Evolution of the hyaluronan-binding module of link protein

The proteomics of the freshwater pearl powder: Insights from biomineralization to biomedical application

The freshwater pearl is one kind of valuable organic jewelry and traditional Chinese medicine (TCM). However, the molecular basis of matrix protein in pearl biomineralization and biomedical applications are largely unknown to date. In this study, the matrix proteins of water-soluble matrix, acid-soluble matrix and acid-insoluble matrix from the freshwater seedless pearl powder were detected using liquid chromatography-tandem mass spectrometry (LC-MS/MS) respectively, and identified against the transcriptomic database of the pearl sac. The results showed that a total of 190 proteins were identified in pearl proteomics, which was divided into eight categories by their potential biomineralization functions. The composition of pearl matrix proteins and the high frequency conserved domains like carbonic anhydrase, von Willebrand factor type A, tyrosinase and chitin binding 2 in protein sequences, implying that the "chitin-silk fibroin gel proteins-acidic macromolecules" model was suitable for description the pearl biomineralization process. Meanwhile, ninety-one of pearl matrix proteins could be classified into seven categories by their potential medical functions including wound healing, osteogenic property, antioxidant activity, neuro-regulation effects, skin lightening effect, anti-inflammatory and anti-apoptotic effects and other immunomodulatory property. In general, these results provided valuable new insights into not only the diversity of pearl matrix protein for mollusc biomineralization, but the molecular basis of pearl matrix proteins responsible for their diverse biological properties in TCM application. SIGNIFICANCE: The significance of this study included the following points.

Zona pellucida-binding protein 2 (ZPBP2) and several proteins containing BX7B motifs in human sperm may have hyaluronic acid binding or recognition properties

STUDY QUESTION

Are there novel hyaladherins in human sperm?

SUMMARY ANSWER

Zona pellucida-binding protein 2 (ZPBP2), containing a Link-like hyaluronic acid (HA)-binding domain, and several other proteins containing BX7B motifs, such as ADAM32 and Midkine, may be novel hyaladherins with HA-binding properties.

WHAT IS KNOWN ALREADY

HA-binding proteins (hyaladherins), which can bind HA surrounding the cumulus-oophorus complex, are distinct from hyases such as PH 20 (SPAM1) and are expressed by mature spermatozoa. Although HABP1 and CD44 are reasonably well characterized hyaladherins and the former has been implicated in sperm-oocyte interactions, the overall significance of sperm hyaladherins for male fertility is still poorly understood.

STUDY DESIGN, SIZE, DURATION

This was a laboratory-based investigation into human sperm hyaladherins undertaken as part of a three year PhD programme sponsored by the EU Marie Curie Training network, Reprotrain.

PARTICIPANTS/MATERIALS, SETTING, METHODS

Protein homogenates of sperm obtained from young men of unknown fertility (N = 4) were partitioned into HA-binding and non-binding fractions by a protein affinity 'panning' method; their subsequent characterization was by liquid chromatography-tandem mass spectrometry (LC-MS-MS) and partitioning behaviour was confirmed by western blotting. Sequences of proteins from both fractions were submitted to PDBsum to look for orthologous entries (PDB codes) and all returned codes were queried against the matching protein using SAS (Sequences Annotated by Structure) looking for structural similarities between them. A systematic search for other common features of hyaladherins was also undertaken.

MAIN RESULTS AND THE ROLE OF CHANCE

The presence of BX7B sequence motifs found in several well-described hyaladherins including RHAMM was used to assess efficacy of potential hyaladherin partitioning by the HA substrate. The data showed that 50% (14/28) and 34.5% (28/81) of proteins in the bound and unbound fractions, respectively, contained these motifs (one-tailed Z-score = 1.45; P = 0.074), indicating weak discrimination by the substrate. Querying PDBsum with sequences for all bound proteins returned several PDB codes matching ZPBP2 with the HA-binding Link domain of the hyaladherin, CD44. Western blot analysis confirmed the affinity partitioning of proteins indicated by the LC-MS/MS results, with ADAM32 (containing two BX7B motifs) and ZPBP2 (containing a Link-like HA-binding domain) present only in the binding fraction. There remains the possibility that the putative hyaladherins uncovered by this study were coincidentally enriched by HA-binding.

LARGE SCALE DATA

The full proteomics data set is available on request.

LIMITATIONS REASONS FOR CAUTION

The protein extraction methods or the HA substrate used to pan them in this study were probably not ideal, as hyaladherins expected to be present in sperm homogenates (such as CD44 and RHAMM) were not detected.

WIDER IMPLICATIONS OF THE FINDINGS

The results provide evidence that ZPBP2, found only in the bound fraction, may have hyaladherin-like properties, which could reflect the evolutionary background context of contemporary sperm-oocyte interaction mechanisms.

STUDY FUNDING AND COMPETING INTEREST(S)

An EU Marie Curie Sklodowska Initial Training Network Scholarship, supporting Ms Torabi, is gratefully acknowledged. This project was also supported and funded by the Efficacy and Mechanism Evaluation Programme, a UK MRC and NIHR partnership (Grant No 11/14/ 34). There is no conflict of interest in relation to this work.

The extracellular matrix molecule hyaluronic acid regulates hippocampal synaptic plasticity by modulating postsynaptic L-type Ca(2+) channels

Although the extracellular matrix plays an important role in regulating use-dependent synaptic plasticity, the underlying molecular mechanisms are poorly understood. Here we examined the synaptic function of hyaluronic acid (HA), a major component of the extracellular matrix. Enzymatic removal of HA with hyaluronidase reduced nifedipine-sensitive whole-cell Ca(2+) currents, decreased Ca(2+) transients mediated by L-type voltage-dependent Ca(2+) channels (L-VDCCs) in postsynaptic dendritic shafts and spines, and abolished an L-VDCC-dependent component of long-term potentiation (LTP) at the CA3-CA1 synapses in the hippocampus. Adding exogenous HA, either by bath perfusion or via local delivery near recorded synapses, completely rescued this LTP component. In a heterologous expression system, exogenous HA rapidly increased currents mediated by Ca(v)1.2, but not Ca(v)1.3, subunit-containing L-VDCCs, whereas intrahippocampal injection of hyaluronidase impaired contextual fear conditioning. Our observations unveil a previously unrecognized mechanism by which the perisynaptic extracellular matrix influences use-dependent synaptic plasticity through regulation of dendritic Ca(2+) channels.

Protumorigenic role of HAPLN1 and its IgV domain in malignant pleural mesothelioma

PURPOSE

Tumor extracellular matrix (ECM) plays a crucial role in cancer progression mediating and transforming host-tumor interactions. Targeting the ECM is becoming an increasingly promising therapeutic approach in cancer treatment. We find that one of the ECM proteins, HAPLN1, is overexpressed in the majority of mesotheliomas. This study was designed to characterize the protumorigenic role of HAPLN1 in mesothelioma.

EXPERIMENTAL DESIGN

Overexpression of HAPLN1 was assessed and validated on a large set of normal/mesothelioma specimens on the RNA and protein levels. We also analyzed DNA copy number alterations in the HAPLN1 genomic locus using the array-based comparative genomic hybridization representational oligonucleotide microarray analysis tool. Tumorigenic activities of the HAPLN1 domains were evaluated in vitro on mesothelioma cells transfected with HAPLN1-expressing constructs.

RESULTS

We found that HAPLN1 is 23-fold overexpressed in stage I mesothelioma and confirmed it for 76% samples (n = 53) on RNA and 97% (n = 40) on protein levels. The majority of lung cancers showed no differential expression of HAPLN1. Analysis of DNA copy number alterations identified recurrent gain in the 5q14.3 HAPLN1 locus in approximately 27% of tumors. Noteworthy, high expression of HAPLN1 negatively correlated with time to progression (P = 0.05, log-rank test) and overall survival (P = 0.006). Proliferation, motility, invasion, and soft-agar colony formation assays on mesothelioma cells overexpressing full-length HAPLN1 or its functional domains strongly supported the protumorigenic role of HAPLN1 and its SP-IgV domain.

CONCLUSION

Overexpression of HAPLN1 and its SP-IgV domain increases tumorigenic properties of mesothelioma. Thus, targeting the SP-IgV domain may be one of the therapeutic approaches in cancer treatment.

Induction of arthritis in BALB/c mice by cartilage link protein: involvement of distinct regions recognized by T and B lymphocytes

Both type II collagen and the proteoglycan aggrecan are capable of inducing an erosive inflammatory polyarthritis in mice. In this study we provide the first demonstration that link protein (LP), purified from bovine cartilage, can produce a persistent, erosive, inflammatory polyarthritis when injected repeatedly intraperitoneally into BALB/c mice. We discovered a single T-cell epitope, located within residues 266 to 290 of bovine LP (NDGAQIAKVGQIFAAWKLLGYDRCD), which is recognized by bovine LP-specific T lymphocytes. We also identified three immunogenic regions in bovine LP that contain epitopes recognized by antibodies in hyperimmunized sera. One of these B-cell regions is found in the most species-variable domain of LP (residues 1 to 36), whereas the other epitopes are located in the most conserved regions (residues 186 to 230 and 286 to 310). The latter two regions contain an AGWLSDGSVQYP motif shared by the G1 globulin domain of aggrecan core protein, versican, neurocan, glial hyaluronan-binding protein, and the hyaluronan receptor CD44. Our data reveal that the induction of arthritis is associated with antibody reactivities to B-cell epitopes located at residues 1 to 19. Together, these observations show that another cartilage protein, LP, like type II collagen and the proteoglycan aggrecan, is capable of inducing an erosive inflammatory arthritis in mice and that the immunity to LP involves recognition of both T- and B-cell epitopes. This immunity may be of importance in the pathogenesis of inflammatory joint diseases, such as juvenile rheumatoid arthritis, in which cellular immunity to LP has been demonstrated.

Identification of a protein in squid cranial cartilage with link protein properties

Squid cranial cartilage extracts were found to contain a protein with a molecular mass of 35 kDa immunoreacting with an antiserum against sheep link protein. Because hyaluronan is not detected in this tissue and the structure of proteoglycans is different to that of aggrecan or versican, this observation was studied further. The 35 kDa protein was purified from cartilage extracts and immunolocalised in Western blots by both the polyclonal antibody and the mAb 8A4. It was found that it was able to bind to hyaluronan and to aggrecan. Direct and competitive microplate binding experiments showed that the squid protein binds to G1 domain of aggrecan, similarly to cartilage link protein and, therefore, it could be a link-like protein molecule of squid cranial cartilage. The 35 kDa protein was also able to bind to squid proteoglycan and this suggested that it might participate in squid cartilage proteoglycan aggregate formation.

Bovine chondrocyte link protein cDNA sequence: interspecies conservation of primary structure and mRNA untranslated regions

The sequence for bovine link protein cDNA, including 108 bases of the 5' untranslated region (UTR) and 768 nucleotides of the 3' UTR, was determined from polymerase chain reaction products and bovine articular chondrocyte cDNA clones. The deduced primary structure for bovine link protein predicts a protein 354 amino acid residues in length. Comparative analysis with link protein sequence from several other species revealed overall high conservation of protein coding sequence. High nucleotide sequence conservation was observed within the extensive 5' and 3' UTRs of bovine, human, pig, chick and rat link protein mRNA. As evidence that the UTRs might play a role in regulation of link protein mRNA turnover, multiple occurrences of the adenosine-uridine binding factor motif A(Ua)A were found to be conserved between species within 3' UTRs. A polyadenylation signal was conserved between the bovine and chicken sequence, use of which would result in the smallest of multiple bovine link protein mRNA species observed by Northern blot analysis.

Structure of the human aggrecan gene: exon-intron organization and association with the protein domains

The complete exon-intron organization of the human aggrecan gene has been defined, and the exon organization has been compared with the individual domains of the protein core. A yeast artificial chromosome containing the aggrecan gene was selected from the Centre d'Etude du Polymorphisme Humaine yeast artificial chromosome library. A cosmid sulibrary was created from this, and direct sequencing of individual cosmids was used to provide the exon-intron organization. The human aggrecan gene was found to be composed of 19 exons ranging in size from 77 to 4224 bp. Exon 1 is non-coding, whereas exons 2-19 code for a protein core of 2454 amino acids with a calculated mass of 254379 Da. Intron 1 of the gene is at least 13 kb. Overall, the sizes of the 18 introns range from 0.5 to greater than 13 kb. Each intron begins with a GT and ends with an AG, thus obeying the GT/AG rule of splice-junction sequences. The entire coding region is contained in 39.4 kb of the gene. The organization of exons is strongly related to the specific domains of the protein core. The A loop of G1 and the interglobular domain are encoded by exons 3 and 7 respectively. The B and B' loops of G1 are encoded by exons 4-6, and those of G2 are encoded by exons 8-10. These sets of exons, coding for the B and B' loops, are identical in size and organization. This is supported by the intron classes associated with these exons. Exon 11 codes for the 5' half of the keratan sulphate-rich region, and exon 12 codes for the 3' half of the keratan sulphate-rich region as well as the entire chondroitin sulphate-rich region. G3 is encoded by exons 13-18, including the alternatively spliced epidermal growth factor-like and complement regulatory protein-like domains. The correspondence between the exon organization and the protein domains argues strongly for modular assembly of the aggrecan gene.

On the existence of a cartilage-like proteoglycan and link proteins in the central nervous system

Monoclonal antibodies (mAbs) against the major constituents of cartilage extracellular matrix, aggrecan and link protein, were screened by indirect immunofluorescence on frozen sections of bovine spinal cord. Antibodies against aggrecan and link protein gave rise to very similar perineuronal labeling in spinal cord gray matter. Aggrecan and link protein reactivities were seen in other regions of the central nervous system (CNS), although their distributions were not always coincident. Pretreatment of the tissue section with Streptomyces hyaluronidase, which is hyaluronate-specific, led to the loss of both reactivities. On Western blots, anti-aggrecan mAbs reacted with a large chondroitin sulfate proteoglycan. The chondroitinase-treated CNS proteoglycan co-migrated with the chondroitinase- and keratanase-treated cartilage proteoglycan. In CNS tissue homogenates, the addition of Streptomyces hyaluronidase brought about the release of the proteoglycan from the tissue. Anti-link protein mAbs were reactive with two species in the bovine CNS, the mobilities of which were very similar to those of the cartilage link proteins. The release of these species from the tissue required hyaluronidase. A rabbit antiserum against aggrecan was used to identify a similar proteoglycan in the rat CNS. In spinal cord-derived cell cultures, the labeled material was associated with astrocytes. An aggrecan cDNA hybridized to a 9.5 kb mRNA in the rat CNS. We conclude that the perineuronal matrix consists, in part, of a hyaluronate-bound aggrecan-like proteoglycan and link proteins, and that the former is produced by astrocytes.