Aberrant heparan sulfate proteoglycan localization, despite normal exostosin, in central chondrosarcoma

Heparan sulfate proteoglycans (HSPGs) of the ocular lens

Heparan sulfate proteoglycans (HSPGs) reside in most cells; on their surface, in the pericellular milieu and/or extracellular matrix. In the eye, HSPGs can orchestrate the activity of key signalling molecules found in the ocular environment that promote its development and homeostasis. To date, our understanding of the specific roles played by individual HSPG family members, and the heterogeneity of their associated sulfated HS chains, is in its infancy. The crystalline lens is a relatively simple and well characterised ocular tissue that provides an ideal stage to showcase and model the expression and unique roles of individual HSPGs. Individual HSPG core proteins are differentially localised to eye tissues in a temporal and spatial developmental- and cell-type specific manner, and their loss or functional disruption results in unique phenotypic outcomes for the lens, and other ocular tissues. More recent work has found that different HS sulfation enzymes are also presented in a cell- and tissue-specific manner, and that disruption of these different sulfation patterns affects specific HS-protein interactions. Not surprisingly, these sulfated HS chains have also been reported to be required for lens and eye development, with dysregulation of HS chain structure and function leading to pathogenesis and eye-related phenotypes. In the lens, HSPGs undergo significant and specific changes in expression and function that can drive pathology, or in some cases, promote tissue repair. As master signalling regulators, HSPGs may one day serve as valuable biomarkers, and even as putative targets for the development of novel therapeutics, not only for the eye but for many other systemic pathologies.

An Atlas of Heparan Sulfate Proteoglycans in the Postnatal Rat Lens

Purpose

The arrangement of lens cells is regulated by ocular growth factors. Although the effects of these inductive molecules on lens cell behavior (proliferation, survival, and fiber differentiation) are well-characterized, the precise mechanisms underlying the regulation of growth factor-mediated signaling in lens remains elusive. Increasing evidence highlights the importance of heparan sulfate proteoglycans (HSPGs) for the signaling regulation of growth factors; however, the identity of the different lens HSPGs and the specific roles they play in lens biology are still unknown.

Methods

Semiquantitative real-time (RT)‐PCR and immunolabeling were used to characterize the spatial distribution of all known HSPG core proteins and their associated glycosaminoglycans (heparan and chondroitin sulfate) in the postnatal rat lens. Fibroblast growth factor (FGF)-2-treated lens epithelial explants, cultured in the presence of Surfen (an inhibitor of heparan sulfate [HS]-growth factor binding interactions) were used to investigate the requirement for HS in FGF-2-induced proliferation, fiber differentiation, and ERK1/2-signaling.

Results

The lens expresses all HSPGs. These HSPGs are differentially localized to distinct functional regions of the lens. In vitro, inhibition of HS-sulfation with Surfen blocked FGF-2-mediated ERK1/2-signaling associated with lens epithelial cell proliferation and fiber differentiation, highlighting that these cellular processes are dependent on HS.

Conclusions

These findings support a requirement for HSPGs in FGF-2 driven lens cell proliferation and fiber differentiation. The identification of specific HSPG core proteins in key functional lens regions, and the divergent expression patterns of closely related HSPGs, suggests that different HSPGs may differentially regulate growth factor signaling networks leading to specific biological events involved in lens growth and maintenance.

What Are the Potential Roles of Nuclear Perlecan and Other Heparan Sulphate Proteoglycans in the Normal and Malignant Phenotype

The recent discovery of nuclear and perinuclear perlecan in annulus fibrosus and nucleus pulposus cells and its known matrix stabilizing properties in tissues introduces the possibility that perlecan may also have intracellular stabilizing or regulatory roles through interactions with nuclear envelope or cytoskeletal proteins or roles in nucleosomal-chromatin organization that may regulate transcriptional factors and modulate gene expression. The nucleus is a mechano-sensor organelle, and sophisticated dynamic mechanoresponsive cytoskeletal and nuclear envelope components support and protect the nucleus, allowing it to perceive and respond to mechano-stimulation. This review speculates on the potential roles of perlecan in the nucleus based on what is already known about nuclear heparan sulphate proteoglycans. Perlecan is frequently found in the nuclei of tumour cells; however, its specific role in these diseased tissues is largely unknown. The aim of this review is to highlight probable roles for this intriguing interactive regulatory proteoglycan in the nucleus of normal and malignant cell types.

Involvement of Syndecan-1 and Heparanase in Cancer and Inflammation

The cell surface heparan sulfate proteoglycan Syndecan-1 acts as an important co-receptor for receptor tyrosine kinases and chemokine receptors, and as an adhesion receptor for structural glycoproteins of the extracellular matrix. It serves as a substrate for heparanase, an endo-β-glucuronidase that degrades specific domains of heparan sulfate carbohydrate chains and thereby alters the functional status of the proteoglycan and of Syndecan-1-bound ligands. Syndecan-1 and heparanase show multiple levels of functional interactions, resulting in mutual regulation of their expression, processing, and activity. These interactions are of particular relevance in the context of inflammation and malignant disease. Studies in animal models have revealed a mechanistic role of Syndecan-1 and heparanase in the regulation of contact allergies, kidney inflammation, multiple sclerosis, inflammatory bowel disease, and inflammation-associated tumorigenesis. Moreover, functional interactions between Syndecan-1 and heparanase modulate virtually all steps of tumor progression as defined in the Hallmarks of Cancer. Due to their prognostic value in cancer, and their mechanistic involvement in tumor progression, Syndecan-1 and heparanase have emerged as important drug targets. Data in preclinical models and preclinical phase I/II studies have already yielded promising results that provide a translational perspective.

Heparanase: A Potential Therapeutic Target in Sarcomas

Sarcomas comprise a heterogeneous group of rare malignancies of mesenchymal origin including more than 70 subtypes. They may arise in muscle, bone, cartilage and other connective tissues. Their high histological and genetic heterogeneity makes diagnosis and treatment very challenging. Deregulation of heparanase has been found in several sarcoma subtypes and high expression levels have been correlated with poor prognosis in Ewing's sarcoma and osteosarcoma. Altered expression of specific heparan sulfate proteoglycans and heparan sulfate biosynthetic enzymes has also been observed. Advances in molecular pathogenesis of sarcomas have evidenced the critical role of several heparan sulfate binding growth factors and receptor tyrosine kinases, highly interconnected with the microenvironment, in sustaining tumor growth and progression. Interference with heparanase/heparan sulfate functions represents a potential therapeutic approach in sarcoma. In this chapter, we summarize the current knowledge about the biological significance of heparanase expression and its potential as a therapeutic target in subtypes of both soft tissue and bone sarcomas. Particular emphasis is given to the involvement of heparan sulfate proteoglycans and their synthesizing and modifying enzymes in bone physiology and disorders leading up to the pathobiology of bone sarcomas. The chapter also describes the cooperation between exostin loss-of-function and heparanase upregulation in hereditary Multiple Osteochondroma syndrome as a paradigmatic example of constitutive alteration of the heparanase/heparan sulfate proteoglycan system which may contribute to progression to malignant secondary chondrosarcoma. Preclinical evidence of the role of heparanase as a promising therapeutic target in various sarcoma subtypes is finally resumed.

Structural Features of Heparan Sulfate from Multiple Osteochondromas and Chondrosarcomas

Multiple osteochondromas (MO) is a hereditary disorder associated with benign cartilaginous tumors, known to be characterized by absence or highly reduced amount of heparan sulfate (HS) in the extracellular matrix of growth plate cartilage, which alters proper signaling networks leading to improper bone growth. Although recent studies demonstrated accumulation of HS in the cytoplasm of MO chondrocytes, nothing is known on the structural alterations which prevent HS from undergoing its physiologic pathway. In this work, osteochondroma (OC), peripheral chondrosarcoma, and healthy cartilaginous human samples were processed following a procedure previously set up to structurally characterize and compare HS from pathologic and physiologic conditions, and to examine the phenotypic differences that arise in the presence of either exostosin 1 or 2 (EXT1 or EXT2) mutations. Our data suggest that HS chains from OCs are prevalently below 10 kDa and slightly more sulfated than healthy ones, whereas HS chains from peripheral chondrosarcomas (PCSs) are mostly higher than 10 kDa and remarkably more sulfated than all the other samples. Although deeper investigation is still necessary, the approach here applied pointed out, for the first time, structural differences among OC, PCS, and healthy HS chains extracted from human cartilaginous excisions, and could help in understanding how the structural features of HS are modulated in the presence of pathological situations also involving different tissues.

The Pulmonary Endothelial Glycocalyx in ARDS: A Critical Role for Heparan Sulfate

The endothelial glycocalyx is a glycosaminoglycan-enriched endovascular layer that, with the development of novel fixation and in vivo microscopy techniques, has been increasingly recognized as a major contributor to vascular homeostasis. Sepsis-associated degradation of the endothelial glycocalyx mediates the onset of the alveolar microvascular dysfunction characteristic of sepsis-induced lung injury (such as the Acute Respiratory Distress Syndrome, ARDS). Emerging evidence indicates that processes of glycocalyx reconstitution are necessary for endothelial repair and, as such, are promising therapeutic targets to accelerate lung injury recovery. This review discusses what has been learned about the homeostatic and pathophysiologic role of the pulmonary endothelial glycocalyx during lung health and injury, with the goal to identify promising new areas for future mechanistic investigation.

Outcome of First-Line Systemic Treatment for Unresectable Conventional, Dedifferentiated, Mesenchymal, and Clear Cell Chondrosarcoma

BACKGROUND

Chondrosarcoma is a heterogeneous group of primary bone sarcoma with an excellent overall survival after local therapy. However, the small percentage of patients who have no surgical treatment options have a very poor prognosis. We retrospectively collected data from these patients in four sarcoma centers and compared the progression-free survival (PFS) for the different treatment regimens used for the four chondrosarcoma subtypes.

MATERIALS AND METHODS

Patients diagnosed with unresectable chondrosarcoma in all four major sarcoma centers were included, and data on first-line systemic therapy were retrospectively collected for analysis.

RESULTS

A total of 112 patients were enrolled in this retrospective analysis: 50 conventional, 25 mesenchymal, 34 dedifferentiated, and 3 clear cell chondrosarcoma patients. In conventional chondrosarcoma patients, the longest mean PFS (6.7 months) was found in the group treated with antihormonal therapy. Patients diagnosed with mesenchymal chondrosarcoma were all treated with multidrug chemotherapy, and the mean PFS was 6.7 months. Doxorubicin monotherapy seems to have an unexplained better PFS than doxorubicin-based combination therapy in patients with dedifferentiated chondrosarcoma (5.5 vs. 2.8 months, respectively; p = .275).

CONCLUSION

Prospective studies need to be conducted based on preclinical work to develop a uniform regimen to treat advanced chondrosarcoma patients according to the diagnosed subtype and improve survival.

IMPLICATIONS FOR PRACTICE

Currently, there are no uniform treatment lines for advanced chondrosarcoma patients, which results in a very diverse group of treatment regimens being used. In this study, the data of 112 patients was collected. It was concluded that some treatment regimens seem to have a better progression-free survival compared with others, and that these results also differ between the chondrosarcoma subtypes. Prospective studies need to be conducted based on preclinical work to develop a uniform regimen to treat advanced chondrosarcoma patients according to the diagnosed histological subtype to improve their survival.

Chondrosarcoma: A Rare Misfortune in Aging Human Cartilage? The Role of Stem and Progenitor Cells in Proliferation, Malignant Degeneration and Therapeutic Resistance

Unlike other malignant bone tumors including osteosarcomas and Ewing sarcomas with a peak incidence in adolescents and young adults, conventional and dedifferentiated chondrosarcomas mainly affect people in the 4th to 7th decade of life. To date, the cell type of chondrosarcoma origin is not clearly defined. However, it seems that mesenchymal stem and progenitor cells (MSPC) in the bone marrow facing a pro-proliferative as well as predominantly chondrogenic differentiation milieu, as is implicated in early stage osteoarthritis (OA) at that age, are the source of chondrosarcoma genesis. But how can MSPC become malignant? Indeed, only one person in 1,000,000 will develop a chondrosarcoma, whereas the incidence of OA is a thousandfold higher. This means a rare coincidence of factors allowing escape from senescence and apoptosis together with induction of angiogenesis and migration is needed to generate a chondrosarcoma. At early stages, chondrosarcomas are still assumed to be an intermediate type of tumor which rarely metastasizes. Unfortunately, advanced stages show a pronounced resistance both against chemo- and radiation-therapy and frequently metastasize. In this review, we elucidate signaling pathways involved in the genesis and therapeutic resistance of chondrosarcomas with a focus on MSPC compared to signaling in articular cartilage (AC).

FOXM1 in sarcoma: role in cell cycle, pluripotency genes and stem cell pathways

FOXM1 is a pro-proliferative transcription factor that promotes cell cycle progression at the G1-S, and G2-M transitions. It is activated by phosphorylation usually mediated by successive cyclin – cyclin dependent kinase complexes, and is highly expressed in sarcoma. p53 down regulates FOXM1 and FOXM1 inhibition is also partly dependent on Rb and p21. Abnormalities of p53 or Rb are frequent in sporadic sarcomas with bone or soft tissue sarcoma, accounting for 36% of index cancers in the high penetrance TP53 germline disorder, Li-Fraumeni syndrome.

FOXM1 stimulates transcription of pluripotency related genes including SOX2, KLF4, OCT4, and NANOG many of which are important in sarcoma, a disorder of mesenchymal stem cell/ partially committed progenitor cells. In a selected specific, SOX2 is uniformly expressed in synovial sarcoma. Embryonic pathways preferentially used in stem cell such as Hippo, Hedgehog, and Wnt dominate in FOXM1 stoichiometry to alter rates of FOXM1 production or degradation. In undifferentiated pleomorphic sarcoma, liposarcoma, and fibrosarcoma, dysregulation of the Hippo pathway increases expression of the effector co-transcriptional activator Yes-Associated Protein (YAP). A complex involving YAP and the transcription factor TEAD elevates FOXM1 in these sarcoma subtypes. In another scenario 80% of desmoid tumors have nuclear localization of β-catenin, the Wnt pathway effector molecule. Thiazole antibiotics inhibit FOXM1 and because they have an auto-regulator loop FOXM1 expression is also inhibited. Current systemic treatment of sarcoma is of limited efficacy and inhibiting FOXM1 represents a potential new strategy.

Molecular oncogenesis of chondrosarcoma: impact for targeted treatment

PURPOSE OF REVIEW

The prognosis of patients with unresectable or metastatic chondrosarcoma of the bone is poor. Chondrosarcomas are in general resistant to chemotherapy and radiotherapy. This review discusses recent developments in the characterization of molecular pathways involved in the oncogenesis of chondrosarcoma that should be explored to improve prognosis of patients with advanced chondrosarcoma.

RECENT FINDINGS

The different oncogenic pathways for chondrosarcoma have become better defined. These include alterations in pathways such as isocitrate dehydrogenase mutation, hedgehog signalling, the retinoblastoma protein and p53 pathways, apoptosis and survival mechanisms, and several tyrosine kinases. These specific alterations can be employed for use in clinical interventions in advanced chondrosarcoma.

SUMMARY

As many different genetic alterations in chondrosarcoma have been identified, it is of the utmost importance to classify druggable targets that may improve the prognosis of chondrosarcoma patients. In recent years an increased number of trials evaluating targeted therapies are being conducted. As chondrosarcoma is an orphan disease consequently all studies are performed with small numbers of patients. The results of clinical studies so far have been largely disappointing. Therapeutic intervention studies of these new targets emerging from preclinical studies are of highest importance to improve prognosis of chondrosarcoma patients with advanced disease.

The heparanase/heparan sulfate proteoglycan axis: A potential new therapeutic target in sarcomas

Heparanase, the only known mammalian endoglycosidase degrading heparan sulfate (HS) chains of HS proteoglycans (HSPG), is a highly versatile protein affecting multiple events in tumor cells and their microenvironment. In several malignancies, deregulation of the heparanase/HSPG system has been implicated in tumor progression, hence representing a valuable therapeutic target. Currently, multiple agents interfering with the heparanase/HSPG axis are under clinical investigation. Sarcomas are characterized by a high biomolecular complexity and multiple levels of interconnection with microenvironment sustaining their growth and progression. The clinical management of advanced diseases remains a challenge. In several sarcoma subtypes, high levels of heparanase expression have been correlated with poor prognosis associated factors. On the other hand, expression of cell surface-associated HSPGs (i.e. glypicans and syndecans) has been found altered in specific sarcoma subtypes. Recent studies provided the preclinical proof-of-principle of the role of the heparanase/HSPG axis as therapeutic target in various sarcoma subtypes. Although currently there are no clinical trials evaluating agents targeting heparanase and/or HSPGs in sarcomas, we here provide arguments for this strategy as potentially able to implement the therapeutic options for sarcoma patients.

[Shuttling from the extracellular matrix to the nucleus]

Several enzymes secreted in the extracellular space, such as matrix metalloproteinases and lysyl oxidase, are internalized and translocated to the nucleus, where they may act as proteases and transcription factors to regulate gene expression and enhance apoptosis. Membrane proteoglycan syndecans, glycosaminoglycans and an anti-angiogenic matricryptin of collagen XVIII have also been identified in the nucleus. The nuclear entry of most extracellular proteins is likely mediated by nuclear localizing sequences. The molecular mechanisms of nuclear import, the physiopathological contexts, which induce it, and the biological roles played in vivo by extracellular proteins and proteoglycans are still underexplored.

Aberrant activation of Wnt/β-catenin signaling drives proliferation of bone sarcoma cells

Bone sarcomas such as osteosarcoma and chondrosarcoma are frequently refractory to conventional chemotherapy and radiotherapy that exhibit poor prognosis. The Wnt signaling are evolutionarily conserved and implicated in cell proliferation and sarcomagenesis. However, the potential role of the Wnt signaling in bone sarcomas is still unclear. Here we demonstrate aberrant activation of Wnt/β-catenin signaling in bone sarcoma cells, involving an autocrine Wnt signaling loop with upregulation of specific Wnt ligands and receptors. Activation of Wnt/β-catenin signaling with Wnt3a or GSK-3β inhibitor drives the proliferation of bone sarcoma cells, whereas downregulation of activated Wnt signaling with dnTCF4 or siLEF1 suppresses bone sarcoma proliferation and induces cell cycle arrest. Taken together, our findings establish the evidence that aberrant activation of Wnt/β-catenin pathway involving an autocrine Wnt singaling drives the proliferation of bone sarcoma cells, and identify the autocrine activation of the Wnt/β-catenin signaling as a potential novel therapeutic target for bone sarcomas.

Inhibition of mutant IDH1 decreases D-2-HG levels without affecting tumorigenic properties of chondrosarcoma cell lines

Mutations in isocitrate dehydrogenase 1 (IDH1) and IDH2 are found in a subset of benign and malignant cartilage tumors, gliomas and leukaemias. The mutant enzyme causes the production of D-2-hydroxyglutarate (D-2-HG), affecting CpG island and histone methylation. While mutations in IDH1/2 are early events in benign cartilage tumors, we evaluated whether these mutations play a role in malignant chondrosarcomas. Compared to IDH1/2 wildtype cell lines, chondrosarcoma cell lines harboring an endogenous IDH1 (n=3) or IDH2 mutation (n=2) showed up to a 100-fold increase in intracellular and extracellular D-2-HG levels. Specific inhibition of mutant IDH1 using AGI-5198 decreased levels of D-2-HG in a dose dependent manner. After 72 hours of treatment one out of three mutant IDH1 cell lines showed a moderate decrease in viability , while D-2-HG levels decreased >90%. Likewise, prolonged treatment (up to 20 passages) did not affect proliferation and migration. Furthermore, global gene expression, CpG island methylation as well as histone H3K4, -9, and -27 trimethylation levels remained unchanged. Thus, while IDH1/2 mutations cause enchondroma, malignant progression towards central chondrosarcoma renders chondrosarcoma growth independent of these mutations. Thus, monotherapy based on inhibition of mutant IDH1 appears insufficient for treatment of inoperable or metastasized chondrosarcoma patients.

In malignant cartilagenous tumors, immunohistochemical expression of procollagen PC1CP peptide is higher and that of PC2CP lower than in benign cartilaginous lesions

Few studies on oncogenesis of chondrosarcoma (CS) are available in the literature. Our previously published experimental evidence suggests that while the C-propeptide of procollagen Iα1 (PC1CP), a component of cartilage, favors tumor progression, the C-propeptide of procollagen IIα1 (PC2CP) exerts antitumor properties. In this study, we analyzed expression of PC1CP and PC2CP by immunohistochemistry in a series of enchondromas and CS. Our retrospective series consisted of 88 cases, including 43 CSs, 34 enchondromas and 11 nontumor samples. Immunohistochemical staining for PC1CP and PC2CP was evaluated in the cytoplasm and in the extracellular matrix (ECM). Diffuse staining for PC1CP in ECM was significantly more frequent in tumor than in nontumor samples (32 % vs. 0 %; p = 0.03), and in CSs than in enchondromas (44 vs. 18 %; p = 0.02). ECM semiquantitative score was higher in tumors than in nontumor samples (p < 0.005) and higher in CSs than in enchondromas (p = 0.05). Staining for PC2CP in ECM was more frequently found in enchondromas than in CSs (59 vs. 33 %; p = 0.02). ECM semiquantitative score was higher in enchondromas than in CSs (p = 0.02). Diffuse staining for PC1CP in combination with absence of staining for PC2CP had 94 % specificity for CS but with a sensitivity of only 35 %. Expression of neither PC1CP nor PC2CP correlated with recurrence-free survival or occurrence of metastases. In conclusion, we show that the expression of PC1CP is higher and that of PC2CP lower in malignant cartilaginous tumors. These results support an oncogenic role of PC1CP and anti-oncogenic property of PC2CP in cartilaginous tumors.

Periosteal chondrosarcoma: a histopathological and molecular analysis of a rare chondrosarcoma subtype

AIMS

Periosteal chondrosarcoma is a rare, malignant cartilage-forming neoplasm originating from the periosteal surface of bone. We collected 38 cases from the archives of the Netherlands Committee on Bone Tumours, with the aim of studying histological features and evaluating the involvement of isocitrate dehydrogenase 1 (IDH1), EXT, Wnt/β-catenin, the pRB pathway (CDK4 and p16), and the TP53 pathway (p53 and MDM2).

METHODS AND RESULTS

Histology showed a moderately cellular matrix with mucoid-myxoid changes and, in 42% of cases, formation of a neocortex. Occasional intramedullary extension (26%) and subsequent host bone entrapment (40%) were seen. Histological grading revealed grade 1 (53%) and grade 2 (45%). The EXT1 protein was normally expressed, and mutations in IDH1 were observed in only 15% of cases. pRb signalling was deregulated by loss of p16 expression in 50% of cases, and Wnt signalling was lost in 89%. No alterations were found in CDK4, p53, or MDM2.

CONCLUSIONS

We report the first large histological and molecular study on periosteal chondrosarcoma showing that histopathological examination and molecular aberrations do not predict prognosis. Although the mutation frequency of IDH1 was low, we confirm the supposed relationship with central chondrosarcoma. Moreover, we identify loss of canonical Wnt signalling and deregulation of pRb signalling as possible events contributing to its histogenesis.

Elevated levels of Dickkopf-1 are associated with β-catenin accumulation and poor prognosis in patients with chondrosarcoma

BACKGROUND

Dickkopf-1 (DKK1) is an antagonist of Wnt/β-catenin signaling implicated in tumorigenesis. However, the biological role of DKK1 and β-catenin involved in chondrosarcoma has not been sufficiently investigated. This study was designed to investigate the expression profiles of DKK1 and β-catenin, and to clarify their clinical values in chondrosarcoma.

METHODS

The mRNA and protein levels of DKK1 and β-catenin in fresh chondrosarcoma and the corresponding non-tumor tissues were analyzed by Real-time PCR and Western blot, respectively. The protein expression patterns of DKK1 and β-catenin were investigated by immunohistochemistry. The associations among DKK1 level, β-catenin accumulation, clinicopathological factors and the overall survival were separately evaluated.

RESULTS

Both DKK1 and β-catenin levels were remarkably elevated in chondrosarcoma compared with the corresponding non-tumor tissues. High DKK1 level and positive β-catenin accumulation in chondrosarcoma specimens were 58.7% and 53.9%, respectively. Elevated DKK1 level significantly correlated with positive β-catenin accumulation, and they were remarkably associated with histological grade and Musculoskeletal Tumor Society stage. Furthermore, DKK1 level and β-catenin accumulation had significant impacts on the prognosis of chondrosarcoma patients. Multivariate analysis revealed that DKK1 level was an independent prognostic factor for overall survival.

CONCLUSIONS

Elevated DKK1 levels associated with β-catenin accumulation play a crucial role in chondrosarcoma. DKK1 can serve as a novel predictor of poor prognosis in patients with chondrosarcoma.

Nuclear translocation of heparan sulfate proteoglycans and their functional significance

BACKGROUND

Heparan sulfate proteoglycans (HSPGs) are important constituents of the cell membrane and they act as co-receptors for cellular signaling. Syndecan-1, glypican and perlecan also translocate to the nucleus in a regulated manner. Similar nuclear transport of growth factors and heparanase indicate a possible co-regulation and functional significance.

SCOPE OF REVIEW

In this review we dissect the structural requirement for the nuclear translocation of HSPGs and their functional implications.s

MAJOR CONCLUSIONS

The functions of the nuclear HSPGs are still incompletely understood. Evidence point to possible functions in hampering cell proliferation, inhibition of DNA topoisomerase I activity and inhibition of gene transcription.

GENERAL SIGNIFICANCE

HSPGs influence the behavior of malignant tumors in many different ways. Modulating their functions may offer powerful tools to control fundamental biological processes and provide the basis for subsequent targeted therapies in cancer. This article is part of a Special Issue entitled Matrix-mediated cell behaviour and properties.

Genetic alterations in chondrosarcomas - keys to targeted therapies?

BACKGROUND

Chondrosarcomas are malignant tumors of chondrocytes and represent the second most common type of primary bone tumors. Within the context of normal chondrogenesis, this review summarizes results from recent research outlining the key molecular changes that occur during the development of this sarcoma type.

RESULTS

Current data support the notion that a two-hit scenario, common to many tumors, also underlies chondrosarcoma formation. First, early-stage mutations alter the normal proliferation and differentiation of chondrocytes, thereby predisposing them to malignant transformation. These early-stage mutations, found in both benign cartilaginous lesions and chondrosarcomas, include alterations affecting the IHH/PTHrP and IDH1/IDH2 pathways. As they are not observed in malignant cells, mutations in the EXT1 and EXT2 genes are considered early-stage events providing an environment that alters IHH/PTHrP signaling, thereby inducing mutations in adjacent cells. Due to normal cell cycle control that remains active, a low rate of malignant transformation is seen in benign cartilaginous lesions with early-stage mutations. In contrast, late-stage mutations, seen in most malignant chondrosarcomas, appear to induce malignant transformation as they are not found in benign cartilaginous lesions. These late-stage mutations primarily involve cell cycle pathway regulators including p53 and pRB, two genes that are also known to be implicated in numerous other human tumor types.

CONCLUSIONS

Now the key genetic alterations involved in both early and late stages of chondrosarcoma development have been identified, focus should be shifted to the identification of druggable molecular targets for the design of novel chondrosarcoma-specific therapies.

Heparan sulfate in the nucleus and its control of cellular functions

Heparan sulfate proteoglycans (HSPG) are present on the cell surface, within the extracellular matrix, and as soluble molecules in tissues and blood. HSPGs are known to regulate a wide range of cellular functions predominantly by serving as co-receptors for growth factors, chemokines, and other regulatory proteins that control inflammation, wound healing and tumorigenesis. Several studies have demonstrated the presence of heparan sulfate (HS) or HSPGs in the cell nucleus, but little attention has been focused on their role there. However, evidence is mounting that nuclear HS and HSPGs have important regulatory functions that impact the cell cycle, proliferation, transcription and transport of cargo to the nucleus. The discovery of proteoglycans in the nucleus extends the list of "non-traditional nuclear proteins" that includes, for example, cytoskeletal proteins such as actin and tubulin, and growth factors and their receptors. In this review we discuss the discovery and fascinating roles of HS and HSPGs in the nucleus and propose a number of key questions that remain to be addressed.

Screening for potential targets for therapy in mesenchymal, clear cell, and dedifferentiated chondrosarcoma reveals Bcl-2 family members and TGFβ as potential targets

The mesenchymal, clear cell, and dedifferentiated chondrosarcoma subtypes are extremely rare, together constituting 10% to 15% of all chondrosarcomas. Their poor prognosis and lack of efficacious treatment emphasizes the need to elucidate the pathways playing a pivotal role in these tumors. We constructed tissue microarrays containing 42 dedifferentiated, 23 clear cell, and 23 mesenchymal chondrosarcomas and performed immunohistochemistry to study the expression of growth plate-signaling molecules and molecules shown to be involved in conventional chondrosarcoma. We observed high expression of SOX-9 and FGFR-3, as well as aberrant cellular localization of heparan sulfate proteoglycans, in all subtypes. TGFβ signaling through p-SMAD2 and PAI-1 was highly active in all chondrosarcoma subtypes, which suggests that TGFβ inhibitors as a possible therapeutic strategy in rare chondrosarcoma subtypes. As in conventional chondrosarcoma, antiapoptotic proteins (Bcl-2, and/or Bcl-xl) were highly expressed in all subtypes. Inhibition with the BH-3 mimetic ABT-737 rendered dedifferentiated chondrosarcoma cell lines sensitive to doxorubicin or cisplatin. Our data indicate that antiapoptotic proteins may play an important role in chemoresistance, suggesting a promising role for targeting Bcl-2 family members in chondrosarcoma treatment, irrespective of the subtype.

Loss of pRB and p107 disrupts cartilage development and promotes enchondroma formation

The pocket proteins pRB, p107 and p130 have established roles in regulating the cell cycle through the control of E2F activity. The pocket proteins regulate differentiation of a number of tissues in both cell cycle-dependent and -independent manners. Prior studies showed that mutation of p107 and p130 in the mouse leads to defects in cartilage development during endochondral ossification, the process by which long bones form. Despite evidence of a role for pRB in osteoblast differentiation, it is unknown whether it functions during cartilage development. Here, we show that mutation of Rb in the early mesenchyme of p107-mutant mice results in severe cartilage defects in the growth plates of long bones. This is attributable to inappropriate chondrocyte proliferation that persists after birth and leads to the formation of enchondromas in the growth plates as early as 8 weeks of age. Genetic crosses show that development of these tumorigenic lesions is E2f3 dependent. These results reveal an overlapping role for pRB and p107 in cartilage development, endochondral ossification and enchondroma formation that reflects their coordination of cell-cycle exit at appropriate developmental stages.

BMP and TGFbeta pathways in human central chondrosarcoma: enhanced endoglin and Smad 1 signaling in high grade tumors

Background

As major regulators of normal chondrogenesis, the bone morphogenic protein (BMP) and transforming growth factor β (TGFB) signaling pathways may be involved in the development and progression of central chondrosarcoma. In order to uncover their possible implication, the aim of this study was to perform a systematic quantitative study of the expression of BMPs, TGFBs and their receptors and to assess activity of the corresponding pathways in central chondrosarcoma.

Methods

Gene expression analysis was performed by quantitative RT-PCR in 26 central chondrosarcoma and 6 healthy articular cartilage samples. Expression of endoglin and nuclear localization of phosphorylated Smad1/5/8 and Smad2 was assessed by immunohistochemical analysis.

Results

The expression of TGFB3 and of the activin receptor-like kinase ALK2 was found to be significantly higher in grade III compared to grade I chondrosarcoma. Nuclear phosphorylated Smad1/5/8 and Smad2 were found in all tumors analyzed and the activity of both signaling pathways was confirmed by functional reporter assays in 2 chondrosarcoma cell lines. Immunohistochemical analysis furthermore revealed that phosphorylated Smad1/5/8 and endoglin expression were significantly higher in high-grade compared to low-grade chondrosarcoma and correlated to each other.

Conclusions

The BMP and TGFβ signaling pathways were found to be active in central chondrosarcoma cells. The correlation of Smad1/5/8 activity to endoglin expression suggests that, as described in other cell types, endoglin could enhance Smad1/5/8 signaling in high-grade chondrosarcoma cells. Endoglin expression coupled to Smad1/5/8 activation could thus represent a functionally important signaling axis for the progression of chondrosarcoma and a regulator of the undifferentiated phenotype of high-grade tumor cells.

Molecular pathology and its diagnostic use in bone tumors

Bone tumors are considered by most pathologists difficult to diagnose as they are rare, have overlapping morphology, need radiological correlation, and the usefulness of immunohistochemistry is limited, making conventional morphology the cornerstone of the diagnosis. Over the past decade, more and more has become known of the molecular background of bone tumors. Three groups of bone tumors are recognized, namely, tumors with specific translocations combined with a relatively simple karyotype involving chromosomal translocations (Ewing sarcoma, aneurysmal bone cyst), tumors with specific gene mutations or amplifications (chondrosarcoma, fibrous dysplasia, chordoma), and sarcomas with genetic instability and as a consequence complex karyotypes (osteosarcoma). Technical advancements will rapidly reveal new alterations in the more rare sarcoma subtypes for which the molecular background has remained enigmatic. Opening the archives and using new technologies, as well as refinement of existing technologies for decalcified paraffin-embedded tissue, may bring to light more specific genetic aberrations in bone tumors that can be applied in molecular diagnostics in the near future.

Cartilage tumour progression is characterized by an increased expression of heparan sulphate 6O-sulphation-modifying enzymes

Chondrosarcomas are malignant cartilage-forming tumours that can arise centrally (in the medulla) or peripherally (at the surface) of the bone. They are classified into three histological grades which correspond to the clinical severity. Previous studies by our group have shown altered signal transduction of the fibroblast growth factor and Wnt signalling pathways during peripheral chondrosarcoma progression. Heparan sulphate (HS) is a glycosaminoglycan that facilitates receptor binding of multiple growth factors, in which the sulphation of 6O position plays a pivotal role. 6O-Sulphation occurs through three HS 6O-sulphotransferases (HS6ST1-3) and is fine-tuned by two endosulphatases (SULF1-2) that remove 6O-sulphate groups. We have investigated whether the expression of HS6STs and SULFs changes during chondrosarcoma progression and have determined 6O-sulphation levels in two chondrosarcoma cell lines. Immunohistochemistry on tissue microarrays of chondrosarcomas showed that HS6ST3 and SULF1 were highly expressed in most chondrosarcomas, whereas SULF2 expression was absent in most cases. HS6ST1 and HS6ST2 expression are significantly increased during chondrosarcoma progression, which suggest that 6O-sulphation is increased during progression. This was confirmed in one grade III chondrosarcoma cell line, which showed a dramatically increased 6O-sulphation compared to an articular chondrocyte cell line by HPLC; another cell line showed an increased expression of one 6O-sulphated HS disaccharide. In conclusion, our results show increased HS6ST1 and HS6ST2 expression during chondrosarcoma progression and increased HS 6O-sulphation in vitro. As 6O-sulphation plays an important role in signal transduction, altered HS6ST expression might be associated with changes in signal transduction pathways in chondrosarcoma progression.

Spinal chondrosarcoma: a review

Chondrosarcoma is the third most common primary malignant bone tumor. Yet the spine represents the primary location in only 2% to 12% of these tumors. Almost all patients present with pain and a palpable mass. About 50% of patients present with neurologic symptoms. Chemotherapy and radiotherapy are generally unsuccessful while surgical resection is the treatment of choice. Early diagnosis and careful surgical staging are important to achieve adequate management. This paper provides an overview of the histopathological classification, clinical presentation, and diagnostic procedures regarding spinal chondrosarcoma. We highlight specific treatment modalities and discuss which is truly the most suitable approach for these tumors. Abstracts and original articles in English investigating these tumors were searched and analyzed with the use of the PubMed and Scopus databases with "chondrosarcoma and spine" as keywords.

No haploinsufficiency but loss of heterozygosity for EXT in multiple osteochondromas

Multiple osteochondromas (MO) is an autosomal dominant disorder caused by germline mutations in EXT1 and/or EXT2. In contrast, solitary osteochondroma (SO) is nonhereditary. Products of the EXT gene are involved in heparan sulfate (HS) biosynthesis. In this study, we investigated whether osteochondromas arise via either loss of heterozygosity (2 hits) or haploinsufficiency. An in vitro three-dimensional chondrogenic pellet model was used to compare heterozygous bone marrow-derived mesenchymal stem cells (MSCs EXT(wt/-)) of MO patients with normal MSCs and the corresponding tumor specimens (presumed EXT(-/-)). We demonstrated a second hit in EXT in five of eight osteochondromas. HS chain length and structure, in vitro chondrogenesis, and EXT expression levels were identical in both EXT(wt/-) and normal MSCs. Immunohistochemistry for HS, HS proteoglycans, and HS-dependent signaling pathways (eg, TGF-β/BMP, Wnt, and PTHLH) also showed no differences. The cartilaginous cap of osteochondroma contained a mixture of HS-positive and HS-negative cells. Because a heterozygous EXT mutation does not affect chondrogenesis, EXT, HS, or downstream signaling pathways in MSCs, our results refute the haploinsufficiency theory. We found a second hit in 63% of analyzed osteochondromas, supporting the hypothesis that osteochondromas arise via loss of heterozygosity. The detection of the second hit may depend on the ratio of HS-positive (normal) versus HS-negative (mutated) cells in the cartilaginous cap of the osteochondroma.

Cartilage tumours and bone development: molecular pathology and possible therapeutic targets

As a group, cartilage tumours are the most common primary bone lesions. They range from benign lesions, such as enchondromas and osteochondromas, to malignant chondrosarcoma. The benign lesions result from the deregulation of the hedgehog signalling pathway, which is involved in normal bone development. These lesions can be the precursors of malignant chondrosarcomas, which are notoriously resistant to conventional chemotherapy and radiotherapy. Cytogenetic studies and mouse models are beginning to identify genes and signalling pathways that have roles in tumour progression, such as hedgehog, p53, insulin-like growth factor, cyclin-dependent kinase 4, hypoxia-inducible factor, matrix metalloproteinases, SRC and AKT, suggesting potential new therapeutic approaches.

Enchondromatosis: insights on the different subtypes

Enchondromatosis is a rare, heterogeneous skeletal disorder in which patients have multiple enchondromas. Enchondromas are benign hyaline cartilage forming tumors in the medulla of metaphyseal bone. The disorder manifests itself early in childhood without any significant gender bias. Enchondromatosis encompasses several different subtypes of which Ollier disease and Maffucci syndrome are most common, while the other subtypes (metachondromatosis, genochondromatosis, spondyloenchondrodysplasia, dysspondyloenchondromatosis and cheirospondyloenchondromatosis) are extremely rare. Most subtypes are non-hereditary, while some are autosomal dominant or recessive. The gene(s) causing the different enchondromatosis syndromes are largely unknown. They should be distinguished and adequately diagnosed, not only to guide therapeutic decisions and genetic counseling, but also with respect to research into their etiology. For a longtime enchondromas have been considered a developmental disorder caused by the failure of normal endochondral bone formation. With the identification of genetic abnormalities in enchondromas however, they were being thought of as neoplasms. Active hedgehog signaling is reported to be important for enchondroma development and PTH1R mutations have been identified in approximately 10% of Ollier patients. One can therefore speculate that the gene(s) causing the different enchondromatosis subtypes are involved in hedgehog/PTH1R growth plate signaling. Adequate distinction within future studies will shed light on whether these subtypes are different ends of a spectrum caused by a single gene, or that they represent truely different diseases. We therefore review the available clinical information for all enchondromatosis subtypes and discuss the little molecular data available hinting towards their cause.

Chemical Tumor Biology of Heparan Sulfate Proteoglycans

Heparan sulfate proteoglycans (HSPGs) play vital roles in every step of tumor progression allowing cancer cells to proliferate, escape from immune response, invade neighboring tissues, and metastasize to distal sites away from the primary site. Several cancers including breast, lung, brain, pancreatic, skin, and colorectal cancers show aberrant modulation of several key HS biosynthetic enzymes such as 3-O Sulfotransferase and 6-O Sulfotransferase, and also catabolic enzymes such as HSulf-1, HSulf-2 and heparanase. The resulting tumor specific HS fine structures assist cancer cells to breakdown ECM to spread, misregulate signaling pathways to facilitate their proliferation, promote angiogenesis to receive nutrients, and protect themselves against natural killer cells. This review focuses on the changes in the expression of HS biosynthetic and catabolic enzymes in several cancers, the resulting changes in HS fine structures, and the effects of these tumor specific HS signatures on promoting invasion, proliferation, and metastasis. It is possible to retard tumor progression by modulating the deregulated biosynthetic and catabolic pathways of HS chains through novel chemical biology approaches.

Syndecan-1 and FGF-2, but not FGF receptor-1, share a common transport route and co-localize with heparanase in the nuclei of mesenchymal tumor cells

Syndecan-1 forms complexes with growth factors and their cognate receptors in the cell membrane. We have previously reported a tubulin-mediated translocation of syndecan-1 to the nucleus. The transport route and functional significance of nuclear syndecan-1 is still incompletely understood. Here we investigate the sub-cellular distribution of syndecan-1, FGF-2, FGFR-1 and heparanase in malignant mesenchymal tumor cells, and explore the possibility of their coordinated translocation to the nucleus. To elucidate a structural requirement for this nuclear transport, we have transfected cells with a syndecan-1/EGFP construct or with a short truncated version containing only the tubulin binding RMKKK sequence. The sub-cellular distribution of the EGFP fusion proteins was monitored by fluorescence microscopy. Our data indicate that syndecan-1, FGF-2 and heparanase co-localize in the nucleus, whereas FGFR-1 is enriched mainly in the perinuclear area. Overexpression of syndecan-1 results in increased nuclear accumulation of FGF-2, demonstrating the functional importance of syndecan-1 for this nuclear transport. Interestingly, exogenously added FGF-2 does not follow the route taken by endogenous FGF-2. Furthermore, we prove that the RMKKK sequence of syndecan-1 is necessary and sufficient for nuclear translocation, acting as a nuclear localization signal, and the Arginine residue is vital for this localization. We conclude that syndecan-1 and FGF-2, but not FGFR-1 share a common transport route and co-localize with heparanase in the nucleus, and this transport is mediated by the RMKKK motif in syndecan-1. Our study opens a new perspective in the proteoglycan field and provides more evidence of nuclear interactions of syndecan-1.

Molecular pathology of sarcomas: concepts and clinical implications

The molecular genetic changes that have been described in sarcomas over the past era have aided our understanding of their pathogenesis. The majority of sarcomas carry nonspecific genetic changes within a background of a complex karyotype. These constitute the challenges in sarcoma research for unraveling a putative multistep genetic model, such as for chondrosarcoma, and finding targets for therapeutic strategies. Approximately 15-20% of mesenchymal tumors carry a specific translocation within a relatively simple karyotype. The resulting fusion products act either as transcription factors upregulating genes responsible for tumor growth, as for instance in Ewing sarcoma, or translocate a highly active promoter in front of an oncogene driving tumor formation, as for instance in aneurysmal bone cyst. In addition, a small subset of mesenchymal tumors have specific somatic mutations driving oncogenesis. The specific genetic changes unraveled so far had great impact on the classification of bone and soft tissue tumors. In addition, these changes can assist the pathologist in the differential diagnosis of some of these entities, especially within the groups of small blue round cell tumors and spindle cell tumors, if performed in specialized centers. While a putative association between certain fusion products and outcome is still under debate, the role of predicting response of targeted therapy has been well established for KIT and PDGFRA mutations in gastrointestinal stromal tumors.

Kinome profiling of chondrosarcoma reveals SRC-pathway activity and dasatinib as option for treatment

Chondrosarcomas are notorious for their resistance to conventional chemotherapy and radiotherapy, indicating there are no curative treatment possibilities for patients with inoperable or metastatic disease. We therefore explored the existence of molecular targets for systemic treatment of chondrosarcoma using kinome profiling. Peptide array was performed for four chondrosarcoma cell lines and nine primary chondrosarcoma cultures with GIST882, MSCs, and colorectal cancer cell lines as controls. Activity of kinases was verified using immunoblot, and active Src- and platelet-derived growth factor receptor (PDGFR) signaling were further explored using imatinib and dasatinib on chondrosarcoma in vitro. The AKT1/GSK3B pathway was clearly active in chondrosarcoma. In addition, the PDGFR pathway and the Src kinase family were active. PDGFR and Src kinases can be inhibited by imatinib and dasatinib, respectively. Although imatinib did not show any effect on chondrosarcoma cell cultures, dasatinib showed a decrease in cell viability at nanomolar concentrations in seven of nine chondrosarcoma cultures. However, inhibition of phosphorylated Src (Y419) was found both in responsive and nonresponsive cells. In conclusion, using kinome profiling, we found the Src pathway to be active in chondrosarcoma. Moreover, we showed in vitro that the inhibitor of the Src pathway, dasatinib, may provide a potential therapeutic benefit for chondrosarcoma patients who are not eligible for surgery.