Disruption of interkringle disulfide bond of plasminogen kringle 1-3 changes the lysine binding capability of kringle 2, but not its antiangiogenic activity

Production in Escherichia coli of a recombinant C-terminal truncated precursor of surfactant protein B (rproSP-BΔc). Structure and interaction with lipid interfaces

SP-B, a protein absolutely required to maintain the lungs open after birth, is synthesized in the pneumocytes as a precursor containing C-terminal and N-terminal domains flanking the mature sequence. These flanking-domains are cleaved to produce mature SP-B, coupled with its assembly into pulmonary surfactant lipid-protein complexes. In the present work we have optimized over-expression in Escherichia coli and purification of rproSP-B(DeltaC), a recombinant form of human proSP-B lacking the C-terminal flanking peptide, which is still competent to restore SP-B function in vivo. rProSP-B(DeltaC) has been solubilized, purified and refolded from bacterial inclusion bodies in amounts of about 4 mg per L of culture. Electrophoretic mobility, immunoreactivity, N-terminal sequencing and peptide fingerprinting all confirmed that the purified protein had the expected mass and sequence. Once refolded, the protein was soluble in aqueous buffers. Circular dichroism and fluorescence emission spectra of bacterial rproSP-B(DeltaC) indicated that the protein is properly folded, showing around 32% alpha-helix and a mainly hydrophobic environment of its tryptophan residues. Presence of zwitterionic or anionic phospholipids vesicles caused changes in the fluorescence emission properties of rproSP-B(DeltaC) that were indicative of lipid-protein interaction. The association of this SP-B precursor with membranes suggests an intrinsic amphipathic character of the protein, which spontaneously adsorbs at air-liquid interfaces either in the absence or in the presence of phospholipids. The analysis of the structure and properties of recombinant proSP-B(DeltaC) in surfactant-relevant environments will open new perspectives on the investigation of the mechanisms of lipid and protein assembly in surfactant complexes.

What the structure of angiostatin may tell us about its mechanism of action

Originally discovered in 1994 by Folkman and coworkers, angiostatin was identified through its antitumor effects in mice and later shown to be a potent inhibitor of angiogenesis. An internal fragment of plasminogen, angiostatin consists of kringle domains that are known to be lysine-binding. The crystal structure of angiostatin was the first multikringle domain-containing structure to be published. This review will focus on what is known about the structure of angiostatin and its implications in function from the current literature.

Inhibition of endothelial cell proliferation by the recombinant kringle domain of tissue-type plasminogen activator

Tissue-type plasminogen activator (tPA) is a multidomain serine protease that converts the zymogen plasminogen to plasmin. tPA contains two kringle domains which display considerable sequence identity with those of angiostatin, an angiogenesis inhibitor. TK1-2, a recombinant kringle domain composed of t-PA kringles 1 and 2 (Ala(90)-Thr(263)), was produced by both bacterial and yeast expression systems. In vitro, TK1-2 inhibited endothelial cell proliferation stimulated by basic fibroblast growth factor, vascular endothelial growth factor, and epidermal growth factor. It did not inhibit proliferation of non-endothelial cells. TK1-2 also inhibited in vivo angiogenesis in the chick embryo chorioallantoic membrane model. These results suggest that the recombinant kringle domain of t-PA is a selective inhibitor of endothelial cell growth and identifies this molecule as a novel anti-angiogenic agent.

Anti-angiogenic activity of the recombinant kringle domain of urokinase and its specific entry into endothelial cells

Urokinase plasminogen activator (uPA) belongs to a family of proteins that contains kringle domain and plays an important role in inflammation, tissue remodeling, angiogenesis, and tumor metastasis by pericellular plasminogen activation. Kringle domains of plasminogen have been shown to demonstrate anti-angiogenic and anti-tumor activities. Here, we report our investigation of the kringle domain of uPA for anti-angiogenic activity and a possible cellular mechanism of action. The recombinant kringle domain of uPA (Asp(45)-Lys(135)) (UK1) inhibited endothelial cell proliferation stimulated by basic fibroblast growth factor, vascular endothelial growth factor (VEGF), or epidermal growth factor. It also inhibited migration of endothelial cells induced by VEGF or uPA, and in vivo angiogenesis on the chick chorioallantoic membrane. It did not block plasminogen activation by activated uPA in clot lysis and chromogenic substrate assays. Neither binding of UK1 to immobilized uPA receptor nor competitive inhibition of uPA binding were confirmed by real-time interaction analysis. However, internalization of UK1 followed by translocation from cytosol to nucleus was determined to be specific to endothelial cells. It also elicited a transient increase of Ca(2+) flux of more than 2-fold within 2 min of exposure in an endothelial cell-specific manner. These results suggest that the kringle domain of uPA exhibits anti-angiogenic activity and that its anti-angiogenic activity may occur through a different mechanism from inhibition of uPA-uPA receptor interaction or uPA proteolytic activity and may be associated with endothelial-cell specific internalization not mediated by the uPA receptor.

Malignant ascites fluid (MAF), including ovarian-cancer-associated MAF, contains angiostatin and other factor(s) which inhibit angiogenesis

OBJECTIVE

The aim was to determine whether human malignant ascites fluid (MAF) associated with abdominal cancer, including ovarian cancer, contained factors which inhibit angiogenesis as well as others which stimulate this process.

METHODS

MAF was collected from six patients, four with ovarian cancer, one with gastric cancer, and one with liver metastases. Using the chick chorioallantoic membrane (CAM) the effect of MAF on 7-day-old CAM capillaries was examined for 48 h. Vascular endothelial growth factor (VEGF) was evaluated by ELISA. Five samples of MAF were fractionated by lysine-Sepharose chromatography and the lysine-bound and -unbound fractions were eluted by epsilon-amino-n-hexanoic acid. Whole MAF, the lysine-bound and -unbound fractions, and human angiostatin were subjected to SDS-PAGE/Western blot analysis and immunostained after exposure to anti-human plasminogen. Human plasminogen was exposed to conditioned medium from ovarian epithelial cancer (HEY) cells and subjected to similar Western blot analysis.

RESULTS

Despite containing VEGF, each MAF sample examined caused a loss of capillaries from the CAM; a similar response was seen using purified human angiostatin. Whole MAF and the lysine-bound fraction contained plasminogen (90 kDa) and a 55-kDa protein which migrated in a similar manner to human angiostatin on Western blot. Both the lysine-bound and -unbound fractions caused a loss of capillaries in the CAM. Human plasminogen exposed to conditioned medium from HEY cells yielded a fragment which was similar in size to angiostatin.

CONCLUSIONS

MAF from patients with various clinical presentations contains angiostatin and VEGF as well as other factors which are capable of inhibiting angiogenesis.

The X-ray crystallographic structure of the angiogenesis inhibitor angiostatin

Angiogenesis inhibitors have gained much public attention recently as anti-cancer agents and several are currently in clinical trials, including angiostatin (Phase I, Thomas Jefferson University Hospital, Philadelphia, PA). We report here the bowl-shaped structure of angiostatin kringles 1-3, the first multi-kringle structure to be determined. All three kringle lysine-binding sites contain a bound bicine molecule of crystallization while the former of kringle 2 and kringle 3 are cofacial. Moreover, the separation of the kringle 2 and kringle 3 lysiner binding sites is sufficient to accommodate the alpha-helix of the 30 residue peptide VEK-30 found in the kringle 2/VEK-30 complex. Together the three kringles produce a central cavity suggestive of a unique domain where they may function in concert.