Incorporation, intracellular trafficking and processing of extracellular heparanase by mast cells: Involvement of syndecan-4-dependent pathway

Mast cell heparanase promotes breast cancer stem-like features via MUC1/estrogen receptor axis

Breast cancer is the most frequent type of tumor in women and is characterized by variable outcomes due to its heterogeneity and the presence of many cancer cell-autonomous and -non-autonomous factors. A major determinant of breast cancer aggressiveness is represented by immune infiltration, which can support tumor development. In our work, we studied the role of mast cells in breast cancer and identified a novel activity in promoting the tumor-initiating properties of cancer cells. Mast cells are known to affect breast cancer prognosis, but show different effects according to the diverse subtypes. Starting from the observation that co-injection of mast cells with limiting concentrations of cancer cells increased their in vivo engraftment rate, we characterized the molecular mechanisms by which mast cells promote the tumor stem-like features. We provide evidence that mast cell heparanase plays a pivotal role since both its activity and the stimulation of mast cells with heparan sulfate, the product of heparanase activity, are crucial for this process. Moreover, the pharmacological inhibition of heparanase prevents the function of mast cells. Our data show that soluble factors released by mast cells favor the expression of estrogen receptor in a MUC1-dependent manner. The MUC1/estrogen receptor axis is eventually essential for cancer stem-like features, specifically in HER2-negative cells, and promotes the capability of cancer cells to form mammospheres and express stem-related genes, also reducing their sensitivity to tamoxifen administration. Altogether our findings describe a novel mechanism by which mast cells could increase the aggressiveness of breast cancer uncovering a molecular mechanism displaying differences based on the specific breast cancer subtype.

The Uptake of Heparanase into Mast Cells Is Regulated by Its Enzymatic Activity to Degrade Heparan Sulfate

Mast cells take up extracellular latent heparanase and store it in secretory granules. The present study examined whether the enzymatic activity of heparanase regulates its uptake efficiency. Recombinant mouse heparanase mimicking both the latent and mature forms (L-Hpse and M-Hpse, respectively) was internalized into mastocytoma MST cells, peritoneal cell-derived mast cells, and bone marrow-derived mast cells. The internalized amount of L-Hpse was significantly higher than that of M-Hpse. In MST cells, L-Hpse was continuously internalized for up to 8 h, while the uptake of M-Hpse was saturated after 2 h of incubation. L-Hpse and M-Hpse are similarly bound to the MST cell surface. The expression level of cell surface heparan sulfate was reduced in MST cells incubated with M-Hpse. The internalized amount of M-Hpse into mast cells was significantly increased in the presence of heparastatin (SF4), a small molecule heparanase inhibitor that does not affect the binding of heparanase to immobilized heparin. Enzymatically quiescent M-Hpse was prepared with a point mutation at Glu335. The internalized amount of mutated M-Hpse was significantly higher than that of wild-type M-Hpse but similar to that of wild-type and mutated L-Hpse. These results suggest that the enzymatic activity of heparanase negatively regulates the mast cell-mediated uptake of heparanase, possibly via the downregulation of cell surface heparan sulfate expression.

Effects of syndecan-4 silencing on the extracellular matrix remodeling in anoikis-resistant endothelial cells

Anoikis is a process of programmed cell death induced by the loss of cell/matrix interactions. In previous work, we have shown that the acquisition of anoikis resistance upregulates syndecan-4 (SDC4) expression in endothelial cells. In addition, SDC4 gene silencing by microRNA interference reverses the transformed phenotype of anoikis-resistant endothelial cells. Due to this role of SDC4 in regulating the behavior of anoikis-resistant endothelial cells, we have evaluated that the functional consequences of SDC4 silencing in the extracellular matrix (ECM) remodeling in anoikis-resistant rabbit aortic endothelial cells submitted to SDC4 gene silencing (miR-Syn4-Adh-1-EC). For this, we evaluated the expression of adhesive proteins, ECM receptors, nonreceptor protein-tyrosine kinases, and ECM-degrading enzymes and their inhibitors. Altered cell behavior was monitored by adhesion, migration, and tube formation assays. We found that SDC4 silencing led to a decrease in migration and angiogenic capacity of anoikis-resistant endothelial cells; this was accompanied by an increase in adhesion to fibronectin. Furthermore, after SDC4 silencing, we observed an increase in the expression of fibronectin, collagen IV, and vitronectin, and a decrease in the expression of integrin α5β1 and αvβ3, besides that, silenced cells show an increase in Src and FAK expression. Quantitative polymerase chain reaction and Western blot analysis demonstrated that SDC4 silencing leads to altered gene and protein expression of MMP2, MMP9, and HSPE. Compared with parental cells, SDC4 silenced cells showed a decrease in nitric oxide production and eNOS expression. In conclusion, these data demonstrate that SDC4 plays an important role in ECM remodeling. In addition, our findings represent an important step toward understanding the mechanism by which SDC4 can reverse the transformed phenotype of anoikis-resistant endothelial cells.

Characterization of Hyaluronidase 4 Involved in the Catabolism of Chondroitin Sulfate

Hyaluronidases (HYALs) are endo-beta-N-acetylhexosaminidases that depolymerize not only hyaluronan but also chondroitin sulfate (CS) at the initial step of their catabolism. Although HYAL1 hydrolyzes both CS and HA, HYAL4 is a CS-specific endoglycosidase. The substrate specificity of HYAL4 and identification of amino acid residues required for its enzymatic activity have been reported. In this study, we characterized the properties of HYAL4 including the expression levels in various tissues, cellular localization, and effects of its overexpression on intracellular CS catabolism, using cultured cells as well as mouse tissues. Hyal4 mRNA and HYAL4 protein were demonstrated to be ubiquitously expressed in various organs in the mouse. HYAL4 protein was shown to be present both on cell surfaces as well as in lysosomes of rat skeletal muscle myoblasts, L6 cells. Overexpression of HYAL4 in Chinese hamster ovary cells decreased in the total amount of CS, suggesting its involvement in the cellular catabolism of CS. In conclusion, HYAL4 may be widely distributed and play various biological roles, including the intracellular depolymerization of CS.

Thy-1 (CD90), Integrins and Syndecan 4 are Key Regulators of Skin Wound Healing

Acute skin wound healing is a multistage process consisting of a plethora of tightly regulated signaling events in specialized cells. The Thy-1 (CD90) glycoprotein interacts with integrins and the heparan sulfate proteoglycan syndecan 4, generating a trimolecular complex that triggers bi-directional signaling to regulate diverse aspects of the wound healing process. These proteins can act either as ligands or receptors, and they are critical for the successful progression of wound healing. The expression of Thy-1, integrins, and syndecan 4 is controlled during the healing process, and the lack of expression of any of these proteins results in delayed wound healing. Here, we review and discuss the roles and regulatory events along the stages of wound healing that support the relevance of Thy-1, integrins, and syndecan 4 as crucial regulators of skin wound healing.

microRNA-140-3p modulates invasiveness, motility, and extracellular matrix adhesion of breast cancer cells by targeting syndecan-4

Syndecan-4, a predicted target of the microRNA miR-140-3p, plays an important role in multiple steps of tumor progression and is the second most abundant heparan sulfate proteoglycan produced by breast carcinoma cell lines. To investigate the potential functional relationship of miR-140-3p and syndecan-4, MDA-MB-231, SKBR3, and MCF-7 breast cancer (BC) cells were transiently transfected with pre-miR-140-3p, syndecan-4 small interfering RNAJ, or control reagents, respectively. Altered cell behavior was monitored by adhesion, migration, and invasion chamber assays. Moreover, the prognostic value of syndecan-4 was assessed by Kaplan-Maier Plotter analysis of gene expression data from tumor samples of 4929 patients. High expression of syndecan-4 was associated with better relapse-free survival in the whole collective of BC patients, but correlated with a worse survival in the subgroup of estrogen receptor negative and estrogen/progesterone-receptor negative patients. miR-140-3p expression was associated with improved survival irrespective of hormone receptor status. miR-140-3p overexpression induced posttranscriptional downregulation of syndecan-4, as demonstrated by quantitative real-time PCR (qPCR), flow cytometry, and luciferase assays, resulting in decreased BC cell migration and matrigel invasiveness. Furthermore, miR-140-3p overexpression and syndecan-4 silencing increased the adhesion of BC to fibronectin and laminin. qPCR analysis demonstrated that syndecan-4 silencing leads to altered gene expression of adhesion-related molecules, such as fibronectin and focal adhesion kinase, as well as in the gene expression of the proinvasive factors matrix metalloproteinase 2 and heparanase (also known as HPSE). We conclude that syndecan-4 is a novel target of miR-140-3p that regulates BC cell invasiveness and cell-matrix interactions in the tumor microenvironment.

Syndecan receptors: pericellular regulators in development and inflammatory disease

The syndecans are the major family of transmembrane proteoglycans, usually bearing multiple heparan sulfate chains. They are present on virtually all nucleated cells of vertebrates and are also present in invertebrates, indicative of a long evolutionary history. Genetic models in both vertebrates and invertebrates have shown that syndecans link to the actin cytoskeleton and can fine-tune cell adhesion, migration, junction formation, polarity and differentiation. Although often associated as co-receptors with other classes of receptors (e.g. integrins, growth factor and morphogen receptors), syndecans can nonetheless signal to the cytoplasm in discrete ways. Syndecan expression levels are upregulated in development, tissue repair and an array of human diseases, which has led to the increased appreciation that they may be important in pathogenesis not only as diagnostic or prognostic agents, but also as potential targets. Here, their functions in development and inflammatory diseases are summarized, including their potential roles as conduits for viral pathogen entry into cells.

Heparanase: A Challenging Cancer Drug Target

Heparanase has been viewed as a promising anti-cancer drug target for almost two decades, but no anti-heparanase therapy has yet reached the clinic. This endoglycosidase is highly expressed in a variety of malignancies, and its high expression is associated with greater tumor size, more metastases, and a poor prognosis. It was first described as an enzyme cleaving heparan sulfate chains of proteoglycans located in extracellular matrices and on cell surfaces, but this is not its only function. It is a multi-functional protein with activities that are enzymatic and non-enzymatic and which take place both outside of the cell and intracellularly. Knowledge of the crystal structure of heparanase has assisted the interpretation of earlier structure-function studies as well as in the design of potential anti-heparanase agents. This review re-examines the various functions of heparanase in light of the structural data. The functions of the heparanase variant, T5, and structure and functions of heparanase-2 are also examined as these heparanase related, but non-enzymatic, proteins are likely to influence the in vivo efficacy of anti-heparanase drugs. The anti-heparanase drugs currently under development predominately focus on inhibiting the enzymatic activity of heparanase, which, in the absence of inhibitors with high clinical efficacy, prompts a discussion of whether this is the best approach. The diversity of outcomes attributed to heparanase and the difficulties of unequivocally determining which of these are due to its enzymatic activity is also discussed and leads us to the conclusion that heparanase is a valid, but challenging drug target for cancer.

Chondroitin sulfate E blocks enzymatic action of heparanase and heparanase-induced cellular responses

We examined whether chondroitin sulfates (CSs) exert inhibitory effects on heparanase (Hpse), the sole endoglycosidase that cleaves heparan sulfate (HS) and heparin, which also stimulates chemokine production. Hpse-mediated degradation of HS was suppressed in the presence of glycosaminoglycans derived from a squid cartilage and mouse bone marrow-derived mast cells, including the E unit of CS. Pretreatment of the chondroitin sulfate E (CS-E) with chondroitinase ABC abolished the inhibitory effect. Recombinant proteins that mimic pro-form and mature-form Hpse bound to the immobilized CS-E. Cellular responses as a result of Hpse-mediated binding, namely, uptake of Hpse by mast cells and Hpse-induced release of chemokine CCL2 from colon carcinoma cells, were also blocked by the CS-E. CS-E may regulate endogenous Hpse-mediated cellular functions by inhibiting enzymatic activity and binding to the cell surface.