Secreted cathepsin L generates endostatin from collagen XVIII

Identification of protease-sensitive sites in Human Endothelial-Monocyte Activating Polypeptide II protein

The cleaved approximately 22-kDa form of Endothelial-Monocyte Activating Polypeptide [mature (m)EMAP II] functions as a potent inhibitor of tumor growth. Although the anti-tumor effect of mEMAP II has been described, little is known regarding the cleavage of mEMAP II from its precursor form (pEMAP II). We determined that pEMAP II is expressed at the cell membrane surface and proteinases MMP-9, elastase, and cathepsin L release protein fragments consistent with mEMAP II molecular mass. MMP-9 and elastase generate a approximately 25-26 kDa spanning fragments, while cathepsin L generates a approximately 22 kDa fragment. Although several fragments are processed from pEMAP II within a 44 AA residue stretch, cathepsin L cleaves pEMAP II within 4 amino acids of the determined N-terminal sequence, suggesting that this region is sensitive to proteinases.

Towards novel anti-cancer strategies based on cystatin function

Cystatins have recently emerged as important players in a multitude of physiological and patho-physiological settings that range from cell survival and proliferation, to differentiation, cell signaling and immunomodulation. This group of cysteine protease inhibitors forms a large super-family of proteins composed of one, two, three, and, in some species, more than three cystatin domains. Over the last 20 years or so, members of the cystatin super-family have been primarily explored with respect to their capacity to inhibit intracellular cysteine proteases. Yet, this classical mode of action does not fully explain their remarkably diverse biological functions. Due to the space limitations, the author will discuss here the most recent findings that suggest that some of the single-domain, cytoplasmic and cell-secreted cystatins may play important roles in the promotion or suppression of tumor growth, invasion and metastasis. Based on the present understanding of cystatin function, novel avenues for anti-cancer strategies are proposed.

Differential Expression of Collagen Types XVIII/Endostatin and XV in Normal, Keratoconus, and Scarred Human Corneas

PURPOSE

This study was designed to clarify the expression of 2 closely related collagen (Col) types XVIII and XV, and the proteolytically derived endostatin fragment of ColXVIII in normal, keratoconus, and scarred human corneas.

METHODS

Immunohistochemistry, in situ hybridization, immunoelectron microscopy, and Western immunoblotting were used for human corneal samples obtained from penetrating keratoplasty.

RESULTS

In the normal cornea, ColXVIII was immunolocalized to the corneal and conjunctival epithelial basement membrane (EBM), Descemet s membrane, and the limbal and conjunctival capillaries. Immunoreaction for endostatin was otherwise similar, but it also was present in corneal epithelial cells. Western immunoblotting showed that normal cornea contains several endostatin fragments ranging from 20 to 100 kDa. ColXV was present in the EBM of the limbus and conjunctiva, but not in EBM of the clear cornea. In situ hybridization revealed that corneal basal epithelial cells were responsible for the synthesis of ColXVIII mRNA. Keratoconus cases were characterized by an irregular EBM immunoreactivity for ColXVIII and endostatin and patchy immunoreactivity beneath EBM. In scarred corneas, highly increased immunoreactivity for ColXVIII, endostatin, and ColXV was present within stroma.

CONCLUSIONS

The results indicate that ColXVIII and ColXV are differentially expressed in normal human corneas. Constant expression of ColXVIII by corneal EBM suggests that it is an important structural molecule. Aberrant expression of ColXVIII, endostatin, and ColXV in keratoconus and scarred corneas emphasizes the active role these molecules in the wound healing process.

Endostatin, the proteolytic fragment of collagen XVIII, induces vasorelaxation

Collagen XVIII is an important component of the extracellular matrix and is expressed in basement membranes. Its degradation results in the generation of endostatin claimed to possess antiangiogenic activity. To date, only limited knowledge exists with regard to the cellular signaling of this molecule. We show in single-cell measurements using the Ca2+ indicator fura-2 acetoxy methylester (fura-2 AM) and the nitric oxide (NO) indicator 4,5-diaminofluorescein diacetate that application of endostatin (ES) (5 pmol/L, 100 ng/mL) induced Ca2+ spikes and an increase of NO production in human and murine endothelial cells. The NO response was independent of an increase in cytosolic Ca2+ and blocked by the endothelial NO synthase (eNOS) inhibitor NG-nitro-L-arginine methyl ester and by incubation with pertussis toxin known to inhibit G(i/o) proteins. The physiological relevance of this novel signaling pathway of ES was assessed with isometric force measurements in large and small arteries of mouse. Physiological concentrations of ES were found to decrease vascular tone in an endothelium-dependent manner. This occurred via an Arg-Gly-Asp (RGD) peptide-independent pathway through activation of G(i/o) proteins, phosphatidylinositol 3-kinase, Akt, and eNOS. We conclude that the proteolytic matrix fragment ES is a prominent vasorelaxing agent. Because ES is constantly released into the blood, it is a novel regulator of blood pressure and, therefore, represents an interesting pharmacological target.

Circulating endothelial cells and angiogenic serum factors during neoadjuvant chemotherapy of primary breast cancer

Circulating endothelial cells (CECs) as well as bone-marrow-derived endothelial precursor cells (EPC) play an important role in neovascularisation and tumour growth. To study the impact of neoadjuvant chemotherapy on the amounts of CEC and their precursor cells, mature CEC and their progenitors were quantified by flow cytometry in peripheral blood of breast cancer patients during anthracycline and/or taxane based neoadjuvant chemotherapy and subsequent surgery in comparison to age-matched healthy controls. Cell numbers were tested for correlation with serum levels of angiopoietin-2, erythropoietin, endostatin, endoglin, VEGF and sVCAM-1 as well as clinical and pathological features of breast cancer disease. Circulating endothelial cells were significantly elevated in breast cancer patients and decreased during chemotherapy, whereas EPC (CD34⁺/VEGFR-2⁺) as well as their progenitor cell population CD133⁺/CD34⁺ and the population of CD34⁺ stem cells increased. Concomitantly with the increase of progenitor cells an increase of VEGF, erythropoietin and angiopoietin-2 was observed. These data suggest that chemotherapy can only reduce the amounts of mature CEC, probably reflecting detached cells from tumour vessels, whereas the EPC and their progenitors are mobilised by chemotherapy. Since this mobilisation of EPC may contribute to tumour neovascularisation an early antiangiogenic therapy in combination with chemotherapy could be beneficial for the success of cancer therapy.

Collagen XVIII/endostatin is associated with the epithelial-mesenchymal transformation in the atrioventricular valves during cardiac development

Type XVIII collagen is a multidomain protein that contains cleavable C-terminal NC1 and endostatin fragments, which have been shown to either induce or inhibit cell migration. Endostatin is being intensely studied because of its anti-angiogenic activity. Three variants of type XVIII collagen have been reported to be distributed in epithelial and endothelial basement membranes in a tissue-specific manner. The single gene encoding collagen XVIII is on chromosome 21 within the region associated with the congenital heart disease phenotype observed in Down's syndrome. In this study, we investigated the expression pattern of collagen XVIII in embryonic mouse hearts during formation of the atrioventricular (AV) valves. We found that collagen XVIII is localized not only in various basement membranes but is also highly expressed throughout the connective tissue core of the endocardial cushions and forming AV valve leaflets. It was closely associated with the epithelial-mesenchymal transformation of endothelial cells into mesenchymal cushion tissue cells and was localized around these cells as they migrated into the cardiac jelly to form the initial connective tissue elements of the valve leaflets. However, after embryonic day 17.5 collagen XVIII expression decreased rapidly in the connective tissue and thereafter remained detectable only in the basement membranes of the endothelial layer covering the leaflets. The staining pattern observed within the AV endocardial cushions suggests that collagen XVIII may have a role in cardiac valve morphogenesis. These results may help us to better understand normal heart development and the aberrant mechanisms that cause cardiac malformations in Down's syndrome.

Cathepsin S controls angiogenesis and tumor growth via matrix-derived angiogenic factors

The cysteine protease cathepsin S is highly expressed in malignant tissues. By using a mouse model of multistage murine pancreatic islet cell carcinogenesis in which cysteine cathepsin activity has been functionally implicated, we demonstrated that selective cathepsin S deficiency impaired angiogenesis and tumor cell proliferation, thereby impairing angiogenic islet formation and the growth of solid tumors, whereas the absence of its endogenous inhibitor cystatin C resulted in opposite phenotypes. Although mitogenic vascular endothelial growth factor, transforming growth factor-beta1, and the anti-angiogenic endostatin levels in either serum or carcinoma tissue extracts did not change in cathepsin S- or cystatin C-null mice, tumor tissue basic fibroblast growth factor and serum type 1 insulin growth factor levels were higher in cystatin C-null mice, and serum type 1 insulin growth factor levels were also increased in cathepsin S-null mice. Furthermore, cathepsin S affected the production of type IV collagen-derived anti-angiogenic peptides and the generation of bioactive pro-angiogenic gamma2 fragments from laminin-5, revealing a functional role for cathepsin S in angiogenesis and neoplastic progression.

Mutations in collagen 18A1 (COL18A1) and their relevance to the human phenotype

Collagen XVIII, a proteoglycan, is a component of basement membranes (BMs). There are three distinct isoforms that differ only by their N-terminal, but with a specific pattern of tissue and developmental expression. Cleavage of its C-terminal produces endostatin, an inhibitor of angiogenesis. In its N-terminal, there is a frizzled motif which seems to be involved in Wnt signaling. Mutations in this gene cause Knobloch syndrome KS), an autosomal recessive disorder characterized by vitreoretinal and macular degeneration and occipital encephalocele. This review discusses the effect of both rare and polymorphic alleles in the human phenotype, showing that deficiency of one of the collagen XVIII isoforms is sufficient to cause KS and that null alleles causing deficiency of all collagen XVIII isoforms are associated with a more severe ocular defect. This review besides illustrating the functional importance of collagen XVIII in eye development and its structure maintenance throughout life, it also shows its role in other tissues and organs, such as nervous system and kidney.

Antiprotease therapy in cancer: hot or not?

The activity of a set of peptidases (proteases) involved in cancer progression is collectively known as the cancer 'degradome'. Invasion and metastasis were initially considered as late events in cancer development and the processes in which proteases were involved. However, recent studies indicate that invasion and metastasis are not late events, but can occur during early stages as well. Moreover, other processes occurring in various stages of cancer progression are also protease-dependent, such as (upregulation of) cell proliferation, (downregulation of) apoptosis, involvement of white blood cells, angiogenesis and induction of multi-drug resistance. Proteolytic activity in tumours is regulated in a complex manner, as both genetically unstable cancer cells and stable stromal cells, such as fibroblasts, endothelial cells and inflammatory cells, are involved. In vitro studies and studies using animal models have clearly shown protease dependency of many processes in carcinogenesis. However, clinical trials using protease inhibitors have thus far been unsuccessful except for a few applications of matrix metalloprotease (MMP) inhibitors when used in combination with cytostatic anticancer agents and/or in the early stages of cancer. Antithrombotics, such as low-molecular-weight heparin and warfarin, were also successful in clinical trials, probably by interfering with proteases of the coagulation cascade. The two-way association between cancer and thrombosis has long been recognised in the clinic. The poor outcome of other clinical trials of protease inhibitors is probably due to the late stages of cancer of the patient populations included, and the limited understanding of the complex regulation and effects of the activity of the various proteases in tumours depending on, among others, tumour type and stage, interactions between the cancer cells, other cells and the extracellular matrix in tumours. Therefore, a better fundamental understanding of the proteolytic complexity in tumours is essential before clinical trials can be rationally designed. At present, antithrombotics, the urokinase-type plasminogen activator system, the membrane-bound membrane-type 1-MMP, cathepsin L and the proteasome seem the most promising candidates as targets for anticancer strategies in early stages of cancer in combination with cytotoxic drugs. Moreover, metronomic therapy is an attractive approach using low doses of inhibitors for prolonged periods of time without interruption to specifically target endothelial cells that are involved in angiogenesis.

Molecular regulation of tumor angiogenesis: mechanisms and therapeutic implications

Angiogenesis, the process of new capillary formation from a pre-existing vessel plays an essential role in both embryonic and postnatal development, in the remodeling of various organ systems, and in several pathologies, particularly cancer. In the last 20 years of angiogenesis research, a variety of angiogenic regulators, both positive and negative, have been identified. The discovery of several anti-angiogenic factors has led to the development of novel cancer therapies based on targeting a tumor's vascular supply. A number of these new therapies are currently being tested in clinical trials in the U.S.A. and elsewhere. A major advance in the field of anti-angiogenic therapy occurred recently when the FDA approved Avastin (bevacizumab), the first solely anti-angiogenesis therapy approved for treatment of human cancer. While it has long been appreciated that tumor growth and progression are dependent on angiogenesis, it is only recently that progress has been made in elucidating the molecular mechanisms that regulate the earliest stage in the angiogenic program, the angiogenic switch. This checkpoint is characterized by the transition of a dormant, avascular tumor into an active, vascular one. Anti-angiogenic therapies to date have essentially been designed to suppress the neovasculature in established tumors. However, identifying the mechanisms that cause a tumor to acquire an angiogenic phenotype may lead to the discovery of new therapeutic modalities and complementary diagnostics that could be used to block the angiogenic switch, thereby preventing subsequent tumor progression. In this chapter on the role of angiogenesis in cancer, we (1) provide an overview of the process of angiogenesis with special regard to the molecules and physiological conditions that regulate this process, (2) review recent studies describing the use of anti-angiogenic approaches in the treatment of a variety of human cancers, and (3) discuss the recent literature focused on the study of the molecules and molecular mechanisms that may be regulating the initiation of the angiogenic phenotype in tumors, and the clinical impact that this knowledge may have in the future.

Corneal angiogenic privilege: angiogenic and antiangiogenic factors in corneal avascularity, vasculogenesis, and wound healing (an American Ophthalmological Society thesis)

PURPOSE

To determine the molecular basis of corneal avascularity during wound healing and determine the role of angiogenic and antiangiogenic factors in corneal vasculogenesis.

METHODS

The expression of proangiogenic factors (vascular endothelial growth factor [VEGF]; basic fibroblast growth factor [bFGF]; matrix metalloproteinase-2 [MMP-2]; and membrane-type 1-MMP [MT1-MMP]) and antiangiogenic factors (pigment epithelium-derived factor [PEDF]; angiostatin; restin; and endostatin) was analyzed in avascular corneas and in models of corneal neovascularization (bFGF pellet implantation, intrastromal injection of MT1-MMP cDNA, and surgically induced partial limbal deficiency).

RESULTS

Immunohistochemistry demonstrated the presence of antiangiogenic factors (PEDF, angiostatin, restin, and endostatin) and proangiogenic molecules (VEGF, bFGF, MMP-2, and MT1-MMP) in the cornea after wounding. Proangiogenic MMPs were upregulated in stromal fibroblasts in the vicinity of invading vessels following bFGF pellet implantation. Corneal neovascularization (NV) was also induced by intrastromal injection of MT1-MMP naked cDNA in conjunction with de-epithelialization. Partial limbal deficiency (HLD-) resulted in corneal NV in MMP-7 and MMP-3 knockout mice but not in wild type controls.

CONCLUSIONS

Corneal angiogenic privilege is an active process involving the production of antiangiogenic factors to counterbalance the proangiogenic factors (which are upregulated after wound healing even in the absence of new vessels). Our finding that the potent antiangiogenic factors, angiostatin and endostatin, are colocalized with several MMPs during wound healing suggests that MMPs may be involved in the elaboration of these antiangiogenic molecules by proteolytic processing of substrates within the cornea.

Pretreatment serum endostatin as a prognostic indicator in metastatic gastric carcinoma

Endostatin is the C-terminal antiangiogenic fragment of the extracellular matrix protein collagen XVIII, and is generated by tumor-derived proteases. The presence of serum endostatin in patients with gastric cancer has not been reported. The authors assessed the serum levels of endostatin in patients with gastric carcinoma and evaluated their association with the levels of vascular endothelial growth factor (VEGF) and the clinical outcome. A total of 107 patients with gastric cancer were included in the study. Pretherapeutic serum levels of endostatin and VEGF were measured using an ELISA, and compared with those in 23 healthy controls. The serum levels of endostatin and VEGF were higher in gastric cancer patients than in healthy controls (endostatin, 70.1 +/- 16.6 vs. 52.2 +/- 6.2 ng/mL [p < 0.001]; VEGF, 55.1 +/- 7.6 vs. 32.1 +/- 2.4 ng/mL [p < 0.001]; mean +/- SD). Serum endostatin levels were significantly associated with the presence of distant metastases (r = 0.556, p < 0.001) and VEGF levels (r = 0.335, p < 0.001), but not with the depth of tumor invasion, differentiation, or regional lymph node status. A serum endostatin level above the 75th percentile of the distribution for the patients (79.2 ng/mL) was associated with a poor outcome (last follow-up at 42 months; median survival time, 9 vs. 20 months [log-rank, p = 0.017]; median time to progression, 5 vs. 10 months [log-rank, p = 0.022]) in the patients with metastatic gastric cancer. The results suggest for the first time that an elevated serum level of endostatin at the diagnosis of metastatic gastric cancer could be predictive of a poor outcome.

Endostatin expression in a pancreatic cell line is modulated by a TNFalpha-dependent elastase

Endostatin, an inhibitor of angiogenesis, is a 20 kDa fragment of the basement membrane protein, collagen XVIII. The formation of endostatin relies upon the action of proteases on collagen XVIII. TNFα, produced by activated macrophages, is a multifunctional proinflammatory cytokine with known effects on endothelial function. We postulated that TNFα may modulate the activities of proteases and thus regulate endostatin formation in pancreatic cells. Collagen XVIII/endostatin mRNA was expressed in one pancreatic cell line, SUIT-2, but not in BxPc-3. The 20 kDa endostatin was found in the cell-conditioned medium of SUIT-2 cells. Precursor forms only were found in the cells. Exogenous endostatin was degraded by cellular lysates of SUIT-2 cells. Elastase activity was found in cell extracts but not the cell-conditioned media of SUIT-2 cells. Incubation of SUIT-2 cells with TNFα increased intracellular elastase activity and also increased secretion of endostatin into the medium. We conclude that endostatin is released by SUIT-2 cells and that increases in intracellular elastase, induced by TNFα, are correlated with increased secretion. Endostatin is however susceptible to degradation by intracellular proteases and if tissue injury accompanies inflammation, endostatin may be degraded, allowing angiogenesis to occur.

Endogenous stimulators and inhibitors of angiogenesis in gastrointestinal cancers: basic science to clinical application

Progression of cancer is dependent on acquisition of vascular networks within the tumor. Tumor angiogenesis is dependent on up-regulation of angiogenesis stimulators to overcome the endogenous anti-angiogenic barrier. Such disruption of angiogenesis balance to favor neovascularization is a key step for progression of tumor growth and metastasis. In this regard, the vascular basement membrane and the extracellular matrix have been found to be rich sources of angiogenesis stimulators and inhibitors that become bioavailable on proteolysis of the matrix by tumor microenvironment-related enzymes. In this review the subgroup of endogenous angiogenesis stimulators and inhibitors is discussed, and their mechanism of action during tumor angiogenesis is evaluated. The role in regulating tumor growth and the possibility of using them as prognostic markers for human gastrointestinal cancers is discussed. Furthermore, we specifically address the role of vascular endothelial growth factor in human gastrointestinal cancers and discuss the development and use of bevacizumab (Avastin; anti-vascular endothelial growth factor antibody [Genentech, CA]) in the treatment of colorectal and other gastrointestinal cancers.

The lysosomal cysteine proteases in MHC class II antigen presentation

The endosomal pathway of antigen presentation leads to the display of peptides on major histocompatibility complex (MHC) class II molecules at the cell surface of antigen-presenting cells (APCs). The pathway involves two major steps, invariant chain degradation and antigen processing, which take place in the late endosomes/lysosomes. So far, of the known lysosomal proteases, only cathepsin L and cathepsin S have been shown to have a non-redundant role in endosomal presentation in vivo. Besides being engaged in the degradation of invariant chain, these enzymes also mediate the processing of antigens in distinct cell types. Surprisingly, these enzymes are active in different types of APCs, and this defined expression pattern seems to be enforced by regulatory mechanisms acting on multiple levels.

The role of the extracellular matrix in angiogenesis in malignant glioma tumors

Angiogenesis is a promising target for the development of effective strategies for the treatment of malignant brain tumors in that it has the potential to starve large tumors and prevent the regrowth of residual margins. Two critical steps in angiogenesis, the proliferation of activated endothelial cells and their migration into the perivascular space (sprouting), require adherence of the endothelial cells to the extracellular matrix (ECM). Thus, the availability of the appropriate ligands within the ECM contributes to the regulation of angiogenesis. In addition, several components of the ECM can act through other mechanisms to further promote angiogenesis or inhibit it. Current evidence suggests that the regulation of angiogenesis is a dynamic process in which the endothelial cells can promote angiogenesis by secreting proteases that remodel the ECM, tumor cells can further promote angiogenesis by secreting ECM components and actively remodeling their environment, and stromal cells may respond to angiogenesis associated with tumors and inflammatory reactions by secreting inhibitory molecules. Here, we provide a critical review of the protein and proteoglycan components of the ECM that have been implicated in angiogenesis with an emphasis on their role in promoting or inhibiting angiogenesis in brain tumors.

Cathepsin L is essential for onset of autoimmune diabetes in NOD mice

Lysosomal proteases generate peptides presented by class II MHC molecules to CD4+ T cells. To determine whether specific lysosomal proteases might influence the outcome of a CD4+ T cell-dependent autoimmune response, we generated mice that lack cathepsin L (Cat L) on the autoimmune diabetes-prone NOD inbred background. The absence of Cat L affords strong protection from disease at the stage of pancreatic infiltration. The numbers of I-A(g7)-restricted CD4+ T cells are diminished in Cat L-deficient mice, although a potentially diabetogenic T cell repertoire persists. Within the CD4+ T cell compartments of Cat L-deficient mice, there is an increased proportion of regulatory T cells compared with that in Cat L-sufficient littermates. We suggest that it is this displaced balance of regulatory versus aggressive CD4+ T cells that protects Cat L-deficient mice from autoimmune disease. Our results identify Cat L as an enzyme whose activity is essential for the development of type I diabetes in the NOD mouse.

Generation of biologically active endostatin fragments from human collagen XVIII by distinct matrix metalloproteases

Endostatin, a potent inhibitor of endothelial cell proliferation, migration, angiogenesis and tumor growth, is proteolytically cleaved from the C-terminal noncollagenous NC1 domain of type XVIII collagen. We investigated the endostatin formation from human collagen XVIII by several MMPs in vitro. The generation of endostatin fragments differing in molecular size (24-30 kDa) and in N-terminal sequences was identified in the cases of MMP-3, -7, -9, -13 and -20. The cleavage sites were located in the protease-sensitive hinge region between the trimerization and endostatin domains of NC1. MMP-1, -2, -8 and -12 did not show any significant activity against the C-terminus of collagen XVIII. The anti-proliferative effect of the 20-kDa endostatin, three longer endostatin-containing fragments generated in vitro by distinct MMPs and the entire NC1 domain, on bFGF-stimulated human umbilical vein endothelial cells was established. The anti-migratory potential of some of these fragments was also studied. In addition, production of endostatin fragments between 24-30 kDa by human hepatoblastoma cells was shown to be due to MMP action on type XVIII collagen. Our results indicate that certain, especially cancer-related, MMP family members can generate biologically active endostatin-containing polypeptides from collagen XVIII and thus, by releasing endostatin fragments, may participate in the inhibition of endothelial cell proliferation, migration and angiogenesis.

Endostatin signaling and regulation of endothelial cell-matrix interactions

The growth and survival of a malignant tumor are dependent on the formation and maintenance of its own microvasculature, a process termed angiogenesis. Inhibition of this phenomenon is an emerging strategy in cancer therapy. The extracellular matrix surrounding the vascular endothelial cells contains cryptic protein domains, which are exposed by changes in the proteolytic homeostasis of the tumor microenvironment. These fragments transmit local signals, which regulate vascular endothelial cell proliferation and migration. Endostatin, the proteolytic fragment of collagen type XVIII, is a potent inhibitor of tumor angiogenesis in various mouse models and is currently in clinical trials for therapeutic use in human cancer. Multiple cell surface receptors have been described for endostatin, but the signals transmitted by these receptors resulting in the inhibition of angiogenesis have so far been poorly characterized. Studies on the effects of endostatin on cultured endothelial cells suggest that the antimigratory and antiproliferative properties of this molecule are the major mechanisms underlying its antiangiogenic potential. These effects may be a consequence of endostatin modulation of endothelial cell-matrix interactions and pericellular proteolysis.

Invasive trophoblasts generate regulatory collagen XVIII cleavage products

Endostatin, the C-terminal proteolytic fragment of the noncollagenous domain 1 (NC1) of the basement membrane protein collagen XVIII, inhibits cell proliferation and migration. Placental and decidual expression of the peptide suggested a role in angiogenesis and/or extravillous trophoblast differentiation. Here, we demonstrate that supernatants of trophoblastic SGHPL-5 cells, purified first trimester villous trophoblasts and villous explant cultures contain proteases which in vitro cleave 20kDa endostatin from purified, recombinant NC1 domains. However, supernatants of decidual and villous fibroblasts failed to generate the 20kDa endostatin fragment. Moreover, we show that recombinant endostatin inhibits invasion of SGHPL-5 cells through Matrigel invasion chambers. Since mesenchymal cells but not trophoblasts produce collagen XVIII we suspect that invasive trophoblasts may produce endostatin upon contacting the extracellular matrix deposited by decidual stromal cells. Generation of endostatin through trophoblast-derived proteases could play a role in the regulation of trophoblast invasiveness.

Cathepsin-L influences the expression of extracellular matrix in lymphoid organs and plays a role in the regulation of thymic output and of peripheral T cell number

Nackt mice, which are deficient in cathepsin-L (CTSL), show an early impairment during positive selection in the context of class II MHC molecules and as a consequence, the percentage and absolute number of CD4(+) thymocytes are significantly decreased. In this study, we show that lymph nodes from nackt mice are hypertrophied, showing normal absolute numbers of CD4(+) T cells and marked increases in the number of CD8(+) T lymphocytes. Basal proliferative levels are increased in the CD4(+) but not in the CD8(+) population. Lymph node T cells show increases in the expression of alpha(5), alpha(6), and beta(1) integrin chains. These alterations correlate with increases in the expression of extracellular matrix (ECM) components in lymph nodes. Interestingly, laminin, fibronectin, and collagen I and IV are markedly decreased in nackt thymus which shows an augmented output of CD8(+) cells. These results demonstrate that a mutation in the Ctsl gene influences the levels of ECM components in lymphoid organs, the thymic output, and the number of T cells in the periphery. They further raise the possibility that, by regulating the level of expression of ECM components in lymphoid organs, CTSL is able to broadly affect the immune system.

Functions for proteinases in the ovulatory process

The ovary is a unique and dynamic organ in respect to rapid and extensive degrees of tissue development and remodeling that are periodically repeated in the female reproductive activity. Ovulation is a directed and sequential process accompanied by broad-spectrum proteolysis and culminates in the follicular rupture to release the matured oocyte. This review will focus on the potential roles of six representative proteinases that are involved in various aspects of ovulatory processes: matrix metalloproteinases (MMPs), plasminogen activator (PA)/plasmin, a disintegrin and metalloproteinase domain with thrombospondin motif (ADAMTS), cathepsin-L, pregnancy-associated plasma protein-A (PAPP-A), and bone morphogenetic protein 1/mammalian Tolloid (BMP-1/mTld). Based on the studies of expression and function, these selected proteinases provide and share diverse functions ranging from cleaving components of the extracellular matrix (ECM) to modulating non-ECM molecules, such as various growth factors and their binding proteins. Consistently, the genetic deletion of each individual gene in mice shows their functional overlap in the reproductive activity.

Liposome transfected to plasmid-encoding endostatin gene combined with radiotherapy inhibits liver cancer growth in nude mice

AIM: To evaluate whether intratumoral injection of liposome-endostatin complexes could enhance the antitumor efficacy of radiation therapy in human liver carcinoma (BEL7402) model.

METHODS: Recombinant plasmid pcDNA3.End was transfected into human liver carcinoma cell line (BEL7402) with lipofectamine to produce conditioned medium. Then BEL7402 cells and human umbilical vein endothelial cells (HUVECs) were treated with the conditioned medium. Cell cycle and apoptosis were analyzed by flow cytometer and endothelial cell proliferation rates were determined by MTT assay. The antitumor efficacy of endostatin gene combined with ionizing radiation in mouse xenograft liver tumor was observed.

RESULTS: Endostatin significantly suppressed the S phase fraction and increased the apoptotic index in HUVECs. In contrast, endostatin treatment had no effect on BEL7402 cell apoptosis (2.1 ± 0.3% vs 8.9 ± 1.3%, t = 8.83, P = 0.009<0.01) or cell cycle distribution (17.2 ± 2.3% vs 9.8 ± 1.2%, t = 4.94, P = 0.016<0.05). The MTT assay showed that endostatin significantly inhibited the proliferation of HUVECs by 46.4%. The combination of local endostatin gene therapy with radiation therapy significantly inhibited the growth of human liver carcinoma BEL7402 xenografts, the inhibition rate of tumor size was 69.8% on d 28 compared to the untreated group. The tumor volume in the pcDNA3.End combined with radiation therapy group (249 ± 83 mm³) was significantly different from that in the untreated group (823 ± 148 mm³, t = 5.86, P = 0.009<0.01) or in the pcDNA3 group (717 ± 94 mm³, t = 6.46, P = 0.003<0.01). Endostatin or the radiation alone also inhibited the growth of liver tumor in vivo, but their inhibition effects were weaker than those of endostatin combined with radiation, the inhibition rates on d 28 were 44.7% and 40.1%, respectively.

CONCLUSION: Endostatin not only significantly suppresses tumor growth but also enhances the antitumor efficacy of radiation therapy in human carcinoma xenograft.

Metalloproteinases and their inhibitors in tumor angiogenesis

Angiogenesis is the process by which new blood vessels are formed from preexisting vasculature. It is an essential feature of the female reproductive cycle, embryonic development and wound repair. Angiogenesis has also been identified as a causal or contributing factor in several pathologies, including cancer, where it is a rate-limiting step during tumor progression. Matrix metalloproteinases (MMPs) are a family of soluble and membrane-anchored proteolytic enzymes that can degrade components of the extracellular matrix (ECM) as well as a growing number of modulators of cell function. Several of the MMPs, in particular the gelatinases and membrane-type 1 MMP (MT1-MMP), have been linked to angiogenesis. Potential roles for these proteases during the angiogenic process include degradation of the basement membrane and perivascular ECM components, unmasking of cryptic biologically relevant sites in ECM components, modulation of angiogenic factors and production of endogenous angiogenic inhibitors. This review brings together what is currently known about the functions of the MMPs and the closely related ADAM (a disintegrin and metalloproteinase domain) and ADAMTS (a disintegrin and metalloproteinase with thrombospondin motifs) families in angiogenesis and considers how this information might be useful in manipulation of the angiogenic process, with a view to constraining tumor progression.

Functional characterization of neostatins, the MMP-derived, enzymatic cleavage products of type XVIII collagen

Several anti-angiogenic factors are derived from proteolytic processing of large molecules including endostatin from type XVIII collagen and angiostatin from plasminogen. In previous studies we showed that neostatin-7, the C-terminal 28kDa endostatin-spanning proteolytic fragment, is generated from the proteolytic action of matrix metalloproteinase matrilysin (MMP)-7 on type XVIII collagen. Now, we report a second member of the neostatin family of proteins, neostatin-14. Given the small quantities of neostatin-7 and -14 generated by the breakdown of naturally occurring collagen XVIII (using MMP-7 and -14, respectively), we used two other approaches to characterize the anti-angiogenic properties of these molecules: murine recombinant neostatin in vitro, and gene therapy. We demonstrate that murine recombinant neostatin-7 inhibits calf pulmonary artery endothelial cell proliferation and that microinjection of neostatin-7 and neostatin-14 naked DNA into the corneal stroma of mice results in significant reduction of basic fibroblast growth factor-induced corneal neovascularization. These results provide supportive evidence of the possible anti-angiogenic effect of neostatins.

HaCaT keratinocytes secrete lysosomal cysteine proteinases during migration

Cathepsin B, a lysosomal cysteine proteinase, was detected within vesicles of cellular protrusions forming cell-cell contact sites between keratinocytes of the stratum spinosum of human skin. This observation suggested the possibility that secretion of the protease into the pericellular spaces could be involved in the dissociation of cell-cell contacts to enable intraepidermal keratinocyte migration. To determine whether cathepsin B is indeed secreted from migrating keratinocytes, we first used subconfluent HaCaT cells as a culture model to study spontaneous keratinocyte migration. A cathepsin B-specific fluorescent affinity label proved the association of mature cathepsin B with the surfaces of HaCaT cells at the leading edges of growing cells. Second, we used scratch-wounds of confluent HaCaT monolayers as a model of induced keratinocyte migration. Cathepsin B was detected within lysosomes, i.e. vesicles within the perinuclear region of non-wounded cells. Expression of cathepsin B was up-regulated and cathepsin B-positive vesicles showed a redistribution from perinuclear to peripheral regions of keratinocytes at the wound margins within 4 h after wounding. Enzyme cytochemistry further showed that cell surface-associated cathepsin B was proteolytically active at the leading fronts of migrating keratinocytes. In addition, increased amounts of mature forms of cathepsin B were detected within the conditioned media of HaCaT cells during the first 4 h after scratch-wounding. In contrast, and as a control, the activity of the cytosolic enzyme lactate dehydrogenase was not significantly higher in media of wounded cells as compared with non-wounded controls, arguing for a specific induction of cathepsin B secretion upon wounding and migration of the cells. This was further substantiated by applying various cathepsin B-specific inhibitors after wounding. These experiments showed that the migration ability of keratinocytes was reduced due to the blockage of functional cathepsin B. Thus, our results strongly suggest that cell surface-associated cathepsin B is a protease that contributes to the remodelling of the extracellular matrix and thereby promotes keratinocyte migration during wound healing.

Endogenous inhibitors of angiogenesis in malignant gliomas: nature's antiangiogenic therapy

Angiogenesis is necessary for tumor growth beyond a volume of approximately 2 mm(3). This observation, along with the accessibility of tumor vessels to therapeutic targeting, has resulted in a research focus on inhibitors of angiogenesis. A number of endogenous inhibitors of angiogenesis are found in the body. Some of these are synthesized by specific cells in different organs, and others are created by extracellular proteolytic cleavage of plasma-derived or extracellular matrix-localized proteins. In this review, we focus on angiostatin, endostatin, PEX, pigment epithelial-derived factor, and thrombospondin (TSP)-1 and -2, either because these molecules are expressed in malignant glioma biopsies or because animal studies in malignant glioma models have suggested that their therapeutic administration could be efficacious. We review the known mechanisms of action, potential receptors, expression in glioma biopsy samples, and studies testing their potential therapeutic efficacy in animal models of malignant glioma. Two conclusions can be made regarding the mechanisms of action of these inhibitors: (1) Several of these inhibitors appear to mediate their antiangiogenic effect through multiple protein-protein interactions that inhibit the function of proangiogenic molecules rather than through a specific receptor-mediated signaling event, and (2) TSP-1 and TSP-2 appear to mediate their antiangiogenic effect, at least in part, through a specific receptor, CD36, which initiates the antiangiogenic signal. Although not proven in gliomas, evidence suggests that expression of specific endogenous inhibitors of angiogenesis in certain organs may be part of a host antitumor response. The studies reviewed here suggest that new antiangiogenic therapies for malignant gliomas offer exciting promise as nontoxic, growth-inhibitory agents.

Asparagine Endopeptidase Is Not Essential for Class II MHC Antigen Presentation but Is Required for Processing of Cathepsin L in Mice

Class II MHC molecules survey the endocytic compartments of APCs and present antigenic peptides to CD4 T cells. In this context, lysosomal proteases are essential not only for the generation of antigenic peptides but also for proteolysis of the invariant chain to allow the maturation of class II MHC molecules. Recent studies with protease inhibitors have implicated the asparagine endopeptidase (AEP) in class II MHC-restricted Ag presentation. We now report that AEP-deficient mice show no differences in processing of the invariant chain or maturation of class II MHC products compared with wild-type mice. In the absence of AEP, presentation to primary T cells of OVA and myelin oligodendrocyte glycoprotein, two Ags that contain asparagine residues within or in proximity to the relevant epitopes was unimpaired. Cathepsin (Cat) L, a lysosomal cysteine protease essential for the development to CD4 and NK T cells, fails to be processed into its mature two-chain form in AEP-deficient cells. Despite this, the numbers of CD4 and NK T cells are normal, showing that the single-chain form of Cat L is sufficient for its function in vivo. We conclude that AEP is essential for processing of Cat L but not for class II MHC-restricted Ag presentation.

Cathepsin B regulates the intrinsic angiogenic threshold of endothelial cells

The lysosomal protease cathepsin B has been implicated in a variety of pathologies including pancreatitis, tumor angiogenesis, and neuronal diseases. We used a tube formation assay to investigate the role of cathepsin B in angiogenesis. When cultured between two layers of collagen I, primary endothelial cells formed tubes in response to exogenously added VEGF. Overexpressing cathepsin B reduced the VEGF-dependent tube response, whereas pharmacologically or molecularly suppressing cathepsin B eliminated the dependence on exogenous VEGF. However, tube formation still required VEGF receptor activity, which suggested that endothelial cells generated VEGF. Indeed, VEGF mRNA and protein was detectable in cells treated with cathepsin B inhibitor, which correlated with a rise in the level of HIF-1alpha. In addition to boosting the level of proangiogenic factors, blocking cathepsin B activity reduced the amount of the antiangiogenic protein endostatin. Thus endothelial cells have the intrinsic capacity to generate pro- and antiangiogenic agents. These observations complement and expand our appreciation of how endothelial cell-derived proteases regulate angiogenesis.

A 27-Amino-Acid Synthetic Peptide Corresponding to the NH2-Terminal Zinc-Binding Domain of Endostatin Is Responsible for Its Antitumor Activity

The first recombinant endostatin that elicited strong antitumor activity was expressed in Escherichia coli and administered as a suspension. Under these conditions, the protein retained its full antiangiogenic activity. Lack of requirement for a folded structure prompted us to investigate antitumor properties of synthetic peptides corresponding to different regions of endostatin. Here, we show that the entire antitumor, antimigration, and antipermeability activities of endostatin are mimicked by a 27-amino-acid peptide corresponding to the NH2-terminal domain of endostatin. This peptide contains three histidines that are responsible for zinc binding. Mutations of the zinc-binding histidines abolished its antitumor and antimigration activities, but not antipermeability properties.

Endostatin inhibits nitric oxide and diminishes VEGF and collagen XVIII in squamous carcinoma cells

Low pO(2) values are a common finding among oral squamous cell carcinomas (SCC). Our objective was to determine the role that oxygen tension plays on the direct tumor effect of endostatin (ES). Squamous carcinoma cell lines were grown under normoxic or hypoxic conditions and treated with endostatin (ES), nitric oxide (NO) donors, NO scavengers, NO synthase inhibitors, or transduced with AdenoVec-hEndo or AdenoVec Null vectors. The expression of vascular endothelial growth factor (VEGF) and collagen XVIII were determined by RT-PCR and protein levels assessed by Western blot analyses. Our studies demonstrated that collagen XVIII and VEGF are expressed and responsive to ES in a limited number of SCC cell lines during normoxia but were most responsive when grown under hypoxic conditions. VEGF and collagen XVIII were downregulated by both ES and transduction of cells with AdenoVec-hEndo. The effects of ES on SCC cells were enhanced by aminoguanidine (Ag), L-NAME, and diphenyleneiodonium chloride (DPI). Endostatin and transduced with ES vectors diminished the levels of NO whereas NO donors enhanced VEGF expression and collagen XVIII expression. In conclusion, the direct effect of endostatins on tumor cells is most effective under conditions of low oxygen tension and can be potentiated by the use of nitric oxide synthase inhibitors or NO scavengers.

Gelatinase-mediated migration and invasion of cancer cells

The matrix metalloproteinases(MMP)-2 and -9, also known as the gelatinases have been long recognized as major contributors to the proteolytic degradation of extracellular matrix during tumor invasion. In the recent years, a plethora of non-matrix proteins have also been identified as gelatinase substrates thus significantly broadening our understanding of these enzymes as proteolytic executors and regulators in various physiological and pathological states including embryonic growth and development, angiogenesis and tumor progression, inflammation, infective diseases, degenerative diseases of the brain and vascular diseases. Although the effect of broad-spectrum inhibitors of MMPs in the treatment of cancer has been disappointing in clinical trials, novel mechanisms of gelatinase inhibition have been now identified. Inhibition of the association of the gelatinases with cell-surface integrins appears to offer highly specific means to target these enzymes without inhibiting their catalytic activity in multiple cell types including endothelial cells, tumor cells and leukocytes. Here, we review the multiple functions of the gelatinases in cancer, and especially their role in the tumor cell migration and invasion.

Endostatin overexpression specifically in the lens and skin leads to cataract and ultrastructural alterations in basement membranes

Endostatin, a proteolytic fragment of type XVIII collagen, has been shown to inhibit angiogenesis, tumor growth, and endothelial cell proliferation and migration. We analyzed its functions in vivo by generating transgenic mice in which it was overexpressed in the skin and lens capsule under the keratin K14 promoter. Opacity of the lens occurred at 4 months of age in the mouse line J4, with the highest level of endostatin expression. The lens epithelial cells appeared to lose contact with the capsule and began to vacuolize. In 1-year-old mice the lens epithelial cell layer had entirely degenerated, and instead, large plaques of spindle-shaped cells had formed in the anterior region of the lens. Moreover, a widening of the epidermal basement membrane (BM) zone of the skin was observed in electron microscopy. The epidermal BM was conspicuously altered in the J4 mice with high transgene expression, including clear broadening and occurrence of pearl-like protrusions in some areas, whereas the BM was more even in appearance but consistently broadened in the mouse line G20 with moderate transgene expression. In both lines the BM was continuous. Measurements indicated that the lamina densa was 78.54 +/- 53.10 nm in line J4, the large variation reflecting the protrusions of the lamina densa, and 44.24 +/- 11.52 nm in line G20, compared with 33.74 +/- 9.96 nm in wild-type adult mice. Immunoelectron microscopy of wild-type mouse skin type XVIII collagen showed a polarized orientation in the BMs, with the C-terminal endostatin region localized in the lamina densa and the N terminus in average approximately 40 nm more on the dermal side. Type XVIII collagen was dispersed in the transgenic skin, suggesting that the transgene-derived endostatin fragment displaces the full-length collagen XVIII. This may impair the anchoring of the lamina densa to the dermis and thereby lead to loosening of the BMs, resembling the previously observed situation in collagen XVIII-null mice.

Matrikines in the regulation of extracellular matrix degradation

The term "matrikines" was coined for designating peptides liberated by partial proteolysis of extracellular matrix macromolecules, which are able to regulate cell activities. Among these peptides, some of them may modulate proliferation, migration, protease production, or apoptosis. In this review, we summarize the activity of matrikines derived from elastin and interstitial or basement membrane collagens on the regulation of matrix metalloproteinases expression and/or activation, and on the plasminogen/plasmin system. Due to their activity, matrikines may play a significant role in physiological or pathological processes such as wound healing or tumor invasion.

Cysteine cathepsins are central contributors of invasion by cultured adenosylmethionine decarboxylase-transformed rodent fibroblasts

Adenosylmethionine decarboxylase (AdoMetDC), a key enzyme in the biosynthesis of polyamines, is often up-regulated in cancers. We have demonstrated previously that overexpression of AdoMetDC alone is sufficient to transform NIH 3T3 cells and induce highly invasive tumors in nude mice. Here, we studied the transformation-specific alterations in gene expression induced by AdoMetDC by using cDNA microarray and two-dimensional electrophoresis technologies. We specifically tried to identify the secreted proteins contributing to the high invasive activity of the AdoMetDC-transformed cells. We found a significant increase in the expression and secretion of procathepsin L, which was cleaved and activated in the presence of glycosaminoglycans (heparin), and a smaller increase in cathepsin B. Inhibition of the cathepsin L and B activity by specific peptide inhibitors abrogated the invasive capacity of the AdoMetDC transformants in Matrigel. The transformed cells also showed a small increase in the activity of gelatin-degrading matrix metalloproteinases (MMPs) and urokinase-type plasminogen activator activities, neither of which was sensitive to the inhibitors of cathepsin L and B. Furthermore, the invasive potency of the transformed cells remained unaffected by specific inhibitors of MMPs. The results suggest that cysteine cathepsins are the main proteases contributing to the high invasiveness of the AdoMetDC-transformed cells and that the invasion potential is largely independent of activation of the MMPs.

Cathepsin L is involved in cathepsin D processing and regulation of apoptosis in A549 human lung epithelial cells

Cathepsins are implicated in a multitude of physiological and pathophysiological processes. The aim of the present study was to investigate the function of cathepsin L (catL) in the proteolytic network of human lung epithelial cells and its role in the regulation of apoptosis. We found that catL-deficient A549 cells as well as lung tissue extracts of catL(-/-) mice express increased amounts of single-chain cathepsin D (catD). Degradation experiments indicate that catL specifically degrades the single-chain isoform of catD. Furthermore, we found that catL-deficient cells showed increased sensitivity to apoptosis. Finally, we demonstrate that the inhibition of catD activity by pepstatin A decreased the number of apoptotic cells in catL-deficient A549 cells after anti-Fas treatment. In conclusion, catL is involved in catD processing and the accumulation of catD isoforms in catL-deficient cells is associated with increased rates of spontaneous and anti-Fas-induced apoptosis.

Site-directed mutagenesis, proteolytic cleavage, and activation of human proheparanase

Heparanase is an endo-beta-D-glucuronidase that degrades heparan sulfate in the extracellular matrix and cell surfaces. Human proheparanase is produced as a latent 65-kDa polypeptide undergoing processing at two potential proteolytic cleavage sites, located at Glu109-Ser110 (site 1) and Gln157-Lys158 (site 2). Cleavage of proheparanase yields 8- and 50-kDa subunits that heterodimerize to form the active enzyme. The fate of the linker segment (Ser110-Gln157) residing between the two subunits, the mode of processing, and the protease(s) engaged in proheparanase processing are currently unknown. We applied multiple site-directed mutagenesis and deletions to study the nature of the potential cleavage sites and amino acids essential for processing of proheparanase in transfected human choriocarcinoma cells devoid of endogenous heparanase but possessing the enzymatic machinery for proper processing and activation of the proenzyme. Although mutagenesis at site 1 and its flanking sequences failed to identify critical residues for proteolytic cleavage, processing at site 2 required a bulky hydrophobic amino acid at position 156 (i.e. P2 of the cleavage site). Substitution of Tyr156 by Ala or Glu, but not Val, resulted in cleavage at an upstream site in the linker segment, yielding an improperly processed inactive enzyme. Processing of the latent 65-kDa proheparanase in transfected Jar cells was inhibited by a cell-permeable inhibitor of cathepsin L. Moreover, recombinant 65-kDa proheparanase was processed and activated by cathepsin L in a cell-free system. Altogether, these results suggest that proheparanase processing at site 2 is brought about by cathepsin L-like proteases. The involvement of other members of the cathepsin family with specificity to bulky hydrophobic residues cannot be excluded. Our results and a three-dimensional model of the enzyme are expected to accelerate the design of inhibitory molecules capable of suppressing heparanase-mediated enhancement of tumor angiogenesis and metastasis.

Comparison of expression of cathepsins B and L and MMP2 in endothelial cells and in capillary sprouting in collagen gel

The lysosomal cysteine proteinases cathepsins B and L are known to play an important role in the invasive growth of tumor cells, but their association with angiogenesis has been less well studied. The aim of this study was to determine the possible role of endothelial cell-associated cathepsins B and L in induced capillary growth in the aorta ring model of angiogenesis. Specific inhibitors of cysteine proteinases did not inhibit capillary growth in aorta ring culture and only slightly inhibited the degradation of surrounding collagen. In contrast, strong inhibition of both processes by the matrix metalloproteinase inhibitor BB-94 was observed, indicating the importance of endogenous MMP production in angiogenesis. In support of this finding, we demonstrated a significant increase in endogenous endothelial mRNA of MMP2, but not of cathepsins B and L, in proliferating primary human dermal microvascular endothelial cells (HMVEC-d) in culture. However, MMP2 mRNA expression was increased only when the cells were embedded in collagen but not when they were grown on plastic, regardless of the addition of the growth factors VEGF or bFGF. Moreover, on plastic the impairment of MMP2 induction by growth factors was observed. The differential effect of growth factors implies the crosstalk with integrin signaling as a consequence of binding to the different matrix. This study suggests that endothelial cell-associated cathepsins B and L are not involved in the invasive growth of capillaries from existing blood vessels and that the presence of collagen is necessary for MMP2 expression in endothelial cells.

Non-heparan sulfate-binding interactions of endostatin/collagen XVIII in murine development

Knobloch syndrome is characterized by a congenital generalized eye disease and cranial defect. Pathogenic mutations preferentially lead to a deletion or functional alteration of collagen XVIII's most C-terminal endostatin domain. Endostatin can be released from collagen XVIII and is a potent inhibitor of angiogenesis and tumor growth. We show differential expression of binding partners for endostatin, vascular endothelial growth factor (VEGF), and the collagen XV endostatin homologue in murine embryonal development using a set of alkaline phosphatase fusion proteins. Consistent with the human phenotype, vascular mesenchyme in the developing eye was identified as endostatin's primary target. While endostatin predominantly bound to blood vessels, the VEGF164 affinity probe labeled nonvascular tissues such as forebrain, hindbrain, the optic nerve, and the surface ectoderm of the future cornea. Strikingly increased staining specificity was observed with a non-heparin/heparan sulfate-binding endostatin probe. In contrast, elimination of the heparan sulfate binding site from VEGF led to complete loss of binding. The collagen XV endostatin homologue showed a highly restricted binding pattern. Oligomerization with endogenous endostatin was ruled out by use of collagen XVIII knockout mice. Our data provide strong evidence that collagen XVIII's C-terminal endostatin domain harbors a prominent tissue-binding site and that binding can occur in the absence of heparan sulfates in situ.

Matrix revolutions: ‘tails’ of basement-membrane components with angiostatic functions

Angiogenesis, the creation of neovasculature from native blood vessels, is a prerequisite for many physiological and pathological processes. Recently, C-terminal tail fragments of several basement-membrane proteins such as endostatin, tumstatin and endorepellin have been shown to inhibit angiogenesis. Although there seems to be little or no homology among them, a common theme is that these fragments modulate endothelial cells by distinct interactions with integrins and activate distinct intracellular signaling cascades that often lead to disruption of the actin cytoskeleton. In this article, we focus on recent advances regarding the mechanism of action of these angiostatic fragments and the emerging concept of similarities among them, with the underlying premise that appreciating these similarities might lead to improved therapeutics.

Serum endostatin levels are elevated and correlate with serum vascular endothelial growth factor levels in patients with pituitary adenomas

Endostatin, a cleaved fragment of collagen XVIII, is a potent endogenous angiogenesis inhibitor. Elevated serum endostatin levels have been recently reported in patients with various types of neoplasms. The purpose of our study was to evaluate serum concentrations of endostatin in patients harbouring various pituitary adenoma types and to examine the relationship of serum endostatin levels to circulating vascular endothelial growth factor (VEGF) levels. Preoperative serum endostatin and VEGF concentrations were measured using competitive enzyme immunoassays in 71 patients with pituitary adenomas (20 somatotropinomas, 3 corticotropinomas, 6 prolactinomas and 42 clinically nonfunctioning pituitary adenomas - CNFPAs) and compared with levels from age-matched controls. In 35 patients postoperative immunohistochemical investigations were performed. Serum endostatin concentrations were significantly higher in all pituitary adenoma types, except for prolactinomas (somatotropinomas: 124 +/- 16; p < 0.02, corticotropinomas: 157 +/- 42; p < 0.02, prolactinomas: 141 +/- 37; p > 0.05, CNFPAs: 169 +/- 11 ng/ml; p < 0.000005 vs 73 +/- 10 ng/ml in controls). There was a significant positive correlation between endostatin and VEGF serum levels in patients with pituitary adenomas (r = +0.322; p = 0.006). In the control group a significant negative correlation xbetween circulating endostatin and VEGF was found (r = -0.653; p = 0.00975). The simultaneous elevation of endostatin and VEGF may attenuate the pro-angiogenic action of VEGF and be responsible for rather weak neovascularization of pituitary adenomas. Prospective studies are required to assess the usefulness of circulating endostatin and VEGF as markers of progression or recurrence of pituitary tumors.

Microenvironmental and cellular consequences of altered blood flow in tumours

Tumour angiogenesis is triggered by various signals characteristic of the tumour microenvironment, including low oxygen tension, low extracellular pH and low glucose concentration. Tumour microvasculature is chaotic, producing perfusion heterogeneities which can be visualized by MRI and other modalities. Inefficient perfusion in tumours produces regions of transient and chronic hypoxia. Tumour hypoxia is associated with adverse clinical outcomes and reduced patient survival. Hypoxia may be a factor in activation of extracellular matrix-degrading proteases, and some studies have correlated primary tumour hypoxia with likelihood of tumour cell dissemination. Exposure to hypoxia either induces or selects for cells that are hyperglycolytic, and this in turn produces local acidosis which is also a common feature of solid tumours. Increased glucose uptake in hyperglycolyzing tumour cells is the basis of lesion-visualization in positron emission tomography using 18F-fluorodeoxyglucose. Tumour acidity can reduce the effectiveness of weak-base drugs, but can be exploited to increase the anti-tumour activity of weak-acid chemotherapeutics. Evidence linking tumour acidity with increased activity of several extracellular matrix-degrading enzyme systems is examined. High levels of lactate, another end-product of glycolysis, in primary lesions have been correlated with increased likelihood of metastasis. In the numerous studies correlating hypoxia, acidity and lactate with metastasis, the direction of the causality has not been adequately established. We hypothesize that adoption of a hyperglycolytic phenotype is a necessary feature of carcinogenesis itself, and confers a survival and proliferative advantage to tumour cells over surrounding normal cells. Empirical evidence supporting this "acid-mediated tumour invasion" model is discussed.

The potentials of MS-based subproteomic approaches in medical science: the case of lysosomes and breast cancer

Because of the great number of women who are diagnosed with breast cancer each year, and though this disease presents the lowest mortality rate among cancers, breast cancer remains a major public health problem. As for any cancer, the tumorigenic and metastatic processes are still hardly understood, and the biochemical markers that allow either a precise monitoring of the disease or the classification of the numerous forms of breast cancer remain too scarce. Therefore, great hopes are put on the development of high-throughput genomic and proteomic technologies. Such comprehensive techniques should help in understanding the processes and in defining steps of the disease by depicting specific genes or protein profiles. Because techniques dedicated to the current proteomic challenges are continuously improving, the probability of the discovery of new potential protein biomarkers is rapidly increasing. In addition, the identification of such markers should be eased by lowering the sample complexity; e.g., by sample fractionation, either according to specific physico-chemical properties of the proteins, or by focusing on definite subcellular compartments. In particular, proteins of the lysosomal compartment have been shown to be prone to alterations in their localization, expression, or post-translational modifications (PTMs) during the cancer process. Some of them, such as the aspartic protease cathepsin D (CatD), have even been proven as participating actively in the disease progression. The present review aims at giving an overview of the implication of the lysosome in breast cancer, and at showing how subproteomics and the constantly refining MS-based proteomic techniques may help in making breast cancer research progress, and thus, hopefully, in improving disease treatment.

Intramuscular delivery of antiangiogenic genes suppresses secondary metastases after removal of primary tumors

The success of surgery to remove primary tumors can be compromised by the subsequent outgrowth of metastases. It is recognized that primary tumors secrete antiangiogenic factors that suppress the outgrowth of their daughter metastases. In accord we show here that surgical removal of primary EL-4 lymphomas led to a marked decrease in the levels of circulating angiostatin and endostatin, and promoted the growth of distant nodular tumors. Expression vectors encoding angiostatin and endostatin, formulated with poly-N-vinyl pyrrolidone (PVP), were injected into the tibialis and gastrocnemia muscles, leading to expression of angiostatin and endostatin in muscle fibers. High levels of biologically active exogenous proteins were secreted into the circulation. Intramuscular gene therapy with angiostatin and endostatin plasmids significantly inhibited tumor vascularity and induced tumor cell apoptosis, and thereby suppressed the growth of secondary subcutaneous and disseminated metastatic tumors in the lung and liver. Simultaneous intramuscular delivery of both angiostatin and endostatin plasmids significantly prolonged the survival of mice after removal of primary tumors. These results suggest that intramuscular gene transfer of angiostatin and endostatin might serve as a prophylactic cancer-prevention strategy to combat the recurrence of cancer after surgical resection of primary tumors.

Angiogenic activation of valvular endothelial cells in aortic valve stenosis

Here, we demonstrate the angiogenic response of valvular endothelial cells to aortic valve (AV) stenosis using a new ex vivo model of aortic leaflets. Histological analysis revealed neovascularization within the cusps of stenotic but not of non-stenotic aortic valves. Correspondingly, the number of capillary-like outgrowth in 3D collagen gel was significantly higher in stenotic than in non-stenotic valves. Capillary-like sprouting was developed significantly faster in stenotic than in non-stenotic valves. New capillary sprouts from stenotic aortic valves exhibited the endothelial cell markers CD31, CD34 and von-Willebrand factor (vWF) as well as carcinoembryonic antigen cell adhesion molecule-1 (CEACAM1), Tie-2 and angiogenesis inhibitor endostatin. Western blot analyses revealed a significant increase of CEACAM1 and endostatin in stenotic aortic valve tissue. Electron microscopic examinations demonstrate that these capillary-like tubes are formed by endothelial cells containing Weibel-Palade bodies. Remarkably, inter-endothelial junctions are established and basement membrane material is partially deposited on the basal side of the endothelial tubes. Our data demonstrate the capillary-like sprout formation from aortic valves and suggest a role of angiogenesis in the pathogenesis of aortic valve stenosis. These data provide new insights into the mechanisms of valvular disorders and open new perspectives for prevention and early treatment of calcified aortic stenosis.

Increased angiogenic response in aortic explants of collagen XVIII/endostatin-null mice

Endostatin, a proteolytic fragment of basement membrane-associated collagen XVIII, has been shown to be a potent angiogenesis inhibitor both in vivo and in vitro when given at high concentrations. The precise molecular mechanisms by which it functions and whether or not it plays a role in physiological regulation of angiogenesis are not clear. In mice with targeted null alleles of Col18a1, there appears to be no major abnormality in vascular patterns or capillary density in most organs. Furthermore, the growth of experimental tumors is not increased. However, a detailed analysis of induced angiogenesis in these mice has not been performed. Therefore, we compared the angiogenic responses induced by in vitro culture of aortic explants from collagen XVIII/endostatin-null mice (ko) to wild-type (wt) littermates. We found a twofold increase in microvessel outgrowth in explants from ko mice, relative to wt explants. This increased angiogenesis was reduced to the wt level by the addition of low levels (0.1 microg/ml) of recombinant mouse or human endostatin during the culture period. To address cellular/molecular mechanisms underlying this difference in angiogenic response between ko and wt mice, we isolated endothelial cells from both strains and compared their biological behavior. Proliferation assays showed no difference between the two types of endothelial cells. In contrast, adhesion assays showed a striking difference in their ability to adhere to fibronectin suggesting that collagen XVIII/endostatin may regulate interactions between endothelial cells and underlying basement membrane-associated components, including fibronectin, such that in the absence of collagen XVIII/endostatin, endothelial cells are more adhesive to fibronectin. In the aortic explant assay, characterized by dynamic processes of microvessel elongation and regression, this may result in stabilization of newly formed vessels, reduced regression, and a net increase in microvessel outgrowth in explants from ko mice compared to the wt littermates.

Overexpression of Collagen XVIII Is Associated with Poor Outcome and Elevated Levels of Circulating Serum Endostatin in Non–Small Cell Lung Cancer

PURPOSE

The aim of this study was to determine whether collagen XVIII expression is correlated with circulating serum endostatin and whether this has any prognostic value in patients with non-small cell lung cancer (NSCLC).

EXPERIMENTAL DESIGN

Serum endostatin levels were measured quantitatively by a competitive enzyme immunoassay, and collagen XVIII expression in tumor tissue was investigated with an immunohistochemical method in a series of 94 patients who underwent surgery for NSCLC.

RESULTS

Sixty cases (63.8%) had positive immunohistochemical staining with anticollagen XVIII polyclonal antibodies, including strongly positive staining in 11 (11.7%) cases. The mean (+/- SD) serum endostatin level was 41.6 +/- 34.4 ng/ml in the patient group and 16.3 +/- 10.3 ng/ml in the control group (P < 0.0001). The 11 cases who were strongly collagen XVIII-positive had significantly higher serum endostatin levels than the cases who were negative or weakly positive (P = 0.0297). The 5-year survival rates of negative, weakly positive, and strongly positive patients were 77.8%, 56.9%, and 43.8%, respectively. The cases with strongly positive collagen XVIII expression had a significantly poorer outcome than cases with negative expression (P = 0.0027). A multivariate analysis with Cox proportional hazards model for disease-specific survival revealed that expression of collagen XVIII (strongly positive versus negative; weakly positive versus negative), tumor classification, and regional lymph node classification were independent prognostic factors.

CONCLUSIONS

Our results suggest that expression of collagen XVIII in tumor tissue is strongly associated with a poorer outcome in NSCLC and correlates with elevated levels of circulating serum endostatin.