A role for membrane-type serine protease (MT-SP1) in intestinal epithelial turnover

Increased expression of matriptase is associated with histopathologic grades of cervical neoplasia

Matriptase is an epithelial-derived, integral serine protease that has been implicated in the progression of epithelial tumors. We investigated whether the expression of matriptase is associated with the progression of cervical neoplasia. Using immunohistochemistry, we evaluated the matriptase expression in 89 formalin-fixed paraffin-embedded cervical tissues that included 10 normal cervical specimens, 19 low-grade squamous intraepithelial lesions, 20 high-grade squamous intraepithelial lesions, 20 invasive squamous cell carcinomas (ISCC) without lymph node (LN) metastasis, and 20 ISCC with lymph node metastasis. We also used the reverse transcriptase-polymerase chain reaction technique to determine the expression of matriptase transcripts in normal cervical and ISCC tissues. The immunohistochemical staining showed that the expression of matriptase was undetectable in all normal cervical squamous epithelia, but had cytoplasmic and membranous staining in the normal endocervical glands. Staining gradually increased in accordance with the histopathologic grades from low-grade squamous intraepithelial lesions to high-grade squamous intraepithelial lesions and ISCC ( P < .001); matriptase was detected in most cases (95%) of ISCC. In addition, matriptase transcripts were expressed in all (n = 26) of the ISCC cases by microdissection and reverse transcriptase-polymerase chain reaction, whereas none of the normal squamous epithelia cases (n = 3) expressed matriptase transcripts. These results suggest that matriptase may play a significant role in the development of cervical carcinoma and may serve as a useful marker of the malignant transformation of cervical squamous cells. Further studies could potentially lead to the development of novel approaches for early detection and therapy for this disease.

CVS-3983, a selective matriptase inhibitor, suppresses the growth of androgen independent prostate tumor xenografts

BACKGROUND

Matriptase, a type-II transmembrane serine protease, is expressed by cancers of epithelial origin including breast, colon, and prostate carcinomas and has been implicated in tumor growth and progression. We studied the effects of CVS-3983, a selective small molecule matriptase inhibitor, on the growth of the androgen independent (AI) CWR22R and CWRSA6 human prostate cancer xenograft models.

METHODS

CVS-3983 was administered i.p. twice-daily 7-days per week for 2-3 weeks to mice with established tumors. Measurements of tumor volume were made twice weekly. The effect of CVS-3983 on CWR22RV1 cell invasion through a reconstituted basement membrane matrix of proteins was also evaluated. Matriptase expression across the tumor lines was assessed by RT-PCR and Western blotting.

RESULTS

CVS-3983 inhibited final mean tumor volume by 65.5% (n = 10, P = 0.0002) in the CWR22R model and by 56.2% (n = 8, P = 0.0017) in the CWRSA6 tumor model compared with vehicle-treated tumors. CVS-3983 did not inhibit the proliferation of CWR22RV1 cells in vitro; however, the small molecule did significantly reduce by 30.2% the invasion of these cells in vitro through a reconstituted basement membrane matrix. Molecular analysis of the xenograft tumors demonstrated high expression levels of matriptase at the RNA and protein levels, which were not affected by CVS-3983 treatment.

CONCLUSIONS

These results identify CVS-3983 as a potent inhibitor of AI prostate cancer cell invasion in vitro and established xenograft tumor growth in vivo.

Regeneration of injured intestinal mucosa is impaired in hepatocyte growth factor activator-deficient mice

BACKGROUND AND AIMS

Hepatocyte growth factor activator (HGFA) is a serum proteinase that specifically converts an inactive single-chain form of hepatocyte growth factor (HGF) into an active 2-chain form. HGFA is produced in its precursor form and then activated in injured tissues. To address the precise role of HGFA and to investigate the mechanisms of HGF activation in injured tissues, we generated mice deficient in HGFA.

METHODS

HGFA-deficient mice were generated using targeted gene disruption. The regenerating process of intestinal mucosa damaged by oral administration of dextran sodium sulfate (DSS) or by rectal administration of acetic acid was examined in both HGFA-deficient and control mice. HGF processing activity was analyzed using Western blotting and an HGF activation assay.

RESULTS

Homozygous mutant mice were viable and fertile without obvious abnormalities. When mice were treated with 3% DSS in drinking water for 6 days followed by distilled water without DSS, 72% of HGFA-deficient mice died through day 12 while 75% of control mice survived injury. Similar results were also observed in the acetic acid-induced intestinal injury; the survival rate was 36.6% in HGFA-deficient mice and 84.2% in control mice. In HGFA-deficient mice, the injured mucosa was not sufficiently covered by regenerated epithelium and the activation of HGF was impaired in the injured colon.

CONCLUSIONS

These results indicate that HGFA is required for repair of injured intestinal mucosa but is not essential for normal development during embryogenesis or after birth.

Quantitative proteomic analysis of proteins released by neoplastic prostate epithelium

Prostate cancer is unusual among neoplasms in that it may be diagnosed at a curable stage through detection of a protein in serum, the serine protease prostate-specific antigen (PSA). PSA is secreted by both normal and neoplastic prostate epithelial cells in response to androgenic hormones and has found widespread use in cancer screening. Because PSA screening is controversial due to sensitivity and specificity issues, efforts continue to focus on the identification and characterization of additional markers that may be used for diagnostic and therapeutic purposes. In this study, we report the application of quantitative proteomic techniques that incorporate isotope coded affinity tag reagents and tandem mass spectrometry to comprehensively identify secreted and cell surface proteins from neoplastic prostate epithelium. LNCaP cells, a prostate tumor-derived cell line that secretes PSA in response to androgen exposure, were grown in a low protein-defined media under androgen-stimulated (A+) and -starved (A-) conditions. Proteomic analysis of the media identified in excess of 600 proteins, 524 of which could be quantified. Nine percent of the proteins had A+/A- ratios > 2.0, including PSA, and 2.5% had ratios < 0.5. A subset of these androgen-regulated proteins appeared to be expressed in abundance. Of these, selected mass spectrometry observations were confirmed by Western analysis. The findings suggest that androgen-mediated release of proteins may occur through the activation of proteolytic enzymes rather than exclusively through transcriptional or translational control mechanisms. On the basis of their known functional roles, several of the abundant androgen-regulated proteins may participate in the progression of neoplastic epithelial cell growth and should be considered as potential serum markers of neoplastic prostate diseases.

Characterization of matriptase expression in normal human tissues

Matriptase is a type II transmembrane serine protease that has been implicated in the progression of epithelium-derived tumors. The role of this protease in the biology of normal epithelial cells remains to be elucidated. Matriptase mRNA has been detected by Northern analysis in tissues rich in epithelial cells, and the protein is expressed in vivo in normal and cancerous breast, ovarian, and colon tissues. However, a systematic analysis of the distribution of matriptase protein and mRNA in normal human tissues rich in epithelium has not been reported. In this study we characterized the expression of the protease in a wide variety of normal human tissues using a tissue microarray and whole tissue specimens. Significant immunoreactivity and mRNA expression were detected in the epithelial components of most epithelium-containing tissues. Matriptase expression was found in all types of epithelium, including columnar, pseudostratified columnar, cuboidal, and squamous. Distinct spatial distributions of reactivity were observed in the microanatomy of certain tissues, however. This suggests that although matriptase is broadly expressed among many types of epithelial cells, its activity within a tissue may be regulated in part at the protein and mRNA levels during the differentiation of selected epithelia.

The activation of matriptase requires its noncatalytic domains, serine protease domain, and its cognate inhibitor

The activation of matriptase requires proteolytic cleavage at a canonical activation motif that converts the enzyme from a one-chain zymogen to an active, two-chain protease. In this study, matriptase bearing a mutation in its catalytic triad was unable to undergo this activational cleavage, suggesting that the activating cleavage occurs via a transactivation mechanism where interaction between matriptase zymogen molecules leads to activation of the protease. Using additional point and deletion mutants, we showed that activation of matriptase requires proteolytic processing at Gly-149 in the SEA domain of the protease, glycosylation of the first CUB domain and the serine protease domain, and intact low density lipoprotein receptor class A domains. Its cognate inhibitor, hepatocyte growth factor activator inhibitor-1, may also participate in the activation of matriptase, based on the observation that matriptase activation did not occur when the protease was co-expressed with hepatocyte growth factor activator inhibitor-1 mutated in its low density lipoprotein receptor class A domain. These results suggest that besides matriptase catalytic activity, matriptase activation requires post-translational modification of the protease, intact noncatalytic domains, and its cognate inhibitor.

Activation of human meprin-alpha in a cell culture model of colorectal cancer is triggered by the plasminogen-activating system

The activation of latent proenzymes is an important mechanism for the regulation of localized proteolytic activity. Human meprin-alpha, an astacin-like zinc metalloprotease expressed in normal colon epithelial cells, is secreted as a zymogen into the intestinal lumen. Here, meprin is activated after propeptide cleavage by trypsin. In contrast, colorectal cancer cells secrete meprin-alpha in a non-polarized way, leading to accumulation and increased activity of meprin-alpha in the tumor stroma. We have analyzed the activation mechanism of promeprin-alpha in colorectal cancer using a co-culture model of the intestinal mucosa composed of colorectal adenocarcinoma cells (Caco-2) cultivated on filter supports and intestinal fibroblasts grown in the companion dish. We provide evidence that meprin-alpha is activated by plasmin and show that the presence of plasminogen in the basolateral compartment of the co-cultures is sufficient for promeprin-alpha activation. Analysis of the plasminogen-activating system in the co-cultures revealed that plasminogen activators produced and secreted by fibroblasts converted plasminogen to active plasmin, which in turn generated active meprin-alpha. This activation mechanism offers an explanation for the observed meprin-alpha activity in the tumor stroma, a prerequisite for a potential role of this protease in colorectal cancer.

Matriptase-2, a membrane-bound mosaic serine proteinase predominantly expressed in human liver and showing degrading activity against extracellular matrix proteins

We have identified and cloned a fetal liver cDNA encoding a new serine proteinase that has been called matriptase-2. This protein exhibits a domain organization similar to other members of an emerging family of membrane-bound serine proteinases known as type II transmembrane serine proteinases. Matriptase-2 contains a short cytoplasmic domain, a type II transmembrane sequence, a central region with several modular structural domains including two CUB (complement factor C1s/C1r, urchin embryonic growth factor, bone morphogenetic protein) domains and three low density lipoprotein receptor tandem repeats, and finally, a C-terminal catalytic domain with all typical features of serine proteinases. The human matriptase-2 gene maps to 22q12-q13, a location that differs from all type II transmembrane serine proteinase genes mapped to date. Immunofluorescence and Western blot analysis of COS-7 cells transfected with the isolated cDNA confirmed that matriptase-2 is anchored to the cell surface. Matriptase-2 was expressed in Escherichia coli, and the purified recombinant protein hydrolyzed synthetic substrates used for assaying serine proteinases and endogenous proteins such as type I collagen, fibronectin, and fibrinogen. Matriptase-2 could also activate single-chain urokinase plasminogen activator, albeit with low efficiency. These activities were abolished by inhibitors of serine proteinases but not by inhibitors of other classes of proteolytic enzymes. Northern blot analysis demonstrated that matriptase-2 transcripts are only detected at significant levels in both fetal and adult liver, suggesting that this novel serine proteinase may play a specialized role in matrix remodeling processes taking place in this tissue during development or in adult tissues.