Activation of small GTPase Rho is required for autocrine motility factor signaling

The hallmark of tumor metastasis is the dissemination of cells from the primary growth site to distant organs. Autocrine motility factor (AMF), a tumor-associated C-X-X-C cytokine, the ligand for a unique 78 kDa seven transmembrane receptor, is a potent simulator of cell motility, a process that is a prerequisite for tumor progression and metastasis. Because little is known about AMF-dependent signaling, we sought to study whether AMF signaling involves family members of the Rho-like GTPases. AMF stimulation of human melanoma cells resulted in stress-fiber formation, concomitant with up-regulation and activation of both RhoA and Rac1 expression with no apparent changes in the expression level or activation state of Cdc42. Treatment of the cells with C3 exoenzyme before AMF stimulation inhibited both the formation of stress-fiber-like structures and the activation of RhoA. In addition, both c-Jun NH(2)-terminal kinase 1 and c-Jun NH(2)-terminal kinase 2 were simultaneously activated by AMF, supporting the notion that they are involved in the signaling pathway of RhoA. We thus conclude that AMF signaling shares a similar pathway to previously established paracrine factors signaling involving cytoskeletal rearrangement and morphological alterations mediated by the small RhoA-like GTPases.

Cyclooxygenase-2 inhibitor treatment enhances photodynamic therapy-mediated tumor response

Photodynamic therapy (PDT) continues to be used in the treatment of solid tumors. Clinical results are promising, but the therapy has not been optimized, and tumor recurrences can occur. Recently, it has been shown that inhibitors of cyclooxygenase (COX)-2 can be effective in combination with conventional chemotherapy and radiation therapy. In the current study, we examined the parameters of PDT-mediated activation of COX-2 expression. We also examined the tumoricidal effectiveness of combining PDT with the selective COX-2 inhibitor NS-398. PDT induced the transcriptional activation of COX-2. Prolonged expression of COX-2 protein was observed in PDT-treated mouse sarcoma and carcinoma cell lines, whereas COX-1 was not inducible by PDT. Prostaglandin (PG) E2 synthesis was also increased in PDT-treated cells, and PGE2 levels were attenuated in cells coincubated with NS-398, indicating that PDT induced the expression of biologically active COX-2. Both porphyrin- and chlorin-based photosensitizers were able to elicit PDT-mediated COX-2 expression. COX-2 was also elevated in radiation-induced fibrosarcoma (RIF) tumors after treatment with PDT. We also observed that systemic administration of NS-398 decreased PDT induction of both PGE2 and vascular endothelial growth factor in treated RIF tumors. Additionally, we demonstrated that NS-398 enhanced PDT responsiveness in RIF tumors without increasing toxicity to normal tissue. These results provide strong evidence that combination procedures involving selective COX-2 inhibitors may improve the therapeutic effectiveness of PDT.

Cumulative influence of elastin peptides and plasminogen on matrix metalloproteinase activation and type I collagen invasion by HT-1080 fibrosarcoma cells

HT-1080 fibrosarcoma cells express at their plasma membrane the elastin-binding protein (EBP). Occupancy of EBP by elastin fragments, tropoelastin or XGVAPG peptides was found to trigger procollagenase-1 (proMMP-1) overproduction by HT-1080 cells at the protein and enzyme levels. RT-PCR analysis indicated that elastin peptides did not modify the MMP-1 mRNA steady state levels, suggesting the involvement of a post-transcriptional mechanism. We previously reported that binding of elastin peptides to EBP induced other matrix metalloproteinases (MMP-2 and MT1-MMP) expression. Since those peptides were here found to also accelerate the secretion of urokinase from HT-1080 cells, culture medium was supplemented with plasminogen together with elastin peptides at aims to induce or potentiate MMPs activation cascades. In such conditions, plasmin activity was generated and exacerbate proMMP-1 and proMMP-2 activation. As a consequence, elastin peptides and plasminogen-treated HT-1080 cells displayed a significant type I collagen matrix invasive capacity.

Stimulation of matrix metalloproteinase-9 expression in human fibrosarcoma cells by synthetic matrix metalloproteinase inhibitors

Enhanced expression and activation of matrix metalloproteinase-2 (MMP-2) and MMP-9 have been associated with tumor progression, invasion, and metastasis. The use of synthetic MMP inhibitors to block the proteolytic activity of these enzymes recently emerged as a potential therapeutic tool to treat cancer. In this study, we report that GI129471, a synthetic broad-spectrum MMP inhibitor, efficiently reduced the in vitro invasiveness of HT1080 cells through type IV collagen, a major component of basement membranes. This reduced invasion was paralleled by a complete inhibition of pro-MMP-2 activation; however, GI129471 strongly increased the amount of secreted pro-MMP-9, which could be subsequently activated through a plasminogen-dependent mechanism. Quantitative RT-PCR and northern blot analysis revealed that GI129471 specifically increased the MMP-9 mRNA steady-state level. Moreover, transient transfection of HT1080 cells with beta-galactosidase reporter vectors containing different lengths of the 5'-flanking region of the MMP-9 gene revealed an upregulation of the transcriptional activity of the corresponding promoter. Well-known modulators of MMP-9 expression such as Il-1beta and TNF-alpha were not involved in this upregulation. These findings emphasize the complexity of the regulation of MMP expression and the requirement for a detailed characterization of the potential adverse side effects associated with the use of broad-spectrum MMPIs.

Plasmid DNA electrotransfer: a new non viral method for gene therapy in oncology

With some defined conditions, electric pulses delivery to tissue in vivo can greatly enhance DNA transfection. We here describe the application in oncology of intratumoral or intramuscular DNA electrotransfer by using muscle as a secretory tissue of transgenic proteins displaying anticancer properties.

Identification of annexin II heterotetramer as a plasmin reductase

Annexin II heterotetramer (AIIt) is a Ca(2+)- and phospholipid-binding protein that consists of two copies of a p36 and p11 subunit. AIIt regulates the production and autoproteolysis of plasmin at the cell surface. In addition to its role as a key cellular protease, plasmin also plays a role in angiogenesis as the precursor for antiangiogenic proteins. Recently we demonstrated that the primary antiangiogenic plasmin fragment, called A(61) (Lys(78)-Lys(468)) was released from cultured cells. In the present study we report for the first time that AIIt possesses an intrinsic plasmin reductase activity. AIIt stimulated the reduction of the plasmin Cys(462)-Cys(541) bond in a time- and concentration-dependent manner, which resulted in the release of A(61) from plasmin. Mutagenesis of p36 C334S and either p11 C61S or p11 C82S inactivated the plasmin reductase activity of the isolated subunits, suggesting that specific cysteinyl residues participated in the plasmin reductase activity of each subunit. Furthermore, we demonstrated that the loss of AIIt from the cell surface of HT1080 cells transduced with a retroviral vector encoding p11 antisense dramatically reduced the cellular production of A(61) from plasminogen. This is the first demonstration that AIIt regulates the cellular production of the antiangiogenic plasminogen fragment, A(61).

Simultaneous inhibition of the receptor kinase activity of vascular endothelial, fibroblast, and platelet-derived growth factors suppresses tumor growth and enhances tumor radiation response

We have investigated the effect of simultaneous inhibition of multiple angiogenic growth factor signaling pathways on tumor growth, tumor blood perfusion, and radiation-induced tumor-growth delay using SU6668, an inhibitor of the receptor-tyrosine kinase activity of vascular endothelial growth factor (VEGF), fibroblast growth factor (FGF), and platelet-derived growth factor (PDGF). The SCK mammary carcinoma, FSaII fibrosarcoma, and CFPAC human pancreatic carcinoma were grown s.c. in the hind leg of A/J mice, C3H mice, and Balb/cAnNCrl-nuBr nude mice, respectively. Daily i.p. injection of 100 mg/kg of SU6668 markedly suppressed the growth of these three tumor types. SU6668 also markedly prolonged the survival time of host mice bearing SCK tumors, which appeared to be caused by a reduction of metastatic tumor growth in the lung. There was little or no change in normal tissue blood perfusion, whereas in SCK tumors the perfusion decreased by 50% at 1 h after a single i.p. injection of SU6668, slightly recovered at 4 h, and completely recovered by 8 h. Interestingly, the tumor blood flow was significantly increased above the baseline level 24 h after SU6668 injection. After extended daily i.p. injections of SU6668, the tumor blood flow in all of the three tumor types studied was markedly decreased compared with control. The observed effects of this drug on tumor blood perfusion may partially explain the effectiveness of the compound in suppressing tumor growth and extending survival of tumor-bearing mice. We also observed that daily SU6668 administration and a single dose of 15 Gy of X-irradiation was significantly more effective than either treatment alone in suppressing tumor growth. Our results suggest that SU6668 increased the radiosensitivity of tumor blood vessels. We conclude that SU6668 is a potent therapeutic agent potentially useful to suppress tumor growth and enhance the response of tumors to radiotherapy.

Inhibition of activator protein-1 binding activity and phosphatidylinositol 3-kinase pathway by nobiletin, a polymethoxy flavonoid, results in augmentation of tissue inhibitor of metalloproteinases-1 production and suppression of production of matrix metalloproteinases-1 and -9 in human fibrosarcoma HT-1080 cells

Medicinal plants contain pharmacological substances including flavonoids, and their extracts have been therapeutically administered for cancer therapy in vitro and in vivo. We investigated the efficacy of a polymethoxy flavonoid, nobiletin, from Citrus depressa on tumor invasion in vitro. Nobiletin inhibited the tumor-invasive activity of human fibrosarcoma HT-1080 cells in the Matrigel model, whereas a similar inhibition was observed upon exogenously adding tissue inhibitors of metalloproteinases (TIMPs)-1 and -2. The gene expression and production of pro-matrix metalloproteinase 9 (proMMP-9)/progelatinase B and proMMP-1/interstitial procollagenase were specifically suppressed by nobiletin in 12-O-tetradecanoylphorbol 13-acetate-stimulated HT-1080 cells. In contrast, the gene expression and production of TIMP-1, but not TIMP-2, were enhanced by nobiletin. We also demonstrated that nobiletin suppressed the 12-O-tetradecanoylphorbol 13-acetate-induced binding activity of activator protein-1. Furthermore, a phosphatidylinositol 3-kinase inhibitor, LY-294002, was found to mimic the different actions of nobiletin on the production of proMMP-9 and TIMP-1. These results suggest that nobiletin inhibits tumor cell invasive activity not only by suppressing the expression of MMPs but also augmenting TIMP-1 production in tumor cells, and that the nobiletin-mediated inhibition of activator protein-1 binding activity is at least partly involved in the suppression of MMP expression. Furthermore, we suggest a possible mechanism by which nobiletin may interfere in the phosphatidylinositol 3-kinase pathway, which divergently regulates the production of MMP and TIMP-1.

Cloning and expression of uridine/cytidine kinase cDNA from human fibrosarcoma cells

Uridine/cytidine kinase which converts uridine and cytidine to their corresponding monophosphates is a rate-limiting enzyme involved in the salvage pathway of pyrimidine synthesis. We isolated cDNA encoding the enzyme from human fibrosarcoma cells, then determined its nucleotide sequence by the 5'-RACE method followed by confirmation employing the human genome DNA library. The isolated uridine/cytidine kinase cDNA (UCK cDNA) consisted of 786 nucleotides encoding 261 amino acids and was found to have approximately 70% homology with mouse UCK cDNA. Northern blot analysis of human leukemia RNAs with labeled UCK gene showed a single band at 1.6 kb to be UCK mRNA, and southern blot analysis of the UCK cDNA after digestion with BamHI, SacI and XbaI enzymes showed four band signals, suggesting the UCK gene to have at least 4 exons. A truncated form of UCK cDNA was expressed as the His-tag conjugated protein in Escherichia coli. The expressed and purified protein specifically converted uridine and cytidine to their corresponding monophosphates and also phosphorylated antitumor nucleosides such as 5-fluorouridine, cyclopentenyl-cytosine and 3'-C-ethynylcytidine. The present results suggest that our cloned human UCK cDNA encodes the correct amino acid sequence for UCK protein, showing high intracellular phosphorylation activity forward natural and synthetic pyrimidine nucleosides.

Deletion mutants of human deoxycytidine kinase mRNA in cells resistant to antitumor cytosine nucleosides

We studied mutational events in deoxycytidine (dCyd) kinase mRNA expression, focusing on aberrant dCyd kinase mRNA, which has been frequently observed in established cell lines resistant to antitumor dCyd nucleoside analogues such as 1-beta-D-arabinofuranosyl cytosine (Ara-C), gemcitabine (dFdC) and 2'-C-cyano-2'-deoxy-1-beta-D-arabinofuranosylcytosine (CNDAC). We describe here the expression of aberrant dCyd kinase mRNAs identified as splicing mutants. These mutants included deletions of the fifth exon in CNDAC-resistant cells (originating from HT-1080 cells), of the third exon in Ara-C-resistant cells (originating from SK-MEL-28 cells) and of the fourth exon in 2'-deoxy-2'-methylidenecytidine (DMDC)-resistant cells (originating from SK-MEL-28 cells). Various nucleoside-resistant cells originating from the same parental HT-1080 cells were established. The resulting cells expressed the same mRNA with deletion of the fifth exon, and the location of splicing was independent of the type of nucleosides used for the establishment of resistant cells. The deletion of the fifth exon in dCyd kinase seems to be a target for acquisition of resistance to antitumor cytosine nucleosides. However, distinct mutations in the dCyd kinase gene seem to be associated with acquisition of resistance to different antitumor cytosine nucleosides.

Insulin like growth factor-1 selectively regulates the expression of matrix metalloproteinase-2 in malignant H-ras transformed cells

The present study demonstrates alterations in the regulation of matrix metalloproteinase-2 (MMP-2) expression in response to insulin like growth factor-1 (IGF-1) in a H-ras transformed cell line, C3, which is capable of metastasis formation. These changes in MMP-2 expression in response to IGF-1 treatment did not occur in either non-transformed parental 10 T 1/2 cells or in H-ras transformed cells (NR3 cells) which are capable of benign tumour formation. IGF-1 treatment of C3 cells resulted in increased expression of MMP-2 gelatinolytic activity and increased expression of MMP-2 mRNA levels. The IGF-1 mediated alterations in MMP-2 mRNA levels were dependent upon de novo protein synthesis and independent of transcriptional events, but dependent upon post-transcriptional regulatory events. Most notably, IGF-1 can regulate MMP-2 mRNA expression in C3 cells through a mechanism involving MMP-2 message stabilization. This study demonstrates aspects of the temporal regulatory mechanisms of MMP-2 expression in response to insulin-like growth factor-1 in a H-ras transformed fibrosarcoma cell line capable of metastasis formation and thereby, provides further insight into the altered growth regulatory program associated with H-ras mediated cellular transformation and malignant progression.

Effects of overexpression of gamma-Glutamyl hydrolase on methotrexate metabolism and resistance

Intracellular metabolism of methotrexate (MTX) to MTX-polyglutamates (MTXPG) is one determinant of cytotoxicity. Steady-state accumulation of MTXPG seems to depend on the activity of two enzymes: folylpolyglutamate synthetase (FPGS), which adds glutamate residues, and gamma-glutamyl hydrolase (GGH), which removes them. Overexpression of GGH would be expected to decrease intracellular MTXPG, thereby increasing efflux of MTX and decreasing cytotoxicity. Increased expression of GGH has been shown to be associated with resistance to MTX in human sarcoma cell lines and a rat hepatoma cell line. To clarify the specific role of GGH in determining MTX sensitivity, we investigated the phenotype produced by forced GGH overexpression in two cell types. Furthermore, because MTX and folic acid share metabolic pathways, we measured the effects of GGH overexpression on folic acid metabolism. The full-length cDNA for GGH, subcloned into a constitutive expression vector, was transfected into a human fibrosarcoma (HT-1080) and a human breast carcinoma (MCF-7) cell line. Compared with the clones containing an empty vector, the GGH-overexpressing cells express 15- to 30-fold more GGH mRNA, more GGH protein, and 15- to 90-fold more GGH enzyme activity. GGH overexpression altered MTX accumulation and metabolism to long-chain polyglutamates. In contrast to expectations, however, GGH overexpression did not confer resistance to short MTX exposures in either cell line. Changes in MTX metabolism were found to be balanced by alterations in accumulation and metabolism of folic acid. The ratio of MTX:folate accumulation may be a better predictor of MTX cytotoxicity than the accumulation of either alone. We conclude that, at least for these two cell lines, GGH overexpression alone is insufficient to produce clinical resistance to MTX.

Cathepsin B acts as a dominant execution protease in tumor cell apoptosis induced by tumor necrosis factor

Death receptors can trigger cell demise dependent or independent of caspases. In WEHI-S fibrosarcoma cells, tumor necrosis factor (TNF) induced an increase in cytosolic cathepsin B activity followed by death with apoptotic features. Surprisingly, this process was enhanced by low, but effectively inhibiting, concentrations of pan-caspase inhibitors. Contrary to caspase inhibitors, a panel of pharmacological cathepsin B inhibitors, the endogenous cathepsin inhibitor cystatin A as well as antisense-mediated depletion of cathepsin B rescued WEHI-S cells from apoptosis triggered by TNF or TNF-related apoptosis-inducing ligand. Thus, cathepsin B can take over the role of the dominant execution protease in death receptor-induced apoptosis. The conservation of this alternative execution pathway was further examined in other tumor cell lines. Here, cathepsin B acted as an essential downstream mediator of TNF-triggered and caspase-initiated apoptosis cascade, whereas apoptosis of primary cells was only minimally dependent on cathepsin B. These data imply that cathepsin B, which is commonly overexpressed in human primary tumors, may have two opposing roles in malignancy, reducing it by its proapoptotic features and enhancing it by its known facilitation of invasion.

Regulation of p53 expression by the RAS-MAP kinase pathway

Activation of MAP kinase leads to the activation of p53-dependent pathways, and vice-versa. Although the amount of p53 protein increases in response to MAP kinase-dependent signaling, the basis of this increase is not yet fully understood. We have isolated the mutant cell line AP14, defective in p53 expression, from human HT1080 fibrosarcoma cells, which have an activated ras allele. The expression of p53 mRNA and protein is approximately 10-fold lower in AP14 cells than in the parental cells. The high constitutive phosphorylation and activities of the MAP kinases ERK1 and ERK2 in HT1080 cells are greatly reduced in AP14 cells, although the levels of these proteins are unchanged, suggesting that the defect in the mutant cells affects the steady-state phosphorylation of ERK1 and ERK2. Overexpression of ERK2 in AP14 cells restored both MAP kinase activity and p53 expression, and incubation of the mutant cells with the phosphatase inhibitor orthovanadate resulted in strong coordinate elevation of MAP kinase activity and p53 expression. The levels of expression of the p53-regulated gene p21 parallel those of p53 throughout, showing that basal p21 expression depends on p53. The levels of p53 mRNA increased by 5-8-fold when activated ras was introduced into wild-type cells, and the levels of the p53 and p21 proteins decreased substantially in wild-type cells treated with the MEK inhibitor U0216. We conclude that MAP kinase-dependent pathways help to regulate p53 levels by regulating the expression of p53 mRNA.

Synthesis and biological evaluation of boronated nucleosides for boron neutron capture therapy (BNCT) of cancer

Several N-3 substituted carboranyl Thd analogs were synthesized. These agents as well as some non-boronated nucleosides were evaluated in phosphoryl transfer assays with recombinant human TK1 and TK2. For some carboranyl thymidine analogs, TK1 phosphorylation rates approached 38% that of thymidine. Their in vitro cytotoxicty appeared to correlate with the TK1 levels in the tested cells. In some cases increased uptake in tumor cell nuclei compared with the surrounding cytoplasm was detected in vitro.

Hypoxia activates a platelet-derived growth factor receptor/phosphatidylinositol 3-kinase/Akt pathway that results in glycogen synthase kinase-3 inactivation

Hypoxia initiates numerous intracellular signaling pathways important in regulating cell proliferation, differentiation, and death. In this study, we investigated the pathway that hypoxia uses to activate Akt and inactivate glycogen synthase kinase-3 (GSK-3), two proteins the functions of which are important in cell survival and energy metabolism. Severe hypoxia (0.01% oxygen) initiated a signaling cascade by inducing the tyrosine phosphorylation of the platelet-derived growth factor (PDGF) receptor within 1 h of treatment and increasing receptor association with the p85 subunit of phosphatidylinositol 3-kinase (PI 3-K). Hypoxia-induced signaling also resulted in PI 3-K-dependent phosphorylation of Akt on Ser-473, a modification of Akt that is important for its activation. This activation of Akt by hypoxia was substantially diminished in cells that possessed mutations in their PDGF receptor-PI 3-K interaction domain. In addition, Akt activation by hypoxia was resistant to treatment with the growth factor receptor poison suramin but was sensitive to treatment with the PI 3-K inhibitor wortmannin. Activation of Akt by hypoxia resulted in the phosphorylation of GSK-3alpha and GSK-3beta at Ser-9 and Ser-21, two well-documented Akt phosphorylation sites, respectively, that are inactivating modifications of each GSK-3 isoform. In support of the phosphorylation data, GSK-3 activity was significantly reduced under hypoxia. In conclusion, we propose that hypoxia activates a growth factor receptor/PI 3-K/Akt cascade that leads to GSK-3 inactivation, a pathway that can impact cell survival, proliferation, and metabolism.

Radiation therapy to a primary tumor accelerates metastatic growth in mice

The surgical removal of a primary tumor can result in the rapid growth of metastases. The production of angiogenesis inhibitors by the primary tumor is one mechanism for the inhibition of metastatic tumor growth. The effect of curative radiotherapy to a primary tumor known to make an inhibitor of angiogenesis and the effects on distant metastases has not been studied. We here show that the eradication of a primary Lewis lung carcinoma (LLC-LM), which is known to generate angiostatin, is followed by the rapid growth of metastases that kill the animal within 18 days after the completion of radiation therapy. The right thighs of C57BL/6 mice (n = 25) were injected s.c. with 1 x 10(6) LLC-LM cells. Animals were randomized to one of five groups: no irradiation, 40 Gy in one fraction, 30 Gy in one fraction, 40 Gy in two 20 Gy fractions, or 50 Gy in five 10 Gy fractions. Tumors were clinically eradicated in each treatment group. All of the surviving animals became dyspneic and were killed within 14-18 days after the completion of radiation therapy. Examination of their lungs revealed >46 (range, 46-62) surface metastases in the treated animals compared with 5 (range, 2-8) in the untreated animals. The lung weights had increased from 0.2 g (range, 0.19-0.22 g) in the controls to 0.58 g (range 0.44-0.84) in the experimental animals. The most effective dose regimen was 10 Gy per fraction for five fractions, and serial experiments were conducted with this fractionation scheme. Complete response of the primary tumor was seen in 25 of 35 (71%) mice. The average weight of the lungs in the nonirradiated animals was 0.22 g (range, 0.19-0.24 g) and in the irradiated animals was 0.66 g (range, 0.61-0.70 g). The average number of surface metastases increased from five per lung (range, 2-13) in the control animals to 53 per lung (range, 46-62) in the irradiated animals. Both differences were statistically significant with P < 0.001. If the nontumor-bearing leg was irradiated or the animals were sham-irradiated, no difference in the number of surface metastases or lung weights was observed between the control group and the treated group. Urinary levels of matrix metalloproteinase 2, the enzyme responsible for angiostatin processing in this tumor model, were measured and correlated with the viability and size of the primary tumor. Administration of recombinant angiostatin prevented the growth of the metastases after the treatment of the primary tumor. In this model, the use of radiation to eradicate a primary LLC-LM tumor results in the growth of previously dormant lung metastases and suggests that combining angiogenesis inhibitors with radiation therapy may control distant metastases.

Regulation of MMP-1 and MMP-2 production through CD147/extracellular matrix metalloproteinase inducer interactions

Extracellular matrix metalloproteinase inducer (EMMPRIN; CD147) is a heavily glycosylated protein containing two immunoglobulin superfamily domains. It is enriched on the surface of tumor cells and stimulates the production of matrix metalloproteinases (MMPs) by adjacent stromal cells. Here we use CD147 transfectants and immobilized recombinant CD147-Fc fusion protein to show that CD147/FMMPRIN engages in a homophilic interaction, predominantly through the first immunoglobulin domain. Anti-CD147 antibody 8G6 and recombinant CD147-Fc fusion protein markedly inhibited not only homophilic interaction, but also the production of secreted MMP-2 by breast cancer cell line MDA-435 and the MMP-2-dependent invasion of MDA-435 cells through reconstituted basement-membrane Matrigel. Purified native CD147 induced the production of secreted MMP not only by dermal fibroblasts (MMP-1) but also by MDA-435 cells themselves (MMP-2), suggesting homophilic CD147-binding may occur in the context of both heterotypic and homotypic cell-cell interactions. Purified deglycosylated CD147 failed to induce MMP-1 or MMP-2, but instead antagonized the MMP-1-inducing activity of purified native CD147. Our results suggest that homophilic CD147 interactions may play a key role in MMP-2 production and tumor cell invasion, and that perturbation of this molecule may have potential therapeutic uses in the prevention of MMP-2 and MMP-1-dependent cancer metastasis.

MT1-MMP initiates activation of pro-MMP-2 and integrin alphavbeta3 promotes maturation of MMP-2 in breast carcinoma cells

We evaluated cellular mechanisms involved in the activation pathway of matrix prometalloproteinase-2 (pro-MMP-2), an enzyme implicated in the malignant progression of many tumor types. Membrane type-1 matrix metalloproteinase (MT1-MMP) cleaves the N-terminal prodomain of pro-MMP-2 thus generating the activation intermediate that then matures into the fully active enzyme of MMP-2. Our results provide evidence on how a collaboration between MT1-MMP and integrin alphavbeta3 promotes more efficient activation and specific, transient docking of the activation intermediate and, further, the mature, active enzyme of MMP-2 at discrete regions of cells. We show that coexpression of MT1-MMP and integrin alphavbeta3 in MCF7 breast carcinoma cells specifically enhances in trans autocatalytic maturation of MMP-2. The association of MMP-2's C-terminal hemopexin-like domain with those molecules of integrin alphavbeta3 which are proximal to MT1-MMP facilitates MMP-2 maturation. Vitronectin, a specific ligand of integrin alphavbeta3, competitively blocked the integrin-dependent maturation of MMP-2. Immunofluorescence and immunoprecipitation studies supported clustering of MT1-MMP and integrin alphavbeta3 at discrete regions of the cell surface. Evidently, the identified mechanisms appear to be instrumental to clustering active MMP-2 directly at the invadopodia and invasive front of alphavbeta3-expressing cells or in their close vicinity, thereby accelerating tumor cell locomotion.

Matrix metalloproteinase 2 in tumor cell-induced platelet aggregation: regulation by nitric oxide

A correlation exists between the ability of tumor cells to aggregate platelets and their tendency to metastasize. Tumor cell-induced platelet aggregation (TCIPA) facilitates the embolization of the vasculature with tumor cells and the formation of metastatic foci. It is well documented that matrix metalloproteinases (MMPs) play an integral part in tumor spread and the metastatic cascade. Therefore, we have examined the role of MMPs during TCIPA and its regulation by nitric oxide (NO) in vitro. Human HT-1080 fibrosarcoma and A549 lung epithelial cancer cells induced TCIPA in a concentration-dependent manner that was monitored by aggregometry. This aggregation resulted in the release of MMIP-2 from platelets and cancer cells, as measured by zymography. HT-1080 cells released significantly more MMP-2 than A549 cells and were more efficacious in inducing TCIPA. Inhibition of MMP-2 with phenanthroline (1-1000 microM), a synthetic inhibitor of MMPs, and by neutralizing anti-MMIP-2 antibody (10 microg/ml) reduced TCIPA induced by HT-1080 cells. TCIPA was abolished by simultaneous inhibition of platelet function with acetylsalicylic acid (100 microM; thromboxane pathway inhibitor), apyrase (250 microg/ml; ADP pathway inhibitor), and phenanthroline. NO donors such as S-nitroso-n-acetylpenicillamine and S-nitrosoglutathione (both at 0.01-100 microM) inhibited TCIPA and MMP-2 release from platelets and tumor cells. The inhibitory actions of S-nitroso-n-acetylpenicillamine and S-nitrosoglutathione were reversed by 1H-[1,2,4]oxadiazole[4,3]quinoxalin-1-one (0.01-30 microM), a selective inhibitor of the soluble guanylyl cyclase. We conclude that (a) human fibrosarcoma cells aggregate platelets via mechanism(s) that are mediated, in part, by MMP-2; (b) NO inhibits TCIPA, in part, by attenuating the release of MMP-2; and (c) these effects of NO are cGMP-dependent.

Type IV collagen induces matrix metalloproteinase 2 activation in HT1080 fibrosarcoma cells

Matrix metalloproteinase 2 (MMP-2) activation has been described as a "master switch" which triggers tumor spread and metastatic progression. We show here that type IV collagen, a major component of basement membranes, promotes MMP-2 activation by HT1080 cells. When plated on plastic, HT1080 cells constitutively processed the 66-kDa pro-MMP-2 into a 62-kDa intermediate activated form, most probably through a membrane type (MT) 1 MMP-dependent mechanism. In the presence of type IV collagen, part of this intermediate form was further processed to fully activated 59-kDa MMP-2. This activation was prevented by tissue inhibitor of MMP (TIMP)-2 and a broad-spectrum hydroxamic acid-based synthetic MMP inhibitor (GI129471). Type IV collagen-mediated pro-MMP-2 activation did not involve either a transcriptional modulation of MMP-2, MT1-MMP, or TIMP-2 expression nor any alteration of MT1-MMP protein synthesis or processing. An inverse relationship between MMP-2 activation and the concentration of secreted TIMP-2 was observed. This is consistent with our previous report that TIMP-2 degradation is probably linked to the MT1-MMP-dependent MMP-2 activation mechanism. Because invasive tumor cells must breach basement membranes at different steps of the metastatic dissemination, the ability of HT1080 cells to activate pro-MMP-2 in the presence of type IV collagen might represent a key regulatory mechanism for the acquisition of an invasive potential.

Phosphoglycerate kinase acts in tumour angiogenesis as a disulphide reductase

Disulphide bonds in secreted proteins are considered to be inert because of the oxidizing nature of the extracellular milieu. An exception to this rule is a reductase secreted by tumour cells that reduces disulphide bonds in the serine proteinase plasmin. Reduction of plasmin initiates proteolytic cleavage in the kringle 5 domain and release of the tumour blood vessel inhibitor angiostatin. New blood vessel formation or angiogenesis is critical for tumour expansion and metastasis. Here we show that the plasmin reductase isolated from conditioned medium of fibrosarcoma cells is the glycolytic enzyme phosphoglycerate kinase. Recombinant phosphoglycerate kinase had the same specific activity as the fibrosarcoma-derived protein. Plasma of mice bearing fibrosarcoma tumours contained several-fold more phosphoglycerate kinase, as compared with mice without tumours. Administration of phosphoglycerate kinase to tumour-bearing mice caused an increase in plasma levels of angiostatin, and a decrease in tumour vascularity and rate of tumour growth. Our findings indicate that phosphoglycerate kinase not only functions in glycolysis but is secreted by tumour cells and participates in the angiogenic process as a disulphide reductase.

Tyrosinase mutants are capable of prodrug activation in transfected nonmelanotic cells

Tyrosinase has been suggested as a prodrug-converting enzyme for the treatment of melanoma. We hypothesized that tyrosinase expression in transfected nonmelanotic cells can be used in a gene therapy paradigm of prodrug activation. To verify our hypothesis, we used the following tyrosinase variants: (a) a full-length human tyrosinase clone (T); (b) a mutant lacking the COOH-terminal cytoplasmic domain (TdeltaC); (c) a mutant lacking the COOH-terminal transmembrane and cytoplasmic domains (TdeltaTC); and (d) a fusion with the eight COOH-terminal amino acids of lysosome-associated membrane protein-1 (TL). Expression of mutant and wild-type tyrosinases was induced by transfection in nontumorigenic human cells of epithelial origin (293HEK, MCF-10A adenoma, and NHDF-Ad human dermal fibroblasts) as well as in tumor cells (9L gliosarcoma, MCF7 adenocarcinoma, and HT-1080 fibrosarcoma). When compared with the wild-type tyrosinase transfectants, truncated mutant expression resulted in higher mRNA levels that paralleled higher enzyme activity of the truncated mutants. Two model tyrosinase prodrugs, hydroxyphenyl-propanol (HPP) and N-acetyl-4-S-cysteaminylphenol (NAcSCAP) inhibited proliferation and caused cell death of transfected cells in a dose-dependent manner. Effects of prodrug treatment were compared for tumorigenic cells and their nontumorigenic counterparts. Two truncated mutants (TdeltaC and TdeltaTC) showed low endogenous cytotoxicity and efficiently suppressed proliferation and induced cytotoxicity in transfected tumor cells in the presence of NAcSCAP. Overall, these results indicate that the developed tyrosinase mutants hold promise as prodrug activation systems for tumoral gene therapy.

Tumor cell-selective cytotoxicity of matrix metalloproteinase-activated anthrax toxin

Matrix metalloproteinases (MMPs) are overexpressed in a variety of tumor tissues and cell lines, and their expression is highly correlated to tumor invasion and metastasis. To exploit these characteristics in the design of tumor cell-selective cytotoxins, we constructed two mutated anthrax toxin protective antigen (PA) proteins in which the furin protease cleavage site is replaced by sequences selectively cleaved by MMPs. These MMP-targeted PA proteins were activated rapidly and selectively on the surface of MMP-overexpressing tumor cells. The activated PA proteins caused internalization of a recombinant cytotoxin, FP59, consisting of anthrax toxin lethal factor residues 1-254 fused to the ADP-ribosylation domain of Pseudomonas exotoxin A. The toxicity of the mutated PA proteins for MMP-overexpressing cells was blocked by hydroxamate inhibitors of MMPs, including BB94, and by a tissue inhibitor of matrix metalloproteinases (TIMP-2). The mutated PA proteins killed MMP-overexpressing tumor cells while sparing nontumorigenic normal cells when these were grown together in a coculture model, indicating that PA activation occurred on the tumor cell surface and not in the supernatant. This method of achieving cell-type specificity is conceptually distinct from, and potentially synergistic with, the more common strategy of retargeting a protein toxin by fusion to a growth factor, cytokine, or antibody.

Prokaryotic expression, purification, and reconstitution of biological activities (Antiprotease, antitumor, and heparin-binding) for tissue factor pathway inhibitor-2

We report the expression of tissue factor pathway inhibitor-2 (TFPI-2) (also known as PP-5, placental protein-5; MSPI, matrix-associated serine protease inhibitor) in E. coli as a 25-kDa nonglycosylated protein with a glycine substituted for aspartic acid at the amino terminus. High-level expression of TFPI-2 was obtained with pRE1 expression vector under the transcriptional and translational controls of the lambdaP(L) promoter and lambdacII ribosome-binding site, respectively, with ATG initiation codon. TFPI-2 was produced as inclusion bodies and accounted for 25-30% of the total E. coli proteins. The inclusion bodies containing TFPI-2 were solubilized with urea, sulfitolyzed, purified, and refolded through a disulfide interchange reaction. The refolded E. coli TFPI-2 inhibited plasmin with an inhibition constant (K(i)) of 5 nM that is similar with the TFPI-2 expressed in a mammalian system. The refolded E. coli TFPI-2 bound heparin and also inhibited plasmin, regardless of whether the enzyme was in the fluid phase or was bound to the membranes of HT-1080 fibrosarcoma cells. In addition, refolded E. coli TFPI-2 inhibited radiolabeled matrix degradation and Matrigel matrix invasion by HT-1080 fibrosarcoma cells and B16-F10 melanoma cells. Together, our results suggest that glycosylation is not essential for antiprotease, antitumor, and matrix-binding activities of TFPI-2. Based on these collective data, we conclude that a biologically active nonglycosylated TFPI-2 can be produced in E. coli and that the protein can be produced in high-enough quantities to conduct in vivo studies for determination of the role of this inhibitor in tumor invasion and metastasis.