The membrane-anchored MMP inhibitor RECK is a key regulator of extracellular matrix integrity and angiogenesis

Matrix metalloproteinases (MMPs) are essential for proper extracellular matrix remodeling. We previously found that a membrane-anchored glycoprotein, RECK, negatively regulates MMP-9 and inhibits tumor invasion and metastasis. Here we show that RECK regulates two other MMPs, MMP-2 and MT1-MMP, known to be involved in cancer progression, that mice lacking a functional RECK gene die around E10.5 with defects in collagen fibrils, the basal lamina, and vascular development, and that this phenotype is partially suppressed by MMP-2 null mutation. Also, vascular sprouting is dramatically suppressed in tumors derived from RECK-expressing fibrosarcoma cells grown in nude mice. These results support a role for RECK in the regulation of MMP-2 in vivo and implicate RECK downregulation in tumor angiogenesis.

Human Semaphorin 6B [(HSA)SEMA6B], A Novel Human Class 6 Semaphorin Gene: Alternative Splicing and All-Trans-Retinoic Acid-Dependent Downregulation in Glioblastoma Cell Lines

We have identified a novel human gene related to the class 6 semaphorin family of axon guidance molecules, termed human semaphorin 6B or (HSA)SEMA6B. Two splicing variants of this gene were identified by RT-PCR: (HSA)SEMA6B.1 (short isoform) and (HSA)SEMA6B.2 (longer isoform). Computational analysis suggests that these isoforms correspond to putative secreted and transmembranous semaphorins, respectively. The levels of (HSA)SEMA6B expression were evaluated by Northern blot analysis in different tissues and in some pathological and pharmacological conditions. We observed that (HSA)SEMA6B is highly expressed in human brain and at lower levels in a variety of other tissues. Interestingly, the (HSA)SEMA6B transcript was downregulated in two different human glioblastoma cell lines (T98G and A172) upon prolonged treatment with all-trans-retinoic acid, an anti-tumor and differentiation-inducing agent.

Involvement of the Sp1 site in ras-mediated downregulation of the RECK metastasis suppressor gene

We have isolated and characterized the 5'-flanking region of the mouse RECK gene aiming to understand the mechanism of oncogene-mediated suppression of RECK gene expression. The upstream 52-base region was found to contain a promoter activity which is, to some extent, suppressed by the ras oncogene. This region contains two Sp1-binding motifs, one cEBPb-binding motif, and one CAAT box. Although both of the Sp1 sites were found to associate with Sp1 as well as Sp3 proteins, ras responsiveness seems to be mediated only by the downstream Sp1 site. Our data indicate that the Sp1 motif in certain contexts can serve as a negative target for the Ras signal.

Oncogene-mediated downregulation of RECK, a novel transformation suppressor gene

The RECK gene was initially isolated as a transformation suppressor gene encoding a novel membrane-anchored glycoprotein and later found to suppress tumor invasion and metastasis by regulating matrix metalloproteinase-9. Its expression is ubiquitous in normal tissues, but undetectable in many tumor cell lines and in fibroblastic lines transformed by various oncogenes. The RECK gene promoter has been cloned and characterized. One of the elements responsible for the oncogene-mediated downregulation of mouse RECK gene is the Sp1 site, where the Sp1 and Sp3 factors bind. Sp1 transcription factor family is involved in the basal level of promoter activity of many genes, as well as in dynamic regulation of gene expression; in a majority of cases as a positive regulator, or, as exemplified by the oncogene-mediated suppression of RECK gene expression, as a negative transcription regulator. The molecular mechanisms of the down-regulation of mouse RECK gene and other tumor suppressor genes are just beginning to be uncovered. Understanding the regulation of these genes may help to develop strategies to restore their expression in tumor cells and, hence, suppress the cells' malignant behavior.

Regulation of matrix metalloproteinase-9 and inhibition of tumor invasion by the membrane-anchored glycoprotein RECK

A human fibroblast cDNA expression library was screened for cDNA clones giving rise to flat colonies when transfected into v-Ki-ras-transformed NIH 3T3 cells. One such gene, RECK, encodes a membrane-anchored glycoprotein of about 110 kDa with multiple epidermal growth factor-like repeats and serine-protease inhibitor-like domains. While RECK mRNA is expressed in various human tissues and untransformed cells, it is undetectable in tumor-derived cell lines and oncogenically transformed cells. Restored expression of RECK in malignant cells resulted in suppression of invasive activity with concomitant decrease in the secretion of matrix metalloproteinase-9 (MMP-9), a key enzyme involved in tumor invasion and metastasis. Moreover, purified RECK protein was found to bind to, and inhibit the proteolytic activity of, MMP-9. Thus, RECK may link oncogenic signals to tumor invasion and metastasis.

Use of cDNA cloning to study the mechanism of action of glucocorticoid hormones at the molecular level

We have previously described a dramatic phenomenon of phenotypic reversion (tumor to normal) caused by glucocorticoid hormones in C6/ST1 rat glioma cells, but not in their hormone-resistant C6/P7 counterpart. Blind cDNA cloning was adopted to search for glucocorticoid-regulated gene sequences responsible for this phenotype reversion. Differential hybridization and differential display of RNA were used in parallel to isolate a number of cDNA clones that were characterized by DNA sequencing and Northern blot analysis. This approach was coupled to the analysis of known growth control genes (oncogenes, tumor suppressor genes, cyclins, cyclin-dependent kinases, other kinases). Glucocorticoid target genes isolated from this cell system are likely to be good anti-tumor candidate molecules which can be used in tumor therapy and anti-tumor drug design.

Molecular genetic approach to cell proliferation control and neoplasia

A number of gene products involved in the control of cell proliferation fall into one of two classes: oncogenes and tumor suppressor genes. The same gene products have also been associated with malignant growth (tumors) caused by radiation, chemicals and tumor viruses. Here we describe our attempts to elucidate the molecular mechanisms underlying polyomavirus-induced cell transformation and the anti-tumor activity of glucocorticoid hormones. Wild type and mutant polyomavirus middle T (MT) overexpressing cell lines, generated with retroviral vector constructs, were used to investigate the role played by peptide growth factor primary response genes (fos, jun, myc, JE, KC) in viral transformation and to map the transduction pathway of the mitogenic signal of MT. Overexpression of MT leads to increased AP-1 (Fos/Jun) transcriptional complex activity. Transformation defective mutant analysis allowed the identification of sites in the MT molecule that are crucial for this activity. Two different approaches were used to investigate the molecular basis for glucocorticoids anti-tumor activity, namely: blind cloning of cDNAs and analysis of growth control genes in C6 glioma cell variants that are either hypersensitive (C6/ST1) or unresponsive to glucocorticoids (C6/P7). Four different glucocorticoid-regulated cDNA sequences were isolated using differential hybridization. A number of differentially expressed sequences were isolated from glucocorticoid-treated C6/ST1 cells by differential display (DDRT-PCR) and are currently being characterized. Expression of known growth control genes in C6/ST1 cells allowed the identification of important candidates for glucocorticoid hormone targets.

Glucocorticoid-regulated gene in transformed to normal phenotypic reversion

Glucocorticoid hormones modulate the actions of peptide growth factors and constitute important therapeutic tools as anti-inflammatory and anti-tumor agents. The C6 rat glioma cell line responds to glucocorticoids with changes in morphology and growth block. The hyper-responsive ST1 cell variant displays a dramatic phenotypic reversion under the influence of these hormones. Thus, the transformed and tumorigenic cells reversibly change to a normal and non-tumorigenic phenotype. In addition, the cells also produce a C-type retrovirus. We used poly A+ mRNA from ST1 cells that had been treated with hydrocortisone to generate a cDNA library that was then screened, by differential hybridization, for glucocorticoid-responsive cellular sequences. The retroviral genomic RNA was used to generate a viral-specific probe. Cross hybridization led to the isolation of at least 4 cDNA clones of which 3 are cellular sequences and one corresponds to a retroviral gene. These clones were characterized by DNA sequencing and Northern blot hybridization analysis.