Antisense targeting of perlecan blocks tumor growth and angiogenesis in vivo

Proteoglycans of basement membranes: Crucial controllers of angiogenesis, neurogenesis, and autophagy

Anti-angiogenic therapy is an established method for the treatment of several cancers and vascular-related diseases. Most of the agents employed target the vascular endothelial growth factor A, the major cytokine stimulating angiogenesis. However, the efficacy of these treatments is limited by the onset of drug resistance. Therefore, it is of fundamental importance to better understand the mechanisms that regulate angiogenesis and the microenvironmental cues that play significant role and influence patient treatment and outcome. In this context, here we review the importance of the three basement membrane heparan sulfate proteoglycans (HSPGs), namely perlecan, agrin and collagen XVIII. These HSPGs are abundantly expressed in the vasculature and, due to their complex molecular architecture, they interact with multiple endothelial cell receptors, deeply affecting their function. Under normal conditions, these proteoglycans exert pro-angiogenic functions. However, in pathological conditions such as cancer and inflammation, extracellular matrix remodeling leads to the degradation of these large precursor molecules and the liberation of bioactive processed fragments displaying potent angiostatic activity. These unexpected functions have been demonstrated for the C-terminal fragments of perlecan and collagen XVIII, endorepellin and endostatin. These bioactive fragments can also induce autophagy in vascular endothelial cells which contributes to angiostasis. Overall, basement membrane proteoglycans deeply affect angiogenesis counterbalancing pro-angiogenic signals during tumor progression, and represent possible means to develop new prognostic biomarkers and novel therapeutic approaches for the treatment of solid tumors.

Chemical, Molecular, and Single-nucleus Analysis Reveal Chondroitin Sulfate Proteoglycan Aberrancy in Fibrolamellar Carcinoma

Fibrolamellar carcinoma (FLC) is an aggressive liver cancer with no effective therapeutic options. The extracellular environment of FLC tumors is poorly characterized and may contribute to cancer growth and/or metastasis. To bridge this knowledge gap, we assessed pathways relevant to proteoglycans, a major component of the extracellular matrix. We first analyzed gene expression data from FLC and nonmalignant liver tissue (n = 27) to identify changes in glycosaminoglycan (GAG) biosynthesis pathways and found that genes associated with production of chondroitin sulfate, but not other GAGs, are significantly increased by 8-fold. We then implemented a novel LC/MS-MS based method to quantify the abundance of different types of GAGs in patient tumors (n = 16) and found that chondroitin sulfate is significantly more abundant in FLC tumors by 6-fold. Upon further analysis of GAG-associated proteins, we found that versican (VCAN) expression is significantly upregulated at the mRNA and protein levels, the latter of which was validated by IHC. Finally, we performed single-cell assay for transposase-accessible chromatin sequencing on FLC tumors (n = 3), which revealed for the first time the different cell types in FLC tumors and also showed that VCAN is likely produced not only from FLC tumor epithelial cells but also activated stellate cells. Our results reveal a pathologic aberrancy in chondroitin (but not heparan) sulfate proteoglycans in FLC and highlight a potential role for activated stellate cells.

Significance

This study leverages a multi-disciplinary approach, including state-of-the-art chemical analyses and cutting-edge single-cell genomic technologies, to identify for the first time a marked chondroitin sulfate aberrancy in FLC that could open novel therapeutic avenues in the future.

Contributions of Immune Cells and Stromal Cells to the Pathogenesis of Systemic Sclerosis: Recent Insights

Systemic sclerosis (SSc) is a multisystem rheumatic disease characterized by vascular dysfunction, autoimmune abnormalities, and progressive organ fibrosis. A series of studies in SSc patients and fibrotic models suggest that immune cells, fibroblasts, and endothelial cells participate in inflammation and aberrant tissue repair. Furthermore, the growing number of studies on single-cell RNA sequencing (scRNA-seq) technology in SSc elaborate on the transcriptomics and heterogeneities of these cell subsets significantly. In this review, we summarize the current knowledge regarding immune cells and stromal cells in SSc patients and discuss their potential roles in SSc pathogenesis, focusing on recent advances in the new subtypes by scRNA-seq.

Decellularized Colorectal Cancer Matrices as Bioactive Scaffolds for Studying Tumor-Stroma Interactions

More than a physical structure providing support to tissues, the extracellular matrix (ECM) is a complex and dynamic network of macromolecules that modulates the behavior of both cancer cells and associated stromal cells of the tumor microenvironment (TME). Over the last few years, several efforts have been made to develop new models that accurately mimic the interconnections within the TME and specifically the biomechanical and biomolecular complexity of the tumor ECM. Particularly in colorectal cancer, the ECM is highly remodeled and disorganized and constitutes a key component that affects cancer hallmarks, such as cell differentiation, proliferation, angiogenesis, invasion and metastasis. Therefore, several scaffolds produced from natural and/or synthetic polymers and ceramics have been used in 3D biomimetic strategies for colorectal cancer research. Nevertheless, decellularized ECM from colorectal tumors is a unique model that offers the maintenance of native ECM architecture and molecular composition. This review will focus on innovative and advanced 3D-based models of decellularized ECM as high-throughput strategies in colorectal cancer research that potentially fill some of the gaps between in vitro 2D and in vivo models. Our aim is to highlight the need for strategies that accurately mimic the TME for precision medicine and for studying the pathophysiology of the disease.

Extracellular matrix guidance of autophagy: a mechanism regulating cancer growth

The extracellular matrix (ECM) exists as a dynamic network of biophysical and biochemical factors that maintain tissue homeostasis. Given its sensitivity to changes in the intra- and extracellular space, the plasticity of the ECM can be pathological in driving disease through aberrant matrix remodelling. In particular, cancer uses the matrix for its proliferation, angiogenesis, cellular reprogramming and metastatic spread. An emerging field of matrix biology focuses on proteoglycans that regulate autophagy, an intracellular process that plays both critical and contextual roles in cancer. Here, we review the most prominent autophagic modulators from the matrix and the current understanding of the cellular pathways and signalling cascades that mechanistically drive their autophagic function. We then critically assess how their autophagic functions influence tumorigenesis, emphasizing the complexities and stage-dependent nature of this relationship in cancer. We highlight novel emerging data on immunoglobulin-containing and proline-rich receptor-1, heparanase and thrombospondin 1 in autophagy and cancer. Finally, we further discuss the pro- and anti-autophagic modulators originating from the ECM, as well as how these proteoglycans and other matrix constituents specifically influence cancer progression.

Cancer stem cells and strategies for targeted drug delivery

Cancer stem cells (CSCs) are a small proportion of cancer cells with high tumorigenic activity, self-renewal ability, and multilineage differentiation potential. Standard anti-tumor therapies including conventional chemotherapy, radiation therapy, and molecularly targeted therapies are not effective against CSCs, and often lead to enrichment of CSCs that can result in tumor relapse. Therefore, it is hypothesized that targeting CSCs is key to increasing the efficacy of cancer therapies. In this review, CSC properties including CSC markers, their role in tumor growth, invasiveness, metastasis, and drug resistance, as well as CSC microenvironment are discussed. Further, CSC-targeted strategies including the use of targeted drug delivery systems are examined.

A functional outside-in signaling network of proteoglycans and matrix molecules regulating autophagy

Proteoglycans and selected extracellular matrix constituents are emerging as intrinsic and critical regulators of evolutionarily conversed, intracellular catabolic pathways. Often, these secreted molecules evoke sustained autophagy in a variety of cell types, tissues, and model systems. The unique properties of proteoglycans have ushered in a paradigmatic shift to broaden our understanding of matrix-mediated signaling cascades. The dynamic cellular pathway controlling autophagy is now linked to an equally dynamic and fluid signaling network embedded in a complex meshwork of matrix molecules. A rapidly emerging field of research encompasses multiple matrix-derived candidates, representing a menagerie of soluble matrix constituents including decorin, biglycan, endorepellin, endostatin, collagen VI and plasminogen kringle 5. These matrix constituents are pro-autophagic and simultaneously anti-angiogenic. In contrast, perlecan, laminin α2 chain, and lumican have anti-autophagic functions. Mechanistically, each matrix constituent linked to intracellular catabolic events engages a specific cell surface receptor that often converges on a common core of the autophagic machinery including AMPK, Peg3 and Beclin 1. We consider this matrix-evoked autophagy as non-canonical given that it occurs in an allosteric manner and is independent of nutrient availability or prevailing bioenergetics control. We propose that matrix-regulated autophagy is an important outside-in signaling mechanism for proper tissue homeostasis that could be therapeutically leveraged to combat a variety of diseases.

Glycosaminoglycan-Protein Interactions and Their Roles in Human Disease

Glycosaminoglycans (GAGs) are a family of linear and negatively charged polysaccharides that exist ubiquitously on the human cell surface as well as in the extracellular matrix. GAGs interact with a wide range of proteins, including proteases, growth factors, cytokines, chemokines and adhesion molecules, enabling them to mediate many physiological processes, such as protein function, cellular adhesion and signaling. GAG-protein interactions participate in and intervene in a variety of human diseases, including cardiovascular disease, infectious disease, neurodegenerative diseases and tumors. The breakthrough in analytical tools and approaches during the last two decades has facilitated a greater understanding of the importance of GAG-protein interactions and their roles in human diseases. This review focuses on aspects of the molecular basis and mechanisms of GAG-protein interactions involved in human disease. The most recent advances in analytical tools, especially mass spectrometry-based GAG sequencing and binding motif characterization methods, are introduced. An update of selected families of GAG binding proteins is presented. Perspectives on development of novel therapeutics targeting specific GAG-protein interactions are also covered in this review.

FGF/FGFR signaling in health and disease

Growing evidences suggest that the fibroblast growth factor/FGF receptor (FGF/FGFR) signaling has crucial roles in a multitude of processes during embryonic development and adult homeostasis by regulating cellular lineage commitment, differentiation, proliferation, and apoptosis of various types of cells. In this review, we provide a comprehensive overview of the current understanding of FGF signaling and its roles in organ development, injury repair, and the pathophysiology of spectrum of diseases, which is a consequence of FGF signaling dysregulation, including cancers and chronic kidney disease (CKD). In this context, the agonists and antagonists for FGF-FGFRs might have therapeutic benefits in multiple systems.

A Role of Agrin in Maintaining the Stability of Vascular Endothelial Growth Factor Receptor-2 during Tumor Angiogenesis

Endothelial cell (EC) recruitment is central to the vascularization of tumors. Although several proteoglycans have been implicated in cancer and angiogenesis, their roles in EC recruitment and vascularization during tumorigenesis remain poorly understood. Here, we reveal that Agrin, which is secreted in liver cancer, promotes angiogenesis by recruiting ECs within tumors and metastatic lesions and facilitates adhesion of cancer cells to ECs. In ECs, Agrin-induced angiogenesis and adherence to cancer cells are mediated by Integrin-β1, Lrp4-MuSK pathways involving focal adhesion kinase. Mechanistically, we uncover that Agrin regulates VEGFR2 levels that sustain the angiogenic property of ECs and adherence to cancer cells. Agrin attributes an ECM stiffness-based stabilization of VEGFR2 by enhancing interactions with Integrin-β1-Lrp4 and additionally stimulates endothelial nitric-oxide synthase (e-NOS) signaling. Therefore, we propose that cross-talk between Agrin-expressing cancer and ECs favor angiogenesis by sustaining the VEGFR2 pathway.

Role of Extracellular Matrix in Gastrointestinal Cancer-Associated Angiogenesis

Gastrointestinal tumors are responsible for more cancer-related fatalities than any other type of tumors, and colorectal and gastric malignancies account for a large part of these diseases. Thus, there is an urgent need to develop new therapeutic approaches to improve the patients' outcome and the tumor microenvironment is a promising arena for the development of such treatments. In fact, the nature of the microenvironment in the different gastrointestinal tracts may significantly influence not only tumor development but also the therapy response. In particular, an important microenvironmental component and a potential therapeutic target is the vasculature. In this context, the extracellular matrix is a key component exerting an active effect in all the hallmarks of cancer, including angiogenesis. Here, we summarized the current knowledge on the role of extracellular matrix in affecting endothelial cell function and intratumoral vascularization in the context of colorectal and gastric cancer. The extracellular matrix acts both directly on endothelial cells and indirectly through its remodeling and the consequent release of growth factors. We envision that a deeper understanding of the role of extracellular matrix and of its remodeling during cancer progression is of chief importance for the development of new, more efficacious, targeted therapies.

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.

Tumor Microenvironment-Associated Extracellular Matrix Components Regulate NK Cell Function

The tumor microenvironment (TME) is composed of multiple infiltrating host cells (e.g., endothelial cells, fibroblasts, lymphocytes, and myeloid cells), extracellular matrix, and various secreted or cell membrane-presented molecules. Group 1 innate lymphoid cells (ILCs), which includes natural killer (NK) cells and ILC1, contribute to protecting the host against cancer and infection. Both subsets are able to quickly produce cytokines such as interferon gamma (IFN-γ), chemokines, and other growth factors in response to activating signals. However, the TME provides many molecules that can prevent the potential effector function of these cells, thereby protecting the tumor. For example, TME-derived tumor growth factor (TGF)-β and associated members of the superfamily downregulate NK cell cytotoxicity, cytokine secretion, metabolism, proliferation, and induce effector NK cells to upregulate ILC1-like characteristics. In concert, a family of carbohydrate-binding proteins called galectins, which can be produced by different cells composing the TME, can downregulate NK cell function. Matrix metalloproteinase (MMP) and a disintegrin and metalloproteinase (ADAM) are also enzymes that can remodel the extracellular matrix and shred receptors from the tumor cell surface, impairing the activation of NK cells and leading to less effective effector functions. Gaining a better understanding of the characteristics of the TME and its associated factors, such as infiltrating cells and extracellular matrix, could lead to tailoring of new personalized immunotherapy approaches. This review provides an overview of our current knowledge on the impact of the TME and extracellular matrix-associated components on differentiation, impairment, and function of NK cells.

Cancer Metastasis: The Role of the Extracellular Matrix and the Heparan Sulfate Proteoglycan Perlecan

Cancer metastasis is the dissemination of tumor cells to new sites, resulting in the formation of secondary tumors. This process is complex and is spatially and temporally regulated by intrinsic and extrinsic factors. One important extrinsic factor is the extracellular matrix, the non-cellular component of tissues. Heparan sulfate proteoglycans (HSPGs) are constituents of the extracellular matrix, and through their heparan sulfate chains and protein core, modulate multiple events that occur during the metastatic cascade. This review will provide an overview of the role of the extracellular matrix in the events that occur during cancer metastasis, primarily focusing on perlecan. Perlecan, a basement membrane HSPG is a key component of the vascular extracellular matrix and is commonly associated with events that occur during the metastatic cascade. Its contradictory role in these events will be discussed and we will highlight the recent advances in cancer therapies that target HSPGs and their modifying enzymes.

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.

Chronic Obstructive Pulmonary Disease and Lung Cancer: Underlying Pathophysiology and New Therapeutic Modalities

Chronic obstructive pulmonary disease (COPD) and lung cancer are major lung diseases affecting millions worldwide. Both diseases have links to cigarette smoking and exert a considerable societal burden. People suffering from COPD are at higher risk of developing lung cancer than those without, and are more susceptible to poor outcomes after diagnosis and treatment. Lung cancer and COPD are closely associated, possibly sharing common traits such as an underlying genetic predisposition, epithelial and endothelial cell plasticity, dysfunctional inflammatory mechanisms including the deposition of excessive extracellular matrix, angiogenesis, susceptibility to DNA damage and cellular mutagenesis. In fact, COPD could be the driving factor for lung cancer, providing a conducive environment that propagates its evolution. In the early stages of smoking, body defences provide a combative immune/oxidative response and DNA repair mechanisms are likely to subdue these changes to a certain extent; however, in patients with COPD with lung cancer the consequences could be devastating, potentially contributing to slower postoperative recovery after lung resection and increased resistance to radiotherapy and chemotherapy. Vital to the development of new-targeted therapies is an in-depth understanding of various molecular mechanisms that are associated with both pathologies. In this comprehensive review, we provide a detailed overview of possible underlying factors that link COPD and lung cancer, and current therapeutic advances from both human and preclinical animal models that can effectively mitigate this unholy relationship.

Perlecan-targeted nanoparticles for drug delivery to triple-negative breast cancer

Aim:

We previously developed two antibodies that bind to a cell surface protein, perlecan, overexpressed in triple-negative breast cancer (TNBC). The goal of this study was to investigate these antibodies as targeting ligands for nanoparticle-mediated drug delivery.

Methods:

Paclitaxel-loaded poly(D,L-lactide-co-glycolide) nanoparticles were functionalized with antibodies using thiol–maleimide chemistry. Effect of antibody functionalization on therapeutic efficacy of drug-loaded nanoparticles was investigated using in vitro and in vivo models of TNBC.

Results:

The antibodies were covalently conjugated to nanoparticles without affecting antibody binding affinity or nanoparticle properties. Perlecan-targeted nanoparticles showed improved cell uptake, retention, cytotoxicity in vitro and enhanced tumor growth inhibition in vivo.

Conclusion:

The data presented here indicates that perlecan-targeted nanoparticles can improve tumor drug delivery to TNBC.

Integrated Analysis of Germline and Tumor DNA Identifies New Candidate Genes Involved in Familial Colorectal Cancer

Colorectal cancer (CRC) shows aggregation in some families but no alterations in the known hereditary CRC genes. We aimed to identify new candidate genes which are potentially involved in germline predisposition to familial CRC. An integrated analysis of germline and tumor whole-exome sequencing data was performed in 18 unrelated CRC families. Deleterious single nucleotide variants (SNV), short insertions and deletions (indels), copy number variants (CNVs) and loss of heterozygosity (LOH) were assessed as candidates for first germline or second somatic hits. Candidate tumor suppressor genes were selected when alterations were detected in both germline and somatic DNA, fulfilling Knudson’s two-hit hypothesis. Somatic mutational profiling and signature analysis were also performed. A series of germline-somatic variant pairs were detected. In all cases, the first hit was presented as a rare SNV/indel, whereas the second hit was either a different SNV (3 genes) or LOH affecting the same gene (141 genes). BRCA2, BLM, ERCC2, RECQL, REV3L and RIF1 were among the most promising candidate genes for germline CRC predisposition. The identification of new candidate genes involved in familial CRC could be achieved by our integrated analysis. Further functional studies and replication in additional cohorts are required to confirm the selected candidates.

Single Cell RNA Sequencing Identifies HSPG2 and APLNR as Markers of Endothelial Cell Injury in Systemic Sclerosis Skin

Objective: The mechanisms that lead to endothelial cell (EC) injury and propagate the vasculopathy in Systemic Sclerosis (SSc) are not well understood. Using single cell RNA sequencing (scRNA-seq), our goal was to identify EC markers and signature pathways associated with vascular injury in SSc skin.

Methods: We implemented single cell sorting and subsequent RNA sequencing of cells isolated from SSc and healthy control skin. We used t-distributed stochastic neighbor embedding (t-SNE) to identify the various cell types. We performed pathway analysis using Gene Set Enrichment Analysis (GSEA) and Ingenuity Pathway Analysis (IPA). Finally, we independently verified distinct markers using immunohistochemistry on skin biopsies and qPCR in primary ECs from SSc and healthy skin.

Results: By combining the t-SNE analysis with the expression of known EC markers, we positively identified ECs among the sorted cells. Subsequently, we examined the differential expression profile between the ECs from healthy and SSc skin. Using GSEA and IPA analysis, we demonstrated that the SSc endothelial cell expression profile is enriched in processes associated with extracellular matrix generation, negative regulation of angiogenesis and epithelial-to-mesenchymal transition. Two of the top differentially expressed genes, HSPG2 and APLNR, were independently verified using immunohistochemistry staining and real-time qPCR analysis.

Conclusion: ScRNA-seq, differential gene expression and pathway analysis revealed that ECs from SSc patients show a discrete pattern of gene expression associated with vascular injury and activation, extracellular matrix generation and negative regulation of angiogenesis. HSPG2 and APLNR were identified as two of the top markers of EC injury in SSc.

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.

The multifaceted roles of perlecan in fibrosis

Perlecan, or heparan sulfate proteoglycan 2 (HSPG2), is a ubiquitous heparan sulfate proteoglycan that has major roles in tissue and organ development and wound healing by orchestrating the binding and signaling of mitogens and morphogens to cells in a temporal and dynamic fashion. In this review, its roles in fibrosis are reviewed by drawing upon evidence from tissue and organ systems that undergo fibrosis as a result of an uncontrolled response to either inflammation or traumatic cellular injury leading to an over production of a collagen-rich extracellular matrix. This review focuses on examples of fibrosis that occurs in lung, liver, kidney, skin, kidney, neural tissues and blood vessels and its link to the expression of perlecan in that particular organ system.

Proteoglycans-Biomarkers and Targets in Cancer Therapy

Proteoglycans (PGs), important constituents of the extracellular matrix, have been associated with cancer pathogenesis. Their unique structure consisting of a protein core and glycosaminoglycan chains endowed with fine modifications constitutes these molecules as capable cellular effectors important for homeostasis and contributing to disease progression. Indeed, differential expression of PGs and their interacting proteins has been characterized as specific for disease evolvement in various cancer types. Importantly, PGs to a large extent regulate the bioavailability of hormones, growth factors, and cytokines as well as the activation of their respective receptors which regulate phenotypic diversibility, gene expression and rates of recurrence in specific tumor types. Defining and targeting these effectors on an individual patient basis offers ground for the development of newer therapeutic approaches which may act as either supportive or a substitute treatment to the standard therapy protocols. This review discusses the roles of PGs in cancer progression, developing technologies utilized for the defining of the PG "signature" in disease, and how this may facilitate the generation of tailor-made cancer strategies.

Heparan Sulfate and Heparan Sulfate Proteoglycans in Cancer Initiation and Progression

Heparan sulfate (HS) are complex unbranched carbohydrate chains that are heavily modified by sulfate and exist either conjugated to proteins or as free, unconjugated chains. Proteins with covalently bound Heparan sulfate chains are termed Heparan Sulfate Proteoglycans (HSPGs). Both HS and HSPGs bind to various growth factors and act as co-receptors for different cell surface receptors. They also modulate the dynamics and kinetics of various ligand-receptor interactions, which in turn can influence the duration and potency of the signaling. HS and HSPGs have also been shown to exert a structural role as a component of the extracellular matrix, thereby altering processes such as cell adhesion, immune cell infiltration and angiogenesis. Previous studies have shown that HS are deregulated in a variety of solid tumors and hematological malignancies and regulate key aspects of cancer initiation and progression. HS deregulation in cancer can occur as a result of changes in the level of HSPGs or due to changes in the levels of HS biosynthesis and remodeling enzymes. Here, we describe the major cell-autonomous (proliferation, apoptosis/senescence and differentiation) and cell-non-autonomous (angiogenesis, immune evasion, and matrix remodeling) roles of HS and HSPGs in cancer. Finally, we discuss therapeutic opportunities for targeting deregulated HS biosynthesis and HSPGs as a strategy for cancer treatment.

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.

VEGF synthesis is induced by prostacyclin and TGF-β in distal lung fibroblasts from COPD patients and control subjects: Implications for pulmonary vascular remodelling

BACKGROUND AND OBJECTIVE

Involvement of pulmonary vascular remodelling is a characteristic sign in COPD. Vascular mediators such as vascular endothelial growth factor (VEGF) and prostacyclin may regulate fibroblast activity. The objective was to study the synthesis of VEGF and interactions with prostacyclin and transforming growth factor (TGF)-β₁ in lung fibroblasts from patients with COPD and healthy control subjects. To further explore the autocrine role of synthesized VEGF on fibroblast activity, studies were performed in human lung fibroblasts (HFL-1).

METHODS

Primary distal lung fibroblast cultures were established from healthy individuals and from COPD patients (GOLD stage IV). Lung fibroblasts were stimulated with the prostacyclin analogue iloprost and the profibrotic stimuli TGF-β₁ . VEGF synthesis was measured in the cell culture medium. Changes in proliferation rate, migration and synthesis of the extracellular matrix (ECM) proteins proteoglycans were analysed after stimulations with VEGF-A isoform 165 (VEGF₁₆₅ ; 1-10 000 pg/mL) in HFL-1.

RESULTS

Iloprost and TGF-β₁ significantly increased VEGF synthesis in both fibroblasts from COPD patients and control subjects. TGF-β₁ -induced VEGF synthesis was significantly reduced by the cyclooxygenase inhibitor indomethacin in fibroblasts from COPD patients. VEGF significantly increased proliferation rate and migration capacity in HFL-1. VEGF also significantly increased synthesis of the ECM proteins biglycan and perlecan. The VEGF receptors (VEGFR), VEGFR1, VEGFR2 and VEGFR3, were all expressed in primary lung fibroblasts and HFL-1.

CONCLUSION

VEGF is synthesized in high amounts by distal lung fibroblasts and may have a crucial role in ongoing vascular remodelling processes in the distal lung compartments.

Role of protein glycosylation in cancer metastasis

Although altered glycosylation has been detected in human cancer cells decades ago, only investigations in the last years have enormously increased our knowledge about the details of protein glycosylation and its role in tumour progression. Many proteins, which are heavily glycosylated, i.e. adhesion proteins or proteases, play an important role in cancer metastasis that represents the crucial and frequently life-threatening step in progression of most tumour types. Compared to normal tissue, tumour cells often show altered glycosylation patters with appearance of new tumour-specific antigens. In this review, we give an overview about the role of glycosylation in tumour metastasis, describing recent results about O-glycans, N-glycans and glycosaminoglycans. We show that glycan structures, glycosylated proteins and glycosylation enzymes have influence on different steps of the metastatic process, including epithelial-mesenchymal transition (EMT), migration, invasion/intravasation and extravasation of tumour cells. Regarding the important role of cancer metastasis for patients survival, further knowledge about the consequences of altered glycosylation patterns in tumour cells is needed which might eventually lead to the development of novel therapeutic approaches.

The Role of Heparan Sulfate and Perlecan in Bone-regenerative Procedures

Tissue engineering, grafting procedures, regeneration, and tissue remodeling are developing therapeutic modalities with great potential medical value, but these regenerative modalities are not as effective or predictable as clinicians and patients would like. Greater understanding of growth factors, cytokines, extracellular matrix molecules, and their roles in cell-mediated healing processes have made these regenerative therapies more clinically viable and will continue advancing the fields of tissue engineering and grafting. However, millions of oral and non-oral bone-grafting procedures are performed annually, and only a small percentage yield the most desirable results. Here we review the heparan-sulfate-decorated extracellular biomolecule named perlecan and the research relating to its potential as an adjunct in bone-regenerative procedures. The review includes an overview of bone graft substitutes and biological adjuncts to bone-regenerative procedures in medicine as they apply to periodontal disease, alveolar ridge augmentation, and barrier membrane therapy. Perlecan is discussed as a potential biological adjunct in terms of growth factor sequestration and delivery, and promoting cell adhesion, proliferation, differentiation, and angiogenesis. Further, we propose delivery and application schemes for perlecan and/or its domains in bone-regenerative procedures, with particular emphasis on its heparan-sulfate-decorated domain I. The perlecan molecule, with its heparan sulfate glycosylation, may provide a multi-faceted approach for the delivery of a more comprehensive stimulus than other single potential adjuncts currently available for bone-regenerative procedures.

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.

A current view of perlecan in physiology and pathology: A mosaic of functions

Perlecan, a large basement membrane heparan sulfate proteoglycan, is expressed in a wide array of tissues where it regulates diverse cellular processes including bone formation, inflammation, cardiac development, and angiogenesis. Here we provide a contemporary review germane to the biology of perlecan encompassing its genetic regulation as well as an analysis of its modular protein structure as it pertains to function. As perlecan signaling from the extracellular matrix converges on master regulators of autophagy, including AMPK and mTOR, via a specific interaction with vascular endothelial growth factor receptor 2, we specifically focus on the mechanism of action of perlecan in autophagy and angiogenesis and contrast the role of endorepellin, the C-terminal fragment of perlecan, in these cellular and morphogenic events.

Endorepellin-evoked Autophagy Contributes to Angiostasis

Endorepellin, the C-terminal domain of perlecan, is an angiostatic molecule that acts as a potent inducer of autophagy via its interaction with VEGFR2. In this study, we examined the effect of endorepellin on endothelial cells using atomic force microscopy. Soluble endorepellin caused morphological and biophysical changes such as an increase in cell surface roughness and cell height. Surprisingly, these changes were not accompanied by alterations in the endothelial cell elastic modulus. We discovered that endorepellin-induced autophagic flux led to co-localization of mammalian target of rapamycin with LC3-positive autophagosomes. Endorepellin functioned upstream of AMP-activated kinase α, as compound C, an inhibitor of AMP-activated kinase α, abrogated endorepellin-mediated activation and co-localization of Beclin 1 and LC3, thereby reducing autophagic progression. Functionally, we discovered that both endorepellin and Torin 1, a canonical autophagic inducer, blunted ex vivo angiogenesis. We conclude that autophagy is a novel mechanism by which endorepellin promotes angiostasis independent of nutrient deprivation.

Identification of a novel splice site HSPG2 mutation and prenatal diagnosis in Schwartz Jampel Syndrome type 1 using whole exome sequencing

Schwartz-Jampel Syndrome type 1 is a rare autosomal recessive musculoskeletal disorder (OMIM #255800) caused by various mutations in the HSPG2 gene encoding protein perlecan, a ubiquitous heparan sulfate proteoglycan, which is an integral component of basement membranes and possesses angiogenic and growth-promoting attributes primarily by acting as a co-receptor for the basic fibroblast growth factors in human body. We report a novel homozygous intronic 5' splice site mutation in this gene (c.4740 + 5G>A) in a child with clinical features of Schwartz-Jampel syndrome type 1. The mutation was detected by exome sequencing and later confirmed by Sanger sequencing. The mother was found to be heterozygous for the mutation and an ongoing pregnancy found to be unaffected. cDNA analysis revealed skipping of exon 37 of HSPG2 gene in the patient due to the splicing error caused by this mutation. This is likely to result in loss of 38 amino acids from the domain III of the perlecan protein and presumably affects its structure and function as per protein modeling predictions. This report demonstrates the utility of exome sequencing as a routine molecular diagnostic approach of choice for this rare disorder.

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.

Radiation-Guided Gene Therapy of Cancer

Gene therapy has been proposed as a means to combat cancer. However, systemic toxicity observed in preclinical trials suggested the importance of selectively targeted delivery and inducible gene expression in tumor tissues. Discovery of radiation-inducible promoter sequences provides one way to minimize inadvertent toxicity from gene therapy in normal tissues. Radiation is administered to selectively induce cytotoxic gene expression in the targeted tumor tissues. With promising results from phase II clinical trials using TNF-expressing adenovirus, it is possible to have radiation-guided gene therapy regimes once the tumor-targeted delivery has been achieved. Tumor endothelium is an attractive biological target for gene therapy, because it has the advantage of stability, accessibility, and bioavailability for therapeutic agents. Technological development of DNA microarray, proteomic profiling, and phage-displayed libraries accelerates the identification of tumor-specific endothelial biomarkers and discovery of its relevant affinity reagents for targeted delivery. The application of radiation-guided gene delivery, its amplification, as well as expression of gene therapy presents great opportunities to be employed as an alternative cancer treatment.

Protein Z: A putative novel biomarker for early detection of ovarian cancer

Ovarian cancer (OC) has the highest mortality of all gynaecological cancers. Early diagnosis offers an approach to achieving better outcomes. We conducted a blinded-evaluation of prospectively collected preclinical serum from participants in the multimodal group of the United Kingdom Collaborative Trial of Ovarian Cancer Screening. Using isobaric tags (iTRAQ) we identified 90 proteins differentially expressed between OC cases and controls. A second targeted mass spectrometry analysis of twenty of these candidates identified Protein Z as a potential early detection biomarker for OC. This was further validated by ELISA analysis in 482 serial serum samples, from 80 individuals, 49 OC cases and 31 controls, spanning up to 7 years prior to diagnosis. Protein Z was significantly down-regulated up to 2 years pre-diagnosis (p = 0.000000411) in 8 of 19 Type I patients whilst in 5 Type II individuals, it was significantly up-regulated up to 4 years before diagnosis (p = 0.01). ROC curve analysis for CA-125 and CA-125 combined with Protein Z showed a statistically significant (p = 0.00033) increase in the AUC from 77 to 81% for Type I and a statistically significant (p= 0.00003) increase in the AUC from 76 to 82% for Type II. Protein Z is a novel independent early detection biomarker for Type I and Type II ovarian cancer; which can discriminate between both types. Protein Z also adds to CA-125 and potentially the Risk of Ovarian Cancer algorithm in the detection of both subtypes.

Endostatin and endorepellin: A common route of action for similar angiostatic cancer avengers

Traditional cancer therapy typically targets the tumor proper. However, newly-formed vasculature exerts a major role in cancer development and progression. Autophagy, as a biological mechanism for clearing damaged proteins and oxidative stress products released in the tumor milieu, could help in tumor resolution by rescuing cells undergoing modifications or inducing autophagic-cell death of tumor blood vessels. Cleaved fragments of extracellular matrix proteoglycans are emerging as key players in the modulation of angiogenesis and endothelial cell autophagy. An essential characteristic of cancer progression is the remodeling of the basement membrane and the release of processed forms of its constituents. Endostatin, generated from collagen XVIII, and endorepellin, the C-terminal segment of the large proteoglycan perlecan, possess a dual activity as modifiers of both angiogenesis and endothelial cell autophagy. Manipulation of these endogenously-processed forms, located in the basement membrane within tumors, could represent new therapeutic approaches for cancer eradication.

Perlecan Diversely Regulates the Migration and Proliferation of Distinct Cell Types in vitro

Perlecan is a multifunctional component of the extracellular matrix. It shows different effects on distinct cell types, and therefore it is thought to show potential for therapies targeting multiple cell types. However, the full range of multifunctionality of perlecan remains to be elucidated. We cultured various cell types, which were derived from epithelial/endothelial, connective and muscle tissues, in the presence of either antiserum against perlecan or exogenous perlecan, and examined the effects of perlecan on cell migration and proliferation. Cell migration was determined using a scratch assay. Blocking of perlecan by anti-perlecan antiserum inhibited the migration of vascular endothelial cells (VECs) and bone marrow-derived mesenchymal stem cells, and exogenous perlecan added to the culture medium promoted the migration of these cell types. The migration of other cell types was inhibited or was not promoted by exogenous perlecan. Cell proliferation was measured using a water-soluble tetrazolium dye. When cells were cultured at low densities, perlecan blocking inhibited the proliferation of VECs, and exogenous perlecan promoted the proliferation of keratinocytes. In contrast, the proliferation of fibroblasts, pre-adipocytes and vascular smooth muscle cells cultured at low densities was inhibited by exogenous perlecan. When cells were cultured at high densities, perlecan blocking promoted the proliferation of most cell types, with the exception of skeletal system-derived cells (chondrocytes and osteoblasts), which were inhibited by exogenous perlecan. Our results provide an overview of the multiple functions of perlecan in various cell types, and implicate a potential role of perlecan to inhibit undesirable activities, such as fibrosis, obesity and intimal hyperplasia.

The Extracellular Matrix in Epithelial Ovarian Cancer - A Piece of a Puzzle

Epithelial ovarian cancer is the fifth leading cause of cancer-related deaths in women and the most lethal gynecological malignancy. Extracellular matrix (ECM) is an integral component of both the normal and tumor microenvironment. ECM composition varies between tissues and is crucial for maintaining normal function and homeostasis. Dysregulation and aberrant deposition or loss of ECM components is implicated in ovarian cancer progression. The mechanisms by which tumor cells induce ECM remodeling to promote a malignant phenotype are yet to be elucidated. A thorough understanding of the role of the ECM in ovarian cancer is needed for the development of effective biomarkers and new therapies.

Utilization of Glycosaminoglycans/Proteoglycans as Carriers for Targeted Therapy Delivery

The outcome of patients with cancer has improved significantly in the past decade with the incorporation of drugs targeting cell surface adhesive receptors, receptor tyrosine kinases, and modulation of several molecules of extracellular matrices (ECMs), the complex composite of collagens, glycoproteins, proteoglycans, and glycosaminoglycans that dictates tissue architecture. Cancer tissue invasive processes progress by various oncogenic strategies, including interfering with ECM molecules and their interactions with invasive cells. In this review, we describe how the ECM components, proteoglycans and glycosaminoglycans, influence tumor cell signaling. In particular this review describes how the glycosaminoglycan hyaluronan (HA) and its major receptor CD44 impact invasive behavior of tumor cells, and provides useful insight when designing new therapeutic strategies in the treatment of cancer.

Extracellular matrix as target for antitumor therapy

The aim of the present review is to survey the accumulated knowledge on the extracellular matrix (ECM) of tumors referring to its putative utility as therapeutic target. Following the traditional observation on the extensive morphological alteration in the tumor-affected tissue, the well-documented aberrant cellular regulation indicated that ECM components have an active role in tumor progression. However, due to the diverse functions and variable expression of proteoglycans, matrix proteins, and integrins, it is rather difficult to identify a comprehensive therapeutic target among ECM components. At present, the elevated level of heparanase and the prominent expression of αvβ5 integrin are considered as promising therapeutic targets. The inhibition of glycosaminoglycan offers another promising approach in the treatment of those tumors which are stimulated by proteoglycans. It can be ascertained that a selective ECM inhibitor would be a great asset to control metastasis driven by ECM-mediated signaling.

Hepatoprotective and anti-tumor effects of targeting MMP-9 in hepatocellular carcinoma and its relation to vascular invasion markers

The current study aims to evaluate the hepatoprotective and antitumor efficacy of doxycycline, as an matrix metalloproteases-9 (MMP-9) inhibitor, in an in vivo model of hepatocellular carcinoma (HCC). HCC was induced experimentally by thiocetamide (200 mg/kg) in rats that were treated with doxycycline (5 mg/kg for 16 weeks). Tumor severity was evaluated by measuring α-fetoprotein (AFP) levels, histopathologically by investigating liver sections stained with hematoxylin/eosin and assessing the survival rate. Liver homogenates were used for the measurements of MMP-9, fascin and hepatic heparan sulfate proteoglycan (HSPG) levels. Oxidative stress markers [malonaldehyde (MDA) and glutathione] as well as fibroblast growth factor-2 (FGF-2) gene expression were also among the assessed indicators. HCC in human and animal samples showed significant elevation in the levels of MMP-9 (231.7, 90 %), fascin (33.17, 140 %), as well as FGF-2 gene expression (342 % in animal samples; all respectively), associated with a significant decrease in hepatic HSPG level. Treatment of rats with doxycycline increased the animal survival rate (90 %) and decreased serum AFP level. Moreover, doxycycline ameliorated fibrosis and the induced massive hepatic tissue breakdown. It also restored the integrity of hepatic HSPGs and showed a magnificent inhibitory effect of tumor invasion cascade by significantly reducing the activities of MMP-9 (42 %) and fascin (50 %), as well as reducing the gene expression of FGF-2 (85.7 %). Furthermore, the antioxidant impact of doxycycline was evidenced by the significant elevation in glutathione level and depressing MDA level. To this end, doxycycline, proved promising hepatoprotective and antitumor activity and opens, thereby, a new horizon against vascular migration ability of the tumor cells.

Proteoglycan form and function: A comprehensive nomenclature of proteoglycans

We provide a comprehensive classification of the proteoglycan gene families and respective protein cores. This updated nomenclature is based on three criteria: Cellular and subcellular location, overall gene/protein homology, and the utilization of specific protein modules within their respective protein cores. These three signatures were utilized to design four major classes of proteoglycans with distinct forms and functions: the intracellular, cell-surface, pericellular and extracellular proteoglycans. The proposed nomenclature encompasses forty-three distinct proteoglycan-encoding genes and many alternatively-spliced variants. The biological functions of these four proteoglycan families are critically assessed in development, cancer and angiogenesis, and in various acquired and genetic diseases where their expression is aberrant.

Proteoglycans as potential microenvironmental biomarkers for colon cancer

Glycosylation changes occur widely in colon tumours, suggesting glycosylated molecules as potential biomarkers for colon cancer diagnostics. In this study, proteoglycans (PGs) expression levels and their transcriptional patterns are investigated in human colon tumours in vivo and carcinoma cells in vitro. According to RT-PCR analysis, normal and cancer colon tissues expressed a specific set of PGs (syndecan-1, perlecan, decorin, biglycan, versican, NG2/CSPG4, serglycin, lumican, CD44), while the expression of glypican-1, brevican and aggrecan was almost undetectable. Overall transcriptional activity of the PGs in normal and cancer tissues was similar, although expression patterns were different. Expression of decorin and perlecan was down-regulated 2-fold in colon tumours, while biglycan and versican expression was significantly up-regulated (6-fold and 3-fold, respectively). Expression of collagen1A1 was also increased 6-fold in colon tumours. However, conventional HCT-116 colon carcinoma and AG2 colon cancer-initiating cells did not express biglycan and decorin and were versican-positive and -negative, respectively, demonstrating an extracellular origin of the PGs in cancer tissue. Selective expression of heparan sulfate (HS) proteoglycans syndecan-1 and perlecan in the AG2 colon cancer-initiating cell line suggests these PGs as potential biomarkers for cancer stem cells. Overall transcriptional activity of the HS biosynthetic system was similar in normal and cancer tissues, although significant up-regulation of extracellular sulfatases SULF1/2 argues for a possible distortion of HS sulfation patterns in colon tumours. Taken together, the obtained results suggest versican, biglycan, collagen1A1 and SULF1/2 expression as potential microenvironmental biomarkers and/or targets for colon cancer diagnostics and treatment.

The role of perlecan and endorepellin in the control of tumor angiogenesis and endothelial cell autophagy

During tumor growth and angiogenesis there is a dynamic remodeling of tissue architecture often accompanied by the release of extracellular matrix constituents full of biological activity. One of the key constituents of the tumor microenvironment is the large heparan sulfate proteoglycan perlecan. This proteoglycan, strategically located at cell surfaces and within basement membranes, is a well-defined pro-angiogenic molecule when intact. However, when partially processed by proteases released during cancer remodeling and invasion, the C-terminal fragment of perlecan, known as endorepellin, has opposite effects than its parent molecule. Endorepellin is a potent inhibitor of angiogenesis by exerting a dual receptor antagonism by simultaneously engaging VEGFR2 and α2β1 integrin. Signaling through the α2β1 integrin leads to actin disassembly and block of endothelial cell migration, necessary for capillary morphogenesis. Signaling through the VEGFR2 induces dephosphorylation of the receptor via activation of SHP-1 and suppression of downstream proangiogenic effectors, especially attenuating VEGFA expression. A novel and emerging role of endorepellin is its ability to evoke autophagy by activating Peg3 and various canonical autophagic markers. This effect is specific for endothelial cells as these are the primary cells expressing both VEGFR2 and α2β1 integrin. Thus, an endogenous fragment of a ubiquitous proteoglycan can regulate both angiogenesis and autophagy through a dual receptor antagonism. The biological properties of this natural endogenous protein place endorepellin as a potential therapeutic agent against cancer or diseases where angiogenesis is prominent.

Agrin and perlecan mediate tumorigenic processes in oral squamous cell carcinoma

Oral squamous cell carcinoma is the most common type of cancer in the oral cavity, representing more than 90% of all oral cancers. The characterization of altered molecules in oral cancer is essential to understand molecular mechanisms underlying tumor progression as well as to contribute to cancer biomarker and therapeutic target discovery. Proteoglycans are key molecular effectors of cell surface and pericellular microenvironments, performing multiple functions in cancer. Two of the major basement membrane proteoglycans, agrin and perlecan, were investigated in this study regarding their role in oral cancer. Using real time quantitative PCR (qRT-PCR), we showed that agrin and perlecan are highly expressed in oral squamous cell carcinoma. Interestingly, cell lines originated from distinct sites showed different expression of agrin and perlecan. Enzymatically targeting chondroitin sulfate modification by chondroitinase, oral squamous carcinoma cell line had a reduced ability to adhere to extracellular matrix proteins and increased sensibility to cisplatin. Additionally, knockdown of agrin and perlecan promoted a decrease on cell migration and adhesion, and on resistance of cells to cisplatin. Our study showed, for the first time, a negative regulation on oral cancer-associated events by either targeting chondroitin sulfate content or agrin and perlecan levels.

Epac1 increases migration of endothelial cells and melanoma cells via FGF2-mediated paracrine signaling

Fibroblast growth factor (FGF2) regulates endothelial and melanoma cell migration. The binding of FGF2 to its receptor requires N-sulfated heparan sulfate (HS) glycosamine. We have previously reported that Epac1, an exchange protein activated by cAMP, increases N-sulfation of HS in melanoma. Therefore, we examined whether Epac1 regulates FGF2-mediated cell–cell communication. Conditioned medium (CM) of melanoma cells with abundant expression of Epac1 increased migration of human umbilical endothelial cells (HUVEC) and melanoma cells with poor expression of Epac1. CM-induced increase in migration was inhibited by antagonizing FGF2, by the removal of HS and by the knockdown of Epac1. In addition, knockdown of Epac1 suppressed the binding of FGF2 to FGF receptor in HUVEC, and in vivo angiogenesis in melanoma. Furthermore, knockdown of Epac1 reduced N-sulfation of HS chains attached to perlecan, a major secreted type of HS proteoglycan that mediates the binding of FGF2 to FGF receptor. These data suggested that Epac1 in melanoma cells regulates melanoma progression via the HS–FGF2-mediated cell–cell communication.

Heparan sulfate signaling in cancer

Heparan sulfate (HS) is a biopolymer consisting of variably sulfated repeating disaccharide units. The anticoagulant heparin is a highly sulfated intracellular variant of HS. HS has demonstrated roles in embryonic development, homeostasis, and human disease via non-covalent interactions with numerous cellular proteins, including growth factors and their receptors. HS can function as a co-receptor by enhancing receptor-complex formation. In other contexts, HS disrupts signaling complexes or serves as a ligand sink. The effects of HS on growth factor signaling are tightly regulated by the actions of sulfyltransferases, sulfatases, and heparanases. HS has important emerging roles in oncogenesis, and heparin derivatives represent potential therapeutic strategies for human cancers. Here we review recent insights into HS signaling in tumor proliferation, angiogenesis, metastasis, and differentiation. A cancer-specific understanding of HS signaling could uncover potential therapeutic targets in this highly actionable signaling network.

Endorepellin evokes autophagy in endothelial cells

Endorepellin, the C-terminal fragment of the heparan sulfate proteoglycan perlecan, possesses angiostatic activity via dual receptor antagonism, through concurrent binding to the α2β1 integrin and vascular endothelial growth factor receptor 2 (VEGFR2). Here, we discovered that soluble endorepellin induced autophagy in endothelial cells by modulating the expression of Beclin 1, LC3, and p62, three established autophagic markers. Moreover, endorepellin evoked expression of the imprinted tumor suppressor gene Peg3 and its co-localization with Beclin 1 and LC3 in autophagosomes, suggesting a major role for this gene in endothelial cell autophagy. Mechanistically, endorepellin induced autophagy by down-regulating VEGFR2 via the two LG1/2 domains, whereas the C-terminal LG3 domain, the portion responsible for binding the α2β1 integrin, was ineffective. Endorepellin also induced transcriptional activity of the BECN1 promoter in endothelial cells, and the VEGFR2-specific tyrosine kinase inhibitor, SU5416, blocked this effect. Finally, we found a correlation between endorepellin-evoked inhibition of capillary morphogenesis and enhanced autophagy. Thus, we have identified a new role for this endogenous angiostatic fragment in inducing autophagy through a VEGFR2-dependent but α2β1 integrin-independent pathway. This novel mechanism specifically targets endothelial cells and could represent a promising new strategy to potentiate the angiostatic effect of endorepellin and perhaps other angiostatic matrix proteins.