Phenotypic alterations in Kaposi's sarcoma cells by antisense reduction of perlecan

Perlecan, a modular instructive proteoglycan with diverse functional properties

This study reviewed some new aspects of the modular proteoglycan perlecan, a colossal proteoglycan with a 467 kDa core protein and five distinct functional domains. Perlecan is a heparan sulphate proteoglycan that transiently displays native CS sulphation motifs 4-C-3 and 7-D-4 during tissue morphogenesis these are expressed by progenitor cell populations during tissue development. Perlecan is susceptible to fragmentation by proteases during tissue development and in pathological tissues particularly in domains IV and V. The fragmentation pattern of domain IV has been suggested as a means of grading prostate cancer. Domain V of perlecan is of interest due to its interactive properties with integrin α5β1 that promotes pericyte migration enhancing PDGF-BB-induced phosphorylation of PDGFRβ, Src homology region 2 domain-containing phosphatase-2, and focal adhesion kinase supporting the repair of the blood brain barrier following ischaemic stroke. Fragments of domain V can also interact with α2β1 integrin disrupting tube formation by endothelial cells. LG1-LG2, LG3 fragments can antagonise VEGFR2, and α2β1 integrin interactions preventing angiogenesis by endothelial cells. These domain V fragments are of interest as potential anti-tumour agents. Perlecan attached to the luminal surfaces of endothelial cells in blood vessels acts as a flow sensor that signals back to endothelial and smooth muscle cells to regulate vascular tone and blood pressure. Perlecan also acts as a flow sensor in the lacuno-canalicular space regulating osteocytes and bone homeostasis. Along with its biomechanical regulatory properties in cartilaginous tissues this further extends the functional repertoire of this amazingly diverse functional proteoglycan.

Expression and Circulating Levels of Perlecan in Breast Cancer - Implications for Oestrogen Dependent Stromal Remodeling

Localised breast cancer can be cured by surgery and adjuvant treatments, but mortality remains high as some tumours metastasize early. Perlecan is a basement membrane (BM) protein involved in tumour development and progression. Here, mRNA and protein expression of perlecan, and mRNA expression of matrix degrading enzymes were studied in normal breast and invasive breast cancer, and correlated to prognostic risk factors, in particular oestrogen status. Moreover, plasma levels of perlecan were measured in patients with breast cancer and compared with controls. mRNA data was extracted from the Cancer Genome Atlas database. Perlecan protein expression was visualized using immunofluorescence and plasma levels measured by ELISA assay. Perlecan mRNA levels were twice as high in normal breast compared with breast cancer tissue. A strong correlation was found between mRNA expression of perlecan and several matrix-degrading enzymes in oestrogen receptor positive (ER+) tumours. Perlecan protein was localized to both epithelial and vascular BMs, but absent in the stroma in normal breast. In breast cancer, the expression of perlecan in epithelial BM was fragmented or completely lost, with a marked upregulation of perlecan expression in the stroma. Significantly higher levels of perlecan were found in plasma of ER+ patients when compared with ER- patients. This study shows that perlecan expression and degradation in breast cancer may be linked to the ER status of the tumour.

Discovery of HSPG2 (Perlecan) as a Therapeutic Target in Triple Negative Breast Cancer

In recent years, there have been significant advances in the treatment of breast cancer resulting in remarkably high survival rates. However, treatment options for metastatic triple negative breast cancer (TNBC) are quite limited due to a lack of identifiable, unique markers. Using a phage display-based whole cell biopanning procedure, we developed two human antibodies that bind to tumor cells with a metastatic TNBC phenotype. Our studies further identified domain 1 of HSPG2 (perlecan) protein as the cognate cell surface antigen bound by the antibody. Immunohistochemistry studies utilizing patient tissue samples revealed significant cell surface expression of HSPG2 in both primary tumors and metastatic lesions. Further, higher HSPG2 expression correlated with poor survival in TNBC. The affinity-matured antibody inhibited the growth of triple negative MDA-MB-231 tumors to a greater extent in nude mice than in NSG mice, pointing to the potential role of natural killer cell-mediated antibody-dependent cell cytotoxicity. This mechanism of action was confirmed through in vitro assays using mouse splenocytes and human peripheral blood mononuclear cells (PBMCs). These results suggest that HSPG2 is a promising target in metastatic TNBC and HSPG2-targeted antibodies could represent a potentially novel class of targeted therapeutics for TNBC.

Cancer Cell Glycocalyx and Its Significance in Cancer Progression

Cancer is a malignant tumor that threatens the health of human beings, and has become the leading cause of death in urban and rural residents in China. The glycocalyx is a layer of multifunctional glycans that covers the surfaces of a variety of cells, including vascular endothelial cells, smooth muscle cells, stem cells, epithelial, osteocytes, as well as cancer cells. The glycosylation and syndecan of cancer cell glycocalyx are unique. However, heparan sulfate (HS), hyaluronic acid (HA), and syndecan are all closely associated with the processes of cancer progression, including cell migration and metastasis, tumor cell adhesion, tumorigenesis, and tumor growth. The possible underlying mechanisms may be the interruption of its barrier function, its radical role in growth factor storage, signaling, and mechanotransduction. In the later sections, we discuss glycocalyx targeting therapeutic approaches reported in animal and clinical experiments. The study concludes that cancer cells’ glycocalyx and its role in cancer progression are beginning to be known by more groups, and future studies should pay more attention to its mechanotransduction of interstitial flow-induced shear stress, seeking promising therapeutic targets with less toxicity but more specificity.

Cell surface chondroitin sulphate proteoglycan 4 (CSPG4) binds to the basement membrane heparan sulphate proteoglycan, perlecan, and is involved in cell adhesion

Chondroitin sulphate proteoglycan 4 (CSPG4) is a cell surface proteoglycan highly expressed by tumour, perivascular and oligodendrocyte cells and known to be involved cell adhesion and migration. This study showed that CSPG4 was present as a proteoglycan on the cell surface of two melanoma cell lines, MM200 and Me1007, as well as shed into the conditioned medium. CSPG4 from the two melanoma cell lines differed in the amount of chondroitin sulphate (CS) decoration, as well as the way the protein core was fragmented. In contrast, the CSPG4 expressed by a colon carcinoma cell line, WiDr, was predominantly as a protein core on the cell surface lacking glycosaminoglycan (GAG) chains. This study demonstrated that CSPG4 immunopurified from the melanoma cell lines formed a complex with perlecan synthesized by the same cultured cells. Mechanistic studies showed that CSPG4 bound to perlecan via hydrophobic protein-protein interactions involving multiple sites on perlecan including the C-terminal region. Furthermore, this study revealed that CSPG4 interacted with perlecan to support cell adhesion and actin polymerization. Together these data suggest a novel mechanism by which CSPG4 expressing cells might attach to perlecan-rich matrices so as those found in connective tissues and basement membranes.

KRAS-mutation status dependent effect of zoledronic acid in human non-small cell cancer preclinical models

Background

In non-small cell lung cancer (NSCLC) KRAS-mutant status is a negative prognostic and predictive factor. Nitrogen-containing bisphosphonates inhibit prenylation of small G-proteins (e.g. Ras, Rac, Rho) and thus may affect proliferation and migration. In our preclinical work, we investigated the effect of an aminobisphosphonate compound (zoledronic acid) on mutant and wild type KRAS-expressing human NSCLC cell lines.

Results

We confirmed that zoledronic acid was unable to inhibit the prenylation of mutant K-Ras unlike in the case of wild type K-Ras. In case of in vitro proliferation, the KRAS-mutant human NSCLC cell lines showed resistance to zoledronic acid wild-type KRAS-cells proved to be sensitive. Combinatory application of zoledronic acid enhanced the cytostatic effect of cisplatin. Zoledronic acid did not induce significant apoptosis. In xenograft model, zoledronic acid significantly reduced the weight of wild type KRAS-EGFR-expressing xenograft tumor by decreasing the proliferative capacity. Futhermore, zoledronic acid induced VEGF expression and improved in vivo tumor vascularization.

Materials and methods

Membrane association of K-Ras was examined by Western-blot. In vitro cell viability, apoptotic cell death and migration were measured in NSCLC lines with different molecular background. The in vivo effect of zoledronic acid was investigated in a SCID mouse subcutaneous xenograft model.

Conclusions

The in vitro and in vivo inhibitory effect of zoledronic acid was based on the blockade of cell cycle in wild type KRAS-expressing human NSCLC cells. The zoledronic acid induced vascularization supported in vivo cytostatic effect. Our preclinical investigation suggests that patients with wild type KRAS-expressing NSCLC could potentially benefit from aminobisphosphonate therapy.

Proteoglycans remodeling in cancer: Underlying molecular mechanisms

Extracellular matrix is a highly dynamic macromolecular network. Proteoglycans are major components of extracellular matrix playing key roles in its structural organization and cell signaling contributing to the control of numerous normal and pathological processes. As multifunctional molecules, proteoglycans participate in various cell functions during morphogenesis, wound healing, inflammation and tumorigenesis. Their interactions with matrix effectors, cell surface receptors and enzymes enable them with unique properties. In malignancy, extensive remodeling of tumor stroma is associated with marked alterations in proteoglycans' expression and structural variability. Proteoglycans exert diverse functions in tumor stroma in a cell-specific and context-specific manner and they mainly contribute to the formation of a permissive provisional matrix for tumor growth affecting tissue organization, cell-cell and cell-matrix interactions and tumor cell signaling. Proteoglycans also modulate cancer cell phenotype and properties, the development of drug resistance and tumor stroma angiogenesis. This review summarizes the proteoglycans remodeling and their novel biological roles in malignancies with particular emphasis to the underlying molecular mechanisms.

Extracellular Matrix, a Hard Player in Angiogenesis

The extracellular matrix (ECM) is a complex network of proteins, glycoproteins, proteoglycans, and polysaccharides. Through multiple interactions with each other and the cell surface receptors, not only the ECM determines the physical and mechanical properties of the tissues, but also profoundly influences cell behavior and many physiological and pathological processes. One of the functions that have been extensively explored is its impingement on angiogenesis. The strong impact of the ECM in this context is both direct and indirect by virtue of its ability to interact and/or store several growth factors and cytokines. The aim of this review is to provide some examples of the complex molecular mechanisms that are elicited by these molecules in promoting or weakening the angiogenic processes. The scenario is intricate, since matrix remodeling often generates fragments displaying opposite effects compared to those exerted by the whole molecules. Thus, the balance will tilt towards angiogenesis or angiostasis depending on the relative expression of pro- or anti-angiogenetic molecules/fragments composing the matrix of a given tissue. One of the vital aspects of this field of research is that, for its endogenous nature, the ECM can be viewed as a reservoir to draw from for the development of new more efficacious therapies to treat angiogenesis-dependent pathologies.

Essential Contribution of Tumor-derived Perlecan to Epidermal Tumor Growth and Angiogenesis

As a major heparan sulfate proteoglycan (PG) in basement membranes, perlecan has been linked to tumor invasion, metastasis, and angiogenesis. Here we produced epidermal tumors in immunocompromised rats by injection of mouse RT101 tumor cells. Tumor sections stained with species-specific perlecan antibodies, together with immuno-electron microscopy, showed that perlecan distributed around blood vessels was of both host and tumor cell origin. Tumor-derived perlecan was also distributed throughout the tumor matrix. Blood vessels stained with rat-specific PECAM-1 antibody showed their host origin. RT101 cells also expressed two other basement membrane heparan sulfate PGs, agrin and type XVIII collagen. Antisense targeting of perlecan inhibited tumor cell growth in vitro, while exogenous recombinant perlecan, but not heparin, restored the growth of antisense perlecan-expressing cells, suggesting that perlecan core protein, rather than heparan sulfate chains from perlecan, agrin, or type XVIII collagen, regulates tumor cell growth. However, perlecan core protein requirement was not related to fibroblast growth factor-7 binding because RT101 cells were unresponsive to and lacked receptors for this growth factor. In vivo, antisense perlecan-transfected cells generated no tumors, whereas untransfected and vector-transfected cells formed tumors with obvious neovascularization, suggesting that tumor perlecan rather than host perlecan controls tumor growth and angiogenesis.

Perlecan Heparan Sulfate Is Required for the Inhibition of Smooth Muscle Cell Proliferation by All-trans-Retinoic Acid

Smooth muscle cell (SMC) proliferation is a key process in stabilization of atherosclerotic plaques, and during restenosis after interventions. A clearer understanding of SMC growth regulation is therefore needed to design specific anti-proliferative therapies. Retinoic acid has been shown to inhibit proliferation of SMCs both in vitro and in vivo and to affect the expression of extracellular matrix molecules. To explore the mechanisms behind the growth inhibitory activity of retinoic acid, we hypothesized that retinoids may induce the expression of perlecan, a large heparan sulfate proteoglycan with anti-proliferative properties. Perlecan expression and accumulation was induced in murine SMC cultures by all-trans-retinoic acid (AtRA). Moreover, the growth inhibitory effect of AtRA on wild-type cells was greatly diminished in SMCs from transgenic mice expressing heparan sulfate-deficient perlecan, indicating that the inhibition is perlecan heparan sulfate-dependent. In addition, AtRA influenced activation and phosphorylation of PTEN and Akt differently in wild-type and mutant SMCs, consistent with previous studies of perlecan-dependent SMC growth inhibition. We demonstrate that AtRA regulates perlecan expression in SMCs and that the inhibition of SMC proliferation by AtRA is, at least in part, secondary to an increased expression of perlecan and dependent upon its heparan sulfate-chains.

Novel interactions of perlecan: unraveling perlecan's role in angiogenesis

Perlecan, a highly conserved and ubiquitous basement membrane heparan sulfate proteoglycan, is essential for life, inasmuch as its absence results in embryonic lethality in mice and C. elegans, and neonatal lethality in humans. Perlecan plays an essential role in vasculogenesis and chondrogenesis, as well as in pathological states where these processes are maladapted. Although a large body of evidence supports a pro-angiogenic role for perlecan, recent findings suggests that portions of the perlecan protein core can be antiangiogenic, requiring a further evaluation of the functioning of this complex molecule. This review is focused on the genetics of mammalian and nonmammalian perlecan, the elucidation of its novel interacting partners and its role in angiogenesis. By more fully understanding perlecan's functioning in angiogenesis, we may gain invaluable insight that could lead to therapeutic interventions in cancer and other pathologic states.

Perlecan knockdown in metastatic prostate cancer cells reduces heparin-binding growth factor responses in vitro and tumor growth in vivo

Perlecan (Pln) is a major heparan sulfate proteoglycan (HSPG) of extracellular matrices and bone marrow stroma. Pln, via glycosaminoglycans in domains I and V, acts as a co-receptor for delivery of heparin binding growth factors (HBGFs) that support cancer growth and vascularization. Specifically, glycosaminoglycans bind HBGFs and activate HBGF receptors, including those for FGF-2 and VEGF-A. The contribution of Pln to prostate cancer growth was tested using a ribozyme approach to knockdown Pln expression levels. Transfection into the androgen-independent, bone targeted prostate cancer line, C4-2B, and efficient stable knockdown of Pln was demonstrated by quantitative PCR, immunohistochemistry and immunoblotting. Three individually isolated subclones with 75-80% knockdown in Pln mRNA, protein expression and secretion into ECM were used to study in vitro growth responses to FGF-2 and VEGF-A. While cells with normal Pln levels responded to both HBGFs, knockdown cells responded poorly. All lines responded to serum growth factors and IGF-I. Anchorage-independent growth assays showed reduced colony size and cohesiveness by all Pln deficient subclones compared to parental C4-2B cells. In vivo effects of Pln knockdown were measured by inoculating knockdown and control ribozyme transfected cell lines into athymic mice. A reduced growth rate, smaller tumor size, diminished vascularization and failure to elevate serum PSA characterized mice bearing Pln knockdown C4-2B cells. Poor vascularization correlated with reduced levels of VEGF-A secreted by Pln knockdown lines. We conclude that Pln is an essential ECM component involved in growth responses of metastatic prostate cancer cells to HBGFs deposited in local and metastatic microenvironment.

Proteoglycan control of cell movement during wound healing and cancer spreading

By virtue of their multifunctional nature, proteoglycans (PGs) are thought to govern the process of cell movement in numerous physiological and pathological contexts, spanning from early embryonic development to tumour invasion and metastasis. The precise mode by which they influence this process is still fragmentary, but evidence is accruing that they may affect it in a multifaceted manner. PGs bound to the plasma membrane mediate the polyvalent interaction of the cell with matrix constituents and with molecules of the neighbouring cells' surfaces; they modulate the activity of receptors implicated in the recognition of these components; and they participate in the perception and convergence of growth- and motility-promoting cues contributed by soluble factors. Through some of these interactions several PGs transduce to pro-motile cells crucial intracellular signals that are likely to be essential for their mobility. A regulated shedding of certain membrane-intercalated PGs seems to provide an additional level of control of cell movement. Coincidentally, matrix-associated PGs may govern cell migration by structuring permissive and non-permissive migratory paths and, when directly secreted by the moving cells, may alternatively create favourable or hostile microenvironments. To exert this latter, indirect effect on cell movement, matrix PGs strongly rely upon their primary molecular partners, such as hyaluronan, link proteins, tenascins, collagens and low-affinity cell surface receptors, whereas a further finer control is provided by a highly regulated proteolytic processing of the PGs accounted by both the migrating cells themselves and cells of their surrounding tissues. Overall, PGs seem to play an important role in determining the migratory phenotype of a cell by initiating, directing and terminating cell movement in a spatio-temporally controlled fashion. This implies that the "anti-adhesive and/or "anti-migratory" properties that have previously been assigned to certain PGs may be re-interpreted as being a means by which these macromolecules elaborate haptotaxis-like mechanisms imposing directionality upon the moving cells. Since these conditions would allow cells to be led to given tissue locations and become immobilized at these sites, a primary function may be ascribed to PGs in the dictation of a "stop or go" choice of the migrating cells.

The angiostatic activity of interferon-inducible protein-10/CXCL10 in human melanoma depends on binding to CXCR3 but not to glycosaminoglycan

Human interferon-inducible protein 10 (IP-10; HGMW-approved gene symbol CXCL10) is an ELR(-) CXC chemokine that contains binding domains for both the chemokine receptor CXCR3 and glycosaminoglycans. IP-10 has been recently demonstrated to be a potent angiostatic protein in vivo. Whether IP-10 exerts its angiostatic function through binding to CXCR3, glycosaminoglycans, or both, is not clear. To clarify this issue, we created expression constructs for mutants of IP-10 that exhibit partial (IP-10C) or total (IP-10C22) loss of binding to CXCR3 or loss of binding to glycosaminoglycans (IP-10H and IP-10C22H). The A375 human melanoma cell line was transfected with these expression vectors, and stable clones were selected and inoculated subcutaneously into nude mice. As expected, tumor cells secreting wild-type IP-10 showed remarkable reduction in tumor growth compared to control vector-transfected tumor cells. Surprisingly, mutation of IP-10 resulting in partial loss of receptor binding (IP-10C), or loss of GAG binding (IP-10H), did not significantly alter the ability to inhibit tumor growth. This tumor growth inhibition was associated with a reduction in microvessel density, leading to the observed increase in both tumor cell apoptosis and necrosis. In contrast, expression of the IP-10C22 mutant failed to inhibit melanoma tumor growth. These data suggest that CXCR3 receptor binding, but not glycosaminoglycan binding, is essential for the tumor angiostatic activity of IP-10. We conclude that the arginine 22 amino acid residue of IP-10 is essential for both CXCR3 binding and angiostasis.

AAV-mediated gene transfer of tissue inhibitor of metalloproteinases-1 inhibits vascular tumor growth and angiogenesis in vivo

The activity of matrix metalloproteinases (MMPs) is a universal feature of cellular invasion, tumor angiogenesis and metastasis, which is counterbalanced and regulated by the natural tissue inhibitors of MMPs (Timps). Here we show that Timp1 gene transfer delivered by an adeno-associated virus (AAV) vector inhibits tumor growth in a murine xenotransplant model. A human Kaposi's sarcoma cell line, forming highly vascularized tumors in vivo and having a high natural permissivity to AAV gene transfer, was transduced to express the Timp1 cDNA. AAV-Timp1-transduced cells secreted high levels of Timp1 that inhibited MMP2 and MMP9 gelatinolytic activity. Following subcutaneous inoculation in nude mice, the AAV-Timp1-transduced cells showed significantly reduced tumor growth when compared to control AAV-LacZ-transduced cells. In addition, direct intratumoral injection of AAV-Timp1 into pre-existing tumors significantly impaired the further expansion of the tumor mass. Histological analyses showed that the AAV-Timp1-transduced tumors had limited development of vascular structures and extensive areas of cell death, suggesting that Timp1 overexpression had an antiangiogenic effect. To further support this conclusion, we demonstrated that AAV-Timp1 transduction significantly reduced endothelial cell migration and the invasion of a Matrigel barrier and strongly inhibited angiogenesis in the chick chorioallantoic membrane assay. These results indicate that transfer and overexpression of the Timp1 gene is a promising therapeutic strategy to target tumor-associated angiogenesis in cancer gene therapy.

Perlecan and tumor angiogenesis

Perlecan is a major heparan sulfate proteoglycan (HSPG) of basement membranes (BMs) and connective tissues. The core protein of perlecan is divided into five domains based on sequence homology to other known proteins. Commonly, the N-terminal domain I of mammalian perlecan is substituted with three HS chains that can bind a number of matrix molecules, cytokines, and growth factors. Perlecan is essential for metazoan life, as shown by genetic manipulations of nematodes, insects, and mice. There are also known human mutations that can be lethal. In vertebrates, new functions of perlecan emerged with the acquisition of a closed vascular system and skeletal connective tissues. Many of perlecan's functions may be related to the binding and presentation of growth factors to high-affinity tyrosine kinase (TK) receptors. Data are accumulating, as discussed here, that similar growth factor-mediated processes may have unwanted promoting effects on tumor cell proliferation and tumor angiogenesis. Understanding of these attributes at the molecular level may offer opportunities for therapeutic intervention.

Tumor attenuation by combined heparan sulfate and polyamine depletion

Cells depend on polyamines for growth and their depletion represents a strategy for the treatment of cancer. Polyamines assemble de novo through a pathway sensitive to the inhibitor, alpha-difluoromethylornithine (DFMO). However, the presence of cell-surface heparan sulfate proteoglycans may provide a salvage pathway for uptake of circulating polyamines, thereby sparing cells from the cytostatic effect of DFMO. Here we show that genetic or pharmacologic manipulation of proteoglycan synthesis in the presence of DFMO inhibits cell proliferation in vitro and in vivo. In cell culture, mutant cells lacking heparan sulfate were more sensitive to the growth inhibitory effects of DFMO than wild-type cells or mutant cells transfected with the cDNA for the missing biosynthetic enzyme. Moreover, extracellular polyamines did not restore growth of mutant cells, but completely reversed the inhibitory effect of DFMO in wild-type cells. In a mouse model of experimental metastasis, DFMO provided in the water supply also dramatically diminished seeding and growth of tumor foci in the lungs by heparan sulfate-deficient mutant cells compared with the controls. Wild-type cells also formed tumors less efficiently in mice fed both DFMO and a xylose-based inhibitor of heparan sulfate proteoglycan assembly. The effect seemed to be specific for heparan sulfate, because a different xyloside known to affect only chondroitin sulfate did not inhibit tumor growth. Hence, combined inhibition of heparan sulfate assembly and polyamine synthesis may represent an additional strategy for cancer therapy.