Acquired Factor XI Deficiency in Systemic Lupus erythematosus

A variety of coagulation abnormalities has been described in systemic lupus erythematosus (SLE). We report a unique SLE patient with an acquired factor XI deficiency. The low factor XI levels were not due to a classical coagulation inhibitor, but to a plasma factor (probably an immunoglobulin) that selectively bound factor XI. The factor XI deficiency improved after treatment with corticosteroids. Thus it is possible that in SLE immune complexes may bind clotting factors making them unavailable for use in the coagulation cascade.

The Ex Vivo Effect of Preadsorbed Vitronectin on Platelet Activation

The activation of ex vivo canine platelets by preadsorbed vitronectin (VN) was sensitive not only to the polymer substrate utilized but also to the adsorption conditions employed. Lower levels of maximal platelet deposition were obtained for VN-coated silicone rubber (SR) than for other VN-coated substrates with comparable levels of adsorbed VN, but this effect was diminished with increased residence time of VN on the SR surface. Submonolayer and monolayer surface concentrations of VN elicited similar maximal levels of platelet deposition at both short (<3 h) and long (>12 h) residence times, but thrombi were larger and more dense for the submonolayer surface concentrations. VN was also more effective in forming thrombi when adsorbed sequentially before albumin instead of after albumin. To further examine these differences in the nature of adsorbed VN between substrates and adsorption conditions, sodium dodecyl sulfate (SDS) elutability measurements and Fourier transform infrared spectroscopy with attenuated total reflectance optics (FTIR-ATR) evaluations of the adsorbed protein were performed. An SDS solution was able to remove a greater percentage of the VN which was adsorbed to a submonolayer than a monolayer surface concentration when SDS displacement was initiated immediately after adsorption was terminated. However, if the adsorbed protein was allowed to reside on the surface for a length of time before the introduction of the SDS displacing media, a greater percentage of the monolayer surface concentration was removed. The submonolayer surface concentration may be better able to increase its strength of contact with the surface during the added residence time than the monolayer surface concentration. FTIR-ATR spectra of VN showed less structural alterations when it was adsorbing to SR than to a segmented polyurethane, a more thrombogenic material when coated with VN. Thus, the ability of VN to stimulate thrombus formation appeared to correlate with the percentage of VN which was nonelutable by SDS and the amount of structural alterations observed by FTIR-ATR, both of which are indications of its extent of contact with the surface.

IL-5-stimulated eosinophils adherent to periostin undergo stereotypic morphological changes and ADAM8-dependent migration

BACKGROUND

IL-5 causes suspended eosinophils to polarize with filamentous (F)-actin and granules at one pole and the nucleus in a specialized uropod, the "nucleopod," which is capped with P-selectin glycoprotein ligand-1 (PSGL-1). IL-5 enhances eosinophil adhesion and migration on periostin, an extracellular matrix protein upregulated in asthma by type 2 immunity mediators.

OBJECTIVE

Determine how the polarized morphology evolves to foster migration of IL-5-stimulated eosinophils on a surface coated with periostin.

METHODS

Blood eosinophils adhering to adsorbed periostin were imaged at different time points by fluorescent microscopy, and migration of eosinophils on periostin was assayed.

RESULTS

After 10 minutes in the presence of IL-5, adherent eosinophils were polarized with PSGL-1 at the nucleopod tip and F-actin distributed diffusely at the opposite end. After 30-60 minutes, the nucleopod had dissipated such that PSGL-1 was localized in a crescent or ring away from the cell periphery, and F-actin was found in podosome-like structures. The periostin layer, detected with monoclonal antibody Stiny-1, shown here to recognize the FAS1 4 module, was cleared in wide areas around adherent eosinophils. Clearance was attenuated by metalloproteinase inhibitors or antibodies to disintegrin metalloproteinase 8 (ADAM8), a major eosinophil metalloproteinase previously implicated in asthma pathogenesis. ADAM8 was not found in podosome-like structures, which are associated with proteolytic activity in other cell types. Instead, immunoblotting demonstrated proteoforms of ADAM8 that lack the cytoplasmic tail in the supernatant. Anti-ADAM8 inhibited migration of IL-5-stimulated eosinophils on periostin.

CONCLUSIONS AND CLINICAL RELEVANCE

Migrating IL-5-activated eosinophils on periostin exhibit loss of nucleopodal features and appearance of prominent podosomes along with clearance of the Stiny-1 periostin epitope. Migration and epitope clearance are both attenuated by inhibitors of ADAM8. We propose, therefore, that eosinophils remodel and migrate on periostin-rich extracellular matrix in the asthmatic airway in an ADAM8-dependent manner, making ADAM8 a possible therapeutic target.

IL-3 up-regulates and activates human eosinophil CD32 and αMβ2 integrin causing degranulation

BACKGROUND

Eosinophils contribute to the pathogenesis of multiple diseases, including asthma. Treatment with antibodies targeting IL-5 or IL-5 receptor α reduces the frequency of asthma exacerbations. Eosinophil receptors for IL-5 share a common ß-chain with IL-3 and GM-CSF receptors. We recently reported that IL-3 is more potent than IL-5 or GM-CSF in maintaining the ERK/p90S6K/RPS6 ribosome-directed signaling pathway, leading to increased protein translation.

OBJECTIVE

We aimed to determine disease-relevant consequences of prolonged eosinophil stimulation with IL-3.

RESULTS

Human blood eosinophils were used to establish the impact of activation with IL-3 on IgG-driven eosinophil degranulation. When compared to IL-5, continuing exposure to IL-3 further induced degranulation of eosinophils on aggregated IgG via increased production and activation of both CD32 (low affinity IgG receptor) and αMß2 integrin. In addition, unlike IL-5 or GM-CSF, IL-3 induced expression of CD32B/C (FCGRIIB/C) subtype proteins, without changing CD32A (FCGRIIA) protein and CD32B/C mRNA expression levels. Importantly, these in vitro IL-3-induced modifications were recapitulated in vivo on airway eosinophils.

CONCLUSIONS AND CLINICAL RELEVANCE

We observed for the first time upregulation of CD32B/C on eosinophils, and identified IL-3 as a potent inducer of CD32- and αMß2-mediated eosinophil degranulation.

A mix of S and ΔS variants of STAT3 enable survival of activated B-cell-like diffuse large B-cell lymphoma cells in culture

Activated B-cell-like diffuse large B-cell lymphoma (ABC DLBCL) is characterized by increased expression and activator of signal transducer and activator of transcription 3 (STAT3). ABC DLBCL cells require STAT3 for growth in culture. In ABC DLBCL cells, eosinophils and perhaps all cells, four variant STAT3 mRNAs (Sα, ΔSα, Sβ and ΔSβ) are present as a result of two alternative splicing events, one that results in the inclusion of a 55-residue C-terminal transactivation domain (α) or a truncated C-terminal domain with 7 unique residues (β) and a second that includes (S) or excludes (ΔS) the codon for Ser-701 in the linker between the SH2 and C-terminal domains. A substantial literature indicates that both α and β variants are required for optimal STAT3 function, but nothing is known about functions of ΔS variants. We used a knockdown/re-expression strategy to explore whether survival of ABC DLBCL cells requires that the four variants be in an appropriate ratio. No single variant rescued survival as well as STAT3Sα-C, Sα with activating mutations (A661C and N663C) in the SH2 domain. Better rescue was achieved when all four variants were re-expressed or Sα and ΔSα or Sβ and ΔSβ were re-expressed in pairs. Rescue correlated with expression of STAT3-sensitive genes NFKBIA and NFKBIZ. We consider a variety of explanations why a mix of S and ΔS variants of STAT3 should enable survival of ABC DLBCL cells.

Anti-IL-5 attenuates activation and surface density of β(2) -integrins on circulating eosinophils after segmental antigen challenge

BACKGROUND

IL-5 activates α(M) β(2) integrin on blood eosinophils in vitro. Eosinophils in bronchoalveolar lavage (BAL) following segmental antigen challenge have activated β(2) -integrins.

OBJECTIVE

To identify roles for IL-5 in regulating human eosinophil integrins in vivo.

METHODS

Blood and BAL eosinophils were analysed by flow cytometry in ten subjects with allergic asthma who underwent a segmental antigen challenge protocol before and after anti-IL-5 administration.

RESULTS

Blood eosinophil reactivity with monoclonal antibody (mAb) KIM-127, which recognizes partially activated β(2) -integrins, was decreased after anti-IL-5. Before anti-IL-5, surface densities of blood eosinophil β(2) , α(M) and α(L) integrin subunits increased modestly post challenge. After anti-IL-5, such increases did not occur. Before or after anti-IL-5, surface densities of β(2) , α(M) , α(L) and α(D) and reactivity with KIM-127 and mAb CBRM1/5, which recognizes high-activity α(M) β(2) , were similarly high on BAL eosinophils 48 h post-challenge. Density and activation state of β(1) -integrins on blood and BAL eosinophils were not impacted by anti-IL-5, even though anti-IL-5 ablated a modest post-challenge increase on blood or BAL eosinophils of P-selectin glycoprotein ligand-1 (PSGL-1), a receptor for P-selectin that causes activation of β(1) -integrins. Forward scatter of blood eosinophils post-challenge was less heterogeneous and on the average decreased after anti-IL-5; however, anti-IL-5 had no effect on the decreased forward scatter of eosinophils in post-challenge BAL compared with eosinophils in blood. Blood eosinophil KIM-127 reactivity at the time of challenge correlated with the percentage of eosinophils in BAL post-challenge.

CONCLUSION AND CLINICAL RELEVANCE

IL-5 supports a heterogeneous population of circulating eosinophils with partially activated β(2) -integrins and is responsible for up-regulation of β(2) -integrins and PSGL-1 on circulating eosinophils following segmental antigen challenge but has minimal effects on properties of eosinophils in BAL. Dampening of β(2) -integrin function of eosinophils in transit to inflamed airway may contribute to the decrease in lung inflammation caused by anti-IL-5.

Structures of thrombospondins

Thrombospondins are large secreted, multimodular, calcium-binding glycoproteins that have complex roles in mediating cellular processes. Determination of high-resolution structures of thrombospondins has revealed unique and interesting protein motifs. Here, we review this progress and discuss implications for function. By combining structures of modules from thrombospondins and related extracellular proteins it is now possible to prepare an overall model of the structure of thrombospondin-1 and thrombospondin-2 and discern features of other thrombospondins. (Part of a multi-author Review).

Role of fibronectin assembly in platelet thrombus formation

Fibronectin is a component of subendothelial matrices and abundant in plasma. A role of fibronectin in thrombogenesis has been suspected for three decades. Soluble fibronectin is assembled by adherent fibroblasts and platelets and thus converted to an insoluble form that mediates cell adhesion. Recently, in vivo studies using intravital videomicroscopy revealed that plasma fibronectin is important for stabilization of platelet aggregates after vascular injury. This review goes over roles of fibronectin in platelet functions with a focus on fibronectin assembly within developing platelet thrombi.

Characterization of fibronectin assembly by platelets adherent to adsorbed laminin-111

BACKGROUND

Various types of laminin (LN) are ubiquitous components of basement membrane and exposed to blood upon localized damage of vascular endothelial cells. Fibronectin is a plasma protein that is insolubilized into fibrils in a regulated fashion by, for example, lysophosphatidic acid (LPA)-stimulated fibroblasts or platelets spread on supportive adhesive ligands.

OBJECTIVE

To study assembly of plasma fibronectin by LPA-activated platelets adherent to LN-111 via alpha6beta1 integrin.

RESULTS

Platelets adherent to LN-111-bound plasma fibronectin or its N-terminal 70 kD fragment in fibrillar arrays at the periphery of spread platelets under static but not shear conditions. Formation of fibronectin arrays under static conditions was inhibited by co-incubation with the N-terminal 70 kD fragment or with a 49-amino acid peptide that binds to the N-terminal region of fibronectin. Approximately 7000 fibronectin dimers bound per adherent platelet with a K(d) of 50 nm. Bound 70 kD fragment was readily solubilized with deoxycholate (DOC), whereas bound fibronectin became progressively insoluble. Bound 70 kD fragment became resistant to DOC extraction after treatment with a cell-impermeable, reducible crosslinker. Crosslinked 70 kD fragment was found in a high molecular weight complex. As with fibroblasts, signaling molecules modulating actin cytoskeletal organization controlled expression of binding sites for the N-terminal 70 kD region of fibronectin on adherent platelets.

CONCLUSIONS

These results indicate that platelets adherent to LN-111 via alpha(6)beta(1) support subsequent assembly of fibronectin, but possibly only under conditions of intermittent or stagnant blood flow.

Extracellular matrix molecules regulate endothelial cell migration stimulated by lysophosphatidic acid

BACKGROUND

Lysophosphatidic acid (LPA) and sphingosine 1-phosphate (S1P) are lipids that bind G-protein coupled receptors and differentially promote transmigration of endothelial cells.

OBJECTIVE

To determine if endothelial cell transmigration stimulated by LPA, not S1P, is dependent on the extracellular matrix.

METHODS

Bovine pulmonary artery (BPAE) endothelial cell transmigration and locomotion were measured using a modified-Boyden chamber and video microscopy, respectively. Results were related to strength of adhesion and characteristics of cell adhesive contacts.

RESULTS AND CONCLUSIONS

BPAEs responded to LPA by transmigration through gelatin- or collagen-coated filters, but not through fibronectin-, vitronectin-, or fibrinogen-coated filters. Fewer cells adhered to collagen or gelatin than to fibronectin in a static cell adhesion assay or after application of a g-force to detach cells. Video microscopy revealed that S1P stimulates large lamellipodia on two-dimensional fibronectin substrate. LPA stimulated lamellipodia on fibronectin, but the trailing edge remained attached, resulting in sting ray-shaped cells in video microscopy. LPA-treated cells on gelatin released the trailing edge. To understand how the extracellular matrix may regulate endothelial cell shape during movement, we surveyed changes in focal adhesion proteins. More Hic-5, a paxillin homolog, was detected in the detergent insoluble fraction of BPAEs attached to gelatin than fibronectin. No such difference was found in paxillin. In BPAEs, Hic-5 was localized to smaller punctate structures on fibronectin and longer, thinner focal adhesions on gelatin. These results indicated that localization of Hic-5 and strength of adhesion correlate with endothelial cell transmigration stimulated by LPA, but not with transmigration stimulated by S1P.

Disulfide connectivity of recombinant C-terminal region of human thrombospondin 2

The thrombospondin (TSP) family of extracellular glycoproteins consists of five members in vertebrates, TSP1 to -4 and TSP5/cartilage oligomeric matrix protein, and a single member in Drosophila. TSPs are modular multimeric proteins. The C-terminal end of a monomer consists of 3-6 EGF-like modules; seven tandem 23-, 36-, or 38-residue aspartate-rich, Ca(2+)-binding repeats; and an approximately 230-residue C-terminal sequence. The Ca(2+)-binding repeats and C-terminal sequence are spaced almost exactly the same in different TSPs and share many blocks of identical residues. We studied the C-terminal portion of human TSP2 from the third EGF-like module through the end of the protein (E3CaG2). E3CaG2, CaG2 lacking the EGF module, and Ca2 composed of only the Ca(2+)-binding repeats were expressed using recombinant baculoviruses and purified from conditioned media of insect cells. As previously described for intact TSP1, E3CaG2 bound Ca(2+) in a cooperative manner as assessed by equilibrium dialysis, and its circular dichroism spectrum was sensitive to the presence of Ca(2+). Mass spectrometry of the recombinant proteins digested with endoproteinase Asp-N revealed that disulfide pairing of the 18 cysteines in the Ca(2+)-binding repeats and C-terminal sequence is sequential, i.e. a 1-2, 3-4, 5-6, etc., pattern.

Specific interactions between F1 adhesin of Streptococcus pyogenes and N-terminal modules of fibronectin

Protein F1 is a surface protein of Streptococcus pyogenes that mediates high affinity binding to fibronectin (Fn) and facilitates S. pyogenes adherence and penetration into cells. The smallest portion of F1 known to retain the full binding potential of the intact protein is a stretch of 49 amino acids known as the functional upstream domain (FUD). Synthetic and recombinant versions of FUD were labeled with fluorescein isothiocyanate and used in fluorescence anisotropy experiments. These probes bound to Fn or the 70-kDa fragment of Fn with dissociation constants of 8-30 nm. Removal of the N-terminal seven residues of FUD did not cause a change in binding affinity. Further N- or C-terminal truncations resulted in complete loss of binding activity. Analysis of recombinant versions of the 70-kDa fragment that lacked one or several type I modules indicates that residues 1-7 of the 49-mer bind to type I modules I1 and I2 of the 27-kDa subfragment and the C-terminal residues bind to modules I4 and I5. Fluorescein isothiocyanate-labeled 49-mer also bound with lower affinity to large Fn fragments that lack the five type I modules of the 27-kDa fragment but contain the other seven type 1 modules of Fn. These results indicate that, although FUD has a general affinity for type I modules, high affinity binding of FUD to Fn is mediated by specific interactions with N-terminal type I modules.

Assembly of a fibronectin matrix by adherent platelets stimulated by lysophosphatidic acid and other agonists

Lysophosphatidic acid (LPA) and sphingosine-1-phosphate (S1P) are agonists of the endothelial differentiation gene (Edg) family of G-protein-coupled receptors. LPA and S1P are generated by platelet activation during blood coagulation. Both lipids induce assembly of exogenous fibronectin (FN) by fibroblasts. This study examined whether LPA and S1P stimulate binding and assembly of fluoresceinated FN (FITC-FN) by adherent platelets. LPA enhanced deposition of FITC-FN into linear arrays overlying platelet surfaces and on edges of platelets adherent to FN or vitronectin (VN). Deposition was greater when platelets were adherent to FN than to VN and was elicited by platelet agonists with the following order of potency: thrombin > LPA = ADP (adenosine diphosphate) > S1P. The linear pattern of FITC-FN deposition was different from the more diffuse pattern of Alexa-fibrinogen (Alexa-FGN) binding to adherent platelets. FITC-FN was deposited by adherent platelets that had dense arrays of cytoskeletal actin when stained with rhodamine-phalloidin. The 70-kd N-terminal fragment of FN or L8 monoclonal antibody to a self-association domain of FN abolished deposition of FITC-FN but had no effect on binding of Alexa-FGN. Conversely, integrilin did not attenuate deposition of FITC-FN but abolished binding of Alexa-FGN. RGDS (Arg-Gly-Asp-Ser) or antibodies to alpha5beta1 or alphaIIbbeta3 integrins caused a partial decrease in LPA-induced deposition of FITC-FN. Correlative electron microscopy with anti-FITC coupled to gold beads revealed linear arrays on platelet surfaces associated with less than 20-nm-diameter filaments. These observations demonstrate that LPA, thrombin, ADP, and S1P induce adherent platelets to bind and assemble FN and suggest that platelets may contribute to early deposition of FN matrix after vascular injury.

A 49-residue peptide from adhesin F1 of Streptococcus pyogenes inhibits fibronectin matrix assembly

F1 is an adhesin of Streptococcus pyogenes which binds the N-terminal 70-kDa region of fibronectin with high affinity. The fibronectin binding region of F1 is comprised of a 43-residue upstream domain and a repeat domain comprised of five tandem 37-residue sequences. We investigated the effects of these domains on the assembly of fibronectin matrix by human dermal fibroblasts, MG63 osteosarcoma cells, or fibroblasts derived from fibronectin-null stem cells. Subequimolar or equimolar concentrations of recombinant proteins containing both the upstream and repeat domains or just the repeat domain enhanced binding of fibronectin or its N-terminal 70-kDa fragment to cell layers; higher concentrations of these recombinant proteins inhibited binding. The enhanced binding did not result in greater matrix assembly and was caused by increased ligand binding to substratum. In contrast, recombinant or synthetic protein containing the 43 residues of the upstream domain and the first 6 residues from the repeat domain exhibited monophasic inhibition with an IC(50) of approximately 10 nm. Truncation of the 49-residue sequence at its N or C terminus caused loss of inhibitory activity. The 49-residue upstream sequence blocked incorporation of both endogenous cellular fibronectin and exogenous plasma fibronectin into extracellular matrix and inhibited binding of 70-kDa fragment to fibronectin-null cells in a fibronectin-free system. Inhibition of matrix assembly by the 49-mer had no effect on cell adhesion to substratum, cell growth, formation of focal contacts, or formation of stress fibers. These results indicate that the 49-residue upstream sequence of F1 binds in an inhibitory mode to N-terminal parts of exogenous and endogenous fibronectin which are critical for fibronectin fibrillogenesis.

Modulation of cell interactions with extracellular matrix by lysophosphatidic acid and sphingosine 1-phosphate

Lysophosphatidic acid (LPA) and sphingosine 1-phosphate (SPP) are lipid mediators released upon platelet activation. The concentration of LPA in serum is estimated at 1-10 microM whereas the concentration in plasma is considerably less. The SPP concentration in serum is 0.5 microM, approximately two-fold higher than the plasma concentration. The lipids are present during tissue injury and promote cellular processes involved in wound repair. LPA and SPP have multiple effects on cells, many of which are pertinent to wound healing and require that the cells interact in some fashion with components of the extracellular matrix. This review focuses on modulation of cell adhesion, cell migration, collagen gel contraction, and fibronectin matrix assembly by LPA and SPP.

Fludarabine and cytarabine as a sequential infusion regimen for treatment of adults with recurrent, refractory or poor prognosis acute leukemia

We did a retrospective analysis on the safety and efficacy of sequential infusion fludarabine and cytosine arabinoside (ara-C) in treating refractory, recurrent or poor prognosis acute leukemia in adult patients. Forty-five adult patients with acute myelogenous leukemia (AML) or acute lymphoblastic leukemia (ALL) received a total of 68 courses of sequential continuous infusion of fludarabine for 2 days (total dose 71.5 mg/m(2) ) followed by 3 days of ara-C (total dose 7590 mg/m(2) ). Thirty-nine patients had refractory or recurrent disease, and six had other adverse prognostic features. Thirty-six patients had AML, seven had ALL, and two had CML in blastic phase. Complete remission was seen in 20 patients (44%), and partial remission in 5 patients (11%), giving a total response rate of 56%, similar for both AML and ALL. Duration of response to prior therapy did not affect the response rate. All 3 patients with Philadelphia chromosome positive ALL obtained complete remission. Median remission duration was 4.7 months (range 0.6-36.6), and median overall survival was 5.0 months (0.7-40+). Median overall survival was 10.1 months in responders. Pulmonary toxicity was seen in 8 patients, of whom 2 died from adult respiratory distress syndrome. No cardiac toxicity was observed, but 3 patients had transient cerebellar toxicity. Profound myelosuppression was seen in all patients. We conclude that the sequential infusion of fludarabine and ara-C is an effective non-cardiotoxic regimen for adults with refractory, recurrent or poor prognosis acute leukemia, may be particularly useful for resistant Philadelphia chromosome positive ALL, and may warrant further investigation in this subset. Pulmonary rather than neurological toxicity may be a unique side effect of the regimen.

Role of the cytoplasmic tyrosines of beta 1A integrins in transformation by v-src

GD25 cells lacking beta 1 integrins or expressing beta 1A with mutations of conserved cytoplasmic tyrosines (Y783, Y795) to phenylalanine have poor directed migration to platelet-derived growth factor or lysophosphatidic acid when compared with GD25 cells expressing wild-type beta 1A. We studied the effects of v-src on these cells. Transformation with v-src caused tyrosine and serine phosphorylation of wild-type beta1 A but not of Y783/795F doubly mutated beta 1A. v-src-transformed cells had rounded and/or fusiform morphology and poor assembly of fibronectin matrix. Adhesion to fibronectin or laminin and coupling of focal contacts to actin-containing cytoskeleton were preserved in transformed Y783/795F cells but lost on transformation when beta 1A was wild type. Transformed Y783/795F cells also retained ability, albeit limited, to migrate across filters, whereas transformed cells with wild-type beta 1A were unable to transverse filters. Studies of single tyrosine mutants showed that the more important tyrosine for retaining ability to adhere, assemble focal contacts, and migrate is Y783. These results suggest that overactive phosphorylation of cytoplasmic residues of beta 1A, particularly Y783, accounts in part for the phenotype of v-src-transformed cells.

C-mannosylation and O-fucosylation of the thrombospondin type 1 module

Thrombospondin-1 (TSP-1) is a multidomain protein that has been implicated in cell adhesion, motility, and growth. Some of these functions have been localized to the three thrombospondin type 1 repeats (TSRs), modules of approximately 60 amino acids in length with conserved Cys and Trp residues. The Trp residues occur in WXXW patterns, which are the recognition motifs for protein C-mannosylation. This modification involves the attachment of an alpha-mannosyl residue to the C-2 atom of the first tryptophan. Analysis of human platelet TSP-1 revealed that Trp-368, -420, -423, and -480 are C-mannosylated. Mannosylation also occurred in recombinant, baculovirally expressed TSR modules from Sf9 and "High Five" cells, contradictory to earlier reports that such cells do not carry out this reaction. In the course of these studies it was appreciated that the TSRs in TSP-1 undergo a second form of unusual glycosylation. By using a novel mass spectrometric approach, it was found that Ser-377, Thr-432, and Thr-489 in the motif CSX(S/T)CG carry the O-linked disaccharide Glc-Fuc-O-Ser/Thr. This is the first protein in which such a disaccharide has been identified, although protein O-fucosylation is well described in epidermal growth factor-like modules. Both C- and O-glycosylations take place on residues that have been implicated in the interaction of TSP-1 with glycosaminoglycans or other cellular receptors.

Physical characterization of the procollagen module of human thrombospondin 1 expressed in insect cells

Thrombospondin 1 (TSP1) is a homotrimeric glycoprotein composed of 150-kDa subunits connected by disulfide bridges. The procollagen module of thrombospondin 1 has been implicated in antiangiogenic activity. Procollagen modules are found in a number of extracellular proteins and are identifiable by 10 cysteines with characteristic spacing. We expressed and studied the procollagen module (C) of human TSP1, both by itself and in the context of the adjoining oligomerization sequence (o) and N-terminal module (N). The coding sequences were introduced into baculoviruses along with an N-terminal signal sequence and C-terminal polyhistidine tag. Proteins were purified from conditioned medium of infected insect cells by nickel-chelate chromatography. NoC is a disulfide bonded trimer and cleaves readily at a site of preferential proteolysis to yield monomeric N and trimeric oC. These are known properties of full-length TSP1. Mass spectroscopy indicated that C is N-glycosylated, and all 10 cysteine residues of C are in disulfides. By equilibrium ultracentrifugation, C is a monomer in physiological salt solution. Circular dichroism, intrinsic fluorescence, and differential scanning calorimetry experiments suggest that the stability of C is determined by the disulfides. The two tryptophans of C are in a polar, exposed environment as assessed by iodide fluorescence quenching and solvent perturbation. The oC far UV circular dichroism spectrum could be modeled as the sum of C and a coiled-coil oligomerization domain. The results indicate that the recombinant C folds autonomously into its native structure, and trimerization of the modules in TSP1 does not perturb their structures.

Activated protein C-protein C inhibitor complex formation: characterization of a neoepitope provides evidence for extensive insertion of the reactive center loop

Protein C inhibitor, a serine proteinase inhibitor (serpin), is the physiologically most important inhibitor of activated protein C. We have made a monoclonal antibody (M36) that binds with equally high affinity to an epitope present in activated protein C-protein C inhibitor complexes and cleaved loop-inserted protein C inhibitor. Insertion of a synthetic N-acetylated tetradecapeptide (corresponding to residues P1-P14 of the reactive center loop) into beta-sheet A of the uncleaved inhibitor also exposed the epitope. The antibody had no apparent affinity for native uncleaved inhibitor or for the free peptide. Synthetic P1-P14 analogues, with Arg P13 or Ala P9 substituted to the residues found in mouse protein C inhibitor (Thr and Ile, respectively), were also inserted in beta-sheet A. The Arg P13/Thr substitution led to a greatly impaired reactivity with the antibody, whereas the Ala P9/Ile mutation resulted in a modest loss of reactivity with the antibody. These results indicate that complex formation leads to insertion of the reactive center loop in beta-sheet A from Arg P14 and presumably beyond Ala P9. Moreover, to the best of our knowledge, this is the first instance where the neoepitope of a complexation-specific monoclonal antibody has been localized to the loop-inserted part of beta-sheet A, the part of the serpin where the complexation-induced conformational change is most conspicuous.

CD14(+) cells are necessary for increased survival of eosinophils in response to lipopolysaccharide

There has been considerable interest in the effect that gram-negative bacterial endotoxin (lipopolysaccharide [LPS]) can have in asthma, given that inhalation of LPS has been shown to cause bronchial hyperresponsiveness. Further, there is evidence that the endotoxin-binding protein CD14 may be a marker for asthma. Inhaled LPS has been shown to cause an influx of eosinophils into the nasal airway and to increase the survival of CD16-negatively selected eosinophils in vitro. In this study, we compared survival of eosinophils isolated via CD16-negative selection with eosinophils that were isolated using both CD16- and CD14-negative selection criteria. Survival of CD16-negatively selected eosinophils was enhanced by LPS in a dose-dependent manner and was inhibited by the endotoxin antagonists polymyxin B or lipid X. In contrast, depletion of CD14(+) cells within the eosinophil preparations (CD14/CD16-negatively selected eosinophils) decreased the effect of LPS on survival. Preincubation of CD16-negatively selected eosinophils with antibody 60bd, which blocks LPS binding to CD14, prevented the survival-enhancing effect of LPS. However, CD14 was not detected on eosinophils by flow cytometry, even after incubation with LPS for up to 24 h. These results suggest that the survival-enhancing effect of LPS on eosinophils requires the presence of CD14(+) cells in the population. It is our hypothesis that enhanced eosinophil survival with LPS involves the contribution of another cell type.

The cytoplasmic tyrosines of integrin subunit beta1 are involved in focal adhesion kinase activation

We have previously shown that mutation of the two tyrosines in the cytoplasmic domain of integrin subunit beta1 (Y783 and Y795) to phenylalanines markedly reduces the capability of beta1A integrins to mediate directed cell migration. In this study, beta1-dependent cell spreading was found to be delayed in GD25 cells expressing beta1A(Y783/795F) compared to that in wild-type GD25-beta1A. Focal adhesion kinase (FAK) tyrosine phosphorylation and activation were severely impaired in response to beta1-dependent adhesion in GD25-beta1A(Y783/795F) cells compared to that in wild-type GD25-beta1A or mutants in which only a single tyrosine was altered (beta1A(Y783F) or beta1A(Y795F)). Phosphorylation site-specific antibodies selective for FAK phosphotyrosine 397 indicated that the defect in FAK phosphorylation via beta1A(Y783/795F) lies at the level of the initial autophosphorylation step. Indeed, beta1A-dependent tyrosine phosphorylation of tensin and paxillin was lost in the beta1A(Y783/795F) cells, consistent with the impairment in FAK activation. In contrast, p130(CAS) overall tyrosine phosphorylation was unaffected by the beta1 mutations. Despite the defect in beta1-mediated FAK activation, FAK was still localized to focal adhesions. Taken together, the phenotype of the GD25-beta1A(Y783/795F) cells resembles, but is distinct from, the phenotype observed in FAK-null cells. These observations argue that tyrosines 783 and 795 within the cytoplasmic tail of integrin subunit beta1A are critical mediators of FAK activation and cell spreading in GD25 cells.

Differential stimulation of signaling pathways initiated by Edg-2 in response to lysophosphatidic acid or sphingosine-1-phosphate

Lysophosphatidic acid (LPA) and sphingosine-1-phosphate (S1P) are produced during cell activation and have multiple effects on cells. A family of seven transmembrane-spanning domain G-protein-coupled receptors, named Edg, mediate these effects of LPA and S1P. In this study, transient overexpression of Edg-2 sensitized MG63 human osteosarcoma cells to both LPA- and S1P-mediated stimulation of fibronectin matrix deposition and actin stress fiber formation. Both lipids were active in the 1-20 nM concentration range on cells transfected with Edg-2 as compared to the 10-200 nM range on mock-transfected cells. The signaling pathway for matrix deposition by Edg-2-transfected cells was Rho dependent. Overexpression of Edg-2 also caused a tenfold decrease in the concentration of either LPA or S1P that activated MAPKinase (Erkl/2) in MG63 cells. LPA- or S1P-stimulated activation of Erkl/2 was Gi dependent. These results indicate that, in MG63 cells, Edg-2 mediates actin stress fiber formation, fibronectin matrix assembly, and MAPKinase activation in response to either LPA or S1P.

Contraction of collagen matrices mediated by alpha2beta1A and alpha(v)beta3 integrins

The (beta)1-null fibroblastic cell line GD25 and its derivatives were studied to gain an understanding of the roles of (beta)1 and (beta)3 integrins in the initial (1-hour) contraction of collagen gels. Stable transfectants of GD25 cells expressing the (beta)1A splice variant of (beta)1 ((beta)1A-GD25) did not express (alpha)2(beta)1A and did not adhere to collagen. After transfection of (alpha)2 into (beta)1A-GD25 cells, the (alpha)2(beta)1A-GD25 transfectants contracted collagen gels in the presence of serum, whereas (beta)1A-GD25 cells did not. The GD25 parental cells, however, also contracted collagen gels. Collagen gel contraction by GD25 cells was blocked by antibodies to (alpha)v(beta)3 or a RGD-containing peptide, indicating that (alpha)v(beta)3 is the integrin responsible for mediation of contraction by GD25 cells. Collagen gel contraction by (alpha)2(beta)1A-GD25 cells was not inhibited by antibodies to (alpha)v(beta)3 or RGD-containing peptide, but was inhibited by anti-(alpha)2 antibody. Flow cytometry demonstrated negligible expression of (alpha)v(beta)3 by (beta)1A-GD25 and (alpha)2(beta)1A-GD25 cells when compared to GD25 cells. Platelet derived growth factor (PDGF) and sphingosine-1-phosphate (S1P) enabled gel contraction by (alpha)2(beta)1A-GD25 and GD25 cells, respectively, in the absence of serum. PDGF-stimulated contraction by (alpha)2(beta)1A-GD25 cells was attenuated in the presence of inhibitors of phosphatidylinositol-3-kinase whereas such inhibitors had no effect on S1P-stimulated contraction by GD25 cells. These experiments using the (beta)1-null GD25 cells and (beta)1A and (alpha)2(beta)1A transfectants demonstrate that (alpha)2(beta)1A and (alpha)v(beta)3 independently mediate collagen gel contraction and are regulated by different serum factors and signaling pathways.

Sphingosine-1-phosphate and lysophosphatidic acid stimulate endothelial cell migration

Endothelial cell migration is necessary for the formation of new blood vessels. We investigated the effects of 2 lysophospholipid mediators, sphingosine-1-phosphate (S1P) and lysophosphatidic acid (LPA), on endothelial cell migration. S1P and LPA stimulated migration of fetal bovine heart endothelial cells (FBHEs) in a 3D-modified Boyden chamber assay with concentrations as low as 15 nmol/L stimulating a 2-fold change and concentrations in the 1- to 2-micromol/L range stimulating 14- to 20-fold changes. S1P specifically stimulated the migration of several endothelial cell strains but did not stimulate the migration of tumor cells or smooth muscle cells. LPA stimulated some endothelial and nonendothelial cell types to migrate. For FBHEs, S1P and LPA were mostly chemokinetic in checkerboard assays. S1P and LPA stimulated extracellular signal-regulated kinase 1/2 phosphorylation and enhanced paxillin localization to focal contacts, with no discernible change in the actin cytoskeleton in FBHEs. To characterize responsible receptor-dependent signaling pathways, we investigated the involvement of G(i), Rho, and phosphoinositide 3-OH kinase in S1P- and LPA-stimulated migration. Although perturbation of all 3 signaling molecules resulted in decreased migration, the mechanisms underlying the decreased migration were different. Pertussis toxin treatment, to target G(i), caused endothelial cells to develop dense bundles of F-actin and distribute paxillin staining to the cell periphery in response to S1P or LPA. Modification of Rho with C3 toxin disrupted the actin cytoskeleton. Inhibition of phosphoinositide 3-OH kinase decreased S1P- or LPA-induced endothelial cell migration with only minor disruption of the actin cytoskeleton. Inhibition of extracellular signal-regulated kinase kinase with PD98059 caused a loss of phosphorylation of extracellular signal-regulated kinase 1/2, similar to pertussis toxin, but only a minimal decrease in migration. These results indicate that S1P and, for some cells, LPA stimulate migration of endothelial cells through a mechanism that likely requires a balance between G(i) and Rho signaling to achieve the cytoskeletal remodeling necessary for cell migration.

Expression of GIRK (Kir3.1/Kir3.4) channels in mouse fibroblast cells with and without beta1 integrins

G protein-activated K+ channel (GIRK) subunits possess a conserved extracellular integrin-binding motif (RGD) and bind directly to beta1 integrins. We expressed GIRK1/GIRK4 channels labeled with green fluorescent protein in fibroblast cell lines expressing or lacking beta1 integrins. Neither plasma membrane localization nor agonist-evoked GIRK currents were affected by the absence of beta1 integrins or by incubation with externally applied RGD-containing peptide. Mutation of the aspartate (D) of RGD impaired currents, GIRK glycosylation, and membrane localization, but the interaction with beta1 integrins remained intact. Thus, beta1 integrins are not essential for functional GIRK expression; and the GIRK-integrin interactions involve structural elements other than the RGD motif.

Engagement of alpha4beta7 integrins by monoclonal antibodies or ligands enhances survival of human eosinophils in vitro

Asthma is characterized by an airway inflammatory infiltrate that is rich in eosinophilic leukocytes. Cellular fibronectin and VCAM-1, ligands for alpha4 integrins, are enriched in the fluid of airways of allergic patients subjected to Ag challenge. We therefore hypothesized that ligands of alpha4 integrins can promote eosinophil survival independent of cell adhesion. Cellular fibronectin and VCAM-1 increased viability of human peripheral blood eosinophil in a dose- and time-dependant manner whether the ligand was coated on the culture well or added to the medium at the beginning of the assay. Eosinophils cultured with cellular fibronectin were not adherent to the bottom of culture wells after 3 days. Treatment with mAb Fib 30 to beta7, but not mAb P4C10 or TS2/16 to beta1, increased eosinophil survival. The increased survival of eosinophils incubated with Fib 30 was blocked by Fab fragments of another anti-beta7 mAb, Fib 504. Eosinophils incubated with soluble cellular fibronectin or mAb Fib 30 for 6 h demonstrated a higher level of GM-CSF mRNA than eosinophils incubated with medium alone. Addition of neutralizing mAb to GM-CSF during incubation, but not mAbs to IL-3 or IL-5, reduced the enhancement of eosinophil survival by soluble cellular fibronectin or mAb Fib 30 to control levels. Thus, viability of eosinophils incubated with cellular fibronectin or VCAM-1 is due to engagement, probably followed by cross-linking, of alpha4beta7 by soluble ligand (or mAb) that stimulates autocrine production of GM-CSF and promotes eosinophil survival.

Bovine thrombospondin-2: complete complementary deoxyribonucleic acid sequence and immunolocalization in the external zones of the adrenal cortex

Given the variety of biological functions in the adrenal cortex that are controlled by ACTH, we hypothesized that some extracellular proteins act as biological relays for this systemic hormone. One candidate protein [corticotropin-induced secreted protein (CISP)] was purified from the conditioned medium of bovine adrenocortical cells on the basis of a 5- to 14-fold increase in its synthesis after the addition of ACTH. We report here the cloning of overlapping complementary DNAs that span the sequence encoding the full-length protein (1170 amino acids). The deduced CISP protein sequence is 89% identical to that of human thrombospondin-2 (TSP2), but only 61% identical to that of bovine TSP1, confirming that CISP is the bovine ortholog of TSP2. The bovine TSP2 sequence aligned perfectly with human, mouse, and chicken TSP2 sequences, except for a gap of 2 amino acids located in a linker region. All 58 cysteine residues that are conserved in other species were present in the bovine sequence as well as most of the functional domains. Most endocrine tissues (adrenal cortex, testis, ovary, and placenta) appeared to express TSP2, as determined by Western blot analysis. The highest levels of TSP2 protein were found in the adrenal cortex, followed by the heart, spleen, brain, and kidney. A differential extent of N-glycosylation or tissular proteolytic maturation may be responsible for the mol wt differences observed between bovine TSP2 detected in the medium from primary cultures and that in fresh tissue extracts. The immunohistochemical analysis of the distribution of TSP2 in the bovine adrenal gland revealed that the protein is much more abundant in the external zones (zona glomerulosa and zona fasciculata) than in the internal reticularis zone, a pattern similar to that reported for ACTH receptors. This distribution clearly suggests that TSP2 is a candidate relay protein for a subset of ACTH actions in the adrenal cortex.

Synergism among lysophosphatidic acid, beta1A integrins, and epidermal growth factor or platelet-derived growth factor in mediation of cell migration

GD25 cells lacking the beta1 integrin subunit or expressing beta1A with certain cytoplasmic mutations have poor directed cell migration to platelet-derived growth factor (PDGF) or epidermal growth factor (EGF), ligands of receptor tyrosine kinases, or to lysophosphatidic acid (LPA), a ligand of G-protein-coupled receptors (Sakai, T., Zhang, Q., Fässler, R., and Mosher, D. F. (1998) J. Cell Biol. 141, 527-538 and Sakai, T., Peyruchaud, O., Fässler, R., and Mosher, D. F. (1998) J. Biol. Chem. 273, 19378-19382). We demonstrate here that LPA synergizes with signals induced by beta1A integrins and ligated EGF or PDGF receptors to modulate migration. When LPA was mixed with EGF or PDGF, migration was greater than with EGF or PDGF alone. The enhancement was greater for beta1A-expressing cells than for beta1-null cells. Cells expressing beta1A with mutations of prolines or tyrosines in conserved cytoplasmic NPXY motifs had blunted migratory responses to mixtures of LPA and EGF or PDGF. The major effects on beta1A-expressing cells of LPA when combined with EGF or PDGF were to sensitize cells so that maximal responses were obtained with >10-fold lower concentrations of growth factor and increase the chemokinetic component of migration. Sensitization by LPA was lost when cells were preincubated with pertussis toxin or C3 exotransferase. There was no evidence for transactivation or sensitization of receptors for EGF or PDGF by LPA. EGF or PDGF and LPA caused activation of mitogen-activated protein kinase by pertussis toxin-insensitive and -sensitive pathways respectively, but activation was not additive. These findings indicate that signaling pathways initiated by the cytoplasmic domains of ligated beta1A integrins and tyrosine kinase receptors interact with signaling pathways initiated by LPA to facilitate directed cell migration.

Sphingosine 1-phosphate stimulates fibronectin matrix assembly through a Rho-dependent signal pathway

Fibronectin matrix assembly is a cell-dependent process mediated by cell surface binding sites for the 70-kD N-terminal portion of fibronectin. We have shown that Rho-dependent cytoskeleton reorganization induced by lysophosphatidic acid (LPA) or the microtubule-disrupting agent nocodazole increases fibronectin binding (Zhang et al, Mol Biol Cell 8:1415, 1997). Sphingosine 1-phosphate (S1P) is a bioactive sphingolipid implicated in mitogenesis and cytoskeletal remodelling. Both LPA and S1P are present in increased amounts in serum as compared with plasma as a result of platelet activation. Addition of S1P to human osteosarcoma MG63 cells or human foreskin fibroblasts increased cell-mediated binding and assembly of fibronectin. MG63 cells expressed the Edg-2 and Edg-4 G-protein-coupled receptors for bioactive lipids, whereas foreskin fibroblasts expressed Edg-2, Edg-3, and Edg-4. The stimulatory effect of S1P on the binding of fibronectin or the N-terminal 70-kD fragment of fibronectin was dynamic and due to increases in both the number and affinity of binding sites. The stimulation of 70-kD fragment binding by nanomolar S1P, like stimulation of binding by LPA or nocodazole, was blocked by inactivation of Rho with C3 exotoxin but not by pertussis toxin-mediated inactivation of Gi. These results indicate a common signal pathway leading to control of cellular fibronectin matrix assembly by bioactive lipids generated during blood coagulation.

Syndecan-4 signals cooperatively with integrins in a Rho-dependent manner in the assembly of focal adhesions and actin stress fibers

The assembly of focal adhesions and actin stress fibers by cells plated on fibronectin depends on adhesion-mediated signals involving both integrins and cell-surface heparan sulfate proteoglycans. These two cell-surface receptors interact with different domains of fibronectin. To attempt to identify the heparan sulfate proteoglycans involved, we used fibronectin-null (FN-/-) mouse fibroblasts to eliminate the contribution of endogenous fibronectin during the analysis. FN-/- fibroblasts plated on the cell-binding domain of fibronectin or on antibodies directed against mouse beta1 integrin chains attach but fail to spread and do not form focal adhesions or actin stress fibers. When such cells are treated with antibodies directed against the ectodomain of mouse syndecan-4, they spread fully and assemble focal adhesions and actin stress fibers indistinguishable from those seen in cells plated on intact fibronectin. These results identify syndecan-4 as a heparan sulfate proteoglycan involved in the assembly process. The antibody-stimulated assembly of focal adhesions and actin stress fibers in cells plated on the cell-binding domain of fibronectin can be blocked with C3 exotransferase, an inhibitor of the small GTP-binding protein Rho. Treatment of cells with lysophosphatidic acid, which activates Rho, results in full spreading and assembly of focal adhesions and actin stress fibers in fibroblasts plated on the cell-binding domain of fibronectin. We conclude that syndecan-4 and integrins can act cooperatively in generating signals for cell spreading and for the assembly of focal adhesions and actin stress fibers. We conclude further that these joint signals are regulated in a Rho-dependent manner.

Segmental antigen challenge increases fibronectin in bronchoalveolar lavage fluid

Fibronectin may contribute to asthma pathogenesis by recruitment and activation of inflammatory cells, and by promotion of subepithelial fibrosis. Fibronectin is produced by several types of airway cells, including epithelial cells, fibroblasts, and alveolar macrophages. To test the hypothesis that antigen-induced airway inflammation is associated with increased local generation of fibronectin, segmental bronchoprovocation (SBP) with antigen and saline was performed in 17 atopic patients. Bronchoalveolar lavage (BAL) was performed at 5 min and 48 h after segmental challenge with saline or antigen. Fibronectin concentrations in BAL fluid, measured by enzyme-linked immunosorbent assay (ELISA), increased more than 5-fold 48 h after antigen challenge (65 [47 to 110] versus 407 [240 to 697] ng/ml, median and 25 to 75% interquartiles, p < 0.05). Fibronectin concentrations 48 h after antigen challenge correlated with histamine concentrations 5 min after antigen challenge and numbers of eosinophils, neutrophils, macrophages, and total cells in BAL fluid 48 h after antigen challenge. BAL was more enriched in fibronectin 48 h after challenge than would be predicted solely from increased permeability of plasma proteins. Western blot analysis showed that fibronectin in BAL fluid was largely intact and contained the extra domain-A (ED-A) splice variant of cellular fibronectin, indicative of local production. We conclude that antigen challenge in atopic subjects causes increased production of fibronectin by airway cells and speculate that this response may contribute to airway remodeling in allergic inflammation.

Dominant effects of the bcr-abl oncogene on Drosophila morphogenesis

We targeted expression of human/fly chimeric Bcr-Abl proteins to the developing central nervous system (CNS) and eye imaginal disc of Drosophila melanogaster. Neural expression of human/fly chimeric P210 Bcr-Abl or P185 Bcr-Abl rescued abl mutant flies from pupal lethality, indicating that P210 and P185 Bcr-Abl can substitute functionally for Drosophila Abl during axonogenesis. However, increased levels of neurally expressed P210 or P185 Bcr-Abl but not Drosophila Abl produced CNS defects and lethality. Expression of P210 or P185 in the eye imaginal disc produced a dominant rough eye phenotype that was dependent on dosage of the transgene. Drosophila Enabled, previously identified as a suppressor of the abl mutant phenotype and substrate for Drosophila Abl kinase, had markedly increased phosphotyrosine levels in Bcr-Abl expressing Drosophila, indicating that it is a substrate for Bcr-Abl as well. Drosophila, therefore, is a suitable model system to identify Bcr-Abl interactions important for signal transduction and oncogenesis.

Functional beta1-integrins release the suppression of fibronectin matrix assembly by vitronectin

beta1-null GD25 fibroblasts adherent to vitronectin fail to bind the N-terminal 70-kDa matrix assembly domain of fibronectin or to assemble fibronectin (Sakai, T., Zhang, Q., Fässler, R., and Mosher, D. F. (1998) J. Cell Biol. 141, 527-538). We have made four observations that extend this finding. First, the presence of vitronectin on a substrate that otherwise can support fibronectin assembly has a dominant-negative effect on assembly. Second, the dominant-negative effect is lost when active beta1A is expressed. Third, beta1A containing the extracellular D130A inactivating mutation has a dominant-negative effect on fibronectin assembly. Fourth, beta1-null cells adherent to vitronectin are flat and lack filopodia, whereas beta1-null cells adherent to fibronectin or beta1A-expressing cells adherent to either vitronectin or fibronectin are contracted and exhibit numerous filopodia. These results reveal, therefore, that GD25 cells adherent to vitronectin can only assume a shape suitable for assembly of fibronectin when there is a countervailing signal from functional beta1-integrins.

Interaction of recombinant procollagen and properdin modules of thrombospondin-1 with heparin and fibrinogen/fibrin

Many properties have been assigned to the procollagen and properdin (Type I) modules of thrombospondin-1 (TSP1) based on activities of large proteolytic fragments of TSP1 or peptides containing TSP1-derived sequences. To examine the activities of the modules more exactly, we expressed the first properdin module (P1); the third properdin module (P3); the first and second properdin modules (P12); the first, second, and third properdin modules (P123); and the procollagen module with the first, second, and third properdin modules (CP123) in the GELEX expression vector (GE1) using the baculovirus system. GE1 encodes the pre-pro sequence, the transglutaminase cross-linking site(s), the protease-sensitive site, and the gelatin binding domain from the amino terminus of rat fibronectin. All five recombinant proteins were expressed by insect cells, secreted into the culture medium, and purified by gelatin-agarose affinity chromatography. P123 shared with TSP1 a resistance to trypsin unless reduced and alkylated. P12/GE1, P123/GE1, and CP123/GE1 bound poorly to heparin-agarose except in the absence of sodium chloride, whereas peptides based on P2 are known to bind to heparin in up to 150 mM sodium chloride. In cross-linking experiments employing activated recombinant factor XIII and the transglutaminase cross-linking site in the fibronectin-derived sequence, P12/GE1, P123/GE1, CP123/GE1, and P3/GE1 but not P1/GE1 became incorporated into a fibrin clot more than GE1 alone. Analysis of the complex indicated that cross-linking was to the portion of the fibrin alpha-chain remaining in the D-dimer of plasmin digests. P123 also cross-linked to the Aalpha-chain of unclotted fibrinogen. P123 competed for 125I-TSP1 incorporation into the fibrin clot. P123 did not cross-link to plasminogen, histidine-rich glycoprotein, fibronectin, or plasma globulins other than fibrinogen/fibrin. These results indicate that the properdin modules of TSP1 specifically interact with fibrinogen/fibrin but not with heparin under physiologic conditions.

Enhanced expression of thrombospondin-1 and hypovascularity in human cholangiocarcinoma

Cholangiocarcinoma (CCC) is relatively hypovascular, in contrast to hepatocellular carcinoma (HCC), which is often highly vascular. We investigated if the diminished vascularity of CCC is related to altered expression of thrombospondin-1 (TSP-1), an antiangiogenic factor, and/or vascular endothelial growth factor (VEGF), a potent angiogenic factor, comparing the relationships with those of high- and low-vascular HCC. We also investigated the relationship between the mutation of the p53 gene and TSP-1 expression or VEGF expression. Northern blot analysis and immunohistochemical staining were performed on surgically resected human CCC and HCC. The ratios of TSP-1 mRNA level in cancer cells versus adjacent noncancerous cells (T/N ratios) were significantly higher in CCC (n = 11) than in HCC with high vascularity (n = 15). In contrast, T/N ratios of VEGF mRNA level in CCC (n = 11) were comparable with those in HCC with low vascularity (n = 5). In CCC, the cancer cells and fibroblasts were positively stained with anti-TSP-1 antibody. We observed that T/N ratios of VEGF mRNA level, but not those of the TSP-1 mRNA level, were significantly correlated with vascularity in HCC. The relative increase in TSP-1 and the relative decrease in VEGF in tumors compared with normal tissue may underlie the limited angiogenesis of CCC. The p53 gene did not affect the expression of TSP-1 in CCC or VEGF in HCC.

Roles of integrins and fibronectin in the entry of Streptococcus pyogenes into cells via protein F1

Entry of group A streptococcus (GAS) into cells has been suggested as an important trait in GAS pathogenicity. Protein F1, a fibronectin (Fn) binding protein, mediates GAS adherence to cells and the extracellular matrix, and efficient cell internalization. We demonstrate that the cellular receptors responsible for protein F1-mediated internalization of GAS are integrins capable of Fn binding. In HeLa cells, bacterial entry is blocked by anti-beta1 integrin monoclonal antibody. In the mouse cell line GD25, a beta1 null mutant, the alphavbeta3 integrin promotes GAS entry. Internalization of these cells by GAS is blocked by a peptide that specifically binds to alphavbeta3 integrin. In both cell lines, entry of GAS requires the occupancy of protein F1 by Fn. Neither the 29 kDa nor the 70 kDa N-terminal fragments or the 120 kDa cell-binding fragment of Fn promote bacterial entry. Fn-coated beads are taken up efficiently by HeLa cells. Both the entry of GAS via protein F1 and the uptake of Fn-coated beads are blocked by anti-beta1 antibody but are unaffected by a large excess of soluble Fn. Internalization of HeLa cells by bacteria bearing increasing amounts of prebound Fn to protein F1 reveals a sigmoidal ultrasensitive curve. These suggest that the ability of particles to interact via Fn with multiple integrin sites plays a central role in their ability to enter cells.

Opposing effects of low and high molecular weight kininogens on cell adhesion

High molecular weight kininogen (HK) blocks cell spreading but not cell attachment to surfaces coated with vitronectin and other ligands of beta3 integrins. We sought to learn the structural basis of this phenomenon. Monoclonal antibodies against the histidine-rich D5 domain in the light chain of 2-chain HK abolished the inhibitory effect of 2-chain HK on spreading of MG-63 osteosarcoma cells on vitronectin-coated tissue-culture plastic. The antibodies were effective only if incubated with 2-chain HK in solution and did not abolish the anti-cell-spreading effect of 2-chain HK that was pre-adsorbed to tissue-culture plastic. Exposure of an epitope in the histidine-rich domain was less when HK was adsorbed to tissue-culture plastic (oxidized polystyrene) than when it was adsorbed to ELISA plastic (untreated polystyrene). Loss of the epitope correlated with increased anti-cell-spreading activity of HK on tissue-culture plastic. The light chain of 2-chain HK containing D5 and that containing recombinant D5 both had anti-cell-spreading activity, but only when present in solution during adhesion assays. Pre-adsorption of recombinant D5 to tissue-culture plastic resulted in a surface on which adsorbed 2-chain HK had little anti-cell-spreading activity. Binding study revealed that HKa bound to immobilized vitronectin. The histidine-rich D5 domain of light chain of HK was identified as one of the binding sites of vitronectin, suggesting that the masking of the RGD cell-binding site of immobilized vitronectin is the molecular mechanism of anti-cell-spreading effect of HKa. In contrast, low molecular weight kininogen (LK), which lacks D5, augmented cell spreading on vitronectin-coated tissue-culture plastic. Thus, HK and LK have opposing effects on VN-dependent cell adhesion. The augmenting effect of LK was greater if LK was preincubated with cells or adsorbed to the surface at pH>7.0. Analysis of fragments of LK and antibody inhibition studies localized the cell-adhesion activity to the D3 domain that is common to LK and HK. These findings indicate that the D5 domain mediates the adsorption of HK or 2-chain HK to vitronectin substratum in anti-adhesive conformations, i.e., masking of the RGD cell-binding site of vitronectin. Such conformers inhibit cell spreading on vitronectin even though a cell-adhesion site is present in D3.

Restoration of beta1A integrins is required for lysophosphatidic acid-induced migration of beta1-null mouse fibroblastic cells

Cells lacking the beta1 integrin subunit or expressing beta1A with certain cytoplasmic mutations have poor directed cell migration to platelet-derived growth factor or epidermal growth factor, ligands of receptor tyrosine kinases (Sakai, T., Zhang, Q., Fässler, R., and Mosher, D. F. (1998) J. Cell Biol. 141, 527-538). We investigated the effect of expression of beta1A integrins on lysophosphatidic acid (LPA)-induced migration of fibroblastic cells derived from beta1-null mouse embryonic stem cells. These cells expressed edg-2, a G-protein-linked receptor for LPA, as well as the related edg-1 receptor. Cells expressing wild type beta1A demonstrated enhanced cell migration across filters coated with gelatin or adhesive proteins in response to LPA, whereas beta1-deficient cells lacked LPA-induced cell migratory ability. Checkerboard analyses indicated that LPA causes both chemotaxis and chemokinesis of beta1-replete cells. Cells expressing beta1A with mutations of prolines or tyrosines in conserved cytoplasmic NPXY motifs, threonine in the inter-motif sequence, or a critical aspartic acid in the extracellular domain had low migratory responses to LPA. These findings indicate that active beta1A integrin is required for cell migration induced by LPA and that the cytoplasmic domain of ligated beta1A interacts with pathways that are common to both receptor tyrosine kinase and G-protein-linked receptor signaling.

Restricted localization of thrombospondin-2 protein during mouse embryogenesis: a comparison to thrombospondin-1

Thrombospondin-1 and -2 (TSP1 and TSP2) are multifunctional, multimodular extracellular matrix proteins encoded by separate genes. We compared the distributions of TSP1 and TSP2 in mouse embryos (day 10 and later) by immunohistochemistry. TSP1 was detected on day 10 in the heart and intestinal epithelium, on day 11 in megakaryocytes, and on day 14 in the lung. TSP2 was not detected until day 14, with strongest staining in mesenchymal condensation that gives rise to cartilage and bone. The distribution of TSP2 was different from but overlapped with the distribution of TSP1. TSP1 was found in cartilage proper with diminished staining around chondrocytes undergoing differentiation and hypertrophy, whereas TSP2 was restricted to the matrix surrounding chondrocytes of the growth zone cartilage. TSP2 and TSP1 were both expressed in centers of intramembranous ossification that form the skull bones, in reticular dermis, on the apical surface of nasal epithelium, in skeletal muscle, and in the sheath surrounding vibrissae. Areas of exclusive staining for TSP2 included the perichondrium surrounding the cartilage of the nasal cavities, developing bone of the lower mandible, and adrenal gland. The distinct localizations of TSP1 and TSP2 indicate that the two proteins have specific functions during mouse embryogenesis.

Modulation of beta1A integrin functions by tyrosine residues in the beta1 cytoplasmic domain

beta1A integrin subunits with point mutations of the cytoplasmic domain were expressed in fibroblasts derived from beta1-null stem cells. beta1A in which one or both of the tyrosines of the two NPXY motifs (Y783, Y795) were changed to phenylalanines formed active alpha5 beta1 and alpha6 beta1 integrins that mediated cell adhesion and supported assembly of fibronectin. Mutation of the proline in either motif (P781, P793) to an alanine or of a threonine in the inter-motif sequence (T788) to a proline resulted in poorly expressed, inactive beta1A. Y783,795F cells developed numerous fine focal contacts and exhibited motility on a surface. When compared with cells expressing wild-type beta1A or beta1A with the D759A activating mutation of a conserved membrane-proximal aspartate, Y783, 795F cells had impaired ability to transverse filters in chemotaxis assays. Analysis of cells expressing beta1A with single Tyr to Phe substitutions indicated that both Y783 and Y795 are important for directed migration. Actin-containing microfilaments of Y783,795F cells were shorter and more peripheral than microfilaments of cells expressing wild-type beta1A. These results indicate that change of the phenol side chains in the NPXY motifs to phenyl groups (which cannot be phosphorylated) has major effects on the organization of focal contacts and cytoskeleton and on directed cell motility.

Isolation of a cDNA encoding a novel member of the transglutaminase gene family from human keratinocytes. Detection and identification of transglutaminase gene products based on reverse transcription-polymerase chain reaction with degenerate primers

We developed a method using a single set of degenerate oligonucleotide primers for amplification of the conserved active site of transglutaminases by reverse transcription-polymerase chain reaction (RT-PCR) and identification of the PCR products by cleavage with diagnostic restriction enzymes. We demonstrate amplification of tissue transglutaminase (TGC), keratinocyte transglutaminase (TGK), prostate transglutaminase (TGP), the a-subunit of factor XIII, and band 4.2 protein from different human cells or tissues. Analysis of normal human keratinocytes revealed expression of a transglutaminase different from the expected and characterized transglutaminase gene products. A full-length cDNA for the novel transglutaminase (TGX) was obtained by anchored PCR. The deduced amino acid sequence encoded a protein with 720 amino acids and a molecular mass of approximately 81 kDa. A comparison of TGX to the other members of the gene family revealed that the domain structure and the residues required for enzymatic activity and Ca2+ binding are conserved and showed an overall sequence identity of about 35%. Two transcripts with an apparent size of 2.2 and 2.8 kilobases were detected with a specific probe for TGX on Northern blots of human foreskin keratinocyte mRNA, indicating the presence of alternatively spliced mRNAs. cDNA sequencing revealed a shorter TGX transcript lacking the sequence homologous to that encoded by exon III of other transglutaminase genes. TGX expression increased severalfold when keratinocyte cultures were induced to differentiate by suspension or growth to postconfluency, suggesting that TGX contributes to the formation of the cornified envelope.

Lysophosphatidic acid and microtubule-destabilizing agents stimulate fibronectin matrix assembly through Rho-dependent actin stress fiber formation and cell contraction

Fibronectin (FN) matrix assembly is a cell-dependent process mediated by cell surface-binding sites for the 70-kDa amino-terminal region of FN. We have shown recently that lysophosphatidic acid (LPA) is a stimulator of FN matrix assembly. Disruption of microtubules has been shown to mimic some of the intracellular effects of LPA including the formation of actin stress fibers and myosin light chain phosphorylation. We compared the effects of microtubule disruption and LPA on FN binding and actin cytoskeleton organization. The disruption of microtubules by nocodazole or vinblastine increased FN binding to adherent cells. The modulation of binding sites was rapid, dynamic, and reversible. Enhanced binding was due to increases in both the number and affinity of binding sites. These effects are similar to the effects of LPA on FN binding. Binding induced by nocodazole was inhibited by the microtubule-stabilizing agent Taxol but not by pretreatment with a concentration of phospholipase B that totally abolished the stimulatory effect of LPA. Fluorescence microscopy revealed a close correlation among actin stress fiber formation, cell contraction, and FN binding. Blockage of the small GTP binding protein Rho or actin-myosin interactions inhibited the effects of both nocodazole and LPA on FN binding. These observations demonstrate that Rho-dependent actin stress fiber formation and cell contraction induce increased FN binding and represent a rapid labile way that cells can modulate FN matrix assembly.

N-terminal type I modules required for fibronectin binding to fibroblasts and to fibronectin's III1 module

Assembly of fibronectin fibrils occurs at the surface of substrate-attached cells and is mediated by the first to the fifth type I modules in the N-terminal 70 kDa portion of the molecule. The first type III module (III1) of fibronectin, not present in the 70 kDa portion, contains a conformation-dependent binding site for the 70 kDa N-terminal region of fibronectin, suggesting that the III1 module on cell-surface fibronectin may serve as a binding site for fibronectin's N-terminus on substrate-attached cells. To explore this possiblility, we compared the ability of mutant recombinant 70 kDa proteins containing deletions of one or several of the first five type I modules to bind to fibroblasts and to III1. Proteins containing the fourth and fiftBiomolecular Chemistry and Medicine, University of Wisconsin, Madison, WI 53706U.S.A. Assembly of fibronectin fibrils occurs at the surface of substrate-attached cells and is mediated by the first to the fifth type I modules in the N-terminal 70 kDa portion of the molecule. The first type III module (III1) of fibronectin, not present in the 70 kDa portion, contains a conh as 70 kDa deletion mutants lacking I4 and I5 also bound to the cell surface, and deletion mutants lacking I1-3 and I4-5 both competed only partially for binding of 125I-labelled fibronectin or 70 kDa protein. These data indicate that the N-terminal part of fibronectin binds to III1 via I4 and I5 and that interactions in addition to that of I4 and I5 with III1 are important for cell-surface-mediated fibronectin polymerization.

Endothelial cell mitogenesis induced by LPA: inhibition by thrombospondin-1 and thrombospondin-2

We examined the effects of thrombospondin-1 (TSP1) and thrombospondin-2 (TSP2) on the uptake of tritiated thymidine by bovine aortic endothelial (BAE) cells in response to two growth factors, basic fibroblast growth factor (bFGF) and lysophosphatidic acid (LPA). bFGF and LPA stimulate cell proliferation through distinct receptors that have convergent signaling pathways. The doses of LPA that trigger proliferation of BAE cells, which have not been reported previously, were 1 to 30 micromol/L, as opposed to the 5 to 100 micromol/L concentrations required to stimulate proliferation of human foreskin fibroblasts. Baseline mitogenic activity and activity stimulated by either bFGF or LPA on BAE cells was inhibited by human TSP1 purified from platelets or a recombinant source with a similar dose response. These results demonstrate that the anti-proliferative effect of platelet TSP1 is not caused by contaminants from the stimulated platelet. Recombinant mouse TSP2 inhibited BAE cell proliferation in response to LPA in a dose range similar to that of TSP1. Inasmuch as TSP2 does not activate latent TGFbeta1 (Schultz-Cherry et al., J Biol Chem 1995;270: 7304), these results show that inhibition of angiogenesis by TSPs is not related to control of activation of TGFbeta. Together, these studies suggest that structural motifs common to TSP1 and TSP2 inhibit endothelial cell proliferation. Furthermore, TSPs inhibit cell proliferation stimulated by two growth factor receptors that act through distinct signaling pathways.

Cross-linking of the NH2-terminal region of fibronectin to molecules of large apparent molecular mass. Characterization of fibronectin assembly sites induced by the treatment of fibroblasts with lysophosphatidic acid

Cell surface molecules on adherent cells that bind 125I-labeled fibronectin or its 70-kDa N-terminal fragment were identified by cross-linking with factor XIIIa and by photoaffinity labeling. Such cross-linking caused the 70-kDa fragment to become associated irreversibly to cell layers and was greater in cells treated with lysophosphatidic acid, an enhancer of fibronectin assembly and strong modulator of cell shape. Cross-linking of the 70-kDa fragment with factor XIIIa was to molecules that migrated in discontinuous sodium dodecyl sulfate-polyacrylamide gels at the top of the 3.3% stacking gel and near the top of the separating gel. Estimated sizes of these large apparent molecular mass molecules (LAMMs) were >>3 MDa and approximately 3 MDa. The label in 70-kDa fragment conjugated with 125I-sulfosuccinimidyl 2-(p-azidosalicylamido)-1, 3'-dithiopropionate was associated with >>3-MDa LAMMs without reduction and with approximately 3-MDa LAMMs after reduction and transfer of the cleavable label. The LAMMs were expressed on monolayer cells shortly after adherence, required both 1% Triton X-100 and 2 M urea for efficient extraction, and were susceptible to digestion with trypsin but not to cathepsin D digestion. Complexes of 125I-70-kDa fragment and LAMMs were also susceptible to limited acid digestion and Glu-C protease digestion but were not cleaved by chondroitin lyase or heparitinase. Neither the uncleaved complexes nor the cleavage products were immunoprecipitated with anti-fibronectin antibodies directed toward epitopes outside the 70-kDa region. Thus, cell surface molecules that are either very large or not dissociated in sodium dodecyl sulfate comprise the labile matrix assembly sites for fibronectin.

Substratum-dependent stimulation of fibroblast migration by the gelatin-binding domain of fibronectin

Nanomolar concentrations of native fibronectin and its RGDS-containing cell-binding domain have previously been reported to stimulate fibroblast migration in the transmembrane (or ‘Boyden chamber’) assay; in contrast, the gelatin-binding domain (GBD) of fibronectin has consistently been reported to be devoid of migration-stimulating activity in this assay. We have examined the effects of fibronectin and several of its purified functional domains on the migration of human skin fibroblasts in what is presumably a more physiologically relevant assay involving the movement of cells into a 3-D matrix of native type I collagen fibrils. We report that: (a) femtomolar concentrations of GBD stimulate fibroblast migration into such collagen matrices; and (b) fibronectin, as well as peptides containing all other of its functional domains, do not exhibit migration-stimulating activity when tested in the femtomolar to nanomolar concentration range (i.e. 0.1 pg/ml to 1 microgram/ml). The correct assignment of migration-stimulating activity to GBD, rather than to a contaminant, was confirmed by: (a) the use of several fibronectin and GBD purification protocols; (b) the neutralization of GBD migration-stimulating activity by monoclonal antibodies directed against epitopes present in this domain; (c) the time-dependent generation of migration-stimulating activity by the proteolytic degradation of native fibronectin; and (d) obtaining an identical dose-response curve with a genetically engineered GBD peptide. The cryptic migration-stimulating activity of GBD was not affected by the presence of serum or native fibronectin, but was inhibited by TGF-beta 1. Parallel experiments using the transmembrane assay confirmed that GBD was devoid of migration-stimulating activity in this assay when membranes coated with gelatin were used, but revealed that significant stimulation of migration was achieved with membranes coated with native type I collagen. Cells preincubated with GBD for 24 hours whilst growing on plastic tissue culture dishes and then plated onto native collagen matrices in the absence of further GBD also displayed an elevated migration compared to controls. Taken together, these observations suggest that: (a) the interaction of GBD with a putative cell surface receptor (and not the collagen substratum) initiates a persistent alteration in cell phenotype which is manifest by an increase in migratory activity when these cells are cultured on a native collagen substratum; and (b) GBD may play a hitherto unrecognised role in the control of cell migration in response to the local release of proteases during pathological processes, such as tumour invasion and wound repair.