Effects of jarastatin, a novel snake venom disintegrin, on neutrophil migration and actin cytoskeleton dynamics

Surface hydrophobic clusters modulate the folding stability and molecular recognition of the disintegrin jarastatin

Disintegrins are cysteine-rich proteins found in snake venoms. These proteins selectively bind to integrins, which play a key role in the regulation of many physiopathological processes. They are coreless proteins that display almost all hydrophobic residues on the protein surface. The exposed hydrophobic residues form surface clusters stabilized by the interaction with the hydrophilic residues in the vicinity and the hydration shell. In the present work, we aimed to determine the stability of surface hydrophobic clusters (SHCs) and their role in protein folding and biological activity. We used urea denaturation curves followed by 1H and 15N chemical shifts to determine the free energy of unfolding (ΔGF-U) and CLEANEX experiments to measure the water exchange rates of the surface amides (kex). The amides with higher local stability and protection from water exchange are those near or at the SHCs, which form a hydrophobic face. SHCs act as foldons, guiding oxidative folding and contributing to the formation of the disulfide bond framework, which is essential for establishing the concave shape and, ultimately, the binding cleft. On the opposite side of the protein are the residues with lower local stability and amides that exchange fast with water. This face coincides with the binding cleft of the protein to the αVβ3 integrin. Taken together, the present work established a correlation between protein hydration and the binding surface.

Jararaca GPIb-binding protein causes thrombocytopenia during Bothrops jararaca envenomation

Inoculation of Bothrops jararaca snake venom (BjV) induces thrombocytopenia in humans and various animal species. Although several BjV toxins acting on hemostasis have been well characterized in vitro, it is not known which one is responsible for inducing thrombocytopenia in vivo. In previous studies, we showed that BjV incubated with metalloproteinase or serine proteinase inhibitors and/or anti-botrocetin antibodies still induced thrombocytopenia in rats and mice. Thus, herein we identified and characterized BjV toxins responsible for inducing thrombocytopenia. Initially, by filtering BjV on ultrafiltration systems, proteins with molecular masses between 30 and 50 kDa were shown to induce thrombocytopenia in mice, but they were not associated with hemorrhagic or coagulating activities. The 50 kDa ultrafiltrate was chromatographed, and two proteins (named fraction D and fraction E) induced thrombocytopenia in mice. However, neither fraction D nor fraction E induced platelet aggregation in platelet-rich plasma or whole blood from humans or mice. By mass spectrometry analysis, fraction E was identified as jararaca glycoprotein Ib (GPIb)-binding protein. Injection of these fractions caused thrombocytopenia in control or Vwf-/- mice, showing that the axis platelet GPIb - von Willebrand factor is not involved in their biological action in vivo. New studies are necessary to understand how these proteins act in vivo.

Toward the mechanism of jarastatin (rJast) inhibition of the integrin αVβ3

Disintegrins are a family of cysteine-rich small proteins that were first identified in snake venom. The high divergence of disintegrins gave rise to a plethora of functions, all related to the interaction with integrins. Disintegrins evolved to interact selectively with different integrins, eliciting many physiological outcomes and being promising candidates for the therapy of many pathologies. We used NMR to determine the structure and dynamics of the recombinant disintegrin jarastatin (rJast) and its interaction with the cancer-related integrin αVβ3. rJast displayed the canonical fold of a medium-sized disintegrin and showed complex dynamic in multiple timescales. We used NMR experiments to map the interaction of rJast with αVβ3, and molecular docking followed by molecular dynamics (MD) simulation to describe the first structural model of a disintegrin/integrin complex. We showed that not only the RGD loop participates in the interaction, but also the N-terminal domain. rJast plasticity was essential for the interaction with αVβ3 and correlated with the main modes of motion depicted in the MD trajectories. In summary, our study provides novel structural insights that enhance our comprehension of the mechanisms underlying disintegrin functionality.

Snake venom disintegrins update: insights about new findings

Snake venom disintegrins are low molecular weight, non-enzymatic proteins rich in cysteine, present in the venom of snakes from the families Viperidae, Crotalidae, Atractaspididae, Elapidae, and Colubridae. This family of proteins originated in venom through the proteolytic processing of metalloproteinases (SVMPs), which, in turn, evolved from a gene encoding an A Disintegrin And Metalloprotease (ADAM) molecule. Disintegrins have a recognition motif for integrins in their structure, allowing interaction with these transmembrane adhesion receptors and preventing their binding to proteins in the extracellular matrix and other cells. This interaction gives disintegrins their wide range of biological functions, including inhibition of platelet aggregation and antitumor activity. As a result, many studies have been conducted in an attempt to use these natural compounds as a basis for developing therapies for the treatment of various diseases. Furthermore, the FDA has approved Tirofiban and Eptifibatide as antiplatelet compounds, and they are synthesized from the structure of echistatin and barbourin, respectively. In this review, we discuss some of the main functional and structural characteristics of this class of proteins and their potential for therapeutic use.

The recombinant disintegrin, jarastatin, inhibits platelet adhesion and endothelial cell migration

Integrins are transmembrane heterodimeric glycoproteins, present in most cell types that act as mechanoreceptors, connecting extracellular matrix proteins to the cytoskeleton of the cell, mediating several physiological and pathological processes. The disintegrins are peptides capable of modulating the activity of integrins, such as αIIbβ3, responsible for the platelet aggregation and αvβ3, related to angiogenesis. The aim of this study was to produce the recombinant disintegrin jarastatin (rJast), to evaluate its secondary structure and biological activity. rJast was expressed in the yeast Komagataella phaffii (earlier Pichia pastoris) purified using molecular exclusion chromatography and the internal sequence and molecular mass were confirmed by mass spectrometry. The yield was approximately 40 mg/L of culture. rJast inhibited platelet aggregation induced by 2-4 μM ADP, 10 nM thrombin, and 1 μg/mL collagen (IC₅₀ of 244.8 nM, 166.3 nM and 223.5 nM, respectively). It also blocked the adhesion of platelets to collagen under continuous flow in approximately 60% when used 1 μM. We also evaluated the effect of rJast on HMEC-1 cells. rJast significantly inhibited the adhesion of these cells to vitronectin, as well as cell migration (IC₅₀ 1.77 μM) without changing the viability. Conclusions: rJast was successfully expressed with activity in human platelets aggregation identical to the native molecule. Also, rJast inhibits adhesion and migration of endothelial cells. Thus, being relevant for the development of anti-thrombotic and anti-angiogenic drugs.

15N, 13C, and 1H resonance assignments of Jarastatin: a disintegrin of Bothrops jararaca

Disintegrins are a group of cysteine-rich proteins found in a wide variety of snake venoms. These proteins selectively bind to integrins, which play a fundamental role in the regulation of many physiological and pathological processes. Here, we report the NMR chemical shift assignments for ¹H, ¹⁵N, and ¹³C nuclei in the backbone and side chains of recombinant disintegrin Jarastatin (rJast), which was further validated by secondary structure prediction using the TALOS-N server. Taken together, these data are essential to perform NMR-based experiments, including structure determination, backbone dynamics, mapping ligand sites and enabling a deeper understanding of the effect of hydrophobic surface clusters, which are important elements to stabilize some 3D proteins structure/folding.

Structure-Function Relationship of the Disintegrin Family: Sequence Signature and Integrin Interaction

Disintegrins are small cysteine-rich proteins found in a variety of snake venom. These proteins selectively modulate integrin function, heterodimeric receptors involved in cell-cell and cell-matrix interaction that are widely studied as therapeutic targets. Snake venom disintegrins emerged from the snake venom metalloproteinase and are classified according to the sequence size and number of disulfide bonds. Evolutive structure and function diversification of disintegrin family involves a stepwise decrease in the polypeptide chain, loss of cysteine residues, and selectivity. Since the structure elucidation of echistatin, the description of the structural properties of disintegrins has allowed the investigation of the mechanisms involved in integrin-cell-extracellular matrix interaction. This review provides an analysis of the structures of all family groups enabling the description of an expanded classification of the disintegrin family in seven groups. Each group presents a particular disulfide pattern and sequence signatures, facilitating the identification of new disintegrins. The classification was based on the disintegrin-like domain of the human metalloproteinase (ADAM-10). We also present the sequence and structural signatures important for disintegrin-integrin interaction, unveiling the relationship between the structure and function of these proteins.

Effects of venoms on neutrophil respiratory burst: a major inflammatory function

Neutrophils play a pivotal role in innate immunity and in the inflammatory response. Neutrophils are very motile cells that are rapidly recruited to the inflammatory site as the body first line of defense. Their bactericidal activity is due to the release into the phagocytic vacuole, called phagosome, of several toxic molecules directed against microbes. Neutrophil stimulation induces release of this arsenal into the phagosome and induces the assembly at the membrane of subunits of the NAPDH oxidase, the enzyme responsible for the production of superoxide anion that gives rise to other reactive oxygen species (ROS), a process called respiratory burst. Altogether, they are responsible for the bactericidal activity of the neutrophils. Excessive activation of neutrophils can lead to extensive release of these toxic agents, inducing tissue injury and the inflammatory reaction. Envenomation, caused by different animal species (bees, wasps, scorpions, snakes etc.), is well known to induce a local and acute inflammatory reaction, characterized by recruitment and activation of leukocytes and the release of several inflammatory mediators, including prostaglandins and cytokines. Venoms contain several molecules such as enzymes (phospholipase A2, L-amino acid oxidase and proteases, among others) and peptides (disintegrins, mastoporan, parabutoporin etc.). These molecules are able to stimulate or inhibit ROS production by neutrophils. The present review article gives a general overview of the main neutrophil functions focusing on ROS production and summarizes how venoms and venom molecules can affect this function.

Tracking the recruitment and evolution of snake toxins using the evolutionary context provided by the Bothrops jararaca genome

Venom is a key adaptive innovation in snakes, and how nonvenom genes were co-opted to become part of the toxin arsenal is a significant evolutionary question. While this process has been investigated through the phylogenetic reconstruction of toxin sequences, evidence provided by the genomic context of toxin genes remains less explored. To investigate the process of toxin recruitment, we sequenced the genome of Bothrops jararaca, a clinically relevant pitviper. In addition to producing a road map with canonical structures of genes encoding 12 toxin families, we inferred most of the ancestral genes for their loci. We found evidence that 1) snake venom metalloproteinases (SVMPs) and phospholipases A2 (PLA2) have expanded in genomic proximity to their nonvenomous ancestors; 2) serine proteinases arose by co-opting a local gene that also gave rise to lizard gilatoxins and then expanded; 3) the bradykinin-potentiating peptides originated from a C-type natriuretic peptide gene backbone; and 4) VEGF-F was co-opted from a PGF-like gene and not from VEGF-A. We evaluated two scenarios for the original recruitment of nontoxin genes for snake venom: 1) in locus ancestral gene duplication and 2) in locus ancestral gene direct co-option. The first explains the origins of two important toxins (SVMP and PLA2), while the second explains the emergence of a greater number of venom components. Overall, our results support the idea of a locally assembled venom arsenal in which the most clinically relevant toxin families expanded through posterior gene duplications, regardless of whether they originated by duplication or gene co-option.

Recombinant and Chimeric Disintegrins in Preclinical Research

Disintegrins are a family of small cysteine-rich peptides, found in a wide variety of snake venoms of different phylogenetic origin. These peptides selectively bind to integrins, which are heterodimeric adhesion receptors that play a fundamental role in the regulation of many physiological and pathological processes, such as hemostasis and tumor metastasis. Most disintegrins interact with integrins through the RGD (Arg-Gly-Asp) sequence loop, resulting in an active site that modulates the integrin activity. Some variations in the tripeptide sequence and the variability in its neighborhood result in a different specificity or affinity toward integrin receptors from platelets, tumor cells or neutrophils. Recombinant forms of these proteins are obtained mainly through Escherichia coli, which is the most common host used for heterologous expression. Advances in the study of the structure-activity relationship and importance of some regions of the molecule, especially the hairpin loop and the C-terminus, rely on approaches such as site-directed mutagenesis and the design and expression of chimeric peptides. This review provides highlights of the biological relevance and contribution of recombinant disintegrins to the understanding of their binding specificity, biological activities and therapeutic potential. The biological and pharmacological relevance on the newest discoveries about this family of integrin-binding proteins are discussed.

Inhibition of αvβ3 integrin induces loss of cell directionality of oral squamous carcinoma cells (OSCC)

The connective tissue formed by extracellular matrix (ECM) rich in fibronectin and collagen consists a barrier that cancer cells have to overpass to reach blood vessels and then a metastatic site. Cell adhesion to fibronectin is mediated by α_vβ₃ and α₅β₁ integrins through an RGD motif present in this ECM protein, thus making these receptors key targets for cell migration studies. Here we investigated the effect of an RGD disintegrin, DisBa-01, on the migration of human fibroblasts (BJ) and oral squamous cancer cells (OSCC, SCC25) on a fibronectin-rich environment. Time-lapse images were acquired on fibronectin-coated glass-bottomed dishes. Migration speed and directionality analysis indicated that OSCC cells, but not fibroblasts, showed significant decrease in both parameters in the presence of DisBa-01 (1μM and 2μM). Integrin expression levels of the α₅, α_v and β₃ subunits were similar in both cell lines, while β1 subunit is present in lower levels on the cancer cells. Next, we examined whether the effects of DisBa-01 were related to changes in adhesion properties by using paxillin immunostaining and total internal reflection fluorescence TIRF microscopy. OSCCs in the presence of DisBa-01 showed increased adhesion sizes and number of maturing adhesion. The same parameters were analyzed usingβ3-GFP overexpressing cells and showed that β3 overexpression restored cell migration velocity and the number of maturing adhesion that were altered by DisBa-01. Surface plasmon resonance analysis showed that DisBa-01 has 100x higher affinity for α_vβ₃ integrin than forα5β1 integrin. In conclusion, our results suggest that the α_vβ₃ integrin is the main receptor involved in cell directionality and its blockage may be an interesting alternative against metastasis.

Effects of Blocking αvβ₃ integrin by a recombinant RGD disintegrin on remodeling of wound healing after induction of incisional hernia in rats

PURPOSE

Incisional hernia (IH) is characterized by defective wound healing process. Disba-01, a αvb₃ integrin blocker has shown to control the rate of wound repair and therefore it could be a target for new wound healing therapies.The objective of the study was to determine the changes induced by Disba-01 on repair of wound healing after induced IH in rats.

METHODS

Thirty two male albino rats were submitted to IH and divided into 4 experimental groups: G1, placebo control; G2, DisBa-01-treated; G3, anti-αvβ₃ antibodies-treated and G4, anti-α₂ antibodies-treated. Histological. biochemical and extracellular matrix remodeling analysis of abdominal wall were evaluated.

RESULTS

After 14 days, 100% of the G2 did not present hernia, and the hernia ring was closed by a thin membrane. In contrast, all groups maintained incisional hernia. DisBa-01 also increased the number macrophages and fibroblasts and induced the formation of new vessels. Additionally, MMP-2 was strongly activated only in G2 (P<0.05). Anti- αvβ₃-integrin antibodies produced similar results than Disba-01 but not anti-α₂ integrin blocking antibodies.

CONCLUSION

These results strongly indicate that Disba-01 has an important role in the control of wound healing and the blocking of this integrin may be an interesting therapeutical strategy in IH.

Applications of snake venom components to modulate integrin activities in cell-matrix interactions

Snake venom proteins are broadly investigated in the different areas of life science. Direct interaction of these compounds with cells may involve a variety of mechanisms that result in diverse cellular responses leading to the activation or blocking of physiological functions of the cell. In this review, the snake venom components interacting with integrins will be characterized in context of their effect on cellular response. Currently, two major families of snake venom proteins are considered as integrin-binding molecules. The most attention has been devoted to the disintegrin family, which binds certain types of integrins through specific motifs recognized as a tri-peptide structurally localized on an integrin-binding loop. Other snake venom integrin-binding proteins belong to the C-type lectin family. Snake venom molecules bind to the cellular integrins resulting in a modulation of cell signaling and in consequence, the regulation of cell proliferation, migration and apoptosis. Therefore, snake venom research on the integrin-binding molecules may have significance in biomedicine and basic cell biology.

A novel protein from the serum of Python sebae, structurally homologous with type-γ phospholipase A(2) inhibitor, displays antitumour activity

Cytotoxic and antitumour factors have been documented in the venom of snakes, although little information is available on the identification of cytotoxic products in snake serum. In the present study, we purified and characterized a new cytotoxic factor from serum of the non-venomous African rock python (Python sebae), endowed with antitumour activity. PSS (P. sebae serum) exerted a cytotoxic activity and reduced dose-dependently the viability of several different tumour cell lines. In a model of human squamous cell carcinoma xenograft (A431), subcutaneous injection of PSS in proximity of the tumour mass reduced the tumour volume by 20%. Fractionation of PSS by ion-exchange chromatography yielded an active protein fraction, F5, which significantly reduced tumour cell viability in vitro and, strikingly, tumour growth in vivo. F5 is composed of P1 (peak 1) and P2 subunits interacting in a 1:1 stoichiometric ratio to form a heterotetramer in equilibrium with a hexameric form, which retained biological activity only when assembled. The two peptides share sequence similarity with PIP {PLI-γ [type-γ PLA(2) (phospholipase A(2)) inhibitor] from Python reticulatus}, existing as a homohexamer. More importantly, although PIP inhibits the hydrolytic activity of PLA(2), the anti-PLA(2) function of F5 is negligible. Using high-resolution MS, we covered 87 and 97% of the sequences of P1 and P2 respectively. In conclusion, in the present study we have identified and thoroughly characterized a novel protein displaying high sequence similarity to PLI-γ and possessing remarkable cytotoxic and antitumour effects that can be exploited for potential pharmacological applications.

Thrombin-dependent modulation of β1-integrin-mediated signaling up-regulates prolidase and HIF-1α through p-FAK in colorectal cancer cells

Products of prolidase [E.C. 3.4.13.9] activity, proline or hydroxyproline, contribute to up-regulation of hypoxia-inducible factor-1α (HIF-1α). Prolidase activity is regulated by β(1)-integrin signaling. We studied the effects of echistatin (a well-known disintegrin) and thrombin (a serine protease capable of activation of integrin α(2)β(1) receptor) on prolidase activity and expressions of prolidase, α(2)β(1)-integrin receptor, focal adhesion kinase (FAK), MAP-kinases (ERK(1) and ERK(2)), and nuclear HIF-1α in human colon adenocarcinoma (DLD-1) cells. It has been found that treatment of the cells with thrombin contributes to decrease in the expression of prolidase and simultaneously increase in its phosphorylation, resulting in maintenance of the enzyme activity. The phenomenon was accompanied by thrombin-dependent recovery of depressed autophosphorylation of FAK (pY(397)) under the effect of FAK inhibitor (1,2,4,5-benzenetetramine tetrahydrochloride). Although integrin α(2)β(1) receptor expression was not affected by thrombin, the signaling induced by thrombin up-regulated nuclear HIF-1α expression. It was accompanied by increase in the expression of MAP kinases, ERK1 and ERK2. It suggests that integrin-dependent signaling through p-FAK is up-regulated in DLD-1 cells and it may represent potential target for anti-cancer therapy.

Snake venom disintegrins and cell migration

Cell migration is a key process for the defense of pluricellular organisms against pathogens, and it involves a set of surface receptors acting in an ordered fashion to contribute directionality to the movement. Among these receptors are the integrins, which connect the cell cytoskeleton to the extracellular matrix components, thus playing a central role in cell migration. Integrin clustering at focal adhesions drives actin polymerization along the cell leading edge, resulting in polarity of cell movement. Therefore, small integrin-binding proteins such as the snake venom disintegrins that inhibit integrin-mediated cell adhesion are expected to inhibit cell migration. Here we review the current knowledge on disintegrin and disintegrin-like protein effects on cell migration and their potential use as pharmacological tools in anti-inflammatory therapy as well as in inhibition of metastatic invasion.

Platelet-active substances in the venom of Bothrops moojeni snake-a novel evaluation method using whole blood aggregometry

The objective of the present study was an investigation of the crude Bothrops moojeni venom, aiming at the identification of new compounds with platelet-activating or -inhibiting activity. The venom was separated by gel filtration chromatography into 18 fractions, which were tested by means of whole blood aggregometry for their activities affecting the aggregation of blood platelets. In order to eliminate interferences caused by prothrombin activators or thrombin like-enzymes, which are frequently present in snake venoms, a test method for screening protein mixtures was developed. To avoid clotting of the blood samples, the thrombin inhibitor hirudin and the synthetic inhibitor of fibrin polymerization Pefabloc FG were applied. In the present study, a platelet aggregation activator with an activity resembling thrombocytin from B. atrox was identified in one of the examined venom fractions. In addition, a platelet antagonist-most likely a disintegrin-with broad inhibitory activity against aggregation triggered by collagen, adenosine diphosphate and thrombin receptor activating peptide, was identified.

A novel anti-platelet aggregation tripeptide from Agkistrodon acutus venom: isolation and characterization

AAP, a tripeptide that inhibited rabbit platelet aggregation, was isolated from Agkistrodon acutus venom by ion-exchange, gel filtration and reverse-phase chromatography. Amino acid sequences which determined mainly by amino acid analyses and NMR spectroscopy indicated it was a tripeptide including pyroglutamic acid, asparagine and tryptophane residues. The ESMS experiment assigned a molecular weight of 429 Da. AAP inhibited rabbit platelet aggregation induced by ADP, PAF-acether, collagen and thrombin, the IC(50)s were 178 microM, 332 microM, 179 microM and 203 microM, respectively. AAP also inhibited thrombus formation in vivo thrombosis model and prevented the combination between fibrinogen and GP IIb/IIIa. Besides, AAP was not toxic after intravenous injection into mice at a higher dose. Those studies might be helpful to delineate unknown mechanisms involved in platelet aggregation and serve as a model for developing antithrombotic agents.

Integrin inhibitors from snake venom: exploring the relationship between the structure and activity of RGD-peptides

alphaIIbbeta3 is an integrin that is involved in platelet adhesion and aggregation. This receptor may be inhibited by cysteine-rich peptides known as disintegrins. We isolated two disintegrins from Bothrops jararaca venom called jarastatin and jararacin. We evaluated the structural characteristics and the effects on human platelet aggregation of these disintegrins. Inhibitory profiles were compared to six distinct peptides synthesized based on their RGD hairpin loop primary sequences. Both jarastatin and jararacin inhibited ADP and thrombin induction. Conversely, none of the cyclic peptides showed high-quality activity in assays induced by ADP or thrombin. We constructed homology models for all of these molecules, and theoretically evaluated their interaction with the alphaIIbbeta3 crystal structure using a molecular modeling approach. These results support the observations that the cyclic peptides had little effects, and also reinforce the observation that residues outside the disintegrin RGD sequence are required for interactions with receptor.

Cytoskeletal rearrangement and cell death induced by Bothrops alternatus snake venom in cultured Madin–Darby canine kidney cells

Bothrops snake venoms cause renal damage, with renal failure being the main cause of death in humans bitten by these snakes. In this work, we investigated the cytoskeletal rearrangement and cytotoxicity caused by Bothrops alternatus venom in cultured Madin–Darby canine kidney (MDCK) cells. Incubation with venom (10 and 100 µg/mL) significantly (p <0.05) decreased the cellular uptake of neutral red dye after 1 and 3 h. Venom (100 µg/mL) also markedly decreased the transepithelial electrical resistance (RT) across MDCK monolayers. Staining with rhodamine-conjugated phalloidin revealed disarray of the cytoskeleton that involved the stress fibers at the basal cell surface and focal adhesion-associated F-actin in the cell–matrix contact region. Feulgen staining showed a significant decrease in the number of cells undergoing mitosis and an increase in the frequency of altered nuclei. Scanning electron microscopy revealed a decrease in the number of microvilli and the presence of cells with a fusiform format. Flow cytometry with annexin V and propidium iodide showed that cell death occurred by necrosis, with little apoptosis, a conclusion supported by the lack of DNA fragmentation characteristic of apoptosis. Pretreating the cells with catalase significantly attenuated the venom-induced loss of viability, indicating a possible involvement of H2O2 in the cellular damage; less protection was observed with superoxide dismutase or Nω-nitro-l-arginine methyl ester. These results indicate that Bothrops alternatus venom is cytotoxic to cultured MDCK cells, possibly via the action of reactive oxygen species. This cytotoxicity could contribute to nephrotoxicity after envenoming by this species.

Prothrombin fragments containing kringle domains induce migration and activation of human neutrophils

The cross-talk between inflammatory and coagulation cascades has been demonstrated. Prothrombin processing releases the protease domain (thrombin) along with two catalytically inactive kringle-containing derivatives: prothrombin fragments 1 (F1) and 2 (F2). It is well established that thrombin is able to trigger an inflammatory response but the possible effects of prothrombin fragments on leukocyte functions are still unknown. In this report, we demonstrate for the first time that both F1 and F2 prothrombin fragments, interfere with intracellular functional signaling pathways to modulate human neutrophil migration. In addition, we show that thrombin, fragment 1 and fragment 2 induce human neutrophil chemotaxis. The effect of fragment 2, but not fragment 1, was partially inhibited by pertussis toxin, an inhibitor of G(alphai)-signaling. The pre-treatment of cells with fragment 2 inhibited thrombin-induced chemotaxis, while both fragments impaired neutrophil migration induced by interleukin-8. F1 and F2 increased the expression and activation of G-protein-coupled receptor kinase-2, which has emerged as a key effector in the desensitization of chemokine receptors. In parallel, prothrombin fragments activated extracellular signal-regulated kinase 1/2, stimulating its phosphorylation and nuclear translocation, and induced inhibitor of kappa-B phosphorylation and degradation followed by nuclear factor-kappa B translocation to nucleus. Furthermore, both prothrombin fragments induced interleukin-8 gene expression in human neutrophils. These findings suggest that the interference with neutrophil signaling and function, caused by kringle-containing prothrombin fragments may desensitize these cells to respond to further activation by thrombin and interleukin-8 during inflammatory and coagulation responses.

Effect of RGD-disintegrins on melanoma cell growth and metastasis: involvement of the actin cytoskeleton, FAK and c-Fos

The effects and molecular mechanisms of RGD-disintegrins isolated from snake venoms on the growth and metastatic potential of B16F10-melanoma cells were investigated. Jarastatin (JT) from Bothrops jararaca is a ligand of alpha(5)beta(1), alpha(v)beta(3) and alpha(m)beta(2) integrins, flavoridin (FL) from Trimeresurus flavoridis binds preferentially to alpha(5)beta(1) and kistrin (KR) from Calloselasma rhodostoma is a selective ligand of alpha(v)beta(3). When injected simultaneously with melanoma cells in mice, the three disintegrins significantly reduced tumor lung colonization. On the other hand, JT and FL, but not KR, inhibited B16F10 cell growth in vitro. Interaction of JT or FL with melanoma cells induced actin cytoskeleton rearrangement, increasing actin polymerization and FAK phosphorylation. The effect of FL correlates with the decrease in the constitutively high nuclear content of c-Fos, whereas JT interfered with NF-kappaB translocation in melanoma cells. None of the disintegrins produced alterations in the nuclear Erk-2. The results provide further evidence to suggest RGD-disintegrins as potent anti-metastatic agents in vivo, and indicate that their interaction with alpha(5)beta(1) integrin interfere with integrin-couple signaling, down-regulating transcription factors and negatively modulating cell proliferation. These effects may contribute to inhibition of melanoma cell invasion in vivo.

Molecular diversity of disintegrin-like domains within metalloproteinase precursors of Bothrops jararaca

Disintegrins are small peptides isolated from the venom of several snake families which act as integrin-antagonists or agonists, interacting with a variety of biological processes mediated by integrins. In this work we describe five new disintegrin-like domains within metalloproteinase precursor sequences, obtained from a Bothrops jararaca venom gland cDNA library. Among the new disintegrin-like domains, four were contained in PIII metalloproteinase precursors, with three of them presenting ECD-motifs and one presenting a new KCD-motif. Moreover, we found three disintegrin-like domains within PII metalloproteinase precursors. Two of them are similar to the already described disintegrins jarastatin and jararacin. The third molecule is unusual, presenting some typical PIII metalloproteinase characteristics but lacking the cysteine-rich domain being, thus, classified as a PII metalloproteinase. Only few reports presented molecules with these characteristics. Sequence analysis suggests that these molecules are intermediate steps between the more ancient PIII and the more recent PII metalloproteinases. We also investigated disintegrin N-terminus diversity in B. jararaca crude venom by purifying jarastatin and jararacin and analyzing them by mass spectrometry.

Activation of human T lymphocytes via integrin signaling induced by RGD-disintegrins

Adhesive interactions play important roles in coordinating T cell migration and activation, which are mediated by binding of integrins to RGD motif found on extracellular matrix proteins. Disintegrins, isolated from snake venoms, contain the RGD sequence that confers selectivity to integrin interaction. We have investigated the ability of three RGD-disintegrins, ligands of alpha(5)beta(1) and alpha(v)beta(3), Flavoridin (Fl), Kistrin (Kr) and Echistatin (Ech), in modulating the activation of human T lymphocyte. The disintegrins induced T cell proliferation and CD69 expression. This activation parallels with actin cytoskeleton reorganization and tyrosine phosphorylation. Furthermore, the peptides induced focal adhesion kinase (FAK) and phosphoinositide 3-kinase (PI3K) activation. Finally, RGD-disintegrins were capable of driving NF-kappaB nuclear translocation and c-Fos expression, in a PI3K and ERK1/2 activities dependent manner. This report is the first to show that RGD-disintegrins interact with integrins on human T lymphocyte surface, modulating cell proliferation and activation of specific pathways coupled to integrin receptor.

Scratching below the surface: wound healing and alanine mutagenesis provide unique insights into interactions between eristostatin, platelets and melanoma cells

To study the molecular mechanism of the disintegrin eristostatin, cellular functional studies were performed using ten recombinant alanine mutants. ADP-induced platelet aggregation revealed critical contributions of seven residues within the 'RGD loop' (R24, R27, G28, N31) and C-terminus (W47, N48, G49) of this disintegrin. Using an in vitro scratch wound healing assay, four human melanoma cell lines yielded similar results when exposed to wildtype eristostatin. All eristostatin-treated cells healed less of the wounded area than control conditions. This phenomenon was reproduced when using fibronectin as the matrix. C8161 cells showed significant delay in wound closure with the N-terminal mutant P4A but not with R24A or G28A. Evidence from our laboratory and others suggests neither alpha IIb, alpha 4 nor alpha 5 integrins are directly involved in eristostatin's interactions. Eristostatin did not affect the number of melanoma cells in culture after 24 h or the development of apoptosis. However, phosphorylation studies performed after these melanoma cells were exposed to eristostatin revealed changes in several tyrosine phosphorylated molecules.

Snake venom metalloproteases--structure and function of catalytic and disintegrin domains

Snake venoms are relevant sources of toxins that have evolved towards the engineering of highly active compounds. In the last years, research efforts have produced great advance in their understanding and uses. Metalloproteases with disintegrin domains are among the most abundant toxins in many Viperidae snake venoms. This review will focus on the structure, function and possible applications of the metalloprotease and disintegrin domains.

Disintegrins: integrin selective ligands which activate integrin-coupled signaling and modulate leukocyte functions

Extracellular matrix proteins and cell adhesion receptors (integrins) play essential roles in the regulation of cell adhesion and migration. Interactions of integrins with the extracellular matrix proteins lead to phosphorylation of several intracellular proteins such as focal adhesion kinase, activating different signaling pathways responsible for the regulation of a variety of cell functions, including cytoskeleton mobilization. Once leukocytes are guided to sites of infection, inflammation, or antigen presentation, integrins can participate in the initiation, maintenance, or termination of the immune and inflammatory responses. The modulation of neutrophil activation through integrin-mediated pathways is important in the homeostatic control of the resolution of inflammatory states. In addition, during recirculation, T lymphocyte movement through distinct microenvironments is mediated by integrins, which are critical for cell cycle, differentiation and gene expression. Disintegrins are a family of low-molecular weight, cysteine-rich peptides first identified in snake venom, usually containing an RGD (Arg-Gly-Asp) motif, which confers the ability to selectively bind to integrins, inhibiting integrin-related functions in different cell systems. In this review we show that, depending on the cell type and the microenvironment, disintegrins are able to antagonize the effects of integrins or to act agonistically by activating integrin-mediated signaling. Disintegrins have proven useful as tools to improve the understanding of the molecular events regulated by integrin signaling in leukocytes and prototypes in order to design therapies able to interfere with integrin-mediated effects.

Differential effects of echistatin and thrombin on collagen production and prolidase activity in human dermal fibroblasts and their possible implication in beta1-integrin-mediated signaling

Prolidase [E.C. 3.4.13.9] is a cytosolic imidodipeptidase that plays an important role in collagen biosynthesis. The enzyme contributes to the recovery of proline from protein degradation products (mainly collagen) for collagen resynthesis. Prolidase activity and collagen biosynthesis are supposed to be regulated by beta(1)-integrins, which initiate a signaling pathway in which several kinases and intracellular proteins are involved, including focal adhesion kinase pp125(FAK) (FAK), Src, Shc, growth factor receptor bound protein 2 (Grb-2), son of sevenless protein (SOS), Ras, Raf and mitogen-activated protein kinases (MAPK), extracellular-signal regulated kinase 1 (ERK(1)) and kinase 2 (ERK(2)). We studied the effects of echistatin, a well-known disintegrin and thrombin, a serine protease capable of activation of platelet integrin alpha(2)beta(1) receptor on collagen production, prolidase activity, expression of prolidase, beta(1)-integrin receptor, FAK, SOS-protein and phosphorylated MAP-kinases (ERK(1) and ERK(2)) in confluent human dermal fibroblasts. It has been found that treatment of the cells with 100nM echistatin contributes to inhibition of collagen production, as well as prolidase activity and expression compared to control cells. These phenomena were accompanied by a decrease in the expression of FAK, SOS-protein and phosphorylated MAP-kinases, ERK(1) and ERK(2). An opposite phenomenon was observed in fibroblasts treated with 0.1IU thrombin. In this case, a significant increase in collagen production and prolidase activity, accompanied by a distinct raise in the expression of prolidase, FAK and phosphorylated MAP-kinases and a slight increase in expression of SOS compared to controls were found. The results suggest that regulation of prolidase activity and collagen biosynthesis in human dermal fibroblasts may involve beta(1)-integrin-dependent signaling.

Analysis methods of human cell migration

The autonomous migration of specialized cells is an essential characteristic in both physiological and pathological functions in the adult human organism. Leukocytes, fibroblasts, and stem cells, but also tumor cells, are thus the subject of intense investigation in a broad range of research fields. A wide spectrum of methods have therefore been established to analyze chemokinetic and chemotactic cell migration, ranging from easy-to-handle two-dimensional surface migration assays to highly specialized three-dimensional and intravital analysis methods. It is now manifest that the results obtained with these various migration assays substantially differ. This review therefore gives an overview of the migration assays which are currently in use, describes the methods, and critically enlightens the particular advantages and disadvantages of each method.

Molecular cloning, functional expression, and molecular modeling of bothrostatin, a new highly active disintegrin from Bothrops jararaca venom

Disintegrins are among the most potent antagonists of several integrins. A cDNA encoding a novel disintegrin, bothrostatin, was cloned from a Bothrops jararaca cDNA library. The precursor of bothrostatin contains a pro, a metalloproteinase, and an RGD-disintegrin domain. The disintegrin domain expressed in Escherichia coli showed high inhibitory activity on collagen-induced platelet aggregation (IC(50) of 12nM), and thus it can be used as a useful tool for studies of integrin-ligand interaction. Furthermore, we used the comparative modeling approach to obtain a model of the 3D structure of bothrostatin. Our results suggest that bothrostatin adopts a globular, closed structure in solution. The RGD motif is exposed to the solution by the loop formed by residues 45-59 and is very close to the C-terminal domain forming a finger-like structure. The proximity of the RGD loop and the C-terminal residues, which is maintained by the Cys47-Cys66 bond, suggests that the C-terminal residues are involved in the ability of bothrostatin to interact with its ligands.

Fast analysis of low molecular mass compounds present in snake venom: identification of ten new pyroglutamate-containing peptides

Characterization of the peptide content in snake venoms can be an important tool for the investigation of new pharmacological lead compounds. For this purpose, single-step analysis of crude venoms has recently been demonstrated using mass spectrometry (MS) techniques. Reproducible profiles of ions in MS and MS/MS spectra may also be used to compare venoms from different species. In this work matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOFMS) was used to obtain mass patterns of the major peptides (<8 kDa) found in pooled venoms from the genera Bothrops and Crotalus. Venoms from five different Bothrops species (B. jararaca, B. insularis, B. alternatus, B. jararacussu, and B. neuwiedi) and three Crotalus species (C. viridis, C. adamanteus and C. durissus terrificus) were analyzed. In agreement with other reports, venoms from Bothrops species contained a variety of peptides in the range m/z 1000-1500, and in some samples larger components (m/z 7000-8000) were detected. In the Crotalus species venoms were rich in peptides ranging from m/z 1000-1500 and 4000-5500. MS/MS experiments on the low molecular mass peptides (m/z 1000-1500) confirmed the presence of ten new bradykinin-potentiating peptides among venoms from genera Bothrops and Crotalus. In order to determine whether additional peptides could be identified after partial purification, B. jararaca venom was subjected to size-exclusion chromatography on Sephacryl S-200, and two distinct low molecular mass pools were analyzed further by MALDI-TOFMS. No additional peptides were detected from the pool with masses below 2000 Da but a substantial improvement with better resolution was observed for the pool with masses above 7000 Da, indicating that complex samples such as crude snake venoms can be analyzed for low molecular mass peptides using a single-step procedure.

Alternagin-C, a Disintegrin-like Protein, Induces Vascular Endothelial Cell Growth Factor (VEGF) Expression and Endothelial Cell Proliferation in Vitro

Alternagin-C (ALT-C), a disintegrin-like protein purified from the venom of the Brazilian snake Bothrops alternatus, interacts with the major collagen I receptor, the alpha(2)beta(1) integrin, inhibiting collagen binding. Here we show that ALT-C also inhibits the adhesion of a mouse fibroblast cell line (NIH-3T3) to collagen I (IC(50) 2.2 microm). In addition, when immobilized on plate wells, ALT-C supports the adhesion of this cell line as well as of human vein endothelial cell (HUVEC). ALT-C (3 microm) does not detach cells that were previously bound to collagen I. ALT-C (5 nm) induces HUVEC proliferation in vitro, and it inhibits the positive effect of vascular endothelial growth factor (VEGF) or FGF-2 on the proliferation of these cells, thus suggesting a common mechanism for these proteins. Gene expression analysis of human fibroblasts growing on ALT-C- or collagen-coated plates showed that ALT-C and collagen I induce a very similar pattern of gene expression. When compared with cells growing on plastic only, ALT-C up-regulates the expression of 45 genes including the VEGF gene and down-regulates the expression of 30 genes. Fibroblast VEGF expression was confirmed by RT-PCR and ELISA assay. Up-regulation of the VEGF gene and other growth factors could explain the positive effect on HUVEC proliferation. ALT-C also strongly activates Akt/PKB phosphorylation, a signaling event involved in endothelial survival and angiogenesis. In conclusion, ALT-C acts as a survival factor, promoting adhesion and endothelial cell proliferation.

RGD- and MLD-disintegrins, jarastatin and EC3, activate integrin-mediated signaling modulating the human neutrophils chemotaxis, apoptosis and IL-8 gene expression

The effects of jarastatin (JT), a monomeric RGD-disintegrin, were compared with those of the heterodimeric MLD-disintegrin, EC3, on human neutrophil activation and functions. Both disintegrins inhibited neutrophil chemotaxis induced by fMet-Leu-Phe and were also potent chemotactic agents. These effects were accompanied by an increase in actin polymerization, and both were inhibited by genistein, a tyrosine kinase inhibitor. While JT, but not other RGD-disintegrins, inhibited EC3-induced chemotaxis, EC3 was not able to inhibit JT effect. The chemotactic effect of JT was blocked by anti-alpha(M) antibody whereas anti-alpha(9)beta(1) inhibited EC3 effect. Both JT and EC3 induced focal adhesion kinase (FAK) and phosphoinositide 3-kinase (PI3K) activation. Accordingly, LY294002, a PI3K inhibitor, impaired their chemotactic effect on neutrophils. JT induced Erk-2 translocation to nucleus and a delay of the spontaneous apoptosis of neutrophils in vitro. In contrast, EC3 inhibited Erk-2 activation and had a proapoptotic effect. These effects were reverted by PD98059, an MEK 1/2 inhibitor and blocked by z-VAD-FMK, a caspase inhibitor. In addition, JT, but not EC3, increased the IL-8 mRNA levels in neutrophils. The data indicate that JT and EC3 directly activate an integrin-coupled signaling and modulate the MAPK pathway in different ways, leading the neutrophils to express different functional response.

Alternagin-C, a nonRGD-disintegrin, induces neutrophil migration via integrin signaling

Recently, a new protein containing a disintegrin domain, alternagin-C (Alt-C), was purified from Bothrops alternatus venom. Unlike other disintegrins, in Alt-C an ECD amino acid mogif takes the place of the RGD sequence. Most disintegrins contain an RGD/KGD sequence and are very potent inhibitors of platelet aggregation, as well as other cell interactions with the extracellular matrix, including tumor cell metastasis and angiogenesis. The present study investigated the effects of Alt-C on human neutrophil chemotaxis in vitro and the activation of integrin-mediated pathways. Alt-C showed a potent chemotactic effect for human neutrophils when compared to N-formyl-methionyl-leucyl-phenylalanine peptide (fMLP), a classic chemotactic agent. Moreover, preincubation of neutrophils with Alt-C significantly inhibited chemotaxis toward fMLP and itself. In addition, a peptide containing an ECD sequence presented a chemotactic activity and significantly inhibited chemotaxis induced by Alt-C and fMLP. A significant increase of F-actin content was observed in cells treated with Alt-C, showing that the chemotactic activity of Alt-C on neutrophils is driven by actin cytoskeleton dynamic changes. Furthermore, this protein was able to induce an increase of phosphotyrosine content triggering focal adhesion kinase activation and its association with phosphatidylinositol 3-kinase. Alt-C was also able to induce a significant increase in extracellular signal-regulated kinase 2 nuclear translocation. The chemotactic activity of Alt-C was partially inhibited by LY294002, a specific phosphatidylinositol 3-kinase inhibitor, and by PD98056, a Map kinase kinase inhibitor. These findings suggest that Alt-C can trigger human neutrophil chemotaxis modulated by intracellular signals characteristic of integrin-activated pathways and that these effects could be related to the ECD mogif present in disintegrin-like domain.

BaG, a new dimeric metalloproteinase/disintegrin from the Bothrops alternatus snake venom that interacts with alpha5beta1 integrin

The alpha(5)beta(1) integrin is one of the major fibronectin receptors which plays an essential role in the adhesion of normal and tumor cells to extracellular matrix. Here, we describe the isolation and characterization of a novel dimeric metalloproteinase/disintegrin, which is an inhibitor of fibronectin binding to the alpha(5)beta(1) integrin. This protein (BaG) was isolated from the venom of the South American snake Bothrops alternatus by gelatin-Sepharose affinity and anion exchange chromatography. The molecular mass of BaG was approximately 130 kDa under non-reducing conditions and 55 kDa under reducing conditions by SDS-PAGE. BaG shows proteolytic activity on casein that was inhibited by EDTA. 1,10-phenanthroline-treated BaG (BaG-I) inhibits ADP-induced platelet aggregation with an IC(50) of 190 nM. BaG-I inhibits fibronectin-mediated K562 cell adhesion with an IC(50) of 3.75 microM. K562 cells bind to BaG-I probably through interaction with alpha(5)beta(1) integrin, since anti-alpha(5)beta(1) antibodies inhibited K562 cell adhesion to BaG-I. In addition, BaG-I induces the detachment of K562 cells that were bound to fibronectin. In summary, we have purified a novel, dimeric snake venom metalloproteinase/disintegrin that binds to the alpha(5)beta(1) integrin.

Neurite outgrowth is impaired on HSP70-positive astrocytes through a mechanism that requires NF-kappaB activation

In the adult central nervous system (CNS), prominent reactive astrocytosis is seen in acute traumatic brain injury, neurodegenerative diseases and a variety of viral infections. Reactive astrocytes synthesize a number of factors that could play different roles in neuronal regeneration. In this study, the effects of thermal stress were evaluated on nuclear factor-kappaB (NF-kappaB) activation and proinflammatory cytokine tumor necrosis factor-alpha (TNF-alpha) secretion in primary astrocytic cultures. The ability of HSP70-positive astrocytes to support or inhibit neurite outgrowth was investigated in neuron-astrocyte cocultures. Cultured astrocytes from cerebral cortex of rats were exposed to transient hyperthermia (42 degrees C/30 min) and incubated at 37 degrees C for different periods of recovery. During HSP70 accumulation, astrocytes extended large and thick processes associated to rearrangement of glial fibrillary acidic protein (GFAP) filaments and an increase in protein synthesis and GFAP, suggesting an astrogliosis event. A delay of NF-kappaB activation appeared closely related to TNF-alpha secretion by HSP70-positive astrocytes. These cells demonstrated a functional shift from neurite growth-promoting to non-permissive substrate. We also found that gliotoxin, a specific NF-kappaB inhibitor, partially abrogated the inhibitory ability of reactive astrocytes. These findings may suggest a involvement of NF-kappaB and TNF-alpha in modulating the failure of HSP70-positive astrocytes to provide functional support to neuritic outgrowth.

Impairment of the cell-to-matrix adhesion and cytotoxicity induced by Bothrops moojeni snake venom in cultured renal tubular epithelia

Bothrops moojeni snake venom induces acute renal failure (ARF) as a consequence of morphological and functional alterations in glomerular and tubular cells. It is still unclear whether the ARF results from a direct cytotoxic effect on renal epithelia or from a renal ischemia due to systemic hemodynamic disturbances. This work investigated the in vitro effect of B. moojeni crude venom, using cultured Madin-Darby canine kidney (MDCK) monolayers as a model. The crude venom induced a significant time- and dose-dependent decrease in transepithelial electrical resistance across MDCK monolayers. In addition, the exposure to the venom resulted in cell detachment from the substratum, as revealed by transmission electron microscopy. Immunocytochemical analysis showed no change in the distribution of some junctional proteins, such as occludin, ZO-1, and E-cadherin. Nevertheless, the staining with labeled phalloidin revealed a disarray of the cytoskeleton, specifically of the stress fibers and of the focal adhesion-associated F-actin at the cell-to-matrix contact region. The treatment with B. moojeni venom also increased the cell release of lactate dehydrogenase and decreased cellular uptake of the vital neutral red. In conclusion, B. moojeni crude venom appears to have a direct cytotoxic effect on a renal tubule-derived cell line, also inducing impairment of the cell-matrix interaction.

Neutrophil activation by heme: implications for inflammatory processes

Heme, a ubiquitous iron-containing compound, is present in large amounts in many cells and is inherently dangerous, particularly when it escapes from intracellular sites. The release of heme from damaged cells and tissues is supposed to be higher in diseases such as malaria and hemolytic anemia or in trauma and hemorrhage. We investigated here the role of free ferriprotoporphyrin IX (hemin) as a proinflammatory molecule, with particular attention to its ability to activate neutrophil responses. Injecting hemin into the rat pleural cavity resulted in a dose-dependent migration of neutrophils, indicating that hemin is able to promote the recruitment of these cells in vivo. In vitro, hemin induced human neutrophil chemotaxis and cytoskeleton reorganization, as revealed by the increase of neutrophil actin polymerization. Exposure of human neutrophils to 3 microM hemin activated the expression of the chemokine interleukin-8, as demonstrated by quantitative reverse-transcription polymerase chain reaction, indicating a putative molecular mechanism by which hemin induces chemotaxis in vivo. Brief incubation of human neutrophils with micromolar concentrations of hemin (1-20 microM) triggered the oxidative burst, and the production of reactive oxygen species was directly proportional to the concentration of hemin added to the cells. Finally, we observed that human neutrophil protein kinase C was activated by hemin in vitro, with a K(1/2) of 5 microM. Taken together, these results suggest a role for hemin as a proinflammatory agent able to induce polymorphonuclear neutrophil activation in situations of clinical relevance, such as hemolysis or hemoglobinemia.

Characterization of a monomeric disintegrin, ocellatusin, present in the venom of the Nigerian carpet viper, Echis ocellatus

Ocellatusin is a new RGD-containing short monomeric disintegrin. It is a better inhibitor of alpha(5)beta(1) integrin and a more potent inducer of the expression of a ligand-induced binding site epitope on beta(1) integrin subunit than echistatin. In further contrast to echistatin, ocellatusin has a direct chemotactic stimulus on human neutrophils in vitro. The distinct effects of these two close evolutionarily related disintegrins might be explained by the presence of methionine-22 and histidine-29 in the RGD loop of ocellatusin, which are arginine and aspartic acid, respectively, in echistatin. These mutations may modulate the conformation and/or recognition properties of the integrin-binding loop of ocellatusin.