A peptide derived from human prothrombin fragment 2 inhibits prothrombinase and angiogenesis

Identification and characterization of a factor Va-binding site on human prothrombin fragment 2

The fragment 2 domain (F2) of prothrombin and its interaction with factor (F) Va is known to contribute significantly to prothrombinase-catalyzed activation of prothrombin. The extent to which the F2-FVa interaction affects the overall thrombin generation, however, is uncertain. To study this interaction, nuclear magnetic resonance spectroscopy of recombinant F2 was used to identify seven residues within F2 that are significantly responsive to FVa binding. The functional role of this region in interacting with FVa during prothrombin activation was verified by the FVa-dependent inhibition of thrombin generation using peptides that mimic the same region of F2. Because six of the seven residues were within a 9-residue span, these were mutated to generate a prothrombin derivative (PT6). These mutations led to a decreased affinity for FVa as determined by surface plasmon resonance. When thrombin generation by an array of FXa containing prothrombinase components was monitored, a 54% decrease in thrombin generation was observed with PT6 compared with the wild-type, only when FVa was present. The functional significance of the specific low-affinity binding between F2 and FVa is discussed within the context of a dynamic model of molecular interactions between prothrombin and FVa engaging multiple contact sites.

Identification and characterization of proteins in amniotic fluid that are differentially expressed before and after antenatal corticosteroid administration

OBJECTIVE

We sought to examine changes in the intraamniotic proteomic environment after the administration of antenatal corticosteroids to women with impending preterm delivery.

STUDY DESIGN

Amniotic fluid samples were collected at the time of clinically indicated amniocentesis before and within 7 days of administration of antenatal corticosteroids for impending preterm delivery (n = 12). Proteins differentially expressed before and after corticosteroids were identified by surface-enhanced laser desorption/ionization time-of-flight mass spectrometry. They were isolated, characterized, and quantified by fast protein liquid chromatography, sodium dodecyl sulfate-polyacrylamide gel electrophoresis, in-gel tryptic digestion, immunodepletion assays, enzyme-linked immunosorbent assay, and electrospray ionization tandem mass spectrometry.

RESULTS

Five protein peaks of interest were identified and characterized, all of which were significantly decreased after antenatal corticosteroid administration. These included 2 isoforms of transthyretin, albumin, prothrombin fragment 2, and lumican.

CONCLUSION

Four proteins, identified and characterized in amniotic fluid, were differentially expressed with antenatal corticosteroid administration. These data may provide additional insight into the molecular mechanisms by which antenatal corticosteroids prevent neonatal complications.

Full-length cDNA cloning and protein three-dimensional structure modeling of porcine prothrombin

Prothrombin is a vitamin K-dependent serine protease and plays pivotal roles in both procoagulant and anticoagulant pathway of hemostasis. In this study, we cloned the full-length cDNA of porcine prothrombin by cDNA library screening and SMART RACE technique. The full-length cDNA is 2027 bp, with a 1869 bp Open Reading Frame (ORF) coding 623 amino acids. The deduced protein of porcine prothrombin contains signal peptide, propeptide, Gla domain, two kringle domains and trypsin domain. Porcine prothrombin shares 86.15% nucleotide similarity and 83% amino acid similarity with human prothrombin. The trypsin domain is highly conserved between the two species with 92.1% amino acid identity. Macromolecular interaction sites comparison between porcine and human prothrombin suggests that the Gla domain in porcine prothrombin contains an additional potential gamma-carboxyglutamic acid site. However, a thrombin cleavage site (Arg284-Thr285) in its light chain is lost. When thrombin heavy chain is concerned, the most important functional sites such as catalytic triad DHS, RGD site, Na+ binding site and anion-binding exosite-I and II are highly conserved. However, great differences have been observed between residues 145 and 158 of heavy chain which is associated with thrombomodulin binding. Two important limited proteolysis sites at Ala150 and Lys154 were lost in porcine sequence, which would affect epsilon-thrombin and gammaT-thrombin generation. Comparison on 3-D protein models demonstrates that these proteins are obviously different in autolysis loop (Lys145 to Gly155). Compared with that of human prothrombin, variation at critical recognition sites would likely alter its binding affinity and reaction velocity, which would contribute to coagulation disorder when porcine liver is transplanted into human body.

Structure-activity relationships of the human prothrombin kringle-2 peptide derivative NSA9: anti-proliferative activity and cellular internalization

The human prothrombin kringle-2 protein inhibits angiogenesis and LLC (Lewis lung carcinoma) growth and metastasis in mice. Additionally, the NSA9 peptide (NSAVQLVEN) derived from human prothrombin kringle-2 has been reported to inhibit the proliferation of BCE (bovine capillary endothelial) cells and CAM (chorioallantoic membrane) angiogenesis. In the present study, we examined the structure-activity relationships of the NSA9 peptide in inhibiting the proliferation of endothelial cells lines e.g. BCE and HUVE (human umbilical vein endothelial). N- or C-terminal truncated derivatives and reverse sequence analogues of NSA9 were prepared and their anti-proliferative activities were assessed using the MTT [3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl-2H-tetrazolium bromide] assay. This cell proliferation assay demonstrated that both the N-terminal region and sequence orientation of NSA9 are important for inhibiting the proliferation of endothelial cells. In particular 2 C-terminal truncation derivatives of NSA9 [NSA7 (NSAVQLV) and NSA8 (NSAVQLVE)] inhibited cellular proliferation to a greater extent than did NSA9. The heptapeptide NSA7, was found to be more potent than NSA9 in inhibiting CAM angiogenesis, and tubular formation and migration of HUVE cells. In addition NSA9, NSA8 and NSA7 peptides exhibited considerable inhibitory effects on the proliferation of tumour cells such as B16F10 (murine melanoma), LLC and L929 (murine fibroblast). Also, cellular internalization studies demonstrated that NSA7 was internalized into both endothelial and tumour cells more easily than was NSA9. In conclusion, these results suggest that NSA7, residing within the full sequence of NSA9, contains the required sequence for anti-proliferative activity and cellular internalization.

Pericellular proteases in angiogenesis and vasculogenesis

Pericellular proteases play an important role in angiogenesis and vasculogenesis. They comprise (membrane-type) matrix metalloproteinases [(MT-)MMPs], serine proteases, cysteine cathepsins, and membrane-bound aminopeptidases. Specific inhibitors regulate them. Major roles in initiating angiogenesis have been attributed to MT1-matrix metalloproteinase (MMP), MMP-2, and MMP-9. Whereas MT-MMPs are membrane-bound by nature, MMP-2 and MMP-9 can localize to the membrane by binding to alphavbeta3-integrin and CD44, respectively. Proteases switch on neovascularization by activation, liberation, and modification of angiogenic growth factors and degradation of the endothelial and interstitial matrix. They also modify the properties of angiogenic growth factors and cytokines. Neovascularization requires cell migration, which depends on the assembly of protease-protein complexes at the migrating cell front. MT1-MMP and urokinase (u-PA) form multiprotein complexes in the lamellipodia and focal adhesions of migrating cells, facilitating proteolysis and sufficient support for endothelial cell migration and survival. Excessive proteolysis causes loss of endothelial cell-matrix interaction and impairs angiogenesis. MMP-9 and cathepsin L stimulate the recruitment and action of blood- or bone-marrow-derived accessory cells that enhance angiogenesis. Proteases also generate fragments of extracellular matrix and hemostasis factors that have anti-angiogenic properties. Understanding the complexity of protease activities in angiogenesis contributes to recognizing new targets for stimulation or inhibition of neovascularization in disease.

The human prothrombin kringle-2 derived peptide, NSA9, is internalized into bovine capillary endothelial cells through endocytosis and energy-dependent pathways

Human prothrombin kringle-2 and its partial peptide, NSA9 (NSAVQLVEN), have been reported to have potent anti-angiogenic activities. Here, the internalization mechanism of NSA9 into bovine capillary endothelial (BCE) cells was examined using lactate dehydrogenase (LDH) release assay, fluorescence microscopy, and flow cytometry. LDH release assay results suggested that the integrity of the BCE cell membrane was unaffected by NSA9. Fluorescence microscopy indicated that internalized NSA9 was localized in the cytoplasm around the nucleus, and showed a punctuated fluorescence pattern, which is indicative of endocytic vesicles. Also, the cellular internalization of NSA9 is significantly inhibited by depletion of the cellular ATP pool, endocytosis inhibitors such as chloroquine and nocodazole, and incubation at low temperature (4 degrees C). In addition, the anti-proliferative activity of NSA9 against BCE cells was diminished in the presence of endocytosis or metabolic inhibitors. In conclusion, these results strongly suggest that NSA9 might exert its anti-proliferative activity through internalization into BCE cells by endocytosis and energy-dependent pathways.

Angiogenesis inhibitors found within the haemostasis pathway

Angiogenesis, the development of new blood vessels from the existing vasculature, and haemostasis, the coagulation cascade leading to formation of a clot, are among the most consistent host responses associated with cancer. Importantly, these two pathways interrelate, with blood coagulation and fibrinolysis influencing tumor angiogenesis directly, thereby contributing to tumor growth. Moreover, many endogenous inhibitors of angiogenesis are found within platelets or harboured as cryptic fragments of haemostatic proteins. In this review we outline ways in which angiogenesis is coordinated and regulated by haemostasis in human cancer. Then we detail the experimental and pre-clinical evidence for the ability of many of these endogenous proteins to inhibit tumor angiogenesis and thus their potential to be anti-cancer agents, with particular reference to any clinical trials.