p22 is a novel plasminogen fragment with antiangiogenic activity

The biochemistry and regulation of S100A10: a multifunctional plasminogen receptor involved in oncogenesis

The plasminogen receptors mediate the production and localization to the cell surface of the broad spectrum proteinase, plasmin. S100A10 is a key regulator of cellular plasmin production and may account for as much as 50% of cellular plasmin generation. In parallel to plasminogen, the plasminogen-binding site on S100A10 is highly conserved from mammals to fish. S100A10 is constitutively expressed in many cells and is also induced by many diverse factors and physiological stimuli including dexamethasone, epidermal growth factor, transforming growth factor-α, interferon-γ, nerve growth factor, keratinocyte growth factor, retinoic acid, and thrombin. Therefore, S100A10 is utilized by cells to regulate plasmin proteolytic activity in response to a wide diversity of physiological stimuli. The expression of the oncogenes, PML-RARα and KRas, also stimulates the levels of S100A10, suggesting a role for S100A10 in pathophysiological processes such as in the oncogenic-mediated increases in plasmin production. The S100A10-null mouse model system has established the critical role that S100A10 plays as a regulator of fibrinolysis and oncogenesis. S100A10 plays two major roles in oncogenesis, first as a regulator of cancer cell invasion and metastasis and secondly as a regulator of the recruitment of tumor-associated cells, such as macrophages, to the tumor site.

Effects of macrophage metalloelastase on the basic fibroblast growth factor expression and tumor angiogenesis in murine colon cancer

BACKGROUND AND AIM

Previous studies have shown that overexpression of macrophage metalloelastase (MME) suppresses tumor growth in mice. The purpose of this study was to investigate the effects of MME on basic fibroblast growth factor (bFGF) expression and tumor angiogenesis in murine colon cancer.

METHODS

Murine CT-26 colon cancer cells stably transfected with MME were inoculated subcutaneously. Reverse-transcriptase polymerase chain reaction (RT-PCR), immunoblotting, and immunohistochemistry were used to explore the bFGF mRNA and protein expression. Immunohistochemical staining of CD34 was used to measure the microvessel density (MVD).

RESULTS

bFGF mRNA levels in tumor tissues of CT-26-EGFP and nontransfected cells were respectively 2.7-fold (0.56 ± 0.063 vs. 0.21 ± 0.042) and 2.5-fold (0.53 ± 0.066 vs. 0.21 ± 0.042) higher than that in tumors of CT-26-EGFP-MME cells (p < 0.01). bFGF protein levels exhibited a similar trend. Tumors of CT-26-EGFP-MME cells demonstrated a lower microvessel density (9.35 ± 2.79) than control tumors of CT-26-EGFP cells (22.85 ± 3.80) and nontransfected cells (23.45 ± 4.49) (p < 0.001).

CONCLUSIONS

We found that expression of MME inversely correlates with the expression of bFGF and tumor angiogenesis in a model of murine colon cancer. These data indicate that manipulation of MME expression could be a novel modality approach to colon cancer therapy.

Matrix metalloproteinase-19 inhibits growth of endothelial cells by generating angiostatin-like fragments from plasminogen

Background

Angiogenesis is the process of forming new blood vessels from existing ones and requires degradation of the vascular basement membrane and remodeling of extracellular matrix (ECM) in order to allow endothelial cells to migrate and invade into the surrounding tissue. Matrix metalloproteinases (MMPs) are considered to play a central role in the remodeling of basement membranes and ECM. However, MMPs contribute to vascular remodeling not only by degrading ECM components. Specific MMPs enhance angiogenesis via several ways; they help pericytes to detach from vessels undergoing angiogenesis, release ECM-bound angiogenic growth factors, expose cryptic pro-angiogenic integrin binding sites in the ECM, generate promigratory ECM component fragments, and cleave endothelial cell-cell adhesions. MMPs can also negatively influence the angiogenic process through generating endogenous angiogenesis inhibitors by proteolytic cleavage. Angiostatin, a proteolytic fragment of plasminogen, is one of the most potent antagonists of angiogenesis that inhibits migration and proliferation of endothelial cells. Reports have shown that metalloelastase, pancreas elastase, plasmin reductase, and plasmin convert plasminogen to angiostatin.

Results

We report here that MMP-19 processes human plasminogen in a characteristic cleavage pattern to generate three angiostatin-like fragments with a molecular weight of 35, 38, and 42 kDa. These fragments released by MMP-19 significantly inhibited the proliferation of HMEC cells by 27% (p = 0.01) and reduced formation of capillary-like structures by 45% (p = 0.05) compared with control cells. As it is known that angiostatin blocks hepatocyte growth factor (HGF)-induced pro-angiogenic signaling in endothelial cells due to structural similarities to HGF, we have analyzed if the plasminogen fragments generated by MMP-19 interfere with this pathway. As it involves the activation of c-met, the receptor of HGF, we could show that MMP-19-dependent processing of plasminogen decreases the phosphorylation of c-met.

Conclusion

Altogether, MMP-19 exhibits an anti-angiogenic effect on endothelial cells via generation of angiostatin-like fragments.

Regulation of fibrinolysis by S100A10 in vivo

Endothelial cells form the inner lining of vascular networks and maintain blood fluidity by inhibiting blood coagulation and promoting blood clot dissolution (fibrinolysis). Plasmin, the primary fibrinolytic enzyme, is generated by the cleavage of the plasma protein, plasminogen, by its activator, tissue plasminogen activator. This reaction is regulated by plasminogen receptors at the surface of the vascular endothelial cells. Previous studies have identified the plasminogen receptor protein S100A10 as a key regulator of plasmin generation by cancer cells and macrophages. Here we examine the role of S100A10 and its annexin A2 binding partner in endothelial cell function using a homozygous S100A10-null mouse. Compared with wild-type mice, S100A10-null mice displayed increased deposition of fibrin in the vasculature and reduced clearance of batroxobin-induced vascular thrombi, suggesting a role for S100A10 in fibrinolysis in vivo. Compared with wild-type cells, endothelial cells from S100A10-null mice demonstrated a 40% reduction in plasminogen binding and plasmin generation in vitro. Furthermore, S100A10-deficient endothelial cells demonstrated impaired neovascularization of Matrigel plugs in vivo, suggesting a role for S100A10 in angiogenesis. These results establish an important role for S100A10 in the regulation of fibrinolysis and angiogenesis in vivo, suggesting S100A10 plays a critical role in endothelial cell function.

Sensitivity of cancer cells to truncated diphtheria toxin

BACKGROUND

Diphtheria toxin (DT) has been utilized as a prospective anti-cancer agent for the targeted delivery of cytotoxic therapy to otherwise untreatable neoplasia. DT is an extremely potent toxin for which the entry of a single molecule into a cell can be lethal. DT has been targeted to cancer cells by deleting the cell receptor-binding domain and combining the remaining catalytic portion with targeting proteins that selectively bind to the surface of cancer cells. It has been assumed that "receptorless" DT cannot bind to and kill cells. In the present study, we report that "receptorless" recombinant DT385 is in fact cytotoxic to a variety of cancer cell lines.

METHODS

In vitro cytotoxicity of DT385 was measured by cell proliferation, cell staining and apoptosis assays. For in vivo studies, the chick chorioallantoic membrane (CAM) system was used to evaluate the effect of DT385 on angiogenesis. The CAM and mouse model system was used to evaluate the effect of DT385 on HEp3 and Lewis lung carcinoma (LLC) tumor growth, respectively.

RESULTS

Of 18 human cancer cell lines tested, 15 were affected by DT385 with IC(50) ranging from 0.12-2.8 microM. Furthermore, high concentrations of DT385 failed to affect growth arrested cells. The cellular toxicity of DT385 was due to the inhibition of protein synthesis and induction of apoptosis. In vivo, DT385 diminished angiogenesis and decreased tumor growth in the CAM system, and inhibited the subcutaneous growth of LLC tumors in mice.

CONCLUSION

DT385 possesses anti-angiogenic and anti-tumor activity and may have potential as a therapeutic agent.

The von Hippel-Lindau Tumor Suppressor Protein Is Destabilized by Src: Implications for Tumor Angiogenesis and Progression

The von Hippel-Lindau tumor suppressor protein (VHL), when mutated and inactivated, has been associated with renal and CNS cancer development. VHL normally plays an important role in targeting for degradation of the HIF-1α (hypoxia inducible factor-1α) transcription factor, a primary positive regulator of vascular endothelial growth factor (VEGF) production. In this report we demonstrate that VHL destabilization can be induced by Src kinase and may be involved in other cancers, including breast cancer. We have found that elevated Src can trigger a drastic reduction in VHL stability even under normoxic conditions, through phosphorylation of VHL tyrosine residue 185, leading to ubiquitination and proteasome-mediated degradation of VHL. The Src-induced degradation of VHL protein leads to increased HIF-1α levels and transcriptional activity and increased VEGF production. In this manner, Src regulation of VHL protein stability may play an important role in promoting VEGF expression, tumor angiogenesis, and cancer progression.

Plasminogen N-terminal activation peptide modulates the activity of angiostatin-related peptides on endothelial cell proliferation and migration

Angiostatin, a potent inhibitor of angiogenesis, is derived from the fibrinolytic proenzyme, plasminogen, by enzymatic processing. Plasminogen N-terminal activation peptide (PAP) is one of the products concomitantly released aside from angiostatin (kringles 1-4) and mini-plasminogen (kringle 5 plus the catalytic domain) when plasminogen is processed. To determine whether PAP alone or together with the angiostatin-related peptides derived from the processing of plasminogen modulate the proliferation and motility of endothelial cells, we have generated a recombinant PAP and used it to study its effects on endothelial cells in the presence and absence of the angiostatin-related peptides. Our results showed that PAP alone slightly increased the migration but not the proliferation of endothelial cells. However, in the presence of the angiostatin-related peptides, PAP attenuated the inhibitory activity of the angiostatin-related peptides on the proliferation and migration of endothelial cells. The inhibitory effect of PAP on the angiostatin-related peptides could be due to its binding to the kringle domains of the latter peptides.

Bacillolysin MA, a Novel Bacterial Metalloproteinase That Produces Angiostatin-like Fragments from Plasminogen and Activates Protease Zymogens in the Coagulation and Fibrinolysis Systems

We isolated a novel protease that converts plasminogen to angiostatin-like fragments (BL-angiostatins) from a culture of Bacillus megaterium A9542 through a single-step chromatography on CM-cellulose. The protease, designated bacillolysin MA (BL-MA), belongs to a family of neutral metalloproteinases based on the nucleotide sequence of its gene. At an enzyme:substrate ratio of 1:540, BL-MA cleaved human plasminogen mainly at Ser441-Val442 to form BL-angiostatin and miniplasminogen with a K(m) of 3.0 +/- 0.8 microM and a k(cat) of 0.70 +/- 0.09 s(-1). The resulting BL-angiostatins inhibited the proliferation, migration, and tube formation of vascular endothelial cells at concentrations of 1-10 microg/ml. Although BL-MA failed to activate plasminogen, it increased urokinase-catalyzed activation of plasminogen caused by production of miniplasminogen, which is highly susceptible to activation. In addition, BL-MA was active in converting prourokinase, prothrombin, coagulation factor X, and protein C to their active forms. BL-MA enhanced both the clotting of human plasma and clot dissolution in the presence of prourokinase. Thus, BL-MA affects blood coagulation and fibrinolysis systems and can be used to produce angiostatin-like plasminogen fragments and active serine proteases of human plasma.

Multiple fragments related to angiostatin and endostatin in fluid from venous leg ulcers

To investigate whether compromised angiogenesis could contribute to the impaired healing of venous leg ulcers, we have analyzed fluids from venous leg ulcers for the presence of the angiogenesis inhibitors angiostatin and endostatin. Multiple fragments related to angiostatin were detected by Western blot analysis. One angiostatin fragment was identified by mass spectrometry as plasminogen kringle domains 1-3 containing amino acids 82-343 of plasminogen, and a fraction containing this fragment inhibited tubule formation of human umbilical vein endothelial cells in a Matrigel assay. The leg ulcer fluids also contained endogenous endostatin (20 kDa) as well as higher molecular weight endostatin-related proteins. The concentrations of endostatin in the wound fluids, which ranged from 12.8 to 65.5 ng/ml, were higher than the concentration in human serum (7.7 ng/ml). Most of the endostatin in leg ulcer fluid appeared to be bound to the proteoglycan glypican-1. These data suggest that anti-angiogenic activity is present at the site of venous leg ulcers, and at least in the case of angiostatin, is biologically active.

Nonlysine-analog plasminogen modulators promote autoproteolytic generation of plasmin(ogen) fragments with angiostatin-like activity

We recently discovered several nonlysine-analog conformational modulators for plasminogen. These include SMTP-6, thioplabin B and complestatin that are low molecular mass compounds of microbial origin. Unlike lysine-analog modulators, which increase plasminogen activation but inhibit its binding to fibrin, the nonlysine-analog modulators enhance both activation and fibrin binding of plasminogen. Here we show that some nonlysine-analog modulators promote autoproteolytic generation of plasmin(ogen) derivatives with its catalytic domain undergoing extensive fragmentation (PMDs), which have angiostatin-like anti-endothelial activity. The enhancement of urokinase-catalyzed plasminogen activation by SMTP-6 was followed by rapid inactivation of plasmin due to its degradation mainly in the catalytic domain, yielding PMD with a molecular mass ranging from 68 to 77 kDa. PMD generation was observed when plasmin alone was treated with SMTP-6 and was inhibited by the plasmin inhibitor aprotinin, indicating an autoproteolytic mechanism in PMD generation. Thioplabin B and complestatin, two other nonlysine-analog modulators, were also active in producing similar PMDs, whereas the lysine analog 6-aminohexanoic acid was inactive while it enhanced plasminogen activation. Peptide sequencing and mass spectrometric analyses suggested that plasmin fragmentation was due to cleavage at Lys615-Val616, Lys651-Leu652, Lys661-Val662, Lys698-Glu699, Lys708-Val709 and several other sites mostly in the catalytic domain. PMD was inhibitory to proliferation, migration and tube formation of endothelial cells at concentrations of 0.3-10 microg.mL(-1). These results suggest a possible application of nonlysine-analog modulators in the treatment of cancer through the enhancement of endogenous plasmin(ogen) fragment formation.

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Interaction of plasminogen-related protein B with endothelial and smooth muscle cells in vitro

Plasminogen-related protein B (PRP-B) closely resembles the N-terminal plasminogen activation peptide, which is released from plasminogen during conversion to plasmin. We have previously demonstrated that the steady-state level of mRNA encoding PRP-B is increased within tumor tissues, and that recombinant PRP-B antagonizes neoplastic growth when administered systemically to mice harboring tumors, but no insights into the cell targets of PRP-B have been presented. Employing serum-free medium optimized for culturing human endothelial or smooth muscle cells, we show that recombinant PRP-B inhibits basic fibroblast growth factor-dependent cell migration for both cell types, as well as tube formation of endothelial cells. Comparison with the angiogenesis inhibitors angiostatin and endostatin revealed similar results. Recombinant PRP-B is effective in promoting cell attachment of endothelial and smooth muscle cells, and antibody interference experiments reveal that the interaction of recombinant PRP-B with endothelial cells is mediated at least in part by alpha(v)-containing integrins. Inhibition of angiogenesis in vivo by PRP-B was demonstrated in the chicken chorioallantoic membrane assay. PRP-B and other antiangiogenic molecules may elicit metabolic perturbations in endothelial cells as well as perivascular mesenchymal cells such as smooth muscle cells and pericytes.