Ching-Hu Chung

Molecular Cloning and Sequence Analysis of Aggretin, a Collagen-like Platelet Aggregation Inducer☆

A cDNA library derived from the Malayan-pit-viper (Calloselasma rhodostoma) venom gland was constructed in the phagemid vector. Using the information of the N-terminal amino acid sequences of two subunits of aggretin, synthetic mixed-base oligonucleotides were employed as a screening probe for colony hybridization. Separate cDNA clones encoding for the alpha and beta chains of aggretin were isolated and sequenced. The results revealed that mature alpha and beta chains contain 136 and 123 amino acid residues, respectively. Aggretin subunits show high degrees of identity with respective subunits (50-60% for alpha, 49-58% for beta) of C-type lectin-like snake venoms. The identity to rattlesnake lectin is relatively lower (i.e., 39 and 30%). All cysteine residues in each chain of aggretin are well conserved and located at the positions corresponding to those of C-type lectins. Thus, three intracatenary disulfide bridges and an interchain disulfide bond between Cys83(alpha) and Cys75(beta) may be allocated. This is the first report regarding the entire sequence of venom GPIa/IIa agonist. According to the alignment of amino acid sequences, hypervariable regions among these C-type lectin-like proteins were revealed. These hypervariable regions are proposed to be the counterparts directly interacting with different receptors or different domains of a receptor on the surface of platelet.

The integrin α2β1 agonist, aggretin, promotes proliferation and migration of VSMC through NF-kB translocation and PDGF production.

Background and purpose:  During the development of atherosclerotic plaques, vascular smooth muscle cells (VSMCs) migrate from the media to the intima through the basement membrane and interstitial collagenous matrix, and proliferate to form neointima. Here, we investigate the mechanism of VSMC migration and proliferation caused by aggretin, a snake venom integrin α2β1 agonist.

A novel mechanism of cytokine release in phagocytes induced by aggretin, a snake venom C-type lectin protein, through CLEC-2 ligation

Summary  Background: Macrophages are major immune cells and play an important role in modulating homeostasis and the immune defense mechanism. In inflammatory responses to the infection of pathogens, macrophages are activated, producing various inflammatory mediators. Snake venom C‐type lectin proteins (snaclecs) have diverse targets, including platelet GPVI, GPIb, integrin α2β1 or CLEC‐2 expressed in platelets, endothelial cells or myeloid cells. Methods: In this study, murine macrophages (RAW 264.7 cells) and human monocytes (THP‐1) were treated with different snaclecs, including aggretin, gramicetin, trowaglerix and convulxin, in the absence or presence of LPS for 24 h. Results: The production of cytokines, such as tumor necrosis factor‐α (TNF‐α) and interleukin‐6 (IL‐6), in supernatants was measured by ELISA. Aggretin increased the production of TNF‐α and IL‐6 in both RAW264.7 and THP‐1 cells; however, the other snaclecs did not. Aggretin induced extracellular signal‐regulated kinase 1/2 (ERK1/2) and c‐Jun N‐terminal kinase (JNK) tyrosine phosphorylation of RAW264.7 cells. Pretreatments with inhibitor of ERK, JNK, p38 or NF‐κB abolished cytokine release caused by aggretin. Aggretin bound to THP‐1 cells in a concentration‐dependent manner and it displaced the CLEC‐2 mAb binding to THP‐1 cells and the immobilized aggretin selectively bound to CLEC‐2 of both platelets and THP‐1 cell lysates. Furthermore, aggretin elevated the plasma level of IL‐6 in ICR mice as it was administered intramuscularly. Conclusion: These results indicate that aggretin may induce cytokine TNF‐α/IL‐6 release via interacting with CLEC‐2 receptor and the subsequent MAPK and NF‐κB activation in monocytes/macrophages.

Butein Inhibits Angiogenesis of Human Endothelial Progenitor Cells via the Translation Dependent Signaling Pathway

Compelling evidence indicates that bone marrow-derived endothelial progenitor cells (EPCs) can contribute to postnatal neovascularization and tumor angiogenesis. EPCs have been shown to play a “catalytic” role in metastatic progression by mediating the angiogenic switch. Understanding the pharmacological functions and molecular targets of natural products is critical for drug development. Butein, a natural chalcone derivative, has been reported to exert potent anticancer activity. However, the antiangiogenic activity of butein has not been addressed. In this study, we found that butein inhibited serum- and vascular endothelial growth factor- (VEGF-) induced cell proliferation, migration, and tube formation of human EPCs in a concentration dependent manner without cytotoxic effect. Furthermore, butein markedly abrogated VEGF-induced vessels sprouting from aortic rings and suppressed microvessel formation in the Matrigel implant assay in vivo. In addition, butein concentration-dependently repressed the phosphorylation of Akt, mTOR, and the major downstream effectors, p70S6K, 4E-BP1, and eIF4E in EPCs. Taken together, our results demonstrate for the first time that butein exhibits the antiangiogenic effect both in vitro and in vivo by targeting the translational machinery. Butein is a promising angiogenesis inhibitor with the potential for treatment of cancer and other angiogenesis-related diseases.

The highly specific platelet glycoprotein (GP) VI agonist trowaglerix impaired collagen-induced platelet aggregation ex vivo through matrix metalloproteinase-dependent GPVI shedding

Summary.  Background: C‐type lectin proteins (CLPs) have diverse targets including platelet GPIb, GPVI and integrin α2β1, and affect platelet function in a various way. In this study, we characterized a huge, heterodimeric venom protein, trowaglerix, which belongs to the CLP family. Methods: We purified a potent platelet‐aggregation inducer, trowaglerix, from the crude venom of Tropidolaemus wagleri. Biotinylated trowaglerix was used for binding assays, and immunoblotting was used to investigate the signal transduction involved. Results: Two distinct subunits of trowaglerix with similar masses of around 16 kDa were eluted by high‐performance liquid chromatography after reduction and alkylation. Trowaglerix induced platelet aggregation of washed human platelets and platelet‐rich plasma (PRP) in a concentration‐dependent manner. Biotinylated trowaglerix specifically bound to platelet membrane GPVI, but not to GPIb or α2 integrin. Treatment with trowaglerix induced GPVI loss in human platelets in vitro and impaired the platelet aggregation of mouse PRP ex vivo in response to collagen but not in response to adenosine diphosphate (ADP). However, GM6001, a matrix metalloproteinase (MMP) inhibitor, inhibited trowaglerix‐induced GPVI cleavage and restored the platelet responsiveness of PRP to collagen. Conclusions: Trowaglerix activates platelets through specific binding to GPVI, leading to kinases‐dependent exposure of functional αIIbβ3 and platelet aggregation, and also induces MMP‐dependent GPVI shedding from platelets.

A novel compound, NP-184, inhibits the vascular endothelial growth factor induced angiogenesis.

Angiogenesis is observed in many diseases, such as tumor progression, diabetes and rheumatoid arthritis; it is a process that involves proliferation, migration, differentiation and tube formation of endothelial cells. Vascular endothelial growth factor (VEGF) plays an important role in angiogenesis by induction of these endothelial functions. Thus, inhibition of these critical angiogenic steps is a practical therapeutic strategy for those diseases. NP-184 is a substituted benzimidazole analogue which exhibits a potent anti-thrombotic activity. In this report, NP-184 inhibited the viability of human umbilical vascular endothelial cells (HUVEC) in a concentration-dependent manner, and caused cell apoptosis as examined by cell-cycle analysis and Annexin V staining with flow cytometry. NP-184 also concentration-dependently inhibited the HUVEC migration, tube formation on Matrigel, and rat aortic ring sprouting stimulated by VEGF. Regarding the intracellular signal transduction, NP-184 concentration-dependently interfered with the activation of AKT, ERK and the nuclear translocation of NF-kappaB. In vivo study showed that NP-184 dose-dependently reduced angiogenesis in Matrigel plug assay. These results indicate that NP-184 is a potential candidate for developing the treatment of angiogenesis related-diseases.

Antirestenosis Effect of Butein in the Neointima Formation Progression

The development of restenosis involves migration and hyperproliferation of vascular smooth muscle cells (VSMCs). Platelet-derived growth factor (PDGF) is one of the major factors. Butein modulates inflammatory pathways and affects the proliferation and invasion of the tumor. We investigated the hypothesis that butein might prevent the restenosis process via a similar pathway. Our results demonstrated that butein inhibited PDGF-induced VSMC proliferation and migration as determined by BrdU proliferation and two-dimensional migration scratch assay. Butein also concentration-dependently repressed PDGF-induced phosphorylation of PDGF-receptor β, mitogen-activated protein kinases, phosphoinositide 3-kinase/Akt, and phopholipase Cγ/c-Src in VSMCs. In addition, in vivo results showed that butein attenuated neointima formation in balloon-injured rat carotid arteries. These results indicate that butein may inhibit PDGF-induced VSMC proliferation and migration, resulting in attenuation of neointima formation after percutaneous transluminal coronary angioplasty. Our study demonstrates for the first time that systemic administration of butein is able to reduce neointima formation after vascular injury.

Inhibitory Effects of Butein on Cancer Metastasis and Bioenergetic Modulation

Tumor metastasis is the major obstacle for cancer treatment. Previous studies have shown that butein exhibits antiangiogenesis property and anticancer effects in different kinds of human cancer cells. However, the effects of butein on metastasis and energy metabolism of cancer cells are mostly unknown. This study showed that butein significantly inhibited invasion of cancer cells without acting in a cytotoxic fashion. It was further demonstrated that butien dramatically suppressed cancer metastasis by an in vivo CAM-intravasation model. Additionally, butein concentration-dependently repressed the expression and activity of matrix metalloproteinase-9 (MMP-9) and urokinase plasminogen activator (uPA). The study indicated that butein may repress MMP-9 and uPA proteolytic activities and subsequently inhibit cancer metastasis via Akt/mTOR/p70S6K translational machinery. Moreover, butein may partly suppress cancer metastasis by down-regulating ATP synthesis via both oxidative and glycolytic metabolism. The results suggest that butein is a potential antimetastatic agent worthy of further development for cancer treatment.

FcγRII mediates platelet aggregation caused by disintegrins and GPIIb/IIIa monoclonal antibody, AP2

OBJECTIVE Disintegrins, snake venom-derived Arg-Gly-Asp (RGD)-containing polypeptides, and GPIIb/IIIa antagonist (AP2) block fibrinogen binding to GPIIb/IIIa of activated platelets, however, the combination of these two agents caused platelet aggregation. We hypothesize that disintegrin initially binds to specific epitope of GPIIb/IIIa, causing conformational change, and the recruitment of FcgammaRII, which can be bound by AP2, and finally triggering platelet aggregation. MATERIALS AND METHODS We prepared human platelet suspensions and measured platelet aggregation, Ca2+ mobilization, thromboxane B2 formation, and signal transduction. RESULTS Disintegrin (e.g., accutin) and AP2 (a monoclonal antibody [mAb]-raised against GPIIb/IIIa) individually inhibited human platelet aggregation caused by collagen. However, as both accutin and AP2 were sequentially added into platelet suspension, platelet aggregation occurred. Accutin/AP2 caused shape change, cytosolic Ca2+ mobilization, P-selectin expression, and thromboxane A2 formation. Tirofiban, FcgammaRII mAb, or indomethacin completely inhibited platelet aggregation caused by accutin/AP2. Accutin/AP2 also caused tyrosine phosphorylation of signal molecules. Disintegrins enhanced AP2 binding to platelets, and AP2 also promoted disintegrin binding to platelets. FcgammaRII mAb inhibited the enhanced fluorescein isothiocyanate-disintegrin binding to platelet caused by AP2. Immunoprecipitation of the lysates of disintegrin/AP2-treated platelets using FcgammaRII Ab showed complex formation of GPIIb/IIIa and FcgammaRII. CONCLUSION FcgammaRII mediates platelet aggregation caused by disintegrin and AP2, triggering a phospholipase C, phospholipase A2, Src-, Syk kinases, and Ca2+-dependent activation process. AP2 triggers platelet aggregation via binding to accessible FcgammaRII and the conformation-altered GPIIb/IIIa caused by disintegrin.

The disintegrin, trimucrin, suppresses LPS-induced activation of phagocytes primarily through blockade of NF-κB and MAPK activation

In addition to antiplatelet activity, disintegrin, a small-mass RGD-containing polypeptide, has been shown to exert anti-inflammatory effects but the mechanism involved remains unclear. In this study, we report that trimucrin, a disintegrin from the venom of Trimeresurus mucrosquamatus, inhibits lipopolysaccharide (LPS)-induced stimulation of THP-1 and RAW 264.7 cells. We also investigate the underlying mechanism. Trimucrin decreased the release of proinflammatory cytokines including tumor necrosis factor α (TNFα), interleukin-6 (IL-6), nitric oxide, and reactive oxygen species (ROS), and inhibited the adhesion and migration of LPS-activated phagocytes. Trimucrin significantly blocked the expression of nuclear factor kappaB (NF-κB)-related downstream inducible enzymes such as inducible nitric oxide synthase (iNOS) and COX-2. In addition, its anti-inflammatory effect was associated with the decreased mitogen-activated protein kinase (MAPK) phosphorylation. Furthermore, trimucrin concentration dependently inhibited LPS-induced phosphorylation of focal adhesion kinase (FAK), PI3K, and Akt. Trimucrin also reversed the DNA-binding activity of NF-κB by suppressing the LPS-induced nuclear translocation of p65 and the cytosolic IκB release. Flow cytometric analyses showed that trimucrin bound to cells in a concentration-dependent manner. The anti-αVβ3 mAb also specifically decreased the binding of fluorescein isothiocyanate (FITC)-conjugated trimucrin. Binding assays demonstrated that integrin αVβ3 was the binding site for trimucrin on THP-1 and RAW 264.7 cells. In conclusion, we showed that trimucrin decreases the inflammatory reaction through the attenuation of iNOS expression and nitric oxide (NO) production by blocking MAP kinase and the NF-κB activation in LPS-stimulated THP-1 and RAW 264.7 cells.