transferase (GST)-cdc25B(31-566) induced germinal vesicle breakdown (GVBD) when microinjected into Xenopus oocytes. Purified, N-terminally truncated forms of cdc25B did not induce GVBD, even though many had phosphatase activity and activated cdc2 in vitro. N-terminally truncated forms of cdc25B inhibited induction of GVBD by longer forms of the enzyme suggesting a direct interaction in vivo. cdc25B(356-556), but not cdc25B(364-529), inhibited GVBD induction by GST-cdc25B(31-566) suggesting that a region of cdc25B near to the C-terminus was responsible for the inhibition. To determine the region of peptide sequence that was inhibitory, cdc25B(356-556) was subjected to proteolysis with endoproteinase lys-C. Following a demonstration that the resulting peptide mixture inhibited GST-cdc25B-dependent GVBD, a series of peptides spanning amino acids at the C-terminus were synthesized. The peptide TRSWAGERSR inhibited GVBD induced by GST-cdc25B. An alanine scan of the peptide revealed residues critical for GVBD inhibition, and site-directed mutagenesis of the corresponding residues in GST-cdc25B(31-566) eliminated its ability to induce GVBD. These results demonstrate that a cdc25B C-terminal domain, involved in dominant-negative inhibition of GVBD-competent cdc25B, is required for induction of GVBD following microinjection into oocytes.

Neutrophil tethering on E-selectin activates beta 2 integrin binding to ICAM-1 through a mitogen-activated protein kinase signal transduction pathway

On inflamed endothelium selectins support neutrophil capture and rolling that leads to firm adhesion through the activation and binding of beta 2 integrin. The primary mechanism of cell activation involves ligation of chemotactic agonists presented on the endothelium. We have pursued a second mechanism involving signal transduction through binding of selectins while neutrophils tether in shear flow. We assessed whether neutrophil rolling on E-selectin led to cell activation and arrest via beta 2integrins. Neutrophils were introduced into a parallel plate flow chamber having as a substrate an L cell monolayer coexpressing E-selectin and ICAM-1 (E/I). At shears >/=0.1 dyne/cm2, neutrophils rolled on the E/I. A step increase to 4.0 dynes/cm2 revealed that approximately 60% of the interacting cells remained firmly adherent, as compared with approximately 10% on L cells expressing E-selectin or ICAM-1 alone. Cell arrest was dependent on application of shear and activation of Mac-1 and LFA-1 to bind ICAM-1. Firm adhesion was inhibited by blocking E-selectin, L-selectin, or PSGL-1 with Abs and by inhibitors to the mitogen-activated protein kinases. A chimeric soluble E-selectin-IgG molecule specifically bound sialylated ligands on neutrophils and activated adhesion that was also inhibited by blocking the mitogen-activated protein kinases. We conclude that neutrophils rolling on E-selectin undergo signal transduction leading to activation of cell arrest through beta 2 integrins binding to ICAM-1.

Shear and time-dependent changes in Mac-1, LFA-1, and ICAM-3 binding regulate neutrophil homotypic adhesion

We examined the relative contributions of LFA-1, Mac-1, and ICAM-3 to homotypic neutrophil adhesion over the time course of formyl peptide stimulation at shear rates ranging from 100 to 800 s-1. Isolated human neutrophils were sheared in a cone-plate viscometer and the kinetics of aggregate formation was measured by flow cytometry. The efficiency of cell adhesion was computed by fitting the aggregate formation rates with a model based on two-body collision theory. Neutrophil homotypic adhesion kinetics varied with shear rate and was most efficient at 800 s-1, where approximately 40% of the collisions resulted in adhesion. A panel of blocking Abs to LFA-1, Mac-1, and ICAM-3 was added to assess the relative contributions of these molecules. We report that 1) LFA-1 binds ICAM-3 as its primary ligand supporting homotypic adhesion, although the possibility of other ligands was also detected. 2) Mac-1 binding to an unidentified ligand supports homotypic adhesion with an efficiency comparable to LFA-1 at low shear rates of approximately 100 s-1. Above 300 s-1, however, Mac-1 and not LFA-1 were the predominant molecules supporting cell adhesion. This is in contrast to neutrophil adhesion to ICAM-1-transfected cells, where LFA-1 binds with a higher avidity than Mac-1 to ICAM-1. 3) Following stimulation, the capacity of LFA-1 to support aggregate formation decreases with time at a rate approximately 3-fold faster than that of Mac-1. The results suggest that the relative contributions of beta2 integrins and ICAM-3 to neutrophil adhesion is regulated by the magnitude of fluid shear and time of stimulus over a range of blood flow conditions typical of the venular microcirculation.