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

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

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

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

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

Epigenetic silencing of maspin gene expression in human breast cancers

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

p53 regulates the expression of the tumor suppressor gene maspin

Maspin has been shown to inhibit tumor cell invasion and metastasis in breast tumor cells. Maspin expression was detected in normal breast and prostate epithelial cells, whereas tumor cells exhibited reduced or no expression. However, the regulatory mechanism of maspin expression remains unknown. We report here a rapid and robust induction of maspin expression in prostate cancer cells (LNCaP, DU145, and PC3) and breast tumor cells (MCF7) following wild type p53 expression from an adenovirus p53 expression vector (AdWTp53). p53 activates the maspin promoter by binding directly to the p53 consensus-binding site present in the maspin promoter. DNA-damaging agents and cytotoxic drugs induced endogenous maspin expression in cells containing the wild type p53. Maspin expression was refractory to the DNA-damaging agents in cells containing mutant p53. These results, combined with recent studies of the tumor metastasis suppressor gene KAI1 and plasminogen activator inhibitor 1 (PAI1), define a new category of molecular targets of p53 that have the potential to negatively regulate tumor invasion and/or metastasis.

Immunohistochemical detection of maspin is a useful adjunct in distinguishing radial sclerosing lesion from tubular carcinoma of the breast

Maspin is a recently described member of the serpin family of protease inhibitors that is consistently expressed at high levels in mammary myoepithelial cells. This feature was used in the immunohistochemical evaluation of tubular carcinoma (TC) and radial sclerosing lesion (RSL) of the breast, and compared with other markers of myoepithelial cells. Ten cases of TC and 11 cases of RSL were studied for the expression of maspin, alpha-smooth muscle actin (alpha-SMA), metallothionein (MT), and S-100 protein by immunohistochemistry. Myoepithelial cells stained strongly and diffusely for maspin creating a pattern of an outer continuous ring surrounding the epithelium of tubules of all RSLs. This pattern was absent in all TCs; however, the single-layered epithelium comprising the tubules of two TCs was positive for maspin with a moderate to strong intensity. Myoepithelial cells were not positive for MT in a consistent manner. Benign nonproliferative epithelium stained focally and weakly for maspin in four of 11 cases of RSL and was negative for MT in all 11 cases. Foci of mild to moderate epithelial hyperplasia noted in five of 11 cases of RSL stained diffusely with a weak to moderate intensity for maspin and focally with a strong intensity for MT. alpha-SMA was consistently expressed in myoepithelial cells but also in stromal myofibroblasts and blood vessels, creating a pattern that was less satisfactory than maspin in distinguishing RSL from TC. Immunohistochemical staining for S-100 protein was of no differential diagnostic value. In conclusion, immunohistochemical staining for maspin is diagnostically useful and superior to MT, S-100, and alpha-SMA, in distinguishing RSL from TC. The epithelial immunoreactivity for maspin in two of 10 TCs merits further investigation from a prognostic viewpoint.

Isolation and mutational analysis of a novel human cDNA, DEC1 (deleted in esophageal cancer 1), derived from the tumor suppressor locus in 9q32

The long arm of chromosome 9 is thought to contain one or more putative tumor suppressor genes that are mutated in squamous cell carcinomas. This region shows frequent loss of heterozygosity (LOH) in carcinomas arising in several developmentally related tissues, including the esophagus, head and neck, lung, and urinary bladder. We previously delineated the commonly deleted region in a panel of esophageal squamous cell carcinomas to a approximately 200 kb genomic segment at 9q32. Here we report the isolation of a novel gene, DEC1 (deleted in esophageal cancer 1), from the target region. Mutational analysis of this gene by reverse-transcriptase polymerase chain reaction disclosed significantly reduced expression of DEC1 in 8 of 13 (62%) esophageal cancer cell lines and in 16 of 30 (53%) primary squamous cell carcinomas of the esophagus. However, no genetic alteration was detected in any of the cancers examined. Introduction of DEC1 cDNA into 3 cancer cell lines that lacked expression of DEC1 significantly suppressed cell growth, whereas antisense cDNA or the vector DNA alone did not. Given the reduced expression of the DEC1 gene in esophageal cancer, the high frequency of LOH at 9q32 in esophageal carcinomas, and the fact that the DEC1 cDNA can suppress growth of some cancer cells in vitro, we suggest that the DEC1 gene is a candidate tumor suppressor in 9q32. Genes Chromosomes Cancer 27:169-176, 2000.

Maspin is an angiogenesis inhibitor

Maspin, a unique member of the serpin family, is a secreted protein encoded by a class II tumor suppressor gene whose downregulation is associated with the development of breast and prostate cancers. Overexpression of maspin in breast tumor cells limits their growth and metastases in vivo. In this report we demonstrate that maspin is an effective inhibitor of angiogenesis. In vitro, it acted directly on cultured endothelial cells to stop their migration towards basic fibroblast growth factor and vascular endothelial growth factor and to limit mitogenesis and tube formation. In vivo, it blocked neovascularization in the rat cornea pocket model. Maspin derivatives mutated in the serpin reactive site lost their ability to inhibit the migration of fibroblasts, keratinocytes, and breast cancer cells but were still able to block angiogenesis in vitro and in vivo. When maspin was delivered locally to human prostate tumor cells in a xenograft mouse model, it blocked tumor growth and dramatically reduced the density of tumor-associated microvessels. These data suggest that the tumor suppressor activity of maspin may depend in large part on its ability to inhibit angiogenesis and raise the possibility that maspin and similar serpins may be excellent leads for the development of drugs that modulate angiogenesis.

Expression of GPC3, an X-linked recessive overgrowth gene, is silenced in malignant mesothelioma

Gene expression changes in rat asbestos-induced malignant mesothelioma (MM) cells were investigated by differential mRNA display. A mRNA transcript identified by this approach was abundant in normal rat mesothelial cells but not expressed in rat MM cell lines. Northern blot analysis confirmed that this transcript is uniformly silenced in rat MM cell lines and primary tumors. Nucleotide sequence analysis revealed that this transcript is encoded by the rat glypican 3 gene (GPC3), whose human homolog is mutated in the Simpson-Golabi-Behmel overgrowth syndrome. Allelic loss at the GPC3 locus was infrequent (6.9%) in MM cell lines, and no mutations were found. GPC3 transcript levels were markedly decreased in 16 of 18 primary tumors and 17 of 22 human MM cell lines. Most of the cell lines were shown to have aberrant methylation of the GPC3 promoter region. In two of four human MM cell lines tested, GPC3 expression was restored after 2-deoxy 5-azacytidine (DAC)-mediated demethylation of its promoter region. Ectopic expression of GPC3 inhibited in vitro colony formation of human MM cells. Collectively, these data suggest that down-regulation of GPC3 is a common occurrence in MM and that GPC3, an X-linked recessive overgrowth gene, may encode a negative regulator of mesothelial cell growth.

Cloning and expression of the mouse Pse gene encoding a novel Ets family member

Human prostate-specific Ets (hPSE) is a novel Ets transcription factor and is exclusively expressed in human prostate glandular epithelium. To explore the role of PSE, we cloned the mouse Pse (mPse) and examined its pattern of expression. A sequence analysis indicated that mPse contains a conserved carboxy-terminal ETS DNA-binding domain and central Pointed domain, and the overall amino acid sequence shares 86% identity with that of hPSE. The ETS DNA-binding domain is highly conserved between human and mouse (98.8% sequence identity) and is similar to Drosophila dets4 (76.7% identity), but not similar to other Ets factors. A Northern blotting analysis revealed that mPse shows organ-specific expression. An in situ hybridization analysis of the prostate and intestine showed that mPse transcripts were present in their epithelial cells. mPse transactivates the promoter of the MASPIN gene in transient transfection assay. These results suggest that mPse encodes a novel Ets family member and is expressed in epithelial cells of restricted organs.

Loss of expression of the DRR 1 gene at chromosomal segment 3p21.1 in renal cell carcinoma

Consistent deletion of DNA sequences in chromosomal band 3p21 observed in a variety of human tumors suggests the presence of one or more tumor suppressor genes within this region. Previously, we reported on the construction of two distinct cosmid contigs and our identification of several new genes within 3p21.1. In our search for tumor suppressor genes from this region, we have cloned a gene that we have called DRR 1 (downregulated in renal cell carcinoma). The gene was first mapped to 3p21.1 by fluorescence in situ hybridization analysis. Further analysis of yeast artificial chromosome clones in 3p14.2-p21.1 refined its localization. DRR 1 spans about 10 Kb of genomic DNA with a 3.5-Kb mature transcript. The putative protein encoded by this gene is 144 amino acids and includes a nuclear localization signal and a coiled domain. The gene showed loss of expression in eight of eight renal cell carcinoma cell lines, one of seven ovarian cancer cell lines, one of one cervical cancer cell line, one of one gastric cancer cell line, and one of one non-small-cell lung cancer cell line. Southern blot analysis did not show any altered bands, indicating that gross structural changes or deletions did not cause the loss of expression. This gene was also found to have reduced expression in 23 of 34 paired primary renal cell carcinomas. Mutational analysis detected three polymorphic sites within the gene, but no point mutations were identified in the 34 primary tumors. However, we did detect base substitutions in 4 of 12 cell lines that had undetectable expression of the gene. We also transfected the gene into DRR 1-negative cell lines and observed clear growth retardation. Our results suggest that loss of expression of the DRR 1 gene may play an important role in the development of renal cell carcinoma and possibly other tumors. Genes Chromosomes Cancer 27:1-10, 2000.

Human ovalbumin serpin evolution: phylogenic analysis, gene organization, and identification of new PI8-related genes suggest that two interchromosomal and several intrachromosomal duplications generated the gene clusters at 18q21-q23 and 6p25

The human ovalbumin (ov) serpins are associated with tumorigenesis, inflammation, and protection from autolysis by granule proteinases. Their genes are located at 18q21 or 6p25, falling into two structurally very similar but distinct categories depending on the presence or absence of a particular exon. Analysis of ov-serpin gene structure provides an opportunity to elucidate the mechanisms contributing to the formation of the larger serpin gene superfamily. Here we have identified a new gene (PI8L1) at 6p25 that is 72% identical to the 18q21 gene PI8. FISH analysis using the 3' untranslated region of PI8 yielded an additional signal at 18q23, separable from the known 18q21.3 signal by the t(1;18)(p32;q23) chromosomal translocation. The presence of more than one PI8-related gene was confirmed by analysis of human genomic DNA using the same probe. Cloning and analysis of PI8 showed that its intron number and phasing are identical to those of the 6p25 genes PI6, PI9, and ELANH2, and it lacks the interhelical variable loop exon found in other 18q21 genes. PCR analysis demonstrated that PI5 at 18q21 also lacks this exon, indicating that it is organized identically to the 6p25 genes. By contrast, PI10 and megsin have this exon and resemble the other 18q21 genes, PLANH2, SCCA-1, and SCCA-2, in structure. Using these data with an ov-serpin phylogenic tree we have constructed, we propose that the ov-serpin gene clusters arose via interchromosomal duplication of PI5 (or a precursor) to 6p25, followed by duplication at 6p25, and a more recent interchromosomal duplication from 6p25 to 18q to yield PI8.

Expression of megsin mRNA, a novel mesangium-predominant gene, in the renal tissues of various glomerular diseases

Mesangial cells play an important role in maintaining a structure and function of the glomerulus and in the pathogenesis of glomerular diseases. Recently, we discovered a new mesangium-predominant gene termed "megsin." Megsin is a novel protein that belongs to the serine protease inhibitor (serpin) superfamily. To elucidate the pathophysiologic role of megsin in the kidney, the expression and localization of megsin mRNA in renal tissues of patients with IgA nephropathy (IgA-N), diabetic nephropathy (DN), minimal change nephrotic syndrome (MCNS), membranous nephropathy (MN), and normal human kidney (NHK) was evaluated by in situ hybridization using digoxigenin-labeled oligonucleotide. Individual cells positive for megsin mRNA were observed only in glomeruli in all renal tissues. Their localization coincided with those of mesangial cells. The percentage of positive cells for megsin mRNA in total glomerular cells was significantly greater in IgA-N than in MCNS, MN, and NHK. It was also significantly greater in DN than in MCNS and NHK. In IgA-N, the percentage of megsin mRNA-positive cells was greater in tissues from those with mesangial cell proliferation and slightly mesangial matrix expansion (periodic acid-Schiff-positive area in the total glomerulus area, <30%; cell number in mesangial matrix area, >30; assessed in cross-sections through their vascular poles) than in tissues from those with severe mesangial matrix expansion (periodic acid-Schiff-positive area in total glomerulus area, >30%; cell number in mesangial matrix area, <30). In conclusion, megsin mRNA was predominantly expressed in glomerular mesangial cells in all renal tissues. The expression of megsin mRNA was upregulated in IgA-N and DN, both of which are diseases accompanied with mesangial cell proliferation and/or mesangial matrix expansion. These data suggest a link of megsin expression to the pathogenesis of IgA-N and DN, two major causes of end-stage renal failure.

Maspin plays an important role in mammary gland development

Maspin is a unique member of the serpin family, which functions as a class II tumor suppressor gene. Despite its known activity against tumor invasion and motility, little is known about maspin's functions in normal mammary gland development. In this paper, we show that maspin does not act as a tPA inhibitor in the mammary gland. However, targeted expression of maspin by the whey acidic protein gene promoter inhibits the development of lobular-alveolar structures during pregnancy and disrupts mammary gland differentiation. Apoptosis was increased in alveolar cells from transgenic mammary glands at midpregnancy. However, the rate of proliferation was increased in early lactating glands to compensate for the retarded development during pregnancy. These findings demonstrate that maspin plays an important role in mammary development and that its effect is stage dependent.

Three-state unfolding and self-association of maspin, a tumor-suppressing serpin

Maspin is a tumor suppressor protein expressed by normal human mammary epithelium but not by many breast tumor cell lines. Recombinant human maspin (rMaspin) inhibits tumor cell motility, invasion, and metastasis and thus has potential value as an anti-cancer therapeutic. Maspin is a member of the serpin family and, although the molecular mechanism by which maspin acts is unknown, recent work suggests that tissue plasminogen activator is a potential target. A puzzling observation in previous cell culture studies was loss of rMaspin activity at higher protein concentrations. One hypothesis to explain these results is self-association of rMaspin at the higher concentrations, which would be consistent with the tendency of serpins to form noncovalent polymers. This hypothesis is addressed by examining the relationship between rMaspin stability and self-association. Urea denaturation of rMaspin at pH 7 and 25 degrees C and at protein concentrations ranging from 0.01 to 0.2 mg/ml has been monitored by circular dichroism and intrinsic tryptophan fluorescence. Denaturation profiles show a protein concentration dependence and indicate the presence of at least one unfolding intermediate. The results suggest that destabilization of native monomeric rMaspin leads to partial unfolding and formation of an intermediate which can self-associate.

Cloning and characterization of hurpin (protease inhibitor 13): A new skin-specific, UV-repressible serine proteinase inhibitor of the ovalbumin serpin family

Epidermal keratinocytes are the primary target of the midrange ultraviolet part (UVB, 280-320 nm) of terrestrial sunlight. Analysis of the resulting UV response at the transcriptional level by differential display PCR identified a formerly unrecognized large group of repressed genes. Among those UV-repressible genes, a novel serine proteinase inhibitor (serpin) termed hurpin (HaCaT UV-repressible serpin) has been identified. The isolated full-length cDNAs harbour a 1176 bp open reading frame encoding a potential protein with 391 amino acid residues and a predicted molecular mass of approximately 44 kDa. The novel serpin has nearly 59 % amino acid identity with the squamous cell carcinoma antigen 1 (SCCA1) and squamous cell carcinoma antigen 2 (SCCA2). In addition, it displays all of the structural features unique to the ovalbumin family of serpins (ov-serpins). The amino acid sequence of the hinge region in the reactive site loop suggests that hurpin has the potential for protease inhibition. The putative reactive center P1-P1'residues were identified as Thr356-Ser357 by alignment with other ov-serpins. The physiological target protease is unknown and the in vitro translated hurpin does not form SDS-stable complexes with a variety of known serine proteases. Expression of hurpin is restricted to epidermal cells where two distinct transcripts of 3.0 and 3.4 kb are detectable. Furthermore, expression of hurpin appears to be related to the activation or proliferation state of keratinocytes, since hurpin transcripts are more abundant in immortalized keratinocytes (HaCaT) and in cultured normal human keratinocytes, compared to the expression in normal skin. Moreover, in psoriasis, a skin disease characterized by hyperproliferation of keratinocytes and responsive to therapeutic UV irradiation, overexpression of hurpin is noted in psoriatic skin lesions compared to non-lesional skin.

Identification and cDNA cloning of headpin, a novel differentially expressed serpin that maps to chromosome 18q

Differential display was used to identify a novel serpin (headpin) underexpressed in squamous cell cancers of the oral cavity. Headpin cDNA encoding a complete open reading frame was cloned and sequenced. Headpin is expressed in normal oral mucosal tissue, skin, and cultured keratinocytes. Using Northern analysis and relative reverse-transcription polymerase chain reaction (relative RT-PCR), downregulation of headpin mRNA expression was demonstrated in oral cavity squamous carcinomas. Northern blot analysis identified a 3. 3-kb headpin mRNA transcript. Headpin is a 391-amino-acid protein with a theoretical molecular weight of 44 kDa. Hinge region homology at the reactive site loop suggests that headpin belongs to the inhibitory class of serine protease inhibitors. Headpin was mapped to 18q21.3/18q22. This region includes the ovalbumin serpins (ov-serpins) maspin, SCCA1, SCCA2, and PAI-2. Furthermore, 18q is recognized as a region for frequent loss of heterozygosity (LOH) in head and neck cancer and other malignancies.

Combinatorial library of serine and cysteine protease inhibitors that interact with both the S and S' binding sites

A combinatorial library of 400 inhibitors has been synthesized and screened against several serine and cysteine proteases including plasmin, cathepsin B, and papain. The inhibitors are based upon a cyclohexanone nucleus and are designed to probe binding interactions in the S2 and S2' binding sites. This methodology has led to the discovery of inhibitor 15A, which incorporates Trp at both the P2 and P2' positions and has an inhibition constant against plasmin of 5 microM. Data from screening of the library shows that plasmin has a strong specificity for Trp at the S2 subsite and prefers to bind hydrophobic and aromatic amino acids such as Ile, Phe, Trp, and Tyr at the S2' subsite. In contrast, the S2' subsites of cathepsin B and papain do not show a strong preference for any particular amino acid.

A Novel Serpin Expressed by Blood-Borne Microfilariae of the Parasitic Nematode Brugia malayi Inhibits Human Neutrophil Serine Proteinases

Serine proteinase inhibitors (serpins) play a vital regulatory role in a wide range of biological processes, and serpins from viruses have been implicated in pathogen evasion of the host defence system. For the first time, we report a functional serpin gene from nematodes that may function in this manner. This gene, named Bm-spn-2, has been isolated from the filarial nematode Brugia malayi, a causative agent of human lymphatic filariasis. Polymerase chain reaction (PCR) and Western blot experiments indicate that Bm-spn-2 is expressed only by microfilariae (Mf), which are the long-lived blood-dwelling larval stage. A survey of the greater than 14,000 expressed sequence tags (ESTs) from B malayi deposited in dbEST shows that greater than 2% of the ESTs sequenced from Mf cDNA libraries correspond to Bm-spn-2. Despite its abundance in the microfilarial stage, Bm-spn-2 has not been found in any other point in the life cycle. The predicted protein encoded byBm-spn-2 contains 428 amino acids with a putative signal peptide. Antibodies to recombinant Bm-SPN-2 protein react specifically with a 47.5-kD native protein in Mf extract. Bm-SPN-2 is one of the largest of the 93 known serpins, due to a 22 amino acid carboxy-terminal extension, and contains the conserved serpin signature sequence. Outside these regions, levels of homology are low, and only a distant relationship can been seen to a Caenorhabditis elegansserpin. The Bm-spn-2 gene contains 6 introns, 2 of which appear to be shared by both nematode species. The B malayi introns have an extended and conserved 3′ splice site and are relatively large compared with C elegans. A panel of mammalian serine proteinases were screened and Bm-SPN-2 protein was found to specifically inhibit enzymatic activity of human neutrophil cathepsin G and human neutrophil elastase, but not a range of other serine proteinases. It is possible that Bm-SPN-2 could function as a stage-specific serpin in the blood environment of the microfilarial parasite in protection from human immunity and thus may be a good candidate for protective vaccine.

A Novel Serpin Expressed by Blood-Borne Microfilariae of the Parasitic Nematode Brugia malayi Inhibits Human Neutrophil Serine Proteinases

Serine proteinase inhibitors (serpins) play a vital regulatory role in a wide range of biological processes, and serpins from viruses have been implicated in pathogen evasion of the host defence system. For the first time, we report a functional serpin gene from nematodes that may function in this manner. This gene, named Bm-spn-2, has been isolated from the filarial nematode Brugia malayi, a causative agent of human lymphatic filariasis. Polymerase chain reaction (PCR) and Western blot experiments indicate that Bm-spn-2 is expressed only by microfilariae (Mf), which are the long-lived blood-dwelling larval stage. A survey of the greater than 14,000 expressed sequence tags (ESTs) from B malayi deposited in dbEST shows that greater than 2% of the ESTs sequenced from Mf cDNA libraries correspond to Bm-spn-2. Despite its abundance in the microfilarial stage, Bm-spn-2 has not been found in any other point in the life cycle. The predicted protein encoded byBm-spn-2 contains 428 amino acids with a putative signal peptide. Antibodies to recombinant Bm-SPN-2 protein react specifically with a 47.5-kD native protein in Mf extract. Bm-SPN-2 is one of the largest of the 93 known serpins, due to a 22 amino acid carboxy-terminal extension, and contains the conserved serpin signature sequence. Outside these regions, levels of homology are low, and only a distant relationship can been seen to a Caenorhabditis elegansserpin. The Bm-spn-2 gene contains 6 introns, 2 of which appear to be shared by both nematode species. The B malayi introns have an extended and conserved 3′ splice site and are relatively large compared with C elegans. A panel of mammalian serine proteinases were screened and Bm-SPN-2 protein was found to specifically inhibit enzymatic activity of human neutrophil cathepsin G and human neutrophil elastase, but not a range of other serine proteinases. It is possible that Bm-SPN-2 could function as a stage-specific serpin in the blood environment of the microfilarial parasite in protection from human immunity and thus may be a good candidate for protective vaccine.

Loss of heterozygosity, differentiation, and clonality in microdissected male germ cell tumours

Testicular germ cell tumours (TGCTs) are heterogeneous neoplasms with different histological patterns and malignant potential. The aim of this study was to determine whether the main TGCT subtypes (seminoma, embryonal carcinoma, yolk sac tumour, choriocarcinoma, and mature teratoma) are distinguished by their loss of heterozygosity (LOH) patterns and whether LOH typing can help to distinguish between clonal and multifocal development of different components in mixed TGCTs. In 76 tumours analysed for allelic losses at 25 chromosomal loci, different LOH patterns were found in distinct histological subtypes. A region around D18S543 frequently lost in yolk sac tumours could harbour one or more tumour suppressor genes. In 20 microdissected mixed tumours, losses of identical alleles in different histological components in 11 of 20 cases (over 50 per cent) were found, which is in favour of current histogenetic models of clonal TGCT development. Clonal losses were most often found at D13S317 (6 of 20 tumours). Two classes of allelic losses may therefore occur during TGCT development: clonal losses which are involved in early transformational events and others related to TGCT differentiation along different lines.

Loss of expression of the candidate tumor suppressor gene ZAC in breast cancer cell lines and primary tumors

Loss of chromosome 6q21-qter is the second most frequent loss of chromosomal material in sporadic breast neoplasms suggesting the presence of at least one tumor suppressor gene on 6q. We recently isolated a cDNA encoding a new zinc finger protein which we named ZAC according to its functional properties, namely induction of apoptosis and control of cell cycle progression. ZAC is expressed in normal mammary gland and maps to 6q24-q25, a recognized breast cancer hot spot on 6q. In the present report, we investigated the possible inactivation of ZAC in breast cancer cell lines and primary tumors. We detected no mutation in ZAC coding region in a panel of 45 breast tumors with allelic imbalance of 6q24-q25. However, a survey of eight breast cancer cell lines showed a deeply reduced (three cell lines) or complete loss of (five cell lines) ZAC expression. Treatment of three of these cell lines with the methylation-interfering agent 5-azacytidine induced ZAC re-expression. In addition, Northern blot and RNase protection assay analysis of ZAC expression in 23 unselected primary breast tumors showed a reduced expression in several samples. Together with its functional properties and chromosomal localization, these findings substantiate ZAC as a good candidate for the tumor suppressor gene on 6q24-q25.

Differentially expressed genes associated with the metastatic phenotype in breast cancer

We have previously shown that human breast carcinoma cells demonstrating an interconverted phenotype, where keratin (epithelial marker) and vimentin (mesenchymal marker) intermediate filaments are both expressed, have an increased ability to invade a basement membrane matrix in vitro. This increase in invasive potential has been demonstrated in MDA-MB-231 cells, which constitutively express keratins and vimentin, and in MCF-7 cells transfected with the mouse vimentin gene (MoVi). However, vimentin expression alone is not sufficient to confer the complete metastatic phenotype in MoVi cells, as determined by orthotopic administration. Thus, in the present study, differential display analysis was utilized to identify genes that are associated with the invasive and/or metastatic phenotype of several human breast cancer cell lines. Forty-four of 84 PCR fragments were differentially expressed as assessed by Northern hybridization analysis of RNA isolated from MCF-7, MoVi, and MB-231 cell lines. Polyadenylated RNA from a panel of poorly invasive, invasive/non-metastatic, and invasive/metastatic breast carcinoma cell lines was used to differentiate between cell-specific gene expression and genes associated with the invasive and/or metastatic phenotype(s). We observed that lysyl oxidase and a zinc finger transcription factor were expressed only in the invasive and/or metastatic cell lines; whereas, a thiol-specific antioxidant and a heterochromatin protein were down-regulated in these cells. In contrast, tissue factor was expressed only in breast carcinoma cell lines having the highest invasive potential. These results suggest that specific genes involved in breast cancer invasion and metastasis can be separated by differential display methodology to elucidate the molecular basis of tumor cell progression.

A partial catalog of proteins secreted by epidermal keratinocytes in culture

Proteins secreted by epidermal keratinocytes are known to engage in functions other than those directly associated with barrier formation. We have used a previously published culture model to collect proteins secreted by adult human epidermal keratinocytes. Electrophoresis and microsequencing allowed us to identify 20 proteins. The list of proteins includes those known to be produced by keratinocytes (beta-2 microglobulin, betaIG-H3, calgranulin A, cathepsin B and D, E-cadherin, gelatinase B, gelsolin, interstitial collagenase, laminin B2t, plasminogen activator inhibitor-1, protein 14-3-3epsilon, SCC antigen, stratifin, and translationally controlled tumor protein) as well as those not previously known to be secreted by keratinocytes (epididymis secretory protein, maspin, and anti-neoplastic urinary protein). In addition, two proteins were identified that are not known to be secreted (glutathione-S-transferase and heat shock protein 27/28 kDa). The varied nature of the proteins identified suggests that epidermal keratinocytes have physiologic functions that have yet to be identified.

Fibronectin and its integrin receptors in cancer

The adhesive extracellular matrix protein fibronectin and its integrin receptors play important roles at several stages of tumor development. Tumor cells are generally less adhesive than normal cells and deposit less extracellular matrix. The loosened matrix adhesion that results may contribute to the ability of tumor cells to leave their original position in the tissue. Normal cells, when detached, stop growing and undergo anoikis (apoptosis caused by loss of adhesion). Integrin-activated pathways mediated by focal adhesion kinase (FAK) and the adapter protein She seem to be particularly important in anchorage dependence; many oncoproteins are capable of shunting these pathways. Malignant cells circumvent anchorage dependence with the help of oncoproteins. Once invading tumor cells have gained access to the circulation, adhesion to the endothelia and other tissue components facilitates the establishment of tumor colonies at distant sites. Specific tissue affinities may underlie the tendency of some tumors to metastasize preferentially to certain tissues. Interfering with tumor cell attachment with integrin-binding peptides has been shown to be an effective antimetastatic strategy in animal experiments. Tumor angiogenesis is yet another aspect of malignancy wherein extracellular matrices and integrins are important. Angiogenic endothelial cells in tumor vessels depend on the alpha v family of integrins for survival. Inhibiting angiogenesis with compounds that block the activity of alpha v integrins, and targeting drugs into tumors through these integrins, show promise as new anticancer strategies.

Identification of a nuclear targeting domain in the insertion between helices C and D in protease inhibitor-10

Protease inhibitor 10 (PI-10), an intracellular ovalbumin-serpin, contains a series of basic amino acids in the loop between helices C and D that exhibit homology to known nuclear targeting signals. Transfection of HeLa cells with plasmids encoding enhanced green fluorescent protein (EGFP) coupled to PI-10 revealed an intense fluorescence of the nucleus. Immunoblotting demonstrated a single Mr 80,000 EGFP.PI-10 complex in isolated nuclei. Mutation of four basic amino acids in the interhelical loop to alanines (i.e. K74A, K75A, R76A, K77A) resulted in the fluorescent complex being confined to the cytoplasm. Further evidence for a nuclear targeting signal in this region was provided by localization of the fluorescent label to the nucleus in cells transfected with a plasmid encoding EGFP fused to the 25 amino acids comprising the interhelical loop of PI-10 (i.e. Arg-63 to Glu-87), whereas a cytoplasmic distribution was noted for the construct encoding EGFP coupled to the mutated interhelical loop. These data raise the possibility that PI-10 may play a role in regulating protease activity within the nucleus, a property unique in the field of serpin biology.

Effects of donor age on the expression of a marker of replicative senescence (EPC-1) in human dermal fibroblasts

EPC-1 (early population doubling level cDNA-1) is a quiescence-specific gene expressed at high levels by early passage WI-38 fibroblasts under conditions of either density-dependent growth arrest or serum deprivation. Late passage WI-38 cells lose the ability to express EPC-1 under all conditions tested. The decline in EPC-1 mRNA is gradual during the replicative life span and correlates inversely with the population doubling level (PDL) of the cells. The objective of this study was to determine whether the decline in EPC-7 mRNA abundance observed during proliferative senescence also occurs in cultures derived from donors of different ages. To address this question, we examined the abundance of EPC-1 mRNA in 28 skin fibroblast lines established from healthy donors of different ages ranging from 12 fetal weeks to 94 years. EPC-1 expression was measured, under conditions of growth arrest, prior to the end of the replicative life span of the cultures. Despite some variability in steady-state transcript levels among the cell lines, EPC-1 expression was significantly lower in cells derived from the fetal donor group (12-20 gestational weeks) than in cells derived from adult donors. An in vitro age-dependent decline in EPC-1 expression was observed in all the skin lines examined, independent of donor age; however, no significant difference was observed between the young adult donor group (17-33 years) and the old adult donor group (78-94 years). Thus, expression of EPC-1 is linked to the replicative age of the cells and whether the cells are derived from fetal skin or adult skin. In adults, EPC-1 expression is independent of donor age.

The Intracellular Serpin Proteinase Inhibitor 6 Is Expressed in Monocytes and Granulocytes and Is a Potent Inhibitor of the Azurophilic Granule Protease, Cathepsin G

The monocyte and granulocyte azurophilic granule proteinases elastase, proteinase 3, and cathepsin G are implicated in acute and chronic diseases thought to result from an imbalance between the secreted proteinase(s) and circulating serpins such as 1-proteinase inhibitor and 1-antichymotrypsin. We show here that the intracellular serpin, proteinase inhibitor 6 (PI-6), is present in monocytes, granulocytes, and myelomonocytic cell lines. In extracts from these cells, PI-6 bound an endogenous membrane-associated serine proteinase to form an sodium dodecyl sulfate (SDS)-stable complex. Using antibodies to urokinase, elastase, proteinase 3, or cathepsin G, we demonstrated that the complex contains cathepsin G. Native cathepsin G and recombinant PI-6 formed an SDS-stable complex in vitro similar in size to that observed in the extracts. Further kinetic analysis demonstrated that cathepsin G and PI-6 rapidly form a tight 1:1 complex (ka = 6.8 ± 0.2 × 106mol/L−1s−1 at 17°C;Ki = 9.2 ± 0.04 × 10−10 mol/L). We propose that PI-6 complements 1-proteinase inhibitor and 1-antichymotrypsin (which control extracellular proteolysis) by neutralizing cathepsin G that leaks into the cytoplasm of monocytes or granulocytes during biosynthesis or phagocytosis. Control of intracellular cathepsin G may be particularly important, because it has recently been shown to activate the proapoptotic proteinase, caspase-7.

Serpins and regulation of cell death

Proteolysis is a key feature of programmed cell death. Extracellular proteinases can activate cell surface receptors which trigger apoptosis, and the effector machinery requires the activation and activity of numerous intracellular proteinases (primarily caspases). Effective control of proteolysis is essential for homeostasis and can occur at two levels: regulation of proteinase activation, and regulation of the activated proteinase. Serpins control activated proteinases and several have been implicated in the regulation of cell death. Serpins that inhibit intracellular processes include the viral proteins CrmA and SPI-1, as well as the granzyme B inhibitor, PI-9. Another endogenous serpin, PN-I, prevents the delivery of an apoptotic signal by inhibiting an extracellular proteinase from cleaving a cell surface receptor. There is evidence to suggest that PAI-2 may target an extracellular as well as an intracellular proteinase. Much of our knowledge of proteolysis within apoptotic cells has come from studies using the poxvirus serpin CrmA/SPI-2. CrmA prevents cytokine processing by inhibiting caspase-1, and protects against Fas-, TNF- and TRAIL-mediated apoptosis by inhibiting an unidentified proteinase specific to these pathways. Work with CrmA has also clearly demonstrated that there are separable effector mechanisms within cells, and that those triggered by growth factor withdrawal, matrix dissociation or cytotoxic ligands are different in several respects to those triggered by radiation, chemicals or steroid hormones. It is likely that analysis of other poxvirus serpins with different inhibitory profiles (especially SPI-1) will yield further insights into these processes. Prospecting for intracellular serpin genes in other virus species may also be fruitful. Finally, all of the serpins known to regulate intracellular proteolysis are members of the ovalbumin subgroup. It remains to be seen whether the more recently described "orphan" ovalbumin serpins (Riewald and Schleef 1995; Sprecher et al. 1995; Sun et al. 1997) also have roles in the regulation of cell death.

Regulation of pro-apoptotic leucocyte granule serine proteinases by intracellular serpins

Caspase activation and apoptosis can be initiated by the introduction of serine proteinases into the cytoplasm of a cell. Cytotoxic lymphocytes have evolved at least one serine proteinase with specific pro-apoptotic activity (granzyme B), as well as the mechanisms to deliver it into a target cell, and recent evidence suggests that other leucocyte granule proteinases may also have the capacity to kill if released into the interior of cells. For example, the monocyte/granulocyte proteinase cathepsin G can activate caspases in vitro, and will induce apoptosis if its entry into cells is mediated by a bacterial pore-forming protein. The potent pro-apoptotic activity of granzyme B and cathepsin G suggests that cells producing these (or other) proteinases would be at risk from self-induced death if the systems involved in packaging, degranulation or targeting fail and allow proteinases to enter the host cell cytoplasm. The purpose of the present review is to describe recent work on a group of intracellular serine proteinase inhibitors (serpins) which may function in leucocytes to prevent autolysis induced by the granule serine proteinases.

The plasminogen activator inhibitor-2 gene is not required for normal murine development or survival

Plasminogen activator inhibitor-2 (PAI-2), a member of the serpin gene family, is thought to serve as a primary regulator of plasminogen activation in the extravascular compartment. High levels of PAI-2 are found in keratinocytes, monocytes, and the human trophoblast, the latter suggesting a role in placental maintenance or embryo development. The primarily intracellular distribution of PAI-2 also may indicate a unique regulatory role in a protease-dependent cellular process such as apoptosis. To examine the potential functions of PAI-2 in vivo, we generated PAI-2-deficient mice by gene targeting in embryonic stem cells. Homozygous PAI-2-deficient mice exhibited normal development, survival, and fertility and were also indistinguishable from normal controls in response to a bacterial infectious challenge or endotoxin infusion. No differences in monocyte recruitment into the peritoneum were observed after thioglycollate injection. Epidermal wound healing was equivalent among PAI-2 -/- null and control mice. Finally, crossing PAI-2 -/- with PAI-1 -/- mice to generate animals deficient in both plasminogen activator inhibitors failed to uncover an overlap in function between these two related proteins.

A murine ortholog of the human serpin SCCA2 maps to chromosome 1 and inhibits chymotrypsin-like serine proteinases

Squamous cell carcinoma antigens (SCCA) 1 and 2 are inhibitory members of the high-molecular-weight serine proteinase inhibitor (serpin) family. The biological functions of SCCA1 and 2 are unknown. One approach to determining the function of human proteins is to study orthologs in other species, such as the mouse. The purpose of this study was to determine whether orthologs to human SCCA1 or 2 exist in the mouse. We report the identification and characterization of a novel serpin, sqn5 (now designated Scca2). Comparative amino acid sequence analysis suggests that Scca2 is a member of the ov-serpin subfamily of serpins with highest homology to SCCA1 and SCCA2. Fluorescence in situ hybridization revealed that the Scca2 mapped near Bcl2 on mouse chromosome 1. This region is syntenic with the human locus for SCCA1 and SCCA2 on 18q21.3. The tissue expression patterns as determined by RT-PCR showed a restricted distribution. Scca2 was detected in the lung, thymus, skin, and uterus, as are SCCA1 and SCCA2. Unlike the SCCAs, however, Scca2 was detected also in the gastrointestinal tract. Enzyme-inhibition assays using a GST-SCCA2 fusion protein revealed that SCCA2 inhibited chymotrypsin-like serine proteinases, but not papain-like cysteine proteinases. SCCA2 inhibited CTSG at 1:1 stoichiometry and with a second-order rate constant of kass = 1.7 x 10(5) M-1 s-1. SCCA2 also inhibited human mast cell chymase but the stoichiometry was 2:1, and the second-order rate constant was kass = 0.9 x 10(4) M-1 s-1. This inhibitory profile is identical to that observed for human SCCA2. Based on these findings, Scca2 appears to be the murine ortholog of human SCCA2.

Secretion of plasminogen activator inhibitor 2 by human peripheral blood monocytes occurs via an endoplasmic reticulum-golgi-independent pathway

Plasminogen activator inhibitor 2 (PAI-2) is a serine protease inhibitor (serpin) that is secreted and accumulated intracellularly by monocytes. We investigated PAI-2 synthesis by isolated human peripheral blood monocytes and found that a 47-kDa nonglycosylated form of PAI-2 was abundant in conditioned medium from monocytes. Secretion of PAI-2 by monocytes was not inhibited by agents that inhibit either ER-Golgi pathway-dependent secretion, brefeldin A, or N-linked glycosylation, tunicamycin. IL-1beta served as a control for a protein that is secreted by an ER-Golgi-independent pathway, and secretion of IL-1beta was not inhibited by brefeldin A. This was in contrast to secretion of TNFalpha, which was dependent on the ER-Golgi pathway. None of the treatments was cytotoxic toward monocytes, as measured by release of the intracellular enzyme lactate dehydrogenase (LDH) into the conditioned medium. Subcellular fractionation revealed that PAI-2 and IL-1beta were colocalized. The mechanism for secretion of PAI-2 was not dependent on calcium or intracellular trafficking via the classical vesicular mechanism(s), distinguishing it from IL-1beta secretion. These studies show that PAI-2 is secreted by primary human monocytes via an ER-Golgi-independent pathway.

The human myoepithelial cell exerts antiproliferative effects on breast carcinoma cells characterized by p21WAF1/CIP1 induction, G2/M arrest, and apoptosis

Ductal carcinoma in situ of the breast (DCIS) is surrounded by a layer of myoepithelial cells. Our previous studies have suggested that these myoepithelial cells exert paracrine tumor-suppressive effects on invasion of breast carcinoma cells. Conditioned medium (CM), concentrated 10-100x of HMS-1, HMS-3, and HMS-4, human myoepithelial cell lines, block Matrigel invasion of a series of carcinoma cell lines. Immunoprecipitation of maspin, a recently described serpin, from these CM abolishes this anti-invasive effect. Both CM and maspin-immunoprecipitated CM, however, exert equal antiproliferative effects on a series of ER+ and ER- cell lines including MCF-7, T47D, MDA-MB-231, and MDA-MB-468. These antiproliferative effects are characterized by induction of a G2/M arrest, a twofold increase in p21(WAF1/CIP1) transcription and expression, and a threefold increase in apoptosis in the breast carcinoma lines examined. The antiproliferative effects mediated by myoepithelial cell CM do not manifest themselves in an autocrine manner, are not mediated by TGF-beta1, nor involve ER- or p53-dependent pathways. Neither the antiproliferative nor the anti-invasive effects of myoepithelial cell CM is observed with nonmyoepithelial cell CM. The in vitro observations of our present study may have relevance in explaining the increased degree of apoptosis exhibited by DCIS cells in vivo. Our findings illustrate another way myoepithelial cells function as natural paracrine tumor suppressors.

Structure and sequence of human M/NEI (monocyte/neutrophil elastase inhibitor), an Ov-serpin family gene

Human monocyte/neutrophil Elastase Inhibitor (M/NEI) is a proteinase inhibitor that regulates the activity of the neutrophil proteases: elastase, cathepsin G and proteinase-3. Evidence indicates that M/NEI belongs to the Ov-serpin family (ovalbumin-related serpins), functionally diverse proteins with shared structural features. Recombinant lambda phage clones were isolated that encompass the full-length M/NEI gene plus upstream and downstream regions. The gene, 9.5kb long, consists of 7 exons and 6 introns. The 5' transcription start site identified by primer extension corresponds to a 60bp exon 1; the translation start site is in exon 2. Southern blots established a gene copy number of one. The 3' untranslated region (UTR) contains three AATAAA/AATTAA sites; these were shown to function as alternative polyadenylation signals. A 14-nucleotide upstream motif including the atypical TATA box TATAAGAG otherwise occurs only twice in GenBank, in the genes encoding neutrophil elastase and proteinase-3, target proteases inhibited by M/NEI. Comparison of M/NEI and previously characterized related genes strongly suggests that all Ov-serpins, despite a difference in chromosomal localization and exon number, nonetheless, share a common basic gene structure.

Isolation, purification, and characterization of a collagen-associated serpin, caspin, produced by murine colon adenocarcinoma cells

A 45-kDa serpin secreted by a murine colon adenocarcinoma cell line, colon26, was isolated, purified, and characterized. It was found to bind specifically to type I collagen with high affinity and to type III collagen with lower affinity. Immunohistochemical studies of murine embryonic tissues showed a specific distribution of this collagen-associated serpin, named caspin, in relation to the formation of bone, cartilage, teeth, and basement membrane. The expression of caspin in high and low lung metastatic subclones of colon26 cell lines was inversely correlated with their metastatic capacity: low lung metastatic cells secreted higher amounts of caspin than their high lung metastatic counterparts. Caspin also demonstrated high homology with human pigment epithelium-derived factor/early population doubling level cDNA-1, which reportedly induces neuronal differentiation of human retinoblastoma cells and is expressed in association with G0 growth arrest. These findings suggest that caspin/pigment epithelium-derived factor/early population doubling level cDNA-1 is a novel factor that might play a crucial role in embryogenesis and tumor metastasis through binding to the extracellular matrix.

The serine proteinase inhibitor (serpin) plasminogen activation inhibitor type 2 protects against viral cytopathic effects by constitutive interferon alpha/beta priming

The serine proteinase inhibitor (serpin) plasminogen activator inhibitor type 2 (PAI-2) is well characterized as an inhibitor of extracellular urokinase-type plasminogen activator. Here we show that intracellular, but not extracellular, PAI-2 protected cells from the rapid cytopathic effects of alphavirus infection. This protection did not appear to be related to an effect on apoptosis but was associated with a PAI-2-mediated induction of constitutive low-level interferon (IFN)-alpha/beta production and IFN-stimulated gene factor 3 (ISGF3) activation, which primed the cells for rapid induction of antiviral genes. This primed phenotype was associated with a rapid development of resistance to infection by the PAI-2 transfected cells and the establishment of a persistent productive infection. PAI-2 was also induced in macrophages in response to viral RNA suggesting that PAI-2 is a virus response gene. These observations, together with the recently demonstrated PAI-2-mediated inhibition of tumor necrosis factor-alpha induced apoptosis, (a) illustrate that PAI-2 has an additional and distinct function as an intracellular regulator of signal transduction pathway(s) and (b) demonstrate a novel activity for a eukaryotic serpin.

The inhibitory specificity of human proteinase inhibitor 8 is expanded through the use of multiple reactive site residues

Serine proteinase inhibitors function as regulators of serine proteinase activity in a variety of physiological processes. Proteinase inhibitor 8 (PI8) is a 45 kDa member of the ovalbumin family of serpins that is an inhibitor of trypsin-like proteinases through the use of Arg339 as the inhibitory P1 amino acid residue in its reactive site loop. In this study, we have described the inhibitory mechanism of recombinant human PI8 towards chymotrypsin. PI8 formed an SDS-stable complex with and inhibited the amidolytic activity of chymotrypsin via a two-step mechanism with an overall equilibrium inhibition constant of 1.7 nM and an overall second-order association rate constant of 1.0 x 10(4) M-1s-1, utilizing Ser341 as the P1 residue. The use of separate reactive site loop residues by PI8 to inhibit distinctly different classes of proteinases not only supports the hypothesis of the existence of the serpin reactive site as a highly mobile and flexible loop, but also suggests an evolved function in which separate amino acid residues can be used to broaden the inhibitory specificity of PI8.

Expression of Bomapin, a Novel Human Serpin, in Normal/Malignant Hematopoiesis and in the Monocytic Cell Lines THP-1 and AML-193

Our group recently cloned the cDNA-encoding bomapin, a member of the serine protease inhibitor (serpin) superfamily, from a human bone marrow cDNA library (J Biol Chem 270:2675, 1995). To understand its expression within the hematopoietic compartment, RNA extracted from bone marrow or peripheral blood from normal donors and patients with leukemia was reverse transcribed and analyzed by polymerase chain reaction (PCR). Bomapin PCR products were readily detected in normal bone marrow, which was designated as a medium mRNA level. In peripheral blood, bomapin expression was low or undetectable in normal donors (n = 6) and patients with chronic lymphocytic leukemia (n = 6). Blood from patients with chronic myeloid leukemia (n = 6), chronic myelomonocytic leukemia (n = 6), acute myeloid leukemia (n = 5), and acute lymphocytic leukemia (n = 5) exhibited low to medium levels of bomapin expression. Furthermore, a high level of bomapin expression was detected in one individual with acute monocytic leukemia. These data suggest that bomapin expression may be elevated in hematopoietic cells of monocytic lineage. Therefore, we analyzed the expression of bomapin within cell lines that exhibited characteristics of the monocytic lineage. Bomapin PCR products were detected in the monocytic THP-1 and AML-193 cell lines but not in CRL 7607, CRL 7541, KG-1, or K562 cells. Induction of bomapin transcripts was not detected in the latter series of cell lines following a 24-hour treatment with phorbol myristate acetate (PMA, 10−8mol/L) or tumor necrosis factor-α (TNF-α, 30 U/mL), whereas treatment of THP-1 or AML-193 cells with these agents reduced the intensity of the bomapin PCR products. Northern blotting confirmed these results and showed that the expression of bomapin in THP-1 cells was downregulated over a 4-day period by PMA and, to a lesser extent, TNF-α. Immunoblotting was used to show the presence of a 40-kD protein in THP-1 cytosol preparations. Bomapin antigen levels were correspondingly reduced after treatment with PMA. Because PMA and TNF-α induce monocytic differentiation in THP-1 and AML-193 cells, these data increase the possibility that bomapin may play a role in the regulation of protease activities specifically in early stages of cellular differentiation.

Terminal differentiation of human breast cancer through PPAR gamma

We have previously demonstrated that PPAR gamma stimulates the terminal differentiation of adipocyte precursors when activated by synthetic ligands, such as the antidiabetic thiazolidinedione (TZD) drugs. We show here that PPAR gamma is expressed at significant levels in human primary and metastatic breast adenocarcinomas. Ligand activation of this receptor in cultured breast cancer cells causes extensive lipid accumulation, changes in breast epithelial gene expression associated with a more differentiated, less malignant state, and a reduction in growth rate and clonogenic capacity of the cells. Inhibition of MAP kinase, shown previously to be a powerful negative regulator of PPAR gamma, improves the TZD ligand sensitivity of nonresponsive cells. These data suggest that the PPAR gamma transcriptional pathway can induce terminal differentiation of malignant breast epithelial cells and thus may provide a novel, nontoxic therapy for human breast cancer.

An atlas of serpin conformations

The serpins are a family of proteins that inhibit chymotrypsin-like serine proteinases, with an unusual mechanism involving a large conformational change known as the stressed-->relaxed (S-->R) transition. This article is a guide to the known serpin conformations and their biological significance.

Expression genetics: a different approach to cancer diagnosis and prognosis

Expression genetics is a new approach to the identification of cancer-related genes. Instead of studying gene mutations at the genome level, it focuses on the investigation of heredity at the RNA level. By isolating genes whose expression is up or down regulated in cancers, expression geneticists study their function in the context of gene regulation. A major goal of expression genetics in cancer is to correct gene expression in tumors by the application of potential therapeutic agents.