5268

SERPINB5

PI5|maspin;serpin peptidase inhibitor, clade B (ovalbumin), member 5;SERPINB5;serpin peptidase inhibitor, clade B (ovalbumin), member 5

PI-5|peptidase inhibitor 5|protease inhibitor 5 (maspin)|serine (or cysteine) proteinase inhibitor, clade B (ovalbumin), member 5|serpin B5

18q21.33

protein-coding

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.

Maspin (mammary serpin) is an inhibitor of serine proteases with tumor suppressor activity in breast cancer. Maspin was originally identified by subtractive hybridization in normal breast epithelial cells, but its expression decreased during tumor progression. The loss of maspin gene expression with increasing malignancy is by transcriptional regulation. Maspin is known to be involved in invasion and metastasis, interact with the p53 tumor suppressor pathway, and act as an inhibitor of angiogenesis. The immunohistochemical analysis and reverse-transcription polymerase chain reaction of maspin in normal human breast tissue and breast carcinoma indicated a stepwise reduction of maspin expression during the progression from ductal carcinoma in situ to invasive carcinoma to lymph node metastasis. The lack of maspin expression in breast cancer seems to be associated with a short disease-free survival and supports maspins function as an indicator for tumor aggressiveness and metastatic potential. New studies on the gene regulation of maspin provide evidence for promising potential of possible re-expression of maspin in tumor cells. The function of maspin as a tumor suppressor gene involved in tumor invasion, metastasis, and angiogenesis may not be limited to breast cancer.

AIM: To investigate the effects of inhibiting factor of cell cycle regulation p57(kip2), retinoblastinoma protein (Rb protein) and proliferating cell nuclear antigen (PCNA) in the genesis and progression of human pancreatic cancer. METHODS: The expression of p57(kip2), Rb protein and PCNA in tumor tissues and adjacent tissues of 32 patients with pancreatic cancer was detected with SP immunohistochemical technique. RESULTS: p57(kip2) protein positive-expression rate in tumor tissues of pancreatic cancer was 46.9 %, which was lower than that in adjacent pancreatic tissues (75.0 %) (chi(2)=5.317, P<0.05), p57(kip2) protein positive-expression correlated significantly with tumor cell differentiation (well-differentiation versus moderate or low-differentiation, P<0.05) but did not correlate significantly with lymph node metastasis (lymph node metastasis versus non-lymph node metastasis, P>0.05); Rb gene protein positive-expression rate in tumor tissues was 50.0 %, which was also lower than that in adjacent pancreatic tissues (78.1 %) (chi(2)=5.497, P<0.05); PCNA positive-expression rate was 71.9 %, being higher than that in adjacent pancreatic tissues (43.8 %) (chi(2)=5.189, P<0.05), PCNA positive-expression also correlated significantly with tumor cell differentiation and lymph node metastasis (well-differentiation versus moderate or low- differentiation, lymph node metastasis versus non-lymph node metastasis, P<0.05). Rb protein positive-expression rate in the tumor tissues of p57(kip2) protein positive-expression group was 53.3 %; and Rb protein positive-expression rate in the tumor tissues of p57(kip2) protein negative-expression group was 47.1 %. There was no significant relationship between the two groups (r=0.16507, P>0.05). CONCLUSION: The decreased expression of p57(kip2), Rb protein or over-expression of PCNA protein might contribute to the genesis or progression of pancreatic cancer, p57(kip2), Rb protein and PCNA may play an important role in genesis and progression of pancreatic cancer.

Maspin is a member of serine protease inhibitor family with tumor suppressing activity for breast and prostate cancers, acting at the level of tumor invasion and metastasis. However, there have been no published data regarding the role of maspin in human bladder cancer. We evaluated maspin expression in 65 series of bladder cancer samples (22 transurethral resection (TUR) and 43 radical cystectomy) and studied the regulatory mechanism of maspin gene activation in bladder cancer cells. Maspin expression was immunohistochemically detected in four (18.2%) patients with TUR and 22 (51.2%) patients with radical cystectomy whereas no expression was observed in normal transitional cells located at tumor-free area in bladder. The maspin expression was significantly correlated with the development of muscle invasive bladder cancer (P=0.00008). Using a luciferase reporter system, maspin promoter activity was induced in the maspin-positive bladder cancer cell lines as well as maspin-negative RT4 cells. Furthermore, treatment with the DNA methyltransferase inhibitor, 5-aza-2 deoxycytidine, and histone deacetylase inhibitor, trichostatin A, led to re-expression of maspin in RT4 cells. Our results indicate that maspin may contribute to bladder cancer development and that DNA methylation and histone deacetylation may be important for regulating maspin gene activation in bladder cancer cells.

PURPOSE: Maspin is a member of the serpin family and has tumor suppressor activity. We evaluated maspin expression in pulmonary adenocarcinoma in relation to a number of clinicopathological features. METHODS: Maspin expression was examined immunohistochemically in a series of 78 pulmonary adenocarcinomas by the EnVision ChemMate method. RESULTS: . Thirty-seven of 78 cases (47%) showed distinct maspin expression (maspin-positive group) and 41 (53%) did not (maspin-negative group). Maspin expression was not associated significantly with most clinicopathological variables including sex, age, tumor size, primary tumor, lymph node metastasis, visceral pleural invasion, pulmonary metastasis, and disease stage. However, the maspin-positive group had a better 5-year survival rate (62%) than did the maspin-negative group (42%). The difference in the 5-year survival rate was greatest in stage II patients (maspin-positive group, 69%; maspin-negative group, 17%; P = 0.048). CONCLUSION: Our data indicate that maspin has prognostic significance for pulmonary adenocarcinoma. A better understanding of the role of maspin in tumor suppression may be helpful for development of novel chemotherapies for patients with this deadly tumor.

Maspin is a Class II tumor suppressor protein and plays a role in tumor growth by inhibiting cellular invasion and motility. It is a member of the serpin family of protease inhibitors and has been shown to reduce angiogenesis. Maspin gene expression can be upregulated by the tumor suppressor p53. We tested 7 p53-related proteins of the p63 and p73 families for their ability to induce maspin expression. The p63 splice form TAp63gamma can substitute for p53 in activating the maspin promoter. TAp63gamma activates the promoter through the same consensus site as p53. In the DLD-1 colorectal adenocarcinoma cell line, harboring a tet-off regulated transgene, induction of TAp63gamma leads to an upregulation of maspin mRNA from the chromosomal gene. With a short lag phase also maspin protein levels are elevated after induced TAp63gamma expression. To assess a potential function of p63-dependent maspin upregulation in tumors we followed expression of p53, p63 and maspin by immunohistochemistry in hepatocellular carcinomas. Two types of tumors with wild-type or mutant p53 were assayed. Interestingly, the majority of tumors expressing only a mutated and inactive p53 protein nonetheless stain positive for maspin, whereas these tumors were positive for p63 protein expression. In summary, we show that TAp63gamma can substitute for p53 in transcriptional activation of the maspin tumor suppressor gene. TAp63gamma employs the same DNA recognition site for this activation as p53. We observe expression patterns of p53, p63 and maspin proteins in tumor tissue that may indicate also a function of maspin induction by p63 in tumors.

BACKGROUND: Maspin is a serpin protease inhibitor, which is known to suppress tumor progression in breast cancer and to be regulated by wild-type p53. This study was performed to elucidate the biologic significance of maspin expression in non-small cell lung cancer. METHODS: To investigate whether maspin is involved in progression, clinicopathologic features, and prognosis of non-small cell lung cancer, we performed an immunohistochemical study using antimaspin antibody and identified the presence of maspin messenger ribonucleic acid in cancerous and noncancerous tissues by reverse transcription-polymerase chain reaction analysis. In addition, we evaluated p53 expression immunohistochemically on the serial sections. RESULTS: Most adenocarcinoma and squamous cell carcinoma showed cytoplasmic staining pattern. The cytoplasmic positive rate was 77.8% (42 of 54 specimens) for the stage III group, and 36.2% (21 of 58 specimens) for the stage I group (p < 0.0001). Three-year survival rates after operation were 30.8% for the maspin-positive group and 71.1% for the maspin-negative group (p = 0.007). In multivariate analysis, immunohistochemical maspin expression in patients with non-small cell lung cancer was an independent prognostic factor for overall survival. No correlation between maspin and p53 expression in cancer cells could be observed. There was an average fourfold increase in maspin messenger ribonucleic acid levels in cancerous tissues compared with those of noncancerous tissues, and stage III cases exhibited significantly higher maspin messenger ribonucleic acid levels than stage I cases (p = 0.003). CONCLUSIONS: The results of this study suggest that overexpression of maspin in cytoplasm may be a useful marker of tumor progression and unfavorable prognosis for overall survival in some patients with non-small cell lung cancer. Furthermore, maspin expression in cytoplasm appears to be unaffected by p53.

Maspin is a serpin that acts as a tumor suppressor in a range of human cancers, including tumors of the breast and lung. Maspin is crucial for development, because homozygous loss of the gene is lethal; however, the precise physiological role of the molecule is unclear. To gain insight into the function of human maspin, we have determined its crystal structure in two similar, but non-isomorphous crystal forms, to 2.1- and 2.8-A resolution, respectively. The structure reveals that maspin adopts the native serpin fold in which the reactive center loop is expelled fully from the A beta-sheet, makes minimal contacts with the core of the molecule, and exhibits a high degree of flexibility. A buried salt bridge unique to maspin orthologues causes an unusual bulge in the region around the D and E alpha-helices, an area of the molecule demonstrated in other serpins to be important for cofactor recognition. Strikingly, the structural data reveal that maspin is able to undergo conformational change in and around the G alpha-helix, switching between an open and a closed form. This change dictates the electrostatic character of a putative cofactor binding surface and highlights this region as a likely determinant of maspin function. The high resolution crystal structure of maspin provides a detailed molecular framework to elucidate the mechanism of function of this important tumor suppressor.

The presented study was aimed to investigate new mechanisms of carcinogenesis in thyroids at the molecular level and to find potential protein markers involved in the initiation of the different histological subtypes of thyroid carcinoma. For this, we performed differential proteome analysis on primary cultured thyrocytes and transformed thyrocytes derived from 238Pu alpha-particle irradiation using two-dimensional electrophoresis (2-DE) and peptide mass fingerprinting (PMF) with matrix-assisted laser desorption/ionisation-time of flight mass spectrometry (MALDI-TOF MS). Proteome analysis identified a strong upregulation of maspin, a serine protease inhibitor and class II tumor suppressor, in irradiated thyrocytes. To clarify the role of maspin in thyroid carcinogenesis, we searched for mRNA/protein expression in 30 normal (tumor-free) thyroid tissues, 35 follicular adenomas, 68 papillary carcinomas, 38 follicular carcinomas, 25 poorly differentiated carcinomas, and 34 undifferentiated carcinomas and compared the results with maspin promoter methylation status, p53 expression, clinicopathological data and prognosis. Maspin expression was detectable in 48 of 68 papillary carcinomas exclusively. There was a low methylation rate of 28% in papillary carcinomas in contrast to the other tissues (89-100%). p53 was positive in 2% of maspin positive cases, and in 80% of maspin negative cases. After 110 month follow-up 83% of the maspin positive patients had recurrence-free disease, whereas only 40% of the maspine negative patients were recurrence-free. Our data suggest: (1) maspin expression is a special feature of papillary thyroid carcinomas, (2) promotor methylation-caused maspin repression plays a major role in gene balance and in the process of tumor determination, (3) maspin protein possibly functions as a clinically relevant inhibitor of tumor progression, (4) our data delivers the hints for a p53-depentent regulatory pathway of the maspin protein in human cancer.

BACKGROUND: Maspin is a member of the serpin family of protease inhibitors and is thought to inhibit carcinoma invasion, metastasis, and angiogenesis and induce apoptosis. We examined maspin expression immunohistochemically and assessed its significance in intraductal papillary mucinous neoplasm (IPMN) of the pancreas. METHODS: We examined 39 surgically resected specimens of IPMN that included 17 adenomas (IPMAs), 5 borderline tumors (IPMBs), 4 non-invasive carcinomas (non-invasive IPMCs), and 13 invasive carcinomas (invasive IPMCs). Immunostaining was performed according to the EnVision ChemMate method. The degree of maspin expression was scored and assessed according to the percentage and staining intensity of positive cells. RESULTS: Maspin expression was minimal in normal pancreatic duct epithelium, whereas in IPMNs, maspin was expressed in neoplasms of all stages. Maspin expression increased with increasing grade from IPMAs, IPMBs, to non-invasive IPMCs but decreased significantly in invasive IPMCs. No specific association between maspin expression and mucin type was found. Analysis of maspin expression with respect to clinicopathologic factors in cases of invasive IPMC revealed a greater extent of invasion in cases of low maspin expression and significantly fewer apoptotic cells in the tumor. CONCLUSIONS: Maspin was expressed at high levels in IPMNs at various stages from adenoma to invasive carcinoma, and our results suggest that maspin may be involved in the occurrence and progression of IPMN. In addition, our data suggest that the apoptosis-inducing action of maspin suppresses invasion and progression of IPMN.

Maspin is a key tumor suppressor gene in prostate and breast cancers with diverse biological functions. However, how maspin regulates prostate tumor progression is not fully understood. In this study, we have used maspin heterozygous knockout mice to determine the effect of maspin haploinsufficiency on prostate development and tumor progression. We report that loss of one copy of maspin gene in Mp(+/-) heterozygous knockout mice leads to the development of prostate hyperplastic lesions, and this effect was mediated through decreased level of cyclin-dependent kinase inhibitors p21 and p27. Prostate hyperplastic lesions in Mp(+/-) mice also induced stromal reaction, which occurred in both aged prostate tissues and in neonatal prostates during early ductal morphogenesis. We showed that maspin was also expressed in prostate smooth muscle cells (PSMC), and recombinant maspin increased PSMC cell adhesion but inhibited cell proliferation. We also observed a defective interaction between epithelial cells and basement membrane in the prostate of Mp(+/-) mice, which was accompanied with a changed pattern of matrix deposition and a loss of epithelial cell polarity. Therefore, we have identified a novel property of maspin, which involves the control of the proliferation in prostate epithelial and smooth muscle cells. This is the first report that a partial loss of maspin caused an early developmental defect of the prostate and prostate hyperplastic lesions in mouse.

Maspin is a tumor suppressor protein that stimulates apoptosis and inhibits motility, invasion and cancer metastasis. We report on a previously uncharacterized Pro/Ser (C to T) polymorphism at amino acid 176 of the human maspin protein. We analyzed the maspin mutation in 17 cancer cell lines and 36 cancer tissues. Association of polymorphic variants on apoptosis, colony formation and in vivo tumor formation was evaluated. Mutant maspin was found to be frequently expressed in gastric cancer (32/36, 89%). According to predicted maspin tertiary structure, the polymorphic residue is located on the surface of the protein proximal to the reactive site loop domain, and thus may significantly affect the protein interactions of maspin. Stable expression of the Pro and Ser forms of maspin in lung cancer cells revealed that cells expressing Ser176 maspin showed significantly decreased apoptosis and increased colony formation compared with those expressing Pro176 maspin. In a mouse model, cells expressing Ser176 maspin showed a higher rate of tumor formation in vivo than those harboring Pro176 maspin. Therefore, P176S (C526T) substitution of maspin may result in a partial loss of the tumor suppressor function of this protein, contributing to decreased susceptibility to apoptosis and malignant progression.

In response to genotoxic stress, p53 induces the tumor suppressors maspin and PTEN. Here we demonstrate that in response to limited oxygen conditions PTEN and p53 work in tandem to induce maspin in glioblastoma cells. In response to hypoxia a portion of PTEN migrates to the nucleus and complexes with p53, while cytoplasmic PTEN prevents Mdm2 nuclear localization by attenuating Akt signaling. Subcellular distribution of PTEN in the cytoplasm or nucleus protects p53 from inactivation and degradation. The presence of nuclear PTEN and p53 coordinates the induction of maspin and p21 (both p53 gene targets) in response to hypoxia. Altering the expression of PTEN and/or p53 attenuated maspin gene induction under hypoxic conditions. Furthermore, implanting U87 (PTEN null) and PTEN reconstituted U87 cells (U87PTEN) in mice we observed by immunohistochemistry and western blot that Maspin was only detectable in cells with PTEN. The integration of PTEN and p53 into a common pathway for the induction of another tumor suppressor, Maspin, constitutes a tumor suppressor network of PTEN/p53/Mapsin that is operational under limited oxygen conditions.

Previous studies have shown that testisin promotes malignant transformation in cancer cells. To define the mechanism of testisin-induced carcinogenesis, we performed yeast two-hybrid analysis and identified maspin, a tumor suppressor protein, as a testisin-interacting molecule. The direct interaction and cytoplasmic co-localization of testisin with maspin was confirmed by immunoprecipitation and confocal analysis, respectively. In cervical cancer cells, maspin modulated cell death and invasion; however, these effects were inhibited by testisin in parallel experiments. Of interest, the doxorubicin resistance was dramatically reduced by testisin knockdown (P=0.016). Moreover, testisin was found to be over-expressed in cervical cancer samples as compared to matched normal cervical tissues. Thus, we postulate that testisin may promote carcinogenesis by inhibiting tumor suppressor activity of maspin.

The grim prognosis of lung cancer, that has an overall 10-15% survival at 5 years, remains in the US the leading cause of cancer mortality, provides a compelling rationale for studying the molecular basis of this malignancy. Surmising the common, general association with smoking, lung cancers differ at the microscopic, anatomical, epidemiological and clinical level and harbor complex genetic and epigenetic alterations. Currently, lung cancer is divided into small cell lung carcinoma (SCLC) and non small cell lung carcinoma (NSCLC) for the purpose of clinical management. (NSCLC) constitutes 80-85% of lung cancers and is further divided into histological subtypes such as adenocarcinoma, squamous cell carcinoma, and large cell carcinoma, etc. The ultimate goal for lung cancer research is to develop a strategy to block the tumor progression and improve the prognosis of lung cancer. This goal can realistically be achieved only when the biological complexity of this disease is taken into account. To this end, identification and understanding of molecular markers that are mechanistically involved in tumor progression is needed. Our recent studies suggest histological subtype-dependent distinct correlations between the expression and/or subcellular localization of tumor suppressive maspin with the progression and prognosis of NSCLC. Maspin is an epithelial specific member of the serine protease inhibitor (serpin) superfamily but recently identified as an endogenous inhibitor of histone deacetylase 1 (HDAC1). This novel biochemical activity coincides with a consensus emerged recently from the evidence that nuclear maspin confers better differentiated epithelial phenotypes, decreased tumor angiogenesis, increased tumor sensitivity to drug-induced apoptosis, and a more favorable prognosis. In the current review, we discuss the evidence that maspin may be a marker that stratifies the progression and prognosis of different subtypes of NSCLC.

The thrombin receptor protease activated receptor-1 (PAR-1) is overexpressed in metastatic melanoma cell lines and tumor specimens. Previously, we demonstrated a significant reduction in tumor growth and experimental lung metastasis after PAR-1 silencing via systemic delivery of siRNA encapsulated into nanoliposomes. gene expression profiling identified a 40-fold increase in expression of Maspin in PAR-1-silenced metastatic melanoma cell lines. Maspin promoter activity was significantly increased after PAR-1 silencing, suggesting that PAR1 negatively regulates Maspin at the transcriptional level. ChIP analyses revealed that PAR-1 decreases binding of Ets-1 and c-Jun transcription factors to the Maspin promoter, both known to activate Maspin transcription. PAR-1 silencing did not affect Ets-1 or c-Jun expression; rather it resulted in increased expression of the chromatin remodeling complex CBP/p300, as well as decreased activity of the CBP/p300 inhibitor p38, resulting in increased binding of Ets-1 and c-Jun to the Maspin promoter and higher Maspin expression. Functionally, Maspin expression reduced the invasive capability of melanoma cells after PAR-1 silencing, which was abrogated after rescuing with PAR-1. Furthermore, tumor growth and experimental lung metastasis was significantly decreased after expressing Maspin in a metastatic melanoma cell line. Moreover, silencing Maspin in PAR-1-silenced cells reverted the inhibition of tumor growth and experimental lung metastasis. Herein, we demonstrate a mechanism by which PAR-1 negatively regulates the expression of the Maspin tumor-suppressor gene in the acquisition of the metastatic melanoma phenotype, thus attributing an alternative function to PAR-1 other than coagulation.

The role of tumor suppressor proteins in the development of malignancy has made the understanding of their molecular mechanisms of action of great importance. Maspin is a tumor suppressor produced by a number of cell types of epithelial origin. Exogenous recombinant maspin has been shown to block the growth, motility, and invasiveness of breast tumor cell lines in vitro and in vivo. Although belonging to the the serine proteinase inhibitor (serpin) superfamily of proteins, the molecular mechanism of maspin is currently unknown. Here we show that the reactive site loop of maspin exists in an exposed conformation that does not require activation by cofactors. The reactive site loop of maspin, however, does not act as an inhibitor of proteinases such as chymotrypsin, elastase, plasmin, thrombin, and trypsin but rather as a substrate. Maspin is also unable to inhibit tissue and urokinase type plasminogen activators. Stability studies show that maspin cannot undergo the stressed-relaxed transition typical of proteinase-inhibitory serpins, and the protein is capable of spontaneous polymerization induced by changes in pH. It is likely, therefore, that maspin is structurally more closely related to ovalbumin and angiotensinogen, and its tumor suppressor activity is independent of a latent or intrinsic trypsin-like serine proteinase-inhibitory activity.

BACKGROUND: The human maspin gene encodes a protein in the serine proteinase inhibitor (serpin) family with tumor-suppressing functions in cell culture and in nude mice. In order to examine the role of maspin in an intact mammal, we cloned and sequenced the cDNA of mouse maspin. The recombinant protein was produced and its activity in cell culture was assessed. MATERIALS AND METHODS: Mouse maspin (mMaspin) was cloned by screening a mouse mammary gland cDNA library with the human maspin cDNA probe. Northern blot analysis was used to examine the expression patterns in mouse tissues, mammary epithelial cells, and carcinomas. Recombinant mMaspin protein was produced in E. coli. Invasion and motility assays were used to assess the biological function of mMaspin. RESULTS: mMaspin is 89% homologous with human maspin at the amino acid level. Like its human homolog, mMaspin is expressed in normal mouse mammary epithelial cells and down-regulated in mouse breast tumor cell lines. The expression is altered at different developmental stages in mammary gland. Addition of the recombinant mMaspin protein to mouse tumor cells was shown to inhibit invasion in a dose-dependent manner. As with the human protein, recombinant mMaspin protein also inhibited mouse mammary tumor motility. Deletion in the putative mMaspin reactive site loop (RSL) region resulted in the loss of its inhibitory functions. CONCLUSIONS: mMaspin is the mouse homolog of a human tumor suppressor gene. The expression of mMaspin is down-regulated in tumor cells and is altered at different developmental stages of mammary gland. mMaspin has inhibitory properties similar to those of human maspin in cell culture, suggesting that the homologous proteins play similar physiological roles in vivo.

The maspin protein has tumor suppressor activity in breast and prostate cancers. It inhibits cell motility and invasion in vitro and tumor growth and metastasis in nude mice. Maspin is structurally a member of the serpin (serine protease inhibitors) superfamily but deviates somewhat from classical serpins. We find that single-chain tissue plasminogen activator (sctPA) specifically interacts with the maspin reactive site loop peptide and forms a stable complex with recombinant maspin [rMaspin(i)]. Major effects of rMaspin(i) are observed on plasminogen activation by sctPA. First, rMaspin(i) activates free sctPA. Second, it inhibits sctPA preactivated by poly-D-lysine. Third, rMaspin(i) exerts a biphasic effect on the activity of sctPA preactivated by fibrinogen/gelatin, acting as a competitive inhibitor at low concentrations (< 0.5 microM) and as a stimulator at higher concentrations. Fourth, 38-kDa C-terminal truncated rMaspin(i) further stimulates fibrinogen/gelatin-associated sctPA. rMaspin(i) acts specifically; it does not inhibit urokinase-type plasminogen activator, plasmin, chymotrypsin, trypsin, or elastase. Our kinetic data are quantitatively consistent with a model in which two segregated domains of maspin interact with the catalytic and activating domains of sctPA. These complex interactions between maspin and sctPA in vitro suggest a mechanism by which maspin regulates plasminogen activation by sctPA bound to the epithelial cell surface.