Biomedical subjects

Rick T Owens

Publications and source records attributed to Rick T Owens.

8 recordsLinked to original sources

PubMed2006

Decorin protein core inhibits in vivo cancer growth and metabolism by hindering epidermal growth factor receptor function and triggering apoptosis via caspase-3 activation.

Decorin is not only a regulator of matrix assembly but also a key signaling molecule that modulates the activity of tyrosine kinase receptors such as the epidermal growth factor receptor (EGFR). Decorin evokes protracted internalization of the EGFR via a caveolar-mediated endocytosis, which leads to EGFR degradation and attenuation of its signaling pathway. In this study, we tested if systemic delivery of decorin protein core would affect the biology of an orthotopic squamous carcinoma xenograft. After tumor engraftment, the animals were given intraperitoneal injections of either vehicle or decorin protein core (2.5-10 mg kg(-1)) every 2 days for 18-38 days. This regimen caused a significant and dose-dependent inhibition of the tumor xenograft growth, with a concurrent decrease in mitotic index and a significant increase in apoptosis. Positron emission tomography showed that the metabolic activity of the tumor xenografts was significantly reduced by decorin treatment. Decorin protein core specifically targeted the tumor cells enriched in EGFR and caused a significant down-regulation of EGFR and attenuation of its activity. In vitro studies showed that the uptake of decorin by the A431 cells was rapid and caused a protracted down-regulation of the EGFR to levels similar to those observed in the tumor xenografts. Furthermore, decorin induced apoptosis via activation of caspase-3. This could represent an additional mechanism whereby decorin might influence cell growth and survival.

Animals↗

PubMed2006

Biglycan regulates the expression and sarcolemmal localization of dystrobrevin, syntrophin, and nNOS.

The dystrophin-associated protein complex (DAPC) provides a linkage between the cytoskeleton and the extracellular matrix (ECM) and is also a scaffold for a host of signaling molecules. The constituents of the DAPC must be targeted to the sarcolemma in order to properly function. Biglycan is an ECM molecule that associates with the DAPC. Here, we show that biglycan null mice exhibit a mild dystrophic phenotype and display a selective reduction in the localization of alpha-dystrobrevin-1 and -2, alpha- and beta1-syntrophin, and nNOS at the sarcolemma. Purified biglycan induces nNOS redistribution to the plasma membrane in cultured muscle cells. Biglycan protein injected into muscle becomes stably associated with the sarcolemma and ECM for at least 2 wk. This injected biglycan restores the sarcolemmal expression of alpha-dystrobrevin-1 and -2, and beta1- and beta2-syntrophin in biglycan null mice. We conclude that biglycan is important for the maintenance of muscle cell integrity and plays a direct role in regulating the expression and sarcolemmal localization of the intracellular signaling proteins dystrobrevin-1 and -2, alpha- and beta1-syntrophin and nNOS.

Animals↗

PubMed2006

WARP is a novel multimeric component of the chondrocyte pericellular matrix that interacts with perlecan.

WARP is a novel member of the von Willebrand factor A domain superfamily of extracellular matrix proteins that is expressed by chondrocytes. WARP is restricted to the presumptive articular cartilage zone prior to joint cavitation and to the articular cartilage and fibrocartilaginous elements in the joint, spine, and sternum during mouse embryonic development. In mature articular cartilage, WARP is highly specific for the chondrocyte pericellular microenvironment and co-localizes with perlecan, a prominent component of the chondrocyte pericellular region. WARP is present in the guanidine-soluble fraction of cartilage matrix extracts as a disulfide-bonded multimer, indicating that WARP is a strongly interacting component of the cartilage matrix. To investigate how WARP is integrated with the pericellular environment, we studied WARP binding to mouse perlecan using solid phase and surface plasmon resonance analysis. WARP interacts with domain III-2 of the perlecan core protein and the heparan sulfate chains of the perlecan domain I with K(D) values in the low nanomolar range. We conclude that WARP forms macromolecular structures that interact with perlecan to contribute to the assembly and/or maintenance of "permanent" cartilage structures during development and in mature cartilages.

Amino Acid Motifs↗

PubMed2006

Biglycan binds to alpha- and gamma-sarcoglycan and regulates their expression during development.

The dystrophin-associated protein complex (DAPC), which links the cytoskeleton to the extracellular matrix, is essential for muscle cell survival, and is defective in a wide range of muscular dystrophies. The DAPC contains two transmembrane subcomplexes-the dystroglycans and the sarcoglycans. Although several extracellular binding partners have been identified for the dystroglycans, none have been described for the sarcoglycan subcomplex. Here we show that the small leucine-rich repeat (LRR) proteoglycan biglycan binds to alpha- and gamma-sarcoglycan as judged by ligand blot overlay and co-immunoprecipitation assays. Our studies with biglycan-decorin chimeras show that alpha- and gamma-sarcoglycan bind to distinct sites on the polypeptide core of biglycan. Both biglycan proteoglycan as well as biglycan polypeptide lacking glycosaminoglycan (GAG) side chains are components of the dystrophin glycoprotein complex isolated from adult skeletal muscle membranes. Finally, our immunohistochemical and biochemical studies with biglycan null mice show that the expression of alpha- and gamma-sarcoglycan is selectively reduced in muscle from young (P14-P21) animals, while levels in adult muscle (> or = P35) are unchanged. We conclude that biglycan is a ligand for two members of the sarcoglycan complex and regulates their expression at discrete developmental ages.

Animals↗

PubMed2005

Interactions of the extracellular matrix proteoglycans decorin and biglycan with C1q and collectins.

Decorin and biglycan are closely related abundant extracellular matrix proteoglycans that have been shown to bind to C1q. Given the overall structural similarities between C1q and mannose-binding lectin (MBL), the two key recognition molecules of the classical and the lectin complement pathways, respectively, we have examined functional consequences of the interaction of C1q and MBL with decorin and biglycan. Recombinant forms of human decorin and biglycan bound C1q via both collagen and globular domains and inhibited the classical pathway. Decorin also bound C1 without activating complement. Furthermore, decorin and biglycan bound efficiently to MBL, but only biglycan could inhibit activation of the lectin pathway. Other members of the collectin family, including human surfactant protein D, bovine collectin-43, and conglutinin also showed binding to decorin and biglycan. Decorin and biglycan strongly inhibited C1q binding to human endothelial cells and U937 cells, and biglycan suppressed C1q-induced MCP-1 and IL-8 production by human endothelial cells. In conclusion, decorin and biglycan act as inhibitors of activation of the complement cascade, cellular interactions, and proinflammatory cytokine production mediated by C1q. These two proteoglycans are likely to down-regulate proinflammatory effects mediated by C1q, and possibly also the collectins, at the tissue level.

Amino Acid Sequence↗

PubMed2005

Decorin evokes protracted internalization and degradation of the epidermal growth factor receptor via caveolar endocytosis.

Decorin inhibits the epidermal growth factor receptor (EGFR) by down-regulating its tyrosine kinase activity, thereby blocking the growth of a variety of transformed cells and tumor xenografts. In this study we provide evidence that decorin directly binds to the EGFR causing its dimerization, internalization, and ultimately its degradation. Using various pharmacological agents to disrupt clathrin-dependent and -independent endocytosis, we demonstrate that decorin evokes a protracted internalization of the EGFR primarily via caveolar-mediated endocytosis. In contrast to EGF, decorin targets the EGFR to caveolae, but not to early or recycling endosomes. Ultimately, however, both EGF- and decorin-induced pathways converge into late endosomes/lysosomes for final degradation. Thus, we have discovered a novel biological mechanism for decorin that could explain its anti-proliferative and anti-oncogenic mode of action.

Antineoplastic Agents↗

PubMed2005

Decorin prevents metastatic spreading of breast cancer.

Metastases in breast cancer are a vital concern in treatment, with epidermal growth factor receptor and ErbB2 strongly implicated in mediating tumor invasion and spreading. In this study, we investigated the role of decorin in suppressing both primary breast carcinomas and pulmonary metastases. We show that decorin causes marked growth suppression both in vitro and in vivo using a metastatic breast cancer cell line and an orthotopic mammary carcinoma model. Treatment with decorin protein core reduced primary tumor growth by 70% and eliminated observed metastases. An adenoviral vector containing the decorin transgene caused primary tumor retardation of 70%, in addition to greatly reducing observed metastases. Moreover, we demonstrate that ErbB2 phosphorylation and total receptor protein levels are reduced in this model system upon de novo expression of decorin under the control of a doxycycline-inducible promoter. Primary tumor growth in vivo was reduced by up to 67% upon decorin induction, and pulmonary metastases were markedly hampered as well. These effects are likely occurring through decorin's long-term downregulation of the ErbB2 tyrosine kinase cascade. These results demonstrate a novel role for decorin in reduction or prevention of tumor metastases in this breast cancer model and could eventually lead to improved therapeutics for metastatic breast cancer.

Adenoviridae↗

PubMed2003

Biologically active decorin is a monomer in solution.

It has been reported that decorin and its protein core can have molecular masses nearly double the size of those previously published, suggesting a dimeric structure. In this study we tested whether biologically active decorin and its glycoprotein core would form dimers in solution. We used homo- and hetero-bifunctional chemical cross-linking reagents, BS3 and sulfo-SMPB, respectively, as well as glutaraldehyde and found no preferential dimer formation, whether chemical cross-linking was performed in the presence or absence of live cells. Under the same experimental conditions, we easily detected dimers of epidermal growth factor receptor and basic fibroblast growth factor, two glycoproteins known to dimerize. Only at very high cross-linker to decorin molar ratios (2000:1) were trimers and multimers observed, but performing the chemical cross-linking in the presence of a reducing agent abolished these. The elution of decorin protein core in Superose 6 gel chromatography gave masses compatible with monomeric proteins, both before and after denaturation with 2.5 M guanidine HCl. Matrix-assisted laser desorption ionization gave a mass of 44,077 Da for decorin protein core, without any evidence of dimers or oligomers. Extensive oligomerization of the decorin protein core was observed only after dialysis against water and freeze-drying. These oligomers were considered artifacts because they were independent of chemical cross-linking and were resistant to heat denaturation and disulfide-bond reduction. Oligomeric preparations showed markedly reduced biological activity in both phosphorylation and collagen fibrillogenesis assays. Thus, biologically active decorin is a monomer in solution and, as such, is a monovalent ligand for various extracellular matrix proteins, growth factors, and cell surface receptors.

Cell Line↗