Functions of the conserved thrombospondin carboxy-terminal cassette in cell-extracellular matrix interactions and signaling

Characterization and function of Japanese flounder (Paralichthys olivaceus) slc2a6 in response to lymphocystis disease virus infection

Slc2a6 is a member of the slc2 family (solute carrier 2 family) and previous reports have indicated its involvement in the inflammatory response. Slc2a6 is regulated by the NF-ĸB signaling pathway. This study investigated the differential expression of slc2a6 in the early embryonic development of Japanese flounder, revealing that the early gastrula stage had the highest level of slc2a6 expression. Moreover, slc2a6 expression was increased in vitro after stimulation by lymphocystis disease virus (LCDV), and in vivo experiments also showed significantly elevated levels in the spleen and muscle tissues following LCDV stimulation. Subcellular localization revealed that Slc2a6 was expressed in both the nucleus and cytoplasm of cells. The pcDNA3.1-slc2a6 overexpression plasmid was successfully constructed; the si-slc2a6 interfering strand was screened and samples were collected. The expression of NF-ĸB signaling pathway-related genes il-1β, il-6, nf-ĸb, and tnf-α was evaluated in overexpressed, silenced, and LCDV-stimulated samples. The results showed that slc2a6 is involved in viral regulation in Japanese flounder by regulating innate immune responses.

An integrated bioinformatic investigation of focal adhesion-related genes in glioma followed by preliminary validation of COL1A2 in tumorigenesis

Focal adhesions (FAs) allow cells to contact the extracellular matrix, helping to maintain tension and enabling signal transmission in cell migration, differentiation, and apoptosis. In addition, FAs are associated with changes in the tumor microenvironment (TME) that lead to malignant progression and drug resistance in tumors. However, there are still few studies on the comprehensive analysis of focal adhesion-related genes (FARGs) in glioma. Expression data and clinical information of glioma samples were downloaded from public databases. Two distinct molecular subtypes were identified based on FARGs using an unsupervised consensus clustering algorithm. A scoring system consisting of nine FARGs was constructed using integrated LASSO regression and multivariate Cox regression. It not only has outstanding prognostic value but also can guide immunotherapy of glioma patients, which was verified in TCGA, CGGA, GSE16011, and IMvigor210 cohorts. The results of bioinformatics analysis, immunohistochemistry staining, and western blotting all revealed that the expression of COL1A2 was up-regulated in glioblastoma and related to poor prognosis outcomes in patients from public datasets. COL1A2 promotes the proliferation, migration, and invasion of glioblastoma cells. A positive correlation between COL1A2 and CD8 was determined in GBM specimens from eight patients. Moreover, the results of cell co-cultured assay showed that COL1A2 participated in the killing of GBM cells by Jurkat cells. Our study indicates that the FARGs have prominent application value in the identification of molecular subtypes and prediction of survival outcomes in glioma patients. Bioinformatics analysis and experimental verification provide a direction for further research on FARGs.

Cartilage extracellular matrix-derived matrikines in osteoarthritis

Osteoarthritis (OA) is among the most frequent diseases of the musculoskeletal system. Degradation of cartilage extracellular matrix (ECM) is a hallmark of OA. During the degradation process, intact/full-length proteins and proteolytic fragments are released which then might induce different downstream responses via diverse receptors, therefore leading to different biological consequences. Collagen type II and the proteoglycan aggrecan are the most abundant components of the cartilage ECM. However, over the last decades, a large number of minor components have been identified and for some of those, a role in the manifold processes associated with OA has already been demonstrated. To date, there is still no therapy able to halt or cure OA. A better understanding of the matrikine landscape occurring with or even preceding obvious degenerative changes in joint tissues is needed and might help to identify molecules that could serve as biomarkers, druggable targets, or even be blueprints for disease modifying drug OA drugs. For this narrative review, we screened PubMed for relevant literature in the English language and summarized the current knowledge regarding the function of selected ECM molecules and the derived matrikines in the context of cartilage and OA.

A newly defined basement membrane-related gene signature for the prognosis of clear-cell renal cell carcinoma

Background: Basement membranes (BMs) are associated with cell polarity, differentiation, migration, and survival. Previous studies have shown that BMs play a key role in the progression of cancer, and thus could serve as potential targets for inhibiting the development of cancer. However, the association between basement membrane-related genes (BMRGs) and clear cell renal cell carcinoma (ccRCC) remains unclear. To address that gap, we constructed a novel risk signature utilizing BMRGs to explore the relationship between ccRCC and BMs.

Methods: We gathered transcriptome and clinical data from The Cancer Genome Atlas (TCGA) and randomly separated the data into training and test sets to look for new potential biomarkers and create a predictive signature of BMRGs for ccRCC. We applied univariate, least absolute shrinkage and selection operator (LASSO) and multivariate Cox regression analyses to establish the model. The risk signature was further verified and evaluated through principal component analysis (PCA), the Kaplan-Meier technique, and time-dependent receiver operating characteristics (ROC). A nomogram was constructed to predict the overall survival (OS). The possible biological pathways were investigated through functional enrichment analysis. In this study, we also determined tumor mutation burden (TMB) and performed immunological analysis and immunotherapeutic drug analysis between the high- and low-risk groups.

Results: We identified 33 differentially expressed genes and constructed a risk model of eight BMRGs, including COL4A4, FREM1, CSPG4, COL4A5, ITGB6, ADAMTS14, MMP17, and THBS4. The PCA analysis showed that the signature could distinguish the high- and low-risk groups well. The K-M and ROC analysis demonstrated that the model could predict the prognosis well from the areas under the curves (AUCs), which was 0.731. Moreover, the nomogram showed good predictability. Univariate and multivariate Cox regression analysis validated that the model results supported the hypothesis that BMRGs were independent risk factors for ccRCC. Furthermore, immune cell infiltration, immunological checkpoints, TMB, and the half-inhibitory concentration varied considerably between high- and low-risk groups.

Conclusion: Employing eight BMRGs to construct a risk model as a prognostic indicator of ccRCC could provide us with a potential progression trajectory as well as predictions of therapeutic response.

Hevin-calcyon interaction promotes synaptic reorganization after brain injury

Hevin, also known as SPARC-like protein 1 (SPARCL1 or SC1), is a synaptogenic protein secreted by astrocytes and modulates the formation of glutamatergic synapses in the developing brain by interacting with synaptic adhesion proteins, such as neurexin and neuroligin. Here, we identified the neuron-specific vesicular protein calcyon as a novel interaction partner of hevin and demonstrated that this interaction played a pivotal role in synaptic reorganization after an injury in the mature brain. Astrocytic hevin was upregulated post-injury in a photothrombotic stroke model. Hevin was fragmented by MMP3 induced during the acute stage of brain injury, and this process was associated with severe gliosis. At the late stage, the functional hevin level was restored as MMP3 expression decreased. The C-terminus of hevin interacted with the N-terminus of calcyon. By using RNAi and binding competitor peptides in an ischemic brain injury model, we showed that this interaction was crucial in synaptic and functional recoveries in the sensory-motor cortex, based on histological and electrophysiological analyses. Regulated expression of hevin and calcyon and interaction between them were confirmed in a mouse model of traumatic brain injury and patients with chronic traumatic encephalopathy. Our study provides direct evidence for the causal relationship between the hevin-calcyon interaction and synaptic reorganization after brain injury. This neuron-glia interaction can be exploited to modulate synaptic reorganization under various neurological conditions.

Proteomic profile alterations in porcine conceptuses during early stages of development

The dynamic embryo development during the early stages of gestation requires precise molecular changes, including proteomic ones. We aimed to find unique proteins for porcine conceptuses specifically during the peri-implantation period, i.e. on days 15-16 of pregnancy. The proteomic profile of these conceptuses was compared with conceptuses at an earlier stage of the development, i.e. collected during maternal recognition of pregnancy on days 12-13 of pregnancy. The 2DE, gel image analysis, and MALDI TOF mass spectrometry were used 500 protein spots were annotated as common to conceptuses harvested during both studied periods. Proteomic profile of the conceptuses collected during the peri-implantation period contains 24 unique proteins. Identified unique for the peri-implantation period proteins are involved in adhesion processes, cadherin, and actin-binding, and actin filament organization, extracellular matrix organization, and cytoskeleton organization. Systemic analysis of identified proteins confirmed their involvement in cell adhesion and cytoskeletal organization as being two major affected functions. The unique proteins might be recognized as factors conditioning the proper peri-implantation embryo development and gaining competences for implantation. In further studies, BRCA1 might be considered as a candidate for a potential marker of embryonic competences for implantation in pigs.

Thrombospondin-1 as a Potential Therapeutic Target: Multiple Roles in Cancers

Thrombospondin-1, an extracellular matrix protein, is the first identified natural angiogenesis inhibitor. Thrombospondin-1 participates in a great number of physiological and pathological processes, including cell-cell and cell-matrix interactions via a number of cell receptors, including CD36 and CD47, which plays a vital role in mediating inflammation and performs a promoting effect in pulmonary arterial vasculopathy and diabetes. Thrombospondin-1 consists of six domains, which combine with different molecules and participate in various functions in cancers, serving as a critical member in diverse pathways in cancers. Thrombospondin-1 works as a cancer promotor in some pathways but as a cancer suppressor in others, which makes it highly possible that its erroneous functioning might lead to opposite effects. Therefore, subdividing the roles of thrombospondin-1 and distinguishing them in cancers are necessary. Complex structure and multiple roles take disadvantage of the research and application of thrombospondin-1. Compared with the whole thrombospondin-1 protein, each thrombospondin- 1 active peptide performs an uncomplicated structure and, nevertheless, a specific role. In other words, various thrombospondin-1 active peptides may function differently. For instance, thrombospondin-1 could both promote and inhibit glioblastoma, which is significantly inhibited by the three type I repeats, a thrombospondin-1 active peptide but promoted by the fragment 167-569, a thrombospondin-1 active peptide consisting of the procollagen homology domain and the three type I repeats. Further studies of the functions of thrombospondin-1 active peptides and applying them reasonably are necessary. In addition to mediating cancerogenesis, thrombospondin-1 is also affected by cancer development, as reflected by its expression in plasma and the cancer tissue. Therefore, thrombospondin-1 may be a potential biomarker for pre-clinical and clinical application. This review summarizes findings on the multiple roles of thrombospondin-1 in cancer processes, with a focus on its use as a potential therapeutic target.

Potential Role of PDGFRβ-Associated THBS4 in Colorectal Cancer Development

Colorectal cancer is a significant cause of death since it frequently metastasizes to several organs such as the lung or liver. Tumor development is affected by various factors, including a tumor microenvironment, which may be an essential factor that leads to tumor growth, proliferation, invasion, and metastasis. In the tumor microenvironment, abnormal changes in various growth factors, enzymes, and cytokines can wield a strong influence on cancer. Thrombospondin-4 (THBS4), which is an extracellular matrix protein, also plays essential roles in the tumor microenvironment and mediates angiogenesis by transforming growth factor-β (TGFβ) signaling. Platelet-derived growth factor receptor β (PDGFRβ), which is a receptor tyrosine kinase and is also a downstream signal of TGFβ, is associated with invasion and metastasis in colorectal cancer. We identified that PDGFRβ and THBS4 are overexpressed in tumor tissues of colorectal cancer patients, and that PDGF-D expression increased after TGFβ treatment in the colon cancer cell line DLD-1. TGFβ and PDGF-D increased cellular THBS4 protein levels and secretion but did not increase THBS4 mRNA levels. This response was further confirmed by the inositol 1,4,5-triphosphate receptor (IP3R) and stromal interaction molecule 1 (STIM1) blockade as well as the PDGFRβ blockade. We propose that the PDGFRβ signal leads to a modification of the incomplete form of THBS4 to its complete form through IP3R, STIM1, and Ca2+-signal proteins, which further induces THBS4 secretion. Additionally, we identified that DLD-1 cell-conditioned medium stimulated with PDGF-D promotes adhesion, migration, and proliferation of colon myofibroblast CCD-18co cells, and this effect was intensified in the presence of thrombin. These findings suggest that excessive PDGFRβ signaling due to increased TGFβ and PDGF-D in colorectal tumors leads to over-secretion of THBS4 and proliferative tumor development.

Direct, gabapentin-insensitive interaction of a soluble form of the calcium channel subunit α2δ-1 with thrombospondin-4

The α₂δ‐1 subunit of voltage-gated calcium channels binds to gabapentin and pregabalin, mediating the analgesic action of these drugs against neuropathic pain. Extracellular matrix proteins from the thrombospondin (TSP) family have been identified as ligands of α₂δ‐1 in the CNS. This interaction was found to be crucial for excitatory synaptogenesis and neuronal sensitisation which in turn can be inhibited by gabapentin, suggesting a potential role in the pathogenesis of neuropathic pain. Here, we provide information on the biochemical properties of the direct TSP/α₂δ-1 interaction using an ELISA-style ligand binding assay. Our data reveal that full-length pentameric TSP-4, but neither TSP-5/COMP of the pentamer-forming subgroup B nor TSP-2 of the trimer-forming subgroup A directly interact with a soluble variant of α₂δ-1 (α₂δ-1_S). Interestingly, this interaction is not inhibited by gabapentin on a molecular level and is not detectable on the surface of HEK293-EBNA cells over-expressing α₂δ‐1 protein. These results provide biochemical evidence that supports a specific role of TSP-4 among the TSPs in mediating the binding to neuronal α₂δ‐1 and suggest that gabapentin does not directly target TSP/α₂δ-1 interaction to alleviate neuropathic pain.

Molecular characterization and functional analysis of Japanese flounder (Paralichthys olivaceus) thbs2 in response to lymphocystis disease virus

In mammals, a matricellular protein, thrombospondin 2 (Thbs2) has been reported to play important roles in modulating cell-matrix interactions, vascular integrity and thrombosis formation. However, the role of gene, thbs2 has not yet been studied in teleost. In the present study, this novel fish gene from Japanese flounder was cloned and its function in resistant to lymphocystis disease virus was elucidated. The Japanese flounder thbs2 encoded a 1176-amino acid protein with 91% identity to medaka. Amino acid sequence indicated that Japanese flounder Thbs2 contained 10 typical conserved domains. The thbs2 was expressed in all stages of embryo development, and in hatched larva stage, its expression was significantly higher than that in other stages (P < 0.05). The relative expression level of thbs2 was significantly higher in the head kidney, liver, blood, gill, and heart of the lymphocystis disease virus resistant fish than in sensitive fish (P < 0.05); and in muscle, this difference was at highly significant (P < 0.01). Additionally, the distribution of Thbs2 in tissue was evaluated by immunohistochemical staining. Subcellular localization analysis showed that Thbs2 was distributed throughout the cytoplasm of the cells. Taken together, our results provide new basic data for thbs2 function, especially its role in anti-lymphocystis disease virus immune response.

N-linked mannose glycoconjugates on shrimp thrombospondin, pmTSP-II, and their involvement in the sperm acrosome reaction

Glycoconjugates in egg extracellular matrices are known to serve several functions in reproductive processes. Here, the presence of N-linked mannose (Man) glycoconjugates on shrimp thrombospondin ( pmTSP-II) and their physiological functions were investigated in the black tiger shrimp Penaeus monodon. A molecular analysis of pmTSP-II demonstrated anchorage sites for N-linked glycans in both the chitin-binding and TSP3 domains. The presence of Man residues was verified by concanavalin A lectin histochemistry on the purified fraction of pmTSP-II (250 kDa with protease inhibitor). The function of the Man glycoconjugates was evident by the Con A interference with the pmTSP-II-induced acrosome reaction (AR) as well as by the ability to recover the induction of the AR by the inclusion of Mans in the treatment mixture. In addition, the recombinant proteins of the three signature pmTSP-II domains expressed in E. coli (lacking glycosylation) and mannosidase-treated pmTSP-II showed a minimal ability to initiate the AR response. Together, these results provide evidence of the pivotal role that Man-linked pmTSP-II plays in modulating the shrimp sperm AR, a novel role for a TSP family protein in shrimp reproductive biology.

Contribution of Human Thrombospondin-1 to the Pathogenesis of Gram-Positive Bacteria

A successful colonization of different compartments of the human host requires multifactorial contacts between bacterial surface proteins and host factors. Extracellular matrix proteins and matricellular proteins such as thrombospondin-1 play a pivotal role as adhesive substrates to ensure a strong interaction with pathobionts like the Gram-positive Streptococcus pneumoniae and Staphylococcus aureus. The human glycoprotein thrombospondin-1 is a component of the extracellular matrix and is highly abundant in the bloodstream during bacteremia. Human platelets secrete thrombospondin-1, which is then acquired by invading pathogens to facilitate colonization and immune evasion. Gram-positive bacteria express a broad spectrum of surface-exposed proteins, some of which also recognize thrombospondin-1. This review highlights the importance of thrombospondin-1 as an adhesion substrate to facilitate colonization, and we summarize the variety of thrombospondin-1-binding proteins of S. pneumoniae and S. aureus.

Functional dissection of astrocyte-secreted proteins: Implications in brain health and diseases

Astrocytes, which are homeostatic cells of the central nervous system (CNS), display remarkable heterogeneity in their morphology and function. Besides their physical and metabolic support to neurons, astrocytes modulate the blood-brain barrier, regulate CNS synaptogenesis, guide axon pathfinding, maintain brain homeostasis, affect neuronal development and plasticity, and contribute to diverse neuropathologies via secreted proteins. The identification of astrocytic proteome and secretome profiles has provided new insights into the maintenance of neuronal health and survival, the pathogenesis of brain injury, and neurodegeneration. Recent advances in proteomics research have provided an excellent catalog of astrocyte-secreted proteins. This review categorizes astrocyte-secreted proteins and discusses evidence that astrocytes play a crucial role in neuronal activity and brain function. An in-depth understanding of astrocyte-secreted proteins and their pathways is pivotal for the development of novel strategies for restoring brain homeostasis, limiting brain injury/inflammation, counteracting neurodegeneration, and obtaining functional recovery.

Structure of thrombospondin type 3 repeats in bacterial outer membrane protein A reveals its intra-repeat disulfide bond-dependent calcium-binding capability

Eukaryotic thrombospondin type 3 repeat (TT3R) is an efficient calcium ion (Ca²⁺) binding motif only found in mammalian thrombospondin family. TT3R has also been found in prokaryotic cellulase Cel5G, which was thought to forfeit the Ca²⁺-binding capability due to the formation of intra-repeat disulfide bonds, instead of the inter-repeat ones possessed by eukaryotic TT3Rs. In this study, we have identified an enormous number of prokaryotic TT3R-containing proteins belonging to several different protein families, including outer membrane protein A (OmpA), an important structural protein connecting the outer membrane and the periplasmic peptidoglycan layer in gram-negative bacteria. Here, we report the crystal structure of the periplasmic region of OmpA from Capnocytophaga gingivalis, which contains a linker region comprising five consecutive TT3Rs. The structure of OmpA-TT3R exhibits a well-ordered architecture organized around two tightly-coordinated Ca²⁺ and confirms the presence of abnormal intra-repeat disulfide bonds. Further mutagenesis studies showed that the Ca²⁺-binding capability of OmpA-TT3R is indeed dependent on the proper formation of intra-repeat disulfide bonds, which help to fix a conserved glycine residue at its proper position for Ca²⁺ coordination. Additionally, despite lacking inter-repeat disulfide bonds, the interfaces between adjacent OmpA-TT3Rs are enhanced by both hydrophobic and conserved aromatic-proline interactions.

Cell Surface CD36 Protein in Monocyte/Macrophage Contributes to Phagocytosis during the Resolution Phase of Ischemic Stroke in Mice

Infiltrating monocyte-derived macrophages (M-M_Φ) influence stroke-induced brain injury. Although the inflammatory nature of M-M_Φ in acute stroke has been well documented, their role during the resolution phase of stroke is less clear. With emerging evidence for the involvement of scavenger receptors in innate immunity, this study addresses an M-M_Φ CD36 role in mediating phagocytosis during the recovery phase of stroke. Stroke increases CD36 and TSP-1/2 mRNA levels in the ipsilateral hemisphere at acute (3-day (d)) and recovery (7d) periods. Quantification of total, intracellular, and cell surface CD36 protein levels showed relatively unchanged expression at 3d post-ischemia. At 7d, there was a significant increase in cell surface CD36 (p < 0.05) with a concurrent reduction of intracellular CD36 (p < 0.05) in the ipsilateral hemisphere. Both cell surface and intracellular CD36 were found in whole brain lysates, whereas cell surface CD36 was predominantly detected in isolated brain mononuclear cells, blood monocytes, and peritoneal macrophages, suggesting that cell surface CD36 expressed in the post-ischemic brain originates from the periphery. The stroke-induced CD36 mRNA level correlated with increased expression of lysosomal acid lipase, an M2 macrophage marker. Functionally, higher CD36 expression in M-M_Φ is correlated with higher phagocytic indices in post-ischemic brain immune cells. Moreover, pharmacological inhibition of CD36 attenuated phagocytosis in peritoneal macrophages and brain M-M_Φ These findings demonstrate that cell surface CD36 on M-M_Φ mediates phagocytosis during the recovery phase in post-stroke brains and suggests that CD36 plays a reparative role during the resolution of inflammation in ischemic stroke.

Calcium-induced conformational changes of Thrombospondin-1 signature domain: implications for vascular disease

CONTEXT

Thrombospondin1 (TSP1) participates in numerous signaling pathways critical for vascular physiology and disease. The conserved signature domain of thrombospondin 1 (TSP1-Sig1) comprises three epidermal growth factor (EGF), 13 calcium-binding type 3 thrombospondin (T3) repeats, and one lectin-like module arranged in a stalk-wire-globe topology. TSP1 is known to be present in both calcium-replete (Holo-) and calcium-depleted (Apo-) state, each with distinct downstream signaling effects.

OBJECTIVE

To prepare a homology model of TSP1-Sig1 and investigate the effect of calcium on its dynamic structure and interactions.

METHODS

A homology model of Holo-TSP1-Sig1 was prepared with TSP2 as template in Swissmodel workspace. The Apo-form of the model was obtained by omitting the bound calcium ions from the homology model. Molecular dynamics (MD) simulation studies (100 ns) were performed on the Holo- and Apo- forms of TSP1 using Gromacs4.6.5.

RESULTS AND DISCUSSION

After simulation, Holo-TSP1-Sig1 showed significant reorientation at the interface of the EGF1-2 and EGF2-3 modules. The T3 wire is predicted to show the maximum mobility and deviation from the initial model. In Apo-TSP1-Sig1 model, the T3 repeats unfolded and formed coils with predicted increase in flexibility. Apo-TSP1-Sig1model also predicted the exposure of the binding sites for neutrophil elastase, integrin and fibroblast growth factor 2. We present a structural model and hypothesis for the role of TSP1-Sig1 interactions in the development of vascular disorders.

CONCLUSION

The simulated model of the fully calcium-loaded and calcium-depleted TSP1-Sig1 may enable the development of its interactions as a novel therapeutic target for the treatment of vascular diseases.

Reciprocal regulation of long noncoding RNAs THBS4‑003 and THBS4 control migration and invasion in prostate cancer cell lines

Increasing evidence implicates long noncoding RNAs (lncRNAs), a class of noncoding RNAs >200 nucleotides in length, in the development of cancer. However, the mechanism underlying the effects of lncRNAs in prostate cancer (PCa) remains to be elucidated. The present study aimed to investigate the role of lncRNA-THBS4-003 in the pathogensis of PCa. In the present study, a microarray containing 8,277 lncRNA probes and 32,207 mRNA probes were used to identify dysregulated mRNAs in three patients with PCa, and reverse transcription-quantitative polymerase chain reaction was used to determine the expression levels of thrombospondin 4 (THBS4) and lncRNA-THBS4-003 in 46 primary PCa and adjacent non-tumor tissue samples. The expression levels of THBS4 were determined in six samples of PCa and adjacent non-tumor tissues using Western blot analysis. The effects of forced THBS4 knockdown and lncRNA-THBS4-003 knockdown in the two PCa cell lines, DU145 and PC-3, were evaluated using cell migration and invasion assays, as well as using Western blot analysis. Of the 40,484 probes in the microarray, 354 were significantly upregulated (P<0.05; fold-change >2). The most significantly upregulated mRNA was THBS4. The expression levels of THBS4 and lncRNA-THBS4-003 in the 46 primary PCa samples was significantly higher, compared with that in the adjacent non-tumor tissue samples. Patients with Gleason scores >7 exhibited higher expression levels of lncRNA-THBS4-003, compared with patients with lower scores. Knockdown of THBS4 or lncRNA-THBS4-003 significantly reduced the migratory and invasive abilities of the PCa cells in vitro, and decreased the expression levels of p38 and matrix metal-loproteinase (MMP)-9. These findings suggested that the reciprocal regulation of lncRNA-THBS4-003 and THBS4 contributed to the pathogenesis of PCa. Therefore silencing lncRNA-THBS4-003 or THBS4 may inhibit PCa cell migration and invasion, and regulate the levels of MMP-9 through the mitogen-activated protein kinase signaling pathway.

A systems biology approach to detect key pathways and interaction networks in gastric cancer on the basis of microarray analysis

The aim of the present study was to explore key molecular pathways contributing to gastric cancer (GC) and to construct an interaction network between significant pathways and potential biomarkers. Publicly available gene expression profiles of GSE29272 for GC, and data for the corresponding normal tissue, were downloaded from Gene Expression Omnibus. Pre‑processing and differential analysis were performed with R statistical software packages, and a number of differentially expressed genes (DEGs) were obtained. A functional enrichment analysis was performed for all the DEGs with a BiNGO plug‑in in Cytoscape. Their correlation was analyzed in order to construct a network. The modularity analysis and pathway identification operations were used to identify graph clusters and associated pathways. The underlying molecular mechanisms involving these DEGs were also assessed by data mining. A total of 249 DEGs, which were markedly upregulated and downregulated, were identified. The extracellular region contained the most significantly over‑represented functional terms, with respect to upregulated and downregulated genes, and the closest topological matches were identified for taste transduction and regulation of autophagy. In addition, extracellular matrix‑receptor interactions were identified as the most relevant pathway associated with the progression of GC. The genes for fibronectin 1, secreted phosphoprotein 1, collagen type 4 variant α‑1/2 and thrombospondin 1, which are involved in the pathways, may be considered as potential therapeutic targets for GC. A series of associations between candidate genes and key pathways were also identified for GC, and their correlation may provide novel insights into the pathogenesis of GC.

Thrombospondin-4 controls matrix assembly during development and repair of myotendinous junctions

Tendons are extracellular matrix (ECM)-rich structures that mediate muscle attachments with the skeleton, but surprisingly little is known about molecular mechanisms of attachment. Individual myofibers and tenocytes in Drosophila interact through integrin (Itg) ligands such as Thrombospondin (Tsp), while vertebrate muscles attach to complex ECM fibrils embedded with tenocytes. We show for the first time that a vertebrate thrombospondin, Tsp4b, is essential for muscle attachment and ECM assembly at myotendinous junctions (MTJs). Tsp4b depletion in zebrafish causes muscle detachment upon contraction due to defects in laminin localization and reduced Itg signaling at MTJs. Mutation of its oligomerization domain renders Tsp4b unable to rescue these defects, demonstrating that pentamerization is required for ECM assembly. Furthermore, injected human TSP4 localizes to zebrafish MTJs and rescues muscle detachment and ECM assembly in Tsp4b-deficient embryos. Thus Tsp4 functions as an ECM scaffold at MTJs, with potential therapeutic uses in tendon strengthening and repair.

DOI:http://dx.doi.org/10.7554/eLife.02372.001

Tendons, the tough connective tissues that link muscles to bones, are essential for lifting, running and other movements in animals. A matrix of proteins, called the extracellular matrix, connects the cells in a tendon, giving it the strength it needs to prevent muscles from detaching from bones during strenuous activities.

To achieve this strength, extracellular matrix proteins bind to one another and to receptors on the muscle cell surface that are linked to its internal scaffolding, thereby organizing other proteins into a structure called a myotendinous junction. However, despite the essential roles of tendons, scientists do not fully understand how this organization occurs, or how it can go awry.

Subramanian and Schilling screened zebrafish for genes that are essential for proper muscle attachment, and zeroed in on a gene encoding a protein called Thrombospondin-4b (Tsp4b). A similar protein helps to connect muscle and tendon cells in fruit flies. Without Tsp4b, zebrafish are able to form connections between muscles and tendons, but the muscles detach easily during movement. This weakened connection is caused by disorganization of the proteins in the extracellular matrix, which results in reduced signaling from the muscle cell receptors.

When a human form of this protein was injected into zebrafish embryos lacking Tsp4b, it settled into the junctions between muscle and tendon cells. The human protein repaired the detached muscles and restored the proper organization of the matrix. This improved the strength of the muscle-tendon attachment in the treated fish embryos, suggesting that similar injections could also help to strengthen and repair muscles and tendons in people.

DOI:http://dx.doi.org/10.7554/eLife.02372.002

Monoclonal antibodies to murine thrombospondin-1 and thrombospondin-2 reveal differential expression patterns in cancer and low antigen expression in normal tissues

There is a considerable interest for the discovery and characterization of tumor-associated antigens, which may facilitate antibody-based pharmacodelivery strategies. Thrombospondin-1 and thrombospondin-2 are homologous secreted proteins, which have previously been reported to be overexpressed during remodeling typical for wound healing and tumor progression and to possibly play a functional role in cell proliferation, migration and apoptosis. To our knowledge, a complete immunohistochemical characterization of thrombospondins levels in normal rodent tissues has not been reported so far. Using antibody phage technology, we have generated and characterized monoclonal antibodies specific to murine thrombospondin-1 and thrombospondin-2, two antigens which share 62% aminoacid identity. An immunofluorescence analysis revealed that both antigens are virtually undetectable in normal mouse tissues, except for a weak staining of heart tissue by antibodies specific to thrombospondin-1. The analysis also showed that thrombospondin-1 was strongly expressed in 5/7 human tumors xenografted in nude mice, while it was only barely detectable in 3/8 murine tumors grafted in immunocompetent mice. By contrast, a high-affinity antibody to thrombospondin-2 revealed a much lower level of expression of this antigen in cancer specimens. Our analysis resolves ambiguities related to conflicting reports on thrombosponding expression in health and disease. Based on our findings, thrombospondin-1 (and not thrombospondin-2) may be considered as a target for antibody-based pharmacodelivery strategies, in consideration of its low expression in normal tissues and its upregulation in cancer.

Control of organization and function of muscle and tendon by thrombospondin-4

Thrombospondins (TSPs) are multifunctional proteins that are deposited in the extracellular matrix where they directly affect the function of vascular and other cell types. TSP-4, one of the 5 TSP family members, is expressed abundantly in tendon and muscle. We have examined the effect of TSP-4 deficiency on tendon collagen and skeletal muscle morphology and function. In Thbs4(-/-) mice, tendon collagen fibrils are significantly larger than in wild-type mice, and there is no compensatory over-expression of TSP-3 and TSP-5, the two TSPs most highly homologous to TSP-4, in the deficient mice. TSP-4 is expressed in skeletal muscle, and higher levels of TSP-4 protein are associated with the microvasculature of red skeletal muscle with high oxidative metabolism. Lack of TSP-4 in medial soleus, red skeletal muscle with predominant oxidative metabolism, is associated with decreased levels of several specific glycosaminoglycan modifications, decreased expression of a TGFβ receptor beta-glycan, decreased activity of lipoprotein lipase, which associates with vascular cell surfaces by binding to glycosaminoglycans, and decreased uptake of VLDL. The soleus muscle is smaller and hind- and fore-limb grip strength is reduced in Thbs4(-/-) mice compared to wild-type mice. These observations suggest that TSP-4 regulates the composition of the ECM at major sites of its deposition, tendon and muscle, and the absence of TSP-4 alters the organization, composition and physiological functions of these tissues.

Astrocyte-secreted matricellular proteins in CNS remodelling during development and disease

Matricellular proteins are secreted, nonstructural proteins that regulate the extracellular matrix (ECM) and interactions between cells through modulation of growth factor signaling, cell adhesion, migration, and proliferation. Despite being well described in the context of nonneuronal tissues, recent studies have revealed that these molecules may also play instrumental roles in central nervous system (CNS) development and diseases. In this minireview, we discuss the matricellular protein families SPARC (secreted protein acidic and rich in cysteine), Hevin/SC1 (SPARC-like 1), TN-C (Tenascin C), TSP (Thrombospondin), and CCN (CYR61/CTGF/NOV), which are secreted by astrocytes during development. These proteins exhibit a reduced expression in adult CNS but are upregulated in reactive astrocytes following injury or disease, where they are well placed to modulate the repair processes such as tissue remodeling, axon regeneration, glial scar formation, angiogenesis, and rewiring of neural circuitry. Conversely, their reexpression in reactive astrocytes may also lead to detrimental effects and promote the progression of neurodegenerative diseases.

Thrombospondin-4 expression is activated during the stromal response to invasive breast cancer

The thromobospondins are a family of extracellular glycoproteins that are activated during tissue remodeling processes such as embryogenesis, wound healing and cancer. Thrombospondin-4 (THBS4) is known to have roles in cellular migration, adhesion and attachment, as well as proliferation in different contexts. Data to support a role in cancer biology is increasing, including for gastrointestinal and prostate tumours. Here, using a combination of immunohistochemistry, immunofluorescence and analysis of publicly available genomic and expression data, we present the first study describing the pattern of expression of THBS4 in normal breast and breast cancer. THBS4 was located to the basement membrane of large ducts and vessels in normal breast tissue, but was absent from epithelium and extracellular matrix. There was a significant induction in expression in cancer-associated stroma relative to normal stroma (P = 0.0033), neoplastic epithelium (P < 0.0001) and normal epithelium (P < 0.0001). There was no difference in stromal expression of THBS4 between invasive ductal carcinomas (IDC) and invasive lobular carcinomas (ILC). The THBS4 mRNA levels were variable yet were generally highest in tumours typically rich in stromal content (ILC, ER positive low grade IDC; luminal A and normal-like subtypes). Genomic alterations of the THBS4 gene (somatic mutations and gene copy number) are rare suggesting this dramatic activation in expression is most likely dynamically regulated through the interaction between invading tumour cells and stromal fibroblasts in the local microenvironment. In summary, THBS4 expression in breast cancer-associated extracellular matrix contributes to the activated stromal response exhibited during tumour progression and this may facilitate invasion of tumour cells.

Characterization of the thrombospondin (TSP)-II gene in Penaeus monodon and a novel role of TSP-like proteins in an induction of shrimp sperm acrosome reaction

We have recently shown that water-soluble materials from the egg extracellular cortical rods (wsCRs) exert the ability to induce the sperm acrosome reaction in Penaeus monodon. In this study, we further demonstrated that the thrombospondin protein family (TSP) existed in wsCRs, and that their mRNA transcripts were detected in developing oocytes as early as stage I. Full sequence analysis revealed that our pmTSP sequence was considerably different from the recently reported pmTSP in the 5' nonconserved region and in many TSP signature domains, hence, the name pmTSP-II was given to our variant. The transcripts of pmTSP-II were detected only in early developing oocytes (stage-I and -II) while TSP-like proteins were detected in all developing oocytes, particularly at the outer rim of cortical rods situated in the extracellular crypts of the mature, stage-IV oocytes. In addition, wsCRs contained anti-TSP-reactive proteins, suggesting that TSP-like proteins are dissolved in and are part of the egg water during spawning. The functional importance of TSP-like proteins was evident by the interference of a wsCR-induced acrosome reaction response with anti-TSP in a concentration-dependent manner. In summary, we found that pmTSP-II transcripts were present in the developing oocytes and pmTSP-II protein accumulated in cortical rods, which are partly secreted and thus solubilized to produce dissolved TSP-like proteins that participate in induction of the sperm acrosome reaction-a novel reproductive role for TSP protein family.

TSP-1 promotes glomerular mesangial cell proliferation and extracellular matrix secretion in Thy-1 nephritis rats

The proliferation of glomerular mesangial cells (GMC) and secretion of the extracellular matrix (ECM) in rat with Thy-1 nephritis (Thy-1N) resembling human mesangioproliferative glomerulonephritis have been explored for many years; however, the molecular mechanisms of GMC proliferation and ECM production remain unclear. Our previous studies have demonstrated that the thrombospondin-1 (TSP-1) gene was involved in mediating rat GMC proliferation and ECM synthesis induced by sublytic C5b-9 in vitro. In the present study, the roles of the TSP-1 gene in GMC proliferation, ECM production, and urinary protein secretion in Thy-1N rats were determined by using TSP-1 small hairpin RNA, and the results revealed that silencing of the TSP-1 gene in rat renal tissues could diminish GMC proliferation (P < 0.01) and ECM secretion (P < 0.01) as well as urinary protein secretion (P < 0.05) in Thy-1N rats. Together, the current findings suggested that TSP-1 gene expression was required for GMC proliferation and ECM production in Thy-1N rats.

Long-standing balancing selection in the THBS4 gene: influence on sex-specific brain expression and gray matter volumes in Alzheimer disease

The THBS4 gene encodes a glycoprotein involved in inflammatory responses and synaptogenesis. THBS4 is expressed at higher levels in the brain of humans compared with nonhuman primates, and the protein accumulates in β-amyloid plaques. We analyzed THBS4 genetic variability in humans and show that two haplotypes (hap1 and hap2) are maintained by balancing selection and modulate THBS4 expression in lymphocytes. Indeed, the balancing selection region covers a predicted transcriptional enhancer. In humans, but not in macaques and chimpanzees, THBS4 brain expression increases with age, and variants in the balancing selection region interact with sex in influencing THBS4 expression (pinteraction = 0.038), with hap1 homozygous females showing lowest expression. In Alzheimer disease (AD) patients, significant interactions between sex and THBS4 genotype were detected for peripheral gray matter (pinteraction = 0.014) and total gray matter (pinteraction = 0.012) volumes. Similarly to the gene expression results, the interaction is mainly mediated by hap1 homozygous AD females, who show reduced volumes. Thus, the balancing selection target in THBS4 is likely represented by one or more variants that regulate tissue-specific and sex-specific gene expression. The selection signature associated with THBS4 might not be related to AD pathogenesis, but rather to inflammatory responses.

Thrombospondin-1 triggers cell migration and development of advanced prostate tumors

The antitumor effects of pharmacologic inhibitors of angiogenesis are hampered in patients by the rapid development of tumor resistance, notably through increased invasiveness and accelerated metastasis. Here, we reevaluated the role of the endogenous antiangiogenic thrombospondin 1 (TSP1) in prostate carcinomas in which angiogenesis is an active process. In xenografted tumors, we observed that TSP1 altogether inhibited angiogenesis and fostered tumor development. Our results show that TSP1 is a potent stimulator of prostate tumor cell migration. This effect required CD36, which also mediates TSP1 antiangiogenic activity, and was mimicked by an antiangiogenic TSP1-derived peptide. As suspected for pharmacologic inhibitors of angiogenesis, the TSP1 capacities to increase hypoxia and to trigger cell migration are thus inherently linked. Importantly, although antiangiogenic TSP1 increases hypoxia in vivo, our data show that, in turn, hypoxia induced TSP1, thus generating a vicious circle in prostate tumors. In radical prostatectomy specimens, we found TSP1 expression significantly associated with invasive tumors and with tumors which eventually recurred. TSP1 may thus help select patients at risk of prostate-specific antigen relapse. Together, the data suggest that intratumor disruption of the hypoxic cycle through TSP1 silencing will limit tumor invasion.

The thrombospondins

Thrombospondins are evolutionarily conserved, calcium-binding glycoproteins that undergo transient or longer-term interactions with other extracellular matrix components. They share properties with other matrix molecules, cytokines, adaptor proteins, and chaperones, modulate the organization of collagen fibrils, and bind and localize an array of growth factors or proteases. At cell surfaces, interactions with an array of receptors activate cell-dependent signaling and phenotypic outcomes. Through these dynamic, pleiotropic, and context-dependent pathways, mammalian thrombospondins contribute to wound healing and angiogenesis, vessel wall biology, connective tissue organization, and synaptogenesis. We overview the domain organization and structure of thrombospondins, key features of their evolution, and their cell biology. We discuss their roles in vivo, associations with human disease, and ongoing translational applications. In many respects, we are only beginning to appreciate the important roles of these proteins in physiology and pathology.

The evolution of thrombospondins and their ligand-binding activities

The extracellular matrix (ECM) is a complex, multiprotein network that has essential roles in tissue integrity and intercellular signaling in the metazoa. Thrombospondins (TSPs) are extracellular, calcium-binding glycoproteins that have biologically important roles in mammals in angiogenesis, vascular biology, connective tissues, immune response, and synaptogenesis. The evolution of these complex functional properties is poorly understood. We report here on the evolution of TSPs and their ligand-binding capacities, from comparative genomics of species representing the major phyla of metazoa and experimental analyses of the oligomerization properties of noncanonical TSPs of basal deuterostomes. Monomeric, dimeric, trimeric, and pentameric TSPs have arisen through separate evolutionary events involving gain, loss, or modification of a coiled-coil domain or distinct domains at the amino-terminus. The relative transience of monomeric forms under evolution implicates a biological importance for multivalency of the C-terminal region of TSPs. Most protostomes have a single TSP gene encoding a pentameric TSP. The pentameric form is also present in deuterostomes, and gene duplications at the origin of deuterostomes and gene loss and further gene duplication events in the vertebrate lineage gave rise to distinct forms and novel domain architectures. Parallel analysis of the major ligands of mammalian TSPs revealed that many binding activities are neofunctions representing either coevolutionary innovations in the deuterostome lineage or neofunctions of ancient molecules such as CD36. Contrasting widely conserved capacities include binding to heparan glycosaminoglycans, fibrillar collagen, or RGD-dependent integrins. These findings identify TSPs as fundamental components of the extracellular interaction systems of metazoa and thus impact understanding of the evolution of ECM networks. The widely conserved activities of TSPs in binding to ECM components or PS2 clade integrins will be relevant to use of TSPs in synthetic extracellular matrices or tissue engineering. In contrast, the neofunctions of vertebrate TSPs likely include interactions suitable for therapeutic targeting without general disruption of ECM.

Thrombospondin-1 as a Paradigm for the Development of Antiangiogenic Agents Endowed with Multiple Mechanisms of Action

Uncontrolled neovascularization occurs in several angiogenesis-dependent diseases, including cancer. Neovascularization is tightly controlled by the balance between angiogenic growth factors and antiangiogenic agents. The various natural angiogenesis inhibitors identified so far affect neovascularization by different mechanisms of action. Thrombospondin-1 (TSP-1) is a matricellular modular glycoprotein that acts as a powerful endogenous inhibitor of angiogenesis. It acts both indirectly, by sequestering angiogenic growth factors and effectors in the extracellular environment, and directly, by inducing an antiangiogenic program in endothelial cells following engagement of specific receptors including CD36, CD47, integrins and proteoglycans (all involved in angiogenesis ). In view of its central, multifaceted role in angiogenesis, TSP-1 has served as a source of antiangiogenic tools, including TSP-1 fragments, synthetic peptides and peptidomimetics, gene therapy strategies, and agents that up-regulate TSP-1 expression. This review discusses TSP-1-based inhibitors of angiogenesis, their mechanisms of action and therapeutic potential, drawing our experience with angiogenic growth factor-interacting TSP-1 peptides, and the possibility of exploiting them to design novel antiangiogenic agents.

The crystal structure of the signature domain of cartilage oligomeric matrix protein: implications for collagen, glycosaminoglycan and integrin binding

Cartilage oligomeric matrix protein (COMP), or thrombospondin-5 (TSP-5), is a secreted glycoprotein that is important for growth plate organization and function. Mutations in COMP cause two skeletal dysplasias, pseudoachondroplasia (PSACH) and multiple epiphyseal dysplasia (EDM1). In this study, we determined the structure of a recombinant protein that contains the last epidermal growth factor repeat, the type 3 repeats and the C-terminal domain (CTD) of COMP to 3.15-A resolution limit by X-ray crystallography. The CTD is a beta-sandwich that is composed of 15 antiparallel beta-strands, and the type 3 repeats are a contiguous series of calcium binding sites that associate with the CTD at multiple points. The crystal packing reveals an exposed potential metal-ion-dependent adhesion site (MIDAS) on one edge of the beta-sandwich that is common to all TSPs and may serve as a binding site for collagens and other ligands. Disease-causing mutations in COMP disrupt calcium binding, disulfide bond formation, intramolecular interactions, or sites for potential ligand binding. The structure presented here and its unique molecular packing in the crystal identify potential interactive sites for glycosaminoglycans, integrins, and collagens, which are key to cartilage structure and function.

Signal regulatory protein alpha (SIRPalpha)/CD47 interaction and function

SIRPalpha is an inhibitory receptor present on myeloid cells that interacts with a widely distributed membrane protein CD47. The activating member SIRPbeta, despite extensive sequence similarity to SIRPalpha in the extracellular region, shows negligible binding to CD47. The SIRPalpha/CD47 interaction is unusual in that it can lead to bidirectional signalling through both SIRPalpha and CD47. This review concentrates on the interactions of SIRPalpha with CD47 where recent data have shed light on the structure of the proteins including determining why the activating SIRPbeta does not bind CD47, evidence of extensive polymorphisms and implication for the evolution and function of this protein and paired receptors in general. The interaction may be modified by endocytosis of the receptors, cleavage by proteolysis and through interactions of surfactant proteins.

Extracellular matrix retention of thrombospondin 1 is controlled by its conserved C-terminal region

Thrombospondins (TSPs) are an evolutionarily ancient family of extracellular calcium-binding glycoproteins. The five mammalian TSPs collectively have important roles in angiogenesis and vascular biology, synaptogenesis, wound repair and connective tissue organisation. Their complex functions relate to the multiple postsecretion fates of TSPs that can involve endocytic uptake, proteolysis or retention within the extracellular matrix (ECM). Surprisingly, the molecular and cellular mechanisms by which TSPs become retained within the ECM are poorly understood. We hypothesised that the highly conserved TSP C-terminal domain mediates ECM retention. We report that ECM incorporation as insoluble punctate deposits is an evolutionarily conserved property of TSPs. ECM retention of TSP1 is mediated by the C-terminal region in trimeric form, and not by C-terminal monomer or trimers of the N-terminal domain or type 1 repeats. Using a novel mRFP-tagged TSP1 C-terminal trimer, we demonstrate that ECM retention involves the RGD site and a novel site in the L-lectin domain with structural similarity to the ligand-binding site of cargo transport proteins. CD47 and beta1 integrins are dispensable for ECM retention, but beta1 integrins enhance activity. These novel data advance concepts of the molecular processes that lead to ECM retention of TSP1.

Structures of thrombospondins

Thrombospondins are large secreted, multimodular, calcium-binding glycoproteins that have complex roles in mediating cellular processes. Determination of high-resolution structures of thrombospondins has revealed unique and interesting protein motifs. Here, we review this progress and discuss implications for function. By combining structures of modules from thrombospondins and related extracellular proteins it is now possible to prepare an overall model of the structure of thrombospondin-1 and thrombospondin-2 and discern features of other thrombospondins. (Part of a multi-author Review).

Fibroblast growth factor-2 binding to the thrombospondin-1 type III repeats, a novel antiangiogenic domain

Thrombospondin-1, an antiangiogenic matricellular protein, binds with high affinity to the angiogenic fibroblast growth factor-2, affecting its bioavailability and activity. The present work aimed at further locating the fibroblast growth factor-2 binding site of thrombospondin-1 and investigating its activity, using recombinant thrombospondin-1 proteins. Only recombinant constructs containing the thrombospondin-1 type III repeats bound fibroblast growth factor-2, whereas other domains, including the known anti-angiogenic type I repeats, were inactive. Binding was specific and inhibited by the anti thrombospondin-1 monoclonal antibody B5.2. Surface plasmon resonance analysis on BIAcore revealed a binding affinity (K(d)) of 310nM for the type III repeats and 11nM for intact thrombospondin-1. Since the type III repeats bind calcium, the effect of calcium on thrombospondin-1 binding to fibroblast growth factor-2 was investigated. Binding was modulated by calcium, as thrombospondin-1 or the type III repeats bound to fibroblast growth factor-2 only in calcium concentrations <0.3mM. The type III repeats inhibited binding of fibroblast growth factor-2 to endothelial cells, fibroblast growth factor-2-induced endothelial cell proliferation in vitro and angiogenesis in the chorioallantoic membrane assay in vivo, thus indicating the antiangiogenic activity of the domain. In conclusion, this study demonstrates that the fibroblast growth factor-2 binding site of thrombospondin-1 is located in the type III repeats. The finding that this domain is active in inhibiting angiogenesis indicates that the type III repeats represent a novel antiangiogenic domain of thrombospondin-1.

Immunochemical analysis of the structure of the signature domains of thrombospondin-1 and thrombospondin-2 in low calcium concentrations

Thrombospondins (TSPs) undergo conformational changes upon removal of calcium. The eight C-type and five N-type calcium-binding repeats of TSP-2 form a circuitous wire that, in 2 mm calcium, interacts at its ends with more N-terminal epidermal growth factor (EGF)-like modules, EGF2 and EGF3, and the C-terminal lectin-like module. These components, along with the other EGF-like module(s), form the signature domain of TSPs. Characterization of conformation-sensitive epitopes of monoclonal antibodies to human TSP-2 and its TSP-1 homolog have given insights into the structure of the signature domain in the absence of calcium. The epitope for 4B6.13 anti-TSP-2 was localized to His-722 and Leu-703 in repeat 1C of the wire; recognition only occurred in constructs that included EGF3, the rest of the wire, and the lectin-like module and in the presence of calcium. The epitope for C6.7 anti-TSP-1 was localized to Glu-609 in the EGF2 module. The C6.7 epitope was preferentially recognized when EGF2 was expressed in the context of EGF1, EGF3, the wire, and the lectin-like module. Preferential recognition of the C6.7 epitope did not require calcium. Rotary shadowing electron microscopy of TSP-1 has shown elongation of the stalk and diminution of the C-terminal globule. We propose a model whereby at low calcium concentrations the lectin-like module drops away from EGF3 concomitant with changes in conformation of the wire and loss of the 4B6.13 epitope. A critical feature of the model is interaction of repeat 12N of the wire with EGF2 in both the presence and absence of calcium.

Thrombospondin-4 and matrix three-dimensionality in axon outgrowth and adhesion in the developing retina

Thrombospondin-4 (TSP-4), a large pentameric glycoprotein of the extracellular matrix, has been described as a neurite outgrowth-promoting molecule. However, the means by which TSP-4 promotes neurite outgrowth in the developing eye is unclear. Here we show that TSP-4 is present at the appropriate time in development and displays a localization pattern within the developing mouse retina consistent with a role in retinal ganglion cell (RGC) neurite outgrowth. Furthermore, results indicate that while TSP-4 alone does not support adhesion or neurite extension, it enhances the ability of laminins to promote adhesion and neurite outgrowth of embryonic retinal cells. The mechanism of enhancement is, in part, based on the ability of TSP-4 to enhance the three-dimensionality and/or clustering of laminins within the substrate matrix. These results support a model where TSP-4 acts as an organizer of adhesive and axon outgrowth-promoting molecules in the ECM to optimize retinal ganglion cell responses.

Bioinformatic analysis of adhesion proteins

Proteins that mediate cell-cell and cell-extracellular matrix (ECM) adhesion have been fundamental in the evolution of multicellular animals. Fibrillar collagens, proteoglycans, integrins, and cadherins are present in all animals from sponges to mammals, and many other adhesion proteins have arisen during animal evolution. In general, adhesion proteins are large multidomain molecules and are encoded in larger gene families in vertebrates than in invertebrates. With the increasing availability of completely sequenced genomes representing different points on the animal tree of life, bioinformatics is proving to be a very valuable approach for the analysis of the domain organization and relationships of adhesion proteins, which can direct or enhance experimental tests. Here we describe, with examples from the literature, the major methods for identifying sequence homologies; analyzing domain organization and potential for oligomerization; analyzing sequence relationships by multiple sequence alignments and phylogenetic trees, and assessing adhesion proteins as components of functional pathways and tissue systems through comparative genomics.

Increased cortical expression of two synaptogenic thrombospondins in human brain evolution

Thrombospondins are extracellular-matrix glycoproteins implicated in the control of synaptogenesis and neurite growth. Previous microarray studies suggested that one gene of this family, thrombospondin 4 (THBS4), was upregulated during human brain evolution. Using independent techniques to examine thrombospondin expression patterns in adult brain samples, we report approximately 6-fold and approximately 2-fold greater expression of THBS4 and THBS2 messenger RNA (mRNA), respectively, in human cerebral cortex compared with chimpanzees and macaques, with corresponding differences in protein levels. In humans and chimpanzees, thrombospondin expression differences were observed in the forebrain (cortex and caudate), whereas the cerebellum and most nonbrain tissues exhibited similar levels of the 2 mRNAs. Histological examination revealed THBS4 mRNA and protein expression in numerous pyramidal and glial cells in the 3 species but humans also exhibited very prominent immunostaining of the synapse-rich cortical neuropil. In humans, additionally, THBS4 antibodies labeled beta-amyloid containing plaques in Alzheimer's cases and some control cases. This is the first detailed characterization of gene-expression changes in human evolution that involve specific brain regions, including portions of cerebral cortex. Increased expression of thrombospondins in human brain evolution could result in changes in synaptic organization and plasticity, and contribute to the distinctive cognitive abilities of humans, as well as to our unique vulnerability to neurodegenerative disease.

Thrombospondin-1 C-terminal-derived peptide protects thyroid cells from ceramide-induced apoptosis through the adenylyl cyclase pathway

Thrombospondin-1, a multi-modular matrix protein is able to interact with a variety of matrix proteins and cell-surface receptors. Thus it is multifunctional. In this work, we examined the role of thrombospondin-1 in ceramide-induced thyroid apoptosis. We focused on the VVM containing sequence localized in the C-terminal domain of the molecule. Primary cultured thyroid cells synthesize thrombospondin-1 depending on their morphological organization. As it leads thyrocytes to organize into monolayers before inducing apoptosis ceramide can modulate this organization. Here, we established that C(2)-ceramide treatment decreased thrombospondin-1 expression by interfering with the adenylyl cyclase pathway, thus leading to apoptosis. Furthermore, we demonstrated that the thrombospondin-1-derived peptide 4N1 (RFYVVMWK) abolished ceramide-induced thyroid cell death by preventing intracellular cAMP levels from dropping. Finally, we reported that 4N1-mediated inhibition of ceramide-induced apoptosis was consistently associated with a down-regulation of the caspase-3 processing. Integrin-associated protein receptor (IAP or CD47) was identified as a molecular relay mediating the observed 4N1 effects. Taken together, our results shed light for the first time on anti-apoptotic activities of the thrombospondin-1-derived peptide 4N1 and provide new information on how thrombospondin-1 may control apoptosis of non-tumoral cells.

Phylogenomic analysis of vertebrate thrombospondins reveals fish-specific paralogues, ancestral gene relationships and a tetrapod innovation

BACKGROUND

Thrombospondins (TSPs) are evolutionarily-conserved, extracellular, calcium-binding glycoproteins with important roles in cell-extracellular matrix interactions, angiogenesis, synaptogenesis and connective tissue organisation. Five TSPs, designated TSP-1 through TSP-5, are encoded in the human genome. All but one have known roles in acquired or inherited human diseases. To further understand the roles of TSPs in human physiology and pathology, it would be advantageous to extend the repertoire of relevant vertebrate models. In general the zebrafish is proving an excellent model organism for vertebrate biology, therefore we set out to evaluate the status of TSPs in zebrafish and two species of pufferfish.

RESULTS

We identified by bioinformatics that three fish species encode larger numbers of TSPs than vertebrates, yet all these sequences group as homologues of TSP-1 to -4. By phylogenomic analysis of neighboring genes, we uncovered that, in fish, a TSP-4-like sequence is encoded from the gene corresponding to the tetrapod TSP-5 gene. Thus, all TSP genes show conservation of synteny between fish and tetrapods. In the human genome, the TSP-1, TSP-3, TSP-4 and TSP-5 genes lie within paralogous regions that provide insight into the ancestral genomic context of vertebrate TSPs.

CONCLUSION

A new model for TSP evolution in vertebrates is presented. The TSP-5 protein sequence has evolved rapidly from a TSP-4-like sequence as an innovation in the tetrapod lineage. TSP biology in fish is complicated by the presence of additional lineage- and species-specific TSP paralogues. These novel results give deeper insight into the evolution of TSPs in vertebrates and open new directions for understanding the physiological and pathological roles of TSP-4 and TSP-5 in humans.

Thrombospondin 1, thrombospondin 2 and the eye

Thrombospondin 1 and thrombospondin 2 (TSP1 and TSP2), which comprise the subgroup A thrombospondins, are matricellular proteins. As matricellular proteins, they modulate interactions between cells and the cellular environment, regulate cell adhesion and typically are expressed during tissue formative processes. In general, TSP1 and TSP2 counter angiogenesis (including tumour angiogenesis) and play important but contrasting roles during cutaneous repair. The two proteins are involved in development, including that of the eye, although evidence suggests that they have their greatest impact during tissue production in the adult. In the normal adult eye, they tend to be found at sites of ongoing matrix synthesis or cell-matrix interactions. At these sites, the two proteins possibly influence cellular differentiation and/or basement membrane deposition. TSP1 is also present in the intraocular fluids and drainage pathway, where it may function in maintaining the anti-angiogenic environment and in intraocular pressure control, respectively. TSP1 could also be involved in ocular immune privilege. Unlike in skin wounds, where TSP1 is derived from the blood and is present only in the early phases of repair, ocular tissue damage appears to lead to protacted TSP1 synthesis by local cells. This response might help suppress angiogenesis in the transparent tissues of the eye and so lessen visual axis opacification following injury. However, TSP2, which is also produced by damaged ophthalmic tissue and may be especially important in matrix organisation, seems to augment contraction in anomalous intraocular fibrosis. Elucidating the roles of TSP1 and TSP2 in ocular physiology and pathobiology may lead to improved therapies for neovascular, neoplastic, reparative and other ophthalmic diseases.

Biophysical characterization of the signature domains of thrombospondin-4 and thrombospondin-2

The signature domain of thrombospondins consists of tandem epidermal growth factor-like modules, 13 calcium-binding repeats, and a lectin-like module. Although very similar, the signature domains of thrombospondin-1 and -2 differ in several potentially important ways from the domains of thrombospondin-3, -4, and -5. We have compared matching recombinant segments representing the signature domains of thrombospondin-2 and -4. In the presence of 2 mM CaCl2, the far UV circular dichroism spectra of thrombospondin-2 and -4 constructs contain a strong negative band at 202 nm, but only the thrombospondin-2 construct has a band at 216 nm. Chelation of calcium shifted the negative bands to lower magnitudes. Titrations of the spectra demonstrated lower cooperativity and affinity for binding of calcium to thrombospondin-4 compared with thrombospondin-2. Atomic absorption spectroscopy demonstrated that the thrombospondin-4 constructs bind seven less calcium than the thrombospondin-2 construct at 0.6 mM CaCl2. In 2 mM CaCl2, the near UV circular dichroism spectra of thrombospondin-2, but not thrombospondin-4, contain a positive band at 292 nm that disappears upon calcium chelation. Intrinsic fluorescence spectra for both proteins were also sensitive to calcium, but the changes were simpler and more marked for thrombospondin-2 than for thrombospondin-4. In differential scanning calorimetry, the thrombospondin-2 construct melted in two distinct transitions at 53.5 and 81.8 degrees C, whereas the first transition for thrombospondin-4 constructs was observed at 63.5 degrees C. Thus, the studies revealed significant differences between the signature domains of thrombospondin-2 and thrombospondin-4 in calcium binding, fine structure, and inter-modular interactions.

Molecular cloning and characterization of Fc-TSP from the Chinese shrimp Fennerpenaeus chinensis

Thrombospondins (TSPs) are extracellular, multidomain, calcium-binding glycoproteins that modulate cell behavior in homeostasis and during development, wound-healing, immune response and tumor growth of adult tissues in vertebrates. In invertebrates these proteins are a major component of cortical rods in mature oocytes. A fragment of a thrombospondin-like gene was generated by screening a subtractive cDNA library constructed from the hemocytes of Chinese shrimp, Fennerpenaeus chinensis. The full length F. chinensis cDNA of thrombospondin was cloned by 3'- and 5'-rapid amplification of cDNA ends (3'- and 5'-RACE). The complete cDNA sequence, named Fc-TSP, is 2886 bp and the open reading frame of the cDNA encodes a 938-residue protein that contains three ChtBD2 domains, an EGF domain, a TSP-3 domain and a common TSP-C (CTD) domain. The protein shares a high sequence identity with the mj-TSPa (46.3%), mj-TSPb (46.9%) and mj-TSPc (51.9%) of Marsupenaeus japonicus. The expression and distribution of Fc-TSP in both challenged and unchallenged shrimps were studied by Northern blot, RT-PCR and in situ hybridization. Northern blot analysis showed that the Fc-TSP transcripts were detected in the hemocytes, heart, intestine, stomach and ovary of both challenged and unchallenged shrimps, but the signal was much stronger in the challenged tissues. A strong hybridization signal was detected only in challenged hepatopancreas, with no signal in the unchallenged tissue. The RT-PCR showed that the Fc-TSP was detected in both challenged and unchallenged tissues including the hemocytes, heart, hepatopancreas, stomach, gills, intestine, spermary and ovary. Except for the ovary and spermary, the signal of challenged tissues was relatively stronger than that of unchallenged ones, especially in hepatopancreas. These results suggest that the thrombospondin was upregulated in the hemocytes, heart, intestine and stomach of challenged shrimp, and induced in the hepatopancreas of challenged shrimps. Therefore, Fc-TSP may be involved in the defense responses of the shrimp.

Roles of fascin in cell adhesion and motility

Many cell interactions depend on the assembly of cell protrusions; these include cell attachment and migration in the extracellular matrix, cell-cell communication, and the ability of cells to sense their local environment. Cell protrusions are extensions of the plasma membrane that are supported internally by actin-based structures that impart mechanical stiffness. Fascin is a small, globular actin-bundling protein that has emerging roles in diverse forms of cell protrusions and in cytoplasmic actin bundles. The fascin-actin interaction is under complex regulation from the extracellular matrix, peptide factors and other actin-binding proteins. Recent developments advance our understanding of the multifaceted regulation of fascin and the roles of fascin-containing structures in cell adhesion, motility and invasion in the life of vertebrate organisms.