Reduced metastasis of transgenic mammary cancer in urokinase-deficient mice

The urokinase receptor promotes cancer metastasis independently of urokinase-type plasminogen activator in mice

The urokinase receptor (uPAR) promotes metastasis of human malignancies; however, its mechanism of action remains incompletely understood. Established models focus on the ability of uPAR to bind urokinase-type plasminogen activator (uPA) and promote protease activation in the tumor cell microenvironment; however, uPAR also regulates cell signaling and migration by both uPA-dependent and -independent mechanisms in vitro. The significance of uPAR as a cell-signaling receptor in vivo remains unclear. In this study, we expressed either human or mouse uPAR in human embryonic kidney (HEK-293) cells. We selected HEK-293 cells because, unlike most cancer cells, they do not express uPA or uPAR endogenously. Both mouse and human uPAR increased cell adhesion and migration on vitronectin. Rac1 was activated and responsible for the increase in cell migration. HEK-293 cells that did not express uPAR formed palpable tumors in severe combined immunodeficient mice; however, metastases were exceedingly rare. The xenografts contained abundant mouse uPA, produced by infiltrating mouse cells, but no human uPA. Mouse uPA bound only to mouse uPAR and not human uPAR and, thus, could not interact with human uPAR-expressing HEK-293 cells in xenografts. Nevertheless, both mouse and human uPAR significantly increased HEK-293 cell metastasis into the lungs. The activity of human uPAR suggests that uPAR may promote cancer metastasis independent of uPA. Candidate mechanisms include its effects on adhesion, migration, and Rac1 activation.

External modulation of HT-1080 human fibrosarcoma cells improves urokinase production

Urokinase was produced in a hollow fiber reactor using HT-1080 human fibrosarcoma cells. External modulation comprised replenishing of the medium in the extracapillary space, reducing the serum concentration in the extracapillary space from 10% to 2% and increasing flow rate of the circulating medium in the intracapillary space from 20 to 80 mL/min, each according to a specific protocol. More than sixfold increase was observed in the cumulative urokinase production for two and three medium replenishing modulations of the extracapillary space. After 15 days of continuous operation, the highest cumulative urokinase obtained was 1.63 x 10(6) PU/mL. SDS-PAGE and zymogram study established that the urokinase obtained was in the high molecular weight range of 54 kDa. The effect of external modulation on cumulative urokinase production was visualized as trajectories with respect to the ratio of lactic acid production rate (LPR) to the glucose uptake rate (GUR). The collective external modulation data showed two separate physiological regions in the cumulative urokinase vs. LPR/GUR plane. The HT-1080 cells exhibited two distinct morphologies in these regions that may be related to acidosis and metastasis. These regions also correspond to low and high urokinase productivity.

Microenvironmental regulation of metastasis

Metastasis is a multistage process that requires cancer cells to escape from the primary tumour, survive in the circulation, seed at distant sites and grow. Each of these processes involves rate-limiting steps that are influenced by non-malignant cells of the tumour microenvironment. Many of these cells are derived from the bone marrow, particularly the myeloid lineage, and are recruited by cancer cells to enhance their survival, growth, invasion and dissemination. This Review describes experimental data demonstrating the role of the microenvironment in metastasis, identifies areas for future research and suggests possible new therapeutic avenues.

Plasminogen activator inhibitor 1 protects fibrosarcoma cells from etoposide-induced apoptosis through activation of the PI3K/Akt cell survival pathway

High levels of plasminogen activator inhibitor (PAI-1) in tumors are associated with poor prognosis in several cancer types, and the reason for this association is not fully understood. Plasminogen activator inhibitor 1 has been suggested to contribute to tumor growth by protecting cancer cells from apoptosis, and we have previously shown that wild type murine fibrosarcoma cells are significantly more resistant to apoptosis induced by chemotherapy than PAI-1-deficient fibrosarcoma cells. Here, we further investigated the molecular mechanisms underlying the antiapoptotic function of PAI-1 focusing on the phosphatidylinositol 3-phosphate kinase (PI3K)/Akt cell survival pathway. We demonstrate that the activation level of the Akt cell survival pathway is reduced in PAI-1-deficient cells. Inhibition of either PI3K or Akt by synthetic inhibitors sensitized the wild type but not the PAI-1-deficient cells to etoposide-induced cell death. More importantly, reintroduction of PAI-1 expression in PAI-1-deficient cells induced an increase in Akt activity and protection against etoposide-induced apoptosis. Concordantly, silencing of PAI-1 by RNA interference in wild type fibrosarcoma cells decreased the level of active Akt, and this was accompanied by a sensitization of the cells to etoposide-induced cell death. Altogether, our data suggest that PAI-1 influences sensitivity to etoposide-induced apoptosis through the PI3K/Akt cell survival pathway by acting upstream of PI3K and Akt. This points to PAI-1 as a possible therapeutic target in cancer diseases where PAI-1 inhibits chemotherapy-induced apoptosis.

Metastasis is strongly reduced by the matrix metalloproteinase inhibitor Galardin in the MMTV-PymT transgenic breast cancer model

Matrix metalloproteinases (MMP) have several roles that influence cancer progression and dissemination. However, low molecular weight metalloproteinase inhibitors (MPI) have not yet been tested in transgenic/spontaneous metastasis models. We have tested Galardin/GM6001, a potent MPI that reacts with most MMPs, in the MMTV-PymT transgenic breast cancer model. We followed a cohort of 81 MMTV-PymT transgenic mice that received Galardin, placebo, or no treatment. Galardin treatment was started at age 6 weeks with 100 mg/kg/d, and all mice were killed at age 13.5 weeks. Galardin treatment significantly reduced primary tumor growth. Final tumor burden in Galardin-treated mice was 1.69 cm3 compared with 3.29 cm3 in placebo-treated mice (t test, P = 0.0014). We quantified the total lung metastasis volume in the same cohort of mice. The median metastasis volume was 0.003 mm(3) in Galardin-treated mice compared with 0.56 mm(3) in placebo-treated mice (t test, P < 0.0001). Thus, metastasis burden was reduced more than 100-fold, whereas primary tumor size was reduced only 2-fold. We also found that primary tumors from Galardin-treated mice exhibited a lower histopathologic tumor grade, increased collagen deposition, and increased MMP-2 activity. MMPs are known to have tumor-promoting and tumor-inhibitory effects, and several clinical trials of broad-spectrum MPIs have failed to show promising effects. The very potent antimetastatic effect of Galardin in the MMTV-PymT model does, however, show that it may be possible to find broad-spectrum MPIs with favorable inhibition profiles, or perhaps combinations of monospecific MPIs, for future clinical application.

Effect of ablation or inhibition of stromal matrix metalloproteinase-9 on lung metastasis in a breast cancer model is dependent on genetic background

Matrix metalloproteinases (MMP) are a family of enzymes with a myriad of functions. Lately, we have come to realize that broad-spectrum inhibition of these enzymes, as was tried unsuccessfully in multiple phase III trials in cancer patients, is likely unwise given the protumorigenic and antitumorigenic functions of various family members. Here, we used the multistage mammary tumor model MMTV-PyVT to investigate roles for either MMP7 or MMP9 in tumor progression. We found no effect of genetic ablation of MMP7 or MMP9 on the multifocal tumors that developed in the mammary glands. Lack of MMP7 also had no effect on the development of lung metastases, suggesting that MMP7 is irrelevant in this model. In contrast, MMP9 deficiency was associated with an 80% decrease in lung tumor burden. The predominant cellular source of MMP9 was myeloid cells, with neutrophils being the largest contributor in tumor-bearing lungs. Experimental metastasis assays corroborated the role of host-derived MMP9 in lung metastasis and also facilitated determination of a time frame most relevant for the MMP9-mediated effect. The lung tumors from MMP9-deficient mice showed decreased angiogenesis. Surprisingly, the antimetastatic outcome of MMP9 ablation seemed to be dependent on strain. Only mice that had genetic background derived from C57BL/6 showed reduced metastasis, whereas mice fully of the FVB/N background showed no significant effect. These strain-specific responses were also observed in a study using a highly selective pharmacologic inhibitor of MMP9 and thus suggest that responses to MMP inhibition are controlled by genetic differences.

Signal transduction in transgenic mouse models of human breast cancer--implications for human breast cancer

The advent of genetically engineered mouse models (GEMs) of human breast cancer, have provided important insight into molecular basis or human breast cancer. This review will focus on two of the most extensively studied mouse models for human breast cancer involving mammary gland specific expression of the polyoma middle T (PyV MT) antigen and of the ErbB2. In addition, this review will discuss past and recent advances in understanding relative contribution of the signaling pathways in tumor induction and metastasis by these potent mammary oncogenes.

Pharmacological inhibition of DNA methylation induces proinvasive and prometastatic genes in vitro and in vivo

The mechanism of action of DNA methylation inhibitor 5-aza-2'-deoxycytidine (5-aza-CdR), a potential anticancer agent is believed to be activated by the demethylation of tumor suppressor genes. We tested here the hypothesis that demethylating agents also demethylate and activate genes involved in invasion and metastasis and therefore might increase the risk of developing tumor metastasis. The effect of 5-aza-CdR on noninvasive human breast cancer cells MCF-7 and ZR-75-1 was evaluated by cell proliferation, invasion, and migration assay. The ability of 5-aza-CdR to activate a panel of silenced prometastatic and tumor suppressor genes was evaluated using reverse transcription-polymerase chain reaction and bisulfite DNA sequence analysis in vitro and for change in tumor growth and gene expression in vivo. Treatment of MCF-7 and ZR-75-1 with 5-aza-CdR diminished cell proliferation, induced tumor suppressor RASSF1A, and altered cell cycle kinetics' G(2)/M-phase cell cycle arrest. While these effects of 5-aza-CdR slowed the growth of tumors in nude mice, it also induced a battery of prometastatic genes, namely, uPA, CXCR4, HEPARANASE, SYNUCLEIN gamma, and transforming growth factor-beta (TGF-beta), by demethylation of their promoters. These results draw attention to the critical role of demethylation as a potential mechanism that can promote the development and progression of tumor metastasis after demethylation therapy as an anticancer treatment.

Inhibition of cell invasion and MMP production by a nutrient mixture in malignant liposarcoma cell line SW-872

Liposarcoma, a malignancy of fat cells, is the most common soft tissue sarcoma. Though rare, poorly differentiated liposarcomas commonly metastasize to lungs and liver, leading to poor prognosis. Prevention of Extracellular matrix (ECM) degradation by inhibition of matrix metalloproteinases (MMPs) activity has been shown to be a promising therapeutic approach to inhibition of cancer progression. A nutrient mixture (NM) containing lysine, proline, ascorbic acid, and green tea extract has shown significant anticancer activity against a number of cancer cell lines. We investigated the effect of NM on liposarcoma cell line SW-872 proliferation (MTT assay), MMP secretion (gelatinase zymography), invasion through Matrigel, and apoptosis and morphology (live green caspase kit and H&E). Liposarcoma cell growth was inhibited by 36 and 61% at 500 and 1,000 microg/ml NM. Zymography demonstrated both MMP-2 and MMP-9 secretion, with PMA-enhanced MMP-9 activity. NM inhibited both MMPs with virtual total inhibition at 500 microg/ml NM. Invasion through Matrigel was inhibited at 100, 500, and 1,000 microg/ml by 44, 75, and 100%, respectively. Dose-dependent apoptosis of liposarcoma cells was evident with NM challenge, with virtually all cells exposed to 1,000 microg/ml NM in late apoptosis. H&E staining did not demonstrate any changes in morphology at lower concentrations. However, some apoptotic changes were evident at higher concentrations. In conclusion, NM significantly inhibited liposarcoma cell growth, MMP activity, and invasion and induced apoptosis in vitro-important parameters for cancer development, suggesting NM as a potential treatment strategy for liposarcoma.

Modeling metastatic breast cancer in mice

Metastatic disease is the major cause of death in breast cancer patients. Patients presenting with metastases cannot be cured, and as a consequence, treatment is palliative and focuses on prolonging survival and maintaining quality of life. Numerous mouse models have been generated in which human breast cancer development and metastasis have been studied, ranging from spontaneous and carcinogen-induced models to transplantation models and genetically engineered mouse models. Here, we summarize past progress and highlight present developments in modeling breast cancer invasion and metastasis in genetically modified mice, and the impact it may have on the development of innovative anticancer therapies.

Deciphering the molecular basis of breast cancer metastasis with mouse models

Breast cancer begins as a localized disease, but has the potential to spread to distant sites within the body. This process--known as metastasis--is the leading cause of death from breast cancer. Whether the ability of cancer cells to metastasize is an intrinsic or acquired feature is currently a topic of considerable debate. Nevertheless, the key cellular events required for metastasis are generally accepted. These include invasion of the surrounding stromal tissue, intravasation, evasion of programmed cell death, arrest within the vasculature at a distant site, extravasation, and establishment and growth within a new microenvironment. The development of mouse models that faithfully mimic critical aspects of human neoplasia has been instrumental in framing our current understanding of multistage carcinogenesis. This review examines the advantages and limitations of existing murine models for mammary carcinogenesis for probing the molecular mechanisms that contribute to metastasis, as well as non-invasive tumor imaging approaches to facilitate these investigations.

Stromal induction of breast cancer: inflammation and invasion

Many investigations of cancer development have pursued the mechanisms by which genetic mutations stimulate tumor development through activation of oncogenes or loss of tumor suppressor genes. However, there is an increasing awareness that signals provided by the stroma can induce the genetic alterations that underlie tumor formation, can stimulate tumor growth and progression, and can dictate both therapeutic response and ultimate clinical outcome. This principle is particularly clear in breast cancer, where recent investigations using sophisticated three-dimensional cell culture models and transgenic animals have been used to define how altered signals from the microenvironment contribute to breakdown of tissue structure, increased cellular proliferation, and transition to the malignant phenotype. We review here recent studies identifying new roles for cancer-associated fibroblasts in promoting tumor progression, through stimulation of inflammatory pathways and induction of extracellular matrix-remodelling proteases. These studies identify mechanisms by which development of a reactive tumor stroma causes mammary hyperproliferation, progression to fibrosis, development of neoplasia, increasing invasiveness, and eventual metastasis, and how intervention in these processes may provide new avenues for therapy.

Systemic administration of anti-urokinase plasminogen activator receptor monoclonal antibodies induces hepatic fibrin deposition in tissue-type plasminogen activator deficient mice

BACKGROUND

Degradation of extracellular matrix proteins, such as fibrin, is pivotal to tumor invasion. Inhibition of the interaction between urokinase plasminogen activator (u-PA) and its receptor (u-PAR), and hence pro-u-PA activation, is an attractive approach to anti-invasive cancer therapy. A number of inhibitors exist for the human system, but because of species specificity none of these are efficient in mice. We have recently generated an inhibitory monoclonal antibody (mAb) against mouse u-PAR (mR1) by immunization of u-PAR-deficient mice.

OBJECTIVES

To evaluate the effect of mR1 in vivo in a physiological setting sensitive to deregulated fibrinolysis, we have administered mR1 systemically and quantitated the effect on liver fibrin accumulation.

METHODS

Wild-type and tissue-type plasminogen activator (t-PA) deficient mice were administered with mR1, or control antibody, during 6 weeks. Thereafter, the livers were retrieved and the amount of liver fibrin measured by unbiased morphometrical analysis of immunofluorescence signal.

RESULTS

Systemic administration of mR1 caused significantly increased fibrin signal in anti-u-PAR treated t-PA-deficient mice compared to mock-treated, which mimics the phenotype of u-PAR;t-PA double-deficient mice. Fibrin and fibronectin accumulated within the sinusoidal space and was infiltrated by inflammatory cells. Analysis of small and rare hepatic fibrin plaques observed in t-PA-deficient mice showed infiltrating macrophages that, contrary to surrounding Kuppfer cells, expressed u-PAR.

CONCLUSION

We show that u-PAR-expressing macrophages are involved in cell-mediated fibrinolysis of liver fibrin deposits, and that the antimouse-u-PAR mAb is effective in vivo and thus suited for studies of the effect of targeting the u-PA/u-PAR interaction in mouse cancer models.

Identification of a novel inhibitor of urokinase-type plasminogen activator

Urokinase-type plasminogen activator (uPA), a highly restricted serine protease, plays an important role in the regulation of diverse physiologic and pathologic processes. Strong clinical and experimental evidence has shown that elevated uPA expression is associated with cancer progression, metastasis, and shortened survival in patients. uPA has been considered as a promising molecular target for development of anticancer drugs. Here, we report the identification of several new uPA inhibitors using a high-throughput screen from a chemical library. From these uPA inhibitors, molecular modeling and docking studies identified 4-oxazolidinone as a novel lead pharmacophore. Optimization of the 4-oxazolidinone pharmacophore resulted in a series of structurally modified compounds with improved potency and selectivity. One of the 4-oxazolidinone analogues, UK122, showed the highest inhibition of uPA activity. The IC(50) of UK122 in a cell-free indirect uPA assay is 0.2 micromol/L. This compound also showed no or little inhibition of other serine proteases such as thrombin, trypsin, plasmin, and the tissue-type plasminogen activator, indicating its high specificity against uPA. Moreover, UK122 showed little cytotoxicity against CFPAC-1 cells (IC(50) >100 micromol/L) but significantly inhibited the migration and invasion of this pancreatic cancer cell line. Our data show that UK122 could potentially be developed as a new anticancer agent that prevents the invasion and metastasis of pancreatic cancer.

Sensitive bioanalysis—combining single-molecule spectroscopy with mono-labeled self-quenching probes

Fluorescence single-molecule spectroscopy is an appropriate tool for modern bioanalysis. This technique enables the development of ultra sensitive assays, especially when combined with self-quenching probes. In this review we report novel DNA, enzyme, and antibody assays based on mono-labeled fluorescent probes that are quenched by photoinduced electron transfer (PET).

Plasminogen binding and activation at the breast cancer cell surface: the integral role of urokinase activity

Introduction

The regulation of extracellular proteolytic activity via the plasminogen activation system is complex, involving numerous activators, inhibitors, and receptors. Previous studies on monocytic and colon cell lines suggest that plasmin pre-treatment can increase plasminogen binding, allowing the active enzyme to generate binding sites for its precursor. Other studies have shown the importance of pre-formed receptors such as annexin II heterotetramer. However, few studies have used techniques that exclusively characterise cell-surface events and these mechanisms have not been investigated at the breast cancer cell surface.

Methods

We have studied plasminogen binding to MCF-7 in which urokinase plasminogen activator receptor (uPAR) levels were upregulated by PMA (12-O-tetradecanoylphorbol-13-acetate) stimulation, allowing flexible and transient modulation of cell-surface uPA. Similar experiments were also performed using MDA-MB-231 cells, which overexpress uPAR/uPA endogenously. Using techniques that preserve cell integrity, we characterise the role of uPA as both a plasminogen receptor and activator and quantify the relative contribution of pre-formed and cryptic plasminogen receptors to plasminogen binding.

Results

Cell-surface plasminogen binding was significantly enhanced in the presence of elevated levels of uPA in an activity-dependent manner and was greatly attenuated in the presence of the plasmin inhibitor aprotinin. Pre-formed receptors were also found to contribute to increased plasminogen binding after PMA stimulation and to co-localise with uPA/uPAR and plasminogen. Nevertheless, a relatively modest increase in plasminogen-binding capacity coupled with an increase in uPA led to a dramatic increase in the proteolytic capacity of these cells.

Conclusion

We show that the majority of lysine-dependent plasminogen binding to breast cancer cells is ultimately regulated by plasmin activity and is dependent on the presence of significant levels of active uPA. The existence of a proteolytic positive feedback loop in plasminogen activation has profound implications for the ability of breast cancer cells expressing high amounts of uPA to accumulate a large proteolytic capacity at the cell surface, thereby conferring invasive potential.

Elevated urokinase-specific surface receptor expression is maintained through its interaction with urokinase plasminogen activator

Urokinase plasminogen activator (uPA) and its receptor (uPAR) are overexpressed in various neoplasms, and play a key role in tumor progression and metastasis. In this study, we examined uPA and uPAR expression in a variety of human breast cancer cell lines and found that lines with elevated uPA expression also exhibited high uPAR expression, suggesting the possibility that uPA and uPAR are regulated in concert. To test this possibility, we introduced antisense uPA RNA and antisense uPAR RNA in MDA-MB-231 and BT-549 lines that express high levels of uPA and uPAR. Antisense uPA RNA not only downregulated uPA expression, but also greatly reduced uPAR expression in both lines. However, antisense uPAR RNA-reduced uPAR expression with no apparent inhibitory effect on the levels of uPA. These results indicate that expression of uPAR requires uPA but not vice versa. With a panel of uPA and uPAR monoclonal antibodies (mAbs), we observed that the mAbs disrupting uPA and uPAR interaction, rather than mAb inhibiting uPA protease activity, reduced uPAR expression. Moreover, adding soluble single chain uPA (scuPA) to MDA-MB-231 or BT-549 cells expressing antisense uPA mRNA-restored uPAR expression. These findings suggest that uPA dictates uPAR expression and that uPA binding to uPAR transmits signals for uPAR expression. Finally, we provided evidence that Fyn, a Src family kinase, is involved in uPA-induced uPAR expression.

Preclinical evaluation of 213Bi-labeled plasminogen activator inhibitor type 2 in an orthotopic murine xenogenic model of human breast carcinoma

Tumor-associated urokinase plasminogen activator (uPA) is a critical marker of invasion and metastasis, has strong prognostic relevance, and is thus a potential therapeutic target. Experimental data published to date has established the proof-of-principle of uPA targeting by (213)Bi-labeled plasminogen activator inhibitor type 2 (alpha-PAI-2) in multiple carcinoma models. Here, we present preclinical toxicologic and efficacy assessment of alpha-PAI-2 in mice, using both single and multiple-dose schedules, administered by an i.p. route. We also present novel data showing that human PAI-2 inhibited murine uPA and was specifically endocytosed by murine fibroblast cells. This diminishes potential problems associated with species specificity of the targeting reagent in toxicologic assessments as human alpha-PAI-2 should interact with any uPA-expressing host cells. In this model, single bolus doses up to 36 mCi/kg alpha-PAI-2 did not reach the maximum tolerated dose (MTD). The MTD for a multiple fractionated (once daily for 5 days) administration schedule was determined to lie between 4.8 and 6.0 mCi/kg/d x 5. Comparison of the tumor growth rates and survival using sub-MTD single and multiple-dose schedules in an orthotopic human breast carcinoma xenograft murine model indicated that 4.8 mCi/kg/d x 5 was the most efficacious schedule. In conclusion, we have determined a safe dose and schedule of alpha-PAI-2 administration in mice, thus confirming that it is an efficacious therapeutic modality against tumor growth. This will allow detailed safety evaluation in a second species and for the initiation of human studies.

Extracellular proteolysis in transgenic mouse models of breast cancer

Growth and invasion of breast cancer require extracellular proteolysis in order to physically restructure the tissue microenvironment of the mammary gland. This pathological tissue remodeling process depends on a collaboration of epithelial and stromal cells. In fact, the majority of extracellular proteases are provided by stromal cells rather than cancer cells. This distinct expression pattern is seen in human breast cancers and also in transgenic mouse models of breast cancer. The similar expression patterns suggest that transgenic mouse models are ideally suited to study the role of extracellular proteases in cancer progression. Here we give a status report on protease intervention studies in transgenic models. These studies demonstrate that proteases are involved in all stages of breast cancer progression from carcinogenesis to metastasis. Transgenic models are now beginning to provide vital mechanistic insight that will allow us to combat breast cancer invasion and metastasis with new protease-targeted drugs.

Inhibition of pulmonary metastasis of melanoma b16fo cells in C57BL/6 mice by a nutrient mixture consisting of ascorbic Acid, lysine, proline, arginine, and green tea extract

The authors investigated the effect of a nutrient mixture (NM) on lung metastasis by B16F0 melanoma cells in C57BL/6 female mice. Mice were divided into equal groups (1 to 6) and injected via tail vein with B16F0 cells (groups 1 to 4), B16FO cells pretreated with NM (group 5), or saline (group 6). Groups 1, 3, 4, 5, and 6 were fed the control diet and group 2 the 0.5% NM supplemented diet. Groups 3 and 4 received NM intraperitoneally (IP) and intravenously (IV), respectively. Two weeks later, pulmonary metastatic colonies were counted. Pulmonary colonization was reduced by 63% in mice supplemented with NM diet, by 86% in mice receiving NM by IP and IV injections, and completely inhibited in mice injected with melanoma cells pretreated with NM. These results show that NM is effective in inhibiting the metastasis of B16FO melanoma cells.

In vivo and in vitro antitumor effect of a unique nutrient mixture on lung cancer cell line A-549

The high incidence of lung cancer and ineffective toxic action of current mono and doublet chemotherapy approaches result in poor patient survival. Further, matrix metalloproteinases (MMPs) are implicated in neoplastic invasion and metastasis. Based on this, the authors investigated the effect of a dietary micronutrient mixture (NM) containing lysine, proline, arginine, ascorbic acid, and green tea extract on the tumor growth of human lung carcinoma cell A-549 xenografts in athymic nude mice. Additionally, the authors tested the in vitro antitumor effect of NM on lung carcinoma A-549 cells by measuring cell proliferation by MTT assay, MMP-2 and -9 secretion by gelatinase zymography, and cell invasion through Matrigel. Nutrient supplementation strongly suppressed the growth of tumors without adverse effects in nude mice; tumor weight was reduced by 44% (P = .0001) and tumor burden was reduced by 47% (P < .0001) with supplementation. Zymography demonstrated in vitro secretion of MMP-2 by uninduced human lung carcinoma cells and both MMP-2 and -9 by phorbol 12-mysristate 13-acetate (PMA) (200 ng/mL)-treated cells. NM inhibited the secretion of both MMPs in a dose-dependent fashion, with virtual total inhibition at 500 microg/mL concentration. The invasion of human lung carcinoma cells through Matrigel was significantly reduced at 100 microg/mL (64%) and totally inhibited at 500 microg/mL concentration of NM (P = .01). Suppression of lung tumor growth in nude mice and inhibition of MMP secretion and Matrigel invasion suggest NM may act as an anticancer agent and as such warrants further investigation.

Stromal cells associated with early invasive foci in human mammary ductal carcinoma in situ coexpress urokinase and urokinase receptor

The transition from ductal carcinoma in situ (DCIS) of the breast to invasive ductal carcinoma is facilitated by proteolytic degradation of basement membrane. The transition can be identified as microinvasive foci in a small proportion of DCIS lesions. We have previously found that MMP-13 is frequently expressed in such foci. To establish whether plasmin-directed proteolysis is likely to be involved in early invasion, we have here studied the expression of urokinase plasminogen activator (uPA) and its receptor (uPAR) in human DCIS lesions with and without microinvasion. uPA mRNA was detected in periductal stromal cells in all of 9 DCIS lesions with microinvasion and in 2 of 9 DCIS lesions without microinvasion by in situ hybridization. The uPA mRNA signal was seen in numerous stromal cells in microinvasive areas together with MMP-13 mRNA expressing cells. Double immunofluorescence analyses, using emission fingerprinting, showed that the uPA expressing stromal cells included both myofibroblasts and macrophages. The early invasive carcinoma cells were negative for uPA. uPAR immunoreactivity was focally upregulated in periductal stromal cells in all of the 9 DCIS lesions with microinvasion and in only 2 of the 9 DCIS lesions without microinvasion. uPAR was seen in both macrophages and myofibroblasts in microinvasive areas, and it was evident that uPA and uPAR colocalized in both fibroblast-like cells and macrophage-like cells. We conclude that periductal macrophages and myofibroblasts are strongly involved in the initial steps of breast cancer invasion by focally upregulating the expression of the plasminogen activation system and MMP-13.

Mouse models of breast cancer metastasis

Metastatic spread of cancer cells is the main cause of death of breast cancer patients, and elucidation of the molecular mechanisms underlying this process is a major focus in cancer research. The identification of appropriate therapeutic targets and proof-of-concept experimentation involves an increasing number of experimental mouse models, including spontaneous and chemically induced carcinogenesis, tumor transplantation, and transgenic and/or knockout mice. Here we give a progress report on how mouse models have contributed to our understanding of the molecular processes underlying breast cancer metastasis and on how such experimentation can open new avenues to the development of innovative cancer therapy.

Mendelian analysis of a metastasis-prone substrain of BALB/c nude mice using a subcutaneously inoculated human tumour

Most nude mice do not allow the formation of metastases after heterotransplantation of human malignant tumours. Here we describe a substrain of BALB/c nude mice (BALB/c/AnNCr) that reproducibly allows some human cancers to metastasize. By Mendelian analysis of hybrids between this substrain and C57BL/6J +/+ mice we found that the ability to allow a human tumour (MDA-MB-435 BAG) to express its metastatic phenotype is determined by a recessively inheritable trait in the mouse host. We are presently working to identify the genetics responsible for development of metastases. The study also includes immunohistochemical and electron microscopic analysis of the test tumour, originally assumed to be a human mammary carcinoma, but shown to possess characteristics of a malignant melanoma (1). The ultimate aim of our ongoing study is to establish a substrain of nude mice that will allow metastasis in all recipients.

Critical involvement of ILK in TGFbeta1-stimulated invasion/migration of human ovarian cancer cells is associated with urokinase plasminogen activator system

The present study investigated the role of integrin-linked kinase (ILK) in TGFbeta1-stimulated invasion/migration of human ovarian cancer cells. We investigated TGFbeta1 regulation of ILK, and effects of ILK knockdown on TGFbeta1-stimulated invasion/migration and the associated proteinase systems, urokinase plasminogen activator (uPA) and matrix metalloproteinases (MMPs) in SKOV3 cells. TGFbeta1 stimulated ILK kinase activity, and had no effect on ILK protein/mRNA levels. Transient transfection of an ILK-specific siRNA (ILK-H) reduced ILK protein level, mRNA level and kinase activity. ILK knockdown by ILK-H suppressed the basal and TGFbeta1-stimulated invasion and migration. Further, ILK-H reduced the basal and TGFbeta1-stimulated secretion of uPA, and increased the secretion of its inhibitor (PAI-1). Conversely, ILK-H did not affect TGFbeta1-stimulated secretion of MMP2 and its cell-associated activator MT1-MMP. Additionally, TGFbeta1 activated Smad2 phosphorylation, and this was not affected by ILK knockdown. Earlier reports indicate that Smad2 activation increased the expression of MMP2 and MT1-MMP. Thus, TGFbeta1 may act through ILK-independent and Smad2-dependent signaling in regulating MMP2 and MT1-MMP in SKOV3 cells. Collectively, this study suggests that ILK serves as a key mediator in TGFbeta1 regulation of uPA/PAI-1 system critical for the invasiveness of human ovarian cancer cells. And ILK is a potential target for cancer therapy.

Antitumor effect of ascorbic acid, lysine, proline, arginine, and green tea extract on bladder cancer cell line T-24

AIMS

Bladder cancer, the fourth highest incident cancer in men and tenth in women, is associated with a high rate of recurrence, even when treated in situ, and prognosis is poor once the cancer metastasizes to distant sites. Based on anticancer properties, we investigated the effect of a mixture of lysine, proline, arginine, ascorbic acid, and green tea extract on human bladder cancer cells T-24 by measuring: proliferation, matrix metalloproteinase (MMP) expression, and cancer cell invasive potential.

METHODS

Human bladder cancer cells T-24 (ATCC) were grown in McCoy medium supplemented with 10% fetal bovine serum, penicillin (100 U/mL) and streptomycin (100 mg/mL) in 24-well tissue culture plates. At near confluence, the cells were treated with the nutrient mixture dissolved in media and tested at 0, 10, 50, 100, 500, and 1000 microg/mL in triplicate at each dose. Cells were also treated with PMA 200 ng/mL to study enhanced MMP-9 activity. Cell proliferation was evaluated by MTT assay, MMP activity by gelatinase zymography, and invasion through Matrigel.

RESULTS

Nutrient mixture inhibited the T-24 cell secretion of MMP-2 and -9, with virtual total inhibition of MMP-2 at 500 microg/mL and MMP-9 at 100 microg/mL. The nutrient mixture significantly reduced the invasion of human bladder cancer cells T-24 through Matrigel in a dose-dependent fashion, with 95% inhibition at 500 microg/mL and 100% at 1000 microg/mL nutrient mixture (P < 0.001).

CONCLUSION

Our results suggest that our nutrient mixture is an excellent candidate for therapeutic use in the treatment of bladder cancer, by inhibiting critical steps in cancer development and spread, such as MMP secretion and invasion.

Inhibition of malignant mesothelioma cell matrix metalloproteinase production and invasion by a novel nutrient mixture

Malignant mesothelioma (MM), an asbestos-associated cancer with no known cure, is a highly aggressive tumor causing profound morbidity and nearly universal mortality. Extracellular matrix (ECM) matrix metalloproteinases (MMPs) produced by tumor and stromal cells play a key role in tumor invasion and metastasis. Prevention of ECM degradation by MMP inhibition has been shown to be a promising therapeutic approach to inhibition of cancer development. Based on reported anticancer properties, the authors investigated the effect of a mixture (NM) containing lysine, proline, ascorbic acid, and green tea extract on MM cell line MSTO-211 H proliferation (by [MTT] [3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide] assay), MMP secretion (by gelatinase zymography), invasion (through Matrigel), and morphology (by hematoxylin and eosin [H&E] staining). MMP-2 and phorbol 12-myristate 13-acetate (PMA)-induced MMP-9 secretion were inhibited by NM in a dose-dependent fashion, with virtual total inhibition at 500 microg/ml NM. Invasion through Matrigel was inhibited at 50, 100, and 500 microg/ml by 27%, 36%, and 100%, respectively. NM was not toxic to the MM cell line, and H&E staining did not indicate any changes at and below 100 microg/ml concentration. In conclusion, NM significantly inhibited MM cell MMP secretion and invasion-both important parameters for cancer prevention, suggesting NM is an effective treatment strategy for MM.

Inhibition of matrix metalloproteinase-2 secretion and invasion by human ovarian cancer cell line SK-OV-3 with lysine, proline, arginine, ascorbic acid and green tea extract

AIMS

Based on the poor prognosis associated with ovarian cancer and reported anticancer properties of specific nutrients, we investigated the effect of a nutrient mixture (NM) containing lysine, proline, arginine, ascorbic acid and epigallocatechin gallate on human ovarian cancer cells SK-OV-3 by measuring: cell proliferation, modulation of matrix metalloproteinase (MMP)-2 and -9 expression, and cancer cell invasive potential.

METHODS

Cell proliferation was evaluated by MTT assay, MMP activity by gelatinase zymography, and invasion through Matrigel.

RESULTS

Human ovarian cancer cell growth was not significantly affected by the NM. Zymography demonstrated inhibition of MMP-2 secretion in a dose-dependent fashion with virtual total inhibition at 50 microg/mL NM concentration. Invasion of human ovarian cancer cells through Matrigel decreased in a dose-dependent fashion, with 90% inhibition at 500 microg/mL NM and 100% inhibition at 1000 microg/mL NM (P < 0.0001).

CONCLUSION

The combination of lysine, proline, arginine, ascorbic acid and green tea extract tested inhibited critical steps in cancer development and spread, such as MMP expression and invasion, indicating its potential as a treatment modality against ovarian cancer.

Diphenyl Phosphonate Inhibitors for the Urokinase-Type Plasminogen Activator: Optimization of the P4 Position

This paper describes the structure-activity relationship in a series of tripeptidyl diphenyl phosphonate irreversible urokinase plasminogen activator (uPA) inhibitors, originally derived from an arginyltripeptide. uPA is considered an interesting target in anticancer drug design. The selectivity of these inhibitors for uPA is enhanced by the optimization of the P4 position. The most interesting compound shows an IC(50) of 5 nM, with a selectivity index of more than 3000 toward other Arg/Lys-specific proteases such as tissue-type plasminogen activator, plasmin, factor Xa, and thrombin. A synthetic strategy for the preparation of small libraries of diphenyl phosphonate analogues of capped tripeptides is described. It is shown that uPA is irreversibly inhibited, and interactions with the active site were modeled. Finally, a diparacetamol phosphonate analogue was developed to circumvent the release of cytotoxic phenol.

Lack of plasminogen leads to milk stasis and premature mammary gland involution during lactation

The extracellular serine protease, plasmin, is activated from its precursor, plasminogen (Plg), by the urokinase-type and tissue-type Plg activators (uPA and tPA respectively). One of the main plasmin substrates, fibrin, is formed from fibrinogen via thrombin activity. We have previously shown that mice deficient for Plg are strikingly less able to support a litter during lactation compared to wild type mice. Here we suggest a mechanism responsible for this lactation defect. Reduced epithelial content and increased apoptosis are observed in Plg-deficient mammary glands at lactation day 7. Immunofluorescence analysis reveals the presence of fibrin(ogen) in the stroma surrounding mammary alveoli and adipocytes and identifies fibrin(ogen) as a component of breast milk in both wild type and Plg-deficient mice. Furthermore, a large accumulation of fibrin(ogen) together with apoptotic epithelial cells is observed in the lactating mammary alveoli and ducts of some Plg-deficient mice. This suggests that fibrin plays a key role in the malfunction of mammary glands in the absence of Plg, possibly through blockade of mammary ducts inducing milk stasis, inhibiting milk expulsion and thereby inducing premature apoptosis and involution.

Plasminogen activator inhibitor-1 is a critical downstream target of p53 in the induction of replicative senescence

p53 limits the proliferation of primary diploid fibroblasts by inducing a state of growth arrest named replicative senescence - a process which protects against oncogenic transformation and requires integrity of the p53 tumour suppressor pathway. However, little is known about the downstream target genes of p53 in this growth-limiting response. Here, we report that suppression of the p53 target gene encoding plasminogen activator inhibitor-1 (PAI-1) by RNA interference (RNAi) leads to escape from replicative senescence both in primary mouse embryo fibroblasts and primary human BJ fibroblasts. PAI-1 knockdown results in sustained activation of the PI(3)K-PKB-GSK3beta pathway and nuclear retention of cyclin D1, consistent with a role for PAI-1 in regulating growth factor signalling. In agreement with this, we find that the PI(3)K-PKB-GSK3beta-cyclin D1 pathway is also causally involved in cellular senescence. Conversely, ectopic expression of PAI-1 in proliferating p53-deficient murine or human fibroblasts induces a phenotype displaying all the hallmarks of replicative senescence. Our data indicate that PAI-1 is not merely a marker of senescence, but is both necessary and sufficient for the induction of replicative senescence downstream of p53.

MMP-9 is differentially expressed in primary human colorectal adenocarcinomas and their metastases

Matrix metalloproteinase-9 (MMP-9) is up-regulated in macrophages in various human cancer types. In human colon cancer, MMP-9 is expressed in a macrophage subpopulation located at the tumor edge, indicating a specific induction of MMP-9 in macrophages in direct association with cancer invasion. To test whether MMP-9 is also induced in tumor edge macrophages in metastases from colorectal adenocarcinomas, we have compared the expression pattern of MMP-9 in primary colorectal adenocarcinomas (n = 15) with that in liver metastases (n = 15) and local lymph node metastases (n = 7) from the same patients by in situ hybridization and immunohistochemistry. In all the colorectal adenocarcinomas, the expression of MMP-9 mRNA and immunoreactivity in macrophages was located at the invasive front. In contrast, only 3 of the 15 liver metastases had MMP-9 mRNA and immunoreactivity at the periphery, and this expression was confined to small foci of macrophages located either among lymphocytes or in a dense desmoplastic stroma. Expression of MMP-9 mRNA and immunoreactivity was in all liver metastases seen in macrophages located in the lumen of malignant glandular structures and in central necrotic tissue. In all the 7 lymph node metastases, MMP-9 mRNA and immunoreactivity was seen in macrophages located in the stromal tissue surrounding the metastases. We conclude that MMP-9 is not up-regulated in tumor edge macrophages in liver metastases like in their primary tumor and local lymph node metastases, suggesting that disseminating colorectal cancer cells can adopt alternative proteolytic mechanisms for invasion depending on the local microenvironment.

Exploring the tumour environment: cancer-associated fibroblasts as targets in cancer therapy

Stroma cells contribute to the microenvironment that is essential for cancer growth, invasion and metastatic progression. Fibroblasts, often termed myofibroblasts or cancer-associated fibroblasts (CAFs), represent the most abundant cell type in the tumour stroma. The demonstrated tumour-promoting capacities of CAFs has increased the interest to exploit them as drug targets for anticancer therapy. Although single factors, such as platelet-derived growth factor, transforming growth factor-beta1, hepatocyte growth factor and matrix metalloproteinases have been identified as mediators in the fibroblast tumour interaction, the morphological and functional differences of CAFs compared with their normal counterparts are only incompletely understood. Recently, novel global methods for gene expression profiling were applied to comprehensively characterise CAFs from breast, pancreas, colon and basal cell cancer in their in situ environment. The analysis of different CAF preparations revealed regulated genes that were previously not described in the tumour-stroma context. Additionally, besides a few striking overlaps, the comparison of the gene lists indicates a high level of heterogeneity in the expression pattern of CAFs from different tumour types. Together, these studies emphasise the importance of cross-talk between stromal and malignant cells of the tumour. It is likely that the continued characterisation of this interaction, and the molecular identification of key mediators, will provide insights into tumour biology and suggest novel therapeutic options.

In vivo and in vitro antitumor effect of ascorbic acid, lysine, proline, arginine, and green tea extract on human fibrosarcoma cells HT-1080

Current treatment of fibrosarcoma, an aggressive cancer of the connective tissue, is generally associated with poor prognosis. Matrix metalloproteinases (MMPs), vascular endothelial growth factor (VEGF), and constituents of the extracellular matrix (ECM), such as fibronectin, play a critical role in angiogenesis and underlie neoplastic invasion and metastasis. This and anticancer properties of lysine, proline, arginine, ascorbic acid, and green tea extract (NM) prompted us to investigate the effect of these nutrients in vitro on human fibrosarcoma cells HT-1080 by measuring cell proliferation, modulation of MMP-2 and MMP-9, and invasive potential. In vivo, we studied the growth of human fibrosarcoma HT-1080 cells in athymic nude mice and the expression of MMPs and VEGF. Cell proliferation was evaluated by MTT assay, MMP expression by gelatinase zymography, and invasion through Matrigel and migration by scratch assay. Tumors were excised, weighed, and processed for histology in both the control and nutrient-supplemented groups. Results showed NM inhibited the growth and reduced the size of tumors in nude mice; decreased MMP-9 and VEGF secretion was found in the supplemented group tissues. NM inhibited invasion through Matrigel and migration with total inhibition at 1,000 microg/mL. These results offer promise in the therapeutic use of the nutrient mixture of lysine, proline, arginine, ascorbic acid, and green tea extract tested in the treatment of fibrosarcoma.

Aspects of extracellular matrix remodeling in development and disease

The extracellular matrix is the major constituent of organic matter in both plants and animals, where it provides the interface between individual cells. In most tissues, with some notable exceptions such as bone marrow, the volume of extracellular matrix equals or exceeds the volume of intracellular space and organelles, making matrix an abundant constituent through which cells exert their functions and receive cues. The matrix may therefore be considered the basic structural entity that supports the function of an organ, and in connective tissues the matrix is the organ itself to which function is tied throughout the life of its resident cells. In this review, a select number of proteinases involved in some of the more conspicuous matrix remodeling events of the mammalian organism are explored. Evidence from both animal models and human diseases is discussed in relation to normal physiological processes, including instances in which aberrant matrix remodeling leads to disease states.

Enhanced Discrimination of Benign from Malignant Prostatic Disease by Selective Measurements of Cleaved Forms of Urokinase Receptor in Serum

Background: Early detection of prostate cancer (PCa) centers on measurements of prostate-specific antigen (PSA), but current testing practices suffer from lack of specificity and generate many unnecessary prostate biopsies. Soluble urokinase plasminogen activator receptor (uPAR) is present in blood in both intact and cleaved forms. Increased uPAR in blood is correlated with poor prognosis in various cancers, but uPAR has not been shown to be useful in PCa diagnostics. We assessed the ability of immunoassays for specific uPAR forms to discriminate PCa from benign conditions.

Methods: We measured total PSA (tPSA), free PSA (fPSA), intact uPAR [uPAR(I-III)], intact uPAR + cleaved uPAR domains II+III [uPAR(I-III) + uPAR(II-III)], and cleaved uPAR domain I [uPAR(I)] in sera from 224 men with and 166 men without PCa. We assessed differences in serum concentrations between the PCa and noncancer groups within the entire cohort and in men with tPSA concentrations of 2–10 μg/L. The diagnostic accuracy of individual analytes and analyte combinations was explored by logistic regression and ROC analyses and evaluations of sensitivity and specificity pairs.

Results: Serum uPAR(I) and uPAR(II-III) were higher in PCa than in benign disease. In men with tPSA between 2 and 10 μg/L, the combination of %fPSA with the ratio uPAR(I)/uPAR(I-III) had a greater area under the ROC curve (0.73) than did %fPSA (0.68).

Conclusions: Specific measurements of different uPAR forms in serum improve the specificity of PCa detection. The uPAR forms may therefore be complementary to PSA for PCa detection, most importantly in men with moderately increased PSA.

Suppression of human cervical cancer cell lines Hela and DoTc2 4510 by a mixture of lysine, proline, ascorbic acid, and green tea extract

Cervical cancer, the second most common cancer in women, once metastasized, leads to poor prognosis. We investigated the antitumor effect of a nutrient mixture (NM) containing lysine, proline, arginine, ascorbic acid, and green tea extract on human cervical cancer cells Hela (CCL-2) and DoTc2 4510 by measuring cell proliferation (MTT assay), modulation of matrix metalloproteinases (MMP)-2 and MMP-9) expression (gelatinase zymography), and cancer cell invasive potential (Matrigel). NM showed significant antiproliferative effect on CCL-2 and DoTc2 4510 cancer cells. The NM inhibited CCL-2 expression of MMP-2 and MMP-9 in a dose-dependent fashion, with virtual total inhibition of MMP-2 at 1000 microg/mL and MMP-9 at 500 microg/mL NM. Untreated DoTc2 4510 cells showed MMP-9 expression, which was enhanced with phorbol 12-myristate 13-acetate treatment. NM inhibited MMP-9 expression in a dose-dependent fashion, with virtual inhibition at 500 microg/mL. Invasion of human cervical cancer cells CCL-2 and DoTc2 4510 through Matrigel decreased in a dose-dependent fashion, with 100% inhibition at 500 microg/mL NM (P < 0.0001) and 1000 microg/mL NM (P < 0.0001), respectively. Our results suggest that the mixture of lysine, proline, arginine, ascorbic acid, and green tea extract has potential in the treatment of cervical cancer by inhibiting critical steps in cancer development and spread.

Activity-based protein profiling implicates urokinase activation as a key step in human fibrosarcoma intravasation

Entry of malignant cells into the vasculature (i.e. intravasation) requires proteolytic remodeling of the extracellular matrix so that tumor cells may pass through the local stroma and penetrate the vessel wall. The circulatory system then provides a means of transporting tumor cells to distant sites where they extravasate and establish metastatic lesions. This study utilizes activity-based protein profiling to compare the active serine hydrolase repertoire in high intravasating (HT-hi/diss) and low intravasating (HT-lo/diss) variants of the human fibrosarcoma HT-1080 cell line to determine which enzyme(s) play a role in intravasation. Activity-based protein profiling revealed multiple serine hydrolases with altered activity between HT-hi/diss and HT-lo/diss cells, with the largest difference being the activity of urokinase-type plasminogen activator (uPA). Levels of inactive uPA zymogen were similar between the two cell variants, but only HT-hi/diss conditioned medium contained active uPA, suggesting that uPA activation may contribute to the enhanced intravasation of HT-hi/diss cells. To analyze the role of uPA activity specifically in the process of intravasation, we grafted cells from the two HT-1080 variants onto the chorioallantoic membrane of chick embryos and measured levels of tumor cell intravasation in the distal chorioallantoic membrane using quantitative human-specific Alu PCR. Inhibition of uPA activity with natural (plasminogen activator inhibitor-1) or synthetic (amiloride) inhibitors diminished HT-hi/diss Matrigel invasion in vitro and intravasation and metastasis in vivo. Additionally, treatment of HT-lo/diss tumors with exogenous active uPA increased the number of intravasated cells in vivo. These results indicate that active uPA promotes tumor cell intravasation and that uPA activation appears to be a key step in tumor progression.

MEKK1 controls matrix degradation and tumor cell dissemination during metastasis of polyoma middle-T driven mammary cancer

Mammary tumor cells are required to degrade the surrounding matrix and disseminate in order to metastasize, and both of these processes are controlled by a tumor cell-signaling network that remains poorly defined. MEKK1 is a MAPKKK that regulates both the extracellular signal regulated kinase (ERK1/2) and the c-Jun amino terminal kinase (JNK) signaling pathways. MEKK1 signaling regulates migration through control of cell adhesion and is required for inducible expression of urokinase-type plasminogen activator (uPA). MEKK1-deficient mice with mammary gland-targeted expression of the polyoma middle T antigen (PyMT) transgene develop primary mammary tumors at a rate and frequency similar to wild-type littermates, indicating that MEKK1 deficiency does not affect PyMT-mediated transformation. However, MEKK1-/- mice display significantly delayed tumor cell dissemination and lung metastasis. Delayed MEKK1-dependent tumor dissemination is associated with markedly reduced tumor uPA expression, gelatinase activity, and prolonged tumor basement membrane integrity. siRNA-mediated MEKK1 knockdown inhibits uPA activity, cell migration and invasion in MDA-MB-231 human breast cancer cells. Thus MEKK1 controls tumor progression by regulating both the migration and proteolysis aspects of tumor cell invasiveness. To our knowledge, this is the first example of a MAPKKK that regulates metastasis through control of tumor invasiveness.

Extracellular protease mRNAs are predominantly expressed in the stromal areas of microdissected mouse breast carcinomas

Solid tumors synthesize a number of extracellular matrix-degrading proteases that are important for tumor progression. Based on qualitative in situ hybridization studies in human cancer tissue, a range of components involved in proteolysis appear to be expressed by stromal cells rather than cancer cells. We have now used laser capture microdissection and real-time PCR to quantify the mRNA expression of components of matrix-degrading proteolytic systems in cancer and stromal areas of mouse mammary tumors genetically induced by the polyoma virus middle T (PyMT) antigen. We examined the mRNA levels of urokinase plasminogen activator, plasminogen activator inhibitor 1 and the matrix metalloproteases MMP-2, -3, -11, -13 and -14, and found that all these seven genes are predominantly expressed by stromal cells. Our results were qualitatively supported by in situ hybridization analysis of the expression of mRNAs for MMP-2, -3 and -13 in the PyMT tumors. Statistical analyses indicated that the quantitative expression patterns observed in cancer and stromal cells isolated from individual tumors from different PyMT mice are quite reproducible. The methodology described in this study provides excellent tools to study the possible interactions between cancer and stromal cells during the development of breast cancer, and the results suggest that stromal cells are involved in carcinogenesis and tumor progression, which may have important implications for the biology and therapy of cancer.