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

Expression of plasminogen activator inhibitor-2 in epithelial ovarian cancer: a favorable prognostic factor related to the actions of CSF-1

In ovarian cancer cells, the macrophage colony-stimulating factor-1 (CSF-1) induces the release of plasminogen activator inhibitor-2 (PAI-2), and high levels of PAI-2 as well as of CSF-1 in ovarian cancer ascites are independently correlated with poor outcome. We now study the effect of CSF-1 on PAI-2 expression in vitro and the significance of cellular PAI-2 expression in vivo. Immunohistochemical detection of PAI-2 was studied in primary and metastatic tissues from 130 epithelial ovarian cancer cases. Kaplan-Meier curves of survival were compared with the results of log-rank test. The Cox regression model was used for multivariate analysis. The effect of CSF-1 on PAI-2 expression in ovarian cancer cells was also examined in vitro. Fifty-eight percent of the primary tumors and 68% of the metastases expressed PAI-2. PAI-2 expression in the metastases of invasive stages III and IV cases was strongly predictive of a prolonged disease-free and overall survival. This finding was associated with low residual disease and was also an independent factor for disease-free survival. In vitro, CSF-1 treatment of ovarian cancer cells resulted in a decrease in cellular staining for PAI-2 while increasing the release of PAI-2 into the conditioned medium. In vivo, we also found an inverse correlation between expression of CSF-1 and that of PAI-2 in the primary tumors. We thus describe the favorable independent prognosis of cellular PAI-2 expression in the metastases of ovarian cancer. Moreover, an inverse correlation was observed between CSF-1 and PAI-2 expression in vivo. This lends support for a primary role of cell-surface (vs. secreted)-mediated events of plasminogen activation in the development of invasive, poor prognostic phenotypes.

Differential expression of human ferritin H chain gene in immortal human breast epithelial MCF-10F cells

Subtractive hybridization was used to isolate genes expressed uniquely in the immortalized human breast epithelial cell (HBEC) line MCF-10F and not in the mortal HBEC line S-130, from which MCF-10F cells were derived. We identified a 233-bp cDNA that was expressed in MCF-10F cells and not in their mortal counterpart S-130 cells. Sequence comparison with the GenBank database revealed that the cDNA was identical to the gene encoding human ferritin heavy H chain. Northern blot analysis using the isolated cDNA as a probe showed a differentially expressed 1.1-kb transcript of ferritin H in total RNA from the immortal MCF-10F cells, MCF-10F cells treated with the chemical carcinogens 7,12-dimethylbenz[a]anthracene and benzo[a]pyrene, and the breast cancer cell lines MCF-7, HBL-100, T-47D, and BT-20. No ferritin H transcript was detected in the mortal line S-130 or in other primary HBEC cultures. Increased levels of mRNA transcript signals were also detected in total RNA from breast cancer tissue samples. Tissue with ductal hyperplasia had higher expression levels than normal adjacent mammary tissue. In situ hybridization showed high levels of ferritin H transcript in mammary tissue areas with ductal hyperplasia, carcinoma in situ, and infiltrating ductal carcinoma. This is the first report of the differential expression and upregulation of human ferritin H chain gene in immortal HBECs. It may be an important factor in the process of immortalization, possibly an early stage of malignant transformation of HBECs, providing cells with iron necessary for growth and clonal expansion. Also, ferritin iron, once released, may increase the level of reactive iron, leading to an increase in oxygen free-radical generation, oxidative DNA damage, and mutation.

Polymerase chain reaction-based identification of a novel serpin from human dendritic cells

A subtraction library of CD40-stimulated human tonsil dendritic cells has been constructed using a polymerase chain reaction approach adapted for low numbers of cells. From this library we identified a cDNA for a serine protease inhibitor, a serpin, which is absent from monocytes, B cells and T cells but expressed in CD40-activated monocyte- and progenitor cell-generated dendritic cells. In addition, the serpin is expressed in a lung fibroblast cell line and keratinocytes. Its mRNA is detected only in tonsil and thymus. The serpin described here reportedly functions as a megakaryocyte maturation factor in the presence of interleukin (IL)-3 and IL-11. This suggests that dendritic cells may promote the immune response by protecting IL-3 and IL-11 or other essential proteins from degradation.

Maspin is an intracellular serpin that partitions into secretory vesicles and is present at the cell surface

The tumor suppressor maspin (mammary serpin) was originally identified as a component of human mammary epithelial cells that is downregulated as mammary tumor cells progress from the benign to the invasive and metastatic states. Maspin inhibits cellular invasion, motility, and proliferation, but its mechanism of action is currently unknown. Because the cellular machinery responsible for these processes is cytoplasmic, we have reexamined the tissue distribution and subcellular localization of maspin. We find that maspin, or a maspin-like protein, is present in many human organs, in which it localizes to epithelia. In cultured human mammary myoepithelial cells, maspin is predominantly a soluble cytoplasmic protein that associates with secretory vesicles and is present at the cell surface. In vitro assays show that the vesicle association is due to the existence of an uncleaved facultative secretion signal that allows small amounts of maspin to partition into the endoplasmic reticulum. These results demonstrate that maspin is more widespread than previously believed. The subcellular localization studies indicate that soluble intracellular and vesicle-associated maspin probably play an important role in controlling the invasion, motility, and proliferation of cells expressing it, whereas extracellular maspin may also regulate these processes in adjacent cells.

'Revertant' DCIS in human axillary breast carcinoma metastases

Recent experimental evidence obtained in Scid mice has suggested that the metastatic process is in large part epigenetically regulated and undergoes partial reversion once the metastatic process is completed: the metastatic colonies become more engaged in the process of growing in situ than actively metastasizing. Based on this experimental evidence, examples were sought of metastatic human cancers where similar reversion to an in situ growth state was occurring. Review of 200 cases of metastatic human breast cancer revealed a 21 per cent incidence of reversion to a ductal carcinoma in situ (DCIS) growth pattern within axillary nodal metastases. The revertant DCIS areas were characterized by an intact and circumferential basement membrane, as demonstrated by extracellular laminin and type IV collagen immunoreactivity. These revertant DCIS areas could be distinguished from primary DCIS, however, by the absence of surrounding myoepithelial cells in the former, identified in the latter by their positive maspin, S-100, and smooth muscle actin immunoreactivity. The pattern of revertant DCIS, poorly differentiated (comedo) (13 per cent), intermediate (non-comedo) (6 per cent), or well-differentiated (non-comedo) (2%), exhibited complete 100 per cent concordance with the primary DCIS pattern. The concordance of histological patterns held true for even the subtypes of DCIS determined by architectural pattern, such as the micropapillary or cribriform subtypes. Nuclear size by digital image analysis and Her-2/neu, p53, and Ki-67 status in the revertant DCIS also exhibited complete concordance with the primary DCIS counterparts. Cases exhibiting a revertant DCIS pattern tended to be ER-negative/EGFR-positive and exhibited significant nodal involvement (mean number, 9; mean area, 90 per cent) compared with cases lacking a revertant pattern (mean number, 4; mean area, 15 per cent) (P < 0.01) These findings suggest that reversion of the metastatic phenotype may also be occurring within autochthonous human metastasis.

New genes for male accessory gland proteins in Drosophila melanogaster

The accessory gland of male insects produces components of the seminal fluid that alter the behavior, physiology and life span of the mated female, and contribute to her efficient storage and utilization of sperm. As a step towards understanding how this occurs, we have isolated genes encoding 12 previously unreported accessory gland-specific mRNAs from the fruit fly Drosophila melanogaster. We report here the restriction maps of the new genes, the chromosome positions--which are all autosomal--of the 11 non-repetitive genes, their expression patterns, and the sequences of the accessory gland proteins (Acps) encoded by nine of the genes. Eight of the proteins predicted from these sequences begin with putative secretion signals. Following their signal sequences, three of the predicted molecules are peptides and the other five are larger polypeptides with characteristics of cleavable prohormones. The ninth molecule, which has an N-terminal hydrophobic region but no consensus signal peptide cleavage site, is predicted to be a 716 amino acid glycoprotein. Of the nine proteins, two have intriguing similarities to sequences in protein databases. Acp76A is a 388 amino acid pro-protein which contains a signature sequence for the serpin class of protease inhibitors. The 115 amino acid Acp62F has a 28 amino acid region of high sequence similarity to a neurotoxin of the Brazilian armed spider Phoneutria nigriventer. Models are discussed in which Acp76A plays a role in the observed regulation of Acp proteolysis and/or in the coagulation of seminal fluid to form a mating plug, and in which Acp62F contributes to the reported toxicity of Drosophila seminal fluid.

Human proteinase inhibitor 9 (PI9) is a potent inhibitor of subtilisin A

Serine proteinase inhibitors function as regulators of serine proteinase activity in a variety of physiological processes. Proteinase inhibitor 9 (PI9) is a 42 kDa member of the ovalbumin family of serpins that is expressed in placenta, lung, and cytotoxic lymphocytes. In this study, we have described the inhibitory mechanism of recombinant human PI9 towards the bacterial endoproteinase subtilisin A. PI9 inhibited the amidolytic activity of subtilisin A via a rapid, single step mechanism with an equilibrium inhibition constant of 3.6 pM and an overall second-order association rate constant of 2.4 x 10(6) M-1s-1, which is the strongest inhibitory mechanism of PI9 that has been described. The inhibitory action of PI9 towards subtilisin as a model proteinase may yield some indication of potential proteinases that may be regulated by PI9 in vivo.

The genomic analysis of human DAN gene

DAN gene is shown to be localized at human chromosome 1p36.11-p36.13, which resides within the consensus deletion observed in neuroblastoma. In the present study, we have isolated the genomic DNA containing the entire human DAN gene and determined its nucleotide sequence. Structural analysis revealed that DAN gene is composed of four exons and spans approximately 15 kb. Its overall structure was basically the same as that of rat DAN gene. Two distinct transcription initiation sites (major and minor) were identified by the primer extension experiment. Putative TATA and CAAT-like elements are present 38 and 366 bp upstream from the major transcription start site, respectively, however, no apparent TATA-like sequence was found in the upstream region of the minor transcription start site. The 400-bp region immediately upstream from the major transcription initiation site was strongly GC-rich (79% GC). Genomic Southern experiments demonstrated that the allelic loss of DAN gene might occur in neuroblastoma. Interestingly, there exist two dinucleotide repeats, (CA)7 and (CA)8, in the first intron of DAN gene, raising the possibility to distinguish two alleles of DAN gene in some of the cancer cells.

Gamma linolenic acid regulates expression of maspin and the motility of cancer cells

Maspin, mammary serine protease inhibitor, is a recently identified tumour suppressor and has a profound effect on cell motility. This study examined the effect of gamma linolenic acid (GLA), an essential fatty acid (EFA) with anticancer properties, on the expression of maspin and motility of cancer cells. Six human cell lines including colon cancer, mammary cancer, and melanoma were used. Expression of maspin protein was determined by immunocytochemistry & Western blotting. Maspin mRNA was detected with reverse transcription-PCR (RT-PCR). Four of the six cell types expressed maspin with MDA MB 231 and ECV304 (endothelial cell) being negative. Treatment of these maspin positive cells with gamma linolenic acid (GLA) resulted in a concentration dependent stimulation of the expression of maspin protein with the effects seen as early as 4 hours. Linoleic acid had an inhibitory effects. Alpha linolenic acid and arachidonic acid had no significant effect. The mRNA levels from cells treated with GLA was seen to increase as shown by RT-PCR. Cell motility, monitored with time-lapse video recording and Hoffmann microscopy, showed a marked reduction in terms of spreading and migration on extracellular matrix coated surface. This reduction was reversed with anti-maspin antibody. It is concluded that GLA, a member of then-6 series of EFAs, up-regulates the expression of maspin which is associated with a reduction in the motility of cancer cells.

Cytoplasmic antiproteinase 2 (PI8) and bomapin (PI10) map to the serpin cluster at 18q21.3

High-molecular-weight serine proteinase inhibitors (serpins) regulate a diverse set of intracellular and extracellular processes such as complement activation, fibrinolysis, coagulation, cellular differentiation, tumor suppression, apoptosis, and cell migration. The ov-serpins are a subset of the serpin superfamily and are characterized by their high degree of homology to chicken ovalbumin, the lack of N- and C-terminal extensions, the absence of a signal peptide, and a Ser rather than an Asn residue at the penultimate position. Recently, we mapped four members of the family [SCCA1, SCCA2, PAI2, and PI5 (maspin)] to a 300-kb region within 18q21.3. Using a panel of 18q21.3 YAC clones, PCR, and DNA blotting, we mapped two additional ov-serpins, cytoplasmic antiproteinase 2 [CAP2 (PI8)] and bone marrow-associated serpin [bomapin (PI10)], to the same region. Three of the serpins, PI8, PI10, and PAI2 mapped to the same YACs, yA27D8 and yA24E4. We estimated that the size of the 18q21.3 serpin cluster spanned approximately 500 kb and contained at least six serpin genes. The order was cen-PI5, SCCA2, SCCA1, PAI2, PI10, PI8-tel. The clustering of serpins at 18q21 provides new opportunities to study coordinate gene regulation and the evolution of gene families.

Identification of drm, a novel gene whose expression is suppressed in transformed cells and which can inhibit growth of normal but not transformed cells in culture

Using differential display analysis, we compared the expression of RNA in v-mos-transformed cells and their flat revertant and isolated a novel gene, drm (down-regulated in mos-transformed cells), whose expression is down-regulated in parental v-mos-transformed cells but which is expressed at a high level in the revertant and normal rat fibroblasts (REF-1 cells). Analysis of different oncogene-transformed cells revealed that drm gene expression was also suppressed in REF-1 cells transformed by v-ras, v-src, v-raf, and v-fos. The drm cDNA contains a 184-amino-acid-protein-encoding open reading frame which shows no significant homologies to known genes in DNA databases. Polyclonal antibodies raised against drm peptide detect a protein with the predicted size of 20.7 kDa in normal cells and under nonpermissive conditions in cells conditionally transformed by v-mos but not in parental v-mos-transformed cells. Northern analysis of normal adult tissues shows that drm is expressed as a 4.4-kb message in a tissue-specific manner, with high expression in the brain, spleen, kidney, and testis and little or no expression in the heart, liver, and skeletal muscle. In situ hybridization analysis in adult rat tissue reveals good correlation with this pattern and indicates that drm mRNA is most highly expressed in nondividing and terminally differentiated cells, such as neurons, type 1 lung cells, and goblet cells. Transfection of a drug-selectable drm expression vector dramatically reduced the efficiency of colony formation in REF-1 and CHO cells, and the drm-transfected REF-1 survivors expressed low or nondetectable levels of exogenous drm mRNA. The toxic effects of drm can be overcome by cotransfection with constructs expressing oncogenic ras; furthermore, cells expressing high levels of drm and conditionally transformed with mos-expressing Moloney murine sarcoma virus rapidly undergo apoptosis when shifted to the nonpermissive temperature. Taken together, our data suggest that cells expressing high levels of drm undergo apoptotic death in the absence of oncogene-induced transformation and that drm represents a novel gene with potential roles in cell growth control or viability and tissue-specific differentiation.

Mutation analysis and loss of heterozygosity of PEDF in central nervous system primitive neuroectodermal tumors

Deletion of 17p is the most frequent abnormality observed in central nervous system (CNS) primitive neuroectodermal tumors (PNETs), implicating the presence of a tumor suppressor gene which maps to 17p. The gene for pigment epithelium-derived factor (PEDF) has been cloned and mapped to 17p13. PEDF belongs to the serine protease inhibitor (SERPIN) gene family. The PEDF protein has neurotrophic and neuronal-survival activities and is expressed in the CNS. Twenty tumor and matched normal DNA samples from patients with PNETs were screened by single-strand conformation polymorphism (SSCP) analysis to determine loss of heterozygosity (LOH) and to identify potential mutations within the 8 exons of the PEDF gene. Ten of the 20 tumors demonstrated LOH, consistent with the deletion status of 17p determined by cytogenetic or fluorescence in situ hybridization studies. SSCP analysis of the genomic DNA from the 10 cases with LOH demonstrated several polymorphisms in exons 4 and 7, but no mutations. Our results are consistent with a loss of alleles on 17p in 50% of CNS PNETs, but do not suggest that PEDF is a candidate for the PNET suppressor gene in 17p13.

A new family of 10 murine ovalbumin serpins includes two homologs of proteinase inhibitor 8 and two homologs of the granzyme B inhibitor (proteinase inhibitor 9)

Serine proteinase inhibitors (serpins) are classically regulators of extracellular proteolysis, however, recent evidence suggests that some function intracellularly. Such "ovalbumin" serpins include the human proteinase inhibitors 6 (PI-6), 8 (PI-8), and 9 (PI-9), plasminogen activator inhibitor 2, and the monocyte/neutrophil elastase inhibitor. PI-9 is a potent granzyme B (graB) inhibitor that has an unusual P1 Glu and is present primarily in lymphocytes. In a search for the murine equivalent of PI-9 we screened cDNA libraries, and performed reverse transcriptase-polymerase chain reaction on RNA isolated from leukocyte cell lines and from lymph nodes and spleens of allo-immunized mice. We identified 10 new ovalbumin serpin sequences: two resemble PI-8, two resemble PI-9, and the remaining six have no obvious human counterparts. By RNA analysis only one of the two sequences resembling PI-9 (designated SPI6) is present in mouse lymphocytes while the other (a partial clone designated mBM2A) is predominantly in testis. SPI6 comprises a 1.8-kilobase cDNA encoding a 374-amino acid polypeptide that is 68% identical to PI-9. mBM2A is 65% identical to PI-9 and over 80% identical to SPI6. Although the reactive loops of SPI6 and mBM2A differ from PI-9, both contain a Glu in a region likely to contain the P1-P1' bond. SPI6 produced in vitro using a coupled transcription/translation system formed an SDS-stable complex with human graB and did not interact with trypsin, chymotrypsin, leukocyte elastase, pancreatic elastase, thrombin, or cathepsin G. Recombinant SPI6 produced in a yeast expression system was used to examine the interaction with human graB in more detail. The second-order rate constant for the interaction was estimated as 8 x 10(4) M-1 s-1, and inhibition depended on the Glu in the SPI6 reactive center. The SPI6 gene was mapped to the same region on mouse chromosome 13 as Spi3, which encodes the murine homolog of PI-6. We conclude that even though their reactive centers are not highly conserved, SPI6 is a functional homolog of PI-9, and that the regulation of graB in the mouse may involve a second serpin encoded by mBM2A. Our identification of multiple sequence homologs of PI-8 and PI-9, and six new ovalbumin serpins, is consonant with the idea that the larger set of granule and other proteinases known to exist in the mouse (compared with human) is balanced by a larger array of serpins.

Purification, cDNA cloning, and characterization of a new serpin with megakaryocyte maturation activity

A new member of the serine protease inhibitor (serpin) superfamily with megakaryocyte maturation activity was purified, and its cDNA was cloned and characterized. The predicted amino acid sequence consisting of 380 residues was unique and was 38% identical to the serpin plasminogen activator inhibitor type 2 (PAI-2). The recombinant factor expressed in Chinese hamster ovary cells showed species-specific activity on the induction of megakaryocyte maturation in vitro. When injected into mice, the factor indeed elicited an increase in the number of platelets in plasma. The sequence alignment indicated that the factor possessed a lysine residue at the P1 position, suggesting that it might function as an inhibitor of Lys-specific proteases. Although we could not show any inhibitory activities toward several known Lys-specific proteases, we detected the activity toward protease activity present in the culture supernatant of COLO 201 cells. These results suggested that the protein might influence the maturation of megakaryocytes via action as a serpin.

Expression of maspin in prostate cells is regulated by a positive ets element and a negative hormonal responsive element site recognized by androgen receptor

Prostate cancer is the most common cancer in men. The molecular mechanisms leading to its development are poorly understood. Maspin is a tumor-suppressing serpin expressed in normal breast and prostate epithelium. We have found that expression of maspin in normal and carcinoma-derived prostate epithelial cells is differentially regulated at the transcriptional level. We have identified two different kinds of cis elements, Ets and hormonal responsive element (HRE), in the maspin promoter. The Ets element is active in regulating maspin expression in normal prostate epithelial cells but inactive in tumor cells. The HRE site is a negative element that is active in both cell types. This negative DNA sequence can repress a heterologous promoter recognized by the androgen receptor. We conclude that expression of maspin is under the influence of both a positive Ets and a negative HRE element. Loss of maspin expression during tumor progression apparently results from both the absence of transactivation through the Ets element and the presence of transcription repression through the negative HRE element recognized by androgen receptor.

Analysis of serpin inhibitory function by mutagenesis of ovalbumin and generation of chimeric ovalbumin/PAI-2 fusion proteins

Ovalbumin is a non-inhibitory serpin which lacks the ability to undergo the S --> R transition or conformational change. Amino acid residues in the hinge region (P11 to P14) of ovalbumin and other non-inhibitory serpins differ from the concensus sequence of this region of inhibitory serpins, and have been proposed to be responsible for lack of inhibitory properties, particularly the P14 charged residue. Site directed mutagenesis using PCR overlap extension was performed on these residues in ovalbumin to create a mutant with three amino acid changes, R340T, V342A and V343A. However analysis of the mutant recombinant ovalbumin with the consensus residues failed to show inhibitory activity or decreased stability, indicating that the hinge region alone is not responsible for lack of inhibition. A series of three fusion proteins were then constructed by replacing varying C-terminal regions of ovalbumin with the corresponding region of the inhibitory ov-serpin PAI-2 in order to further analyse serpin inhibitory function. Fusion proteins F1 and F2 contained approximately 16% and 35% PAI-2, respectively. This resulted in the replacing of structural features such as the reactive site loop, hinge region and beta sheet strands 5A and 6A. However both fusion proteins showed no inhibitory activity with the PAI-2 target protease urokinase (uPA) and no decrease in stability as analysed by transverse urea gradient (TUG) gels. The third chimeric fusion protein constructed (F3) contained 64% PAI-2 and did demonstrate inhibition of uPA, SDS-PAGE stable complex formation with uPA and increased instability on TUG gels. Structural differences between the inactive F2 and active F3 include the replacement of helix F and beta sheet strand 3A of ovalbumin with those of PAI-2, suggesting that these features may have a key role in serpin beta-sheet opening and inhibitory function.

Alpha 1-antitrypsin blocks the release of transforming growth factor-alpha from MCF-7 human breast cancer cells

Human breast cancer cells synthesize and release a variety of growth-modulating substances in response to estrogen stimulation, and it is generally accepted that the growth-promoting effects of estrogens are due at least in part to this autocrine/paracrine mechanism. Several of these growth-modulating substances, including transforming growth factor-alpha (TGF alpha) and its analogs, have been shown to require pericellular proteolysis for activation or release. Recently, we reported that MCF-7 human breast cancer cells are able to synthesize alpha 1-antitrypsin (alpha 1-AT), the major elastase inhibitor in human serum, and that there is a negative correlation between anchorage-independent growth of MCF-7 cells in soft agar and synthesis of alpha 1-AT. The studies we present here were undertaken to gain an understanding of the mechanisms responsible for this observation. We show that release of TGF alpha from its membrane-bound precursor on MCF-7 cells is blocked by alpha 1-AT whether the cells were maintained in the presence or absence of estradiol and that there is a clear dose-response relationship between the alpha 1-AT concentration and both the release of TGF alpha and growth in soft agar. Consistent with this, TGF alpha release was increased in the presence of antibody to alpha 1-AT. In contrast, TGF alpha release and growth in soft agar were not blocked by peptide inhibitors specific for trypsin- or chymotrypsin-like enzymes. The alpha 1-AT concentration required for a half-maximal effect is lower for inhibition of TGF alpha release than it is for inhibition of colony formation (0.4 vs. 1.5 mumol/L). However, both values are in the range of concentrations one might expect at the cell surface in vivo. A new MCF-7 cell subline producing 10-fold higher levels of alpha 1-AT than its parent cell line was constructed by stable transfection of MCF-7 ML cells (a subline producing low levels of alpha 1-AT) with an alpha 1-AT complementary DNA. Growth in soft agar and release of TGF alpha were significantly decreased in cells transfected with the alpha 1-AT complementary DNA compared to those in cells transfected with vector alone, although, TGF alpha expression was the same. The above observations support a model for growth regulation in human breast ductal epithelial cells in which growth factor activation and release are dependent on the coordinate action of proteases and protease inhibitors. This model would predict that alpha 1-AT can act as a tumor suppressor in inhibiting the growth of breast cancer cells.

Rat and human maspins: structures, metastatic suppressor activity and mutation in prostate cancer cells

The rat homologue of human maspin cDNA was cloned. The deduced amino acid sequence of rat maspin was homologous to human maspin with 88% of the amino acids conserved. Rat maspin mRNA was detected in rat mammary gland, vagina, urinary bladder, thymus, small intestine, skin, ventral prostate, seminal vesicles, and thyroid but not in many other organs, such as heart, lung, liver, brain and kidney. Rat maspin cDNA retrovirally introduced into highly metastatic Dunning AT3.1 rat prostate cancer cells did not suppress metastasis of these tumor cells in Copenhagen rats. Maspin mRNA was detected in 5/10 human prostatic carcinoma tissue samples. Two human prostate cancer cell lines, PC-3 and LNCaP, and two human prostatic carcinoma and two benign prostatic hyperplasia tissue samples contained maspin mRNA having an isoleucine to valine mutation at amino acid 319.

Growth-inhibitory activity and downregulation of the class II tumor-suppressor gene H-rev107 in tumor cell lines and experimental tumors

The H-rev107 gene is a new class II tumor suppressor, as defined by its reversible downregulation and growth-inhibiting capacity in HRAS transformed cell lines. Overexpression of the H-rev107 cDNA in HRAS-transformed ANR4 hepatoma cells or in FE-8 fibroblasts resulted in 75% reduction of colony formation. Cell populations of H-rev107 transfectants showed an attenuated tumor formation in nude mice. Cells explanted from tumors or maintained in cell culture for an extended period of time no longer exhibited detectable levels of the H-rev107 protein, suggesting strong selection against H-rev107 expression in vitro and in vivo. Expression of the truncated form of H-rev107 lacking the COOH-terminal membrane associated domain of 25 amino acids, had a weaker inhibitory effect on proliferation in vitro and was unable to attenuate tumor growth in nude mice. The H-rev107 mRNA is expressed in most adult rat tissues, and immunohistochemical analysis showed expression of the protein in differentiated epithelial cells of stomach, of colon and small intestine, in kidney, bladder, esophagus, and in tracheal and bronchial epithelium. H-rev107 gene transcription is downregulated in rat cell lines derived from liver, kidney, and pancreatic tumors and also in experimental mammary tumors expressing a RAS transgene. In colon carcinoma cell lines only minute amounts of protein were detectable. Thus, downregulation of H-rev107 expression may occur at the level of mRNA or protein.

Differential display of reticulocalbin in the highly invasive cell line, MDA-MB-435, versus the poorly invasive cell line, MCF-7

Matrigel invasion assays were used to characterize the invasive abilities of five breast cancer cell lines. Reverse Transcription Polymerase Chain Reaction (RT-PCR) was used to detect the differential gene expression of estrogen receptor (ER), E-cadherin, vimentin and cathepsin D in these cell lines. Using mRNA differential display, we identified novel cDNA clones representing the partial sequences of genes overexpressed in the invasive MDA-MB-435 cells as compared to that of the less invasive MCF-7 cells. One of the cDNAs was homologous to reticulocalbin. The studies were repeated in all of the cell lines and the overexpression of this cDNA was confirmed by RT-PRC and Northern hybridization analysis. Reticulocalbin was expressed in the highly invasive breast cancer cell lines but was not expressed in poorly invasive ones. Although its function is still unknown, reticulocalbin is implicated in tumor cell invasiveness because of its differential expression in breast tumor cell lines.

Expression genetics in cancer: shifting the focus from DNA to RNA

Expression genetics is a conceptually different approach to the identification of cancer-related genes than the search for mutations at the genome level. While mutations lie at the heart of cancer, at least in its early stages, what is recognized here are phenotypic changes usually many steps removed from the initiating mutation. Classically cancer geneticists have concentrated on genomic changes and have ignored the productive potential of examining downstream events based on screening for differential gene expression between tumor cells and well matched normal counterparts. Genes involved in cancer affect the normal functions of many cellular processes: not only proliferation but cell-cell and cell-matrix interactions, DNA repair, invasion and motility, angiogenesis, senescence, apoptosis, and others. Yet very few cancer-related genes affecting these processes have been identified in human cancers by classical methods to find mutated genes despite enormous efforts. I report here our success in readily isolating more than 100 candidate tumor suppressor genes from human tissue, estimated to represent roughly 20% of the total genes recoverable by this approach. Half of the genes are unknown and the other half include representatives of most known cancer processes. Because their expression is lost during cancer progression, they may be useful tumor markers for diagnosis and prognosis. Because these genes are not mutated, they provide opportunities for pharmacological intervention by inducing their reexpression.

The myoepithelial defense: a host defense against cancer

The behavior of human tumors depends not only on the nature of the tumor cells themselves but also on the modifying effects of various normal host cells such as fibroblasts and endothelial cells. One cell type, however--the myoepithelial cell--has not been studied scientifically. Myoepithelial cells normally surround ducts and acini of glandular organs such as the breast and salivary glands and contribute to the synthesis of a surrounding basement membrane. This relationship suggests that myoepithelial cells may exert paracrine effects on glandular epithelium and also regulate the progression of ductal carcinoma in situ (DCIS) to invasive carcinoma. Myoepithelial tumors, in turn, tend to be benign or low-grade neoplasms that exhibit the rare property of accumulating rather than degrading extracellular matrix material. To better understand the nature of myoepithelial tumors, as well as the possible role of normal myoepithelial host cells in cancer, we have established immortal cell lines and a number of transplantable xenografts from various human myoepithelial tumors of the salivary gland and breast. The cell lines exhibit a normal myoepithelial phenotype and the xenografts continue to accumulate an abundant extracellular matrix. Further ultrastructural, immunocytochemical, molecular, and biochemical studies reveal that myoepithelial cells secrete relatively low levels of matrix-degrading proteinases but relatively high levels of maspin and various other anti-invasive proteinase inhibitors, that some of these inhibitors accumulate within the myoepithelial matrix, and that myoepithelial cells can induce epithelial morphogenesis (spheroid formation) and inhibit tumor-cell invasion in vitro. Myoepithelial cells, which surround normal breast ducts and DCIS, have also been found to selectively express maspin and certain proteinase inhibitors in situ. These inherent myoepithelial properties are likely to contribute to the low-grade nature of myoepithelial neoplasms and advance our hypothesis that host myoepithelial cells regulate the progression of in situ to invasive carcinoma by providing an important host defense against cancer invasion.

Immunohistochemical expression of SKALP/elafin in squamous cell carcinoma of the oesophagus

In this study, the immunohistochemical expression of a new inducible elastase inhibitor, SKALP (skin-derived anti-leucoproteinase)/elafin, in the tissue of squamous cell carcinoma and uninvolved oesophageal mucosa was studied using a polyclonal rabbit anti-serum against SKALP/elafin. The results were compared with the immunohistochemical staining of proliferating cell nuclear antigen (PCNA) and the TUNEL assay in serial sections. In non-malignant oesophageal mucosa, the expression of SKALP/elafin was localized in the cells of the stratified zone overlying the PCNA-positive basal zone. In oesophageal cancer, the incidence of the expression was significantly related to the degree of the differentiation of the tumour. Characteristically, the expression was almost limited in tumour cell nests that had a clear squamous phenotype. In tumour cell nests, the expression of SKALP/elafin was localized in the cells overlying PCNA-expressing cells and no expression was found in the cells that expressed PCNA; DNA fragmentation was often observed in the same cell layers as those in which SKALP/elafin immunoreactivity was found. This enzyme inhibitor is speculated to be involved in the induction of the cell differentiation and apoptosis of human squamous cell carcinoma cells of the oesophagus.

A cytosolic granzyme B inhibitor related to the viral apoptotic regulator cytokine response modifier A is present in cytotoxic lymphocytes

Using a polymerase chain reaction strategy we identified a serine proteinase inhibitor (serpin) in human bone marrow that is related to the cellular serpin proteinase inhibitor 6 (PI-6) and the viral serpin cytokine response modifier A (CrmA). This serpin, proteinase inhibitor 9 (PI-9), has an unusual reactive center P1(Glu)-P1'(Cys), which suggests that it inhibits serine proteinases that cleave after acidic residues. The only known serine proteinase with this specificity is granzyme B, a granule cytotoxin produced by cytotoxic lymphocytes. To test the interaction of PI-9 with granzyme B we prepared recombinant hexa-histidine tagged PI-9 in a yeast expression system. Addition of the recombinant protein to native granzyme B resulted in an SDS-resistant complex typical of serpin-serine proteinase interactions. Further analysis showed that complex formation followed bimolecular kinetics with a second order rate constant of 1.7 +/- 0.3 x 10(6) M-1 s-1, which is in the range for a physiologically significant serpin-proteinase interaction. Recombinant PI-9 also completely abrogated granzyme B and perforin-mediated cytotoxicity in vitro. Examination of PI-9 mRNA distribution demonstrated that it is expressed in immune tissue, primarily in lymphocytes. The highest levels of PI-9 mRNA and protein were observed in natural killer cell leukemia cell lines and in interleukin-2 stimulated peripheral blood mononuclear cells, which also produce granzyme B. Like PI-6, PI-9 was shown to be a cytosolic protein that is not secreted. Fractionation of natural killer cells and stimulated peripheral blood mononuclear cells demonstrated that PI-9 is in a separate subcellular compartment to granzyme B. These results suggest that PI-9 serves to inactivate misdirected granzyme B following cytotoxic cell degranulation. This may explain why cytotoxic cells are not damaged by their own granzyme B during destruction of abnormal cells.

The exon 3 encoded sequence of the intracellular serine proteinase inhibitor plasminogen activator inhibitor 2 is a protein binding domain

We have used a combination of biochemical and immunological methods to probe for proteins that interact with the cytoplasmic form of plasminogen activator inhibitor 2 (PAI-2) and to identify the structure in PAI-2 that mediates the binding. By affinity chromatography on immobilized PAI-2, we purified a collection of PAI-2-binding proteins. These proteins bound 125I-labeled PAI-2 in vitro (IC50, approximately 10-100 nM) in a calcium-independent reaction that did not abrogate the proteinase inhibitory function of PAI-2. Annexin I was identified among the eluted proteins, and purified annexins I, II, IV, and V, but not III and VI, possessed 125I-labeled PAI-2 binding activity. Immune precipitation by anti-PAI-2 monoclonal and polyclonal antibodies of metabolically labeled melanoma cells treated with a cleavable cross-linker prior to analysis revealed three prominent proteins with apparent masses of 100, 70, and 50 kDa. We localized the protein binding domain in PAI-2 between amino acid residues 66 and 98, as determined by using a PAI-2 mutant lacking this domain and a synthetic peptide spanning this region. This region of PAI-2 corresponds to exon 3 of the gene sequence thought to be critical for PAI-2 functions.

Maspin acts at the cell membrane to inhibit invasion and motility of mammary and prostatic cancer cells

Maspin, a novel serine protease inhibitor (serpin), inhibits tumor invasion and metastasis of mammary carcinoma. We show here that recombinant maspin protein blocks the motility of these carcinoma cells in culture over 12 h, as demonstrated by time-lapse video microscopy. Lamellopodia are withdrawn but ruffling continues. Both exogenous recombinant maspin and maspin expressed by tumor transfectants exhibit inhibitory effects on cell motility and cell invasion as shown in modified Boyden chamber assays. In addition, three prostatic cancer cell lines treated with recombinant maspin exhibited similar inhibition of both invasion and motility, suggesting a similar mode of maspin action in these two glandular epithelial cancers. When mammary carcinoma cells were treated with recombinant maspin, the protein was shown by immunostaining to bind specifically to the cell surface, suggesting that maspin activity is membrane associated. When pretreated with antimaspin antibody, maspin loses its inhibitory effects on both invasion and motility. However, when maspin is added to these cells preceding antibody treatment, the activity of maspin is no longer inhibited by subsequent addition of the antibody. It is concluded therefore that the inhibition of invasion and motility by maspin is initially localized to the cell surface.

The metastatic phenotype--prognostic implications

Strong efforts are being made in order to better understand the molecular mechanisms underlying cancer dissemination. We have attempted to summarise some of the findings in this area. A large number of differences in gene expression have been described in metastatic and non-metastatic cells. In the mouse B16 melanoma system, more than 50 different markers have been described. It is likely that many of these differences reflect the same genetic alteration (i.e. a mutation in a regulatory gene alters the expression of a set of co-regulated target genes). One could argue that it is more effective to study mutations in regulatory as opposed to expression of down-stream target genes. However, we feel that proto-oncogenes are less suitable as markers compared to target genes, since it is difficult to screen for mutations at multiple levels in regulatory pathways. In contrast, measuring the expression of a small number of target genes (i.e. one of the targets in Fig. 1), the expression of which are stimulated by upstream regulators, is accomplished more easily. It is anticipated that the future of optimised panels of independent markers will sharpen cancer diagnosis and lead to individualised therapy.

Sensitive detection of circulating breast cancer cells by reverse-transcriptase polymerase chain reaction of maspin gene

BACKGROUND

Maspin, a recently identified protein related to the family of serpins, is believed to play a role in human breast cancer. In an effort to improve the present methods of detection, we have developed a reverse-transcriptase polymerase chain reaction (RT-PCR) assay for maspin transcript to identify small numbers of mammary carcinoma cells in the peripheral blood and bone marrow of patients with breast cancer.

PATIENTS AND METHODS

Five non-neoplastic mammary tissue samples, 13 breast cancer specimens as well as 17 peripheral blood and 4 bone marrow samples from normal subjects were screened for the presence of maspin mRNA by RT-PCR. The same assay was applied to peripheral blood or bone marrow samples obtained from 29 patients with stages I to IV breast cancer.

RESULTS

By RT-PCR it was possible to amplify maspin mRNA in all of the primary and metastatic breast cancer specimens, but in none of the normal hemopoietic samples from healthy donors. Thus, detection of maspin transcript in the peripheral blood or marrow of a patient known to have breast cancer is indicative of the presence of mammary carcinoma cells. In reconstitution experiments, maspin RT-PCR reliably detected 10 mammary carcinoma cells in 1 million normal peripheral-blood mononuclear cells (PBMCs). None of the 9 patients with stages I, II, or III breast cancer had maspin transcript in peripheral blood. Of note, 3 of 9 patients with stage IV breast cancer receiving systemic therapy at the time of sample collection, but only 1 of 11 patients with stage IV not receiving therapy, had detectable maspin transcript in peripheral blood. Moreover, 3 marrow specimens from stage IV patients tested positive by this assay.

CONCLUSIONS

This pilot study suggests that maspin RT-PCR assay is a sensitive, specific and sufficiently rapid method for detection of small numbers of circulating cells and marrow micrometastases in breast cancer patients. The possibility of applying this assay in the detection of tumor cell contamination of both marrow and stem-cell apheresis harvests of breast cancer patients merits further investigation.

Human cytoplasmic antiproteinase neutralizes rapidly and efficiently chymotrypsin and trypsin-like proteases utilizing distinct reactive site residues

Human cytoplasmic antiproteinase (CAP) is an intracellular serpin that has been reported to utilize Arg341 as the reactive site P1 residue to neutralize a broad variety of extracellular serine proteases with trypsin-like specificity. Both native CAP and recombinant CAP purified from Escherichia coli were observed to form SDS-stable complexes not only with 125I-thrombin and 125I-urokinase, but also with 125I-chymotrypsin. Kinetic studies indicated that the amidolytic activity of chymotrypsin is inhibited efficiently and rapidly by CAP in a two-step process with a dissociation constant Ki of an initial loose complex of 3.3 nM, a forward isomerization rate constant k2 to the tight complex of 0.014 s-1, and an overall second order association rate constant of 6 x 10(6) M-1 s-1, similar to the kinetic constants obtained for the formation of the trypsin-CAP complex. N-terminal amino acid sequencing and mass spectrometry indicated that chymotrypsin interacts with CAP at Met340, in contrast to thrombin, which interacts as expected at Arg341. Thus, CAP is the first serpin that has been shown to be capable to inhibit efficiently and with similar association rate constants different proteases at distinct reactive site residues, strongly supporting the notion of a highly mobile and flexible serpin reactive site loop and suggesting that this inhibitor may have evolved separate reactive sites for the specific regulation of different proteolytic activities.

Tissue kallikrein inhibitors in mammals

We have discovered, purified and cloned a new kallikrein-binding protein (KBP or kallistatin) from humans and rodents. Kallistatins are members of the serine proteinase inhibitor (serpin) superfamily. They are acidic glycoproteins with molecular masses of 58-62 kDa and pI values of 4.6-5.2. Kallistatin forms a SDS-stable complex with tissue kallikrein and inhibits kallikrein's activities. Human kallistatin has a unique cleavage site with Phe-Phe-Ser at the P2-P1-P1' positions. The protein sequence of mature human kallistatin shares 44-46% identity with other serpins such as human alpha 1-antitrypsin, protein C inhibitor and rat kallikrein-binding protein. The kallistatin genes display the typical five exon-four intron serpin gene structure. The human kallistatin gene is localized on chromosome 14q31-32.1 and the RKBP gene is on chromosome 6. Kallistatin is evolutionarily diverse but functionally conserved in mammalian species. This overview summarizes the biochemistry, molecular biology and potential physiology and/or pathophysiology of this new tissue kallikrein inhibitor.

Genetic analysis of breast cancer progression

At the histological level, breast tumors display a variety of morphologic lesions which suggest the existence of an increasingly aberrant pathway of intermediate steps leading to the invasive primary tumor and its metastatic dissemination. In order to obtain direct evidence for this presumed progression, underlying genetic changes must be identified. Analyses of primary breast tumors have revealed a large number of dominant and recessive gene alterations encompassing several cellular attributes and activities. It is quite likely that some of these alterations are of a causal nature and thus enable the tumor to attain distinctive malignant phenotypes, such as, dysregulated proliferation, invasion, angiogenesis, and ability to metastasize. Considerable heterogeneity has been observed in the sequence of acquisition of these genetic changes, which is substantiated by recent comparative analyses between carefully microdissected preinvasive and invasive tumor. The data are evaluated here in the context of existing models of breast cancer progression. Implication and prospects for translational application to the clinic are also discussed.

Identification and characterization of the cytoplasmic antiproteinase (CAP) in human platelets. Evidence for the interaction of CAP with endogenous platelet proteins

To define the presence and potential role of platelet-associated protease inhibitors, we initiated a study designed to characterize the platelet components that are responsible for the formation of two SDS-stable complexes of approximately 58 and 70 kDa initially observed following the incubation of 125I-thrombin and human platelets. We demonstrate that thermal-mediated unfolding of the 58-kDa complex between 125I-thrombin and a nonsecreted platelet protein leads to an apparent molecular mass of 70 kDa. This platelet component is functionally and immunologically indistinguishable from the cytoplasmic antiproteinase (CAP), also known as placental thrombin inhibitor, a recently cloned member of the ovalbumin family of intracellular serpins (serine proteinase inhibitors). CAP-specific mRNA and antigen were detected in human platelets, suggesting that CAP synthesis occurs concurrent with platelet development. Utilizing quantitative immunoblotting, CAP antigen was estimated at 1.014 +/- 0.181 microg/10(9) nonstimulated platelets. After platelet activation with the calcium ionophore A23187, CAP antigen was detected in released microparticles at approximately 0. 195 +/- 0.031 microg/10(9) platelets and a fraction of platelet CAP was proteolytically modified. We provide evidence that these lower molecular mass species arise by cleavage of CAP at or near the reactive site loop. Most importantly, molecular sieving chromatography indicates the presence of an approximately 68-kDa SDS-labile complex between cleaved CAP and a cellular component in A23187-stimulated platelets, suggesting a physiological target of this intracellular serpin and a potential role for this inhibitor in regulating proteolytic activity that may be formed during platelet activation.

Metastasis from human breast cancer cell lines

Immunodeficient animals, principally nude mice, when used in appropriately designed studies have been shown to be useful for the experimental analysis of human breast cancer metastasis. As with many other human tumors, the implantation of breast cancer cells into an anatomically appropriate tissue (the mammary fatpad) results in increased tumor take and incidence of metastasis for certain cell lines compared with subcutaneous injection. Testing a number of widely available human breast cancer cell lines identified the MDA-MB-435 cell line as the most metastatic, producing lung and lymph node metastases in a high proportion of nude and severe combined immunodeficient (SCID) mice after injection in the mammary fatpad. Mixing human breast cancer cells with normal fibroblasts or with Matrigel also increases the tumor incidence and growth rates in nude mice. Different routes of injection can be used to assess the ability of human breast cancer cells to form metastatic lesions in the lungs (i.v. injection), the liver (injection in the spleen), the brain (direct or intracarotid artery injection) and the bone marrow and bone (injection into the left ventricle of the heart). These different approaches demonstrate the potential of experimental studies of human breast cancer growth and metastasis using immunodeficient mice; this model is valuable for experiments that test the role of metastasis-associated genes and the efficacy of novel forms of therapy.

Anti-invasion drugs

Most of the pharmaceuticals in clinical practice today for treatment of breast and other cancers are cytotoxic or cytostatic inhibitors of tumor growth. While this type of drug has found its place, along with surgery and radiotherapy, in treatment of disease, the breast cancer death rate has not decreased. This appears to be the result of rising incidence, resistance to therapy, and metastasis of the disease. Since distant metastasis (usually indicated by lymph node involvement) of breast cancer is related only indirectly to tumor size, it would appear that a concerted effort should be made to discover drugs which directly interfere with this complex process. Metastasis appears to depend upon tumor cell motility, dedifferentiation, local invasion, and angiogenesis. Significant progress has been recently made in the creation of new animal models of metastasis and in identifying several new drugs which may be suitable for clinical inhibition of this process. This article reviews current findings on anti-invasion/metastasis drugs with a focus on breast cancer.

Protease inhibitors and carcinogenesis: a review

This brief review article deals with the subject of anticarcinogenic activity of protease inhibitors (PI). Three basic premises are made: (1) Although PI are prevalent constituents of dietary staples such as soy products, which have been epidemiologically associated with reduced cancer incidences at multiple target sites, they are unlikely to be the active anticarcinogenic entities. Cooked soy products, which are devoid of PI activity, are equally as effective at reducing cancer development as raw soy products. Isoflavones are likely to represent major chemopreventive agents in soy, although other constituents may well contribute. (2) Although supplementation of diets with PI (natural or synthetic), or direct topical administration, results in lower cancer incidences in many experimental models in vivo, this effect appears to be indirect. Dietary PI are, in general, poorly absorbed from the GI tract, and never reach target organs in any measurable quantity. The most attractive hypothesis is that dietary PI could induce synthesis and distribution of endogenous PI (acute-phase reactants), which have widespread effects on cell growth and behavior. Effects of topical administration of PI also encompass prominent anti-inflammatory effects. (3) A spectrum of PI inhibit in vitro transformation induced by a variety of carcinogenic agents. Their effects can be grouped into three basic categories, affecting: (a) signal transduction pathways; (b) DNA repair processes; and (c) nuclear proteases. I suggest that the nuclear multicatalytic protease activity, in particular the chymotrypsin-like activity, represents an important cellular target for which considerable anecdotal support can be garnered.

Cloning of mouse DAN cDNA and its down-regulation in transformed cells

Recently, we have demonstrated that DAN gene product exhibits a tumor-suppressive activity in vitro. We report here the cloning and sequencing of a mouse DAN cDNA that contains the entire coding region. Sequence analysis revealed that mouse DAM cDNA is 1691 nucleotides in length and contains an open reading frame of 178 amino acids. The deduced mouse DAN protein sequence shows 96% and 93% identity with the counterparts isolated from rat 3Y1 fibroblasts and normal human lung, respectively. Genomic Southern blot hybridization indicated that DAN gene exists as a single copy in the mouse genome. The expression of DAN gene was suppressed in a variety of transformed NIH3T3 cells when compared with that in the parental NIH3T3 cells.

Clotting and immune defense in Limulidae

The blue blood of the horseshoe crab contains a sophisticated defense system very sensitive to pathogens or foreign materials. The hemocytes circulating in the hemolymph detect trace amounts of LPS molecules on the invading microorganisms and respond quickly to release the granular components into the external milieu. The coagulation system composed of three serine protease zymogens, factor C, factor B, and proclotting enzyme, and a clottable protein, coagulogen, is activated by LPS to form insoluble coagulin gel. The coagulation system also responds to beta-(1,3) glucan through the activation of unique heterodimeric serine protease zymogen, factor G. The pathogens are, thus, engulfed in the gel and subsequently killed by antimicrobial substances with various specificities, which are also released from cells. The horseshoe crab has developed two kinds of serine protease zymogens as biological sensors, factor C and factor G, which are responsive to LPS and beta-(1,3) glucan on the surface of Gram-negative bacteria and fungi, respectively. These are possible invaders for horseshoe crabs and also for most animals including humans. This novel heterodimeric serine protease zymogen, factor G, may open a new way to develop an innovative assay system to quantitate beta-(1,3) glucans. Furthermore, these LPS and beta-(1,3) glucan sensitive factors could be utilized as a unique tool to analyze other biological reactions caused by LPS or the glucan. Although the coagulation reaction in horseshoe crabs is famous, it is not the only defense mechanism of this animal. Many agglutinins are present either in hemolymph plasma or in the cell. The hemolymph plasma also has cytolytic activity against foreign cells. These cellular and humoral defense systems, in concert, defend themselves from invading foreign organisms. Such a sophisticated defense system has allowed the horseshoe crab to survive for more than 200 million years on the earth. Horseshoe crabs are often called ¿living fossils." However, they are not fossils. They are living.

Maspin: a tumor suppressing serpin

Maspin, a serpin found in mammary epithelial cells, has been shown to have tumor suppressor activity. The gene is expressed in normal human mammary epithelial cells but down-regulated in invasive breast carcinomas. Similar patterns of expression at the RNA and protein levels are seen by Northern analysis with cells grown in culture and by immunostaining of tissues. Biological assays of invasion by tumor cells through matrigel membranes and of motility have shown that recombinant maspin inhibits both processes, and that its inhibitory action is totally lost by a single cleavage at the reaction center. Tumor transfectants expressing maspin are inhibited in growth and invasion in nude mice. Maspin is located in the cell membrane and extracellular matrix, and does not behave as a classical inhibitory serpin against any known target protease. Its mode of action is presently unknown.

Molecular cloning, expression, and partial characterization of two novel members of the ovalbumin family of serine proteinase inhibitors

A human placental lambda gt11 cDNA library was screened for sequences encoding proteins related to human proteinase inhibitor 6 (PI6), and two plaques were identified that displayed weak hybridization at high stringency. Isolation and characterization of the DNA inserts revealed two novel sequences encoding proteins composed of 376 and 374 amino acids with predicted molecular masses of approximately 42 kDa. The novel proteins displayed all of the structural features unique to the ovalbumin family of intracellular serpins including the apparent absence of a cleavable N-terminal signal sequence. The degree of amino acid sequence identity between the novel serpins and PI6 (63-68%) significantly exceeds that of any other combination of known intracellular serpins. The two novel serpins encoded by the two novel cDNA sequences have been designated as proteinase inhibitor 8 (PI8) and proteinase inhibitor 9 (PI9). The putative reactive center P1-P1' residues for PI8 and PI9 were identified as Arg339-Cys340 and Glu340-Cys341, respectively. PI9 appears to be unique in that it is the first human serpin identified with an acidic residue in the reactive center P1 position. In addition, the reactive center loop of PI9 exhibits 54% identity with residues found in the reactive center loop of the cowpox virus CrmA serpin. Two PI8 transcripts of 1.4 kilobases (kb) and 3.8 kb were detected by Northern analysis in equal and greatest abundance in liver and lung, while the 1.4-kb mRNA was in excess over the 3.8-kb mRNA in skeletal muscle and heart. Two PI9 transcripts of 3.4 and 4.4 kb were detected in equal and greatest abundance in lung and placenta and were weakly detected in all other tissues. PI8 and PI9 were expressed in baby hamster kidney and yeast cells, respectively. Immunoblot analyses using rabbit anti-PI6 IgG indicated the presence of PI8 in the cytosolic fraction of stably transfected cells that formed an SDS-stable 67-kDa complex with human thrombin. PI9 was purified to homogeneity from the yeast cell lysate by a combination of heparin-agarose chromatography and Mono Q fast protein liquid chromatography and migrated as a single band in SDS-polyacrylamide gel electrophoresis with an apparent molecular mass of 42 kDa. Purified recombinant PI9 failed to inhibit the amidolytic activities of trypsin, papain, thrombin, or Staphylococcus aureus endoproteinase Glu-C and did not form an SDS-stable complex when incubated with thrombin. The cognate intracellular proteinases that interact with PI8 and PI9 are unknown.