Maspin, a serpin with tumor-suppressing activity in human mammary epithelial cells

Evidence for a direct interaction between the tumor suppressor serpin, maspin, and types I and III collagen

Maspin (mammary serine protease inhibitor) was originally identified as a tumor suppressor protein in human breast epithelial cells and is a member of the serine proteases inhibitor (serpin) superfamily. It inhibits tumor cell motility and angiogenesis, and although predominantly cytoplasmic, it is also localized to the cell surface. In this study we have investigated the use of the yeast two-hybrid interaction trap to identify novel maspin targets. A target human fibroblast cDNA library was screened, and the alpha-2 chain of type I collagen was identified as a potential interactant. Binding studies with isolated proteins showed interaction between recombinant maspin and types I and III collagen but not other collagen subtypes, a profile strikingly similar to mouse pigment epithelium-derived factor (caspin), which is similarly down-regulated in murine adenocarcinoma tumors and is a potent inhibitor of angiogenesis. Kinetic analysis using an IAsys resonant mirror biosensor determined the dissociation constant of maspin for collagen type I to be 0.63 microm. Further two-hybrid interactions with maspin truncation constructs suggest that collagen binding is localized to amino acids 84-112 of maspin, which aligns with the collagen-binding region of colligin. A direct interaction between exogenous or cell surface maspin and extracellular matrix collagen may contribute to a cell adhesion role in the prevention of tumor cell migration and angiogenesis.

Expression of maspin in pancreatic neoplasms: application of maspin immunohistochemistry to the differential diagnosis

Maspin is a unique member of the serpin family, which inhibits tumor invasion and metastasis of the human breast and prostate cancers. Immunohistochemical evaluation of the maspin expression in pancreatic neoplasms has never been performed. The authors examined the expression of maspin in various pancreatic neoplasms to investigate its usefulness as an adjunct diagnostic marker. Formalin-fixed, paraffin-embedded tissue sections from 107 pancreatic neoplasms were immunostained with anti-maspin antibody using an EnVision+ System. Maspin was expressed in all ductal adenocarcinomas, of which 78.9% (30/38) were high expressors and 21.1% (8/38) were low expressors. All 13 intraductal papillary mucinous tumors and 11 of the 13 mucinous cystic tumors reacted to maspin with stronger expressions in carcinomatous lesions. In contrast, acinar cell carcinoma, pancreatic endocrine tumors, solid-pseudopapillary tumors, and serous cystadenomas demonstrated no maspin expression. In addition, nonneoplastic pancreatic parenchyma and chronic pancreatitis lacked expression. The current study suggests that maspin may be of importance in the pathobiology of pancreatic neoplasms with epithelial origin, especially pancreatic tumors that are composed of mucin-producing cells. It may be useful in separating ductal adenocarcinoma from acinar cell carcinoma, pancreatic endocrine tumor, solid-pseudopapillary tumor, and chronic pancreatitis, especially in needle biopsy specimens.

Analysis of mechanisms underlying BRMS1 suppression of metastasis

Introduction of normal, neomycin-tagged human chromosome 11 (neo11) reduces the metastatic capacity of MDA-MB-435 human breast carcinoma cells by 70-90% without affecting tumorigenicity. Differential display comparing MDA-MB-435 and neo11/435 led to the discovery of a human breast carcinoma metastasis suppressor gene, BRMS1, which maps to chromosome 11q13.1-q13.2. Stable transfectants of MDA-MB-435 and MDA-MB-231 breast carcinoma cells with BRMS1 cDNA still form progressively growing, locally invasive tumors when injected in mammary fat pads of athymic mice but exhibit significantly lower metastatic potential (50-90% inhibition) to lungs and regional lymph nodes. To begin elucidating the mechanism(s) of action, we measured the ability of BRMS1 to perturb individual steps of the metastatic cascade modeled in vitro. Consistent differences were not observed for adhesion to extracellular matrix components (laminin, fibronectin, type IV collagen, type I collagen, Matrigel); growth rates in vitro or in vivo; expression of matrix metalloproteinases, heparanase, or invasion. Likewise. BRMS1 expression did not up regulate expression of other metastasis suppressors, such as NM23, Kai1, KiSS1 or E-cadherin. Motility of BRMS1 transfectants was modestly inhibited (30-60%) compared to parental and vector-only transfectants. Ability to grow in soft agar was also decreased in MDA-MB-435 cells by 80-89%, but the decrease for MDA-MB-231 was less (13-15% reduction). Also, transfection and re-expression of BRMS1 restored the ability of human breast carcinoma cells to form functional homotypic gap junctions. Collectively, these data suggest that BRMS1 suppresses metastasis of human breast carcinoma by complex, atypical mechanisms.

The importance of being a myoepithelial cell

The mammary myoepithelial cell was named the 'Cinderella of mammary cell biology' in light of the earlier focus on the luminal cell. Mammary myoepithelial cells have recently been described as 'natural tumour suppressors'. We now need to understand more about their origin and to reconsider their place in the complex process of mammary morphogenesis. In the present review, we discuss the lineage segregation of mammary myoepithelial cells and their functions in mammary gland development. These functions include their effects on luminal cell growth and differentiation, their key role in the establishment of the polarised mammary epithelial bilayer and the control of stromal invasion in breast cancer.

Expression of the granzyme B inhibitor, protease inhibitor 9, by tumor cells in patients with non-Hodgkin and Hodgkin lymphoma: a novel protective mechanism for tumor cells to circumvent the immune system?

In tumor cells, the serine protease granzyme B is the primary mediator of apoptosis induced by cytotoxic T lymphocytes (CTLs)/natural killer (NK) cells. The human intracellular serpin proteinase inhibitor 9 (PI9) is the only known human protein able to inhibit the proteolytic activity of granzyme B. When present in the cytoplasm of T lymphocytes, PI9 is thought to protect CTLs against apoptosis induced by their own misdirected granzyme B. Based on the speculation that tumors may also express PI9 to escape CTL/NK cell surveillance, immunohistochemical studies on the expression of PI9 in various lymphomas were performed. Ninety-two cases of T-cell non-Hodgkin lymphoma (NHL), 75 cases of B-cell NHL, and 57 cases of Hodgkin lymphomas were stained with a PI9-specific monoclonal antibody. In T-cell NHL, highest PI9 expression was found in the extranodal T-cell NHL. In nearly 90% of enteropathy-type T-cell NHLs and 80% of NK/T-cell, nasal-type lymphomas, the majority of the tumor cells expressed PI9. In nodal T-anaplastic large cell lymphomas and peripheral T-cell lymphomas (not otherwise specified), PI9 expression occurred less frequently. In B-cell NHL, PI9 expression was associated with high-grade malignancy; 43% of diffuse large B-cell lymphomas showed PI9(+) tumor cells. Finally, PI9 expression was also found in 10% of Hodgkin lymphomas. This is the first report describing the expression of the granzyme B inhibitor PI9 in human neoplastic cells in vivo. Expression of this inhibitor is yet another mechanism used by tumor cells to escape their elimination by cytotoxic lymphocytes.

Normal and tumor-derived myoepithelial cells differ in their ability to interact with luminal breast epithelial cells for polarity and basement membrane deposition

The signals that determine the correct polarity of breast epithelial structures in vivo are not understood. We have shown previously that luminal epithelial cells can be polarized when cultured within a reconstituted basement membrane gel. We reasoned that such cues in vivo may be given by myoepithelial cells. Accordingly, we used an assay where luminal epithelial cells are incorrectly polarized to test this hypothesis. We show that culturing human primary luminal epithelial cells within collagen-I gels leads to formation of structures with no lumina and with reverse polarity as judged by dual stainings for sialomucin, epithelial specific antigen or occludin. No basement membrane is deposited, and β4-integrin staining is negative. Addition of purified human myoepithelial cells isolated from normal glands corrects the inverse polarity, and leads to formation of double-layered acini with central lumina. Among the laminins present in the human breast basement membrane (laminin-1, -5 and -10/11), laminin-1 was unique in its ability to substitute for myoepithelial cells in polarity reversal.

Myoepithelial cells were purified also from four different breast cancer sources including a biphasic cell line. Three out of four samples either totally lacked the ability to interact with luminal epithelial cells, or conveyed only correction of polarity in a fraction of acini. This behavior was directly related to the ability of the tumor myoepithelial cells to produce α-1 chain of laminin. In vivo, breast carcinomas were either negative for laminin-1 (7/12 biopsies) or showed a focal, fragmented deposition of a less intensely stained basement membrane (5/12 biopsies). Dual staining with myoepithelial markers revealed that tumor-associated myoepithelial cells were either negative or weakly positive for expression of laminin-1, establishing a strong correlation between loss of laminin-1 and breast cancer. We conclude that the double-layered breast acinus may be recapitulated in culture and that one reason for the ability of myoepithelial cells to induce polarity is because they are the only source of laminin-1 in the breast in vivo. A further conclusion is that a majority of tumor-derived/-associated myoepithelial cells are deficient in their ability to impart polarity because they have lost their ability to synthesize sufficient or functional laminin-1. These results have important implications for the role of myoepithelial cells in maintenance of polarity in normal breast and how they may function as structural tumor suppressors.

Maspin is a tumour suppressor that inhibits breast cancer tumour metastasis in vivo

Maspin is a member of the serpin family of serine proteases and functions as a tumour suppressor. A study using a new syngeneic mouse model for breast cancer suggests that maspin can inhibit metastasis in vivo.

Maspin expression in stage I and II oral tongue squamous cell carcinoma

BACKGROUND

A relatively high failure rate in the therapy of patients with early oral tongue squamous cell carcinomas (SCCs) is evidenced by untreated clinically negative neck lymph node metastasis. It is important to predict the malignant potential of oral tongue SCC in stage I and II patients, because the development of lymph node metastasis directly affects the prognosis of the patients.

METHODS

We evaluated maspin expression immunohistochemically in patients with stage I and II oral tongue SCCs and determined whether the expression level may be a useful factor in predicting metastatic potential and prognosis of these SCCs.

RESULTS

Clinical follow-up data showed a longer disease-free interval and overall survival periods for tumors immunohistochemically positive for maspin than for tumors negative for maspin, with the difference in disease-free interval being statistically significant (p =.01). The absence of maspin expression was found more frequently in cases of subsequent cervical lymph node metastasis than in cases without metastasis (p =.03).

CONCLUSIONS

Decreased maspin expression may be a significant factor associated with the metastatic potential of stage I and II oral tongue SCCs.

A novel function of tissue factor pathway inhibitor-2 (TFPI-2) in human glioma invasion

Human tissue factor pathway inhibitor-2 (TFPI-2) is a Kunitz-type serine protease inhibitor that inhibits plasmin, trypsin, chymotrypsin, cathepsin G, and plasma kallikrein but not urokinase-type plasminogen activator, tissue plasminogen activator, or thrombin. Preliminary findings in our laboratory suggested that the expression of TFPI-2 is downregulated or lost during tumor progression in human gliomas. To investigate the role of TFPI-2 in the invasiveness of brain tumors, we stably transfected the human high-grade glioma cell line SNB19 and the human low-grade glioma cell line Hs683 with a vector capable of expressing a transcript complementary to the full-length TFPI-2 mRNA in either sense (0.7 kb) or antisense (1 kb) orientations. Parental cells and stably transfected cell lines were analysed for TFPI-2 protein by Western blotting and for TFPI-2 mRNA by Northern blotting. The levels of TFPI-2 protein and mRNA were higher in the sense clones (SNB19) and decreased in the antisense (Hs683) clones than in the corresponding parental and vector controls. In spheroid and matrigel invasion assays, the SNB19 parental cells were highly invasive, but the sense-transfected SNB-19 clones were much less invasive; the antisense-transfected Hs683 clones were more invasive than their parental and vector controls. After intracerebral injection in mice, the sense-transfected SNB19 clones were less able to form tumors than were their parental and vector controls, and the antisense-Hs683 clones but not the parental or vector controls formed small tumors. This is the first study to demonstrate that down- or upregulation of TFPI-2 plays a significant role in the invasive behavior of human gliomas.

Reverse-transcriptase polymerase chain reaction of the maspin gene in the detection of bone marrow breast carcinoma cell contamination

BACKGROUND

Maspin is a molecular marker used for the detection of contaminating breast carcinoma (BC) cells in peripheral blood and lymph nodes. However, its specificity has been questioned recently. The objective of this study was to verify the specificity of this marker and to determine the incidence of positive bone marrow results in patients with BC who are eligible for high-dose chemotherapy (HDT) both in early and advanced disease stages and before and after treatment.

METHODS

Bone marrow specimens from 41 patients with BC as well as from 35 normal volunteers and 17 patients with hematologic tumors were examined for maspin transcript expression by a modified nested reverse transcriptase-polymerase chain reaction technique.

RESULTS

Maspin transcript was found in all normal and neoplastic breast tissues and in none of the 35 normal bone marrow specimens (specificity, 100%; 95% confidence interval, 90-100%). However, the transcript was found in 40% of the bone marrow samples from patients with hematologic malignancies. Thus, this marker appears very specific for discriminating between normal controls and patients with BC, but it cannot be considered disease specific. Among patients with BC, bone marrow was positive for the maspin transcript in 32% of patients with early-stage disease and in 75% of patients with metastatic disease before chemotherapy. After treatment, in 75% of patients with early-stage disease and in 50% of patients with metastatic disease, the bone marrow results became maspin negative.

CONCLUSIONS

On the basis of the current data, although it is not disease specific, maspin is a reliable marker for detecting bone marrow molecular disease in patients with BC and should be considered for prospective studies as a prognostic indicator and as an assay for monitoring residual disease.

Maspin expression inversely correlates with breast tumor progression in MMTV/TGF-alpha transgenic mouse model

Maspin is a novel serine protease inhibitor (serpin) with tumor suppressive activity. To date, despite the mounting evidence implicating the potential diagnostic/prognostic and therapeutic value of maspin in breast and prostate carcinoma, the lack of a suitable animal model hampers the in vivo investigation on the role of maspin at different stages of tumor progression. In this study, we used MMTV/TGF-alpha transgenic mouse model to study the expression profile of maspin in mammary tumor progression. Histopathological examinations of MMTV/TGF-alpha transgenic mice revealed TGF-alpha expression leading to hyperproliferation, hyperplasia, and occasional carcinoma in mammary gland. Interestingly, when MMTV/TGF-alpha transgenic mice were breed to homozygocity, they also developed characteristic skin papillomas. Immunohistochemistry analysis of maspin expression in the breast tissues of TGF-alpha transgenic mice showed a direct correlation between down-regulation of maspin expression and tumor progression. The loss of maspin expression was concomitant with the critical transition from carcinoma in situ to invasive carcinoma. Subsequent in-situ hybridization analyses suggest that the down-regulation of maspin expression is primarily a transcriptional event. This data is consistent with the tumor suppressive role of maspin. Furthermore, our data suggests that MMTV/TGF-alpha transgenic mouse model is advantageous for in vivo evaluation of both the expression and the biological function of maspin during the slow multi-stage carcinogenesis of mammary gland.

Decline in the expression of the serine proteinase inhibitor maspin is associated with tumour progression in ductal carcinomas of the breast

Maspin is an inhibitor of serine proteinases with tumour suppressor activity. Its expression appears to be reduced in advanced stages of breast cancer. A large series of archival breast tissue specimens has been examined, including normal glands (n=7), fibrocystic change (n=22), ductal carcinoma in situ (DCIS, n=12), infiltrating carcinomas (n=128) and their lymph node metastases (n=65), using a specific monoclonal antibody. Myoepithelium invariably showed strong maspin expression. In epithelial cells, the strongest expression was found in normal breast and fibrocystic change. A significant stepwise decrease in maspin expression (p<0.0001) occurred in the sequence DCIS - invasive cancer - lymph node metastasis. However, a subset of infiltrating carcinomas showed strong maspin expression, significantly associated with a lower rate of lymph node metastasis at the time of diagnosis (p<0.01). This was independent of tumour size and grade. The in vivo observations presented here are in keeping with data obtained in prior in vitro experiments. Maspin emerges as an indicator of tumour progression and metastatic potential, and might be exploited to predict breast cancer prognosis. According to in vitro data, its tumour suppressor activity is likely to involve both the modulation of cell motility/invasiveness and the inhibition of angiogenesis.

Putting tumours in context

The interactions between cancer cells and their micro- and macroenvironment create a context that promotes tumour growth and protects it from immune attack. The functional association of cancer cells with their surrounding tissues forms a new 'organ' that changes as malignancy progresses. Investigation of this process might provide new insights into the mechanisms of tumorigenesis and could also lead to new therapeutic targets.

Association of maspin expression with the malignancy grade and tumor vascularization in breast cancer tissues

Maspin belongs to a tumor suppressing protein which is usually expressed highly in myoepithelial cells, and is significantly downregulated in breast cancer cells. We focused on identifying the correlation between maspin expression and the clinicopathological features of human breast cancer tissues using immunohistochemistry. There was a significant correlation in that maspin-positive tumor specimens showed a low pathological grade of malignancy, such as a lower infiltration of the tumor into the surrounding tissue and a downregulation of c-erbB2 expression. Moreover, maspin-positive cases showed a significant decrease in tumor vessels positively stained with anti-factor VIII-related antigen antibody. These results suggest that maspin production in myoepithelial cells could downregulate the malignant phenotype of breast cancer.

Expression of the p53 and Maspin protein in primary prostate cancer: correlation with clinical features

The serine protease inhibitor Maspin has been reported to inhibit the invasiveness and motility of prostate cancer tumor cells. Additionally, a p53-dependent regulatory pathway of Maspin in prostate cancer cell lines has been indicated. The first aim of our study was to determine the prognostic value of Maspin protein expression for the recurrence-free survival of patients undergoing radical prostatectomy for the treatment of clinically localized prostate cancer. Secondly, Maspin expression was correlated to p53 protein expression in order to gain additional information on a possible and previously suggested regulatory influence of the wild-type p53 protein on the Maspin protein expression. Tumor specimens obtained from 84 patients undergoing radical prostatectomy for localized prostate cancer were investigated for the expression of the Maspin and p53 protein by an immunohistochemic approach. Maspin protein expression was correlated with further patients' and tumor characteristics such as tumor stage, histologic grading, regional lymph node status, p53 protein expression and recurrence-free survival of the patients following radical prostatectomy. After a median follow-up of 64 months (24-197 months), 23 of 40 patients (58%) with a negative or decreased Maspin expression (group 1) developed local recurrence or systemic tumor progression in contrast to 8 of 44 patients (18%) with a retained expression of the Maspin protein (group 2) (p = 0.02; log-rank test). The median recurrence-free survival following radical prostatectomy was 26 months (12-37 months) for group 1 patients and 41 months (5-134 months) for patients from group 2 (p = 0.04). A positive immunohistochemic staining reaction for the p53 protein was significantly correlated with a decreased expression of the Maspin protein (p = 0.015; Spearman correlation coefficient). Additionally, loss of Maspin protein expression was correlated to higher tumor stages (p = 0.002) and an increasing histologic dedifferentiation (p = 0.03). This is the first study to indicate that Maspin protein possibly functions as a clinically relevant inhibitor of tumor progression, preventing the local invasiveness and further systemic progression of prostate cancer. Our investigation delivers first hints for a p53-dependent regulatory pathway of the Maspin protein in human prostate cancer.

Chromosomal imbalances in gastric and esophageal adenocarcinoma: specific comparative genomic hybridization-detected abnormalities segregate with junctional adenocarcinomas

The incidence of adenocarcinoma arising at the esophagogastric junction (EGJ) is increasing at a rate greater than that for any other form of solid malignancy. Commensurate with this, the incidence of histologically similar tumors arising in the gastric body and antral mucosa is declining. The increased incidence of the proximal group of tumors may reflect, in part, the higher prevalence of Barrett esophagus. These epidemiological features suggest that histologically similar tumors arising at the EGJ and from the distal stomach are different, which may be reflected in the genetic abnormalities that characterize the two groups of tumors. The purpose of this study was to screen genomic DNA from adenocarcinomas of the esophagus and stomach for regions of chromosomal imbalance, using comparative genomic hybridization to determine whether tumors at the EGJ (junctional tumors) have a different profile compared with tumors of the distal stomach. Tumor samples were derived from a series of 48 gastroesophageal adenocarcinomas (20 junctional and 28 distal) that were acquired prospectively from patients undergoing esophagogastrectomy. These tumors are characterized by several regions of chromosomal imbalance with no obvious correlation between most regions of abnormal copy number and tumor type. However, our study shows for the first time cytogenetic abnormalities (5p+ and 18q-) that identify statistically significant differences (P < 0.02 and < 0.05, respectively) between junctional and distal gastric tumors. These differences are gain of 5p (55% [11/20] of junctional tumors vs. 21% [6/28] of distal gastric tumors) and loss of 18q (25% [5/20] cases of junctional tumors vs. 4% [1/28] of distal tumors) segregating with tumors of the EGJ. These abnormalities may distinguish distinct tumor subtypes that are recognized in epidemiological and clinical studies but that are otherwise histologically identical.

Microvillar cell surface as a natural defense system against xenobiotics: a new interpretation of multidrug resistance

The phenomenon of multidrug resistance (MDR) is reinterpreted on the basis of the recently proposed concept of microvillar signaling. According to this notion, substrate and ion fluxes across the surface of differentiated cells occur via transporters and ion channels that reside in membrane domains at the tips of microvilli (MV). The flux rates are regulated by the actin-based cytoskeletal core structure of MV, acting as a diffusion barrier between the microvillar tip compartment and the cytoplasm. The expression of this diffusion barrier system is a novel aspect of cell differentiation and represents a functional component of the natural defense system of epithelial cells against environmental hazardous ions and lipophilic compounds. Because of the specific organization of epithelial Ca(2+) signaling and the secretion, lipophilic compounds associated with the plasma membrane are transferred from the basal to the apical cell surface by a lipid flow mechanism. Drug release from the apical pole occurs by either direct secretion from the cell surface or metabolization by the microvillar cytochrome P-450 system and efflux of the metabolites and conjugation products through the large multifunctional anion channels localized in apical MV. The natural microvillar defense system also provides a mechanistic basis of acquired MDR in tumor cells. The microvillar surface organization is lost in rapidly growing cells such as tumor or embryonic cells but is restored during exposure of tumor cells to cytotoxins by induction of a prolonged G(0)/G(1) resting phase.

Nucleocytoplasmic distribution of the ovalbumin serpin PI-9 requires a nonconventional nuclear import pathway and the export factor Crm1

Proteinase inhibitor 9 (PI-9) is a human serpin present in the cytoplasm of cytotoxic lymphocytes and epithelial cells. It inhibits the cytotoxic lymphocyte granule proteinase granzyme B (graB) and is thought to protect cytotoxic lymphocytes and bystander cells from graB-mediated apoptosis. Following uptake into cells, graB promotes DNA degradation, rapidly translocating to the nucleus, where it binds a nuclear component. PI-9 should therefore be found in cytotoxic lymphocyte and bystander cell nuclei to ensure complete protection against graB. Here we demonstrate by microscopy and subcellular fractionation experiments that PI-9 is present in the nuclei of human cytotoxic cells, endothelial cells, and epithelial cells. We also show that the related serpins, PI-6, monocyte neutrophil elastase inhibitor (MNEI), PI-8, plasminogen activator inhibitor 2 (PAI-2), and the viral serpin CrmA exhibit similar nucleocytoplasmic distributions. Because these serpins lack classical nuclear localization signals and are small enough to diffuse through nuclear pores, we investigated whether import occurs actively or passively. Large (approximately 70 kDa) chimeric proteins comprising PI-9, PI-6, PI-8, MNEI, or PAI-2 fused to green fluorescent protein (GFP) show similar nucleocytoplasmic distributions to the parent proteins, indicating that nuclear import is active. By contrast, CrmA-GFP is excluded from nuclei, indicating that CrmA is not actively imported. In vitro nuclear transport assays show that PI-9 accumulates at a rate above that of passive diffusion, that it requires cytosolic factors but not ATP, and that it does not bind an intranuclear component. Furthermore, PI-9 is exported from nuclei via a leptomycin B-sensitive pathway, implying involvement of the export factor Crm1p. We conclude that the nucleocytoplasmic distribution of PI-9 and related serpins involves a nonconventional nuclear import pathway and Crm1p.

SCCA1 expression in T-lymphocytes peripheral to cancer cells is associated with the elevation of serum SCC antigen in squamous cell carcinoma of the tongue

Squamous cell carcinoma (SCC) antigen has been used for the management of SCC arising in various cites including head and neck region. However, the true mechanism of the elevation of this protein in the serum of patients with SCC is still unknown. SCC antigen belongs to the superfamily of serine protease inhibitors. Recently, molecular studies show that serum SCC antigen is transcribed by two nearly identical genes (SCCA1 and SCCA2), and is mainly produced by SCCA1. The objective of this study is to clarify the mechanism of the elevation of SCC antigen in oral tongue SCC patients and to identify cells histologically, which are responsible for serum SCC antigen production. In this study, we examined SCCA1 expression in a series of four head and neck SCC (HNSCC) cell lines, and found that all expressed equal to low SCCA1 protein as compared with the normal human oral keratinocyte. Using the double immunohistochemical technique to examine the expression pattern of SCCA1 in 86 cases of oral tongue squamous cell carcinoma, SCCA1 immunostaining was observed in the cytoplasm of cancer cells and T-lymphocytes peripheral to cancer cells. We also compared the clinicopathological features including serum SCC antigen level of the oral tongue SCC cases with the immunohistochemical SCCA1 expression pattern, and found that elevated serum SCC antigen level was significantly correlated with SCCA1 expression not in cancer cells, but in T-lymphocytes peripheral to cancer cells. These results suggest that T-lymphocytes peripheral to cancer cells may be responsible for serum SCC antigen production in HNSCC patients.

Down regulation of the tumor suppressor gene maspin in breast carcinoma is associated with a higher risk of distant metastasis

BACKGROUND

Maspin (mammary serpin) is a relatively novel serine protease inhibitor with tumor suppressing function in breast cancer. Maspin expression was found in normal breast epithelial cells, but was decreased during tumor progression. Only a few systematic analyses of this phenomenon have been undertaken so far. In this study we developed specific nested reverse transcription polymerase chain reaction (RT-PCR) conditions for the detection of maspin expression in human breast carcinoma and assessed maspin's association with the clinical behavior of primary breast cancers.

METHODS

Tumor specimens obtained from 45 primary breast cancer patients were analyzed for maspin expression by a nested RT-PCR assay. Recurrence free survival was evaluated and correlated to maspin expression.

RESULTS

The maspin transcript was detected in 29 (64%) breast cancer specimens whereas no expression was found in 16 (36%) cancer specimens. This expression was unrelated to any of the established prognostic factors. However, 6 out of 8 patients who developed distant metastasis (lymph nodes, lung, liver, bone, pleura) within 3 yr after their initial diagnosis showed no maspin expression of the primary breast cancer (p < 0.05).

CONCLUSIONS

The lack of maspin expression in breast cancer seems to be associated with a short disease free survival and supports maspin's function as an indicator of tumor aggressiveness and metastatic potential. Nested RT-PCR is a sensitive method to determine maspin expression in human breast cancer tissue.

Structure and properties of ovalbumin

Ovalbumin is a protein of unknown function found in large quantities in avian egg-white. Surprisingly, ovalbumin belongs to the serpin family although it lacks any protease inhibitory activity. We review here what is known about the amino acid sequence, post-translational modifications and tertiary structure of ovalbumin. The properties of ovalbumin are discussed in relation to their possible functional significance. These include reasons for failure of ovalbumin to undergo a typical serpin conformational change involving the reactive centre loop, which explains why ovalbumin is not a protease inhibitor, and also the natural conversion of ovalbumin to the more stable "S" form.

Proteomic dissection of dome formation in a mammary cell line: role of tropomyosin-5b and maspin

In this work we extended the study of genes controlling the formation of specific differentiation structures called "domes" formed by the rat mammary adenocarcinoma cell line LA7 under the influence of DMSO. We have reported previously that an interferon-inducible gene, rat-8, and the beta-subunit of the epithelial sodium channel (ENaC) play a fundamental role in this process. Now, we used a proteomic approach to identify proteins differentially expressed either in DMSO-induced LA7 or in 106A10 cells. Two differentially expressed proteins were investigated. The first, tropomyosin-5b, strongly expressed in DMSO-induced LA7 cells, is needed for dome formation because its synthesis inhibition by the antisense RNA technology abolished domes. The second protein, maspin, strongly expressed in the uninduced 106A10 cell line, inhibits dome formation because 106A10 cells, transfected with rat8 cDNA (the function of which is required for the organization of these structures), acquired the ability to develop domes when cultured in presence of an antimaspin antibody. Dome formation in these cultures are accompanied by ENaC beta-subunit expression in the absence of DMSO. Therefore, dome formation requires the expression of tropomyosin-5b, in addition to the ENaC beta-subunit and the rat8 proteins, and is under the negative control of maspin.

Down-regulation in multiple human cancers of a novel gene, DMHC, from 17q25.1 that encodes an integral membrane protein

Frequent observations of allelic loss in chromosomal band 17q25.1 in a variety of human cancers have suggested that one or more tumor suppressor genes are present in that region. Moreover, a genetic locus for hereditary focal non-epidermolytic palmoplantar keratoderma, a condition associated with cancer of the esophagus (TOC; Tylosis with Oesophageal Cancer), lies in the same region. We screened cell lines derived from a variety of human cancers by reverse transcription-polymerase chain reaction (RT-PCR) to detect alterations in expression of genes within the region in question, by examining expressed sequence tags located there. These experiments identified an 1834-bp full-length cDNA encoding a novel, 441-amino acid integral membrane protein with seven putative transmembrane domains. This gene showed loss or extreme decrease of expression in 6 of 10 uterine cancer-cell lines, 2 of 11 hepatic cell carcinoma-cell lines, 2 of 7 lung cancer-cell lines, 1 of 6 gastric cancer-cell lines, and 1 of 10 breast cancer-cell lines. (We named it DMHC ("down-regulated in multiple human cancers").) Our results suggest that loss of expression of DMHC at 17q25.1 may play an important role in development of variety of human cancers.

Conformational properties of serine proteinase inhibitors (serpins) confer multiple pathophysiological roles

Serine proteinase inhibitors (Serpins) are irreversible suicide inhibitors of proteases that regulate diverse physiological processes such as coagulation, fibrinolysis, complement activation, angiogenesis, apoptosis, inflammation, neoplasia and viral pathogenesis. The molecular structure and physical properties of serpins permit these proteins to adopt a number of variant conformations under physiological conditions including the native inhibitory form and several inactive, non-inhibitory forms, such as complexes with protease or other ligands, cleaved, polymerised and oxidised. Alterations of a serpin which affect its structure and/or secretion and thus reduce its functional levels may result in pathology. Serpin dysfunction has been implicated in thrombosis, emphysema, liver cirrhosis, immune hypersensitivity and mental disorders. The loss of inhibitory activity of serpins necessarily results in an imbalance between proteases and their inhibitors, but it may also have other physiological effects through the generation of abnormal concentrations of modified, non-inhibitory forms of serpins. Although these forms of inhibitory serpins are detected in tissues and fluids recovered from inflammatory sites, the important questions of which conditions result in generation of different molecular forms of serpins, what biological function these forms have, and which of them are directly linked to pathologies and/or may be useful markers for characterisation of disease states, remain to be answered. Elucidation of the biological activities of non-inhibitory forms of serpins may provide useful insights into the pathogenesis of diseases and suggest new therapeutic strategies.

Maspin--a novel protease inhibitor with tumor-suppressing activity in breast cancer

Maspin (mammary serpin) is a novel serine protease inhibitor related to the serpin family with a tumor-suppressing function in breast cancer. Maspin was originally identified from normal mammary epithelium by subtractive hybridization and might function as a class II tumor-suppressor gene. Maspin's decreased expression with increased level of malignancy and its loss in metastatic cells is regulated at the transcriptional level. Cytosin methylation and heterochromatinization in the promoter region might account for this down-regulation of maspin. Transfection of tumor cells with maspin cDNA inhibits invasion and motility and decreases tumor growth and metastatic ability in nude mice. Maspin interacts with the p53 tumor-suppressor pathway and function as an inhibitor of angiogenesis in vitro and in vivo. The progressive loss of expression of maspin during tumor progression makes this new protein an interesting diagnostic and prognostic marker. The re-expression of maspin by pharmacological intervention potentially offers a promising approach as a therapeutic option in breast cancer therapy.

Detection of breast cancer cell contamination in leukapheresis product by real-time quantitative polymerase chain reaction

Identification of sensitive techniques for breast cancer cell detection might be relevant for high-dose chemotherapy programs with autologous stem cell transplantation. We investigated the feasibility of Maspin, Mammaglobin and c-ErbB-2 amplification by real-time quantitative polymerase chain reaction (RQ-PCR) for the detection of breast cancer cells in leukaphereses. Expression of the three markers was determined in primary breast cancers and cell lines. Peripheral blood (PB), bone marrow (BM), and leukapheresis samples from patients with malignancies other than breast cancer were used as controls. Sensitivity was evaluated by dilution of primary tumors and cell lines with mononuclear blood cells. We found expression of the three markers in all primary tumors and most cell lines. No blood specimen from control patients had the Maspin transcript, while only one was positive for Mammaglobin. Weak c-ErbB-2 expression was detectable in most PB, all BM and all leukapheresis samples from controls. We observed a low sensitivity of Maspin RQ-PCR and a sensitivity of Mammaglobin RQ-PCR up to one tumor cell in 10(6) mononuclear cells. One out of 18 leukaphereses from breast cancer patients screened for the presence of Mammaglobin mRNA was positive. We conclude that Mammaglobin RQ-PCR might be a useful tool for detection of leukapheresis contamination.

A human breast epithelial cell type with stem cell characteristics as target cells for carcinogenesis

Two types of human breast epithelial cells (HBEC) have been characterized. In contrast to Type II HBEC, which express basal epithelial cell phenotypes, Type I HBEC are deficient in gap junctional intercellular communication and are capable of anchorage-independent growth and of expressing luminal epithelial cell markers, estrogen receptors, and stem cell characteristics (i.e. the ability to differentiate into other cell types and to form budding/ductal organoids on Matrigel). A comparative study of these two types of cells has revealed a high susceptibility of Type I HBEC to immortalization by SV40 large T antigen, although both types of cells are equally capable of acquiring an extended life span (bypassing senescence) after transfection with SV40. The immortalization was accompanied by elevation of a low level of telomerase activity in the parental cells after mid-passage ( approximately 60 cumulative population doubling levels). Thus HBEC do have a low level of telomerase activity, and Type I HBEC with stem cell characteristics are more susceptible to telomerase activation and immortalization, a mechanism which might qualify them as target cells for breast carcinogenesis. The immortalized Type I HBEC can be converted to highly tumorigenic cells by further treatment with X rays (2 Gy x 2) and transfection with a mutated ERBB2 (also known as NEU) oncogene, resulting in the expression of p185(ERBB2) which is tyrosine phosphorylated.

The plasticity of human breast carcinoma cells is more than epithelial to mesenchymal conversion

The human breast comprises three lineages: the luminal epithelial lineage, the myoepithelial lineage, and the mesenchymal lineage. It has been widely accepted that human breast neoplasia pertains only to the luminal epithelial lineage. In recent years, however, evidence has accumulated that neoplastic breast epithelial cells may be substantially more plastic in their differentiation repertoire than previously anticipated. Thus, along with an increasing availability of markers for the myoepithelial lineage, at least a partial differentiation towards this lineage is being revealed frequently. It has also become clear that conversions towards the mesenchymal lineage actually occur, referred to as epithelial to mesenchymal transitions. Indeed, some of the so-called myofibroblasts surrounding the tumor may have an epithelial origin rather than a mesenchymal origin. Because myoepithelial cells, epithelial to mesenchymal transition-derived cells, genuine stromal cells and myofibroblasts share common markers, we now need to define a more ambitious set of markers to distinguish these cell types in the microenvironment of the tumors. This is necessary because the different microenvironments may confer different clinical outcomes. The aim of this commentary is to describe some of the inherent complexities in defining cellular phenotypes in the microenvironment of breast cancer and to expand wherever possible on the implications for tumor suppression and progression.

Reduced mammary tumor progression in WAP-TAg/WAP-maspin bitransgenic mice

Maspin is a unique serpin involved in the suppression of tumor growth and metastasis. To investigate whether increased levels of maspin protect against tumor progression in vivo, we established a transgenic model in which maspin is targeted to mammary epithelial cells by the Whey Acidic Protein (WAP) promoter for overexpression. We crossed these WAP-maspin transgenic mice with the WAP-TAg mouse model of tumor progression. Maspin overexpression increased the rate of apoptosis of both preneoplastic and carcinomatous mammary epithelial cells. Maspin reduced tumor growth through a combination of reduced angiogenesis and increased apoptosis. The number of pulmonary metastases was reduced in the presence of maspin overexpression. These data demonstrate that targeted overexpression of maspin can inhibit tumor progression in vivo, likely through a combination of increased apoptosis, decreased angiogenesis, and inhibition of tumor cell migration.

Endometrial angiogenesis

The endometrium is one of the few tissues in the adult where physiological angiogenesis occurs. Studies of endometrial angiogenesis are complicated by the continual changes in tissue growth and regression during the menstrual cycle, and differences between the two different zones of the endometrium--the functionalis and basalis. The mechanisms of angiogenesis in the endometrium may be different to those in solid tumours, requiring a re-evaluation of the relative importance of various angiogenesis promoters and inhibitors. None of the angiogenesis promoters or inhibitors have yet been demonstrated beyond doubt to have a biological role in endometrial angiogenesis in vivo. Thus, the mechanisms, timing and control of angiogenesis in the endometrium are far from being fully understood.

Phylogeny of the Serpin Superfamily: Implications of Patterns of Amino Acid Conservation for Structure and Function

We present a comprehensive alignment and phylogenetic analysis of the serpins, a superfamily of proteins with known members in higher animals, nematodes, insects, plants, and viruses. We analyze, compare, and classify 219 proteins representative of eight major and eight minor subfamilies, using a novel technique of consensus analysis. Patterns of sequence conservation characterize the family as a whole, with a clear relationship to the mechanism of function. Variations of these patterns within phylogenetically distinct groups can be correlated with the divergence of structure and function. The goals of this work are to provide a carefully curated alignment of serpin sequences, to describe patterns of conservation and divergence, and to derive a phylogenetic tree expressing the relationships among the members of this family. We extend earlier studies by Huber and Carrell as well as by Marshall, after whose publication the serpin family has grown functionally, taxonomically, and structurally. We used gene and protein sequence data, crystal structures, and chromosomal location where available. The results illuminate structure–function relationships in serpins, suggesting roles for conserved residues in the mechanism of conformational change. The phylogeny provides a rational evolutionary framework to classify serpins and enables identification of conserved amino acids. Patterns of conservation also provide an initial point of comparison for genes identified by the various genome projects. New homologs emerging from sequencing projects can either take their place within the current classification or, if necessary, extend it.

The necrotic gene in Drosophila corresponds to one of a cluster of three serpin transcripts mapping at 43A1.2

Mutants of the necrotic (nec) gene in Drosophila melanogaster die in the late pupal stage as pharate adults, or hatch as weak, but relatively normal-looking, flies. Adults develop black melanized spots on the body and leg joints, the abdomen swells with hemolymph, and flies die within 3 or 4 days of eclosion. The TOLL-mediated immune response to fungal infections is constitutively activated in nec mutants and pleiotropic phenotypes include melanization and cellular necrosis. These changes are consistent with activation of one or more proteolytic cascades. The nec gene corresponds to Spn43Ac, one of a cluster of three putative serine proteinase inhibitors at 43A1.2, on the right arm of chromosome 2. Although serpins have been implicated in the activation of many diverse pathways, lack of an individual serpin rarely causes a detectable phenotype. Absence of Spn43Ac, however, gives a clear phenotype, which will allow a mutational analysis of critical features of the molecular structure of serpins.

The serpin secreted by Brugia malayi microfilariae, Bm-SPN-2, elicits strong, but short-lived, immune responses in mice and humans

Understanding the basic immunology of an infectious disease requires insight into the pattern of T cell reactivity and specificity. Although lymphatic filariasis is a major tropical disease, the predominant T cell Ags of filarial species such as Brugia malayi are still undefined. We have now identified a prominent T cell Ag from B. malayi microfilariae (Mf) as Bm-SPN-2, a serpin secreted exclusively by this stage. Mf-infected mice mounted strong, but short-lived, Bm-SPN-2-specific Th1 responses, measured by in vitro production of IFN-gamma, but not IL-4 or IL-5, 14 days postinfection. By day 35, responsiveness to Bm-SPN-2 was lost despite enhanced reactivity to whole Mf extract. Single immunization with Mf extract also stimulated typical Th1 reactions to Bm-SPN-2, but IgG1 Ab responses dominated after repeated immunizations. Human patients displayed potent humoral responses to Bm-SPN-2 in both IgG1 and IgG4 subclasses. Thus, 100% (20 of 20) of the microfilaremic (MF(+)) patients bore IgG4 responses to Bm-SPN-2, while only 30% of endemic normal subjects were similarly positive. Following chemotherapy, Bm-SPN-2-specific Abs disappeared in 12 of 13 MF(+) patients, although the majority remained seropositive for whole parasite extract. PBMC from most, but not all, endemic subjects were induced to secrete IFN-gamma when stimulated with Bm-SPN-2. These findings demonstrate that Bm-SPN-2 is recognized by both murine and human T and B cells and indicate that their responses are under relatively stringent temporal control. This study also provides the first example of a stage-specific secreted molecule that acts as a major T cell Ag from filarial parasites and is a prime candidate for a serodiagnostic probe.

New molecular mediators in tumor angiogenesis

Angiogenesis is essential for tumor growth and progression. It has been demonstrated that tumor growth beyond a size 1 to 2 mm(3) requires the induction of new vessels. Angiogenesis is regulated by several endogenous stimulators and inhibitors of endothelial cell migration, proliferation and tube formation. Under physiological conditions these mediators of endothelial cell growth are in balance and vessel growth is limited. In fact, within the angiogenic balance endothelial cell turnover is sufficient to maintain a functional vascular wall but does not allow vessel growth. Tumor growth an progression has successfully been correlated to the serum concentration of angiogenic mediators. Furthermore, the vascular density of tumor tissues could be correlated to the clinical course of the disease in several tumor entities. Within the last years several new mediators of endothelial cell growth have been isolated e.g. angiopoietin 1, angiopoietin 2, midkine, pleiotropin, leptin and maspin. In this review we discuss the mechanisms leading to tumor angiogenesis and describe some of the newer mediators of endothelial cell stimulation and inhibition.

Tamoxifen enhances myoepithelial cell suppression of human breast carcinoma progression in vitro by two different effector mechanisms

Our previous studies have indicated that myoepithelial cells surrounding ductal and acinar epithelium of glandular organs, such as the breast, exert multiple paracrine suppressive effects on incipient and developing cancers that arise from this epithelium. Myoepithelial cells and derived cell lines (HMS 1-6) exert these effects through the secretion of a number of different effector molecules that exert anti-invasive, anti-proliferative, and anti-angiogenic activities. Since previous basic and clinical studies have examined the role of estrogen agonists and antagonists on human breast cancer cells and because issues of hormone replacement therapy (HRT) and tamoxifen chemoprevention are such timely issues in breast cancer, we wondered whether or not hormonal manipulations might affect myoepithelial cells in vitro as far as their paracrine suppressive activities on breast cancer were concerned. The present in vitro study demonstrates that treatment of myoepithelial cells with tamoxifen but not 17beta-estradiol increases both maspin secretion and invasion-blocking ability. Furthermore tamoxifen but not 17beta-estradiol increases inducible nitric oxide synthase (iNOS) expression and nitric oxide (NO) production by myoepithelial cells when they are co-cultured with conditioned media from or breast carcinoma cells directly. This increased myoepithelial NO exerts both autocrine and paracrine antiproliferative effects which can be blocked by inhibition of iNOS. 17beta-Estradiol, however, competes with all of these suppressive effects of tamoxifen suggesting that the mechanism of tamoxifen action is estrogen receptor mediated. Myoepithelial cells lack ER-alpha but express ER-beta. Tamoxifen, but not 17beta-estradiol, increases AP-1 CAT but not ERE-CAT activity. Again, 17beta-estradiol competes with the transcription-activating effects of tamoxifen. These experiments collectively suggest that the actions of tamoxifen on the increased secretion of maspin and increased production of NO by myoepithelial cells are mediated through ER-beta and the transcription-activation of an ER-dependent AP-1 response element.

The human myoepithelial cell displays a multifaceted anti-angiogenic phenotype

Human myoepithelial cells which surround ducts and acini of certain organs such as the breast form a natural border separating epithelial cells from stromal angiogenesis. Myoepithelial cell lines (HMS-1-6), derived from diverse benign myoepithelial tumors, all constitutively express high levels of active angiogenic inhibitors which include TIMP-1, thrombospondin-1 and soluble bFGF receptors but very low levels of angiogenic factors. These myoepithelial cell lines inhibit endothelial cell chemotaxis and proliferation. These myoepithelial cell lines sense hypoxia, respond to low O2 tension by increased HIF-1 alpha but with only a minimal increase in VEGF and iNOS steady state mRNA levels. Their corresponding xenografts (HMS-X-6X) grow very slowly compared to their non-myoepithelial carcinomatous counterparts and accumulate an abundant extracellular matrix devoid of angiogenesis but containing bound angiogenic inhibitors. These myoepithelial xenografts exhibit only minimal hypoxia but extensive necrosis in comparison to their non-myoepithelial xenograft counterparts. These former xenografts inhibit local and systemic tumor-induced angiogenesis and metastasis presumably from their matrix-bound and released circulating angiogenic inhibitors. These observations collectively support the hypothesis that the human myoepithelial cell (even when transformed) is a natural suppressor of angiogenesis. Oncogene (2000) 19, 3449 - 3459

High tumoral maspin expression is associated with improved survival of patients with oral squamous cell carcinoma

Maspin, a member of the serpin family of protease inhibitors, is known to have tumor-suppressor functions. However, the association between its expression level and survival has not been demonstrated in human cancer. Using the immunohistochemical technique to examine the expression levels of maspin in 44 cases of oral squamous cell carcinoma (SCC), we found that 66% of the cases expressed low to intermediate levels of maspin and 34% of the cases expressed high levels of maspin. We further examined maspin protein expression in a series of six SCC cell lines from the head and neck, and found that all but one expressed low or no maspin protein. We also compared the clinicopathological features of the oral SCC cases with the maspin expression level, and found that high maspin expression was associated with the absence of lymph node metastasis. More importantly, we showed that higher maspin expression was significantly associated with better rates of overall survival, suggesting that high maspin expression may be a favorable prognostic marker for oral SCC.

Detection of circulating tumor cells by reverse transcriptase polymerase chain reaction of maspin in patients with breast cancer undergoing conventional-dose chemotherapy

PURPOSE

To establish, in patients with breast cancer subjected to primary conventional chemotherapy and enrolled in a prospective study, the mobilizing effect of therapy on potentially neoplastic cells by means of a reverse transcriptase polymerase chain reaction (RT-PCR) assay for mRNA of maspin, a protein related to the serpin family of protease inhibitors.

PATIENTS AND METHODS

Peripheral-blood samples were collected from 30 patients with histologically proven breast cancer before and 4 and 8 days after conventional chemotherapy for three consecutive courses. A total of 216 samples were screened for the presence of maspin mRNA by RT-PCR.

RESULTS

Before therapy, all samples but one were negative. After chemotherapy, 11 patients (38%) had positive samples. No difference in the rate of positivity was observed between groups defined according to initial stage, type of chemotherapy, Ki-67-related proliferative activity, or CA 15.3 expression.

CONCLUSION

Our results confirm that RT-PCR for maspin mRNA is a sensitive assay for the study of circulating potentially neoplastic mammary cells in patients with breast cancer. Moreover, our findings indicate a marked effect of conventional-dose chemotherapy on the mobilization of these cells in breast tumors. In our series of patients, this phenomenon does not seem to be associated with other known risk factors. Finally, the data suggest, without proving, an association between the presence of circulating maspin positive cells and a higher risk of disease progression. If this association could be confirmed, then the assay could have prognostic significance. However, larger confirmatory studies are necessary.

Characterization of spontaneous metastasis in an aggressive breast carcinoma model using flow cytometry

Studies of metastasis can be accelerated and provide more mechanistic information using cell lines which reproducibly and aggressively metastasize, and which are accurately and easily detected in tissues at all stages of the metastatic process. Although reporter proteins such as green fluorescent protein (GFP) and beta-galactosidase have improved the tracking of tumor cells in vivo, their measurement has often been limited to visual observation and manual counting. In this study, we exploited the highly sensitive and objective quantitation provided by flow cytometry to characterize, in detail, the sequence of events associated with orthotopic metastasis in a highly aggressive mouse model. Following stable transfection of the MDA-MB-435 breast carcinoma cell line with GFP, we utilized an in vivo selection process to isolate a variant exhibiting increased primary tumor growth and metastasis. As few as one fluorescent tumor cell per 200,000 host cells could be accurately detected in dissociated tissues by flow cytometry, allowing us to demonstrate that metastatic cells migrate to the lungs of SCID mice very early after orthotopic implantation. Tumor burden in lungs increased in a smooth continuous manner, until death approximately eight weeks later. Levels of circulating tumor cells in blood were also detectable at an early timepoint, but remained relatively low throughout the course of secondary tumor development in the lungs. Surgical removal of the primary tumor at various times after inoculation significantly affected lung tumor burden, supporting the concept that circulating tumor cells in blood inefficiently initiate distal metastases. Furthermore, the continuing contribution to metastasis by the primary tumor was independent of tumor mass. The combined characteristics of enhanced orthotopic metastasis and quantitative detection in blood and tissues will make this a useful new model for the characterization of the multi-stage progression of cancer, and the preclinical evaluation of anti-neoplastic therapies.

Characterization of a human angiotensinogen cleaved in its reactive center loop by a proteolytic activity from Chinese hamster ovary cells

Angiotensinogen, the renin (E.C. 3.4.23.15) substrate, belongs to the serpins superfamily and has been classified as a noninhibitory serpin. Using mass spectroscopy, angiotensinogen purified from Chinese hamster ovary cell supernatant shows a broad spectrum. The absence of protease inhibitors throughout the purification leads to an angiotensinogen cleaved within the reactive center loop. This cleavage does not affect the Ang I generation because kinetic parameters are similar to the values of the full-length angiotensinogen. Although cleavage is complete, the cleaved angiotensinogen migrates after deglycosylation on SDS-polyacrylamide gel electrophoresis as a doublet differing by 4 kDa. To test whether the circulating angiotensinogen is cleaved in the reactive center loop, it was purified from a pool of human plasma and was shown to be uncleaved. Its migration was obviously slower than of cleaved angiotensinogen but also consisted of two bands pointing to a so far unexplained residual heterogeneity. We then compared the heat-induced polymerization of full-length- and reactive center loop-cleaved angiotensinogens. Both monomers were able to aggregate, revealing a particular behavior of angiotensinogen distinct from that of reactive center loop-cleaved serpins. Lacking the three-dimensional structure of angiotensinogen, we propose and discuss a structural model of the serpin fold within the renin substrate.

Epitope mapping of monoclonal antibodies directed to PAI-1 using PAI-1/PAI-2 chimera and PAI-1-derived synthetic peptides

Plasminogen activator inhibitor type-1 is a key regulatory protein of the fibrinolytic system that is involved in a variety of physiological and pathophysiological processes. A panel of 14 monoclonal antibodies directed against plasminogen activator inhibitor type-1 was analyzed regarding epitope specificity on plasminogen activator inhibitor type-1. For this purpose, chimera consisting of plasminogen activator inhibitor type-1 and another plasminogen activator inhibitor, plasminogen activator inhibitor type-2, with different portions of the respective wild-type proteins, were generated and plasminogen activator inhibitor type-1-derived 20-mer and 10-mer linear peptides were synthesized. Nine of the 14 monoclonal antibodies recognized an epitope located in the region between amino acid 76-188 of plasminogen activator inhibitor type-1, which encompasses the binding sites for vitronectin, heparin, and part of the fibrin binding region. Of these nine monoclonal antibodies, six reacted with a quadruple plasminogen activator inhibitor type-1 mutant (N152H, K156T, Q321L, M356I), and seven detected a plasminogen activator inhibitor type-1 deletion mutant (DeltaF111-H114). Two of the remaining five monoclonal antibodies recognized epitopes located between amino acid 209-227 and amino acid 352-371, respectively, while the other three antibodies reacted with wild-type plasminogen activator inhibitor type-1, only. Additional experiments revealed that two of the 14 mAbs neutralized and one monoclonal antibodies increased plasminogen activator inhibitor type-1 activity toward urokinase-type plasminogen activator, one of its target proteases.

AZU-1: a candidate breast tumor suppressor and biomarker for tumor progression

To identify genes misregulated in the final stages of breast carcinogenesis, we performed differential display to compare the gene expression patterns of the human tumorigenic mammary epithelial cells, HMT-3522-T4-2, with those of their immediate premalignant progenitors, HMT-3522-S2. We identified a novel gene, called anti-zuai-1 (AZU-1), that was abundantly expressed in non- and premalignant cells and tissues but was appreciably reduced in breast tumor cell types and in primary tumors. The AZU-1 gene encodes an acidic 571-amino-acid protein containing at least two structurally distinct domains with potential protein-binding functions: an N-terminal serine and proline-rich domain with a predicted immunoglobulin-like fold and a C-terminal coiled-coil domain. In HMT-3522 cells, the bulk of AZU-1 protein resided in a detergent-extractable cytoplasmic pool and was present at much lower levels in tumorigenic T4-2 cells than in their nonmalignant counterparts. Reversion of the tumorigenic phenotype of T4-2 cells, by means described previously, was accompanied by the up-regulation of AZU-1. In addition, reexpression of AZU-1 in T4-2 cells, using viral vectors, was sufficient to reduce their malignant phenotype substantially, both in culture and in vivo. These results indicate that AZU-1 is a candidate breast tumor suppressor that may exert its effects by promoting correct tissue morphogenesis.

v-Src suppresses SHPS-1 expression via the Ras-MAP kinase pathway to promote the oncogenic growth of cells

We investigated the effect of cell transformation by v-src on the expression and tyrosine phosphorylation of SHPS-1, a putative docking protein for SHP-1 and SHP-2. We found that transformation by v-src virtually inhibited the SHPS-1 expression at mRNA level. While nontransforming Src kinases including c-Src, nonmyristoylated forms of v-Src had no inhibitory effect on SHPS-1 expression, transforming Src kinases including wild-type v-Src and chimeric mutant of c-Src bearing v-Src SH3 substantially suppressed the SHPS-1 expression. In cells expressing temperature sensitive mutant of v-Src, suppression of the SHPS-1 expression was temperature-dependent. In contrast, tyrosine phosphorylation of SHPS-1 was rather activated in cells expressing c-Src or nonmyristoylated forms of v-Src. SHPS-1 expression in SR3Y1 was restored by treatment with herbimycin A, a potent inhibitor of tyrosine kinase, or by the expression of dominant negative form of Ras. Contrary, active form of Mekl markedly suppressed SHPS-1 expression. Finally, overexpression of SHPS-1 in SR3Y1 led to the drastic reduction of anchorage independent growth of the cells. Taken together, our results suggest that the suppression of SHPS-1 expression is a pivotal event for cell transformation by v-src, and the Ras-MAP kinase cascade plays a critical role in the suppression.

Epigenetic silencing of maspin gene expression in human breast cancers

Maspin is a tumor suppressor whose expression is lost in many advanced breast cancers. Maspin has been shown to inhibit cell motility, invasion and metastasis; however, its precise role in normal mammary epithelium remains to be elucidated. Although expression of maspin mRNA is low or absent in most human breast cancer cells, the maspin gene is rarely re-arranged or deleted. We hypothesized that aberrant cytosine methylation and chromatin condensation of the maspin promoter participates in the silencing of maspin expression during neoplastic progression. To test this hypothesis, we compared cultured normal human mammary epithelial cells (HMECs) to 9 cultured human breast cancer cell lines. HMECs expressed maspin mRNA and displayed a completely non-methylated maspin gene promoter with an open chromatin structure. In contrast, 7 of 9 breast cancer cell lines had no detectable maspin expression and 6 of these 7 maspin-negative breast cancer cell lines also displayed an aberrant pattern of cytosine methylation of the maspin promoter. Interestingly, the maspin promoter was completely methylated in maspin-negative normal peripheral blood lymphocytes. This indicates that the maspin promoter is not a functional CpG island and that cytosine methylation of this region may contribute to normal tissue-restricted gene expression. Chromatin accessibility studies with MCF-7 cells, which lack maspin expression and have a methylated maspin promoter, showed a closed chromatin structure compared with HMECs. Moreover, maspin gene expression could be re-activated in MCF-7 cells by treatment with 5-aza-2;-deoxycytidine, a DNA demethylating agent. Thus, aberrant cytosine methylation and heterochromatinization of the maspin promoter may silence maspin gene expression, thereby contributing to the progression of human mammary cancer.