Maspin inhibits cell migration in the absence of protease inhibitory activity

Maspin expression is directly associated with biological aggressiveness of thyroid carcinoma

Maspin belongs to the serpin superfamily and has been identified as a tumor suppressor because it inhibits cell motility, invasion, and angiogenesis. However, its physiological activity in carcinoma tissues seems to differ according to the origin of the carcinoma. In this study, we investigated maspin expression in thyroid neoplasms originating in follicular cells by means of immunohistochemistry. Neither normal follicular cells nor stromal cells expressed maspin. Follicular adenomas were all negative for maspin, but 12.5% of follicular carcinomas and 30.5% of papillary carcinomas were positive for it. However, the staining pattern was only focal in all positive specimens except for one and maspin-expressing cells were present mainly at the edge of carcinoma nests. Widely invasive follicular carcinomas tended to be more frequently positive for maspin than minimally invasive ones. In papillary carcinoma, maspin expression was directly linked to stage, tumor size, and extrathyroidal invasion. Papillary and follicular carcinomas involving lesions with solid, trabecular, or scirrhous growth patterns (poorly differentiated carcinoma as designated by Sakamoto et al.) expressed maspin in significantly higher incidence than those with pure papillary or follicular patterns. Furthermore, 48.2% of anaplastic (undifferentiated) carcinomas diffusely expressed maspin, and the rest were completely negative. These findings indicate that, in contrast to other carcinomas, maspin expression is directly associated with the biological aggressiveness of thyroid carcinoma. Further studies regarding the function of maspin in this carcinoma are required.

Maspin – the most commonly-expressed gene of the 18q21.3 serpin cluster in lung cancer – is strongly expressed in preneoplastic bronchial lesions

Maspin, SCCA1/2 and hurpin were identified by cDNA microarray analyses as dramatically differentially expressed transcripts in primary non-small cell lung cancer (NSCLC). These sequences are located within a 10-gene serpin cluster on 18q21.3. Using comparative RT-PCR, we have investigated the expression of each of these serpins, including their flanking loci, in an independent NSCLC series. Whereas six of the genes (maspin, SCCA1, SCCA2, hurpin, megsin and pAI-2) were commonly differentially expressed in primary lesions, each significantly more often in squamous cell tumours, maspin was identified as the most frequently over-represented sequence in both squamous cell carcinoma and adenocarcinoma. Using a well-characterized monoclonal antibody, we have shown strong maspin expression in tumour protein extracts, detected multiple isoforms of the 42 kDa protein and shown that maspin is localized specifically to the tumour cells within neoplastic lesions. In contrast, most cells in non-neoplastic lung tissue appear not to express the gene, with the exception of the multipotent basal epithelial cells that line the bronchial airway. These reserve cells generally show strong predominantly nuclear localization of maspin. Strong nuclear expression of maspin within primary tumour cells is correlated with increased survival (P=0.05) and a longer remission duration (P=0.02) in resectable-staged patients. However, within the airways of cancer patients and somewhat in contrast to this observation, such expression was more frequently detected in the superficial cells of preneoplastic over non-neoplastic epithelia (P<0.0001), consistent with a role for the protein in early neoplasia.

Regulation of plasminogen activation: a role for melanotransferrin (p97) in cell migration

We recently reported that human recombinant melanotransferrin (p97) presents a high transport rate across the blood-brain barrier that might involve the low-density lipoprotein receptor-related protein (LRP). We now report new interactions between p97 and another LRP ligand, the urokinase plasminogen activator (uPA) complex. By using biospecific interaction analysis, both pro-uPA and plasminogen are shown to interact with immobilized p97. Moreover, the activation of plasminogen by pro-uPA is increased by soluble p97. Because the uPA system plays a crucial role in cell migration, both in cancer and in angiogenesis, we also measured the impact of both endogenous membrane-bound and exogenous p97 on cell migration. The monoclonal antibody L235 (which recognizes a conformational epitope on p97) inhibited the migration of human microvascular endothelial cells (HMECs-1) and of human melanoma SK-MEL-28 cells, indicating that endogenous membrane-bound p97 could be associated with this process. In addition, low concentrations of exogenous p97 (10 and 100 nM) inhibited HMEC-1 and SK-MEL28 cell migration by more than 50%. These results indicate that membrane-bound and soluble p97 affect the migration capacity of endothelial and melanoma cells and suggest that p97 could be involved in the regulation of plasminogen activation by interacting with pro-uPA and plasminogen.

Sufficiency of the reactive site loop of maspin for induction of cell-matrix adhesion and inhibition of cell invasion. Conversion of ovalbumin to a maspin-like molecule

Maspin, an ov-serpin, inhibits tumor invasion and induces cell adhesion to extracellular matrix molecules. Here, we use maspin/ovalbumin chimeric proteins and the maspin reactive site loop (RSL) peptide to characterize the role of the RSL in maspin-mediated functions. Replacement of the RSL plus the C-terminal region or the RSL alone of maspin with that of ovalbumin resulted in the loss of the stimulatory effect on adhesion of corneal stromal cells to type I collagen, fibronectin, and laminin and of mammary carcinoma MDA-MB-231 cells to fibronectin. Maspin with ovalbumin as the C-terminal region retained activity, suggesting the maspin C-terminal polypeptide is not required. An R340Q mutant retained full maspin activity; however, an R340A mutant lost activity. This indicates the arginine side chain at the putative P1 site forms a hydrogen bond and not an ionic bond. The RSL peptide (P10-P5', amino acids 330-345) alone induced cell-matrix adhesion of mammary carcinoma cells and corneal stromal cells and inhibited invasion of the carcinoma cells. Substitution of the RSL of ovalbumin with that of maspin converted inactive ovalbumin into a fully active molecule. Maspin bound specifically to the surface of the mammary carcinoma cells with a kd of 367 +/- 67 nM and 32.0 +/- 2.2 x 10(6) binding sites/cell. The maspin RSL peptide inhibited binding, suggesting the RSL is involved in maspin binding to cells. Sufficiency of the maspin RSL for activity suggests the mechanism by which maspin regulates cell-matrix adhesion and tumor cell invasion does not involve the serpin mechanism of protease inhibition.

Maspin expression inhibits osteolysis, tumor growth, and angiogenesis in a model of prostate cancer bone metastasis

Emerging evidence indicates that tumor-associated proteolytic remodeling of bone matrix may underlie the capacity of tumor cells to colonize and survive in the bone microenvironment. Of particular importance, urokinase-type plasminogen activator (uPA) has been shown to correlate with human prostate cancer (PC) metastasis. The importance of this protease may be related to its ability to initiate a proteolytic cascade, leading to the activation of multiple proteases and growth factors. Previously, we showed that maspin, a serine protease inhibitor, specifically inhibits PC-associated uPA and PC cell invasion and motility in vitro. In this article, we showed that maspin-expressing transfectant cells derived from PC cell line DU145 were inhibited in in vitro extracellular matrix and collagen degradation assays. To test the effect of tumor-associated maspin on PC-induced bone matrix remodeling and tumor growth, we injected the maspin-transfected DU145 cells into human fetal bone fragments, which were previously implanted in immunodeficient mice. These studies showed that maspin expression decreased tumor growth, reduced osteolysis, and decreased angiogenesis. Furthermore, the maspin-expressing tumors contained significant fibrosis and collagen staining, and exhibited a more glandular organization. These data represent evidence that maspin inhibits PC-induced bone matrix remodeling and induces PC glandular redifferentiation. These results support our current working hypothesis that maspin exerts its tumor suppressive role, at least in part, by blocking the pericellular uPA system and suggest that maspin may offer an opportunity to improve therapeutic intervention of bone metastasis.