Serglycin proteoglycan expression and synthesis in embryonic stem cells

The Glycosaminoglycan Side Chains and Modular Core Proteins of Heparan Sulphate Proteoglycans and the Varied Ways They Provide Tissue Protection by Regulating Physiological Processes and Cellular Behaviour

This review examines the roles of HS-proteoglycans (HS-PGs) in general, and, in particular, perlecan and syndecan as representative examples and their interactive ligands, which regulate physiological processes and cellular behavior in health and disease. HS-PGs are essential for the functional properties of tissues both in development and in the extracellular matrix (ECM) remodeling that occurs in response to trauma or disease. HS-PGs interact with a biodiverse range of chemokines, chemokine receptors, protease inhibitors, and growth factors in immune regulation, inflammation, ECM stabilization, and tissue protection. Some cell regulatory proteoglycan receptors are dually modified hybrid HS/CS proteoglycans (betaglycan, CD47). Neurexins provide synaptic stabilization, plasticity, and specificity of interaction, promoting neurotransduction, neurogenesis, and differentiation. Ternary complexes of glypican-1 and Robbo-Slit neuroregulatory proteins direct axonogenesis and neural network formation. Specific neurexin-neuroligin complexes stabilize synaptic interactions and neural activity. Disruption in these interactions leads to neurological deficits in disorders of functional cognitive decline. Interactions with HS-PGs also promote or inhibit tumor development. Thus, HS-PGs have complex and diverse regulatory roles in the physiological processes that regulate cellular behavior and the functional properties of normal and pathological tissues. Specialized HS-PGs, such as the neurexins, pikachurin, and Eyes-shut, provide synaptic stabilization and specificity of neural transduction and also stabilize the axenome primary cilium of phototoreceptors and ribbon synapse interactions with bipolar neurons of retinal neural networks, which are essential in ocular vision. Pikachurin and Eyes-Shut interactions with an α-dystroglycan stabilize the photoreceptor synapse. Novel regulatory roles for HS-PGs controlling cell behavior and tissue function are expected to continue to be uncovered in this fascinating class of proteoglycan.

Regulation of stem cell fate by HSPGs: implication in hair follicle cycling

Heparan sulfate proteoglycans (HSPGs) are part of proteoglycan family. They are composed of heparan sulfate (HS)-type glycosaminoglycan (GAG) chains covalently linked to a core protein. By interacting with growth factors and/or receptors, they regulate numerous pathways including Wnt, hedgehog (Hh), bone morphogenic protein (BMP) and fibroblast growth factor (FGF) pathways. They act as inhibitor or activator of these pathways to modulate embryonic and adult stem cell fate during organ morphogenesis, regeneration and homeostasis. This review summarizes the knowledge on HSPG structure and classification and explores several signaling pathways regulated by HSPGs in stem cell fate. A specific focus on hair follicle stem cell fate and the possibility to target HSPGs in order to tackle hair loss are discussed in more dermatological and cosmeceutical perspectives.

Cancer-associated fibroblasts secrete hypoxia-induced serglycin to promote head and neck squamous cell carcinoma tumor cell growth in vitro and in vivo by activating the Wnt/β-catenin pathway

BACKGROUND

The tumor microenvironment (TME) is known to play a prominent role in the pathology of head and neck squamous cell carcinoma (HNSCC). Cancer-associated fibroblasts (CAFs) have been reported to regulate tumor progression, and serglycin (SRGN), one of the paracrine cytokines of CAFs, has been reported to play an important role in various signaling pathways. Hypoxia is a distinct feature of the HNSCC TME. Here, we investigated the mechanism underlying CAF-secreted SRGN leading to HNSCC progression under hypoxia.

METHODS

Immunohistochemical staining was used to detect SRGN expression in clinical HNSCC samples, after which its relation with patient survival was assessed. CAFs were isolated and SRGN expression and secretion by CAFs under normoxia and hypoxia were confirmed using qRT-PCR and ELISA assays, respectively. HNSCC sphere-forming abilities, stemness-related gene expression, and chemoresistance were assessed with or without SRGN treatment. A Wnt/β-catenin pathway inhibitor (PNU-75,654) was used to block its activation, after which nuclear translocation of β-catenin in the presence of SRGN with or without PNU-75,654 was evaluated. shRNAs were used to stably knock down SRGN expression in CAFs. HNSCC tumor cells with or without (SRGN silenced) CAFs were inoculated submucosally in nude mice after which tumor weights and sizes were determined to assess the effects of CAFs and SRGN on tumor growth.

RESULTS

We found that SRGN was expressed in both HNSCC tumor and stroma cells, and that high SRGN expression in the stroma cells, but not in the tumor cells, was significantly related to a poor patient survival. After the extraction of CAFs and normal fibroblasts (NFs) from paired tumor samples and adjacent normal tissues, respectively, we found that the expression of CAF-specific genes, including fibroblast activation protein (FAP) and alpha-smooth muscle actin (α-SMA), was clearly upregulated compared to the expression in NFs. The hypoxia marker HIF-1α was found to be expressed in tumor stroma cells. Hypoxyprobe immunofluorescence staining confirmed stromal hypoxia in an orthotopic tongue cancer mouse model. Using qRT-PCR and ELISA we found that a hypoxic TME upregulated SRGN expression and secretion by CAFs. SRGN markedly enhanced the sphere-forming ability, stemness-related gene expression and chemoresistance of HNSCC tumor cells. SRGN activated the Wnt/β-catenin pathway and promoted β-catenin nuclear translocation. An in vivo study confirmed that CAFs can accelerate HNSCC tumor growth, and that this effect can be counteracted by SRGN silencing.

CONCLUSIONS

Our data indicate that a hypoxic tumor stroma can lead to upregulation of SRGN expression. SRGN secreted by CAFs can promote β-catenin nuclear translocation to activate downstream signaling pathways, leading to enhanced HNSCC cell stemness, chemoresistance and accelerated tumor growth.

The relationship between plasma serglycin levels and the diagnosis of diabetic retinopathy

Background

Diabetic retinopathy (DR), a microvascular complication which is closely related to diabetes, remains the leading cause of vision loss around the world among older adults. Serglycin (SRGN) was known as a hematopoietic cell granule proteoglycan, exerting its function in the formation of mast cell secretory granules and mediates the storage of various compounds in secretory vesicles. The present study illustrates the potential clinical value and experimental mechanisms of SRGN in the DR.

Methods

Firstly, the mRNA expression and protein expression of SRGN in plasma samples from NPDR, PDR patients, type 2 diabetes mellitus (T2Dm) cases, and healthy controls were measured by qPCR and Western blotting assays, respectively. Then, the potentials of SRGN functioning as a diagnostic indicator in DR were verified by the receiver operating characteristic (ROC) analysis. We established in vitro DR model of human retinal endothelial cells through high‐glucose treatment. The expression of SRGN and its mechanisms of regulating cellular processes were illustrated subsequently.

Results

Our data revealed that SRGN was dramatically upregulated in NPDR and PDR cases compared with healthy controls and T2DM patients; meanwhile, the expression of SRGN was further increased in the PDR group with regard to the NPDR group. Furthermore, the ROC analysis demonstrated that SRGN could distinguish the DR cases from type 2 diabetes mellitus (T2DM) patients and healthy controls with the area under the curve (AUC) of 0.7680 (95% CI = 0.6780 ~ 0.8576, sensitivity = 47.27%, specificity = 100%, cutoff value = 1.4727) and 0.8753 (95% CI = 0.8261 ~ 0.9244, sensitivity = 69.23%, specificity = 100%, cutoff value = 1.6923), respectively. In vitro high‐glucose treatment showed that the SRGN expressions were dramatically increased. The loss of SRGN could partially counteract the inhibition of HREC proliferation caused by high‐glucose stimulation. Meanwhile, SRGN knockdown could reverse the promotion of HREC apoptosis induced by high glucose as well.

Conclusions

Consequently, our study implied that SRGN might serve as a promising biomarker with high specificity and sensitivity in the DR diagnosis and progression.

Heparan Sulfate Proteoglycans Biosynthesis and Post Synthesis Mechanisms Combine Few Enzymes and Few Core Proteins to Generate Extensive Structural and Functional Diversity

Glycosylation is a common and widespread post-translational modification that affects a large majority of proteins. Of these, a small minority, about 20, are specifically modified by the addition of heparan sulfate, a linear polysaccharide from the glycosaminoglycan family. The resulting molecules, heparan sulfate proteoglycans, nevertheless play a fundamental role in most biological functions by interacting with a myriad of proteins. This large functional repertoire stems from the ubiquitous presence of these molecules within the tissue and a tremendous structural variety of the heparan sulfate chains, generated through both biosynthesis and post synthesis mechanisms. The present review focusses on how proteoglycans are “gagosylated” and acquire structural complexity through the concerted action of Golgi-localized biosynthesis enzymes and extracellular modifying enzymes. It examines, in particular, the possibility that these enzymes form complexes of different modes of organization, leading to the synthesis of various oligosaccharide sequences.

Serglycin activates pro-tumorigenic signaling and controls glioblastoma cell stemness, differentiation and invasive potential

Despite the functional role of serglycin as an intracellular proteoglycan, a variety of malignant cells depends on its expression and constitutive secretion to advance their aggressive behavior. Serglycin arose to be a biomarker for glioblastoma, which is the deadliest and most treatment-resistant form of brain tumor, but its role in this disease is not fully elucidated. In our study we suppressed the endogenous levels of serglycin in LN-18 glioblastoma cells to decipher its involvement in their malignant phenotype. Serglycin suppressed LN-18 (LN-18shSRGN) glioblastoma cells underwent astrocytic differentiation characterized by induced expression of GFAP, SPARCL-1 and SNAIL, with simultaneous loss of their stemness capacity. In particular, LN-18shSRGN cells presented decreased expression of glioma stem cell-related genes and ALDH1 activity, accompanied by reduced colony formation ability. Moreover, the suppression of serglycin in LN-18shSRGN cells retarded the proliferative and migratory rate, the invasive potential in vitro and the tumor burden in vivo. The lack of serglycin in LN-18shSRGN cells was followed by G2 arrest, with subsequent reduction of the expression of cell-cycle regulators. LN-18shSRGN cells also exhibited impaired expression and activity of proteolytic enzymes such as MMPs, TIMPs and uPA, both in vitro and in vivo. Moreover, suppression of serglycin in LN-18shSRGN cells eliminated the activation of pro-tumorigenic signal transduction. Of note, LN-18shSRGN cells displayed lower expression and secretion levels of IL-6, IL-8 and CXCR-2. Concomitant, serglycin suppressed LN-18shSRGN cells demonstrated repressed phosphorylation of ERK1/2, p38, SRC and STAT-3, which together with PI3K/AKT and IL-8/CXCR-2 signaling control LN-18 glioblastoma cell aggressiveness. Collectively, the absence of serglycin favors an astrocytic fate switch and a less aggressive phenotype, characterized by loss of pluripotency, block of the cell cycle, reduced ability for ECM proteolysis and pro-tumorigenic signaling attenuation.

SRGN crosstalks with YAP to maintain chemoresistance and stemness in breast cancer cells by modulating HDAC2 expression

Background: Chemoresistance is a significant obstacle to the effective treatment of breast cancer (BC), resulting in more aggressive behavior and worse clinical outcome. The molecular mechanisms underlying breast cancer chemoresistance remain unclear. Our microarray analysis had identified the overexpression of a small molecular glycoprotein serglycin (SRGN) in multidrug-resistant BC cells. Here, we aimed to investigate the role of SRGN in chemoresistance of breast cancer and elucidate the underlying mechanisms. Methods: SRNG overexpression was identified using microarray analysis and its clinical relevance was analyzed. To investigate the role of SRGN, we performed various in vitro and in vivo studies, as well as characterization of serum and tissue samples from BC patients. Chemosensitivity measurement, gene expression interference, immunofluorescence staining, mammosphere assay, flow cytometry analysis, luciferase reporter assay, ChIP-qPCR, coimmunoprecipitation, and immunohistochemistry were performed to explore the potential functions and mechanisms of SRGN. Results: We confirmed overexpression of SRGN in chemoresistant BC cells and in serum and tissue samples from BC patients with poor response to chemotherapy. SRGN specifically predicted poor prognosis in BC patients receiving chemotherapy. Mechanistically, SRGN promoted chemoresistance both in vitro and in vivo by cross-talking with the transcriptional coactivator YES-associated protein (YAP) to maintain stemness in BC cells. Ectopic YAP expression restored the effects of SRGN knockdown. Inversely, YAP knockdown rescued the effects of SRGN overexpression. The secreted SRGN triggered ITGA5/FAK/CREB signaling to enhance YAP transcription. Reciprocally, YAP promoted SRGN transcription in a TEAD1-dependent manner to form a feed-forward circuit. Moreover, the YAP/RUNX1 complex promoted HDAC2 transcription to induce chemoresistance and stemness in BC cells. Importantly, the SRGN levels were positively correlated with the YAP and HDAC2 levels in chemoresistant BC tissues. YAP and HDAC2 acted downstream of SRNG and correlated with poor outcomes of BC patients receiving chemotherapy. Conclusions: Our findings clarify the roles and mechanisms of SRGN in mediating chemoresistance in breast cancer and suggest its use a potential biomarker for chemotherapeutic response. We believe that novel therapeutic strategies for breast cancer can be designed by targeting the signaling mediated by the crosstalk between SRGN and YAP.

The Tumor Microenvironment: Focus on Extracellular Matrix

The extracellular matrix (ECM) regulates the development and maintains tissue homeostasis. The ECM is composed of a complex network of molecules presenting distinct biochemical properties to regulate cell growth, survival, motility, and differentiation. Among their components, proteoglycans (PGs) are considered one of the main components of ECM. Its composition, biomechanics, and anisotropy are exquisitely tuned to reflect the physiological state of the tissue. The loss of ECM's homeostasis is seen as one of the hallmarks of cancer and, typically, defines transitional events in tumor progression and metastasis. In this chapter, we discuss the types of proteoglycans and their roles in cancer. It has been observed that the amount of some ECM components is increased, while others are decreased, depending on the type of tumor. However, both conditions corroborate with tumor progression and malignancy. Therefore, ECM components have an increasingly important role in carcinogenesis and this leads us to believe that their understanding may be a key in the discovery of new anti-tumor therapies. In this book, the main ECM components will be discussed in more detail in each chapter.

Increased levels of serum serglycin and agrin is associated with adverse perinatal outcome in early onset preeclampsia

Goal: Our aim was to determine whether alterations in serum serglycin and agrin levels in early-onset preeclampsia (EOPE) are useful in predicting adverse perinatal outcomes such as fetal growth restriction (FGR), intrauterine fetal demise (IUFD), preterm delivery and/or neonatal unit admission. Materials and Methods: A prospective case-controlled study enrolled 88 pregnant patients (44 EOPE and 44 controls). Maternal serum serglycin and agrin levels were determined before the 34th gestational week by enzyme-linked immunosorbent assay. Results: Compared with controls, women with EOPE had significantly higher serglycin and agrin levels (p = .018; p = .048). Multivariable logistic regression analysis revealed serglycin was independently associated with FGR in EOPE (OR 0.866; 95% CI 0.779-0.953). Agrin was independently associated with IUFD in EOPE (OR 0.757, 95% CI 0.636-0.879). Conclusions: The current study suggests that increased maternal serum serglycin is associated with FGR, and increased maternal serum agrin is associated with IUFD in EOPE.

Extracellular serglycin upregulates the CD44 receptor in an autocrine manner to maintain self-renewal in nasopharyngeal carcinoma cells by reciprocally activating the MAPK/β-catenin axis

Serglycin is a proteoglycan that was first found to be secreted by hematopoietic cells. As an extracellular matrix (ECM) component, serglycin promotes nasopharyngeal carcinoma (NPC) metastasis and serves as an independent, unfavorable NPC prognostic indicator. The detailed mechanism underlying the roles of serglycin in cancer progression remains to be clarified. Here, we report that serglycin knockdown in NPC cells inhibited cell sphere formation and tumor seeding abilities. Serglycin downregulation enhanced high-metastasis NPC cell sensitivity to chemotherapy. It has been reported that serglycin is a novel ligand for the stem cell marker CD44. Interestingly, we found a positive correlation between serglycin expression and CD44 in nasopharyngeal tissues and NPC cell lines. Further study revealed that CD44 was an ERK-dependent downstream effector of serglycin signaling, and serglycin activated the MAPK/β-catenin axis to induce CD44 receptor expression in a positive feedback loop. Taken together, our novel findings suggest that ECM serglycin upregulated CD44 receptor expression to maintain NPC stemness by interacting with CD44 and activating the MAPK/β-catenin pathway, resulting in NPC cell chemoresistance. These findings suggest that the intervention of serglycin/CD44 axis and downstream signaling pathway is a rational strategy for targeting NPC cancer stem cell therapy.

Targeting Serglycin Prevents Metastasis in Murine Mammary Carcinoma

In hematopoietic cells, serglycin proteoglycans mainly contribute to proper storage and secretion of inflammatory mediators via their negatively charged glycosaminoglycans. Serglycin proteoglycans are also expressed in cancer cells where increased expression has been linked to poor prognosis. However, the serglycin-dependent mediators promoting cancer progression remain to be determined. In the present study we report that genetic ablation of serglycin proteoglycan completely blocks lung metastasis in the MMTV-PyMT-driven mouse breast cancer model, while serglycin-deficiency did not affect primary tumour growth or number of mammary tumours. Although E-cadherin expression was higher in the serglycin-deficient primary tumour tissue, indicating reduced invasiveness, serglycin-deficient tumour cells were still detected in the circulation. These data suggest that serglycin proteoglycans play a role in extravasation as well as colonization and growth of metastatic cells. A microarray expression analysis and functional annotation of differentially expressed genes identified several biological pathways where serglycin may be important. Our results suggest that serglycin and serglycin-dependent mediators are potential drug targets to prevent metastatic disease/dissemination of cancer.

Serglycin: at the crossroad of inflammation and malignancy

Serglycin has been initially characterized as an intracellular proteoglycan expressed by hematopoietic cells. All inflammatory cells highly synthesize serglycin and store it in granules, where it interacts with numerous inflammatory mediators, such as proteases, chemokines, cytokines, and growth factors. Serglycin is implicated in their storage into the granules and their protection since they are secreted as complexes and delivered to their targets after secretion. During the last decade, numerous studies have demonstrated that serglycin is also synthesized by various non-hematopoietic cell types. It has been shown that serglycin is highly expressed by tumor cells and promotes their aggressive phenotype and confers resistance against drugs and complement system attack. Apart from its direct beneficial role to tumor cells, serglycin may promote the inflammatory process in the tumor cell microenvironment thus enhancing tumor development. In the present review, we discuss the role of serglycin in inflammation and tumor progression.

Changes in glycosaminoglycan structure on differentiation of human embryonic stem cells towards mesoderm and endoderm lineages

BACKGROUND

Proteoglycans are found on the cell surface and in the extracellular matrix, and serve as prime sites for interaction with signaling molecules. Proteoglycans help regulate pathways that control stem cell fate, and therefore represent an excellent tool to manipulate these pathways. Despite their importance, there is a dearth of data linking glycosaminoglycan structure within proteoglycans with stem cell differentiation.

METHODS

Human embryonic stem cell line WA09 (H9) was differentiated into early mesoderm and endoderm lineages, and the glycosaminoglycanomic changes accompanying these transitions were studied using transcript analysis, immunoblotting, immunofluorescence and disaccharide analysis.

RESULTS

Pluripotent H9 cell lumican had no glycosaminoglycan chains whereas in splanchnic mesoderm lumican was glycosaminoglycanated. H9 cells have primarily non-sulfated heparan sulfate chains. On differentiation towards splanchnic mesoderm and hepatic lineages N-sulfo group content increases. Differences in transcript expression of NDST1, HS6ST2 and HS6ST3, three heparan sulfate biosynthetic enzymes, within splanchnic mesoderm cells compared to H9 cells correlate to changes in glycosaminoglycan structure.

CONCLUSIONS

Differentiation of embryonic stem cells markedly changes the proteoglycanome.

GENERAL SIGNIFICANCE

The glycosaminoglycan biosynthetic pathway is complex and highly regulated, and therefore, understanding the details of this pathway should enable better control with the aim of directing stem cell differentiation.

Serglycin (SRGN) overexpression predicts poor prognosis in hepatocellular carcinoma patients

Hepatocellular carcinoma (HCC) is known for its high rate of recurrence and poor prognosis, which makes it necessary to identify new predictive markers for HCC and to explore the underlying mechanism(s). Emerging evidence suggests that the proteoglycan serglycin (SRGN) might play a crucial role in tumor metastasis. However, currently, the function of SRGN in HCC remains unknown. Here, we evaluated the expression pattern of SRGN in 127 HCC specimens and their adjacent, non-tumorous tissues using immunohistochemical assays. We observed that SRGN was significantly upregulated in HCC tissues. Elevated expression levels of SRGN were detectable in 72/127 (56.7%) of the HCC specimens and in 4/127 (3.1%) of adjacent non-tumorous tissues (p < 0.001). Further correlation analysis demonstrated that the increased expression of SRGN was positively associated with HBV infection, GGT level, vascular invasion, advanced BCLC stage and early recurrence (p < 0.05). Increased SRGN expression correlated with unfavorable prognosis in HCC patients. In multivariate analyses, SRGN expression levels were found to represent an independent predictor for overall survival (p = 0.002) and time to recurrence (p = 0.010) of HCC patients. Furthermore, the elevated expression of SRGN in the HCC tissues was accompanied by elevated levels of vimentin and the absence of E-cadherin. Similarly, the reduced expression of SRGN was accompanied by elevated levels of E-cadherin and the absence of vimentin. E-cadherin and vimentin are well-accepted biomarkers of the epithelial-mesenchymal transition (EMT), and the expression of SRGN might correlate with EMT. Our results demonstrate that the elevated expression of SRGN represents a crucial event in HCC patients that is indicative of poor clinical outcome.

Proteoglycans in stem cells

The remarkable promise of pluripotent and multipotent stem cells (SCs) imparts tremendous optimism for advancement of regenerative medicine, developmental biology, and drug discovery. Perhaps the greatest challenge is to finely direct, control, and command their differentiation. As those processes are managed on many levels, including genomic, transcriptomic, and epigenomic, examination of all of these components will yield powerful tools for manipulation of SCs. Carbohydrates surround all cells, including SCs as a glycocalyx. Of particular interest is the class of carbohydrates known as proteoglycans (PGs), which are a diverse group of glycoconjugates consisting of core protein with one or more glycosaminoglycan (GAG) chains attached. They are primarily located in the extracellular matrix as well as at cell surfaces, where they are bound or anchored to the membrane through their core proteins. GAG chains are linear, anionic, and highly heterogeneous carbohydrates consisting of repeating disaccharides. PGs facilitate interaction of cells with the extracellular environment by interacting with chemokines, growth factors, and other signaling molecules. Core proteins are involved in many signaling pathways, both individually, as well as through attached proteins via GAG-mediated interactions. These essential and accessible functions make PGs an excellent target for manipulating SCs and guiding their fate. Studying the role of PGs in cell development will yield valuable insight into the mechanism of SC differentiation and suggest approaches toward directing those pathways. Such studies may also help identify valuable markers for distinguishing between various cell populations during differentiation.

Molecular shuttle between extracellular and cytoplasmic space allows for monitoring of GAG biosynthesis in human articular chondrocytes

BACKGROUND

Cell surface proteoglycans play vital functional roles in various biological processes such as cell proliferation, differentiation, adhesion, inflammation, immune response, sustentation of cartilage tissue and intensity of tissues. We show here that serglycin-like synthetic glycopeptides function efficiently as a molecular shuttle to hijack glycosaminoglycan (GAG) biosynthetic pathway within cells across the plasma membrane.

METHODS

Fluorescence (FITC)-labeled tetrapeptide (H-Ser(1)-Gly(2)-Ser(3)-Gly(4)-OH) carrying Galβ(1➝4)Xylβ1➝ defined as proteoglycan initiator (PGI) monomer and its tandem repeating PGI polymer was employed for direct imaging of cellular uptake and intracellular traffic by confocal laser-scanning microscopy. Novel method for enrichment analysis of GAG-primed PGIs by combined use of anti-FITC antibody and LC/mass spectrometry was established.

RESULTS

PGI monomer was incorporated promptly into human articular chondrocytes and distributed in whole cytoplasm including ER/Golgi while PGI polymer localized specifically in nucleus. It was demonstrated that PGIs become good substrates for GAG biosynthesis within the cells and high molecular weight GAGs primed by PGIs is chondroitin sulfate involving N-acetyl-d-galactosamine residues substituted by 4-O-sulfate or 6-O-sulfate group as major components. PGIs activated chondrocytes proliferation and induced up-regulation of the expression level of type II collagen, suggesting that PGIs can function as new class cytokine-like molecules to stimulate cell growth.

CONCLUSION

Synthetic serglycin-type PGIs allow for live cell imaging during proteoglycan biosynthesis and structural characterization of GAG-primed PGIs by an antibody-based enrichment protocol.

GENERAL SIGNIFICANCE

Novel glycomics designated for investigating proteoglycan biosynthesis, namely real-time GAGomics using synthetic glycopeptides as PGIs, should facilitate greatly dynamic profiling of GAGs in the living cells. This article is part of a Special Issue entitled Glycoproteomics.

Transcriptional profiling identifies upregulated genes following induction of epithelial-mesenchymal transition in squamous carcinoma cells

During the progression of head and neck squamous cell carcinoma (HNSCC), the induction of an epithelial-mesenchymal transition (EMT) program may play a critical role in the dissemination of cells from the primary tumor to distant metastatic foci. The process of EMT involves the activation of several important genes and pathways to help maintain survival and growth and evolve into highly invasive and metastatic variants. In this study, expression microarray analysis identified a set of 145 upregulated genes in EMT-like HNSCC cells. Some of the strongly upregulated transcripts include genes that are reportedly involved in invasion and metastasis, such as DOCK10, LOX, ROBO1 and SRGN. Importantly, the Tbx3 gene, a member of the T-box transcription factor, was strongly upregulated in SCC cells displaying an EMT-like phenotype compared to cells with an epitheloid, non-EMT behavior. Tbx3 was also found to be strongly upregulated at the protein and gene expression level in an experimental model of snail-induced EMT cells. In addition, siRNA-induced Tbx3 depletion modestly suppressed cell invasion while enhancing Tbx3-mediated resistance to anoikis. Our findings provide evidence that Tbx3 overexpression promotes SCC cell survival displaying an EMT phenotype. This set of newly identified genes that are modulated during EMT-like conversion may be important diagnostic biomarkers during the process of HNSCC progression.

Serglycin is a theranostic target in nasopharyngeal carcinoma that promotes metastasis

Nasopharyngeal carcinoma (NPC) is known for its high-metastatic potential. Here we report the identification of the proteoglycan serglycin as a functionally significant regulator of metastasis in this setting. Comparative genomic expression profiling of NPC cell line clones with high- and low-metastatic potential revealed the serglycin gene (SRGN) as one of the most upregulated genes in highly metastatic cells. RNAi-mediated inhibition of serglycin expression blocked serglycin secretion and the invasive motility of highly metastatic cells, reducing metastatic capacity in vivo. Conversely, serglycin overexpression in poorly metastatic cells increased their motile behavior and metastatic capacity in vivo. Growth rate was not influenced by serglycin in either highly or poorly metastatic cells. Secreted but not bacterial recombinant serglycin promoted motile behavior, suggesting a critical role for glycosylation in serglycin activity. Serglycin inhibition was associated with reduced expression of vimentin but not other epithelial-mesenchymal transition proteins. In clinical specimens, serglycin expression was elevated significantly in liver metastases from NPC relative to primary NPC tumors. We evaluated the prognostic value of serglycin by immunohistochemical staining of tissue microarrays from 263 NPC patients followed by multivariate analyses. High serglycin expression in primary NPC was found to be an unfavorable independent indicator of distant metastasis-free and disease-free survival. Our findings establish that glycosylated serglycin regulates NPC metastasis via autocrine and paracrine routes, and that it serves as an independent prognostic indicator of metastasis-free survival and disease-free survival in NPC patients.

Serglycin proteoglycan deletion in mouse platelets: physiological effects and their implications for platelet contributions to thrombosis, inflammation, atherosclerosis, and metastasis

Serglycin is found in all nucleated hematopoietic cells and platelets, blood vessels, various reproductive and developmental tissues, and in chondrocytes. The serglycin knockout mouse has demonstrated that this proteoglycan is required for proper generation and function of secretory granules in several hematopoietic cells. The effects on platelets are profound, and include diminishing platelet aggregation responses and formation of platelet thrombi. This chapter will review cell-specific aspects of serglycin structure, its gene regulation, cell and tissue localization, and the effects of serglycin deletion on hematopoietic cell granule structure and function. The effects of serglycin knockout on platelets are described and discussed in detail. Rationales for further investigations into the contribution of serglycin to the known roles of platelets in thrombosis, inflammation, atherosclerosis, and tumor metastasis are presented.

Age-related enlargement of lymphoid tissue and altered leukocyte composition in serglycin-deficient mice

Serglycin (SG) is a proteoglycan that is located predominantly in the secretory granules of hematopoietic cells. Previous studies have established a crucial role for SG in promoting the storage of various secretory granule compounds that are of importance in the immune defense system. Here, we show that mice lacking SG spontaneously develop enlargement of multiple lymphoid organs, including the spleen, Peyer's patches (PP), and bronchus-associated lymphoid tissue. In the spleen, the lack of SG resulted in a significant decrease in the proportion of CD4(+) cells as well as an increase of the CD45RC(+) leukocyte population, indicating an expansion of naïve lymphocytes. In the PP, the lack of SG resulted in a general increase in cellularity, without significant alterations in the proportion of individual leukocyte populations. The enlargement of lymphoid tissues was not accompanied by increased serum levels of inflammatory cytokines. The number of mast cells in the peritoneum was not affected by the lack of SG, as judged by surface staining for CD117 (c-kit). However, the intensity of c-kit staining was reduced significantly in SG null animals. Moreover, the number of peritoneal macrophages, defined by morphological criteria and by CD11b staining, was decreased markedly in older, SG-deficient animals. Finally, experiments in which airway inflammation was induced by bacterial LPS revealed a more pronounced inflammatory response in old, SG-deficient as compared with wild-type mice. Taken together, our data show that SG deficiency causes multiple, age-related effects on the lymphoid system.

Serglycin proteoglycan deletion induces defects in platelet aggregation and thrombus formation in mice

Serglycin (SG), the hematopoietic cell secretory granule proteoglycan, is crucial for storage of specific secretory proteins in mast cells, neutrophils, and cytotoxic T lymphocytes. We addressed the role of SG in platelets using SG-/- mice. Wild-type (WT) but not SG-/- platelets contained chondroitin sulfate proteoglycans. Electron microscopy revealed normal alpha-granule structure in SG-/- platelets. However, SG-/- platelets and megakaryocytes contained unusual scroll-like membranous inclusions, and SG-/- megakaryocytes showed extensive emperipolesis of neutrophils. SG-/- platelets had reduced ability to aggregate in response to low concentrations of collagen or PAR4 thrombin receptor agonist AYPGKF, and reduced fibrinogen binding after AYPGKF, but aggregated normally to ADP. 3H-serotonin and ATP secretion were greatly reduced in SG-/- platelets. The alpha-granule proteins platelet factor 4, beta-thromboglobulin, and platelet-derived growth factor were profoundly reduced in SG-/- platelets. Exposure of P-selectin and alphaIIb after thrombin treatment was similar in WT and SG-/- platelets. SG-/- mice exhibited reduced carotid artery thrombus formation after exposure to FeCl3. This study demonstrates that SG is crucial for platelet function and thrombus formation. We propose that SG-/- platelet function deficiencies are related to inadequate packaging and secretion of selected alpha-granule proteins and reduced secretion of dense granule contents critical for platelet activation.

Glycomics of proteoglycan biosynthesis in murine embryonic stem cell differentiation

Glycosaminoglycans (GAGs) play a critical role in binding and activation of growth factors involved in cell signaling critical for developmental biology. The biosynthetic pathways for GAGs have been elucidated over the past decade and now analytical methodology makes it possible to determine GAG composition in as few as 10 million cells. A glycomics approach was used to examine GAG content, composition, and the level of transcripts encoding for GAG biosynthetic enzymes as murine embryonic stem cells (mESCs) differentiate to embryoid bodies (EBs) and to extraembryonic endodermal cells (ExE) to better understand the role of GAGs in stem cell differentiation. Hyaluronan synthesis was enhanced by 13- and 24-fold, most likely due to increased expression of hyaluronan synthase-2. Chondroitin sulfate (CS)/dermatan sulfate (DS) synthesis was enhanced by 4- and 6-fold, and heparan sulfate (HS) synthesis was enhanced by 5- and 8-fold following the transition from mESC to EB and ExE. Transcripts associated with the synthesis of the early precursors were largely unaltered, suggesting other factors account for enhanced GAG synthesis. The composition of both CS/DS and HS also changed upon differentiation. Interestingly, CS type E and highly sulfated HS both increase as mESCs differentiate to EBs and ExE. Differentiation was also accompanied by enhanced 2-sulfation in both CS/DS and HS families. Transcript levels for core proteins generally showed increases or remained constant upon mESC differentiation. Finally, transcripts encoding selected enzymes and isoforms, including GlcNAc-4,6-O-sulfotransferase, C5-epimerases, and 3-O-sulfotransferases involved in late GAG biosynthesis, were also enriched. These biosynthetic enzymes are particularly important in introducing GAG fine structure, essential for intercellular communication, cell adhesion, and outside-in signaling. Knowing the changes in GAG fine structure should improve our understanding the biological properties of differentiated stem cells.

Serglycin constitutively secreted by myeloma plasma cells is a potent inhibitor of bone mineralization in vitro

Although the biological significance of proteoglycans (PGs) has previously been highlighted in multiple myeloma (MM), little is known about serglycin, which is a hematopoietic cell granule PG. In this study, we describe the expression and highly constitutive secretion of serglycin in several MM cell lines. Serglycin messenger RNA was detected in six MM cell lines. PGs were purified from conditioned medium of four MM cell lines, and serglycin substituted with 4-sulfated chondroitin sulfate was identified as the predominant PG. Flow cytometry and confocal microscopy showed that serglycin was also present intracellularly and on the cell surface, and attachment to the cell surface was at least in part dependent on intact glycosaminoglycan side chains. Immunohistochemical staining of bone marrow biopsies showed the presence of serglycin both in benign and malignant plasma cells. Immunoblotting in bone marrow aspirates from a limited number of patients with newly diagnosed MM revealed highly increased levels of serglycin in 30% of the cases. Serglycin isolated from myeloma plasma cells was found to influence the bone mineralization process through inhibition of the crystal growth rate of hydroxyapatite. This rate reduction was attributed to adsorption and further blocking of the active growth sites on the crystal surface. The apparent order of the crystallization reaction was found to be n=2, suggesting a surface diffusion-controlled spiral growth mechanism. Our findings suggest that serglycin release is a constitutive process, which may be of fundamental biological importance in the study of MM.

Intracellular proteoglycans

Proteoglycans (PGs) are proteins with glycosaminoglycan chains, are ubiquitously expressed and have a wide range of functions. PGs in the extracellular matrix and on the cell surface have been the subject of extensive structural and functional studies. Less attention has so far been given to PGs located in intracellular compartments, although several reports suggest that these have biological functions in storage granules, the nucleus and other intracellular organelles. The purpose of this review is, therefore, to present some of these studies and to discuss possible functions linked to PGs located in different intracellular compartments. Reference will be made to publications relevant for the topics we present. It is beyond the scope of this review to cover all publications on PGs in intracellular locations.

Serglycin is essential for maturation of mast cell secretory granule

To address the biological function of the scarcely studied intracellular proteoglycans, we targeted the gene for serglycin (SG), the only known committed intracellular proteoglycan. SG-/- mice developed normally and were fertile, but their mast cells (MCs) were severely affected. In peritoneum there was a complete absence of normal granulated MCs. Furthermore, peritoneal cells and ear tissue from SG-/- animals were devoid of the various MC-specific proteases. However, mRNA for the proteases was present in SG+/+, SG+/-, and SG-/- tissues, indicating that SG is essential for the storage, but not expression, of the MC proteases. Experiments, in which the differentiation of bone marrow stem cells into mature MCs was followed, showed that secretory granule maturation was compromised in SG-/- cells. Moreover, SG+/+ and SG+/- cells, but not SG-/- cells, synthesized proteoglycans of high anionic charge density. Taken together, we demonstrate a key role for SG proteoglycan in MC function.