Inhibition of vitronectin-mediated haptotaxis and haptoinvasion of MG-63 cells by domain 5 (D5(H)) of human high-molecular-weight kininogen and identification of a minimal amino acid sequence

Molecular Peptide Grafting as a Tool to Create Novel Protein Therapeutics

The study of peptides (synthetic or corresponding to discrete regions of proteins) has facilitated the understanding of protein structure-activity relationships. Short peptides can also be used as powerful therapeutic agents. However, the functional activity of many short peptides is usually substantially lower than that of their parental proteins. This is (as a rule) due to their diminished structural organization, stability, and solubility often leading to an enhanced propensity for aggregation. Several approaches have emerged to overcome these limitations, which are aimed at imposing structural constraints into the backbone and/or sidechains of the therapeutic peptides (such as molecular stapling, peptide backbone circularization and molecular grafting), therefore enforcing their biologically active conformation and thus improving their solubility, stability, and functional activity. This review provides a short summary of approaches aimed at enhancing the biological activity of short functional peptides with a particular focus on the peptide grafting approach, whereby a functional peptide is inserted into a scaffold molecule. Intra-backbone insertions of short therapeutic peptides into scaffold proteins have been shown to enhance their activity and render them a more stable and biologically active conformation.

Hexapod Assassins' Potion: Venom Composition and Bioactivity from the Eurasian Assassin Bug Rhynocoris iracundus

Assassin bug venoms are potent and exert diverse biological functions, making them potential biomedical goldmines. Besides feeding functions on arthropods, assassin bugs also use their venom for defense purposes causing localized and systemic reactions in vertebrates. However, assassin bug venoms remain poorly characterized. We collected the venom from the assassin bug Rhynocoris iracundus and investigated its composition and bioactivity in vitro and in vivo. It caused lysis of murine neuroblastoma, hepatoma cells, and healthy murine myoblasts. We demonstrated, for the first time, that assassin bug venom induces neurolysis and suggest that it counteracts paralysis locally via the destruction of neural networks, contributing to tissue digestion. Furthermore, the venom caused paralysis and melanization of Galleria mellonella larvae and pupae, whilst also possessing specific antibacterial activity against Escherichia coli, but not Listeria grayi and Pseudomonas aeruginosa. A combinatorial proteo-transcriptomic approach was performed to identify potential toxins responsible for the observed effects. We identified neurotoxic Ptu1, an inhibitory cystin knot (ICK) toxin homologous to ω-conotoxins from cone snails, cytolytic redulysins homologous to trialysins from hematophagous kissing bugs, and pore-forming hemolysins. Additionally, chitinases and kininogens were found and may be responsible for insecticidal and cytolytic activities. We demonstrate the multifunctionality and complexity of assassin bug venom, which renders its molecular components interesting for potential biomedical applications.

Tc-99m Glu-Cys-Gly-His-Gly-Lys (ECG-HGK), a novel Tc-99m labeled hexapeptide for molecular tumor imaging

Domain 5 of kinin-free high molecular weight kininogen inhibits the adhesion of many tumor cell lines, and it has been reported that the histidine-glycine-lysine (HGK)-rich region might be responsible for inhibition of cell adhesion. The authors developed HGK-containing hexapeptide, glutamic acid-cysteine-glycine (ECG)-HGK, and evaluated the utility of Tc-99m ECG-HGK for tumor imaging. Hexapeptide, ECG-HGK was synthesized using Fmoc solid-phase peptide synthesis. Radiolabeling efficiency was evaluated. The uptake of Tc-99m ECG-HGK within HT-1080 cells was evaluated in vitro. In HT-1080 tumor-bearing mice, gamma imaging and biodistribution studies were performed. The complexes Tc-99m ECG-HGK was prepared in high yield. The uptake of Tc-99m ECG-HGK within the HT-1080 tumor cells had been demonstrated by in vitro studies. The gamma camera imaging in the murine model showed that Tc-99m ECG-HGK was accumulated substantially in the HT-1080 tumor (tumor-to-muscle ratio = 5.7 ± 1.4 at 4 h), and the tumoral uptake was blocked by the co-injection of excess HGK (tumor-to-muscle ratio = 2.8 ± 0.6 at 4 h). In the present study, Tc-99m ECG-HGK was developed as a new tumor imaging agents. Our in vitro and in vivo studies revealed specific function of Tc-99m ECG-HGK for tumor imaging.

Domain 5 of high molecular weight kininogen inhibits collagen-mediated cancer cell adhesion and invasion in association with α-actinin-4

High molecular weight kininogen (HK) is a plasma glycoprotein with multiple functions, including the regulation of coagulation. We previously demonstrated that domain 5 (D5(H)), a functional domain of HK, and its derived peptides played an important role in the vitronectin-mediated suppression of cancer cell adhesion and invasion. However, the underlying mechanisms of the D5(H)-mediated suppressive effects remain to be elucidated. Here, we showed that D5(H) and its derivatives inhibited the collagen-mediated cell adhesion and invasion of human osteosarcoma MG63 cells. Using purified D5(H) fused to glutathione-S-transferase (GST) and D5(H)-derived peptides for column chromatography, an actin-binding protein, α-actinin-4, was identified as a binding protein of D5(H) with high-affinity for P-5m, a core octapeptide of D5(H). Immunofluorescence microscopy demonstrated that D5(H) co-localized with α-actinin-4 inside MG63 cells. In addition, exogenous GST-D5(H) added to the culture media was transported into MG63 cells, although GST alone as a control was not. As α-actinin-4 regulates actin polymerization necessary for cell adhesion and is related to the integrin-dependent attachment of cells to the extracellular matrix, our results suggest that D5(H) may modulate cell adhesion and invasion together with actinin-4.

Chimeric glutathione S-transferases containing inserts of kininogen peptides: potential novel protein therapeutics

The study of synthetic peptides corresponding to discrete regions of proteins has facilitated the understanding of protein structure-activity relationships. Short peptides can also be used as powerful therapeutic agents. However, in many instances, small peptides are prone to rapid degradation or aggregation and may lack the conformation required to mimic the functional motifs of the protein. For peptides to function as pharmacologically active agents, efficient production or expression, high solubility, and retention of biological activity through purification and storage steps are required. We report here the design, expression, and functional analysis of eight engineered GST proteins (denoted GSHKTs) in which peptides ranging in size from 8 to 16 amino acids and derived from human high molecular weight kininogen (HK) domain 5 were inserted into GST (between Gly-49 and Leu-50). Peptides derived from HK are known to inhibit cell proliferation, angiogenesis, and tumor metastasis, and the biological activity of the HK peptides was dramatically (>50-fold) enhanced following insertion into GST. GSHKTs are soluble and easily purified from Escherichia coli by affinity chromatography. Functionally, these hybrid proteins cause inhibition of endothelial cell proliferation. Crystallographic analysis of GSHKT10 and GSHKT13 (harboring 10- and 13-residue HK peptides, respectively) showed that the overall GST structure was not perturbed. These results suggest that the therapeutic efficacy of short peptides can be enhanced by insertion into larger proteins that are easily expressed and purified and that GST may potentially be used as such a carrier.

GHGKHKNK octapeptide (P-5m) inhibits metastasis of HCCLM3 cell lines via regulation of MMP-2 expression in in vitro and in vivo studies

P-5m, an octapeptide derived from domain 5 of HKa, was initially found to inhibit the invasion and migration of melanoma cells. The high metastatic potential of melanoma cells was prevented by the HGK motif in the P-5m peptide in vitro and in an experimental lung metastasis model, suggesting that P-5m may play an important role in the regulation of tumor metastasis. The aim of this study was to measure the effect of P-5m on tumor metastasis of human hepatocarcinoma cell line (HCCLM3) in vitro and in vivo in a nude mouse model of hepatocellular carcinoma (HCC), and detect the mechanisms involved in P-5m-induced anti-metastasis. By gelatin zymography, matrix metallo-proteinases 2 (MMP-2) activity in HCCLM3 was dramatically diminished by P-5m peptide. In addition, the migration and metastasis of HCCLM3 cells was also inhibited by the peptide in vitro. In an orthotopic model of HCC in nude mice, P-5m treatment effectively reduced the lung metastasis as well as the expression of MMP-2 in the tumor tissues. Overall, these observations indicate an important role for P-5m peptide in HCC invasion and metastasis, at least partially through modulation MMP-2 expression. These data suggests that P-5m may have therapeutic potential in metastatic human hepatocarcinoma.

The Fragments of Bovine High Molecular Weight Kininogen Promote Osteoblast Proliferation In Vitro

High molecular weight (HMW) kininogen is known to be a large plasma protein and cleaved by plasma proteinase kallikrein, then it generates four fragments in the blood coagulation cascade: heavy chain, bradykinin, fragment 1.2, and light chain. The fragment 1.2 has also been found in the basic protein fraction of bovine milk as a bioactive protein which promotes osteoblast proliferation. The milk basic protein has been shown to be a multi functional edible protein which promotes bone formation and inhibits bone resorption. In the present study, we purified the fragment 1.2 from bovine plasma and assessed it could promote osteoblast proliferation and posses the activity after pepsin digestion. Purified plasma HMW kininogen did not promote the proliferation, however, the kallikrein-cleaved HMW kininogen promoted the proliferation. The fragment 1.2, purified from the proteolysate, also promoted the proliferation. The pepsin digestion was performed according to the method of the assessment of allergenesity of genetically modified crops. After pepsin digestion, the fragment 1.2 generated resistant fragments and showed the promoting activity of osteoblast proliferation. These results suggest that the enzymatically-digested fragments of bovine HMW kininogen are able to be a naturally occurred active protein that promotes the bone formation by oral administration.

Effect of His-Gly-Lys motif derived from domain 5 of high molecular weight kininogen on suppression of cancer metastasis both in vitro and in vivo

We have demonstrated previously that kinin-free high molecular weight kininogen, its domain 5 (D5H, Gly402-Lys502), and peptides derived from D5H inhibited vitronectin-mediated migration and invasion of cancer cells in vitro (Kamiyama, F., Maeda, T., Yamane, T., Li, Y. H., Ogikubo, O., Otsuka, T., and Ohkubo, I. (2001) Biochem. Biophys. Res. Commun. 288, 975-980). In this study, we found that the amino acid sequence His-Gly-Lys (HGK) in D5H is the core motif for inhibition of adhesion and invasion of MDA-MB-231 cells in vitro. P-5m (484GHGKHKNK491, Gly484-Lys491), an octapeptide including the HGK motif derived from D5H, and HGK, a tripeptide, inhibited both cell adhesion and invasion in vitro. However, an octapeptide designated P-5m (K487R), in which Lys487 was changed to Arg, did not inhibit either cell adhesion or invasion, and peptides HGR and HGG also had no inhibitory effect. Recombinant GST-D5H expressed in Escherichia coli had a stronger inhibitory effect on cell adhesion and invasion in vitro than did GST-D5H (K487R) in which Lys487 was changed to Arg. Furthermore, P-5m (Gly484-Lys491) peptide clearly suppressed lung metastasis in mice experimentally induced by using B16-F10 cells, but P-5m (G487R) had no effect. These data strongly indicate that both the HGK motif and lysine residue (Lys487) play essential roles in inhibition of cell adhesion and invasion in vitro and in prevention of metastasis of cancer cells in vivo. We tried to identify the HGK motif binding protein on the surface of cancer cells. A 95-kDa surface biotin-labeled membrane protein was specifically detached from GST-D5H by P-5 (His479-Lys493) peptide but not by P-1 (Gly402-Lys420) peptide originating from the N-terminal region of D5H.