Heparanase 2 Attenuates Head and Neck Tumor Vascularity and Growth

Current understanding of heparanase 2 regulation, a non-heparanase

Heparan sulfate (HS) proteoglycans are life-supporting proteins comprising a core protein to which one or more HS glycan chains are covalently bound. HS proteoglycans act as binding sites for circulating cells and molecules, allow gradient formation, and provide local storage capacities. They act as coreceptors, fine-tuning growth factor receptors and activating intracellular signaling pathways. HS glycan chains are cleaved and regulated by heparanase 1 (Hpa1). Heparanase 2 (Hpa2) is a close homolog of Hpa1. Unlike Hpa1, Hpa2 lacks enzymatic activity but nonetheless binds HS with high affinity, thus modulating HS-mediated biological processes. Only a few functions of Hpa2 have been unraveled. Under disease conditions that include the Mendelian urofacial syndrome, Hpa2 expression is markedly down-regulated, most compellingly demonstrated in several cancers. Hpa2 also circulates in the bloodstream, potentially originating from secretory organs such as liver and pancreas. The Hpa2 promotor is inducible by cellular stressors including cytotoxic, proteostatic, and endoplasmic reticulum stress. Activating transcription factor 3 (ATF3) induces Hpa2 gene expression. We summarize Hpa2 regulation in the framework of health and disease to foster research into its function. The underlying mystery remains: ‘How does this “heparanase,” which is actually a non-heparanase, work, and what are the ramifications?

Tumor- and host-derived heparanase-2 (Hpa2) attenuates tumorigenicity: role of Hpa2 in macrophage polarization and BRD7 nuclear localization

Little attention was given to heparanase 2 (Hpa2) over the last two decades, possibly because it lacks a heparan sulfate (HS)-degrading activity typical of heparanase. Emerging results suggest, nonetheless, that Hpa2 plays a role in human pathologies, including cancer progression where it functions as a tumor suppressor. Here, we examined the role of Hpa2 in cervical carcinoma. We report that high levels of Hpa2 correlate with prolonged survival of cervical carcinoma patients. Strong staining intensity of Hpa2 also correlates with low tumor grade. Overexpression of Hpa2 in SiHa cervical carcinoma cells resulted in tumor xenografts that were two-fold smaller than control tumors. Interestingly, even smaller tumor xenografts were developed by SiHa cells overexpressing the Pro140Arg and Asn543Ile Hpa2 missense mutations that were identified in patients diagnosed with urofacial syndrome (UFS). Utilizing the Ras recruitment system, we identified bromodomain-containing protein 7 (BRD7) to interact with Hpa2 and found that both BRD7 and the Hpa2 mutants are translocated to the cell nucleus in tumors developed by the Pro140Arg and Asn543Ile Hpa2 mutants. Utilizing our newly developed conditional Hpa2-KO mice, we further show that Hpa2 plays a critical role in macrophage polarization; in the absence of Hpa2, macrophages are shifted towards pro-tumorigenic, M2 phenotype. Notably, implanting SiHa cervical carcinoma cells together with Hpa2-KO macrophages promoted tumor growth. These results support, and further expand, the notion that Hpa2 functions as a tumor suppressor, co-operating with another tumor suppressor, BRD7.

Impact of heparanase-2 (Hpa2) on cancer and inflammation: Advances and paradigms

HPSE2, the gene-encoding heparanase 2 (Hpa2), is mutated in urofacial syndrome (UFS), a rare autosomal recessive congenital disease attributed to peripheral neuropathy. Hpa2 lacks intrinsic heparan sulfate (HS)-degrading activity, the hallmark of heparanase (Hpa1), yet it exhibits a high affinity toward HS, thereby inhibiting Hpa1 enzymatic activity. Hpa2 regulates selected genes that promote normal differentiation, tissue homeostasis, and endoplasmic reticulum (ER) stress, resulting in antitumor, antiangiogenic, and anti-inflammatory effects. Importantly, stress conditions induce the expression of Hpa2, thus establishing a feedback loop, where Hpa2 enhances ER stress which, in turn, induces Hpa2 expression. In most cases, cancer patients who retain high levels of Hpa2 survive longer than patients bearing Hpa2-low tumors. Experimentally, overexpression of Hpa2 attenuates the growth of tumor xenografts, whereas Hpa2 gene silencing results in aggressive tumors. Studies applying conditional Hpa2 knockout (cHpa2-KO) mice revealed an essential involvement of Hpa2 contributed by the host in protecting against cancer and inflammation. This was best reflected by the distorted morphology of the Hpa2-null pancreas, including massive infiltration of immune cells, acinar to adipocyte trans-differentiation, and acinar to ductal metaplasia. Moreover, orthotopic inoculation of pancreatic ductal adenocarcinoma (PDAC) cells into the pancreas of Hpa2-null vs. wild-type mice yielded tumors that were by far more aggressive. Likewise, intravenous inoculation of cancer cells into cHpa2-KO mice resulted in a dramatically increased lung colonization reflecting the involvement of Hpa2 in restricting the formation of a premetastatic niche. Elucidating Hpa2 structure-activity-relationships is expected to support the development of Hpa2-based therapies against cancer and inflammation.

Nuclear localization of heparanase 2 (Hpa2) attenuates breast carcinoma growth and metastasis

Unlike the intense research effort devoted to exploring the significance of heparanase in cancer, very little attention was given to Hpa2, a close homolog of heparanase. Here, we explored the role of Hpa2 in breast cancer. Unexpectedly, we found that patients endowed with high levels of Hpa2 exhibited a higher incidence of tumor metastasis and survived less than patients with low levels of Hpa2. Immunohistochemical examination revealed that in normal breast tissue, Hpa2 localizes primarily in the cell nucleus. In striking contrast, in breast carcinoma, Hpa2 expression is not only decreased but also loses its nuclear localization and appears diffuse in the cell cytoplasm. Importantly, breast cancer patients in which nuclear localization of Hpa2 is retained exhibited reduced lymph-node metastasis, suggesting that nuclear localization of Hpa2 plays a protective role in breast cancer progression. To examine this possibility, we engineered a gene construct that directs Hpa2 to the cell nucleus (Hpa2-Nuc). Notably, overexpression of Hpa2 in breast carcinoma cells resulted in bigger tumors, whereas targeting Hpa2 to the cell nucleus attenuated tumor growth and tumor metastasis. RNAseq analysis was performed to reveal differentially expressed genes (DEG) in Hpa2-Nuc tumors vs. control. The analysis revealed, among others, decreased expression of genes associated with the hallmark of Kras, beta-catenin, and TNF-alpha (via NFkB) signaling. Our results imply that nuclear localization of Hpa2 prominently regulates gene transcription, resulting in attenuation of breast tumorigenesis. Thus, nuclear Hpa2 may be used as a predictive parameter in personalized medicine for breast cancer patients.

Heparanase 2 (Hpa2)- a new player essential for pancreatic acinar cell differentiation

Heparanase 2 (Hpa2, HPSE2) is a close homolog of heparanase. Hpa2, however, lacks intrinsic heparan sulfate (HS)-degrading activity, the hallmark of heparanase enzymatic activity. Mutations of HPSE2 were identified in patients diagnosed with urofacial syndrome (UFS), a rare genetic disorder that exhibits abnormal facial expression and bladder voiding dysfunction, leading to renal damage and eventually renal failure. In order to reveal the role of HPSE2 in tissue homeostasis, we established a conditional Hpa2-KO mouse. Interestingly, the lack of Hpa2 was associated with a marked decrease in the expression of key pancreatic transcription factors such as PTF1, GATA6, and Mist1. This was associated with a two-fold decrease in pancreas weight, increased pancreatic inflammation, and profound morphological alterations of the pancreas. These include massive accumulation of fat cells, possibly a result of acinar-to-adipocyte transdifferentiation (AAT), as well as acinar-to-ductal metaplasia (ADM), both considered to be pro-tumorigenic. Furthermore, exposing Hpa2-KO but not wild-type mice to a carcinogen (AOM) and pancreatic inflammation (cerulein) resulted in the formation of pancreatic intraepithelial neoplasia (PanIN), lesions that are considered to be precursors of invasive ductal adenocarcinoma of the pancreas (PDAC). These results strongly support the notion that Hpa2 functions as a tumor suppressor. Moreover, Hpa2 is shown here for the first time to play a critical role in the exocrine aspect of the pancreas.

Heparanase-A single protein with multiple enzymatic and nonenzymatic functions

Heparanase (Hpa1) is expressed by tumor cells and cells of the tumor microenvironment and functions extracellularly to remodel the extracellular matrix (ECM) and regulate the bioavailability of ECM-bound factors, augmenting, among other effects, gene transcription, autophagy, exosome formation, and heparan sulfate (HS) turnover. Much of the impact of heparanase on tumor progression is related to its function in mediating tumor-host crosstalk, priming the tumor microenvironment to better support tumor growth, metastasis, and chemoresistance. The enzyme appears to fulfill some normal functions associated, for example, with vesicular traffic, lysosomal-based secretion, autophagy, HS turnover, and gene transcription. It activates cells of the innate immune system, promotes the formation of exosomes and autophagosomes, and stimulates signal transduction pathways via enzymatic and nonenzymatic activities. These effects dynamically impact multiple regulatory pathways that together drive tumor growth, dissemination, and drug resistance as well as inflammatory responses. The emerging premise is that heparanase expressed by tumor cells, immune cells, endothelial cells, and other cells of the tumor microenvironment is a key regulator of the aggressive phenotype of cancer, an important contributor to the poor outcome of cancer patients and a valid target for therapy. So far, however, antiheparanase-based therapy has not been implemented in the clinic. Unlike heparanase, heparanase-2 (Hpa2), a close homolog of heparanase (Hpa1), does not undergo proteolytic processing and hence lacks intrinsic HS-degrading activity, the hallmark of heparanase. Hpa2 retains the capacity to bind heparin/HS and exhibits an even higher affinity towards HS than heparanase, thus competing for HS binding and inhibiting heparanase enzymatic activity. It appears that Hpa2 functions as a natural inhibitor of Hpa1 regulates the expression of selected genes that maintain tissue hemostasis and normal function, and plays a protective role against cancer and inflammation, together emphasizing the significance of maintaining a proper balance between Hpa1 and Hpa2.

Potential roles of heparanase in cancer therapy: Current trends and future direction

Heparanase (HPSE; heparanase-1) is an endo-β-glucuronidase capable of degrading the carbohydrate moiety of heparan sulfate proteoglycans, thus modulating and facilitating the remodeling of the extracellular matrix and basement membrane. HPSE activity is strongly associated with major human pathological complications, including but not limited to tumor progress and angiogenesis. Several lines of literature have shown that overexpression of HPSE leads to enhanced tumor growth and metastatic transmission, as well as poor prognosis. Gene silencing of HPSE or treatment of tumor with compounds that block HPSE activity are shown to remarkably attenuate tumor progression. Therefore, targeting HPSE is considered as a potential therapeutical strategy for the treatment of cancer. Intriguingly, recent findings disclose that heparanase-2 (HPSE-2), a close homolog of HPSE but lacking enzymatic activity, can also regulate antitumor mechanisms. Given the pleiotropic roles of HPSE, further investigation is in demand to determine the precise mechanism of regulating action of HPSE in different cancer settings. In this review, we first summarize the current understanding of HPSE, such as its structure, subcellular localization, and tissue distribution. Furthermore, we systematically review the pro- and antitumorigenic roles and mechanisms of HPSE in cancer progress. In addition, we delineate HPSE inhibitors that have entered clinical trials and their therapeutic potential.

Heparanase 2 (Hpa2) attenuates the growth of human sarcoma

The pro-tumorigenic properties of heparanase are well documented and established. In contrast, the role of heparanase 2 (Hpa2), a close homolog of heparanase, in cancer is not entirely clear. In carcinomas, Hpa2 is thought to attenuate tumor growth, possibly by inhibiting heparanase enzymatic activity. Here, we examine the role of Hpa2 in sarcoma, a group of rare tumors of mesenchymal origin, accounting for approximately 1% of all malignant tumors. Consistently, we found that overexpression of Hpa2 attenuates tumor growth while Hpa2 gene silencing results in bigger tumors. Mechanistically, attenuation of tumor growth by Hpa2 was associated with increased tumor stress conditions, involving ER stress, hypoxia, and JNK phosphorylation, leading to increased apoptotic cell death. In addition, overexpression of Hpa2 induces the expression of the p53 family member, p63 which, in sarcoma, functions to attenuate tumor growth. Moreover, we show that Hpa2 profoundly reduces stem cell characteristics of the sarcoma cells (stemness), most evident by failure of Hpa2 cells to grow as spheroids typical of stem cells. Likewise, expression of CD44, a well-established stem cell marker, was prominently decreased in Hpa2 cells. CD44 is also a cell surface receptor for hyaluronic acid (HA), a nonsulfated glycosaminoglycan that is enriched in connective tissues. Reduced expression of CD44 by Hpa2 may thus represent impaired cross-talk between Hpa2 and the extracellular matrix. Clinically, we found that Hpa2 is expressed by leiomyosarcoma tumor biopsies. Interestingly, nuclear localization of Hpa2 was associated with low-stage tumors. This finding opens a new direction in Hpa2 research.

miR-429 negatively regulates the progression of hypoxia-induced retinal neovascularization by the HPSE-VEGF pathway

Heparanase (HPSE) and vascular endothelial growth factor (VEGF) are believed to play a vital role in hypoxia-induced retinal neovascularization (RNV). HPSE is a target gene of miR-429. Our study aimed to investigate the effect of the miR-429-HPSE-VEGF pathway on hypoxia-induced RNV. The gene and protein expression of miR-429, HPSE and VEGF in human retinal endothelial cells and retinas was determined by real-time PCR and Western blot assays. The effects of miR-429 on human retinal endothelial cells and retinal neovascularization under hypoxia condition were verified by in vitro and in vivo experiments. First, we studied the effect of the miR-429-HPSE-VEGF pathway in HRECs under hypoxic conditions. HREC functions such as migration and tube formation were enhanced under hypoxic conditions. Overexpression of miR-429 in HRECs reversed these changes. Then, we investigated the effect of miR-429 on hypoxia-induced RNV in vivo. When miR-429 agomirs were injected into the vitreous cavity of mice with oxygen-induced retinopathy to overexpress miR-429, the mRNA and protein expression of VEGF was significantly reduced. In addition, indicators of retinal neovascularization, such as the retinal avascular area, and morphology of vessels, were reduced significantly in the miR-429 overexpression group. In this study, our data showed that miR-429 plays an important role by inhibiting the HPSE-VEGF pathway in hypoxia-induced retinopathy.

Heparanase 1 Upregulation Promotes Tumor Progression and Is a Predictor of Low Survival for Oral Cancer

Background: Oral cavity cancer is still an important public health problem throughout the world. Oral squamous cell carcinomas (OSCCs) can be quite aggressive and metastatic, with a low survival rate and poor prognosis. However, this is usually related to the clinical stage and histological grade, and molecular prognostic markers for clinical practice are yet to be defined. Heparanase (HPSE1) is an endoglycosidase associated with extracellular matrix remodeling, and although involved in several malignancies, the clinical implications of HPSE1 expression in OSCCs are still unknown.

Methods: We sought to investigate HPSE1 expression in a series of primary OSCCs and further explore whether its overexpression plays a relevant role in OSCC tumorigenesis. mRNA and protein expression analyses were performed in OSCC tissue samples and cell lines. A loss-of-function strategy using shRNA and a gain-of-function strategy using an ORF vector targeting HPSE1 were employed to investigate the endogenous modulation of HPSE1 and its effects on proliferation, apoptosis, adhesion, epithelial–mesenchymal transition (EMT), angiogenesis, migration, and invasion of oral cancer in vitro.

Results: We demonstrated that HPSE1 is frequently upregulated in OSCC samples and cell lines and is an unfavorable prognostic indicator of disease-specific survival when combined with advanced pT stages. Moreover, abrogation of HPSE1 in OSCC cells significantly promoted apoptosis and inhibited proliferation, migration, invasion, and epithelial–mesenchymal transition by significantly decreasing the expression of N-cadherin and vimentin. Furthermore, a conditioned medium of HPSE1-downregulated cells resulted in reduced vascular endothelial growth.

Conclusion: Our results confirm the overexpression of HPSE1 in OSCCs, suggest that HPSE1 expression correlates with disease progression as it is associated with several important biological processes for oral tumorigenesis, and can be managed as a prognostic marker for patients with OSCC.

Induction of heparanase 2 (Hpa2) expression by stress is mediated by ATF3

Activity of heparanase, endoglycosidase that cleaves heparan sulfate side chains in heparan sulfate proteoglycans, is highly implicated in tumor progression and metastasis. Heparanase inhibitors are therefore being evaluated clinically as anti-cancer therapeutics. Heparanase 2 (Hpa2) is a close homolog of heparanase that lacks HS-degrading activity and functions as an endogenous inhibitor of heparanase. As a result, Hpa2 appears to attenuate tumor growth but mechanisms that regulate Hpa2 expression and determine the ratio between heparanase and Hpa2 are largely unknown. We have recently reported that the expression of Hpa2 is induced by endoplasmic reticulum (ER) and proteotoxic stresses, but the mechanism(s) underlying Hpa2 gene regulation was obscure. Here we expand the notion that Hpa2 is regulated by conditions of stress. We report that while ER and hypoxia, each alone, resulted in a 3-7 fold increase in Hpa2 expression, combining ER stress and hypoxia resulted in a noticeable, over 40-fold increase in Hpa2 expression. A prominent induction of Hpa2 expression was also quantified in cells exposed to heat shock, proteotoxic stress, lysosomal stress, and chemotherapy (cisplatin), strongly implying that Hpa2 is regulated by conditions of stress. Furthermore, analyses of the Hpa2 gene promoter led to the identification of activating-transcription-factor 3 (ATF3) as a transcription factor that mediates Hpa2 induction by stress, thus revealing, for the first time, a molecular mechanism that underlies Hpa2 gene regulation. Induction of Hpa2 and ATF3 by conditions of stress that often accompany the rapid expansion of tumors is likely translated to improved survival of cancer patients.

Extracellular matrix-based cancer targeting

Tumor extracellular matrix (ECM) operates in a coordinated mode with cancer and stroma cells to evoke the multistep process of metastatic potential. The remodeled tumor-associated matrix provides a point for direct or complementary therapeutic targeting. Here, we cover and critically address the importance of ECM networks and their macromolecules in cancer. We focus on the roles of key structural and functional ECM components, and their degradation enzymes and extracellular vesicles, aiming at improving our understanding of the mechanisms contributing to tumor initiation, growth, and dissemination, and discuss potential new approaches for ECM-based therapeutic targeting and diagnosis.

Role of heparanase 2 (Hpa2) in gastric cancer

We report that gastric cancer patients exhibiting high levels of heparanase 2 (Hpa2) survive longer. Similarly, mice administrated with gastric carcinoma cells engineered to overexpress Hpa2 produced smaller tumors and survived longer than mice administrated with control cells. These beneficial effects were found to associate with increased phosphorylation of AMP-activated protein kinase (AMPK) that play an instrumental role in cell metabolism and is situated at the center of a tumor suppressor network. We also found that MG132, an inhibitor of the proteasome that results in proteotoxic stress, prominently enhances Hpa2 expression. Notably, Hpa2 induction by MG132 appeared to be mediated by AMPK, thus establishing a loop that feeds itself where Hpa2 enhances AMPK phosphorylation that, in turn, induces Hpa2 expression, possibly leading to attenuation of gastric tumorigenesis.

Heparanase is highly implicated in tumor metastasis due to its capacity to cleave heparan sulfate and, consequently, remodel the extracellular matrix underlying epithelial and endothelial cells. In striking contrast, only little attention was given to its close homolog, heparanase 2 (Hpa2), possibly because it lacks heparan sulfate-degrading activity typical of heparanase. We subjected sections of gastric carcinoma to immunostaining and correlated Hpa2 immunoreactivity with clinical records, including tumor grade, stage and patients' status. We over-expressed Hpa2 in gastric carcinoma cell lines and examined their tumorigenic properties in vitro and in vivo. We also evaluated the expression of Hpa2 by gastric carcinoma cells following inhibition of the proteasome, leading to proteotoxic stress, and the resulting signaling responsible for Hpa2 gene regulation. Here, we report that gastric cancer patients exhibiting high levels of Hpa2 survive longer. Similarly, mice administrated with gastric carcinoma cells engineered to over-express Hpa2 produced smaller tumors and survived longer than mice administrated with control cells. This was associated with increased phosphorylation of AMP-activated protein kinase (AMPK), a kinase that is situated at the center of a tumor suppressor network. We also found that MG132, an inhibitor of the proteasome that results in proteotoxic stress, prominently enhances Hpa2 expression. Notably, Hpa2 induction by MG132 appeared to be mediated by AMPK, and AMPK was found to induce the expression of Hpa2, thus establishing a loop that feeds itself where Hpa2 enhances AMPK phosphorylation that, in turn, induces Hpa2 expression, leading to attenuation of gastric tumorigenesis. These results indicate that high levels of Hpa2 in some tumors are due to stress conditions that tumors often experience due to their high rates of cell proliferation and high metabolic demands. This increase in Hpa2 levels by the stressed tumors appears critically important for patient outcomes.

Heparanase 2 (Hpa2) attenuates tumor growth by inducing Sox2 expression

The pro-tumorigenic properties of heparanase are well documented, and heparanase inhibitors are being evaluated clinically as anti-cancer therapeutics. In contrast, the role of heparanase 2 (Hpa2), a close homolog of heparanase, in cancer is largely unknown. Previously, we have reported that in head and neck cancer, high levels of Hpa2 are associated with prolonged patient survival and decreased tumor cell dissemination to regional lymph nodes, suggesting that Hpa2 functions to restrain tumorigenesis. Also, patients with high levels of Hpa2 were diagnosed as low grade and exhibited increased expression of cytokeratins, an indication that Hpa2 promotes or maintains epithelial cell differentiation and identity. To reveal the molecular mechanism underlying the tumor suppressor properties of Hpa2, and its ability to induce the expression of cytokeratin, we employed overexpression as well as gene editing (Crispr) approaches, combined with gene array and RNAseq methodologies. At the top of the list of many genes found to be affected by Hpa2 was Sox2. Here we provide evidence that silencing of Sox2 resulted in bigger tumors endowed with reduced cytokeratin levels, whereas smaller tumors were developed by cells overexpressing Sox2, suggesting that in head and neck carcinoma, Sox2 functions to inhibit tumor growth. Notably, Hpa2-null cells engineered by Crispr/Cas 9, produced bigger tumors vs control cells, and rescue of Hpa2 attenuated tumor growth. These results strongly imply that Hpa2 functions as a tumor suppressor in head and neck cancer, involving Sox2 upregulation mediated, in part, by the high-affinity interaction of Hpa2 with heparan sulfate.

A Pro-Tumorigenic Effect of Heparanase 2 (Hpa2) in Thyroid Carcinoma Involves Its Localization to the Nuclear Membrane

Activity of the endo-beta-glucuronidase heparanase, capable of cleaving heparan sulfate (HS), is most often elevated in many types of tumors, associating with increased tumor metastasis and decreased patients' survival. Heparanase is therefore considered to be a valid drug target, and heparanase inhibitors are being evaluated clinically in cancer patients. Heparanase 2 (Hpa2) is a close homolog of heparanase that gained very little attention, likely because it lacks HS-degrading activity typical of heparanase. The role of Hpa2 in cancer was not examined in detail. In head and neck cancer, high levels of Hpa2 are associated with decreased tumor cell dissemination to regional lymph nodes and prolonged patients' survival, suggesting that Hpa2 functions to attenuate tumor growth. Here, we examined the role of Hpa2 in normal thyroid tissue and in benign thyroid tumor, non-metastatic, and metastatic papillary thyroid carcinoma (PTC) utilizing immunostaining in correlation with clinicopathological parameters. Interestingly, we found that Hpa2 staining intensity does not significantly change in the transition from normal thyroid gland to benign, non-metastatic, or metastatic thyroid carcinoma. Remarkably, we observed that in some biopsies, Hpa2 is accumulating on the membrane (envelop) of the nucleus and termed this cellular localization NM (nuclear membrane). Notably, NM localization of Hpa2 occurred primarily in metastatic PTC and was associated with an increased number of positive (metastatic) lymph nodes collected at surgery. These results describe for the first time unrecognized localization of Hpa2 to the nuclear membrane, implying that in PTC, Hpa2 functions to promote tumor metastasis.

Heparanase 2 (Hpa2) attenuates the growth of pancreatic carcinoma

While the pro-tumorigenic properties of the ECM-degrading heparanase enzyme are well documented, the role of its close homolog, heparanase 2 (Hpa2), in cancer is largely unknown. We examined the role of Hpa2 in pancreatic cancer, a malignancy characterized by a dense fibrotic ECM associated with poor response to treatment and bad prognosis. We show that pancreatic ductal adenocarcinoma (PDAC) patients that exhibit high levels of Hpa2 survive longer than patients with low levels of Hpa2. Strikingly, overexpression of Hpa2 in pancreatic carcinoma cells resulted in a most prominent decrease in the growth of tumors implanted orthotopically and intraperitoneally, whereas Hpa2 silencing resulted in bigger tumors. We further found that Hpa2 enhances endoplasmic reticulum (ER) stress response and renders cells more sensitive to external stress, associating with increased apoptosis. Interestingly, we observed that ER stress induces the expression of Hpa2, thus establishing a feedback loop by which Hpa2 enhances ER stress that, in turn, induces Hpa2 expression. This leads to increased apoptosis and attenuated tumor growth. Altogether, Hpa2 emerges as a powerful tumor suppressor in pancreatic cancer.

Elucidating the Consequences of Heparan Sulfate Binding by Heparanase 2

Unlike the intense research effort devoted to exploring the significance of heparanase in human diseases, very little attention was given to its close homolog, heparanase 2 (Hpa2). The emerging role of Hpa2 in a rare autosomal recessive congenital disease called urofacial syndrome (UFS), clearly indicates that Hpa2 is not a pseudogene but rather a gene coding for an important protein. Hpa2 lacks the heparan sulfate (HS)-degrading activity typical of heparanase, yet exhibits high affinity to HS, affinity that is 10-fold higher than that of heparanase. The consequences of this high-affinity interaction of Hpa2 with plasma membrane HSPG has not been explored yet. Here, we used highly purified Hpa2 protein to examine this aspect. We provide evidence that cells adhere to and spread on dishes coated with Hpa2. We also show that cell migration is attenuated markedly by exogenous addition of Hpa2 to primary and transformed cells, a function that agrees with the anti-cancer properties of Hpa2. Interestingly, we found that exogenous addition of Hpa2 also disrupts the morphology of cell colonies, resulting in cell scattering. This implies that under certain conditions and experimental settings, Hpa2 may exhibit pro-tumorigenic properties. We further developed a panel of anti-Hpa2 monoclonal antibodies (mAb) and show that these properties of Hpa2 are prevented by some of the newly-developed mAb, thus providing new molecular tools to better appreciate the significance of Hpa2 in health and disease.

The Good and Bad Sides of Heparanase-1 and Heparanase-2

In this chapter, we will emphasize the importance of heparan sulfate proteoglycans (HSPG) in controlling various physiological and pathological molecular mechanisms and discuss how the heparanase enzyme can modulate the effects triggered by HSPG. Additionally, we will also navigate about the existing knowledge of the possible role of heparanase-2 in biological events. Heparan sulfate is widely distributed and evolutionarily conserved, evidencing its vital importance in cell development and functions such as cell proliferation, migration, adhesion, differentiation, and angiogenesis. During remodeling of the extracellular matrix, the breakdown of heparan sulfate by heparanase results in the release of molecules containing anchored glycosaminoglycan chains of great interest in heparanase-mediated cell signaling pathways in various physiological states, tumor development, inflammation, and other diseases. Taken together, it appears that heparanase plays a key role in the maintenance of the pathology of cancer and inflammatory diseases and is a potential target for anti-cancer therapies. Therefore, heparanase inhibitors are currently being examined in clinical trials as novel cancer therapeutics. Heparanase-2 has no enzymatic activity, displays higher affinity for heparan sulfate and the coding region alignment shows 40% identity with the heparanase gene. Heparanase-2 plays an important role in embryogenic development however its mode of action and biological function remain to be elucidated. Heparanase-2 functions as an inhibitor of the heparanase-1 enzyme and also inhibits neovascularization mediated by VEGF. The HPSE2 gene is repressed by the Polycomb complex, together suggesting a role as a tumor suppressor.

Hpa2 Gene Cloning

From 1999-2003, Oxford GlycoSciences (OGS) ran a successful drug discovery oncology programme to discover small molecule inhibitors of the Heparanase I enzyme (HPSE1). HPSE1 at the time was widely regarded as being the sole mammalian enzyme capable of cleaving Heparan Sulfate (HS). A second family protein member however called Heparanase 2 (HPSE2) including splice forms was subsequently discovered by PCR analysis based on EST sequences. HPSE2 was found to be expressed mainly in smooth muscle containing tissues, particularly bladder and brain. HPSE2 is poorly expressed in haematopoietic cells and placenta which contrasts with the HPSE1 distribution pattern. HPSE2 binds more strongly to HS than HPSE1 and is believed to out compete for substrate binding and so in effect act as a tumor suppressor. So far, all attempts to show specific HPSE2 endoglycosidase activity against HS have failed suggesting that the enzyme may act as a pseudoenzyme that has evolved to retain only certain non-catalytic heparanase like functions. A breakthrough in the elucidation of functional roles for HPSE2 came about in 2010 with the linkage of HPSE2 gene deletions and mutations to the development of Ochoa/Urofacial Syndrome. Future work into the mechanistic analysis of HPSE2's role in signalling, tumor suppression and bladder/nerve functioning are needed to fully explore the role of this family of proteins.

Opposing Effects of Heparanase and Heparanase-2 in Head & Neck Cancer

Squamous cell carcinoma of head and neck (SCCHN) is the most common cancer in the head and neck and is the sixth most common neoplasm worldwide. SCCHN has a high propensity to lymph node metastases, especially cancer of the pharynx. Prognosis of patients with SCCHN is severely influenced by the status of metastatic cervical lymph nodes and survival rates drop down to half when patients are presented with a metastatic node. The clinical relevance of heparanase as a prognostic marker in SCCHN was reported in several publications. Low levels of heparanase in SCCHN tumor cells was correlated with prolonged disease-free and overall survival. Furthermore, nuclear localization of heparanase predicts a favorable outcome compared to cytoplasmic localization. Heparanase staining was positively correlated with lymphatic vessel density and lymph node metastasis associated with the elevation of vascular endothelial growth factor C (VEGF-C). Heparanase ability to enhance phosphorylation of epidermal growth factor receptor (EGFR), and signal transducer and activator of transcription 3 (STAT3) were postulated to serve as critical molecular mechanisms by which heparanase facilitates tumor growth.Heparanase-2 (HPA2) is a close homolog of heparanase that lacks intrinsic HS-degrading activity but retains the capacity to bind HS with high affinity. HPA2 expression was markedly elevated in SCCHN patients, correlating with prolonged follow-up time to recurrence and inversely correlating with patients' N-stage. HPA2 appears to inhibit tumor dissemination, suggesting that HPA2 functions as a tumor suppressor. Thus, Heparanase and Heparanase-2 seem to exert opposing effects on SCCHN.

Forty Years of Basic and Translational Heparanase Research

This review summarizes key developments in the heparanase field obtained 20 years prior to cloning of the HPSE gene and nearly 20 years after its cloning. Of the numerous publications and review articles focusing on heparanase, we have selected those that best reflect the progression in the field as well as those we regard important accomplishments with preference to studies performed by scientists and groups that contributed to this book. Apart from a general 'introduction' and 'concluding remarks', the abstracts of these studies are presented essentially as published along the years. We apologize for not being objective and not being able to include some of the most relevant abstracts and references, due to space limitation. Heparanase research can be divided into two eras. The first, initiated around 1975, dealt with identifying the enzyme, establishing the relevant assay systems and investigating its biological activities and significance in cancer and other pathologies. Studies performed during the first area are briefly introduced in a layman style followed by the relevant abstracts presented chronologically, essentially as appears in PubMed. The second era started in 1999 when the heparanase gene was independently cloned by 4 research groups [1-4]. As expected, cloning of the heparanase gene boosted heparanase research by virtue of the readily available recombinant enzyme, molecular probes, and anti-heparanase antibodies. Studies performed during the second area are briefly introduced followed by selected abstracts of key findings, arranged according to specific topics.

An Overview of the Structure, Mechanism and Specificity of Human Heparanase

The retaining endo-β-D-glucuronidase Heparanase (HPSE) is the primary mammalian enzyme responsible for breakdown of the glycosaminoglycan heparan sulfate (HS). HPSE activity is essential for regulation and turnover of HS in the extracellular matrix, and its activity affects diverse processes such as inflammation, angiogenesis and cell migration. Aberrant heparanase activity is strongly linked to cancer metastasis, due to structural breakdown of extracellular HS networks and concomitant release of sequestered HS-binding growth factors. A full appreciation of HPSE activity in health and disease requires a structural understanding of the enzyme, and how it engages with its HS substrates. This chapter summarizes key findings from the recent crystal structures of human HPSE and its proenzyme. We present details regarding the 3-dimensional protein structure of HPSE and the molecular basis for its interaction with HS substrates of varying sulfation states. We also examine HPSE in a wider context against related β-D-glucuronidases from other species, highlighting the structural features that control exo/endo - glycosidase selectivity in this family of enzymes.

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.

Heparanase-2 protects from LPS-mediated endothelial injury by inhibiting TLR4 signalling

The endothelial glycocalyx and its regulated shedding are important to vascular health. Endo-β-D-glucuronidase heparanase-1 (HPSE1) is the only enzyme that can shed heparan sulfate. However, the mechanisms are not well understood. We show that HPSE1 activity aggravated Toll-like receptor 4 (TLR4)-mediated response of endothelial cells to LPS. On the contrary, overexpression of its endogenous inhibitor, heparanase-2 (HPSE2) was protective. The microfluidic chip flow model confirmed that HPSE2 prevented heparan sulfate shedding by HPSE1. Furthermore, heparan sulfate did not interfere with cluster of differentiation-14 (CD14)-dependent LPS binding, but instead reduced the presentation of the LPS to TLR4. HPSE2 reduced LPS-mediated TLR4 activation, subsequent cell signalling, and cytokine expression. HPSE2-overexpressing endothelial cells remained protected against LPS-mediated loss of cell-cell contacts. In vivo, expression of HPSE2 in plasma and kidney medullary capillaries was decreased in mouse sepsis model. We next applied purified HPSE2 in mice and observed decreases in TNFα and IL-6 plasma concentrations after intravenous LPS injections. Our data demonstrate the important role of heparan sulfate and the glycocalyx in endothelial cell activation and suggest a protective role of HPSE2 in microvascular inflammation. HPSE2 offers new options for protection against HPSE1-mediated endothelial damage and preventing microvascular disease.

Lrig2 and Hpse2, mutated in urofacial syndrome, pattern nerves in the urinary bladder

Mutations in leucine-rich-repeats and immunoglobulin-like-domains 2 (LRIG2) or in heparanase 2 (HPSE2) cause urofacial syndrome, a devastating autosomal recessive disease of functional bladder outlet obstruction. It has been speculated that urofacial syndrome has a neural basis, but it is unknown whether defects in urinary bladder innervation are present. We hypothesized that urofacial syndrome features a peripheral neuropathy of the bladder. Mice with homozygous targeted Lrig2 mutations had urinary defects resembling those found in urofacial syndrome. There was no anatomical blockage of the outflow tract, consistent with a functional bladder outlet obstruction. Transcriptome analysis revealed differential expression of 12 known transcripts in addition to Lrig2, including 8 with established roles in neurobiology. Mice with homozygous mutations in either Lrig2 or Hpse2 had increased nerve density within the body of the urinary bladder and decreased nerve density around the urinary outflow tract. In a sample of 155 children with chronic kidney disease and urinary symptoms, we discovered novel homozygous missense LRIG2 variants that were predicted to be pathogenic in 2 individuals with non-syndromic bladder outlet obstruction. These observations provide evidence that a peripheral neuropathy is central to the pathobiology of functional bladder outlet obstruction in urofacial syndrome, and emphasize the importance of LRIG2 and heparanase 2 for nerve patterning in the urinary tract.

The prognostic significance of heparanase expression in metastatic melanoma

BACKGROUND

Heparanase expression is induced in many types of cancers, including melanoma, and promotes tumor growth, angiogenesis and metastasis. However, there is insufficient data regarding heparanase expression in the metastatic lesions that are the prime target for anti-cancer therapeutics. To that end, we examined heparanase expression in metastatic melanoma and its correlation with clinical parameters.

RESULTS

Heparanase staining was detected in 88% of the samples, and was strong in 46%. For the entire cohort of metastatic melanoma patients, no apparent correlation was found between heparanase staining intensity and survival. However, in a sub group of 46 patients diagnosed as stage IVc melanoma, strong heparanase staining was associated with reduced survival rates [hazard ratio=2.1; 95%CI 1.1-4.1, p=0.025].

MATERIAL AND METHODS

Paraffin sections from 69 metastatic melanomas were subjected to immunohistochemical analysis, applying anti-heparanase antibody. The clinical and pathological data, together with heparanase staining intensity, were evaluated in a logistic regression model for site of metastasis and survival. Slides were also stained for the heparanase-homolog, heparanase-2 (Hpa2).

CONCLUSIONS

Heparanase is highly expressed in metastatic melanoma and predicts poor survival of stage IVc melanoma patients, justifying the development and implementation of heparanase inhibitors as anti-cancer therapeutics.

Activated HGF-c-Met Axis in Head and Neck Cancer

Head and neck squamous cell carcinoma (HNSCC) is a highly morbid disease. Recent developments including Food and Drug Administration (FDA) approved molecular targeted agent’s pembrolizumab and cetuximab show promise but did not improve the five-year survival which is currently less than 40%. The hepatocyte growth factor receptor; also known as mesenchymal–epithelial transition factor (c-Met) and its ligand hepatocyte growth factor (HGF) are overexpressed in head and neck squamous cell carcinoma (HNSCC); and regulates tumor progression and response to therapy. The c-Met pathway has been shown to regulate many cellular processes such as cell proliferation, invasion, and angiogenesis. The c-Met pathway is involved in cross-talk, activation, and perpetuation of other signaling pathways, curbing the cogency of a blockade molecule on a single pathway. The receptor and its ligand act on several downstream effectors including phospholipase C gamma (PLCγ), cellular Src kinase (c-Src), phosphotidylinsitol-3-OH kinase (PI3K) alpha serine/threonine-protein kinase (Akt), mitogen activate protein kinase (MAPK), and wingless-related integration site (Wnt) pathways. They are also known to cross-talk with other receptors; namely epidermal growth factor receptor (EGFR) and vascular endothelial growth factor receptor (VEGFR) and specifically contribute to treatment resistance. Clinical trials targeting the c-Met axis in HNSCC have been undertaken because of significant preclinical work demonstrating a relationship between HGF/c-Met signaling and cancer cell survival. Here we focus on HGF/c-Met impact on cellular signaling in HNSCC to potentiate tumor growth and disrupt therapeutic efficacy. Herein we summarize the current understanding of HGF/c-Met signaling and its effects on HNSCC. The intertwining of c-Met signaling with other signaling pathways provides opportunities for more robust and specific therapies, leading to better clinical outcomes.

Opposing Functions of Heparanase-1 and Heparanase-2 in Cancer Progression

Heparanase, the sole heparan sulfate (HS)-degrading endoglycosidase, regulates multiple biological activities that enhance tumor growth, metastasis, angiogenesis, and inflammation. Heparanase accomplishes this by degrading HS and thereby regulating the bioavailability of heparin-binding proteins; priming the tumor microenvironment; mediating tumor-host crosstalk; and inducing gene transcription, signaling pathways, exosome formation, and autophagy that together promote tumor cell performance and chemoresistance. By contrast, heparanase-2, a close homolog of heparanase, lacks enzymatic activity, inhibits heparanase activity, and regulates selected genes that promote normal differentiation, endoplasmic reticulum stress, tumor fibrosis, and apoptosis, together resulting in tumor suppression. The emerging premise is that heparanase is a master regulator of the aggressive phenotype of cancer, while heparanase-2 functions as a tumor suppressor.

Extracellular matrix alterations in the Peyronie's disease

Peyronie’s disease is characterized by fibrous plaque formation of the tunica albuginea, causing penile deformity and fertility problems. The aim of the present study was to investigate alterations in the extracellular matrix in Peyronie’s disease. The study used tissues collected by surgical procedure from individuals that presented a well-established disease, while control samples were obtained by biopsies of fresh cadavers. Immunohistochemistry analysis followed by digital quantification was performed to evaluate TGF-β, heparanases and metalloproteinases (MMPs). The profile of sulfated glycosaminoglycans, chondroitin sulfate and dermatan sulfate was determined by agarose gel electrophoresis, while hyaluronic acid quantification was obtained by an ELISA-like assay. The expression of mRNA was investigated for syndecan-1 proteoglycan (Syn-1), interleukine-6 (IL-6), hyaluronic acid synthases, and hyaluronidases. Pathologic features showed decreased apoptosis and blood vessel number in Peyronie’s tissues. TGF-β and IL-6 were significantly enhanced in Peyronie’s disease. There was an increased expression of heparanases, though no alteration was observed for MMPs. Hyaluronic acid as well as hyaluronic acid synthases, hyaluronidases, and dermatan sulfate were not changed, while the level of chondroitin sulfate was significantly (P = 0.008, Mann-Whitney test) increased in Peyronie’s samples. Heparanases and sulfated glycosaminoglycans seem to be involved in extracellular matrix alterations in Peyronie’s disease.

Overexpression of heparanase attenuated TGF-β-stimulated signaling in tumor cells

Heparan sulfate (HS) mediates the activity of various growth factors including TGF-β. Heparanase is an endo-glucuronidase that specifically cleaves and modifies HS structure. In this study, we examined the effect of heparanase expression on TGF-β1-dependent signaling activities. We found that overexpression of heparanase in human tumor cells (i.e., Fadu pharyngeal carcinoma, MCF7 breast carcinoma) attenuated TGF-β1-stimulated Smad phosphorylation and led to a slower cell proliferation. TGF-β1-stimulated Akt and Erk phosphorylation was also affected in the heparanase overexpression cells. This effect involved the enzymatic activity of heparanase, as overexpression of mutant inactive heparanase did not affect TGF-β1 signaling activity. Analysis of HS isolated from Fadu cells revealed an increase in sulfation of the HS that had a rapid turnover in cells overexpressing heparanase. It appears that the structural alterations of HS affect the ability of TGF-β1 to signal via its receptors and elicit a growth response. Given that heparanase expression promotes tumor growth in most cancers, this finding highlights a crosstalk between heparanase, HS, and TGF-β1 function in tumorigenesis.

The Heparanase Inhibitor PG545 Attenuates Colon Cancer Initiation and Growth, Associating with Increased p21 Expression

Heparanase activity is highly implicated in cellular invasion and tumor metastasis, a consequence of cleavage of heparan sulfate and remodeling of the extracellular matrix underlying epithelial and endothelial cells. Heparanase expression is rare in normal epithelia, but is often induced in tumors, associated with increased tumor metastasis and poor prognosis. In addition, heparanase induction promotes tumor growth, but the molecular mechanism that underlines tumor expansion by heparanase is still incompletely understood. Here, we provide evidence that heparanase down regulates the expression of p21 (WAF1/CIP1), a cyclin-dependent kinase inhibitor that attenuates the cell cycle. Notably, a reciprocal effect was noted for PG545, a potent heparanase inhibitor. This compound efficiently reduced cell proliferation, colony formation, and tumor xenograft growth, associating with a marked increase in p21 expression. Utilizing the APC Min^+/− mouse model, we show that heparanase expression and activity are increased in small bowel polyps, whereas polyp initiation and growth were significantly inhibited by PG545, again accompanied by a prominent induction of p21 levels. Down-regulation of p21 expression adds a novel feature for the emerging pro-tumorigenic properties of heparanase, while the potent p21 induction and anti-tumor effect of PG545 lends optimism that it would prove an efficacious therapeutic in colon carcinoma patients.

Heparanase: From basic research to therapeutic applications in cancer and inflammation

Heparanase, the sole heparan sulfate degrading endoglycosidase, regulates multiple biological activities that enhance tumor growth, angiogenesis and metastasis. Heparanase expression is enhanced in almost all cancers examined including various carcinomas, sarcomas and hematological malignancies. Numerous clinical association studies have consistently demonstrated that upregulation of heparanase expression correlates with increased tumor size, tumor angiogenesis, enhanced metastasis and poor prognosis. In contrast, knockdown of heparanase or treatments of tumor-bearing mice with heparanase-inhibiting compounds, markedly attenuate tumor progression further underscoring the potential of anti-heparanase therapy for multiple types of cancer. Heparanase neutralizing monoclonal antibodies block myeloma and lymphoma tumor growth and dissemination; this is attributable to a combined effect on the tumor cells and/or cells of the tumor microenvironment. In fact, much of the impact of heparanase on tumor progression is related to its function in mediating tumor-host crosstalk, priming the tumor microenvironment to better support tumor growth, metastasis and chemoresistance. The repertoire of the physio-pathological activities of heparanase is expanding. Specifically, heparanase regulates gene expression, activates cells of the innate immune system, promotes the formation of exosomes and autophagosomes, and stimulates signal transduction pathways via enzymatic and non-enzymatic activities. These effects dynamically impact multiple regulatory pathways that together drive inflammatory responses, tumor survival, growth, dissemination and drug resistance; but in the same time, may fulfill some normal functions associated, for example, with vesicular traffic, lysosomal-based secretion, stress response, and heparan sulfate turnover. Heparanase is upregulated in response to chemotherapy in cancer patients and the surviving cells acquire chemoresistance, attributed, at least in part, to autophagy. Consequently, heparanase inhibitors used in tandem with chemotherapeutic drugs overcome initial chemoresistance, providing a strong rationale for applying anti-heparanase therapy in combination with conventional anti-cancer drugs. Heparin-like compounds that inhibit heparanase activity are being evaluated in clinical trials for various types of cancer. Heparanase neutralizing monoclonal antibodies are being evaluated in pre-clinical studies, and heparanase-inhibiting small molecules are being developed based on the recently resolved crystal structure of the heparanase protein. Collectively, the emerging premise is that heparanase expressed by tumor cells, innate immune cells, activated endothelial cells as well as other cells of the tumor microenvironment is a master regulator of the aggressive phenotype of cancer, an important contributor to the poor outcome of cancer patients and a prime target for therapy.